JP7822779B2 - Electrode, battery, battery pack, and vehicle - Google Patents

Description

Embodiments of the present invention relate to electrodes, batteries, battery packs, and vehicles.

In recent years, research and development of high-energy density secondary batteries, such as lithium-ion secondary batteries and non-aqueous electrolyte secondary batteries, has been actively pursued. Secondary batteries are expected to be used as power sources for vehicles such as hybrid electric vehicles and electric vehicles, as well as for large-scale storage of electricity, such as uninterruptible power supplies for mobile phone base stations. Demand for power sources for mobile services, such as autonomous industrial robots and drones, is also rapidly increasing. Therefore, in addition to high energy density, secondary batteries are also required to have excellent performance in other areas, such as rapid charge/discharge capability and long-term reliability.

Rapid charging and discharging is possible when lithium ions and electrons move quickly between the positive electrode and negative electrode, which are capable of absorbing and releasing lithium ions and electrons, respectively, via an electrolyte and an external circuit. Batteries capable of such rapid charging and discharging have the advantage of significantly shortening charging times. Furthermore, using such batteries capable of rapid charging and discharging as a vehicle power source can improve the vehicle's power performance and also enable the efficient recovery of regenerative energy.

To improve the energy density per volume, for example, the density of the material that makes up the electrode can be increased. However, as electrode density increases, it becomes more difficult for the liquid electrolyte to penetrate deep into the electrode. Poor electrolyte penetration not only makes rapid charging and discharging difficult, but also makes it more likely that parts of the electrode will contribute little to charging and discharging. In addition, uneven distribution of charge and discharge within the electrode can cause partial deterioration of the electrode, which could also undermine long-term reliability.

In order to efficiently impregnate electrodes with electrolyte (liquid electrolyte) during the secondary battery manufacturing process, a conventional electrolyte injection method has been proposed in which the electrolyte is injected into the exterior material of the secondary battery and then allowed to penetrate the battery elements, including the electrodes, in a reduced-pressure atmosphere. However, because the constituent materials of the electrodes are packed at a high density, it is difficult to consistently achieve stable impregnation.

JP 2016-58247 A Special table 2015-511389 publication Japanese Patent Application Publication No. 10-50339 JP 2012-28290 A

The objective is to provide electrodes that can realize a battery that can achieve its designed capacity, a battery and battery pack that can achieve its designed capacity, and a vehicle equipped with this battery pack.

According to an embodiment, an electrode is provided that includes an active material-containing layer including a first end and a central portion adjacent to the first end in a first direction. The electrode is an electrode for a battery containing a liquid electrolyte. The first end is either a portion where the thickness of the active material-containing layer increases in a gradient from the outer edge of the cross-sectional shape of the active material-containing layer toward the central portion, or a portion where the density is lower than that of the central portion. The first width of the first end in the first direction is 5% to 40% of the length of the active material-containing layer in the first direction. The first basis weight of the active material-containing layer at the first end is less than the central basis weight of the active material-containing layer at the central portion. The ratio _dm1 of the first basis weight difference between the first basis weight and the central basis weight to the central basis weight is within the range of 1% < _dm1 < 10%. The active material-containing layer has a first density distribution in which the density varies along the first direction. A ratio d _d1 of a first density difference between the first maximum density and the first minimum density to the first maximum density in the first density distribution is within the range of 5%<d _d1 <20%.

According to another embodiment, a battery is provided comprising a negative electrode, a positive electrode, and an electrolyte. At least one of the negative electrode and the positive electrode includes an electrode according to the above embodiment.

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

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

FIG. 2 is a cross-sectional view schematically illustrating an example of an electrode according to the embodiment. FIG. 10 is a cross-sectional view schematically illustrating another example of an electrode according to the embodiment. FIG. 2 is a plan view schematically illustrating an example of an electrode according to the embodiment. FIG. 10 is a plan view schematically illustrating another example of an electrode according to the embodiment. FIG. 1 is a cross-sectional view schematically illustrating an example of a preferred mode of an electrode according to an embodiment. FIG. 10 is a cross-sectional view schematically illustrating another example of a preferred aspect of the electrode according to the embodiment. FIG. 1 is a cross-sectional view schematically illustrating an example of a conventional electrode. FIG. 1 is a cross-sectional view schematically illustrating an example of a battery according to an embodiment. 9 is an enlarged cross-sectional view of part A of the battery shown in FIG. 8 . FIG. 10 is a partially cutaway perspective view schematically showing another example of a battery according to an embodiment. FIG. 11 is an enlarged cross-sectional view of part B of the battery shown in FIG. 10 . FIG. 1 is a perspective view schematically illustrating an example of a battery pack according to an embodiment. FIG. 1 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. FIG. 14 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 13 . 1 is a partially see-through view schematically 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;

Embodiments will be described below with reference to the drawings. Note that common components throughout the embodiments will be assigned the same reference numerals, and duplicate explanations will be omitted. Each figure is a schematic diagram intended to facilitate explanation and understanding of the embodiments, and while the shape, dimensions, and ratios may differ from those of the actual device, these can be appropriately modified in design, taking into account the following explanation and known technology.

[First embodiment]
According to a first embodiment, there is provided an electrode. The electrode comprises an active material-containing layer including a first end portion and a central portion adjacent to the first end portion in a first direction. The active material-containing layer has a basis weight such that the first basis weight at the first end portion is less than the central basis weight at the central portion. A ratio _dm1 of the first basis weight difference between the first basis weight and the central basis weight to the central basis weight is within the range of 1% < _dm1 < 10%.

Such an electrode may be, for example, a battery electrode. The battery in which the electrode is used may be, for example, a primary battery or a secondary battery such as a lithium secondary battery. The secondary battery referred to here includes a nonaqueous electrolyte secondary battery containing a nonaqueous electrolyte. As a specific example, the electrode may be a nonaqueous electrolyte battery electrode in which an active material-containing layer (electrode layer) is formed on a foil-shaped current collector (current collector foil). The electrode may be included in the battery as, for example, a negative electrode or a positive electrode.

The active material-containing layer contains an electrode active material. Examples of the electrode active material include oxides and sulfides. In addition to the active material, the active material-containing layer can optionally further contain a conductive agent and a binder.

The electrode may further include a current collector. The active material-containing layer may be provided, for example, on at least one major surface of the current collector. The active material-containing layer may be provided on one major surface of the current collector. Alternatively, the active material-containing layer may be provided on both major surfaces of the current collector, for example, on both the front and back surfaces of a foil-shaped current collector.

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

In this electrode, the active material-containing layer has a basis weight distribution between a first end portion and a central portion adjacent to that end portion in a first direction along the in-plane direction of the electrode. Specifically, the basis weight of the active material-containing layer is relatively low at at least one end portion (first end portion) in the first direction, and high in the central portion adjacent to that end portion. By providing such a basis weight distribution for the active material-containing layer, it is possible to improve the impregnation of the electrode with a liquid electrolyte. For example, the in-plane direction of the electrode along which the first direction runs may be the direction along the main surface of the current collector.

The basis weight distribution of the active material-containing layer in this embodiment is not limited to a configuration in which there is a basis weight distribution between the end portions and the central portion adjacent to the end portions. It may not only be a configuration in which the basis weight differs between the end portions and the central portion, but also a configuration in which the basis weight changes stepwise, or a gradient (slope) in which the basis weight is relatively low at at least one end portion (first end portion) in the first direction and gradually increases toward the central portion. By providing a gradient in these basis weight distribution configurations, the impregnation of the liquid electrolyte into the electrode can be further improved.

To increase the energy density of a battery, an electrode is often stacked with a counter electrode (a negative electrode for a positive electrode, or a positive electrode for a negative electrode) via an insulating member such as a separator. In both stacked electrode groups constructed by stacking multiple electrodes and counter electrodes with an insulating member interposed therebetween, and wound electrode groups constructed by winding a laminate of an electrode, an insulating member, and a counter electrode, most of the electrode's main surface is in close contact with the insulating member. Because almost no main surface is exposed, electrolyte impregnation into the electrode occurs mostly via the edge of the electrode, i.e., the edge in the in-plane direction. In other words, the surface of the active material-containing layer accessible to the electrolyte is small.

By increasing the basis weight of the active material-containing layer in the center relative to the basis weight at the first end, preferably by providing a slope that increases from the first end to the center, it is possible to provide an area on the electrode main surface that is not in close contact with the insulating material, etc., from the first end to the center. This area allows the electrolyte to penetrate into the electrode interior in addition to the end surface of the electrode, thereby promoting electrolyte impregnation. In addition to providing a slope in this shape, similar effects can also be achieved by distributing the basis weight by density, for example.

In this way, the difference between the first basis weight at the first end and the central basis weight at the central portion is defined as the first basis weight difference, and by providing a distribution in which the ratio _dm1 of the first basis weight difference to the central basis weight is within the range of 1% < _dm1 < 10% (0.01 < [first basis weight difference/central basis weight] < 0.1), the electrolyte is easily impregnated without increasing the diffusion resistance of the carrier (e.g., lithium ions) in the thickness direction of the electrode (toward the counter electrode). If the electrolyte is not impregnated sufficiently, portions of the electrode will not be used for charging and discharging, resulting in a battery that exhibits less than the designed capacity. However, if the electrolyte is well impregnated into the electrode, the designed capacity can be exhibited even if the time required for battery production is shortened.

