JP7542469B2 - Secondary battery, battery pack, and vehicle - Google Patents

Description

Embodiments of the present invention relate to electrodes and secondary batteries, etc.

In recent years, research and development of high-energy density secondary batteries, such as lithium-ion secondary batteries and nonaqueous electrolyte secondary batteries, has been actively conducted. Secondary batteries are expected to be used as power sources for vehicles such as hybrid cars and electric cars, or as uninterruptible power sources for mobile phone base stations. Therefore, in addition to energy density, secondary batteries are also required to have other excellent performances, such as rapid charge/discharge performance and long-term reliability.

When batteries using carbon-based negative electrodes are repeatedly charged and discharged rapidly, lithium metal dendrites are formed on the electrodes, which can cause internal short circuits and lead to heat generation and fire. Therefore, batteries using metal composite oxides instead of carbonaceous materials for the negative electrode have been developed. For example, batteries using Li ₄ Ti ₅ O ₁₂ for the negative electrode are capable of stable rapid charging and discharging, and have a longer life than batteries using carbon-based negative electrodes.

JP 2001-176549 A JP 2014-143185 A JP 2015-56318 A JP 2018-49716 A JP 2018-156899 A

The present invention aims to provide an electrode that can realize a secondary battery with reduced capacity loss, and a secondary battery with reduced capacity loss, etc.

According to the embodiment, a secondary battery including a first electrode and a second electrode is provided. The first electrode includes a first active material-containing layer and a first solid electrolyte layer . The first active material-containing layer contains a first active material that undergoes a two-phase coexistence reaction and has a first main surface including a pair of first sides along a first direction. The second electrode includes a counter electrode for the first electrode. The second electrode includes a second active material-containing layer that contains a second active material that undergoes a single solid-phase reaction. The first solid electrolyte layer is provided on the first main surface of the first active material-containing layer and contains a solid electrolyte. The first solid electrolyte layer includes a first portion along at least one of the pair of first sides and having a first peripheral width F _S of 0.03 F _A or more and 0.25 F _A or less with respect to a first width F _A between the pair of first sides. The first active material-containing layer includes a first solid electrolyte non-supporting portion on which the first solid electrolyte layer is not provided.

According to yet another embodiment, a battery pack is provided that includes the secondary battery according to the above embodiment.

According to yet another embodiment, a vehicle is provided that includes a battery pack according to the above embodiment.

FIG. 2 is a plan view illustrating an example of an electrode according to the embodiment. Schematic cross-sectional view taken along line II-II' in FIG. 1 . FIG. 11 is a plan view illustrating another example of an electrode according to the embodiment. 4 is a schematic cross-sectional view taken along line IV-IV' in FIG. 3; Schematic cross-sectional view taken along line V-V' in FIG. 3. FIG. 1 is a cross-sectional view illustrating an example of a secondary battery according to an embodiment. FIG. 7 is an enlarged cross-sectional view of a portion A of the secondary battery shown in FIG. 6 . FIG. 4 is a partially cutaway perspective view illustrating a schematic diagram of another example of a secondary battery according to an embodiment. FIG. 9 is an enlarged cross-sectional view of a portion B of the secondary battery shown in FIG. 8 . FIG. 2 is a plan view illustrating an example of a second electrode that may be included in the secondary battery according to the embodiment. 11 is a schematic cross-sectional view taken along line XI-XI' in FIG. 10 . FIG. 4 is a plan view illustrating another example of a second electrode that may be included in the secondary battery according to the embodiment. 13 is a schematic cross-sectional view taken along line XIII-XIII' in FIG. 12 . Schematic cross-sectional view taken along line XIV-XIV' in Figure 12. FIG. 1 is a perspective view illustrating an example of a battery pack according to an embodiment. FIG. 1 is an exploded perspective view illustrating an example of a battery pack according to an embodiment. FIG. 17 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 16 . FIG. 1 is a partially see-through view illustrating an example of a vehicle according to an embodiment. 1 is a diagram illustrating an example of a control system for an electrical system in a vehicle according to an embodiment;

In lithium titanium oxides having a spinel structure, such as Li ₄ Ti ₅ O ₁₂ , the charge and discharge reaction proceeds as a two-phase coexistence reaction. Therefore, unlike many other negative electrode active materials, lithium titanium oxides having a spinel structure show a flat charge and discharge potential. In a negative electrode using lithium titanium oxide with a flat potential, the concentration distribution of lithium ions in the electrode is difficult to relax because there is no potential gradient. Therefore, in a negative electrode using an active material that undergoes a two-phase coexistence reaction, the relaxation rate is slower than that of an electrode using an active material in which charging and discharging proceeds by a single solid-phase reaction. As a result, for example, in a battery that combines a negative electrode using spinel-type Li ₄ Ti ₅ O ₁₂ as an active material and a positive electrode using lithium nickel cobalt manganese composite oxide, which is a solid solution that undergoes a single solid-phase reaction, a difference occurs in the relaxation rate of the concentration distribution of lithium ions between the negative electrode and the positive electrode.

If there is a difference in the rate at which the Li (lithium) concentration distribution relaxes between the negative electrode and the positive electrode, unevenness in the Li concentration distribution may occur within the surface of each electrode as a result of high-rate charging and discharging. Repeated rapid charging and discharging will not eliminate the uneven Li concentration distribution, but will further bias the distribution, and the battery capacity will decrease as the bias in the Li concentration distribution progresses.

A similar phenomenon may occur in a battery that combines a positive electrode using an active material that undergoes a two-phase coexistence reaction with a negative electrode using an active material that undergoes a single solid-phase reaction. For example, in lithium iron phosphate having an olivine structure, represented by LiFePO ₄ , which is commonly used as a positive electrode active material, the charge and discharge reaction proceeds by a two-phase coexistence reaction. For example, in a battery that combines a positive electrode using olivine-type LiFePO ₄ as an active material and a negative electrode using niobium titanium oxide, which is a solid solution, as an active material, the battery capacity may decrease when rapid charge and discharge are repeated due to the difference in the relaxation rate of the Li concentration distribution between the positive electrode and the negative electrode.

The above capacity decrease is a temporary decrease in battery performance, not a permanent deterioration of the battery. After repeated rapid charging and discharging, the battery capacity can be restored by performing multiple charge and discharge cycles at a non-rapid rate (e.g., 1C/1C rate). From the perspective of convenience, it is desirable to suppress the decrease in battery capacity, even if it is a temporary phenomenon. In the embodiment described below, the above-mentioned temporary capacity decrease is suppressed.

The following describes the embodiments with reference to the drawings. In the following description, components that perform the same or similar functions are given the same reference numerals throughout the drawings, and duplicate descriptions are omitted. Each figure is a schematic diagram to facilitate the explanation and understanding of the embodiments, and the shapes, dimensions, ratios, etc. may differ from the actual device, but these can be appropriately modified in design by taking into account the following explanation and known technology.

[First embodiment]
According to the first embodiment, an electrode is provided. The electrode includes an active material-containing layer containing an active material that undergoes a two-phase coexistence reaction. Here, the active material that undergoes a two-phase coexistence reaction is sometimes called a first active material, and the active material-containing layer containing this first active material is sometimes called a first active material-containing layer. The active material-containing layer (first active material-containing layer) has a main surface including a pair of first sides along a first direction. Here, the main surface of the first active material-containing layer is sometimes called a first main surface. The lithium diffusion coefficient Dt E in the thickness direction intersecting with the main surface (first main surface) of the active material-containing layer (first active material-containing layer) at the outer edge portion including the first region in the main surface (first main surface) is higher than the lithium diffusion coefficient Dt _C in the thickness direction at the center portion of the main surface (first main surface) excluding the outer edge _portion . The first region is along at least one of the pair of first sides. Furthermore, the first region has a first peripheral width F _S of 0.03F _A or more and 0.25F _A or less with respect to a first width F _A between the pair of first sides.

According to a specific aspect of the electrode, the electrode further comprises a first solid electrolyte layer provided on the first main surface of the first active material-containing layer. The first solid electrolyte layer contains a solid electrolyte. The first solid electrolyte layer includes a first portion along at least one of the pair of first sides. The first portion has _{a first peripheral width F S of} 0.03 F _A or more and 0.25 F _A or less with respect to a first width F A between the pair of first sides. According to this aspect, the first region corresponds to a portion of the electrode where the first portion of the first solid electrolyte layer is provided. The first active material-containing layer includes a first solid electrolyte-free portion where the first solid electrolyte layer is not provided.

The electrode may be a battery electrode. The electrode may be an electrode used in a secondary battery, such as a lithium ion battery or a nonaqueous electrolyte battery. The electrode may be a negative electrode or a positive electrode of the secondary battery depending on the form. A secondary battery including the electrode may include a counter electrode for the battery. To distinguish between the two, the electrode according to the first embodiment may be called a first electrode, and the counter electrode may be called a second electrode.

The electrode (first electrode) may include a current collector. The active material-containing layer (first active material-containing layer) may be supported on one main surface or both main surfaces of the current collector. The active material-containing layer (first active material-containing layer) may further include a conductive agent and a binder in addition to the active material (first active material) that undergoes a two-phase coexistence reaction.

In a secondary battery, for example, alkali metal ions are used as charge carrier ions, and charging and discharging can be performed by the movement of carrier ions between the positive electrode and the negative electrode. Examples of carrier ions include lithium ions and sodium ions. A specific example of a secondary battery is a lithium ion secondary battery, in which charging and discharging are performed by the movement of lithium ions between the positive electrode and the negative electrode. Typically, the positive electrode and the negative electrode are arranged so that their faces face each other within the battery in order to ensure an area for the movement of carrier ions between the positive electrode and the negative electrode.

When a secondary battery is rapidly charged and discharged, there may be a difference in the diffusion rate of carrier ions between the center and the edge of each surface of the positive and negative electrodes. Specifically, carrier ion diffusion in the thickness direction tends to be fast in the center of each electrode, and carrier ion diffusion in the thickness direction tends to be slow in the edge portions. The thickness direction here means the direction that intersects with the opposing surfaces, and is along the direction from the positive electrode to the negative electrode and the direction from the negative electrode to the positive electrode, respectively. Because there is such a difference in the diffusion rate of carrier ions in the thickness direction between the center and edge regions of each surface of the positive and negative electrodes, repeated rapid charge and discharge cycles tend to result in a concentration distribution in which there are more carrier ions in the center of each electrode and fewer carrier ions at the edges.

If the rate at which the concentration distribution of carrier ions caused by the active material relaxes differs between the positive and negative electrodes, the difference in the relaxation rates will cause a difference in the degree of unevenness in the concentration distribution caused by the rapid charging and discharging described above between the positive and negative electrodes. As repeated cycles of rapid charging and discharging progress, the difference in the concentration distribution between the positive and negative electrodes increases, and the battery capacity decreases.

In the electrode (first electrode) according to the embodiment, the lithium diffusion coefficient _DtE in the thickness direction at the outer edge including the first region of the main surface of the active material-containing layer corresponding to the end region of the electrode surface is higher than the lithium diffusion coefficient _DtC in the thickness direction at the center of the main surface excluding the outer edge. The thickness direction here is the direction intersecting the main surface of the active material-containing layer. In this way, the diffusion rate of carrier ions in the thickness direction in the end region is faster than that in the central region of the electrode surface, so that the unevenness of the concentration distribution of carrier ions in the electrode surface due to rapid charging and discharging can be reduced. Therefore, the deviation of the concentration distribution between the two electrodes in a secondary battery using a positive electrode and a negative electrode with different relaxation rates of the concentration distribution can be reduced, and thus the temporary capacity decrease that may occur when rapid charging and discharging is repeated can be suppressed.

The first active material-containing layer of the first electrode contains a first active material that undergoes a two-phase coexistence reaction. The first active material-containing layer has a first main surface. The first main surface may have, for example, a band shape or a rectangular shape. The first main surface includes a pair of first sides that are aligned along a first direction.

The outer edge portion, in which the lithium diffusion coefficient _DtE in the thickness direction of the electrode is higher than the lithium diffusion coefficient _DtC in the center of the first main surface, includes a first region along at least one of the pair of first sides. That is, the outer edge portion corresponds to an end portion of the first main surface. The outer edge portion may include one first region along one of the pair of first sides, or may include a pair of first regions along each of the pair of first sides.

The first region included in the outer edge portion within the first main surface corresponds to a region having a first peripheral width F _S along one or both of the pair of first sides. Here, the first peripheral width F _S of each first region is in the range of 0.03 F _A or more and 0.25 F _A or less with respect to the first width _F A between the pair of first sides, i.e., the width of the first active material-containing layer in the second direction (the width of the electrode excluding the current collector). The first peripheral width F _S between the pair of first regions may be the same or different.

The outer edge portion within the first main surface may further include a second region in addition to the first region. The first main surface may further include a pair of second sides along a second direction intersecting the first direction, and the second region is along at least one of the pair of second sides. The outer edge portion may include one second region along one of the pair of second sides, or may include a pair of second regions along each of the pair of second sides.

Each second region has a second width S _A between a pair of second sides, i.e., a second peripheral width S _S of 0.25 S _A or less relative to the width of the first active material-containing layer in the first direction (the width of the electrode excluding the current collector). The second peripheral width S _S of the second region is preferably 0.03 S _A or more. The second peripheral width S _S between a pair of second regions may be the same or different. Furthermore, the second peripheral width S _S of each second region may be the same as or different from the first peripheral width F _S of the first region.

