JP7708542B2 - Lithium secondary battery - Google Patents

Description

The present invention relates to a lithium secondary battery.

In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to combat global warming. In the automotive industry, there is hope that the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) will help reduce carbon dioxide emissions, and there has been active development of non-aqueous electrolyte secondary batteries, such as motor drive secondary batteries, which hold the key to putting these into practical use.

Secondary batteries for driving motors are required to have extremely high output characteristics and high energy compared to consumer lithium-ion secondary batteries used in mobile phones, laptops, etc. Therefore, lithium-ion secondary batteries, which have the highest theoretical energy of all practical batteries, have attracted attention and are currently being developed at a rapid pace.

The currently widely used lithium-ion secondary batteries use a flammable organic electrolyte as the electrolyte. These liquid-based lithium-ion secondary batteries require stricter safety measures against leakage, short circuits, overcharging, etc. than other batteries.

In recent years, therefore, research and development of all-solid-state batteries, such as all-solid-state lithium secondary batteries using oxide- or sulfide-based solid electrolytes, has been actively conducted. A solid electrolyte is a material composed mainly of an ion conductor capable of ion conduction in a solid state. For this reason, in principle, all-solid-state lithium secondary batteries do not cause various problems caused by flammable organic electrolytes, as in conventional liquid-based lithium-ion secondary batteries. In addition, in general, the use of a high-potential, large-capacity positive electrode material and a large-capacity negative electrode material can significantly improve the output density and energy density of the battery. All-solid-state lithium secondary batteries using positive electrode active materials made of elemental sulfur (S) or sulfide-based materials, and solid electrolytes containing sulfur, are promising candidates.

In a lithium secondary battery, the negative electrode potential decreases as the charging proceeds. When the negative electrode potential decreases below 0 V (vs. Li/Li ⁺ ), metallic lithium precipitates at the negative electrode, forming dendrite crystals (this phenomenon is also called electrodeposition of metallic lithium). When electrodeposition of metallic lithium occurs, the precipitated dendrites penetrate the electrolyte layer, causing an internal short circuit in the battery. This problem of internal short circuit is particularly evident when the solid electrolyte layer is made thin in order to improve the energy density of the battery.

For the purpose of preventing such electrodeposition of metallic lithium, for example, Patent Document 1 discloses a technique in which a mixture of granular metallic lithium and carbon black is used as the negative electrode active material in a secondary battery having a solid electrolyte layer containing a lithium ion conductive inorganic solid electrolyte, and the mixture ratio of these is controlled within a specific range.

JP 2009-218005 A

According to the inventors' investigations, it was found that if the technology described in Patent Document 1 is used to prevent the electrodeposition of metallic lithium, there is a problem in that sufficient capacity cannot be extracted during charging and discharging at high charge and discharge rates (i.e., the so-called charge and discharge rate characteristics are insufficient). A secondary battery with such insufficient charge and discharge rate characteristics cannot utilize sufficient capacity in response to rapid charging and discharging.

The present invention aims to provide a means for improving the charge/discharge rate characteristics of a lithium secondary battery having a solid electrolyte layer containing a lithium ion conductive solid electrolyte.

According to one aspect of the present invention, a lithium secondary battery is provided that includes a power generating element having a positive electrode, a negative electrode, and a solid electrolyte layer that is interposed between the positive electrode and the negative electrode and includes a lithium ion conductive solid electrolyte. The lithium secondary battery is characterized in that the negative electrode includes a lithium ion/electron conductive structure that includes a conductive porous body and a lithium ion conductive solid electrolyte that covers at least a portion of the inner surface of the porous body, and that the porosity of the lithium ion/electron conductive structure is greater than the porosity of the solid electrolyte layer.

Another aspect of the present invention also relates to a lithium secondary battery including a power generating element having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and including a lithium ion conductive solid electrolyte. In the lithium secondary battery according to this aspect, the negative electrode includes a lithium ion/electron conductive structure including a conductive porous body and a lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body, and the porosity of the lithium ion/electron conductive structure is larger than the porosity of the solid electrolyte layer, and metallic lithium is held in the pores of the lithium ion/electron conductive structure.

In the lithium secondary battery according to the present invention, the presence of a lithium ion/electron conductive structure in which a conductive porous body is coated with a solid electrolyte ensures sufficient conduction paths for lithium ions and electrons in the negative electrode. As a result, according to the present invention, it is possible to improve the charge and discharge rate characteristics in a lithium secondary battery having a solid electrolyte layer containing a lithium ion conductive solid electrolyte.

FIG. 1 is a perspective view showing the appearance of a flat laminated battery which is one embodiment of an all-solid-state battery according to the present invention. FIG. 2 is a cross-sectional view taken along line 2-2 shown in FIG. FIG. 3 is a cross-sectional view of a single cell layer constituting the power generating element of the stacked battery shown in FIGS.

One embodiment (first embodiment) of the present invention is a lithium secondary battery comprising a power generating element having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and including a first lithium ion conductive solid electrolyte, the negative electrode including a lithium ion/electron conductive structure including a conductive porous body and a second lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body, the porosity of the lithium ion/electron conductive structure being greater than the porosity of the solid electrolyte layer. When the lithium secondary battery according to the first embodiment is in a fully discharged state, the negative electrode (specifically, the pores of the lithium ion/electron conductive structure) does not contain metallic lithium. On the other hand, when the lithium secondary battery according to the first embodiment is in a charged state, the negative electrode contains metallic lithium.

Another embodiment (second embodiment) of the present invention is a lithium secondary battery comprising a power generating element having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a first lithium ion conductive solid electrolyte, the negative electrode containing a lithium ion/electron conductive structure including a conductive porous body and a second lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body, the porosity of the lithium ion/electron conductive structure being greater than the porosity of the solid electrolyte layer, and metallic lithium being held in the pores of the lithium ion/electron conductive structure. In other words, the lithium secondary battery according to the second embodiment is in a charged state.

The following describes the above-mentioned embodiment of the present invention with reference to the drawings. However, the technical scope of the present invention should be determined based on the claims and is not limited to the following embodiment. Note that the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios.