The region with a smaller basis weight from the first end toward the center along the first direction, preferably the inclined region, is preferably provided over a length of 5% to 40% of the length of the active material-containing layer in the first direction. In other words , the first width of the first end in the first direction is preferably 5% to 40% of the first distance between both ends of the active material-containing layer along the first direction (0.05≦[first width/first distance]≦0.4). The first distance may be, for example, 150 mm or more.

It is preferable that a distribution of low basis weights is provided not only at one end along the first direction but also at both ends of the active material-containing layer. That is, the ratio _dm1 of the first basis weight difference to the central basis weight is within the above-mentioned range, and the active material-containing layer has an end adjacent to the center at a position opposite the first end in the first direction from the first end, and a second end. The second basis weight of the active material-containing layer at this second end is less than the central basis weight, and the ratio _dm2 of the second basis weight difference between the second basis weight and the central basis weight is preferably within the range of 1% < _dm2 < 10% (0.01 < [second basis weight difference/central basis weight] < 0.1). When introducing an electrolyte into a battery, the electrolyte is poured into an exterior member housing battery elements, such as an electrode group including electrodes. Here, the battery elements are immersed in the electrolyte to impregnate the electrodes. Therefore, the electrolyte penetrates into the electrodes not only from the end facing the opening of the exterior member where the electrolyte is introduced, but also from other parts of the outer periphery of the active material-containing layer. By reducing the basis weight of the active material-containing layer at the second end in addition to the first end, it is possible to promote impregnation of the electrolyte from both ends in the first direction.

It is desirable to provide a distribution of low basis weight on the second end side as well, similar to the first end side. In this case, too, it is desirable that the region with low basis weight, preferably an inclined region, be provided over a length of 5% to 40% of the length of the active material-containing layer in the first direction. Therefore, it is desirable that the second width of the second end in the first direction be 5% to 40% of the first distance between both ends of the active material-containing layer along the first direction (0.05≦[second width/first distance]≦0.4).

In a specific example electrode, the average basis weight at each of the first end and second end of the active material-containing layer is 120 g/ ^m2 , the average basis weight at the center between those ends is 160 g/ ^m2 , and the average basis weight of the active material-containing layer as a whole along the first direction is 150 g/ ^m2 .

The electrode may have a shape in which the dimension in one direction within its plane is not equal to the dimension in another direction intersecting that direction. For example, the electrode may have a plate shape with a rectangular main surface including long and short sides. For example, the direction intersecting the first direction in the active material-containing layer is defined as the second direction. The ends adjacent to the center of the active material-containing layer and located at both ends of the active material- containing layer in the second direction are defined as the third end and the fourth end, respectively. The distance between both ends of the active material-containing layer along the second direction is defined as the second distance. The aspect ratio r (r = longer distance/shorter distance) of the longer distance to the shorter distance of the first distance between the ends of the active material-containing layer in the first direction and the second distance between the ends of the active material-containing layer in the second direction may be within the range of 1 < r < 50. For example, in a rectangular electrode, the ratio of the long side length to the short side length of the rectangle (long side/short side) may be greater than 1 and less than 50.

The shape of the electrode is not limited to a rectangle, and may be, for example, a quadrilateral or polygonal surface with one or more chamfered corners, or an elliptical surface. Furthermore, the outer edges defining the shape of the electrode's main surface do not have to be straight lines, and may be, for example, arc-shaped or wavy.

In an electrode that is long in one direction, the long side direction may be defined as the first direction, and the basis weight at the end (the first end, or both the first end and the second end) may be reduced to provide a basis weight distribution in this direction. For example, when a stacked electrode group is constructed using rectangular electrodes having long and short sides, it is preferable to provide a basis weight distribution along the long side direction of the electrode. Because the distance from both ends of the long side direction to the center is longer than the distance from both ends of the short side direction, it is effective to reduce the basis weight at the end of the long side direction to promote electrolyte impregnation along the long side direction. Specifically, in an electrode of this type, the long side direction is defined as the first direction, and the first distance is longer than the second distance.

The first end where the basis weight of the active material-containing layer is reduced is not limited to the end in the long side direction; for example, the first direction may be along the short side direction of the electrode. For example, when a wound electrode group is constructed by winding a laminate including a strip-shaped electrode with the winding axis aligned along the short side direction of the strip, the long side of the strip is wound to form a wound end surface that intersects with the winding axis. When electrolyte is impregnated into a wound electrode group, the electrolyte mainly penetrates through the wound end surface. Therefore, with electrodes of this type, it is effective to reduce the basis weight at the end in the short side direction to promote electrolyte impregnation along the short side direction. In this embodiment, the short side direction of the electrode is the first direction, and the first distance is shorter than the second distance.

The shape of the electrode principal surface is not limited to those including long and short dimensions, and may be, for example, square or circular. For an active material-containing layer having a polygonal shape such as a square, the first direction may correspond to, for example, a direction from one side toward the center. For a circular active material-containing layer, the first direction may correspond to a direction from any point on the periphery toward the center.

In addition to the basis weight distribution along the first direction of the active material-containing layer, it is preferable to also include a basis weight distribution along a second direction intersecting the first direction. As described above, when a battery element such as an electrode group including an electrode is immersed in an electrolyte, the electrolyte penetrates into the active material-containing layer not only from the first end and second end of the active material-containing layer at both ends in the first direction, but also from the third end and fourth end at both ends in the second direction. Therefore, by reducing the basis weight at at least one of the ends in the second direction, the effect of promoting electrolyte impregnation from the third end and/or fourth end is further achieved. Specifically, the third basis weight of the active material-containing layer at the third end is smaller than the central basis weight, and a distribution is set in which the ratio d _m3 of the third basis weight difference between the third basis weight and the central basis weight to the central basis weight is within the range of 1% < d _m3 < 10% (0.01 < [third basis weight difference/central basis weight] < 0.1). Alternatively, a distribution is provided in which the fourth basis weight of the active material-containing layer at the fourth end is smaller than the central basis weight, and the ratio _dm4 of the fourth basis weight difference between the fourth basis weight and the central basis weight to the central basis weight is within the range of 1% < _dm4 < 10% (0.01 < [fourth basis weight difference/central basis weight] < 0.1). Alternatively, both a distribution from the third end to the central part and a distribution from the fourth end to the central part are provided.

At each of the third end and fourth end, it is desirable that a region with a lower basis weight than the central portion be provided over a length that is 5% to 40% of the length of the active material-containing layer in the second direction. In other words, it is desirable that the third width of the third end in the second direction be 5% to 40% of the second distance (0.05≦[third width/second distance]≦0.4). It is also desirable that the fourth width of the fourth end in the second direction be 5% to 40% of the second distance (0.05≦[fourth width/second distance]≦0.4).

The density of the active material-containing layer at the first end may be different from the density at the central portion. Alternatively, the density at the first end may be equal to the density at the central portion. It is preferable that the density at the first end is lower than the density at the central portion. A lower density at the first end can further promote impregnation of the electrolyte from the first end.

Similarly, the density of the active material-containing layer at the second end may be different from the density at the central portion. Alternatively, the density at the second end may be equal to the density at the central portion. It is preferable that the density at the second end is lower than the density at the central portion. A lower density at the second end can further promote impregnation of the electrolyte from the second end.

That is, the active material-containing layer may have a first density distribution in which the density varies along the first direction. The maximum and minimum densities in the first density distribution are defined as the first maximum density and the first minimum density, respectively, and the difference between the first maximum density and the first minimum density is defined as the first density difference. Preferably, the ratio d _d1 of the first density difference to the first maximum density is within the range of 5% < d _d1 < 20% (0.05 < [(first maximum density - first minimum density)/first maximum density] < 0.2). Here, the first maximum density is defined as the average density in the central portion. If the average densities at the first end and second end are different, the smaller one is defined as the first minimum density. If the average densities at the first end and second end are equal, that value is defined as the first minimum density.

The density of the active material-containing layer at the third end and the fourth end is also different from or equal to the density of the central portion. It is preferable that the density at the third end and/or the fourth end is lower than the density at the central portion, as this further promotes electrolyte impregnation from these ends. The active material-containing layer may have a second density distribution in which the density varies along the second direction. The maximum and minimum densities in the second density distribution are defined as the second maximum density and the second minimum density, respectively, and the difference between the second maximum density and the second minimum density is defined as the second density difference. The ratio d _d2 of the second density difference to the second maximum density is preferably within the range of 5% < d _d2 < 20% (0.05 < [(second maximum density - second minimum density)/second maximum density] < 0.2). Here, the second maximum density is defined as the average density at the central portion. If the average densities at the third end and the fourth end are different, the smaller of the two is defined as the second minimum density. If the average densities at the third end and the fourth end are equal, that value is defined as the second minimum density.

Next, we will explain in detail the negative and positive electrode aspects of the electrode according to the first embodiment.

(Negative electrode)
The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode active material-containing layer may be formed on one or both sides of the negative electrode current collector. The negative electrode active material-containing layer may include a negative electrode active material and, optionally, a conductive agent and a binder. The negative electrode current collector and the negative electrode active material-containing layer may be the current collector and the active material-containing layer described above, respectively.