In both the first and second regions of the outer edge, the lithium diffusion coefficient (Dt _E ) in the thickness direction of the electrode is higher than the lithium diffusion coefficient Dt _C in the thickness direction at the center.

When the outer edge portion includes only the first region, the outer edge portion may have, for example, a band shape including a long side along the first side of the first main surface. In other words, the outer edge portion may include a band-shaped first region whose long side is along one of the pair of first sides, or a pair of band-shaped first regions whose long sides are along both first sides.

In an electrode including a second region, the first region and the second region may overlap. For example, in an electrode including at least one first region and at least one second region, the first region and the second region may overlap at a portion near one or more corners of the first main surface. As a specific example, in an electrode including a first active material-containing layer having a rectangular first main surface, when the outer edge portion includes a pair of first regions and a pair of second regions, the first region and the second region may overlap at each of the four corners of the first main surface in a portion having an area of F _S ×S S _S. In this example, the first region and the second region may be combined to form a frame-shaped outer edge portion that traces the inside of the periphery of the first main surface.

According to a specific embodiment, a first solid electrolyte layer is provided on a portion of the first main surface that corresponds to the outer edge. The first solid electrolyte layer is not provided on a portion that corresponds to the center except for the outer edge. This portion is called a first solid electrolyte non-supporting portion. The first solid electrolyte layer contains a solid electrolyte and exhibits conductivity to carrier ions such as lithium ions. By including the first solid electrolyte layer in the outer edge, the lithium diffusion coefficient Dt _E in the thickness direction at the outer edge is higher than the lithium diffusion coefficient Dt _C in the thickness direction at the center (first solid electrolyte non-supporting portion) that does not include a solid electrolyte layer.

The first solid electrolyte layer includes at least a first portion along at least one of the first sides of the first main surface. The first portion of the first solid electrolyte layer corresponds to a portion of the first solid electrolyte layer on the first main surface that is provided on a first region of the outer edge portion. Thus, the first solid electrolyte layer can include one first portion along one of the pair of first sides, or can include a pair of first portions along each of the pair of first sides. Each first portion has a first peripheral width F _S of 0.03 F _A or more and 0.25 F _A or less with respect to a first width F _A between the pair of first sides. The first peripheral width F _S between the pair of first portions may be the same or different. The first width F _A between the first sides and the first peripheral width F _S of the first portion are widths in the same direction.

The first solid electrolyte layer may further include a second portion along at least one of the second sides of the first main surface. The second portion of the first solid electrolyte layer corresponds to a portion of the first solid electrolyte layer on the first main surface that is provided on the second region of the outer edge. Thus, the first solid electrolyte layer may include one second portion along one of the pair of second sides, or may include a pair of second portions along each of the pair of second sides. Each second portion has a second peripheral width S _S of 0.25 S _A or less with respect to the second width S _A between the pair of second sides. It is preferable that the second peripheral width S _S is 0.03 S _A or more. Between the pair of second portions, the second peripheral width S _S may be the same or different. The second peripheral width S _S of each second portion may be the same as the first peripheral width F _S of the first portion, or may be different. The second width S _A between the second sides and the second peripheral width S _S of the second portion are each widths in the same direction.

In an electrode in which a first active material-containing layer is formed on each of the two main surfaces of a current collector, the position and width (first peripheral width F _S ) of the first part of the first solid electrolyte layer provided on the first main surface of the first active material-containing layer on one main surface of the current collector is preferably consistent with the position and width (first peripheral width F S ) of the first part on the first main surface of the first active material-containing layer on the other main surface of the current collector. Similarly, the position and width (second peripheral width S _S ) of the second part of the first solid electrolyte layer provided on the first main surface of the first active material-containing layer on one main surface of the current collector is preferably consistent with the position and width (second peripheral width _{S S} ) of the second part on the first main surface of the first active material-containing layer on the other main surface of the current collector. In other words, it is desirable that the layout of the outer edge and the first solid electrolyte layer match on both sides of the electrode. Alternatively, the first solid electrolyte layer may be provided only on one of the first active material-containing layers formed on both main surfaces of the current collector.

For example, when the first solid electrolyte layer includes only the first portion, the first solid electrolyte layer may have a band shape including a long side along the first side of the first main surface. That is, the first solid electrolyte layer may include a band-shaped first portion whose long side is along one of the pair of first sides, or a pair of band-shaped first portions whose long sides are along both first sides. In one specific example including the second portion, the first and second portions may be combined to form a frame-shaped first solid electrolyte layer that is arranged to trace the inside of the outer periphery of the first main surface. When the first main surface of the first active material-containing layer includes a long side and a short side, it is desirable that the first solid electrolyte layer is provided along at least one of the long sides.

As described above, the first electrode embodiment includes an embodiment as a negative electrode and an embodiment as a positive electrode. On the one hand, in the embodiment as a negative electrode, the first active material may be called the first negative electrode active material or simply the negative electrode active material, and the first active material-containing layer may be called the first negative electrode active material-containing layer or simply the negative electrode active material-containing layer. On the other hand, in the embodiment as a positive electrode, the first active material may be called the first positive electrode active material or simply the positive electrode active material.

As a first active material that undergoes a two-phase coexistence reaction that can be used in the embodiment of the negative electrode, that is, a first negative electrode active material, there is a lithium titanium oxide having a spinel structure (for example, a compound represented by Li _4+v Ti ₅ O ₁₂ where 0≦v≦3). When lithium ions are inserted by charging, a spinel type Li ₄ Ti ₅ O ₁₂ , which is an example of such a lithium titanium oxide, changes to Li ₇ Ti ₅ O _12. Until the battery is fully charged, the two phases of Li ₄ Ti ₅ O ₁₂ and Li ₇ Ti ₅ O ₁₂ coexist, and during that time, the charging potential hardly changes and the potential is kept constant. However, the charging potential changes sharply at the end of charging.

As a first active material that undergoes a two-phase coexistence reaction that can be used in the embodiment of the positive electrode, that is, a first positive electrode active material, there is lithium iron phosphate having an olivine structure (for example, a compound represented by Li _x FePO ₄ , where 0<x≦1). In LiFePO ₄ , which is an example of lithium iron phosphate of the olivine type, FePO ₄ is generated when lithium ions are desorbed by charging. Until it is fully charged, two phases of LiFePO ₄ and FePO ₄ coexist, and during that time, the charging potential hardly changes and the potential is kept constant.

The conductive agent is blended to improve the current collection performance and reduce the contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as vapor grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanotubes, and carbon nanofibers. One of these may be used as the conductive agent, or two or more may be used in combination as the conductive agent. The conductive agent may also be omitted. Alternatively, instead of using a conductive agent, a carbon coating or an electronically conductive inorganic material coating may be applied to the surface of the active material particles. The current collection performance of the active material-containing layer can also be improved by using a conductive agent and coating the active material surface with carbon or a conductive material.

The binder is blended to fill the gaps between the dispersed active materials and to bind the active materials and the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber (SBR), polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as the binder, or two or more may be used in combination as the binder.

The mixing ratio of the active material, conductive agent, and binder in the active material-containing layer can be changed as appropriate depending on the application of the electrode.

For example, when the electrode is used as the negative electrode of a secondary battery, it is preferable to mix the active material (negative electrode active material), conductive agent, and binder in proportions of 68% by mass or more and 96% by mass or less, 2% by mass or more and 30% by mass or less, and 2% by mass or more and 30% by mass or less, respectively. By making the amount of conductive agent 2% by mass or more, the current collection performance of the active material-containing layer can be improved. Also, by making the amount of binder 2% by mass or more, the binding between the active material-containing layer and the current collector becomes sufficient, and excellent cycle performance can be expected. On the other hand, it is preferable to make the conductive agent and binder 30% by mass or less each in order to achieve high capacity.

When the active material surface is coated with carbon or a conductive material, the amount of coating material can be considered to be included in the amount of conductive agent. The amount of carbon or conductive material coated is preferably 0.5% by mass or more and 5% by mass or less. A coating amount within this range can improve current collection performance and electrode density.

For example, when the electrode is used as the positive electrode of a secondary battery, the active material (positive electrode active material) and binder are preferably mixed in proportions of 80% to 99% by mass and 1% to 20% by mass, respectively. By making the amount of binder 1% by mass or more, sufficient electrode strength can be obtained. In addition, the binder can function as an insulator. Therefore, by making the amount of binder 20% by mass or less, the amount of insulator contained in the electrode is reduced, and the internal resistance can be reduced.

When a conductive agent is added, it is preferable to mix the active material (positive electrode active material), binder, and conductive agent in proportions of 77% by mass to 96% by mass, 1% by mass to 20% by mass, and 3% by mass to 15% by mass, respectively. By setting the amount of conductive agent to 3% by mass or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. If this proportion is low, decomposition of the electrolyte can be reduced during high-temperature storage.

The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted and extracted from the first active material.

For example, in the case of a negative electrode, the current collector (negative electrode current collector) is preferably made of copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing one or more elements selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can balance the strength and weight of the electrode.

For example, in the case of a positive electrode, the current collector (positive electrode current collector) is preferably an aluminum foil or an aluminum alloy foil containing one or more elements selected from the group consisting of Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si. The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

The current collector may also include a portion on its surface where the first active material-containing layer is not formed. This portion can function as a current collecting tab.

The density of the negative electrode active material-containing layer (excluding the current collector) is preferably 1.8 g/cm ³ or more and 2.8 g/cm ³ or less. A negative electrode having a density of the negative electrode active material-containing layer within this range has excellent energy density and retention of a liquid or gel electrolyte. The density of the negative electrode active material-containing layer is more preferably 2.1 g/cm ³ or more and 2.6 g/cm ³ or less.

The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. Positive electrode active materials with a primary particle size of 100 nm or more are easy to handle in industrial production. Positive electrode active materials with a primary particle size of 1 μm or less allow lithium ions to diffuse smoothly within the solid.

The specific surface area of the positive electrode active material is preferably 0.1 ^m2 /g or more and 10 ^m2 /g or less. A positive electrode active material having a specific surface area of ^{0.1 m2} /g or more can secure sufficient insertion and desorption sites for Li ions. A positive electrode active material having a specific surface area of ^{10 m2} /g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

The first solid electrolyte layer contains a solid electrolyte. The solid electrolyte may be contained in the first solid electrolyte layer, for example, in the form of particles. In addition to the solid electrolyte, the first solid electrolyte layer may further contain inorganic compound particles and a binder, which will be described later.

The first solid electrolyte layer may contain, for example, 50% by mass or more and 100% by mass or less of a solid electrolyte. The first solid electrolyte layer preferably contains 80% by mass or more and 100% by mass or less of a solid electrolyte.

The first solid electrolyte layer may have a thickness, for example, in the range of 1 μm to 50 μm. It is preferable that the thickness of the first solid electrolyte layer is in the range of 3 μm to 20 μm.

Examples of the solid electrolyte include LiM ₂ (PO ₄ ) ₃ having a NASICON structure, amorphous LIPON compounds, and oxides such as oxides having a garnet structure.

Examples of _LiM2 ( _PO4 ) ₃ having a NASICON type framework include Li1 _{+ aAlaGe2 -a} ( _PO4 ) ₃ , Li1 _{+ aAlaZr2 -a} ( _PO4 ) ₃ , and Li1 _{+ aAlaTi2 -a} ( _PO4 ) ₃ , where the subscript a is in the range of 0 to 2, preferably 0 to 0.5.

Specific examples of _LiM2 ( _PO4 ) ₃ having a NASICON skeleton include an LATP compound represented by Li1 _{+ bAlbTi2 -b} ( _PO4 ) ₃ , where 0.1≦b≦0.5; a compound represented by _{Li1+ cAldM12 -d} ( _PO4 ) ₃ , where M1 is one or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca, and where 0≦c≦1 and 0≦d≦1; a compound represented by Li1 _{+ aAlaGe2 -a} ( _PO4 ) ₃ , where 0≦a≦2; and a compound represented by Li1 _{+ aAlaZr2 -a} ( _PO4 ) ₃ , where 0≦a≦2; Li1 _{+e+ fAleM22 - eSifP3 -vO 12} , in which M2 is 1 or more selected from the group consisting of Ti and Ge, and 0<e≦2, 0≦f<3; and a compound represented by Li1 _{+2gZr1 -gCag ( PO4} ) ₃ , in which 0≦g<1.

Amorphous LIPON compounds include, for example, compounds represented by Li _h PO _i N _j , where 2.6≦h≦3.5, 1.9≦i≦3.8, and 0.1≦j≦1.3. A specific example of LIPON is Li _2.9 PO _3.3 N _0.46 .

Examples of oxides having a garnet type structure include compounds represented by Li5 _{+ mAnLa3 - nM32O12} , where A is one or more selected from the group consisting of Ca, Sr, and Ba, M3 is at least one selected from the group consisting of _Nb and Ta, and 0≦m<0.8 and 0≦n _< 2; compounds represented by _{Li3M32 - mZr2O12} , where M3 is one or more selected from the group consisting of Ta and Nb, _and 0 _≦ m<_0.8; _and LLZ compounds represented by _{Li7-3mAlmLa3Zr3O12} , where 0≦m<0.8. In the above, the subscript m is preferably within the range of 0≦m≦0.5. The oxide having a garnet type structure may be composed of one of these compounds, or may contain a mixture of two or more of these compounds. Among these, _{Li6.25Al0.25La3Zr3O12} and _{Li7La3Zr2O12 ( LLZ )} are preferably used because _they have high ionic conductivity and _{are electrochemically stable} .