Figure 1 is a perspective view showing the appearance of a flat-layered all-solid-state battery, which is one embodiment of the secondary battery according to the present invention. Figure 2 is a cross-sectional view taken along line 2-2 in Figure 1. The layered structure allows the battery to be compact and have a high capacity. In this specification, the flat-layered non-bipolar all-solid-state lithium secondary battery shown in Figures 1 and 2 (hereinafter also simply referred to as a "layered battery") will be described in detail as an example. However, when viewed from the perspective of the internal electrical connection form (electrode structure) of the all-solid-state battery according to this embodiment, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

As shown in FIG. 2, the stacked battery 10a has a flat rectangular shape, and a negative electrode current collector 25 and a positive electrode current collector 27 for extracting power are pulled out from both sides. The power generating element 21 is wrapped in the battery exterior material (laminate film 29) of the stacked battery 10a, and its periphery is heat-sealed, and the power generating element 21 is sealed with the negative electrode current collector 25 and the positive electrode current collector 27 pulled out to the outside.

The all-solid-state battery according to this embodiment is not limited to a laminated flat shape. A wound all-solid-state battery may be cylindrical, or may be a cylindrical shape that has been deformed to have a rectangular flat shape, and is not particularly limited. The cylindrical shape may be a laminate film or a conventional cylindrical can (metal can) as the exterior material, and is not particularly limited. Preferably, the power generating element is housed inside a laminate film containing aluminum. This form can achieve weight reduction.

Also, there is no particular restriction on the removal of the current collectors (25, 27) shown in FIG. 1. The negative current collector 25 and the positive current collector 27 may be pulled out from the same side, or the negative current collector 25 and the positive current collector 27 may each be divided into multiple pieces and removed from each side, and are not limited to those shown in FIG. 1 and FIG. 2. Also, in a wound type lithium secondary battery, the terminals may be formed using, for example, a cylindrical can (metal can) instead of tabs.

As shown in FIG. 2, the stacked battery 10a of this embodiment has a structure in which a flat, approximately rectangular power generating element 21, in which a charge/discharge reaction actually proceeds, is sealed inside a laminate film 29, which is a battery exterior material. Here, the power generating element 21 has a structure in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are laminated. In this embodiment, the solid electrolyte layer 17 contains an argyrodite-type sulfide solid electrolyte (Li ₆ PS ₅ Cl), which is a type of sulfide solid electrolyte. The negative electrode has a structure in which a lithium ion/electron conductive structure 13 is disposed on both sides of a negative electrode current collector 11'. Here, the lithium ion/electron conductive structure 13 contains a conductive porous body and a lithium ion conductive solid electrolyte that covers at least a part of the inner surface of the porous body (details of the lithium ion/electron conductive structure 13 will be described later). Note that when the stacked battery 10a is in a fully discharged state, no metallic lithium is present in the negative electrode. On the other hand, when the stacked battery 10a is charged, lithium ions reach the lithium ion/electron conductive structure 13 of the negative electrode from the positive electrode active material layer 15 through the solid electrolyte layer 17, and are precipitated as metallic lithium or a lithium-containing alloy in the voids of the structure 13. The positive electrode has a structure in which positive electrode active material layers 15 containing a positive electrode active material are disposed on both sides of a positive electrode current collector 11". Specifically, the negative electrode, the solid electrolyte layer, and the positive electrode are stacked in this order such that one lithium ion/electron conductive structure 13 and an adjacent positive electrode active material layer 15 face each other with the solid electrolyte layer 17 interposed therebetween. As a result, the adjacent negative electrode, solid electrolyte layer, and positive electrode constitute one single cell layer 19. Therefore, the stacked battery 10a shown in FIG. 2 can be said to have a structure in which a plurality of single cell layers 19 are stacked and electrically connected in parallel.

As shown in FIG. 2, the outermost negative electrode current collectors located on both outermost layers of the power generating element 21 each have a lithium ion/electron conductive structure 13 disposed on only one side, but lithium ion/electron conductive structures may be provided on both sides. In other words, instead of using a current collector dedicated to the outermost layer with the structure provided on only one side, a current collector with the structure on both sides may be used as the outermost layer current collector as it is.

A negative electrode collector (tab) 25 and a positive electrode collector (tab) 27 that are electrically connected to the electrodes (positive and negative electrodes) are attached to the negative electrode collector 11' and the positive electrode collector 11", respectively, and are structured so as to be sandwiched between the ends of the laminate film 29, which is the battery exterior material, and are led out of the laminate film 29. The negative electrode collector 25 and the positive electrode collector 27 may be attached to the negative electrode collector 11' and the positive electrode collector 11" of each electrode by ultrasonic welding, resistance welding, or the like, respectively, via negative electrode leads and positive electrode leads (not shown) as necessary.

3 is an enlarged cross-sectional view of the cell layer 19 constituting the power generating element 21 of the laminated battery 10a shown in FIGS. 1 and 2. In FIG. 3, the negative electrode current collector 11', the lithium ion/electron conductive structure 13, the solid electrolyte layer 17, the positive electrode active material layer 15, and the positive electrode current collector 11" constituting the cell layer 19 are laminated in this order. In the embodiment shown in FIG. 3, the shape of the lithium ion/electron conductive structure 13 is determined by a porous body made of stainless steel (here, SUS304) which is a porous body having electrical conductivity (conductive porous body). The inner surface of the conductive porous body (stainless steel porous body) is filled with an argyrodite-type sulfide solid electrolyte (Li ₆ PS ₅ Cl). Here, the porosity of the lithium ion/electron conductive structure 13 having the above-mentioned configuration is, for example, 60%, which is configured to be a value larger than the porosity of the solid electrolyte layer (for example, 5%). Furthermore, when the stacked battery 10a is in a charged state, metallic lithium is held in the pores of the conductive porous body (stainless steel porous body). The porosity value of the conductive porous body described above is a value measured in a state in which metallic lithium is not held in the pores.