Examples of negative _electrode active materials include lithium titanate having a ramsdellite structure (e.g., Li2 _{+yTi3O7 ,} 0≦y≦3), lithium titanate having a spinel structure (e.g., _{Li4 + xTi5O12} , 0≦x≦3), monoclinic titanium dioxide ( _TiO2 (B)), anatase titanium dioxide, rutile titanium dioxide, niobium pentoxide ( _{Nb2O5 )} , hollandite titanium composite oxide, orthorhombic titanium-containing composite oxide, and monoclinic niobium titanium composite oxide.

An example of an orthorhombic titanium-containing composite oxide is a compound represented by Li2 _+aM (I) _2- bTi6 _-cM (II) _{dO14 +σ} . Here, M(I) is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. M(II) is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦a≦6, 0≦b<2 _, 0≦c<6, 0≦d<6, and -0.5≦σ≦0.5. A specific example of an orthorhombic titanium-containing composite oxide is Li2 _{+ aNa2Ti6O14} (0≦a≦ ₆ ).

An example of the monoclinic niobium titanium composite oxide is a compound represented by Li _x Ti _1-y M1 _y Nb _2-z M2 _z O _7+δ . Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3. A specific example of the monoclinic niobium titanium composite oxide is Li _x Nb ₂ TiO ₇ (0≦x≦5).

Another example of a monoclinic niobium titanium composite oxide is a compound represented by Li _x Ti _1-y M3 _y+z Nb _2-z O _7-δ , where M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

Conductive agents are added to improve current collection performance and reduce 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 nanofibers, and carbon nanotubes. One of these may be used as the conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surface of the active material particles may be coated with carbon or an electronically conductive inorganic material.

The binder is added to fill the gaps between the dispersed active material and to bind the active material and the negative electrode 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 CMC salts. One of these may be used as the binder, or two or more may be used in combination.

The blending ratios of the negative electrode active material, conductive agent, and binder in the negative electrode active material-containing layer can be adjusted appropriately depending on the application of the negative electrode. For example, the negative electrode active material, conductive agent, and binder are preferably blended in ratios 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 using a conductive agent content of 2% by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved. Furthermore, by using a binder content of 2% by mass or more, sufficient binding between the negative electrode active material-containing layer and the current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to use a conductive agent and binder content of 30% by mass or less each in order to achieve high capacity.

The negative electrode current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and extracted from the active material. For example, the current collector is preferably made of copper, nickel, stainless steel, aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The current collector preferably has a thickness of 5 μm or more and 20 μm or less. A current collector with this thickness can balance the strength and weight of the electrode.

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

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

(positive electrode)
The positive electrode may include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer may be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer may include a positive electrode active material and, optionally, a conductive agent and a binder. The positive electrode current collector and the positive electrode active material-containing layer may be the current collector and the active material-containing layer described above, respectively.

For example, oxides or sulfides can be used as the positive electrode active material. The positive electrode may contain one type of compound alone as the positive electrode active material, or may contain a combination of two or more types of compounds. Examples of oxides and sulfides include compounds that can insert and extract Li or Li ions.

Examples of such compounds include manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxides (e.g., Li _x Mn ₂ O ₄ or Li _x MnO ₂ ; 0<x≦1), lithium nickel composite oxides (e.g., Li _x NiO ₂ ; 0<x≦1), lithium cobalt composite oxides (e.g., Li _x CoO ₂ ; 0<x≦1), lithium nickel cobalt composite oxides (e.g., Li _x Ni _1-y Co _y O ₂ ; 0<x≦1, 0<y<1), lithium manganese cobalt composite oxides (e.g., Li _x Mn _y Co _1-y O ₂ ; 0<x≦1, 0<y<1), and lithium manganese nickel composite oxides having a spinel structure (e.g., Li _x Mn _2-y Ni _y O ₄ ; 0<x≦1, 0<y<2), lithium phosphate oxides having an olivine _structure (e.g., _LixFePO4 ; 0<x≦1, _{LixFe1 - yMnyPO4} ; 0<x≦1, 0<y< ₁ , _LixCoPO4 ; 0<x≦ ₁ ), iron sulfate ( _Fe2 ( _SO4 ) ₃ ), vanadium oxides (e.g., _V2O5 ), and lithium nickel cobalt manganese composite oxides ( _{LixNi1 - yzCoyMnzO2} ; 0<x≦1 _, 0<y<1 _{, 0} <z<1, y+z<1).

Among the above, examples of more preferred compounds as the positive electrode active material include lithium manganese composite oxides having a spinel structure (e.g., Li _x Mn ₂ O ₄ ; 0<x≦1), lithium nickel composite oxides (e.g., Li _x NiO ₂ ; 0<x≦1), lithium cobalt composite oxides (e.g., Li _x CoO ₂ ; 0<x≦1), lithium nickel cobalt composite oxides (e.g., Li _x Ni _1-y Co _y O ₂ ; 0<x≦1, 0<y<1), lithium manganese nickel composite oxides having a spinel structure (e.g., Li _x Mn _2-y Ni _y O ₄ ; 0<x≦1, 0<y<2), lithium manganese cobalt composite oxides (e.g., Li _x Mn _y Co _1-y O ₂ ; 0<x≦1, 0<y<1), and lithium iron phosphate (e.g., Li _x FePO ₄ ; 0<x≦1) and lithium nickel cobalt manganese composite oxide (Li _x Ni _1-yz Co _y Mn _z O ₂ ; 0<x≦1, 0<y<1, 0<z<1, y+z<1). When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

When a room-temperature molten salt is used as the battery electrolyte, it is preferable to use a positive electrode active material containing lithium iron phosphate, Li _x VPO ₄ F (0≦x≦1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or a mixture thereof. These compounds have low reactivity with room-temperature molten salts, and therefore can improve cycle life. Details of room-temperature molten salts will be described later.

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

The binder is added to fill the gaps between the dispersed positive electrode active material and to bind the positive electrode active material to the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, 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 binders.

Conductive agents are added to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanofibers, and carbon nanotubes. One of these may be used as the conductive agent, or two or more may be used in combination. The conductive agent may also be omitted.

In the positive electrode active material-containing layer, the positive electrode active material and binder are preferably blended in proportions of 80% by mass or more and 98% by mass or less, and 2% by mass or more and 20% by mass or less, respectively.

By using a binder amount of 2% by mass or more, sufficient electrode strength can be achieved. The binder can also function as an insulator. Therefore, by using a binder amount of 20% by mass or less, the amount of insulator contained in the electrode is reduced, thereby reducing internal resistance.

When a conductive agent is added, the positive electrode active material, binder, and conductive agent are preferably blended in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, 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 that comes into contact with the electrolyte can be reduced. This low proportion can reduce electrolyte decomposition during high-temperature storage.

The positive electrode current collector is preferably aluminum foil or aluminum alloy foil containing one or more elements selected from 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 positive electrode current collector may also include a portion on its surface where the positive electrode active material-containing layer is not formed. This portion can function as a positive electrode current collecting tab.

<Manufacturing method>
The electrode can be produced, for example, by the following method. The following method is an example in which a gradient is provided as the basis weight distribution. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. The obtained slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of an active material-containing layer and a current collector. Then, the laminate is pressed.

When applying the slurry, the amount of slurry applied to at least one edge is reduced. For example, when applying the slurry using a die coater, slowing the feed rate in a portion of the die head can reduce the amount of slurry applied in the corresponding portion of the coating width. Specifically, by applying the slurry using the following die head, the amount of slurry applied to both ends of the coating width, with the direction intersecting the coating direction defined as the first direction, can be reduced. This results in the active material-containing layer obtained after drying having a first end and a second end with a lower basis weight than the central portion between them. For example, by using a trapezoidal shim, the space within the die head is shaped to expand from the manifold that stores the slurry toward the discharge port. With this type of die head, the feed rate of the slurry supplied from the manifold to the discharge port is fastest at the center of the die head width and decreases toward the outside. Therefore, the amount of slurry discharged from both ends is smaller than the amount of slurry discharged from the center of the discharge port, resulting in a smaller amount of slurry applied at the edges of the coating width.

Alternatively, when applying the slurry using a die coater, the amount of slurry applied can be varied along the direction of current collector transport by controlling the flow rate of the slurry supplied to the die head or the transport speed of the current collector relative to the die head. After drying and pressing, the electrode can be cut so that the portions with a lower basis weight are at the edges, resulting in an electrode with an active material-containing layer with a lower basis weight at the edges. In one example, by combining the use of the trapezoidal shim described above with control of the slurry flow rate and current collector transport, an electrode with a gradient in the basis weight distribution in both the first and second directions can be obtained.

Alternatively, the slurry can be applied multiple times in layers, reducing the coating area with each application, creating a gradient in the slurry coating. The degree of reduction depends on the desired gradient in basis weight and the amount applied per coat, but for example, the coating width can be narrowed by 1 cm.

By pressing a laminate including a dried coating film with locally different basis weights along the surface of a current collector to which the slurry has been applied, it is possible to obtain an active material-containing layer with a density distribution that varies locally. For example, if the entire coating film of dried slurry is pressed uniformly, the density after pressing will naturally be higher in areas with a higher basis weight, and lower in areas with a lower basis weight. Furthermore, by performing roll pressing using a roller with steps or inclinations, for example, partial pressing can be performed according to the areas where the coating film comes into contact with the roll, further controlling the density distribution.