For reference, the lithium ion conductivity at 25° C. of an inorganic compound having a NASICON skeleton and represented by _LiM2 ( _{PO4 ) 3} is, for example, in the range of 1× ^10-3 S/cm to _{1×10-1 S/cm. The lithium ion conductivity at 25° C. of Li2.9PO3.3N0.46, a specific example of LIPON, is 3×10-6 S/cm. The lithium ion conductivity at 25° C. of Li7La3Zr2O12} ^, _{a specific} ^example _{of garnet} -type _LLZ , is 3× ^10-4 S/cm.

The first solid electrolyte layer may contain polymer-type solid electrolyte particles as the solid electrolyte. The polymer-type solid electrolyte particles contain an organic compound having lithium ion conductivity and a lithium salt. Examples of the lithium salt include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenic (LiAsF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), and lithium bistrifluoromethylsulfonylimide (LiN(CF ₃ SO ₂ ) ₂ ), and lithium bis(fluorosulfonyl)imide (LiN(SO ₂ F) ₂ ; LiFSI). One of these may be selected and used as the lithium salt, or two or more may be mixed and used as the lithium salt. The polymer-type solid electrolyte particles may further contain a solvent such as an organic solvent.

Examples of polymeric materials include polyethers, polyesters, polyamines, polyethylenes, silicones and polysulfides.

The inorganic compound particles may be, for example, at least one selected from the group consisting of alumina, titanium oxide, titanium hydroxide, barium titanate, iron oxide, silicon oxide, aluminum hydroxide, gibbsite, boehmite, bayerite, magnesium oxide, silica, zirconium oxide, magnesium hydroxide, silica, lithium tetraborate, lithium tantalate, mica, silicon nitride, aluminum nitride, and zeolite.

The binder may be, for example, at least one selected from the group consisting of cellulose acetate, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid compounds, and imide compounds.

The area of the first solid electrolyte layer covering the first main surface on the first active material-containing layer is desirably larger as the thickness of the first active material-containing layer, for example, the basis weight of the first active material-containing layer supported on the current collector, increases. In other words, it is desirably to adjust the dimensions of both the first peripheral width F _S of the first portion and the second peripheral width S _S of the second portion of the first solid electrolyte layer in accordance with the thickness of the first active material-containing layer.

Next, the electrode (first electrode) according to the first embodiment will be described in more detail with reference to the drawings.

Figure 1 is a plan view that shows a schematic example of an electrode according to an embodiment. Figure 2 is a schematic cross-sectional view taken along line II-II' in Figure 1. In the example electrode shown in Figures 1 and 2, the outer edge portion in the first main surface of the first active material-containing layer includes the first region but does not include the second region. In other words, the electrode shown in Figures 1 and 2 is an example in which the first solid electrolyte layer includes the first portion but does not include the second portion.

The first electrode 3 in the example illustrated in FIG. 1 and FIG. 2 has a band shape defined by a pair of long sides along the first direction 11 and a pair of short sides along the second direction 12 intersecting the first direction 11. An electrode having such a band shape is suitable for forming a wound-type electrode group, for example. The band shape may be rectangular. The first electrode 3 includes a first current collector 3a having a band shape, a first active material-containing layer 3b having a band shape provided on one of its main surfaces, and a first solid electrolyte layer 3d provided on the first active material-containing layer 3b.

The first current collector 3a includes a portion where the first active material-containing layer 3b is not supported, and this portion functions as the first current collector tab 3c. In the illustrated example, the first current collector tab 3c is aligned along the long side of the band shape.

A pair of first solid electrolyte layers 3d are supported on the first main surface of the first active material-containing layer 3b. Each of the first solid electrolyte layers 3d has a band shape and is arranged so that its long sides are aligned with a pair of first sides 21 along the first direction 11 of the first active material-containing layer 3b.

In this example, the first solid electrolyte layer 3d includes a pair of first portions 31a provided within a first region 31 in a first main surface of the first active material-containing layer 3b. Each of the first portions 31a is disposed along each of the first sides 21. A first peripheral width F _S in the second direction 12 of each of the first portions 31a takes a value in the range of 0.03 F A or more and 0.25 F A or less with respect to a first width F _A which is also the width of the first active material-containing layer 3b in the second direction ₁₂ and the width between the first sides ₂₁ .

The portion of the first main surface excluding the outer edge portion including the first region 31 corresponds to the central portion 30. The first active material-containing layer 3b corresponds to the central portion 30 in the first main surface, and includes a first solid electrolyte non-supporting portion 30a where the first solid electrolyte layer 3d is not provided.

In the first electrode 3, the first solid electrolyte layer 3d is not provided in the region corresponding to the central portion 30, and the first solid electrolyte layer 3d is provided in the region corresponding to the outer edge portion (first region 31). As a result, the lithium diffusion coefficient _DtE in the thickness direction in the outer edge portion (first portion 31a) is higher than the lithium diffusion coefficient _DtC in the thickness direction in the central portion 30. The thickness direction here is a direction intersecting the first main surface and is along the stacking direction of the first active material-containing layer 3b and the first solid electrolyte layer 3d. In FIG. 2, the thickness direction corresponds to the vertical direction.

In the example illustrated in FIG. 2, which shows a cross section along the second direction 12, the first active material-containing layer 3b is supported only on one side of the first current collector 3a, but the first active material-containing layer 3b may be supported on both the front and back sides of the first current collector 3a. In that case, a first solid electrolyte layer 3d may be provided on one or both first main surfaces of the first active material-containing layers 3b on both sides.

In the above example, the first solid electrolyte layer 3d is provided along both long sides of the band-shaped first main surface, i.e., along the first sides 21 on both sides, but the first solid electrolyte layer 3d may be provided along only one of the first sides 21. In addition, the first sides 21 may be the short sides instead of the long sides of the band shape.

Figure 3 is a plan view that shows a schematic diagram of another example of an electrode according to an embodiment. Figure 4 is a schematic cross-sectional view taken along line IV-IV' in Figure 3. Figure 5 is a schematic cross-sectional view taken along line V-V' in Figure 3. In the example electrodes shown in Figures 3 to 5, the outer edge portion in the first main surface of the first active material-containing layer includes a first region and a second region. That is, the electrodes shown in Figures 3 to 5 are examples in which the first solid electrolyte layer includes a first portion and a second portion.

The first electrode 3 in the example illustrated in Figures 3 to 5 has a rectangular shape defined by a pair of short sides along the first direction 11 and a pair of long sides along the second direction 12 intersecting the first direction 11. An electrode having such a rectangular shape is suitable for forming, for example, a stacked electrode group. The first electrode 3 includes a flat first current collector 3a, a rectangular first active material-containing layer 3b provided on one of its main surfaces, and a first solid electrolyte layer 3d provided on the first active material-containing layer 3b.

The first current collector 3a includes a portion where the first active material-containing layer 3b is not supported, and this portion functions as the first current collector tab 3c. In the illustrated example, the first current collector tab 3c is provided on the short side of the first electrode 3, but the first current collector tab 3c may be provided on the long side. In this example, the first current collector tab 3c is a narrow portion having a width narrower than the other portions, but the shape of the first current collector tab 3c is not limited to this shape. In order to increase the mechanical strength, a part of the first active material-containing layer 3b is provided at the base of the first current collector tab 3c, but this part of the first active material-containing layer 3b may be omitted.

In this example, the first solid electrolyte layer 3d has a frame shape. The first solid electrolyte layer 3d includes a pair of first portions 31a that are aligned along a pair of first sides 21 that are aligned along the first direction 11 of the first active material-containing layer 3b. The first portions 31a are provided within a range of a first region 31 in a first main surface of the first active material-containing layer 3b. The first solid electrolyte layer 3d also includes a pair of second portions 32a that are aligned along a pair of second sides 22 that are aligned along the second direction 12 of the first active material-containing layer 3b. The second portions 32a are provided within a range of a second region 32 in a first main surface of the first active material-containing layer 3b.

Each first portion 31a included in the first solid electrolyte layer 3d is disposed along each first side 21. A first peripheral width F _S in the second direction 12 of each first portion 31a takes a value in the range of 0.03 F A or more and 0.25 F _A or less, relative to a first width F _A which is also the width of the first active material-containing layer 3b in the second direction ₁₂ and is the width between the first sides 21.

Each second portion 32a included in the first solid electrolyte layer 3d is disposed along each second side 22. The second peripheral width S _S in the first direction 11 of each second portion 32a is 0.25 S A or less with respect to the second width S A which is also the width of the first active material containing layer 3b in the first direction 11 and the width between the second sides 22. The second peripheral width _{S S preferably} has a value within a range of 0.03 S _A or more and 0.25 _{S A or} less.

The portion of the first main surface excluding the outer edge portion including the first region 31 and the second region 32 corresponds to the central portion 30. The first active material-containing layer 3b corresponds to the central portion 30 in the first main surface, and includes a first solid electrolyte non-supporting portion 30a where the first solid electrolyte layer 3d is not provided.

In the first electrode 3, the first solid electrolyte layer 3d is not provided in the region corresponding to the central portion 30, and the first solid electrolyte layer 3d is provided in the region corresponding to the outer edge portion including the first region 31 and the second region 32. As a result, the lithium diffusion coefficient _DtE in the thickness direction in the outer edge portion is higher than the lithium diffusion coefficient _DtC in the thickness direction in the central portion 30. The thickness direction here is a direction intersecting the first main surface and aligned with the stacking direction of the first active material-containing layer 3b and the first solid electrolyte layer 3d. In Figs. 4 and 5, the thickness direction corresponds to the vertical direction.

In the example illustrated in FIG. 4 showing a cross section along the second direction 12 and FIG. 5 showing a cross section along the first direction 11, the first active material-containing layer 3b is supported on both the front and back sides of the first current collector 3a, but the first active material-containing layer 3b may be supported on only one side of the first current collector 3a. Also, the first solid electrolyte layer 3d may be provided on only one of the first active material-containing layers 3b on both sides instead of both sides. In addition, instead of the frame-shaped first solid electrolyte layer 3d, for example, a U-shaped first solid electrolyte layer 3d in which one first portion 31a is omitted or a C-shaped first solid electrolyte layer 3d in which one second portion 32a is omitted ("U-shaped") may be adopted.

Here, the short side of the rectangular first main surface has been described as the first side 21, and the long side as the second side 22, but the first side 21 may be the long side and the second side 22 may be the short side. Also, the first side 21 and the second side 22 may have the same dimensions. In other words, the rectangular shape of the first main surface may be a rectangle or a square.

<Production Method>
Such an electrode can be manufactured, for example, by the following method. First, a first active material, a conductive agent, and a binder are suspended in a solvent to prepare an active material-containing slurry. The active material-containing slurry is applied to one or both sides of a current collector. Next, the applied active material-containing slurry is dried to obtain a laminate of the first active material-containing layer and the current collector. After that, the laminate is pressed.

Next, a solid electrolyte, which is the material of the first solid electrolyte layer, and optionally inorganic compound particles and a binder are dispersed in an appropriate solvent such as water to prepare a solid electrolyte-containing slurry. The solid electrolyte-containing slurry is sprayed by an air jet and applied onto the region to be the outer edge of the first main surface of the first active material-containing layer. After application, the solid electrolyte-containing slurry is dried to form a first solid electrolyte layer on the first active material-containing layer.

This is how the electrodes are manufactured.

The method of applying the solid electrolyte-containing slurry may be not only the spray deposition method as described above, but also, for example, gravure printing, slot die method, microgravure printing, electrospinning, application using a brush, or dip coating. In addition, a coating device capable of simultaneously applying the active material-containing slurry and the solid electrolyte-containing slurry may be used. The application of the solid electrolyte-containing slurry may be performed by only one of these application methods, or may be performed by combining multiple application methods.

<Measurement method>
The measurement methods for the electrodes are described below, specifically, a method for confirming the active material, a method for determining the lithium diffusion coefficient _DtE at the outer edge and the lithium diffusion coefficient _DtC at the center, a method for measuring the first peripheral width F _S of the first region at the outer edge and the first portion of the first solid electrolyte layer, and a method for measuring the second peripheral width S _S of the second region at the outer edge and the second portion of the second solid electrolyte layer.

(Checking the active material)
The active material contained in the electrode can be identified by a combination of X-ray diffraction (XRD) measurement and inductively coupled plasma (ICP) emission spectroscopy. The crystal structure of the material contained in the active material-containing layer can be confirmed by XRD measurement. The elements in the active material-containing layer can be quantified by ICP measurement.

When the active material contained in a battery electrode is used as a sample, the following pretreatment method is used to prepare a measurement sample. First, the battery is fully discharged (e.g., SOC (State Of Charge) is 0%). Next, the battery is disassembled in an inert atmosphere glove box, for example, a glove box under an argon atmosphere, and the electrodes are removed. Next, the removed electrodes are washed using a solvent such as ethyl methyl carbonate. The electrodes are vacuum-dried in a room temperature environment to obtain a measurement sample.

Next, the obtained measurement sample is directly attached to a glass holder and measured. When measuring, the peaks originating from the metal foil current collector, the conductive agent, the binder, etc. are measured in advance using XRD to understand them. Of course, if these are known in advance, this step can be omitted.

When the peak of the current collector and the peak of the active material overlap, it is desirable to peel off the active material-containing layer from the current collector and measure it. This is to separate the overlapping peaks when quantitatively measuring the peak intensity. The active material-containing layer may be physically peeled off, but it is easier to peel off by applying ultrasonic waves in a solvent. When ultrasonic treatment is performed to peel off the active material-containing layer from the current collector, the electrode powder (including the active material, conductive agent, and binder) can be recovered by volatilizing the solvent. The recovered electrode powder can be filled into, for example, a Lindemann glass capillary and measured to perform powder X-ray diffraction measurement of the active material. The electrode powder recovered by ultrasonic treatment can also be used for ICP measurement.