In a preferred embodiment, the negative electrode further contains a metal that can be alloyed with lithium. Specifically, for example, particles of silver (Ag), which is a metal that can be alloyed with lithium, are attached in a dispersed state on the surface of the solid electrolyte that covers the inner surface of the conductive porous body. With this configuration, lithium ions that reach the negative electrode during charging of the stacked battery 10a are alloyed with silver (Ag) and held in the voids of the lithium ion/electron conductive structure 13 as a lithium-containing alloy. Compared to when metallic lithium is precipitated as a single substance, the precipitation energy is smaller when it is precipitated as a lithium-containing alloy, so that the above-mentioned configuration makes it possible to precipitate metallic lithium more uniformly. In addition, the interface resistance between the lithium ion/electron conductive structure and the solid electrolyte layer is also reduced, making it possible to achieve a higher current density. As a result, the rate characteristics can be further improved. In this specification, the concept of "metallic lithium is held in the voids of the lithium ion/electron conductive structure" also includes a form in which metallic lithium is held in the voids of the lithium ion/electron conductive structure 13 as a lithium-containing alloy.

In the embodiment shown in FIG. 3, for example, when the stacked battery 10a is charged, dendrites made of metallic lithium may be generated by electrodeposition at the interface between the lithium ion/electron conductive structure 13 and the solid electrolyte layer 17. These dendrites grow toward the positive electrode active material layer 15. In this embodiment, the porosity of the conductive porous body constituting the lithium ion/electron conductive structure 13 is greater than the porosity of the solid electrolyte layer 17, so that the generated dendrites tend to grow toward the conductive porous body side rather than toward the solid electrolyte layer 17 side (i.e., the positive electrode active material layer 15 side). Therefore, in the embodiment shown in FIG. 3, the growth of dendrites toward the solid electrolyte layer 17 side (i.e., the positive electrode active material layer 15 side) is suppressed, and the occurrence of an internal short circuit can be prevented.

In addition, when charging and discharging the stacked battery 10a, it is important from the viewpoint of input/output characteristics that the lithium ions and electrons are smoothly conducted in each electrode. Here, in the embodiment shown in FIG. 3, among the lithium ion/electron conductive structure 13 constituting the negative electrode, the conductive porous body (stainless steel porous body) functions as a conductive path for electrons. Also, among the lithium ion/electron conductive structure 13 constituting the negative electrode, the solid electrolyte (Argyrodite-type sulfide solid electrolyte) covering the inner surface of the conductive porous body functions as a conductive path for lithium ions. Thus, in the lithium secondary battery according to this embodiment, both the conductive paths for electrons and lithium ions in the negative electrode are sufficiently secured. As a result, according to the lithium secondary battery according to this embodiment, it is possible to improve the charge/discharge rate characteristics in a lithium secondary battery having a solid electrolyte layer containing a lithium ion conductive solid electrolyte.

The main components of the all-solid-state battery according to this embodiment are described below.

[Current collector]
The current collector has a function of mediating the movement of electrons from the electrode active material layer. There are no particular limitations on the material constituting the current collector. For example, metals and conductive resins can be used as the material constituting the current collector.

Specific examples of metals include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, clad materials of nickel and aluminum, clad materials of copper and aluminum, etc. may also be used. Also, foils in which the metal surface is coated with aluminum may be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoints of electronic conductivity, battery operating potential, etc.

The latter conductive resin includes resins in which conductive fillers are added as necessary to non-conductive polymeric materials.

Examples of non-conductive polymeric materials include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyethernitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such non-conductive polymeric materials may have excellent electric potential resistance or solvent resistance.

A conductive filler can be added to the conductive polymer material or non-conductive polymer material as necessary. In particular, when the resin that serves as the base material of the collector is made of only a non-conductive polymer, a conductive filler is necessarily required to impart conductivity to the resin.

The conductive filler can be used without any particular restriction as long as it is a material having electrical conductivity. For example, metals and conductive carbon can be mentioned as materials having excellent electrical conductivity, potential resistance, or lithium ion blocking properties. There are no particular restrictions on the metal, but it is preferable that it contains at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or an alloy or metal oxide containing these metals. There are also no particular restrictions on the conductive carbon. It is preferable that it contains at least one selected from the group consisting of acetylene black, Vulcan (registered trademark), Black Pearl (registered trademark), carbon nanofiber, Ketjen Black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

There are no particular restrictions on the amount of conductive filler added, so long as it is an amount that can impart sufficient conductivity to the current collector, and it is generally 5 to 80% by mass relative to the total mass of the current collector (100% by mass).

The current collector may be a single layer structure made of a single material, or may be a laminate structure made of a suitable combination of layers made of these materials. From the viewpoint of reducing the weight of the current collector, it is preferable that the current collector contains at least a conductive resin layer made of a resin having conductivity. From the viewpoint of blocking the movement of lithium ions between the single cell layers, a metal layer may be provided on a part of the current collector. In the all-solid-state lithium secondary battery according to this embodiment, the shape of the negative electrode is determined by the conductive porous body. Therefore, in some cases, it is possible to make the conductive porous body function as the negative electrode current collector without separately providing a negative electrode current collector. In this case, the negative electrode lead described later can be directly connected to the conductive porous body.

[Negative electrode]
In the lithium secondary battery according to the present invention, the negative electrode is characterized in that it contains a lithium ion/electron conductive structure including a conductive porous body and a lithium ion conductive solid electrolyte that covers at least a part of the inner surface of the porous body. As described above, when the lithium secondary battery according to the present invention is in a fully discharged state, the negative electrode does not contain metallic lithium. On the other hand, when the lithium secondary battery according to the present invention is in a charged state, the negative electrode contains metallic lithium in the form of a simple substance or a lithium-containing alloy. In addition, when a separate negative electrode current collector is not used and the conductive porous body itself is made to function as a negative electrode current collector, the lithium ion/electron conductive structure itself becomes the negative electrode.

(Conductive porous body)
A conductive porous body (conductive porous body) is a member having a porous structure (a large number of voids) inside and having conductivity. The material constituting the conductive porous body may be any material having conductivity, and the above-mentioned materials may be similarly adopted as the constituent material of the current collector. In particular, from the viewpoint of being inexpensive and easy to obtain and having excellent effects of the present invention, the conductive porous body preferably contains a metal material or a carbon material. Here, examples of the metal material include aluminum, nickel, iron, stainless steel (SUS304, SUS316L, etc.), titanium, and copper. Examples of the carbon material include hard carbon, acetylene black, Vulcan (registered trademark), Black Pearl (registered trademark), carbon nanofiber, Ketjen Black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, fullerene, mesoporous carbon, and activated carbon. In particular, it is more preferable that the conductive porous body contains stainless steel, nickel, carbon black, hard carbon, mesoporous carbon, or activated carbon.