<Measurement method>
The measurement methods for the electrode will be described below. Specifically, the methods for measuring the distribution of the basis weight and density in the active material-containing layer and the aspect ratio of the active material-containing layer will be described.

If you are measuring electrodes that are built into a battery, remove the electrodes from the battery using the following procedure.

First, the battery is placed in a discharged state. "Discharged" here refers to a state in which the battery is discharged at a constant current of 0.2 C or less to the lower discharge voltage limit in an environment of 25°C. The discharged battery is placed in an inert atmosphere glove box, such as a glove box filled with argon gas. Next, the target electrode is removed from the battery inside the glove box. Specifically, the battery's exterior is cut open while taking care not to short-circuit the positive and negative electrodes. For example, if the electrode used as the negative electrode is to be used as the measurement sample, the electrode connected to the negative terminal is removed. Alternatively, if the electrode used as the positive electrode is to be used as the measurement sample, the electrode connected to the positive terminal is removed. The removed electrode is then washed with, for example, ethyl methyl ether solvent, and dried.

(Method for measuring basis weight distribution and density distribution)
The distribution of the basis weight and density of the active material-containing layer can be measured as follows.

For the electrode used as the measurement sample, punch out multiple circular sample pieces with a diameter of 15 mm from both ends in one arbitrary direction and in another direction intersecting that direction, as well as from the center where those directions intersect. The intersecting angle between the arbitrary direction and the other direction can be a right angle (90°). For example, for a rectangular electrode, select the long side direction and the short side direction. The number of sample pieces to be collected is determined by dividing the area from the end to the center at equal intervals, and collecting sample pieces from the center of each divided area. For example, the area should be divided into five or more parts, i.e., five or more sample pieces should be collected.

The total mass of each sample piece is measured and recorded. Next, the sample piece is coated with a binder such as polyvinylidene fluoride (PVdF). The binder is used to fill as many pores in the active material-containing layer as possible. The coated sample piece is placed in a liquid such as water in a container such as a measuring cylinder, and the volume of the sample piece is determined based on the increase in the liquid level. The sample piece is then immersed in N-methylpyrrolidone or pure water, and ultrasonic waves are applied to separate the active material-containing layer from the current collector. The separated current collector is dried, and the mass of the current collector alone is measured. The current collector is also placed in a liquid in a container, and the volume of the current collector is determined based on the increase in the liquid level.

The mass of the active material-containing layer is calculated based on the mass of the entire sample piece and the mass of the current collector, and the calculated mass of the active material-containing layer is divided by the area of the sample piece (π×(15 mm/2) ² ) to calculate the basis weight for each sample piece (basis weight = (total mass of sample piece - mass of current collector) / area of sample piece). The average basis weight of the active material-containing layer of the obtained sample piece is calculated for each sampling point, and this is taken as the average basis weight for each sampling point.

The volume of the active material-containing layer is calculated based on the volume of the entire sample piece and the volume of the current collector, and the density of each sample piece is calculated by dividing the calculated volume of the active material-containing layer by the mass of the active material-containing layer (density = (total mass of sample piece - mass of current collector) / (total volume of sample piece - volume of current collector)). The average density of the active material-containing layer of the sample piece obtained for each sampling point is calculated, and this is taken as the average density of each sampling point.

If any of the ends of the sample piece has an average basis weight less than that of the central portion, that end is deemed to be the first end. If there are multiple ends with an average basis weight less than that of the central portion, any one of them is arbitrarily selected and deemed to be the first end. The end sampled on the opposite side of the active material-containing layer from the point selected as the first end, across the central portion, is deemed to be the second end. The direction along the line connecting the point selected as the first end and the point selected as the second end is deemed to be the first direction, and the remaining two ends sampled, lined up on either side of the central portion along a direction intersecting the first direction, are arbitrarily deemed to be the third end and the fourth end, respectively.

The first basis weight difference is calculated by subtracting the average basis weight (first basis weight) at the first end portion determined as above from the average basis weight (center basis weight) at the center portion. Then, the first basis weight difference is divided by the average basis weight (center basis weight) at the center portion to calculate the ratio _dm1 of the first basis weight difference to the center basis weight ( _dm1 = [(average basis weight at center portion - average basis weight at first end portion) / average basis weight at center portion] × 100%). Similarly, ratios _dm2 , _dm3 , and _dm4 are calculated for the second to fourth end portions.

The average densities of the first end, second end, and central portion identified as described above are compared. The largest value among them is defined as the first maximum density in the first density distribution along the first direction. The smallest value is defined as the first minimum density in the first density distribution. In the electrode according to the first embodiment, the average density of the central portion is defined as the first maximum density, and the average density of either or both of the first end and second end portions is defined as the first minimum density. The first density difference is calculated by subtracting the first minimum density from the first maximum density. The ratio d _d1 of the first density difference to the first maximum density is then calculated by dividing the first density difference by the first maximum density (d _d1 = [(first maximum density - first minimum density) / first maximum density] × 100%). The ratio d _d2 of the second density difference to the second maximum density in the second direction is similarly calculated based on the average densities of the third end, fourth end, and central portion.

(Method of measuring aspect ratio)
The aspect ratio of the active material-containing layer can be determined by identifying the first and second directions and dividing the longer dimension in those directions by the shorter dimension.

The first distance is determined by measuring the length of the active material-containing layer along the first direction identified when measuring the basis weight distribution and density distribution. The second direction is determined as the direction along the line connecting the extraction points of the third end and the fourth end, and the second distance is determined by measuring the length of the active material-containing layer along that direction. The aspect ratio is calculated by dividing the longer of the first distance and the second distance by the shorter one.

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

A specific example of an electrode according to an embodiment is shown in Figure 1. Figure 1 is a cross-sectional view that schematically illustrates an example of an electrode according to an embodiment. The example shown in Figure 1 illustrates an embodiment of the electrode as a negative electrode of a battery. Figure 1 is a schematic cross-sectional view that illustrates a cross section that intersects with the main surface of the negative electrode 3.

The negative electrode 3 shown in FIG. 1 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b provided on the negative electrode current collector 3a. The negative electrode current collector 3a includes a portion that does not support the negative electrode active material-containing layer 3b, i.e., a negative electrode current collector tab 3c. In the example shown, the negative electrode active material-containing layer 3b is supported on one main surface of the negative electrode current collector 3a. The negative electrode 3 may also be an electrode that supports the negative electrode active material-containing layer 3b on both the front and back main surfaces of the negative electrode current collector 3a.

1 is defined as a first direction 11 including the in-plane direction of the negative electrode 3, and the negative electrode active material containing layer 3b includes a first end _3b1 , a central portion _3b0 , and a second end _3b2 that are aligned along the first direction 11. The average basis weights (first basis _weight and second basis weight) of the negative electrode active material containing layer 3b at the first end 3b1 and the second end _3b2 are smaller than the average basis weight (central basis weight) at the central portion _3b0 , and the cross-sectional shape of the negative electrode active material containing layer 3b along the first direction ₁₁ has a gradient such that the thickness of the negative electrode active material containing layer 3b increases from the outer edges of the first end 3b1 and the second end _3b2 toward the central portion _3b0 .

The difference between the average basis weight of the first end portion _3b1 and the average basis weight of the central portion _3b0 (first basis weight difference) is greater than 1% and less than 10% (1% < _dm1 < 10%) compared to the average basis weight of the central portion _3b0 . Also, the difference between the average basis weight of the second end portion _3b2 and the average basis weight of the central portion 3b0 (second basis weight difference) is greater than 1% and less than 10% (1% < _dm2 < 10%) compared to the average basis weight of _the central portion _3b0 .

Figure 7 shows a cross-sectional view that schematically illustrates an example of a conventional electrode. The conventional electrode 10 shown in Figure 7 includes a current collector 10a and an active material-containing layer 10b provided on the current collector 10a. The current collector 10a includes a portion that does not support the active material-containing layer 10b, i.e., a current collecting tab 10c. Unlike the negative electrode 3 according to the first embodiment shown in Figure 1, the electrode 10 has a generally uniform basis weight throughout the active material-containing layer 10b, and a substantially constant thickness.

The main surface of the negative electrode active material-containing layer 3b of the negative electrode 3 included in the electrode group of the battery is in close contact with the negative electrode current collector 3a or faces the positive electrode active material-containing layer with a separator sandwiched therebetween. Therefore, the main path of electrolyte penetration into the negative electrode active material-containing layer 3b is the end located at the outer edge of the negative electrode active material-containing layer 3b. In the negative electrode 3 according to the first embodiment shown in FIG. 1, the first end _3b1 and the second end _3b2 of the negative electrode active material-containing layer 3b each have a larger surface area through which the electrolyte can penetrate than both ends of the active material-containing layer 10b of the conventional electrode 10 shown in FIG. 7. Therefore, the electrode according to the first embodiment has improved electrolyte impregnation compared to conventional electrodes.

The proportion of the length of the negative electrode active material-containing layer 3b in the first direction 11 corresponding to the first distance D1 that is accounted for by the first width W1 of the first end _3b1 and the second width W2 of the second end _3b2 is 5% or more and 40% or less (1/20 or more and 2/5 or less).