Next, the active material-containing layer is enclosed in a capillary and placed on a rotating sample stage for measurement. This method makes it possible to obtain an XRD pattern of the active material while reducing the influence of orientation.

As an apparatus for powder X-ray diffraction measurement, for example, SmartLab manufactured by Rigaku Corporation is used. The measurement conditions are as follows:
X-ray source: Cu target Output: 45 kV, 200 mA
Soller slit: 5° for both incidence and reception
Step width (2θ): 0.02 deg
Scan speed: 20 deg/min Semiconductor detector: D/teX Ultra 250
Sample plate holder: Flat glass sample plate holder (thickness 0.5 mm)
Measurement range: 5°≦2θ≦90°.

When using other equipment, perform measurements using standard Si powder for powder X-ray diffraction to find conditions that give peak intensity, half-width, and diffraction angle results equivalent to those obtained with the above equipment, and then measure the sample under those conditions.

The conditions for the above powder X-ray diffraction measurement are preferably such that an XRD pattern applicable to Rietveld analysis can be obtained. To collect data for Rietveld analysis, specifically, the step width is set to 1/3-1/5 of the minimum half-width of the diffraction peak, and the measurement time or X-ray intensity is appropriately adjusted so that the intensity at the peak position of the most intense reflection is 5000 cps or more.

To measure the composition of the active material contained in an electrode by ICP emission spectroscopy, first, the active material-containing layer is peeled off from the electrode. For example, the portion containing the electrode active material can be peeled off by irradiating it with ultrasonic waves. As a specific example, the active material-containing layer containing the electrode active material can be peeled off from the electrode current collector by placing the electrode in ethyl methyl carbonate in a glass beaker and vibrating it in an ultrasonic cleaner.

Next, the peeled off portion is heated in air for a short period of time (for example, at 500°C for about an hour) to burn off unnecessary components such as binder components and carbon. This residue is dissolved in acid to produce a liquid sample containing the active material. The acid that can be used in this case is hydrochloric acid, nitric acid, sulfuric acid, hydrogen fluoride, etc. This liquid sample can be subjected to ICP analysis to determine the composition of the active material.

(Measurement of lithium diffusion coefficient Dt _E , lithium diffusion coefficient Dt _C , first peripheral width F _S and first peripheral width F _S )
The lithium diffusion coefficient _DtE in the thickness direction at the outer edge and the lithium diffusion coefficient _DtC in the thickness direction at the center can be measured as follows. Here, the lithium diffusion coefficients _DtE and _DtC are collectively referred to as the lithium diffusion coefficient Dt.

When using electrodes contained in a battery as samples, prepare the measurement sample by pretreating it using the following method.

First, the battery is fully discharged. Next, the battery is disassembled in an inert atmosphere glove box, for example, a glove box under an argon atmosphere, and the electrodes are removed. Here, both the positive and negative electrodes are removed. Next, each of the removed electrodes is washed with a solvent such as ethyl methyl carbonate and vacuum dried in a room temperature environment.

A circular sample with a diameter of 10 mm is punched out from each electrode, and a coin cell is made using the obtained circular positive and negative electrodes. A separator and an electrolyte are further used in the coin cell. As the separator and electrolyte, those described in the second embodiment can be used. Here, it is preferable to use the same separator and electrolyte as those used in the disassembled battery. Circular samples are punched out from multiple points from the end to the center of the main surface of each electrode. However, between the positive electrode and the negative electrode, the points from which the circular samples are punched are overlapped as much as possible. Specifically, the circular samples are punched out from the points where the positive electrode and the negative electrode faced each other in the battery. The coin cell is made using the circular samples punched out from the corresponding points on both electrodes. In addition, instead of removing the positive and negative electrodes separately from the battery, the electrode group for the coin cell may be prepared by washing and drying them while overlapping as an electrode group, and punching them into a circle while overlapping.

For electrodes with a solid electrolyte layer, at least one circular sample is punched out from the part with the solid electrolyte layer and one from the part without the solid electrolyte layer. However, for electrodes with a solid electrolyte layer over the entire main surface of the electrode, it is not necessary to punch out a sample from the part without the solid electrolyte layer.

The coin cell is then charged to a half-charged state. A half-charged state here refers to a state where the SOC (State Of Charge) is 50%, for example. A laminate including a negative electrode and a positive electrode is removed from the half-charged coin cell. This laminate is washed and vacuum-dried at room temperature to obtain a measurement sample.

Then, the AC impedance of this measurement sample is measured using a Solartron Frequency Response Analyzer Model 1260. The measurement frequency range is from 5 Hz to 32 MHz. The measurement is performed in a 25°C environment, with the measurement sample placed in a dry argon atmosphere without being exposed to the air.

The lithium diffusion coefficient Dt is expressed as the reciprocal of the resistance value in the thickness direction of the electrode, and is calculated as follows. A complex impedance plot (Cole-Cole plot) is created based on the measured AC impedance. The Cole-Cole plot plots the real component on the horizontal axis and the imaginary component on the vertical axis. The resistance value in the thickness direction of the electrode is calculated using the following formula (1). In the following formula (1), Z is the resistance value calculated from the diameter of the arc of the Cole-Cole plot, and S is the electrode area (area of the circle).

Dt = 1/(Z/S)...(1).

The lithium diffusion coefficients Dt measured at multiple locations on the main surface of the electrode are compared. Based on the increase or decrease in the lithium diffusion coefficient Dt on the main surface of the electrode, the portion of the main surface of the electrode that corresponds to the outer edge and the portion that corresponds to the center may be determined. However, if a solid electrolyte layer is included, the outer edge and center are determined based on the layout of the solid electrolyte layer. If the target electrode itself does not have a solid electrolyte layer but the counter electrode does, the portions that overlap with the outer edge and center of the counter electrode may be considered to be the outer edge and center of the electrode.

The lithium diffusion coefficient Dt obtained for the portion corresponding to the portion determined to be the outer edge is defined as the lithium diffusion coefficient Dt _E at the outer edge. Similarly, the lithium diffusion coefficient Dt obtained for the portion corresponding to the portion determined to be the center is defined as the lithium diffusion coefficient Dt _C at the center.

The first peripheral width F _S of the first region of the outer edge or the first part of the first solid electrolyte layer, and the second peripheral width S _S of the second region of the outer edge or the second part of the second solid electrolyte layer are determined by performing dimensional measurements based on the layout of the part determined to be the outer edge or the solid electrolyte layer. The first and second regions in the outer edge can be set arbitrarily. The first and second parts in the first solid electrolyte layer can be set arbitrarily. However, the second region is not set without setting the first region. Similarly, the second part is not set without setting the first part.

The electrode according to the first embodiment includes an active material-containing layer that contains an active material that undergoes a two-phase coexistence reaction. The active material-containing layer has a main surface that includes a pair of first sides along a first direction, and the lithium diffusion coefficient _DtE in the thickness direction at the outer edge of the main surface and the lithium diffusion coefficient _DtC in the thickness direction at the center satisfy the relationship _DtE > _DtC . The thickness direction here intersects with the main surface of the active material-containing layer. The outer edge includes a first region along at least one of the first sides. The first peripheral width F _S of the first region is 0.03F _A or more and 0.25F _A or less with respect to the first width F _A between the pair of first sides. The center corresponds to the portion of the main surface excluding the outer edge. Such an electrode can provide a secondary battery in which capacity reduction is suppressed.

Second Embodiment
According to a second embodiment, there is provided a secondary battery including a first electrode and a second electrode, the first electrode including the electrode according to the first embodiment, and the second electrode including a counter electrode for the first electrode.

The first electrode can be the negative electrode or positive electrode of the secondary battery. In other words, the secondary battery includes the electrode according to the first embodiment as the negative electrode or positive electrode.

The second electrode corresponds to a counter electrode for the first electrode. In other words, the second electrode is included as a positive electrode in a secondary battery that includes the first electrode as a negative electrode. And the second electrode is included as a negative electrode in a secondary battery that includes the first electrode as a positive electrode.

The secondary battery according to the second embodiment may further include a separator disposed between the first electrode and the second electrode. The first electrode, the second electrode, and the separator may constitute an electrode group. The electrolyte may be held in the electrode group. With regard to the lithium diffusion coefficient Dt in the thickness direction of the electrode group, i.e., in the stacking direction of the first electrode and the second electrode, the lithium diffusion coefficient Dt _E in a portion corresponding to the outer edge of the first electrode is higher than the lithium diffusion coefficient Dt _C in a portion corresponding to the center of the first electrode.

The secondary battery according to the second embodiment may further include an exterior member that contains the electrode group and the electrolyte.

Furthermore, the secondary battery according to the second embodiment may further include a first electrode terminal electrically connected to the first electrode and a second electrode terminal electrically connected to the second electrode. Here, the first electrode terminal and the second electrode terminal are referred to as negative electrode terminals when they are electrically connected to the first electrode as a negative electrode or the second electrode as a negative electrode. Similarly, the first electrode terminal and the second electrode terminal are referred to as positive electrode terminals when they are electrically connected to the first electrode as a positive electrode or the second electrode as a positive electrode.

The secondary battery according to the second embodiment may be, for example, a lithium secondary battery. The secondary battery also includes a non-aqueous electrolyte secondary battery that contains a non-aqueous electrolyte.

The first electrode, second electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal are described in detail below.

1) First Electrode The details of the first electrode overlap with the details of the electrode according to the first embodiment, and therefore the description thereof will be omitted here.

2) Second Electrode The second electrode may include a second active material-containing layer. The second active material-containing layer may contain a second active material that is a solid solution in which a charge/discharge reaction proceeds through a single solid-state reaction.

The second electrode may include a current collector. The second active material-containing layer may be supported on one main surface or both main surfaces of the current collector. The second active material-containing layer may further include a conductive agent and a binder in addition to the second active material.

The second electrode may further include a second solid electrolyte layer provided on the second main surface of the second active material-containing layer. The second solid electrolyte layer contains a solid electrolyte. The second solid electrolyte layer may further include a binder. The various materials that the second solid electrolyte layer may contain are similar to the various materials (solid electrolyte, inorganic compound, and binder) that the first solid electrolyte layer may contain in the electrode according to the first embodiment. The composition of the second solid electrolyte layer may be the same as or different from the composition of the first solid electrolyte layer.

In the second electrode including the second solid electrolyte layer, it is preferable that the second active material-containing layer includes a second solid electrolyte non-supporting portion where the second solid electrolyte layer is not provided. Below, we will explain the second electrode including the second solid electrolyte non-supporting portion.

The second main surface of the second electrode active material-containing layer includes a pair of third sides along the third direction. The second solid electrolyte layer may include a third portion along at least one of the pair of third sides. The second solid electrolyte layer may include one third portion along one of the pair of third sides, or a pair of third portions along each of the pair of third sides. Each third portion may have a third peripheral width T _S of 0.25 T _A or less with respect to the third width T _A between the pair of third sides. The third peripheral width T _S is preferably 0.03 T _A or more. Between the pair of third portions, the third peripheral width T _S may be the same or different. The third peripheral width T _S of each third portion may be the same as the first peripheral width F _S of the first portion and/or the second peripheral width S _S of the second portion, or may be different. The third width _TA between the third sides and the third peripheral width _TS of the third portion are each widths in the same direction.

The third direction here may be parallel to the first direction and intersect with the second direction. Alternatively, the third direction may intersect with the first direction and be parallel to the second direction. It is preferable that the third direction and the first direction are parallel.

The second solid electrolyte layer may further include a fourth portion. The second main surface of the second electrode active material-containing layer may further include a pair of fourth sides along a fourth direction intersecting with the third direction, and the fourth portion is along at least one of the pair of fourth sides. Thus, the second solid electrolyte layer may include one fourth portion along one of the pair of fourth sides, or may include a pair of fourth portions along each of the pair of fourth sides. In addition, each fourth portion has a fourth peripheral width U _S of 0.25 U _A or less with respect to the fourth width U _A between the pair of fourth sides. The fourth peripheral width U _S is preferably 0.03 U _A or more. Between the pair of fourth portions, the fourth peripheral width U _S may be the same or different. The fourth peripheral width U _S of each fourth portion may be the same as or different from the first peripheral width F _S of the first portion and/or the second peripheral width S _S of the second portion and/or the third peripheral width T _S of the third portion. The fourth width U _A between the fourth sides and the fourth peripheral width U _S of the fourth portion are each widths in the same direction.

The fourth direction intersects the third direction. The fourth direction can intersect the first direction and be parallel to the second direction. Alternatively, the fourth direction can be parallel to the first direction and intersect the second direction.

The third and fourth parts of the second solid electrolyte layer may have the same configuration as the first and second parts of the first solid electrolyte layer. In other words, the second electrode having the second solid electrolyte layer has the same configuration as the electrode (first electrode) according to the first embodiment, except that it has a second active material-containing layer containing a second active material instead of the first active material-containing layer containing the first active material. Details are omitted here to avoid duplication.

The second electrode that does not include a second solid electrolyte layer has a similar configuration to the second electrode that includes a second solid electrolyte layer, except for the presence or absence of the second solid electrolyte layer. Details are omitted here to avoid duplication.