There are no particular limitations on the shape of the conductive porous body, but if it is made of a metal material, preferred examples include shapes such as mesh, expanded grid (expanded metal), punched metal, and foam. In addition, a molded body obtained by molding powder of a metal material or carbon material by a method such as powder compaction may be used as the conductive porous body.

As described above, the conductive porous body has a porous structure (a large number of voids) inside, but the porosity value is not particularly limited as long as it is greater than the porosity of the solid electrolyte layer. The porosity of the conductive porous body is preferably 5 to 95%, more preferably 30 to 90%, and even more preferably 50 to 70%. The porosity value of the conductive porous body can be controlled by appropriately adopting conventionally known methods.

There are no particular limitations on the thickness of the conductive porous body, but it is preferably 20 to 300 μm, more preferably 30 to 250 μm, and even more preferably 50 to 200 μm.

(Lithium ion conductive solid electrolyte)
Examples of the lithium ion conductive solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes, but from the viewpoint of excellent lithium ion conductivity and durability, a sulfide solid electrolyte is preferable. In this specification, the lithium ion conductive solid electrolyte contained in the solid electrolyte layer 17 may also be referred to as a "first lithium ion conductive solid electrolyte", and the lithium ion conductive solid electrolyte constituting the lithium ion/electron conductive structure may also be referred to as a "second lithium ion conductive solid electrolyte". These names are intended only to distinguish the portion in which the solid electrolyte is arranged, and the ordinal numbers "first" and "second" themselves have no substantial meaning. That is, in the present invention, it is preferable that both the first lithium ion conductive solid electrolyte and the second lithium ion conductive solid electrolyte are sulfide solid electrolytes.

Examples of the sulfide solid electrolyte include LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ S-P ₂ S ₅ (LPS), LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS _4, Li ₃ PS _4, Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiI, Li ₂ SP ₂ S ₅ -Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ S-B ₂ S ₃ , Li ₂ S-P ₂ S ₅ -Z _m S _n (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (wherein x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In). Note that the description "Li ₂ S-P ₂ S ₅ " means a sulfide solid electrolyte obtained by using a raw material composition containing Li ₂ S and P ₂ S ₅ , and the same applies to other descriptions.

The sulfide solid electrolyte may have, for example, a Li ₃ PS ₄ skeleton, a Li ₄ P ₂ S ₇ skeleton, or a Li ₄ P ₂ S ₆ skeleton. Examples of sulfide solid electrolytes having a Li ₃ PS ₄ skeleton include LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS _{4, and} Li ₃ PS _4. Examples of sulfide solid electrolytes having a Li ₄ P ₂ S ₇ skeleton include Li-P-S solid electrolytes called LPS (for example, Li ₇ P ₃ S ₁₁ ). Examples of sulfide solid electrolytes include LGPS represented by Li _(4-x) Ge _(1-x) P _x S ₄ (x satisfies 0<x<1). Among them, the sulfide solid electrolyte contained in the active material layer is preferably a sulfide solid electrolyte containing a P element. Furthermore, the sulfide solid electrolyte may contain a halogen (F, Cl, Br, I). From the viewpoint of excellent ion conductivity, in a preferred embodiment, the lithium ion conductive solid electrolyte contains a sulfide solid electrolyte selected from the group consisting of Li ₂ S-P ₂ S ₅ , Li ₇ P ₃ S ₁₁ , Li _3.2 P _0.96 S, Li ₂ S-SiS ₂ , Li ₂ S-B ₂ S ₃ , Li ₂ S-GeS ₂ , Li _3.25 Ge _0.25 P _0.75 S ₄ , Li ₁₀ GeP ₂ S ₁₂ and Li ₆ PS ₅ X (X is Cl, Br or I).

When the sulfide solid electrolyte is a Li ₂ S-P ₂ S ₅ system, the ratio of Li ₂ S and P ₂ S ₅ , in terms of molar ratio, is preferably within the range of Li ₂ S:P ₂ S ₅ =50:50 to 100:0, and more preferably Li ₂ S:P ₂ S ₅ =70:30 to 80:20.

The sulfide solid electrolyte may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by a solid phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (ball mill, etc.) on the raw material composition. The crystallized sulfide glass can be obtained, for example, by heat treating the sulfide glass at a temperature equal to or higher than the crystallization temperature. The ion conductivity (for example, Li ion conductivity) of the sulfide solid electrolyte at room temperature (25° C.) is preferably, for example, 1×10 ⁻⁵ S/cm or more, and more preferably 1×10 ⁻⁴ S/cm or more. The ion conductivity value of the lithium ion conductive solid electrolyte can be measured by an AC impedance method.

Examples of oxide solid electrolytes include compounds having a NASICON structure. Examples of compounds having a NASICON structure include compounds (LAGP) represented by the general formula Li _1+x Al _x Ge _2-x (PO ₄ ) ₃ (0≦x≦2), and compounds (LATP) represented by the general formula Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ (0≦x≦2). Other examples of oxide solid electrolytes include LiLaTiO (e.g., Li _0.34 La _0.51 TiO ₃ ), LiPON (e.g., Li _2.9 PO _3.3 N _0.46 ), and LiLaZrO (e.g., Li ₇ La ₃ Zr ₂ O ₁₂ ).

The shape of the lithium ion conductive solid electrolyte may be, for example, a particulate shape such as a true sphere or an oval sphere, a thin film shape, etc. When the solid electrolyte is particulate, its average particle size ( _D50 ) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. On the other hand, the average particle size ( _D50 ) is preferably 0.01 μm or more, and more preferably 0.1 μm or more.

In the lithium secondary battery according to the present invention, the lithium ion/electron conductive structure constituting the negative electrode has a configuration in which the inner surface of the conductive porous body is coated with a lithium ion conductive solid electrolyte. Here, there is no particular restriction on the coating thickness of the lithium ion conductive solid electrolyte on the inner surface of the conductive porous body, but it is preferably about 1 to 100 μm, and more preferably 10 to 80 μm.