1, the basis weight at both ends of the negative electrode active material-containing layer 3b along the first direction 11, i.e., at both the first end _3b1 and the second end _3b2, is smaller than that at the central portion _3b0 . However, the electrode according to the first embodiment also includes an embodiment in which the basis weight is smaller at the first end but equal to or greater than that at the second end. Also, although the first end _3b1 is located adjacent to the negative electrode current collector tab 3c in FIG. 1, the first end can be any end in the in-plane direction of the active material-containing layer.

Fig. 2 shows another example of an electrode according to an embodiment. The negative electrode 3 shown in Fig. 2 includes a negative electrode current collector 3a, a negative electrode active material-containing layer 3b, and a negative electrode current collecting tab 3c, similar to the case of Fig. 1. While the density of the negative electrode active material-containing layer 3b is uniform throughout in the example of Fig. ₁ , in the example of Fig. 2, the density at the first end 3b1 and the second end _3b2 is lower than the density at the central portion _3b0 . Fig. 2 may represent an electrode in which the negative electrode 3 of Fig. 1 has been subjected to uniform pressing over the entire first distance D1.

2, the thickness of the negative electrode active material-containing layer 3b is approximately the same among the first end 3b1, the central portion _3b0 , and the second end _3b2 , but the density _of the first end _3b1 and the second end _3b2 is lower than the density of the central portion _3b0 , and therefore the basis weight at the first end _3b1 and the second end _3b2 is lower than the basis weight at the central portion _3b0 . In the negative electrode 3, the impregnation of the electrolyte from the first end _3b1 and the second end _3b2 , which have lower density, is high.

In the first density distribution of the negative electrode active material-containing layer 3b along the first direction 11, when the first maximum density corresponding to the density at the central portion _3b0 is compared with the first minimum density corresponding to at least _one of the density at the first end portion 3b1 and the density at the second end portion _3b2 , the first density difference between the first maximum density and the first minimum density is greater than 1/20 and less than 1/5 of the first maximum density (5% < d _d1 < 20%).

In the electrode according to the first embodiment, the first direction may be, for example, a direction along the long side of the electrode. Alternatively, the first direction may be, for example, a direction along the short side of the electrode. Examples of such electrodes are shown in Figures 3 and 4, respectively.

Figure 3 is a plan view schematically illustrating an example of an electrode whose long side direction is the first direction. The negative electrode 3 shown in Figure 3 includes a negative electrode current collector and a negative electrode active material-containing layer 3b provided thereon. The negative electrode current collector includes a negative electrode current collector tab 3c that does not support the negative electrode active material-containing layer 3b. The negative electrode 3 in Figure 3 may be the negative electrode 3 shown in Figure 1 or the negative electrode 3 shown in Figure 2. Figures 1 and 2 may be cross-sectional views taken along the second direction 12, which corresponds to the short side direction of the negative electrode 3 in Figure 3. The negative electrode 3 in Figure 3 may be, for example, a negative electrode used in a stacked electrode group.

In the example of Figure 3, the direction in which the negative electrode current collector tab 3c protrudes outward from the negative electrode active material-containing layer 3b is the first direction 11, and the direction in which the negative electrode current collector tab 3c runs adjacent to the negative electrode active material-containing layer 3b is the second direction 12. However, the first embodiment also includes electrodes in which the first direction 11 and the second direction 12 are reversed.

Figure 4 is a plan view schematically illustrating an example of an electrode whose short side direction is the first direction. The negative electrode 3 illustrated in Figure 4 includes a negative electrode current collector and a negative electrode active material-containing layer 3b disposed thereon. The negative electrode current collector includes a negative electrode current collector tab 3c that does not support the negative electrode active material-containing layer 3b. The negative electrode 3 in Figure 4 may be the negative electrode 3 illustrated in Figure 1 or the negative electrode 3 illustrated in Figure 2. Figures 1 and 2 may be cross-sectional views of the negative electrode 3 in Figure 4 taken along the second direction 12, which corresponds to the short side direction. The negative electrode 3 in Figure 4 may be, for example, a negative electrode used in a wound electrode group. The negative electrode 3 may be included in the wound electrode group in a wound state around a virtual axis along the short side direction.

Figures 5 and 6 show examples of preferred electrode configurations in which the active material-containing layer has a reduced basis weight not only at the first and second ends in the first direction, but also at the third and fourth ends in the second direction. Figures 5 and 6 are cross-sectional views that schematically show one preferred configuration and another example, respectively. The negative electrode 3 shown in Figures 5 and 6 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b disposed on the negative electrode current collector 3a. Both Figures 5 and 6 may be cross-sectional views along the first direction 11 of the negative electrode 3 in Figure 3 or the negative electrode 3 in Figure 4.

5 and 6, the difference between the average basis weight of the third end portion _3b3 and the average basis weight of the central portion _3b0 (third basis weight difference) is greater than 1% and less than 10% (1% < _dm3 < 10%) compared to the average basis weight of the central portion _3b0 . Also, the difference between the average basis weight of the fourth end portion _3b4 and the average basis weight of the central portion _3b0 (fourth basis weight difference) is greater than 1% and less than 10% (1% < _dm4 < 10%) compared to the average basis weight of the central portion _3b0 .

In the example shown in Fig. 5, the density of the anode active material containing layer 3b is uniform throughout, as in the example shown in Fig. 1. In the example shown in Fig. 6, the density of the anode active material containing layer 3b at the third end _3b3 and the fourth end _3b4 is lower than the density at the central portion _3b0 , as in the example shown in Fig. 2. Specifically, in the second density distribution of the anode active material containing layer 3b along the second direction ₁₂ , when the second maximum density corresponding to the density at the central portion _3b0 is compared with the second minimum density corresponding to at least one of the density at the third end 3b3 and the density at the fourth end _3b4 , the second density difference between the second maximum density and the second minimum density is greater than 1/20 and less than 1/5 of the second maximum density (5% < d _d2 < 20%).

Since the third end _3b3 and the fourth end _3b4 are configured as described above, the negative electrode 3 of FIGS. 5 and 6 has improved electrolyte impregnation from both ends in the first direction 11 as well as improved electrolyte impregnation from both ends in the second direction 12.

The proportion of the length of the negative electrode active material-containing layer 3b in the second direction 12 corresponding to the second distance D2 that is accounted for by the third width W3 of the third end _3b3 and the fourth width W4 of the fourth end _3b4 is 5% or more and 40% or less (1/20 or more and 2/5 or less).

In the preferred example shown in FIGS. 5 and 6 , the basis weight at both end portions of the negative electrode active material-containing layer 3 b along the second direction 12, i.e., the third end portion 3 b ₃ and the fourth end portion 3 b ₄ , is smaller than that at the central portion 3 b _0. However, the electrode according to the first embodiment also includes an embodiment in which the basis weight at the third end portion and/or the fourth end portion is equal to or greater than the basis weight at the central portion.

The electrode according to the first embodiment includes an active material-containing layer including a first end portion and a central portion adjacent to each other along a first direction. The first basis weight of the active material-containing layer at the first end portion is smaller than the central basis weight of the active material-containing layer at the central portion. The first basis weight difference between the first basis weight and the central basis weight is such that the ratio _dm1 of the first basis weight to the central basis weight is within the range of 1% < _dm1 < 10%. By using this electrode, a secondary battery capable of achieving the designed capacity can be manufactured in a short period of time.

Second Embodiment
According to a second embodiment, there is provided a battery including a negative electrode, a positive electrode, and an electrolyte. This battery includes the electrode according to the first embodiment as at least one of the negative electrode and the positive electrode.

The battery according to the second embodiment may further include a separator disposed between the negative electrode and the positive electrode. The negative electrode, positive electrode, and separator may form an electrode assembly. The electrolyte may be held in the electrode assembly.

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

Furthermore, the battery according to the second embodiment may further include a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the positive electrode.

The battery according to the second embodiment may be a primary battery or a secondary battery. The secondary battery may be, for example, a lithium secondary battery. Secondary batteries also include non-aqueous electrolyte secondary batteries containing a non-aqueous electrolyte.

Since this battery includes the electrode according to the first embodiment as the negative electrode and/or positive electrode, it has excellent electrolyte impregnation into the electrode and, in turn, into the electrode group. This allows the electrolyte to be stably impregnated into the electrode group, resulting in a battery that exhibits the performance as designed. Furthermore, the battery can be produced with high productivity.

By introducing vacuum impregnation or pressure impregnation into the battery manufacturing process, the impregnation of the electrolyte into the electrodes and electrode group can be further improved. Vacuum impregnation and pressure impregnation are performed, for example, as follows.

After preparing a negative electrode, a positive electrode, and a separator and using these components to form an electrode assembly, the resulting electrode assembly is housed in a housing. Next, an electrolyte (e.g., a liquid electrolyte) is poured into the housing. After the electrolyte is poured, the electrode assembly housed in the housing together with the electrolyte is held in a reduced-pressure environment of -60 kPa to -90 kPa for 30 to 60 minutes to perform reduced-pressure impregnation. The temperature when holding in the reduced-pressure environment may be room temperature (approximately 15°C to 25°C), but reduced-pressure impregnation may also be performed in a temperature environment elevated to, for example, 45°C.

The impregnation under reduced pressure may be performed while the exterior member containing the electrode group and electrolyte is restrained. For example, after the electrolyte is poured in, plates are placed on both sides of the exterior member from the outside and held in place using a jig or similar tool. Rigid plates made of metal or resin, for example, are used as the restraining plates.