The second electrode is included in the secondary battery as a counter electrode to the first electrode. On the one hand, in the case of a positive electrode, the second active material may be called a second positive electrode active material or simply a positive electrode active material. On the other hand, in the case of a negative electrode, the second active material may be called a second negative electrode active material or simply a negative electrode active material, and the second active material-containing layer may be called a second negative electrode active material-containing layer or simply a negative electrode active material-containing layer.

Examples of the second active material undergoing a single solid-phase reaction that can be contained in the second electrode, i.e., the second positive electrode active material, include lithium manganese nickel composite oxides having a spinel structure (e.g., a compound represented by Li _x Mn _2-w Ni _w O ₄ where 0<x≦1 and 0<w<2) and lithium nickel cobalt manganese composite oxides (e.g., a compound represented by Li _x Ni _1-yz Co _y Mn _z O ₂ where 0<x≦1, 0<y<1, 0<z<1, and y+z<1).

An example of a second active material undergoing a single solid-phase reaction that can be contained in the second electrode, i.e., the negative electrode active material, includes monoclinic niobium titanium composite oxide.

An example of the monoclinic niobium titanium composite oxide is a compound represented by Li _s Ti _1-t M4 _t Nb _2-u M5 _u O _7+δ . Here, M4 is at least one selected from the group consisting of Zr, Si, and Sn. M5 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦s≦5, 0≦t<1, 0≦u<2, and −0.3≦δ≦0.3. A specific example of the monoclinic niobium titanium composite oxide is Li _s Nb ₂ TiO ₇ (0≦s≦5).

Another example of the monoclinic niobium titanium composite oxide is a compound represented by Li _s Ti _1-t M6 _t+u Nb _2-u O _7-δ , where M6 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦s≦5, 0≦t<1, 0≦u<2, and −0.3≦δ≦0.3.

The details of the conductive agent, binder, and current collector are the same as those in the electrode according to the first embodiment. Therefore, a description thereof will be omitted here.

The density of the second negative electrode active material-containing layer (excluding the current collector) is preferably 1.8 g/cm ³ or more and 2.8 g/cm ³ or less. The reason is the same as that of the density of the first negative electrode active material-containing layer described in the first embodiment. The density of the negative electrode active material-containing layer is more preferably 2.1 g/cm ³ or more and 2.6 g/cm ³ or less.

The primary particle size of the second positive electrode active material is preferably 100 nm to 1 μm, and the specific surface area of the second positive electrode active material is preferably 0.1 m ² /g to 10 m ² /g for the same reasons as those for the first positive electrode active material described in the first embodiment.

The second electrode can be produced in the same manner as the electrode according to the first embodiment, except that the second active material-containing layer is formed using the second active material instead of the first active material-containing layer. In addition, in producing the second electrode, the formation of the solid electrolyte layer (first solid electrolyte layer), that is, the application and drying of the solid electrolyte-containing slurry, may be omitted. When providing a solid electrolyte layer, the second solid electrolyte layer is formed on the second active material-containing layer in the same procedure as the formation of the first solid electrolyte layer, instead of forming the first solid electrolyte layer on the first active material-containing layer.

The various measurement methods described in the first embodiment, i.e., the measurement methods for the first electrode, can be similarly applied to the second electrode. For example, the third peripheral width T _S and the fourth peripheral width U _S of the second electrode can be measured in the same manner as the measurement method for the first peripheral width F _S and the second peripheral width S _S of the first electrode.

3) Electrolyte As the electrolyte, for example, a liquid nonaqueous electrolyte or a gel nonaqueous electrolyte can be used. The liquid nonaqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol/L or more and 2.5 mol/L or less.

Examples of the electrolyte salt include lithium perchlorate ( _LiClO4 ), lithium hexafluorophosphate ( _LiPF6 ), lithium tetrafluoroborate ( _LiBF4 ), lithium hexafluoroarsenic ( _LiAsF6 ), lithium trifluoromethanesulfonate ( _LiCF3SO3 ), and lithium salts such as _{lithium bistrifluoromethylsulfonylimide (LiN(CF3SO2)2), lithium bis(fluorosulfonyl)imide (LiN(SO2F)2 ; LiFSI ) ,} and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potentials, _{and LiPF6} is most preferred.

Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as a mixed solvent.

The gelled non-aqueous electrolyte is prepared by combining a liquid non-aqueous electrolyte with a polymeric material. Examples of the polymeric material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or a mixture thereof.

Alternatively, in addition to liquid nonaqueous electrolytes and gel nonaqueous electrolytes, room temperature molten salts containing lithium ions (ionic melts), polymer solid electrolytes, inorganic solid electrolytes, etc. may be used as the nonaqueous electrolyte.

A room temperature molten salt (ionic melt) refers to a compound that can exist as a liquid at room temperature (15°C or higher and 25°C or lower) among organic salts consisting of a combination of organic cations and anions. Room temperature molten salts include room temperature molten salts that exist as liquid by themselves, room temperature molten salts that become liquid when mixed with an electrolyte salt, room temperature molten salts that become liquid when dissolved in an organic solvent, and mixtures of these. In general, the melting point of room temperature molten salts used in secondary batteries is 25°C or lower. In addition, organic cations generally have a quaternary ammonium skeleton.

Polymer solid electrolytes are prepared by dissolving an electrolyte salt in a polymer material and solidifying it.

An inorganic solid electrolyte is a solid material that has Li ion conductivity.

Alternatively, instead of a non-aqueous electrolyte, a liquid aqueous electrolyte or a gel aqueous electrolyte can be used as the electrolyte. The liquid aqueous electrolyte is prepared by dissolving, for example, the above-mentioned electrolyte salt as a solute in an aqueous solvent. The gel aqueous electrolyte is prepared by compounding the liquid aqueous electrolyte with the above-mentioned polymer material. As the aqueous solvent, a solution containing water can be used. The solution containing water may be pure water or a mixed solvent of water and an organic solvent.

4) Separator The separator is formed, for example, from a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene. This is because these porous films melt at a certain temperature and are capable of cutting off electric current.

5) Exterior Member As the exterior member, for example, a container made of a laminate film or a metal container can be used.

The thickness of the laminate film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

As the laminate film, a multilayer film containing multiple resin layers and metal layers interposed between these resin layers is used. The resin layers contain polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior member by sealing it by heat fusion.

The thickness of the metal container wall is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content is preferably 1 mass% or less.

The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior member can be appropriately selected depending on the battery dimensions and the application of the battery.

6) Negative electrode terminal The negative electrode terminal can be formed from a material that is electrochemically stable in a potential range of 0.8V to 3V (vs. Li/Li ⁺ ) relative to the redox potential of lithium and has electrical conductivity. Specifically, the material of the negative electrode terminal can be copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The material of the negative electrode terminal is preferably aluminum or an aluminum alloy. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce the contact resistance with the negative electrode current collector.

7) Positive Electrode Terminal The positive electrode terminal can be formed from a material that is electrically stable in a potential range of 3 V to 4.5 V with respect to the redox potential of lithium (vs. Li/Li ⁺ ) and has electrical conductivity. Examples of the material for the positive electrode terminal include aluminum and aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably formed from the same material as the positive electrode collector in order to reduce the contact resistance with the positive electrode collector.

Next, the secondary battery according to the second embodiment will be described in more detail with reference to the drawings.

Figure 6 is a cross-sectional view that shows a schematic example of a secondary battery according to the second embodiment. Figure 7 is an enlarged cross-sectional view of part A of the secondary battery shown in Figure 6. Specifically, Figure 7 shows a cross-section along the first side of the first electrode included in the secondary battery shown in Figure 6.

The secondary battery 100 shown in Figs. 6 and 7 includes an electrode group 1 shown in Fig. 6, a bag-shaped exterior member 2 shown in Figs. 6 and 7, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the bag-shaped exterior member 2. The electrolyte (not shown) is held in the electrode group 1.

The bag-shaped exterior member 2 is made of a laminate film that includes two resin layers and a metal layer interposed between them.

As shown in FIG. 6, the electrode group 1 is a flat wound electrode group. As shown in FIG. 7, the flat wound electrode group 1 includes a first electrode 3, a separator 4, and a second electrode 5. The separator 4 is interposed between the first electrode 3 and the second electrode 5.

The first electrode 3 includes a first current collector 3a, a first active material-containing layer 3b, and a first solid electrolyte layer 3d. In the first electrode 3, the portion located at the outermost shell of the wound electrode group 1 has the first active material-containing layer 3b formed only on the inner surface side of the first current collector 3a as shown in FIG. 7. In the other portion of the first electrode 3, the first active material-containing layer 3b is formed on both sides of the first current collector 3a. The first solid electrolyte layer 3d is formed on the first active material-containing layer 3b on the opposite side to the first current collector 3a. The first solid electrolyte layer 3d is interposed between the first active material-containing layer 3b and the separator 4.

The part of the first electrode 3 located at the outermost shell of the wound electrode group 1 may have a structure similar to that of the first electrode 3 illustrated in FIG. 1 and FIG. 2. The other parts of the first electrode 3 may have a structure similar to that of the first electrode 3 illustrated in FIG. 1 and FIG. 2, except that the first active material-containing layer 3b and the first solid electrolyte layer 3d are provided on both sides of the first current collector 3a, not just one side. In this way, if the first electrode 3 illustrated in FIG. 6 and FIG. 7 is considered to correspond to the first electrode 3 illustrated in FIG. 1 and FIG. 2, it can be said that FIG. 6 and FIG. 7 are cross sections along the first direction 11 illustrated in FIG. 1. In this case, the wound electrode group 1 can be said to be a laminate of the first electrode 3, the separator 4, and the second electrode 5 wound around a virtual axis parallel to the second direction 12.

The second electrode 5 includes a second current collector 5a and a second active material-containing layer 5b formed on both sides of the second current collector 5a.

As shown in FIG. 6, the first electrode terminal 6 and the second electrode terminal 7 are located near the outer periphery of the wound electrode group 1. The first electrode terminal 6 is connected to a portion located on the outermost shell of the first current collector 3a. The second electrode terminal 7 is connected to a portion located on the outermost shell of the second current collector 5a. The first electrode terminal 6 and the second electrode terminal 7 extend outward from the opening of the bag-shaped exterior member 2. A thermoplastic resin layer is provided on the inner surface of the bag-shaped exterior member 2, and the opening is closed by heat sealing the layer.

The secondary battery according to the second embodiment is not limited to the secondary battery having the configuration shown in FIGS. 6 and 7, but may be, for example, a battery having the configuration shown in FIGS. 8 and 9.

Figure 8 is a partially cutaway perspective view showing a schematic diagram of another example of a secondary battery according to the second embodiment. Figure 9 is an enlarged cross-sectional view of part B of the secondary battery shown in Figure 8.

The secondary battery 100 shown in Figs. 8 and 9 includes an electrode group 1 shown in Figs. 8 and 9, an exterior member 2 shown in Fig. 8, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the exterior member 2. The electrolyte is held in the electrode group 1.

The exterior member 2 is made of a laminate film that includes two resin layers and a metal layer interposed between them.

As shown in FIG. 9, the electrode group 1 is a laminated electrode group. The laminated electrode group 1 has a structure in which first electrodes 3 and second electrodes 5 are alternately laminated with a separator 4 interposed therebetween.

The electrode group 1 includes a plurality of first electrodes 3. Each of the plurality of first electrodes 3 includes a first current collector 3a, a first active material-containing layer 3b supported on both sides of the first current collector 3a, and a first solid electrolyte layer 3d supported along the edge portion on the main surface of the first active material-containing layer 3b on each side. The first solid electrolyte layer 3d is not supported on the central portion of the main surface of the first active material-containing layer 3b. The electrode group 1 also includes a plurality of second electrodes 5. Each of the plurality of second electrodes 5 includes a second current collector 5a and a second active material-containing layer 5b supported on both sides of the second current collector 5a.

The first current collector 3a of each first electrode 3 includes a portion on one side where the first active material-containing layer 3b is not supported on any surface, i.e., a first current collector tab 3c. As shown in FIG. 9, the first current collector tab 3c does not overlap with the second electrode 5. In addition, the multiple first current collector tabs 3c are electrically connected to a strip-shaped first electrode terminal 6. The tip of the strip-shaped first electrode terminal 6 is pulled out to the outside of the exterior member 2.

Each first electrode 3 may be the first electrode 3 illustrated in Figures 3 to 5.

Although not shown, the second current collector 5a of each second electrode 5 includes a portion on one side where the second active material-containing layer 5b is not supported on any surface. This portion serves as a second current collector tab. The second current collector tab, like the first current collector tab 3c, does not overlap with the first electrode 3. The second current collector tab is located on the opposite side of the electrode group 1 to the first current collector tab 3c. The second current collector tab is electrically connected to the band-shaped second electrode terminal 7. The tip of the band-shaped second electrode terminal 7 is located on the opposite side to the first electrode terminal 6 and is drawn out to the outside of the exterior member 2.

In the above example, a secondary battery in which the second electrode does not have a solid electrolyte layer on the second active material-containing layer was exemplified. However, as described above, in addition to the first solid electrolyte layer provided on the outer edge of the main surface of the first active material-containing layer of the first electrode, a second solid electrolyte layer can also be provided on the outer edge of the main surface of the second active material-containing layer of the second electrode. An example of a second electrode including a second solid electrolyte layer is shown below.

Figure 10 is a plan view that shows a schematic example of a second electrode that may be included in a secondary battery according to an embodiment. Figure 11 is a schematic cross-sectional view taken along line XI-XI' in Figure 10. In the example electrode shown in Figures 10 and 11, the outer edge portion in the second main surface of the second active material-containing layer includes the third region but does not include the fourth region. In other words, the second electrode shown in Figures 10 and 11 is an example in which the second solid electrolyte layer includes the third portion but does not include the fourth portion.