In a preferred embodiment of the lithium secondary battery according to the present invention, the negative electrode contains a metal that can be alloyed with lithium. Examples of elements that can be alloyed with lithium include aluminum, magnesium, zinc, bismuth, tin, lead, indium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, cadmium, gallium, thallium, silicon, and germanium. Among these, from the viewpoint of being able to configure a battery with excellent capacity and energy density, it is preferable that the material that can be alloyed with lithium contains at least one metal selected from the group consisting of silver, silicon, gold, indium, germanium, tin, lead, aluminum, and zinc, and more preferably contains silver, silicon, gold, or indium. These metals that can be alloyed with lithium may be used in the form of a conductive porous body made of itself, or may be used in the form of a coating formed on the surface of a conductive porous body made of a material that does not alloy with lithium. In this case, the metal that can be alloyed with lithium may be present so as to be exposed on the coating layer formed by coating the inner surface of the conductive porous body with the solid electrolyte, or may be present between the conductive porous body and the coating layer, with the former form being more preferred.

According to the above-mentioned configuration, lithium ions that reach the negative electrode during charging of the lithium secondary battery are alloyed with a metal that can be alloyed with lithium. The lithium-containing alloy is then held in the voids of the lithium ion/electron conductive structure 13. Compared to when metallic lithium is precipitated as a single substance, the precipitation energy is smaller when the lithium-containing alloy is precipitated. Therefore, by adopting the above-mentioned configuration, metallic lithium can be precipitated more uniformly. In addition, the interfacial resistance between the lithium ion/electron conductive structure and the solid electrolyte layer is also reduced, making it possible to achieve a higher current density. As a result, the rate characteristics can be further improved.

[Solid electrolyte layer]
In the lithium secondary battery according to this embodiment, the solid electrolyte layer is a layer that contains a solid electrolyte as a main component and is interposed between the positive electrode and the negative electrode. There is no particular limitation on the specific form of the solid electrolyte contained in the solid electrolyte layer, and conventionally known knowledge can be appropriately referred to. Here, the specific form and preferred examples of the solid electrolyte are as described above, so the description will be omitted here.

The solid electrolyte layer may further contain a binder in addition to the solid electrolyte described above. Binders that may be contained in the solid electrolyte layer are not particularly limited, but examples include the following materials:

Thermoplastic polymers such as polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are replaced by other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyether nitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrogenated product, styrene-isoprene-styrene block copolymer and its hydrogenated product, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene Fluorine resins such as ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), etc., vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE fluororubber), vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP fluororubber), vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP fluororubber), etc. Examples of the fluororubber include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), and vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), and epoxy resins. Among these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

The porosity value of the solid electrolyte layer is not particularly limited as long as it is smaller than the porosity of the lithium ion/electron conductive structure constituting the negative electrode. Ideally, the porosity of the solid electrolyte layer is preferably as close to 0% as possible. On the other hand, the upper limit of the porosity of the solid electrolyte layer is preferably 25% or less, more preferably 20% or less, even more preferably 15% or less, and particularly preferably 10% or less. The porosity value of the solid electrolyte layer can be controlled by appropriately adopting a conventionally known method. As an example, when the solid electrolyte layer is produced by compacting the powder of the solid electrolyte, the porosity of the solid electrolyte layer can be controlled by adjusting the pressure applied during the compacting. In addition, by making the solid electrolyte amorphous (non-crystalline) or making it into a hybrid form with an organic solid electrolyte, the density of the solid electrolyte can be improved, and as a result, the porosity can be reduced. Here, the solid electrolyte layer may be composed of a single layer having a uniform composition and density (porosity), or may be a laminate of multiple layers having different compositions and densities (porosities).

The thickness of the solid electrolyte layer varies depending on the configuration of the intended lithium secondary battery, but is preferably within the range of 0.1 to 1000 μm, and more preferably within the range of 0.1 to 500 μm.

[Positive electrode]
The positive electrode includes a positive electrode active material capable of absorbing and releasing lithium ions. Here, when a battery is produced in a fully discharged state during the production of the battery, metallic lithium is not held in the negative electrode. For this reason, the positive electrode needs to include a positive electrode active material capable of releasing lithium ions during charging. Examples of such positive electrode active materials include layered rock salt active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , and Li(Ni-Mn-Co)O ₂ , spinel active materials such as LiMn ₂ O ₄ and LiNi _0.5 Mn _1.5 O ₄ , olivine active materials such as LiFePO ₄ and LiMnPO ₄ , Si-containing active materials such as Li ₂ FeSiO ₄ and Li ₂ MnSiO ₄ , and Li ₄ Ti ₅ O ₁₂ . Also, a reduction product of sulfur (S) (eg, fed lithium (Li ₂ S ₈ )) may be used as the positive electrode active material.

On the other hand, when a battery is produced in a fully charged state during the production of the battery, metallic lithium is held in the negative electrode (for example, metallic lithium is filled in the voids of the lithium ion/electron conductive structure). For this reason, the positive electrode needs to contain a positive electrode active material capable of absorbing lithium ions during discharge. Examples of such positive electrode active materials include sulfur element (S) as well as particles or thin films of organic sulfur compounds or inorganic sulfur compounds. These positive electrode active materials can absorb lithium ions during discharge and release lithium ions during charging by utilizing the oxidation-reduction reaction of sulfur. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitrile, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), polycarbonate sulfide, etc., which are typified by compounds described in International Publication No. 2010/044437. Among them, disulfide compounds, sulfur-modified polyacrylonitrile, and rubeanic acid are preferred, and sulfur-modified polyacrylonitrile is particularly preferred. As the disulfide compound, those having a dithiobiurea derivative, a thiourea group, a thioisocyanate, or a thioamide group are more preferable. Here, the sulfur-modified polyacrylonitrile is a modified polyacrylonitrile containing sulfur atoms obtained by mixing sulfur powder and polyacrylonitrile and heating under an inert gas or under reduced pressure. Its estimated structure is a structure in which polyacrylonitrile is ring-closed to form a polycyclic ring, and at least a part of S is bonded to C, as shown in, for example, Chem. Mater. 2011, 23, 5024-5028. The compound described in this document has strong peak signals near 1330 cm ^-1 and 1560 cm ^-1 in the Raman spectrum, and further has peaks near 307 cm ^-1 , 379 cm ^-1 , 472 cm ^-1 , and 929 cm ^-1 . On the other hand, inorganic sulfur compounds are preferred because of their excellent stability, and specific examples thereof include sulfur element (S), S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , NiS, NiS ₂ , CuS, FeS ₂ , Li ₂ S, MoS ₂ , and MoS _3. Among these, S, S-carbon composite, TiS ₂ , TiS ₃ , TiS ₄ , FeS ₂ , and MoS ₂ are preferred, sulfur element (S), S-carbon composite, TiS ₂ , and FeS ₂ are more preferred, and sulfur element (S) is particularly preferred. Here, the S-carbon composite is a compound state containing sulfur powder and a carbon material, which are subjected to a heat treatment or mechanical mixing to form a composite. More specifically, this refers to a state in which sulfur is distributed on the surface or within the pores of the carbon material, a state in which sulfur and the carbon material are uniformly dispersed at the nano level and aggregate to form particles, a state in which the carbon material is distributed on the surface or inside of fine sulfur powder, or a combination of two or more of these states.