Also, before holding in a reduced pressure environment, a cycle of reducing the pressure from -60 kPa to -90 kPa and then returning to normal pressure may be performed two or more times. After the reduced pressure-normal pressure cycle, the environment is adjusted to a reduced pressure of -60 kPa to -90 kPa and held for 30 to 60 minutes to perform reduced pressure impregnation.

After vacuum impregnation is performed by holding the material in a reduced pressure environment, the exterior component is sealed while maintaining the reduced pressure.

After vacuum impregnation, further pressure impregnation may be performed. After vacuum impregnation and sealing of the exterior components, the sealed battery is placed in a pressure vessel. The air pressure inside the pressure vessel is then set to 0.6 MPa. Pressure impregnation is performed by leaving the battery pressurized at 0.6 MPa for 3 to 12 hours. Before leaving the battery pressurized, a cycle of pressurizing the battery to 0.6 MPa and then returning it to normal pressure (0 MPa) may be performed two or more times. After the pressure-normal pressure cycle, the battery is adjusted to a pressurized state of 0.6 MPa and left for 3 to 12 hours before pressure impregnation.

The negative electrode, positive electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal are explained below.

1) Negative Electrode The negative electrode may be in the form of the negative electrode of the electrode according to the first embodiment. Alternatively, in a battery including the electrode according to the first embodiment as a positive electrode, the negative electrode may be a negative electrode other than the electrode according to the first embodiment.

In the other negative electrodes, the ratio _dm1 of the first basis weight difference to the central basis weight in the first direction of the negative electrode active material-containing layer is outside the range of 1% < _dm1 < 10%. Otherwise, the details of the other negative electrodes are the same as those of the electrode according to the first embodiment.

Since this overlaps with the explanation in the first embodiment, detailed explanation will be omitted.

2) Positive Electrode The positive electrode may be the positive electrode of the electrode according to the first embodiment. Alternatively, in a battery including the electrode according to the first embodiment as a negative electrode, the positive electrode may be a positive electrode other than the electrode according to the first embodiment.

In the other positive electrodes, the ratio _dm1 of the first basis weight difference to the central basis weight in the first direction of the positive electrode active material-containing layer is outside the range of 1% < _dm1 < 10%. Otherwise, the details of the other positive electrodes are the same as those of the electrode according to the first embodiment.

Since this overlaps with the explanation in the first embodiment, detailed explanation will be omitted.

3) Electrolyte The electrolyte may be, for example, a liquid nonaqueous electrolyte or a gel nonaqueous electrolyte. 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 electrolyte salts include lithium salts such as lithium perchlorate ( _LiClO4 ), lithium hexafluorophosphate ( _LiPF6 ), lithium tetrafluoroborate ( _LiBF4 ), lithium hexafluoride ( _LiAsF6 ), lithium trifluoromethanesulfonate ( _LiCF3SO3 ), and lithium bistrifluoromethylsulfonylimide (LiN( _CF3SO2 ) _{2 )} , 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); linear 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); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or in combination.

Gel-type non-aqueous electrolytes are prepared by combining a liquid non-aqueous electrolyte with a polymeric material. Examples of polymeric materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

Alternatively, in addition to liquid nonaqueous electrolytes and gel nonaqueous electrolytes, room-temperature molten salts (ionic melts) containing lithium ions may also be used as nonaqueous electrolytes.

A room-temperature molten salt (ionic melt) refers to an organic salt composed of a combination of organic cations and anions that can exist as a liquid at room temperature (15°C or higher and 25°C or lower). Room-temperature molten salts include room-temperature molten salts that exist as a liquid on their own, 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. Generally, the melting point of room-temperature molten salts used in secondary batteries is 25°C or lower. Furthermore, organic cations generally have a quaternary ammonium skeleton.

A polymer solid electrolyte, an inorganic solid electrolyte, etc. may also be used in combination with the above non-aqueous electrolyte.

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

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

4) Separator The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. Separators in which an inorganic or organic compound is applied to a porous film can also be used. From a safety standpoint, 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 interrupting 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.

The laminate film used is a multilayer film containing multiple resin layers with metal layers sandwiched between them. The resin layers include 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 component by sealing it with heat.

The wall thickness of the metal container 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 100 ppm by mass or less. Batteries equipped with such a metal container can dramatically improve long-term reliability and heat dissipation in high-temperature environments.

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, button-shaped, sheet-shaped, laminated, or the like. The exterior member can be selected appropriately depending on the battery dimensions and the intended use of the battery. For example, the exterior member may be an exterior member for a small battery mounted in a portable electronic device, etc. Furthermore, the exterior member may be an exterior member for a large battery mounted in a vehicle such as a two- or four-wheeled automobile.

6) Negative Electrode Terminal The negative electrode terminal can be formed from a material that is electrically stable and conductive in a potential range of 0.8 V to 3 V relative to the redox potential of lithium (vs. Li/Li ⁺ ). Specific examples of the material for the negative electrode terminal include copper, nickel, stainless steel, aluminum, and aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. Aluminum or an aluminum alloy is preferably used as the material for the negative electrode terminal. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce 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 and conductive in a potential range of 3 V to 4.5 V relative to the redox potential of lithium (vs. Li/Li ⁺ ). Examples of materials 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 current collector in order to reduce contact resistance with the positive electrode current collector.

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

Figure 8 is a cross-sectional view schematically showing an example of a battery according to the second embodiment. Figure 9 is an enlarged cross-sectional view of part A of the battery shown in Figure 8.

The battery 100 shown in Figures 8 and 9 includes a bag-shaped exterior member 2 shown in Figure 8, an electrode group 1 shown in Figures 8 and 9, and an electrolyte (not shown). The electrode group 1 and electrolyte are housed within 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 containing two resin layers and a metal layer sandwiched between them.

As shown in Figure 8, the electrode group 1 is a flat, wound electrode group. As shown in Figure 9, the flat, wound electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5. The separator 4 is interposed between the negative electrode 3 and the positive electrode 5.

The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b. In the portion of the negative electrode 3 located at the outermost shell of the wound electrode group 1, the negative electrode active material-containing layer 3b is formed only on the inner surface of the negative electrode current collector 3a, as shown in Figure 9. In other portions of the negative electrode 3, the negative electrode active material-containing layer 3b is formed on both sides of the negative electrode current collector 3a.

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

As shown in Figure 8, the negative electrode terminal 6 and positive electrode terminal 7 are located near the outer peripheral edge of the wound electrode group 1. The negative electrode terminal 6 is connected to the outermost portion of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to the outermost portion of the positive electrode current collector 5a. The negative electrode terminal 6 and positive 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 this.

The battery according to the second embodiment is not limited to the battery having the configuration shown in Figures 8 and 9, but may also have the configuration shown in Figures 10 and 11, for example.

Figure 10 is a partially cutaway perspective view schematically showing another example of a battery according to the second embodiment. Figure 11 is an enlarged cross-sectional view of part B of the battery shown in Figure 10.

The battery 100 shown in Figures 10 and 11 includes an electrode group 1 shown in Figures 10 and 11, an exterior member 2 shown in Figure 10, and an electrolyte (not shown). The electrode group 1 and electrolyte are housed within the exterior member 2. The electrolyte is held in the electrode group 1.

The exterior member 2 consists of a laminate film containing two resin layers and a metal layer sandwiched between them.

As shown in Figure 11, the electrode group 1 is a laminated electrode group. The laminated electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately stacked with separators 4 interposed between them.

The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a.

The negative electrode current collector 3a of each negative electrode 3 includes a portion on one side where the negative electrode active material-containing layer 3b is not supported on any surface. This portion functions as a negative electrode current collector tab 3c. As shown in FIG. 11, the negative electrode current collector tab 3c does not overlap with the positive electrode 5. Furthermore, the multiple negative electrode current collector tabs 3c are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 is extended outside the exterior member 2.

Although not shown, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion functions as a positive electrode current collecting tab. Like the negative electrode current collecting tab 3c, the positive electrode current collecting tab does not overlap with the negative electrode 3. The positive electrode current collecting tab is located on the opposite side of the electrode group 1 from the negative electrode current collecting tab 3c. The positive electrode current collecting tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side from the negative electrode terminal 6 and is extended to the outside of the exterior member 2.

The separator 4 may be, for example, a plurality of separators, each arranged between a positive electrode and a negative electrode. Alternatively, the separator 4 may be a single separator folded zigzag. In the latter case, the positive electrodes and negative electrodes are arranged alternately in the spaces created by folding the separator 4.

The battery according to the second embodiment includes the electrode according to the first embodiment. Therefore, the battery according to the second embodiment can achieve its designed capacity even if it is manufactured in a short period of time.

[Third embodiment]
According to a third embodiment, there is provided a battery pack, which includes a plurality of 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 connected in a combination of series and parallel.

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

Figure 12 is a perspective view that schematically illustrates an example of a battery pack according to the third embodiment. The battery pack 200 shown in Figure 10 includes five cells 100a to 100e, four bus bars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five cells 100a to 100e is a battery according to the second embodiment.

The bus bar 21 connects, for example, the negative terminal 6 of one cell 100a to the positive terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four bus bars 21. In other words, the battery pack 200 in Figure 12 is a five-series battery pack. Although an example is not shown, in a battery pack including multiple cells electrically connected in parallel, the multiple cells can be electrically connected, for example, by connecting multiple negative terminals together by a bus bar and connecting multiple positive terminals together by a bus bar.