The second electrode 5 of the example illustrated in FIG. 10 and FIG. 11 has a band shape defined by a pair of long sides along the third direction 13 and a pair of short sides along the fourth direction 14 intersecting the third direction 13. The second electrode 5 having such a band shape may be, for example, a modified example of the second electrode 5 included in the wound-type electrode group 1 shown in FIG. 6 and FIG. 7. The band shape may be a rectangular shape. The second electrode 5 includes a second current collector 5a having a band shape, a second active material-containing layer 5b having a band shape provided on one of its main surfaces, and a second solid electrolyte layer 5d provided on the second active material-containing layer 5b.

The configuration of the second electrode 5 in this example is essentially the same as the configuration of the first electrode 3 illustrated in Figures 1 and 2, except that it includes a second active material-containing layer 5b containing a second active material that undergoes a single solid-phase reaction instead of the first active material-containing layer 3b containing a first active material that undergoes a two-phase coexistence reaction, and therefore a partial description will be omitted.

A pair of band-shaped second solid electrolyte layers 5d are arranged such that their long sides are aligned with a pair of third sides 23 aligned with the third direction 13 of the second active material-containing layer 5b. The second solid electrolyte layer 5d includes a pair of third portions 53a provided within a range of a third region 53 in the second main surface of the second active material-containing layer 5b. Each of the third portions 53a is arranged along each of the third sides 23. The third peripheral width T _S of each of the third portions 53a in the fourth direction 14 is 0.25T _A or less with respect to the third width T _A which is also the width of the second active material-containing layer 5b in the fourth direction 14 and is the width between the third sides 23. It is preferable that the third peripheral width T _S is a value in the range of 0.03T _A or more and 0.25T _A or less.

The portion of the second main surface excluding the outer edge portion including the third region 53 corresponds to the central portion 50. The second active material-containing layer 5b corresponds to the central portion 50 in the second main surface, and includes a second solid electrolyte non-supporting portion 50a where the second solid electrolyte layer 5d is not provided.

In the second electrode 5 in which the second solid electrolyte layer 5d is provided in the region corresponding to the outer edge portion (third region 53), the lithium diffusion coefficient _DtE in the thickness direction at the outer edge portion (third portion 53a) is higher than the lithium diffusion coefficient _DtC in the thickness direction at the central portion 50. The thickness direction here is a direction intersecting the second main surface and aligned with the stacking direction of the second active material-containing layer 5b and the second solid electrolyte layer 5d. In FIG. 11, the thickness direction corresponds to the vertical direction.

Figure 12 is a plan view that shows a schematic diagram of another example of a second electrode that may be included in a secondary battery according to an embodiment. Figure 13 is a schematic cross-sectional view taken along line XIII-XIII' in Figure 12. Figure 14 is a schematic cross-sectional view taken along line XIV-XIV' in Figure 12.

The second electrode 5 in the example illustrated in Figures 12 to 14 has a rectangular shape defined by a pair of short sides along the third direction 13 and a pair of long sides along the fourth direction 14 intersecting the third direction 13. An electrode having such a rectangular shape may be, for example, a modified example of the second electrode 5 included in the stacked electrode group 1 shown in Figures 8 and 9. The second electrode 5 includes a flat second current collector 5a, a rectangular second active material-containing layer 5b provided on one of its main surfaces, and a second solid electrolyte layer 5d provided on the second active material-containing layer 5b.

The configuration of the second electrode 5 in this example is essentially the same as the configuration of the first electrode 3 illustrated in Figures 3 to 5, except that it includes a second active material-containing layer 5b containing a second active material that undergoes a single solid-phase reaction instead of a first active material-containing layer 3b containing a first active material that undergoes a two-phase coexistence reaction, and therefore a partial description will be omitted.

The frame-shaped second solid electrolyte layer 5d is provided within the range of the third region 53 in the second main surface of the second active material-containing layer 5b, and includes a pair of third portions 53a along a pair of third sides 23 along the third direction 13. The second portion 32a of the first solid electrolyte layer 3d is provided within the range of the fourth region 54 in the second main surface of the second active material-containing layer 5b, and also includes a pair of fourth portions 54a along a pair of fourth sides 24 along the fourth direction 14.

The third peripheral width T _S of each third portion 53a in the fourth direction 14 is 0.25T A or less relative to the third width T _A , which is also the width of the second active material-containing layer 5b in the fourth direction 14 and the width between the third sides 23. It is preferable that the third peripheral width T _S is a value in the range of 0.03T _{A or more and 0.25T A or} less. The fourth peripheral width U _S of each fourth portion 54a in the third direction 13 is 0.25U _A or less relative to the fourth width U _A , which is also the width of the second active material-containing layer 5b in the third direction 13 and the width between the fourth sides 24. It is preferable that the fourth peripheral width U _S is a value in the range of 0.03U _A or more and 0.25U _A or less.

The portion of the second main surface excluding the outer edge portion including the third region 53 and the fourth region 54 corresponds to the central portion 50. The second active material-containing layer 5b corresponds to the central portion 50 in the second main surface, and includes a second solid electrolyte non-supporting portion 50a on which the second solid electrolyte layer 5d is not provided.

In the second electrode 5 in which the second solid electrolyte layer 5d is provided in the region corresponding to the outer edge including the third region 53 and the fourth region 54, the lithium diffusion coefficient _DtE in the thickness direction at the outer edge is higher than the lithium diffusion coefficient _DtC in the thickness direction at the central portion 50. The thickness direction here is a direction intersecting the second main surface and aligned with the stacking direction of the second active material-containing layer 5b and the second solid electrolyte layer 5d. In Figs. 13 and 14, the thickness direction corresponds to the vertical direction.

The secondary battery according to the second embodiment includes the electrode according to the first embodiment. Therefore, the secondary battery according to the second embodiment is prevented from decreasing in capacity.

[Third embodiment]
According to a third embodiment, there is provided a battery pack including a plurality of secondary batteries according to the second embodiment.

In the battery pack according to the third embodiment, the individual cells may be electrically connected in series or parallel, or may be arranged in a combination of series and parallel connections.

Next, an example of a battery pack according to the third embodiment will be described with reference to the drawings.

Figure 15 is a perspective view that shows a schematic example of a battery pack according to the third embodiment. The battery pack 200 shown in Figure 15 includes five cells 100a to 100e, four bus bars 201, a positive electrode lead 202, and a negative electrode lead 203. Each of the five cells 100a to 100e is a secondary battery according to the second embodiment.

The bus bar 201 connects, for example, the negative terminal 206 of one cell 100a to the positive terminal 207 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by the four bus bars 201. That is, the battery pack 200 in FIG. 15 is a five-cell battery pack. Although no example is shown, in a battery pack including a plurality of cells electrically connected in parallel, for example, the plurality of negative terminals are connected to each other by a bus bar and the plurality of positive terminals are connected to each other by a bus bar, so that the plurality of cells are electrically connected.

The positive terminal 207 of at least one of the five cells 100a to 100e is electrically connected to the positive lead 202 for external connection. The negative terminal 206 of at least one of the five cells 100a to 100e is electrically connected to the negative lead 203 for external connection.

The battery pack according to the third embodiment includes the secondary battery according to the second embodiment. Therefore, the capacity reduction is suppressed in the battery pack.

[Fourth embodiment]
According to a fourth embodiment, there is provided a battery pack. The battery pack includes the battery assembly according to the third embodiment. The battery pack may include a single secondary battery according to the second embodiment, instead of the battery assembly according to the third embodiment.

The battery pack according to the fourth embodiment may further include a protection circuit. The protection circuit has a function of controlling charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobiles, etc.) may be used as the protection circuit for the battery pack.

The battery pack according to the fourth embodiment may further include an external terminal for current flow. The external terminal for current flow is for outputting current from the secondary battery to the outside and/or for inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminal for current flow. When the battery pack is charged, a charging current (including regenerative energy from the power of an automobile or the like) is supplied to the battery pack through the external terminal for current flow.

Next, an example of a battery pack according to the fourth embodiment will be described with reference to the drawings.

Figure 16 is an exploded perspective view that shows a schematic example of a battery pack according to the fourth embodiment. Figure 17 is a block diagram showing an example of an electrical circuit of the battery pack shown in Figure 16.

The battery pack 300 shown in Figures 16 and 17 includes a container 301, a lid 302, a protective sheet 303, a battery pack 200, a printed wiring board 340, wiring 347, and an insulating plate (not shown).

The storage container 301 shown in FIG. 16 is a bottomed, square container having a rectangular bottom. The storage container 301 is configured to be able to store the protective sheet 303, the battery pack 200, the printed wiring board 340, and the wiring 347. The lid 302 has a rectangular shape. The lid 302 covers the storage container 301 to store the battery pack 200 and the like. Although not shown, the storage container 301 and the lid 302 are provided with openings or connection terminals for connection to external devices and the like.

The battery pack 200 includes a plurality of cells 100, a positive electrode lead 202, a negative electrode lead 203, and an adhesive tape 204.

At least one of the multiple cells 100 is a secondary battery according to the second embodiment. Each of the multiple cells 100 is electrically connected in series as shown in FIG. 17. The multiple cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. When the multiple cells 100 are connected in parallel, the battery capacity is increased compared to when they are connected in series.

The adhesive tape 204 fastens the multiple cells 100 together. Instead of the adhesive tape 204, heat shrink tape may be used to secure the multiple cells 100 together. In this case, protective sheets 303 are placed on both sides of the battery pack 200, the heat shrink tape is wrapped around the battery pack 200, and the heat shrink tape is then thermally shrunk to bind the multiple cells 100 together.

One end of the positive electrode lead 202 is connected to the battery pack 200. One end of the positive electrode lead 202 is electrically connected to the positive electrode of one or more single cells 100. One end of the negative electrode lead 203 is connected to the battery pack 200. One end of the negative electrode lead 203 is electrically connected to the negative electrode of one or more single cells 100.

The printed wiring board 340 is installed along one of the short sides of the inner surface of the container 301. The printed wiring board 340 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for supplying electricity, a positive wiring (positive wiring) 348a, and a negative wiring (negative wiring) 348b. One main surface of the printed wiring board 340 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed wiring board 340 and the battery pack 200.

The other end 202a of the positive electrode lead 202 is electrically connected to the positive electrode connector 342. The other end 203a of the negative electrode lead 203 is electrically connected to the negative electrode connector 343.

The thermistor 345 is fixed to one main surface of the printed wiring board 340. The thermistor 345 detects the temperature of each of the cells 100 and transmits the detection signal to the protection circuit 346.

The external terminals 350 for electrical current flow are fixed to the other main surface of the printed wiring board 340. The external terminals 350 for electrical current flow are electrically connected to a device that is external to the battery pack 300. The external terminals 350 for electrical current flow include a positive terminal 352 and a negative terminal 353.

The protection circuit 346 is fixed to the other main surface of the printed wiring board 340. The protection circuit 346 is connected to the positive terminal 352 via the positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative wiring 348b. The protection circuit 346 is also electrically connected to the positive connector 342 via the wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via the wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the multiple single cells 100 via the wiring 347.

The protective sheet 303 is disposed on both inner surfaces of the long sides of the container 301 and on the inner surface of the short side that faces the printed wiring board 340 via the battery pack 200. The protective sheet 303 is made of, for example, resin or rubber.

The protection circuit 346 controls the charging and discharging of the multiple single cells 100. In addition, the protection circuit 346 cuts off the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for supplying electricity to an external device based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from each single cell 100 or the battery pack 200.

The detection signal transmitted from the thermistor 345 may be, for example, a signal that detects that the temperature of the cell 100 is equal to or higher than a predetermined temperature. The detection signal transmitted from each cell 100 or the battery pack 200 may be, for example, a signal that detects overcharging, overdischarging, or overcurrent of the cell 100. When detecting overcharging or the like for each cell 100, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

The protection circuit 346 may be a circuit included in a device (e.g., electronic device, automobile, etc.) that uses the battery pack 300 as a power source.

As described above, the battery pack 300 is provided with an external terminal 350 for current flow. Therefore, the battery pack 300 can output current from the assembled battery 200 to an external device and input current from the external device to the assembled battery 200 via the external terminal 350 for current flow. In other words, when the battery pack 300 is used as a power source, the current from the assembled battery 200 is supplied to the external device through the external terminal 350 for current flow. When the battery pack 300 is charged, a charging current from the external device is supplied to the battery pack 300 through the external terminal 350 for current flow. When the battery pack 300 is used as an in-vehicle battery, regenerative energy of the vehicle's power can be used as the charging current from the external device.

The battery pack 300 may include a plurality of assembled batteries 200. In this case, the assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 340 and the wiring 347 may be omitted. In this case, the positive electrode lead 202 and the negative electrode lead 203 may be used as the positive terminal 352 and the negative terminal 353, respectively, of the external terminal 350 for current supply.

Such battery packs are used in applications that require excellent cycle performance, for example, when drawing a large current. Specifically, these battery packs are used, for example, as power sources for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. These battery packs are particularly suitable for use as on-board batteries.

The battery pack according to the fourth embodiment includes the secondary battery according to the second embodiment or the battery pack according to the third embodiment. Therefore, the capacity reduction is suppressed in such a battery pack.

[Fifth embodiment]
According to a fifth embodiment, a vehicle is provided. The vehicle is equipped with the battery pack according to the fourth embodiment.