In some cases, two or more types of positive electrode active materials may be used in combination. Of course, positive electrode active materials other than those mentioned above may also be used.

The shape of the positive electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the positive electrode active material is particulate, the average particle size (D ₅₀ ) is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm. In this specification, the average particle size (D ₅₀ ) of the active material can be measured by a laser diffraction scattering method.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably within the range of 40 to 99% by mass, and more preferably within the range of 50 to 90% by mass. The positive electrode active material layer may further contain a conductive assistant and/or a binder.

[Positive and negative current collector plates]
The material constituting the current collector plate (25, 27) is not particularly limited, and a known highly conductive material conventionally used as a current collector plate for a secondary battery can be used. As the material constituting the current collector plate, for example, a metal material such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof is preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. In addition, the same material may be used for the positive electrode current collector plate 27 and the negative electrode current collector plate 25, or different materials may be used.

[Positive and negative electrode leads]
Although not shown in the figures, the current collectors (11', 11") and the current collector plates (25, 27) may be electrically connected via positive and negative electrode leads. As the constituent materials of the positive and negative electrode leads, materials used in known lithium secondary batteries may be similarly adopted. Note that the portion removed from the exterior is preferably covered with a heat-resistant insulating heat-shrink tube or the like so as to prevent contact with peripheral devices or wiring, causing electric leakage and affecting products (e.g., automobile parts, particularly electronic devices, etc.).

[Battery exterior material]
As the battery exterior material, a known metal can case can be used, and a bag-shaped case using a laminate film 29 containing aluminum, which can cover the power generating element as shown in Figures 1 and 2, can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited thereto. A laminate film is preferable from the viewpoint of being excellent in high output and cooling performance and being suitable for use in batteries for large equipment for EVs and HEVs. In addition, since the group pressure applied from the outside to the power generating element can be easily adjusted, a laminate film containing aluminum is more preferable as the exterior body.

The lithium secondary battery according to the present invention has a configuration in which multiple single cell layers are connected in parallel, and as a result has high capacity and excellent cycle durability and charge/discharge rate characteristics. Therefore, the lithium secondary battery according to the present invention is suitable for use as a power source for driving EVs and HEVs.

Although one embodiment of an all-solid-state battery has been described above, the present invention is not limited to the configuration described in the above embodiment, and can be modified as appropriate based on the claims.

For example, the lithium secondary battery according to this embodiment does not have to be an all-solid-state type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). There is no particular limit to the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferable that the amount is such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolytic solution) does not occur.

The liquid electrolyte (electrolyte) that can be used has a form in which a lithium salt is dissolved in an organic solvent. Examples of organic solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propionate (MP), methyl acetate (MA), methyl formate (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), propylene carbonate (PC), butylene carbonate (BC), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL). Among these, from the viewpoint of further improving the rapid charging characteristics and output characteristics, the organic solvent is preferably a chain carbonate, more preferably at least one selected from the group consisting of diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), and more preferably selected from ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

Examples of the lithium salt include Li( _FSO2 ) _2N (lithium bis(fluorosulfonyl)imide; _LiFSI ), _Li ( _C2F5SO2 ) _2N , _LiPF6 , _LiBF4 , _LiClO4 , _LiAsF6 , and _LiCF3SO3 . Among _these , the lithium salt is preferably Li( _FSO2 ) _2N (LiFSI) from the viewpoints of battery output and charge/discharge cycle characteristics.

The liquid electrolyte (electrolyte) may further contain additives other than the above-mentioned components. Specific examples of such compounds include, for example, ethylene carbonate, vinylene carbonate, methylvinylene carbonate, dimethylvinylene carbonate, phenylvinylene carbonate, diphenylvinylene carbonate, ethylvinylene carbonate, diethylvinylene carbonate, vinylethylene carbonate, 1,2-divinylethylene carbonate, 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, and 1-ethyl-2-vinylethylene carbonate. Examples of the additives include ethylene carbonate, vinyl vinylene carbonate, allyl ethylene carbonate, vinyloxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloxymethyl ethylene carbonate, methacryloxymethyl ethylene carbonate, ethynyl ethylene carbonate, propargyl ethylene carbonate, ethynyloxymethyl ethylene carbonate, propargyloxyethylene carbonate, methylene ethylene carbonate, and 1,1-dimethyl-2-methylene ethylene carbonate. These additives may be used alone or in combination of two or more. The amount of additive used in the electrolyte can be adjusted as appropriate.

[Battery pack]
A battery pack is a device that consists of multiple batteries connected together. More specifically, it is a device that uses at least two batteries and is connected in series or parallel or both. By connecting them in series or parallel, it is possible to freely adjust the capacity and voltage.

A small, removable battery pack can be formed by connecting multiple batteries in series or in parallel. Then, multiple such small, removable battery packs can be connected in series or in parallel to form a large-capacity, high-output battery pack suitable for vehicle drive power sources and auxiliary power sources that require high volumetric energy density and high volumetric output density. How many batteries are connected to form a battery pack, and how many stages of small battery packs are stacked to form a large-capacity battery pack, can be determined based on the battery capacity and output of the vehicle (electric vehicle) in which it will be installed.