The positive electrode terminal 7 of at least one of the five cells 100a-100e is electrically connected to a positive electrode lead 22 for external connection. The negative electrode terminal 6 of at least one of the five cells 100a-100e is electrically connected to a negative electrode lead 23 for external connection.

The battery pack according to the third embodiment includes the battery according to the second embodiment. Therefore, the battery pack can achieve its designed capacity even if it is manufactured in a short period of time.

[Fourth embodiment]
According to a fourth embodiment, a battery pack is provided. This battery pack includes the battery assembly according to the third embodiment. This battery pack may include a single 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 the function of controlling the charging and discharging of the battery (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 external current-carrying terminals. The external current-carrying terminals are for outputting current from the battery to the outside and/or inputting current from the outside to the battery (secondary battery). In other words, when the battery pack is used as a power source, current is supplied to the outside through the external current-carrying terminals. Furthermore, when the battery pack is charged, charging current (including regenerative energy from the power of an automobile, etc.) is supplied to the battery pack through the external current-carrying terminals.

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

Figure 13 is an exploded perspective view schematically illustrating an example of a battery pack according to the fourth embodiment. Figure 14 is a block diagram illustrating an example of the electrical circuit of the battery pack shown in Figure 13.

The battery pack 300 shown in Figures 13 and 14 includes a container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown).

The storage container 31 shown in Figure 13 is a bottomed, square container with a rectangular bottom. The storage container 31 is configured to be able to accommodate a protective sheet 33, a battery pack 200, a printed wiring board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the storage container 31 to accommodate the battery pack 200 and other components. Although not shown, the storage container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices, etc.

The battery pack 200 includes multiple cells 100, a positive electrode lead 22, a negative electrode lead 23, and adhesive tape 24.

At least one of the multiple cells 100 is a battery according to the second embodiment. Each of the multiple cells 100 is electrically connected in series as shown in FIG. 14 . The multiple cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. Connecting multiple cells 100 in parallel increases the battery capacity compared to connecting them in series.

Adhesive tape 24 fastens the multiple cells 100 together. Instead of adhesive tape 24, heat-shrinkable tape may be used to secure the multiple cells 100 together. In this case, protective sheets 33 are placed on both sides of the battery pack 200, heat-shrinkable tape is wrapped around the cells, and the heat-shrinkable tape is then thermally shrunk to bind the multiple cells 100 together.

One end of the positive electrode lead 22 is connected to the battery pack 200. One end of the positive electrode lead 22 is electrically connected to the positive electrode of one or more cells 100. One end of the negative electrode lead 23 is connected to the battery pack 200. One end of the negative electrode lead 23 is electrically connected to the negative electrode of one or more cells 100.

The printed wiring board 34 is installed along one of the shorter sides of the inner surface of the container 31. The printed wiring board 34 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 current, a positive wiring (positive wiring) 348a, and a negative wiring (negative wiring) 348b. One main surface of the printed wiring board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed wiring board 34 and the battery pack 200.

The other end 22a of the positive electrode lead 22 is electrically connected to the positive electrode connector 342. The other end 23a of the negative electrode lead 23 is electrically connected to the negative electrode connector 343.

The thermistor 345 is fixed to one main surface of the printed wiring board 34. The thermistor 345 detects the temperature of each battery cell 100 and transmits the detection signal to the protection circuit 346.

The external terminals 350 for current flow are fixed to the other main surface of the printed wiring board 34. The external terminals 350 for current flow are electrically connected to devices external to the battery pack 300. The external terminals 350 for 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 34. 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 wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via wiring 343a. The protection circuit 346 is also electrically connected to each of the multiple cells 100 via wiring 35.

The protective sheet 33 is arranged on both inner surfaces of the long sides of the container 31 and on the inner surface of the short side that faces the printed wiring board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

The protection circuit 346 controls the charging and discharging of the multiple cells 100. Furthermore, 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 external devices based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from an individual cell 100 or the battery pack 200.

Examples of detection signals transmitted from the thermistor 345 include signals detecting that the temperature of a cell 100 is equal to or higher than a predetermined temperature. Examples of detection signals transmitted from an individual cell 100 or the battery pack 200 include signals detecting overcharge, overdischarge, and overcurrent of a cell 100. When detecting overcharge, etc. for an individual 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 also be a circuit included in a device (e.g., electronic equipment, automobile, etc.) that uses the battery pack 300 as a power source.

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

The battery pack 300 may include multiple battery assemblies 200. In this case, the multiple battery assemblies 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 34 and wiring 35 may also be omitted. In this case, the positive electrode lead 22 and the negative electrode lead 23 may be used as the positive and negative terminals of the external terminals for current flow, respectively.

Such battery packs are used in applications that require excellent cycle performance, for example, when drawing large currents. Specific examples of such battery packs include power sources for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as an on-board battery.

The battery pack according to the fourth embodiment includes the battery according to the second embodiment or the battery pack according to the third embodiment. Therefore, the battery pack has excellent life performance.

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 recovers, for example, regenerative energy from the vehicle's power. The vehicle may also include a mechanism (regenerator) that converts the vehicle's kinetic energy into regenerative energy.

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

The location where the battery pack is installed in a vehicle is not particularly limited. For example, when the battery pack is installed in an automobile, the battery pack can be installed in the engine compartment, the rear of the vehicle, or under the seat.

A vehicle may be equipped with multiple battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, in parallel, or a combination of series and parallel connections. For example, if each battery pack includes a battery assembly, the battery assembly may be electrically connected in series, in parallel, or a combination of series and parallel connections. Alternatively, if each battery pack includes a single battery, the batteries may be electrically connected in series, in parallel, or a combination of series and parallel connections.

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

Figure 15 is a partially transparent view that schematically illustrates an example of a vehicle according to the fifth embodiment.

The vehicle 400 shown in Figure 15 includes a vehicle body 40 and a battery pack 300 according to the third embodiment. In the example shown in Figure 15, 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 battery packs) included in the battery packs 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

Figure 15 illustrates an example in which the battery pack 300 is mounted in an engine compartment located in the front of the vehicle body 40. As mentioned above, the battery pack 300 may also be mounted, for example, at the rear of the vehicle body 400 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 powering the vehicle 400.

Next, referring to Figure 16, we will explain the implementation of the vehicle related to the fifth embodiment.

Figure 16 is a diagram that schematically illustrates an example of a control system for an electrical system in a vehicle according to the fifth embodiment. The vehicle 400 shown in Figure 16 is an electric vehicle.

The vehicle 400 shown in Figure 16 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 supply 41, for example, in the engine compartment, at the rear of the vehicle body, or under a seat. Note that the location of the vehicle power supply 41 in the vehicle 400 shown in Figure 16 is shown schematically.

The vehicle 400 is equipped with a vehicle power supply 41, for example, in the engine compartment, at the rear of the vehicle body, or under a seat. Note that the location of the vehicle power supply 41 in the vehicle 400 shown in Figure 14 is shown schematically.

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 301a (e.g., VTM: Voltage Temperature Monitoring). Battery pack 300b includes battery pack 200b and battery pack monitoring device 301b. Battery pack 300c includes battery pack 200c and battery pack monitoring device 301c. Battery packs 300a-300c are similar to battery pack 300 described above, and battery packs 200a-200c are similar to battery pack 200 described above. Battery packs 200a-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 unit cells is a secondary battery according to the second embodiment. The assembled batteries 200a to 200c are charged and discharged via the positive terminal 413 and the negative terminal 414, respectively.

The battery management unit 411 communicates with the assembled battery monitoring units 301a-301c and collects information on the voltage, temperature, and other characteristics of each of the cells 100 contained in the assembled batteries 200a-200c included in the vehicle power supply 41. In this way, the battery management unit 411 collects information related to the maintenance of the vehicle power supply 41.

The battery management unit 411 and the assembled battery monitoring units 301a-301c are connected via a communication bus 412. In the communication bus 412, one set of communication lines is shared by multiple nodes (the battery management unit 411 and one or more assembled battery monitoring units 301a-301c). The communication bus 412 is a communication bus configured based on, for example, the CAN (Control Area Network) standard.

The battery pack monitoring devices 301a-301c measure the voltage and temperature of each cell that makes up the battery packs 200a-200c based on commands received via communication from the battery management device 411. However, the temperature can be measured at only a few locations per battery pack; it is not necessary to measure the temperature of all the cells.

The vehicle power supply 41 may also have an electromagnetic contactor (e.g., the switch device 415 shown in FIG. 16) that switches the electrical connection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that turns on when the assembled batteries 200a-200c are being charged, and a main switch (not shown) that turns on when output from the assembled batteries 200a-200c is being supplied to a load. The pre-charge switch and the main switch each include a relay circuit (not shown) that is switched on or off by a signal supplied to a coil located near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on control signals from the battery management unit 411 or the vehicle ECU 42, which controls the operation of the entire vehicle 400.