In the vehicle according to the fifth embodiment, the battery pack, for example, recovers regenerative energy from the vehicle's motive power. The vehicle may include a mechanism (regenerator) that converts the kinetic energy of the vehicle into regenerative energy.

Examples of vehicles according to the fifth embodiment include hybrid electric vehicles with two to four wheels, electric vehicles with two to four wheels, power-assisted bicycles, and rail vehicles.

The mounting position of the battery pack in the vehicle according to the fifth embodiment is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack can be mounted in the engine compartment, the rear of the vehicle body, or under the seat of the vehicle.

The vehicle according to the fifth embodiment may be equipped with a plurality of battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. For example, when each battery pack includes a battery pack, the battery packs may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. Alternatively, when each battery pack includes a single battery, the batteries may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections.

Next, an example of a vehicle according to the fifth embodiment will be described with reference to the drawings.

Figure 18 is a partially transparent view that shows an example of a vehicle according to the fifth embodiment.

The vehicle 400 shown in FIG. 18 includes a vehicle body 40 and a battery pack 300 according to the fourth embodiment. In the example shown in FIG. 18, the vehicle 400 is a four-wheeled automobile.

The vehicle 400 may be equipped with multiple battery packs 300. In this case, the batteries (e.g., single cells or assembled batteries) included in the battery packs 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

Figure 18 illustrates an example in which the battery pack 300 is mounted in an engine compartment located in front of the vehicle body 40. As described above, the battery pack 300 may be mounted, for example, at the rear of the vehicle body 40 or under a seat. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy for the power of the vehicle 400.

Next, an implementation of a vehicle according to the fifth embodiment will be described with reference to FIG.

Figure 19 is a diagram that shows an example of a control system for an electrical system in a vehicle according to the fifth embodiment. The vehicle 400 shown in Figure 19 is an electric vehicle.

The vehicle 400 shown in FIG. 19 includes a vehicle body 40, a vehicle power supply 41, a vehicle ECU (Electric Control Unit) 42 which is a higher-level control device for the vehicle power supply 41, an external terminal (terminal for connecting to an external power supply) 43, an inverter 44, and a drive motor 45.

The vehicle 400 is equipped with a vehicle power source 41, for example, in the engine compartment, at the rear of the vehicle body, or under the seat. Note that in the vehicle 400 shown in FIG. 19, the location where the vehicle power source 41 is installed is shown diagrammatically.

The vehicle power supply 41 includes multiple (e.g., three) battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

Battery pack 300a includes battery pack 200a and battery pack monitoring device 310a (e.g., VTM: Voltage Temperature Monitoring). Battery pack 300b includes battery pack 200b and battery pack monitoring device 310b. Battery pack 300c includes battery pack 200c and battery pack monitoring device 310c. Battery packs 300a to 300c are battery packs similar to battery pack 300 described above, and battery packs 200a to 200c are battery packs similar to battery pack 200 described above. Battery packs 200a to 200c are electrically connected in series. Battery packs 300a, 300b, and 300c can each be removed independently and replaced with another battery pack 300.

Each of the assembled batteries 200a to 200c includes a plurality of unit cells connected in series. At least one of the plurality of unit cells is a secondary battery according to the second embodiment. Each of the assembled batteries 200a to 200c is charged and discharged through a positive terminal 413 and a negative terminal 414.

The battery management device 411 communicates with the battery pack monitoring devices 310a to 310c and collects information on the voltage, temperature, and the like for each of the cells 100 included in the battery packs 200a to 200c included in the vehicle power supply 41. In this way, the battery management device 411 collects information on the maintenance of the vehicle power supply 41.

The battery management unit 411 and the assembled battery monitoring units 310a to 310c are connected via a communication bus 412. In the communication bus 412, a set of communication lines is shared by multiple nodes (the battery management unit 411 and one or more assembled battery monitoring units 310a to 310c). The communication bus 412 is a communication bus configured based on, for example, the CAN (Control Area Network) standard.

The battery pack monitoring devices 310a to 310c measure the voltage and temperature of each of the cells that make up the battery packs 200a to 200c based on commands received through communication from the battery management device 411. However, the temperature can be measured at only a few points per battery pack, and it is not necessary to measure the temperature of all of the cells.

The vehicle power supply 41 may also have an electromagnetic contactor (e.g., the switch device 415 shown in FIG. 19) that switches between the presence and absence of electrical connection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that is turned on when the assembled batteries 200a to 200c are charged, and a main switch (not shown) that is turned on when the output from the assembled batteries 200a to 200c is supplied to a load. Each of the pre-charge switch and the main switch includes a relay circuit (not shown) that is switched on or off by a signal supplied to a coil arranged near the switch element. The electromagnetic contactor such as the switch device 415 is controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 that controls the operation of the entire vehicle 400.

The inverter 44 converts the input DC voltage into a three-phase AC high voltage for driving the motor. The three-phase output terminals of the inverter 44 are connected to the three-phase input terminals of the drive motor 45. The inverter 44 is controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 for controlling the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

The drive motor 45 rotates using the power supplied from the inverter 44. The drive force generated by the rotation of the drive motor 45 is transmitted to the axle and drive wheels W, for example, via a differential gear unit.

Although not shown, the vehicle 400 is also equipped with a regenerative braking mechanism (regenerator). The regenerative braking mechanism rotates the drive motor 45 when the vehicle 400 is braked, and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 44 and converted into direct current. The converted direct current is input to the vehicle power source 41.

One terminal of the connection line L1 is connected to the negative terminal 414 of the vehicle power supply 41. The other terminal of the connection line L1 is connected to the negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 in the battery management device 411 is provided on the connection line L1 between the negative terminal 414 and the negative input terminal 417.

One terminal of the connection line L2 is connected to the positive terminal 413 of the vehicle power supply 41. The other terminal of the connection line L2 is connected to the positive input terminal 418 of the inverter 44. A switch device 415 is provided on the connection line L2 between the positive terminal 413 and the positive input terminal 418.

The external terminal 43 is connected to the battery management device 411. The external terminal 43 can be connected to, for example, an external power source.

In response to operational inputs from the driver, etc., the vehicle ECU 42 coordinates with other management and control devices, including the battery management device 411, to control the vehicle power supply 41, the switch device 415, the inverter 44, etc. Through coordinated control by the vehicle ECU 42, etc., the output of power from the vehicle power supply 41 and the charging of the vehicle power supply 41 are controlled, and the entire vehicle 400 is managed. Data related to the maintenance of the vehicle power supply 41, such as the remaining capacity of the vehicle power supply 41, is transferred between the battery management device 411 and the vehicle ECU 42 via a communication line.

The vehicle according to the fifth embodiment is equipped with the battery pack according to the fourth embodiment. Since the capacity loss is suppressed in the battery pack, it is possible to provide a highly reliable vehicle.

[Example]
Examples will be described below, but the embodiments are not limited to the examples described below.

Example 1
<Preparation of First Electrode>
Spinel-type lithium titanate Li ₄ Ti ₅ O ₁₂ (LTO) was prepared as the first active material. Carbon black (CB) was prepared as the conductive agent. Polyvinylidene fluoride (PVdF) was prepared as the binder. These materials were added to N-methyl-2-pyrrolidone (NMP) as a dispersion solvent in a mass ratio of LTO:CB:PVdF=100:4:2 and mixed to prepare an active material-containing slurry. This slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 12 μm. The slurry coating was then dried and pressed to form a first active material-containing layer. The first active material-containing layer was then cut out so that the outline of the main surface of the first active material-containing layer was rectangular. However, a current collecting tab was formed by leaving a portion of the current collector on one side of the rectangle where the active material-containing layer was not formed.

Next, _{Li1.5Al0.5Ti1.5} ( _PO4 ) ₃ (LATP) was prepared as a solid electrolyte. _{Carboxymethylcellulose} (CMC) and styrene butadiene rubber (SBR ₎ were prepared as binders. These materials were weighed out so that the mass ratio of LATP:CMC:SBR was 100:1:1, and mixed with water as a dispersion solvent to prepare a solid electrolyte-containing slurry. This slurry was applied to the first active material-containing layer on both sides by a spray deposition method, and dried to remove water, thereby forming a first solid electrolyte layer.

Here, the solid electrolyte-containing slurry was applied along the four sides of the rectangle on the main surface of the first active material-containing layer on each side to form a frame-shaped first solid electrolyte layer. On each side, the first solid electrolyte layer was formed with a width 0.1 times the total width of the first active material-containing layer. That is, the first peripheral width F _S of the first part of the first solid electrolyte layer along two parallel sides of the four sides of the rectangle was 0.1F _A with respect to the first width F _A between those two sides, and the second peripheral width S _S of the second part of the first solid electrolyte layer along the remaining two sides was 0.1S _A with respect to the second width S _A between those two sides.

In this way, a first electrode having a first active material-containing layer and a first solid electrolyte layer was produced.

<Preparation of Second Electrode>
A lithium nickel cobalt manganese composite oxide LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM) was prepared as the second active material. Acetylene black (AB) and carbon black (CB) were prepared as the conductive agent. Polyvinylidene fluoride (PVdF) was prepared as the binder. These materials were added to N-methyl-2-pyrrolidone (NMP) as a dispersion solvent in a mass ratio of NCM:AB:CB:PVdF=100:3.33:1.67:1.2 and mixed to prepare an active material-containing slurry. This slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 12 μm. The slurry coating was then dried and pressed to form a second active material-containing layer. The second active material-containing layer was then cut out so that the outline of the main surface was rectangular. However, a current collecting tab was formed by leaving a portion of one side of the rectangle where the active material-containing layer was not formed in the current collector.

In this way, a second electrode having a second active material-containing layer was produced.

<Preparation of electrode group>
A cellulose separator having a thickness of 15 μm was prepared. A plurality of the first electrodes, a separator, and a plurality of the second electrodes were laminated in the order of "-first electrode-separator-second electrode-separator-first electrode-separator-second electrode-separator" to obtain a laminated electrode group.

<Preparation of Liquid Electrolyte>
A mixed solvent was obtained by mixing propylene carbonate (PC) and diethyl carbonate (DEC) in a volume ratio of PC:DEC = 1:2. A liquid non-aqueous electrolyte was prepared by dissolving 1.0 M of lithium hexafluorophosphate (LiPF ₆ ) in the mixed solvent.

<Battery assembly>
The electrode group was housed in a pack made of a laminate film composed of an aluminum foil and a polypropylene layer formed on both sides of the aluminum foil. The liquid nonaqueous electrolyte was then injected into the laminate film pack containing the electrode group. The laminate film pack was completely sealed by heat sealing to prepare a battery.

Example 2
A battery was fabricated in the same manner as in Example 1, except that the first peripheral width _F.sub.S of the first portion of the first solid electrolyte layer was changed to _0.25FA and the second peripheral width _S.sub.S of the second portion was changed to _0.25SA .

Example 3
A battery was fabricated in the same manner as in Example 1, except that second solid electrolyte layers were formed on both main surfaces of the second active material-containing layer of the second electrode as described below.

A solid electrolyte-containing slurry having the same composition as that prepared for forming the first solid electrolyte layer was prepared. This slurry was applied to both sides of the second active material-containing layer by spray deposition, and then dried to remove water, forming a second solid electrolyte layer.

Here, the solid electrolyte-containing slurry was applied along the four sides of the rectangle on the main surface of the second active material-containing layer on each side to form a frame-shaped second solid electrolyte layer. On each side, the second solid electrolyte layer was formed with a width 0.1 times the total width of the second active material-containing layer. That is, the third peripheral width T _S of the third part of the second solid electrolyte layer along two parallel sides of the four sides of the rectangle was 0.1T _A with respect to the third width T _A between those two sides, and the fourth peripheral width U _S of the fourth part of the second solid electrolyte layer along the remaining two sides was 0.1U _A with respect to the fourth width U _A between those two sides.

Example 4
A battery was produced in the same manner as in Example 1, except that the production conditions for the first electrode and the second electrode were changed as follows.

A first electrode was prepared in the same manner as in Example 1, except that the composition of the active material-containing slurry used to prepare the first electrode was changed as follows. Lithium iron phosphate LiFePO ₄ (LFP) having an olivine structure was prepared as the first active material. Acetylene black (AB) and carbon black (CB) were prepared as conductive agents. Polyvinylidene fluoride (PVdF) was prepared as a binder. These materials were added to N-methyl-2-pyrrolidone (NMP) as a dispersion solvent in a mass ratio of LFP:AB:CB:PVdF=100:3.33:1.67:1.2 and mixed to prepare a slurry containing the active material.

A second electrode was prepared in the same manner as in Example 1, except that the composition of the active material-containing slurry used in preparing the second electrode was changed as follows. Monoclinic niobium titanium composite oxide Nb ₂ TiO ₇ (NTO) was prepared as the first active material. Carbon black (CB) was prepared as the conductive agent. Polyvinylidene fluoride (PVdF) was prepared as the binder. These materials were added to N-methyl-2-pyrrolidone (NMP) as a dispersion solvent in a mass ratio of NTO:CB:PVdF = 100:4:2 and mixed to prepare an active material-containing slurry.

Example 5
A battery was produced in the same manner as in Example 4, except that a second solid electrolyte layer similar to the second solid electrolyte layer formed in Example 3 was formed on both sides of the second active material-containing layer of the second electrode.

(Comparative Example 1)
A battery was produced in the same manner as in Example 1, except that the formation of the first solid electrolyte layer was omitted when producing the first electrode.