[vehicle]
The lithium secondary battery according to the present invention maintains its discharge capacity even after long-term use, and has good cycle characteristics and charge/discharge rate characteristics. Furthermore, it has a high volumetric energy density. In vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles, higher capacity, larger size, and longer life are required compared to electric and portable electronic device applications. Therefore, the nonaqueous electrolyte secondary battery can be suitably used as a power source for vehicles, for example, a power source for driving a vehicle or an auxiliary power source.

Specifically, the battery or a battery pack consisting of a combination of multiple batteries can be mounted on a vehicle. In the present invention, a long-life battery with excellent long-term reliability and output characteristics can be constructed, so that by mounting such a battery, a plug-in hybrid electric vehicle with a long EV driving distance or an electric vehicle with a long driving distance per charge can be constructed. For example, if the battery or a battery pack consisting of a combination of multiple batteries is used in a hybrid vehicle, a fuel cell vehicle, or an electric vehicle (all of which include four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, and buses, and light vehicles, etc.), as well as two-wheeled vehicles (motorcycles) and three-wheeled vehicles), it will become a vehicle with a long life and high reliability. However, the use is not limited to automobiles, and it can be applied to various power sources of other vehicles, such as mobile bodies such as trains, and can also be used as a mounted power source for uninterruptible power supplies, etc.

The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples.

Example of test cell preparation
[Example 1-1]
(Preparation of negative electrode)
A predetermined amount of an argyrodite-type sulfide solid electrolyte (Li ₆ PS ₅ Cl), which is a lithium ion conductive solid electrolyte, was weighed out and dispersed in an appropriate amount of dehydrated ethanol to prepare solution A.

On the other hand, a mesh made of stainless steel (SUS304) was prepared as a conductive porous body and immersed in solution A for a sufficient period of time. It was then removed from solution A and dried in a thermostatic chamber at 150°C for a sufficient period of time to produce a negative electrode made of an electrolyte-coated stainless steel mesh (lithium ion/electron conductive structure).

(Preparation of test cell)
As the positive electrode active material, a lithium _- containing composite oxide having a uniform composition of _{LiNi0.8Mn0.1Co0.1O2 and a} form of secondary particles which are aggregates of primary particles was prepared. The average particle diameter (D50) of this lithium-containing composite oxide (secondary particles) was measured by a laser diffraction scattering method and found to be 11.5 μm. In addition, an argyrodite-type sulfide solid electrolyte similar to that described above was prepared as a solid electrolyte for the positive electrode mixture. In addition, acetylene black was prepared as a conductive assistant for the positive electrode mixture.

60 parts by mass of the positive electrode active material prepared above, 6 parts by mass of the conductive additive, and 34 parts by mass of the argyrodite-type sulfide solid electrolyte were weighed out and mixed using a table mill to prepare a positive electrode mixture.

Next, the same argyrodite-type sulfide solid electrolyte as above was placed in a jig (McCool tube) and compressed at a molding pressure of 400 MPa to produce a solid electrolyte layer (disk shape with a diameter of 10 mm and a thickness of 600 μm).

Next, the positive electrode mixture prepared above was placed on one side of the solid electrolyte layer prepared above, and the mixture was pressed under a molding pressure of 200 MPa to produce a positive electrode active material layer (disk-shaped with a diameter of 10 mm and a thickness of 70 μm).

Then, the (lithium ion/electron conductive structure) prepared above was placed on the other side of the solid electrolyte layer prepared above. Next, the jig was fastened with a restraining pressure of 100 [MPa], and then leads for current extraction were connected to each electrode to prepare a test cell of this example. Note that the porosity of the solid electrolyte layer and the negative electrode (lithium ion/electron conductive structure) in the test cell prepared in this manner was 5% and 60%, respectively.

[Example 1-2]
A predetermined amount of silver (Ag) powder was weighed as a metal capable of being alloyed with lithium. This was then dispersed in an appropriate amount of dehydrated ethanol to prepare solution B. Then, before the fabrication of a test cell, solution B was uniformly sprayed onto a negative electrode made of an electrolyte-coated stainless steel mesh (lithium ion/electron conductive structure) and allowed to dry naturally.

A test cell for this example was produced in the same manner as in Example 1-1 described above, except that the negative electrode that had been subjected to the above treatment was used. The porosity of the solid electrolyte layer and the negative electrode (lithium ion/electron conductive structure) in the test cell produced in this manner was 5% and 60%, respectively.

[Comparative Example 1-1]
In the above-mentioned Example 1-1, when disposing the negative electrode of the test cell, instead of the negative electrode (lithium ion / electronic conductive structure) prepared above, a stainless steel mesh not covered with a solid electrolyte and 7 mg of an argyrodite-type sulfide solid electrolyte (Li ₆ PS ₅ Cl) were simply enclosed at the same time, and a restraining pressure was applied under the same conditions as above. Except for this, the test cell of this comparative example was prepared by the same method as in the above-mentioned Example 1-1. The porosity of the solid electrolyte layer and the negative electrode in the test cell prepared in this way was 5% and 60%, respectively.

[Comparative Example 1-2]
A test cell of this comparative example was produced in the same manner as in Comparative Example 1-1 described above, except that when arranging the negative electrode of the test cell in Comparative Example 1-1, only a stainless steel mesh not covered with a solid electrolyte was arranged, and no solid electrolyte was simultaneously sealed in. The porosity of the solid electrolyte layer and the negative electrode in the test cell produced in this manner were 5% and 60%, respectively.

[Example 2-1]
As a constituent material of the conductive porous body, a carbon material, Ketjen Black (registered trademark) (manufactured by Ketjen Black International, Inc.) EC300, was prepared. Next, this carbon material was immersed for a sufficient time in the above-prepared solution A. Thereafter, this was taken out of solution A and dried for a sufficient time in a thermostatic chamber at 150° C. to produce an electrolyte-coated carbon material.

Next, a laminate of a solid electrolyte layer and a positive electrode active material layer was produced using a method similar to that described in Example 1-1 above.

Next, the electrolyte-coated carbon material prepared above was placed on the other side of the solid electrolyte layer prepared above, and the mixture was pressed under a molding pressure of 100 MPa to produce a negative electrode (lithium ion/electron conductive structure) (disk shape with a diameter of 10 mm and a thickness of 70 μm). After that, leads for current extraction were connected to each electrode to produce a test cell of this example. The porosity of the solid electrolyte layer and the negative electrode (lithium ion/electron conductive structure) in the test cell thus produced were 5% and 60%, respectively.

[Example 2-2]
Before preparing the test cell, the solution B prepared above was sprayed uniformly onto the electrolyte-coated carbon material, and the material was allowed to dry naturally.

The test cell of this example was produced in the same manner as in Example 2-1 described above, except that the negative electrode (lithium ion/electron conductive structure) was produced using the electrolyte-coated carbon material that had been subjected to the above treatment. The porosity of the solid electrolyte layer and the negative electrode (lithium ion/electron conductive structure) in the test cell produced in this manner was 5% and 60%, respectively.

[Comparative Example 2]
In the above-mentioned Example 2-1, instead of the electrolyte-coated carbon material, a mixture obtained by mixing 1 mg of a carbon material (Ketjen Black EC300) and 5.6 mg of an Argyrodite-type sulfide solid electrolyte in a roll mill was used to prepare a negative electrode. Except for this, a test cell of this comparative example was prepared in the same manner as in the above-mentioned Example 2-1. The porosity of the solid electrolyte layer and the negative electrode in the test cell thus prepared were 5% and 60%, respectively.

[Example 3-1]
A test cell of this example was produced in the same manner as in Example 2-1 described above, except that hard carbon, another carbon material, was used as the constituent material of the conductive porous body instead of Ketjen Black (registered trademark). The porosity of the solid electrolyte layer and the negative electrode (lithium ion/electron conductive structure) in the test cell produced in this manner was 5% and 60%, respectively.

[Example 3-2]
Before preparing the test cell, the solution B prepared above was sprayed uniformly onto the electrolyte-coated carbon material, and the material was allowed to dry naturally.

The test cell of this example was produced in the same manner as in Example 3-1 described above, except that the negative electrode (lithium ion/electron conductive structure) was produced using the electrolyte-coated carbon material that had been subjected to the above treatment. The porosity of the solid electrolyte layer and the negative electrode (lithium ion/electron conductive structure) in the test cell produced in this manner was 5% and 60%, respectively.

[Comparative Example 3]
In the above-mentioned Example 3-1, instead of the electrolyte-coated carbon material, a mixture obtained by mixing 1 mg of a carbon material (hard carbon) and 5.6 mg of an argyrodite-type sulfide solid electrolyte in a roll mill was used to prepare a negative electrode. Except for this, a test cell of this comparative example was prepared in the same manner as in the above-mentioned Example 3-1. The porosity of the solid electrolyte layer and the negative electrode in the test cell thus prepared were 5% and 60%, respectively.

<Test example of test cell (evaluation of charge/discharge rate characteristics)>
The charge/discharge rate characteristics of the test cells fabricated in the above-mentioned Examples and Comparative Examples were evaluated.

The charge and discharge tests were performed in a voltage range of 4.3V/2.5V against Li, with charging in constant current/low voltage (CCCV) mode and discharging in constant current (CC) mode at rates of 0.2C (low rate conditions) and 2C (high rate conditions). The evaluation temperature was 298K (25°C), with a 30-minute pause between charging and discharging. Note that "1C" refers to the current value at which the battery will be fully charged (100% charged) when charged at that current value for 1 hour.

From the discharge capacities at 0.2C and 2C measured in this way, the discharge capacity retention rate (= 2C discharge capacity / 0.2C discharge capacity x 100) was calculated and used as an index of charge/discharge rate characteristics (the higher this value, the better the charge/discharge rate characteristics). The results are shown in Table 1 below.

The results shown in Table 1 show that, when comparing the examples and comparative examples in which the conductive porous body is made of the same material, the charge/discharge rate characteristics can be significantly improved by providing the configuration of the present invention. It can also be seen that the charge/discharge rate characteristics are further improved by providing the negative electrode with a metal (Ag) that can be alloyed with lithium.

10a stacked battery,
11′ negative electrode current collector,
11” positive electrode current collector,
13 Lithium ion/electron conductive structures;
15 positive electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 power generating element,
25 negative electrode current collector (negative electrode tab),
27 Positive electrode current collector (positive electrode tab),
29 Laminating film.

Claims (8)

A positive electrode and
A negative electrode;
a solid electrolyte layer interposed between the positive electrode and the negative electrode and including a first lithium ion conductive solid electrolyte;
A power generating element having
the negative electrode comprises a lithium ion/electron conductive structure including a conductive porous body made of a metal material (excluding those having a three-dimensional network structure, those having a foam shape, and those having a shape of a bonded body of metal powder) having a porosity of 60 to 95% and a second lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body;
A lithium secondary battery, wherein the porosity of the lithium ion/electron conductive structure is greater than the porosity of the solid electrolyte layer. A positive electrode and
A negative electrode;
a solid electrolyte layer interposed between the positive electrode and the negative electrode and including a first lithium ion conductive solid electrolyte;
A power generating element having
the negative electrode comprises a lithium ion/electron conductive structure including a conductive porous body made of a metal material (excluding those having a three-dimensional network structure, those having a foam shape , and those having a shape of a bonded body of metal powder) having a porosity of 60 to 95% and a second lithium ion conductive solid electrolyte covering at least a part of the inner surface of the porous body;
The porosity of the lithium ion/electron conductive structure is greater than the porosity of the solid electrolyte layer; and
A lithium secondary battery, wherein metallic lithium is held in the voids of the lithium ion/electron conductive structure. The lithium secondary battery according to claim 1 or 2, wherein the conductive porous body includes a metal material having a shape of a mesh, an expanded grid (expanded metal), or a punched metal. The lithium secondary battery according to claim 3, wherein the conductive porous body contains stainless steel or nickel. The lithium secondary battery according to any one of claims 1 to 4, wherein the negative electrode contains a metal capable of being alloyed with lithium selected from the group consisting of magnesium, zinc, bismuth, indium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, cadmium, gallium, and thallium . The lithium secondary battery according to claim 5, wherein the metal capable of being alloyed with lithium is silver. The lithium secondary battery according to any one of claims 1 to 6, wherein the first lithium ion conductive solid electrolyte and the second lithium ion conductive solid electrolyte include a sulfide solid electrolyte. The lithium secondary battery according to any one of claims 1 to 7, which is an all-solid-state lithium secondary battery.