<Measurement of Lithium Diffusion Coefficient Dt>
A circular sample having a diameter of φ10 mm was punched out from each of the first and second electrodes prepared in Examples 1-5 and Comparative Example 1. A circular cellulose separator having a thickness of 15 μm was also prepared. For each example, a coin cell was prepared using the circular electrode punched out from each of the first and second electrodes, the circular separator, and the liquid nonaqueous electrolyte. For each of Examples 1-5 and Comparative Example 1, the coin cell was prepared using a circular electrode punched out from a portion regarded as the outer edge and a portion regarded as the center, as described below.

For the first electrodes of Examples 1-5, the portion where the frame-shaped first solid electrolyte layer was formed was regarded as the outer edge portion. The portion corresponding to the first solid electrolyte non-supporting portion where no solid electrolyte was provided inside the frame shape of the first solid electrolyte layer was regarded as the center portion. For the first electrode of Comparative Example 1, the portions corresponding to the portions regarded as the outer edge portion and center portion of the first electrode of Example 1 were regarded as the outer edge portion and center portion, respectively. For each second electrode, a portion that overlaps with the circular portion punched out from the first electrode in the electrode group was punched out.

According to the above-mentioned method, each coin cell was charged to a half-charged state, a measurement sample was prepared, the AC impedance was measured, and the lithium diffusion coefficient Dt (Dt _E and Dt _C ) in the electrode thickness direction was calculated from the measurement results. The electrode thickness direction here refers to the direction parallel to the stacking direction of the current collector and the active material-containing layer.

Table 1 below shows details of the first and second electrodes prepared in Examples 1-5 and Comparative Example 1, and the measurement results of the lithium diffusion coefficient Dt. The details of the first and second electrodes show the first active material, the second active material, the widths of the first and second parts of the first solid electrolyte layer, and the widths of the third and fourth parts of the second solid electrolyte layer. The lithium diffusion coefficient Dt shows the lithium diffusion coefficient _DtC in the thickness direction of a part considered to be the central part, and the lithium diffusion coefficient _DtE in the thickness direction of a part considered to be the outer edge part.

<Life evaluation>
The life performance of each of the batteries prepared in Examples 1 to 5 and Comparative Example 1 was evaluated as follows.

First, the initial discharge capacity was measured as follows. The battery was charged to 100% SOC at a constant current of 1C rate (600 mA) in a temperature environment of 25°C. After a 10-minute rest period, the battery was discharged to 0% SOC at a constant current of 0.2C rate (120 mA). The capacity during discharge was measured and recorded.

The above initial charge/discharge was counted as cycle 0, and 12,000 charge/discharge cycles were then repeated. However, a capacity confirmation test was conducted every 2,000 cycles, and the capacity retention rate at each cycle was calculated (discharge capacity retention rate = [discharge capacity at each cycle/initial (cycle 0) discharge capacity] x 100%).

Charging and discharging for each cycle were performed under the following conditions. The temperature was 25°C, and charging and discharging were performed within the range of SOC 27.5% to 42.5%. Charging was performed at a constant current of 5C rate (3A), and discharging was performed at a constant current of 5C rate (3A). There was no rest period between charging and discharging.

The capacity confirmation test every 2000 cycles was performed under the same conditions as the measurement of the initial discharge capacity. That is, the temperature was 25°C, and charging and discharging were performed within the range of SOC 0% to 100%. Charging was performed at a constant current of 1C rate (600 mA), and discharging was performed at a constant current of 0.2C rate (120 mA). After charging, a rest period of 10 minutes was provided before starting discharging.

The results of the evaluation of life performance are shown in Table 2 below. Specifically, the initial discharge capacity and the discharge capacity retention rate every 2000 cycles are shown.

As shown in Table 2, the batteries according to Examples 1-5 and Comparative Example 1 all showed the same initial discharge capacity. In addition, the battery according to Examples 1-5 showed less decrease in discharge capacity than the battery according to Comparative Example 1. In the battery according to Examples 1-5, as shown in Table 1, the first solid electrolyte layer was provided at the outer edge of the first electrode containing the first active material that undergoes at least a two-phase coexistence reaction, and thus the lithium diffusion coefficient Dt _E in the thickness direction of the portion considered as the outer edge was higher than the lithium diffusion coefficient Dt _C in the thickness direction of the center. From the comparison between Examples 1-5 and Comparative Example 1, it was found that the capacity decrease associated with repeated rapid charge and discharge cycles was suppressed by increasing the lithium diffusion coefficient Dt in the thickness direction at the outer edge of the electrode compared to the center.

According to one or more of the embodiments and examples described above, an electrode is provided. The electrode includes an active material-containing layer that contains an active material that undergoes a two-phase coexistence reaction and has a main surface including a pair of first sides along a first direction. The lithium diffusion coefficient Dt E in the thickness direction of the _active material-containing layer at the outer edge portion including the first region in the main surface along at least one of the pair of first sides and having a first peripheral width F _S of 0.03 F _A or more and 0.25 F _A or less with respect to the first width F A between the first sides is higher than the lithium diffusion coefficient Dt _C in the thickness direction at the center of the main surface excluding the outer _edge portion. The thickness direction intersects with the main surface of the active material-containing layer. Such an electrode can provide a secondary battery and a battery pack with suppressed capacity reduction, and a vehicle equipped with the battery pack.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.
The invention as originally claimed in the present application is set forth below.
[1] An electrode comprising an active material-containing layer containing an active material that undergoes a two-phase coexistence reaction and having a main surface including a pair of first sides along a first direction, wherein a lithium diffusion coefficient DtE in a thickness direction intersecting with the main surface of the active material-containing layer in an outer edge portion including a first region within the main surface that is along at least one of the pair of first sides and has a first periphery width F _S of 0.03 F _{A or} more and 0.25 F _A or less with respect to a first width F A between the pair of _first sides is higher than a lithium diffusion coefficient _DtC in the thickness direction in a central portion of the main surface excluding the outer edge portion .
[2] The electrode according to [1], wherein the outer edge portion includes a pair of the first regions respectively along the pair of first sides.
[3] The electrode described in [1] or [2], wherein the main surface further includes a pair of second sides along a second direction intersecting the first direction, and the outer edge portion further includes a second region in the main surface that is along at least one of the pair of second sides and has a second peripheral width S _S that is 0.25 S _A or less with respect to a second width S _A between the pair of second sides.
[4] A first active material-containing layer containing a first active material that undergoes a two-phase coexistence reaction and having a first main surface including a pair of first sides along a first direction;
a first solid electrolyte layer provided on the first main surface of the first active material-containing layer and containing a solid electrolyte;
Equipped with
the first solid electrolyte layer includes a first portion that is along at least one of the pair of first sides and has a first periphery width F _S that is 0.03 F _A or more and 0.25 F _A or less with respect to a first width F _A between the pair of first sides, and the first active material-containing layer includes a first solid electrolyte-free portion where the first solid electrolyte layer is not provided.
[5] The electrode according to [4], wherein the first solid electrolyte layer includes a pair of the first portions respectively along the pair of first sides.
[6] The electrode described in [4] or [5], wherein the first main surface further includes a pair of second sides extending along a second direction intersecting the first direction, and the first solid electrolyte layer further includes a second portion along at least one of the pair of second sides and having a second peripheral width S S that is 0.25 S A or less with respect to a second width S _A between _{the pair} of second sides.
[7] The electrode according to any one of [4] to [6], wherein the first active material contains a lithium titanium oxide having a spinel structure.
[8] The electrode according to any one of [4] to [6], wherein the first active material contains lithium iron phosphate having an olivine structure.
[9] A first electrode comprising the electrode according to any one of [1] to [8];
a second electrode including a counter electrode for the first electrode;
A secondary battery comprising:
[10] The secondary battery according to [9], wherein the second electrode comprises a second active material-containing layer containing a second active material that undergoes a single solid-state reaction.
[11] A first electrode comprising the electrode according to any one of [4] to [8];
a second electrode including a counter electrode including a second active material-containing layer containing a second active material that undergoes a single solid-phase reaction and having a second main surface including a pair of third sides along a third direction, and a second solid electrolyte layer that is provided on the second main surface of the second active material-containing layer and contains a solid electrolyte;
Equipped with
the second solid electrolyte layer includes a third portion that is along at least one of the pair of third sides and has a third periphery width T _S that is 0.25T _A or less with respect to a third width T _A between the pair of third sides, and the second active material-containing layer includes a second solid electrolyte-free portion where the second solid electrolyte layer is not provided.
[12] The secondary battery according to [11], wherein the second main surface further includes a pair of fourth sides along a fourth direction intersecting the third direction, and the second solid electrolyte layer further includes a fourth portion along at least one of the pair of fourth sides and having a fourth peripheral width U S that is 0.25 U A or less _with respect to _a fourth width _U A between the pair of fourth sides.
[13] A battery pack comprising the secondary battery according to any one of [9] to [12].
[14] An external terminal for supplying electricity;
Protection circuit and
The battery pack according to [13], further comprising:
[15] A storage battery comprising a plurality of the secondary batteries,
The battery pack according to [13] or [14], wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.
[16] A vehicle comprising the battery pack according to any one of [13] to [15].
[17] The vehicle according to [16], further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy.

DESCRIPTION OF SYMBOLS 1... Electrode group, 2... Exterior member, 3... First electrode, 3a... First current collector, 3b... First active material containing layer, 3c... First current collecting tab, 3d... First solid electrolyte layer, 4 ...Separator, 5...Second electrode, 5a...Second current collector, 5b...Second active material containing layer, 5c...Second current collection tab, 5d...Second solid electrolyte layer, 6...First electrode terminal, 7 ...Second electrode terminal, 40...Vehicle main body, 41...Vehicle power supply, 42...Electrical control control device, 43... external terminal, 44... inverter, 45... drive motor, 100... secondary battery, 200... assembled battery, 200a... assembled battery, 200b... assembled battery, 200c... assembled battery, 201... bus bar, 202... positive electrode side lead, 203... negative electrode side lead, 204... adhesive tape, 206... negative electrode terminal, 207... positive electrode terminal, 300... battery pack, 300a... battery pack, 300b... battery pack 300c... battery pack, 301... container, 302... lid, 303... protective sheet, 310a... assembled battery monitoring device, 310b... assembled battery monitoring device, 310c... assembled battery monitoring device, 340... printed wiring board, 342... Positive electrode connector, 342a...wiring, 343...negative electrode connector, 343a...wiring, 345...thermistor, 346...protection circuit, 347...wiring, 350...energizer external terminal for the battery, 352... positive terminal, 353... negative terminal, 348a... positive wiring, 348b... negative wiring, 400... vehicle, 411... battery management device, 412... communication bus, 413... positive terminal, 414 ...negative terminal, 415...switching device, 416...current detection unit, 417...negative input terminal, 418...positive input terminal, L1...connection line, L2...connection line, W...drive wheel.

Claims (12)

A first electrode;
a second electrode including a counter electrode for the first electrode;
Equipped with
The first electrode includes a first active material- containing layer that contains a first active material that undergoes a two-phase coexistence reaction and has a first main surface that includes a pair of first sides along a first direction;
a first solid electrolyte layer provided on the first main surface of the first active material-containing layer and containing a solid electrolyte;
the second electrode comprises a second active material-containing layer containing a second active material that undergoes a single solid-state reaction;
the first solid electrolyte layer includes a first portion that is along at least one of the pair of first sides and has a first periphery width F _S that is 0.03 F _A or more and 0.25 F _A or less with respect to a first width F _A between the pair of first sides, and the first active material-containing layer includes a first solid electrolyte-free portion where the first solid electrolyte layer is not provided. The secondary battery according to claim 1 , wherein the first solid electrolyte layer includes a pair of the first portions respectively along the pair of first sides. 3. The secondary battery according to claim 1, wherein the first main surface further includes a pair of second sides extending along a second direction intersecting the first direction, and the first solid electrolyte layer further includes a second portion extending along at least one of the pair of second sides and having a second peripheral width S _S that is 0.25 S _A or less with respect to a second width S _A between the pair of second sides. The secondary battery according to claim 1 , wherein the first active material contains a lithium titanium oxide having a spinel structure. The secondary battery according to claim 1 , wherein the first active material contains lithium iron phosphate having an olivine structure. the second active material-containing layer has a second main surface including a pair of third sides along a third direction,
the second electrode further includes a second solid electrolyte layer provided on the second main surface of the second active material-containing layer and containing a solid electrolyte;
6. The secondary battery according to claim 1, wherein the second solid electrolyte layer includes a third portion having a third periphery width T _S along at least one of the pair of third sides and a third width T _A between the pair of third sides that is 0.25T _A or less with respect to the third width T A between the pair of third sides, and the second active material-containing layer includes a second solid electrolyte-free portion where the second solid electrolyte layer is not provided. 7. The secondary battery according to claim 6, wherein the second main surface further includes a pair of fourth sides along a fourth direction intersecting the third direction, and the second solid electrolyte layer further includes a fourth portion along at least one of the pair of fourth sides and having a fourth peripheral width U _S that is 0.25 U _A or less with respect to a fourth width U _A between the pair of fourth sides. A battery pack comprising the secondary battery according to claim 1 . An external terminal for supplying electricity;
9. The battery pack of claim 8 , further comprising a protection circuit. A battery comprising a plurality of the secondary batteries,
The battery pack according to claim 8 or 9 , wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle comprising the battery pack according to any one of claims 8 to 10 . The vehicle of claim 11 including a mechanism for converting kinetic energy of the vehicle into regenerative energy.