The inverter 44 converts the input DC voltage into a three-phase alternating current (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 control signals from the battery management unit 411 or the vehicle ECU 42, which controls 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 power supplied from the inverter 44. The driving force generated by the rotation of the drive motor 45 is transmitted to the axles 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. The regenerative braking mechanism (e.g., a regenerator) rotates the drive motor 45 when the vehicle 400 is braked, converting kinetic energy into regenerative energy in the form of 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 supply 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 within 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 and other devices, the vehicle ECU 42 coordinates control of the vehicle power supply 41, switch device 415, inverter 44, etc. together with other management and control devices, including the battery management device 411. Through coordinated control by the vehicle ECU 42 and other devices, 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 via a communication line between the battery management device 411 and the vehicle ECU 42.

The vehicle according to the fifth embodiment is equipped with the battery pack according to the fourth embodiment. Therefore, it is highly reliable.

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

( Reference example 1)
In Reference Example 1, a secondary battery was fabricated in the following procedure.

<Preparation of positive electrode>
A slurry for forming an active material _- containing layer was _prepared by blending 90% by mass of _{a LiNi0.5Co0.2Mn0.3O2} composite oxide with an average primary particle diameter of 2 μm as the positive electrode active material, 5% by mass of graphite powder as a conductive agent, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder in an N-methyl-2-pyrrolidone (NMP) solvent. The blending amounts are expressed by mass relative to the mass of the positive electrode active material-containing layer. The prepared slurry was applied to both sides of a rectangular aluminum alloy foil (purity 99.3%) with a thickness of 15 μm and dried to obtain a laminate. When applying the slurry to the current collector, the slurry was applied multiple times. Each time the slurry was applied, the coating area in the long side direction of the current collector was reduced by 1 cm, creating a slope at both ends of the slurry coating. This laminate was pressed to prepare a positive electrode having a positive electrode active material-containing layer with a thickness of 40 μm.

<Preparation of negative electrode>
_{Li4Ti5O12 particles} with an average particle diameter of 0.6 μm and a specific surface area of 10 ^m2 _/ g were prepared as the active material. These active material particles, graphite powder with an average particle diameter of 6 μm as a conductive agent, and PVdF as a binder were blended in a mass ratio of 95:3:2 and dispersed in NMP solvent. This dispersion was stirred for 2 hours using a ball mill (rotation speed 1000 rpm) to prepare a slurry. The resulting slurry was applied to both sides of a 15 μm thick aluminum alloy foil (purity 99.3%), the coating was dried, and a negative electrode was fabricated by a hot pressing process. The fabricated negative electrode had a negative electrode active material-containing layer thickness of 59 μm per side and an electrode density (excluding the current collector) of 2.2 g/ ^cm3 . The negative electrode porosity excluding the current collector of this negative electrode was 35%.

<Preparation of electrolyte>
A mixed solvent was prepared by mixing propylene carbonate (PC) and diethyl carbonate (DEC) in a volume ratio of 1:2. _LiPF6 was then dissolved in this mixed solvent to a concentration of 1 M to prepare a liquid nonaqueous electrolyte.

<Preparation of secondary battery>
A plurality of sheets of 20 μm thick resin nonwoven fabric were prepared as separators. A plurality of the positive electrodes, separators, and negative electrodes were stacked with the positive electrode active material-containing layer and the negative electrode active material-containing layer facing each other, with the separator interposed therebetween, to obtain a laminate. Next, the laminate was hot-pressed at 80° C. to produce a laminated electrode group.

A container was prepared, consisting of a 0.1 mm-thick laminate film with a three-layer structure of nylon, aluminum, and polyethylene. The electrode assembly prepared above was placed in this container. Next, with a portion of the container's periphery open, the interior of the container was dried in a vacuum at 80°C for 16 hours. The nonaqueous electrolyte was introduced into the container, and the container was held at room temperature for 30 minutes in a reduced-pressure environment of -60 kPa, allowing the electrode assembly to be impregnated with the nonaqueous electrolyte. Next, the open portion of the container's periphery was heat-sealed in a -60 kPa environment to hermetically seal the container. This resulted in the production of a secondary battery with a design capacity of 3 Ah. A total of 50 secondary batteries were produced.

<Measurement of Positive Electrode Active Material-Containing Layer>
The basis weight and density of the positive electrode active material-containing layer at the ends and central portion in the long side direction of the positive electrode were measured by the method described above. Specifically, the long side direction of the positive electrode was defined as the first direction, and the basis weight and density of the positive electrode active material-containing layer at both ends and the central portion were measured. The differences in basis weight and density between each end and the central portion were calculated, and the basis weight and density of the end with the larger difference from the central portion were defined as the first basis weight and the first minimum density, respectively. The ratio d _m1 of the first basis weight difference to the central basis weight and the ratio d d _d1 of the first density difference to the first maximum density (density at the central portion) were calculated (d _m1 = [(central basis weight - first basis weight) / central basis weight] × 100%; d _d1 = [(first maximum density - first minimum density) / first maximum density] × 100%).

The ratio of the long side length to the short side width of the positive electrode active material-containing layer was also calculated to determine the aspect ratio r of the positive electrode.

The measurement results are shown in Table 1 below.

( Reference Examples 2-3, Examples 4-5)
In Reference Examples 2-3 and Examples 4-5, secondary batteries were produced in the same manner as in Reference Example 1, except for the following changes: When the slurry for forming the positive electrode active material-containing layer was applied to the current collector, the inclination of the slurry coating film was controlled by adjusting the coating range in the long side direction, which was reduced each time the slurry was applied, to be further reduced so that the ratio _dm1 of the difference in first basis weight to the central basis weight shown in Table 1 below was obtained.

( Reference example 6)
In Reference Example 6, a secondary battery was fabricated in the same procedure as in Reference Example 2, except for the following change: The amount of pressing performed after drying the slurry for forming the positive electrode active material-containing layer applied to the current collector was adjusted to be small so as to obtain the ratio d _d1 of the first density difference to the first maximum density, which is shown in Table 1 below.

(Examples 7 to 9)
In Examples 7 to 9, secondary batteries were fabricated in the same procedure as in Reference Example 2, except for the following change: The amount of pressing performed after drying the slurry for forming the positive electrode active material-containing layer applied to the current collector was increased so as to obtain the ratio d _d1 of the first density difference to the first maximum density shown in Table 1 below.

( Reference example 10-12)
In Reference Examples 10 to 12, secondary batteries were fabricated in the same manner as in Reference Example 2, except for the following change: The dimensions of the current collector used in the positive electrode were changed so as to obtain the aspect ratio r shown in Table 1 below.

( Reference example 13-15)
In Reference Examples 13 to 15, secondary batteries were fabricated in the same manner as in Reference Example 2, except for the following change: the conditions (pressure and/or holding time) of the reduced pressure environment maintained after introducing the nonaqueous electrolyte into the container housing the electrode group in order to impregnate the electrode group with the nonaqueous electrolyte were changed as shown in Table 1 below.

( Reference example 16)
A secondary battery was fabricated using the same procedure as in Reference Example 2. The resulting secondary battery was placed in a pressure vessel. The air pressure in the pressure vessel was set to 0.6 MPa, and the vessel was left standing for 3 hours. The air pressure was then returned to normal pressure, and the secondary battery was removed. A total of 50 secondary batteries were fabricated in this manner, which were further subjected to pressure impregnation.

( Reference example 17-18)
In Reference Examples 17 and 18, secondary batteries were fabricated in the same manner as in Reference Example 15, except that the conditions for pressure impregnation were changed as follows: In Reference Example 17, the waiting time was changed to 6 hours; and in Reference Example 18, the waiting time was changed to 12 hours.

( Reference example 19)
A secondary battery was fabricated using the same procedure as in Reference Example 2. The resulting secondary battery was placed in a pressure vessel. The air pressure in the pressure vessel was set to 0.6 MPa, and when it reached 0.6 MPa, it was set to normal pressure (0 MPa), and when normal pressure was reached, it was set to 0.6 MPa again. This cycle of alternating between 0.6 MPa and normal pressure was repeated five times, and then the battery was left at 0.6 MPa for three hours. The air pressure was then returned to normal pressure, and the secondary battery was removed. A total of 50 secondary batteries were fabricated that underwent further pressure impregnation in this manner.

( Reference example 20)
In Reference Example 20, a secondary battery was fabricated in the same manner as in Reference Example 19, except that the number of cycles between 0.6 MPa and normal pressure was changed to 20.

(Comparative Example 1)
In Comparative Example 1, a secondary battery was produced in the same manner as in Reference Example 1, except for the following change: When the slurry for forming the positive electrode active material-containing layer was applied to the current collector, the inclination of the slurry coating film was controlled by adjusting the reduction in the coating area in the long side direction each time the slurry was applied again to be small, so that the ratio dm1 of the first basis weight difference to the median basis weight shown in Table 1 below was obtained.

(Comparative Example 2)
In Comparative Example 2, a secondary battery was fabricated in the same manner as in Comparative Example 1, except for the following change: After introducing the nonaqueous electrolyte into the container housing the electrode group in order to impregnate the electrode group with the nonaqueous electrolyte, the time for which the container was kept in a reduced pressure environment of −60 kPa was changed to 60 minutes.

(Comparative Example 3)
A secondary battery was fabricated in the same manner as in Comparative Example 2. Pressure impregnation was further carried out under the conditions shown in Table 1 below.

(Comparative Example 4-5)
In Comparative Examples 4 and 5, secondary batteries were fabricated in the same manner as in Comparative Example 2, except for the following change: When the slurry for forming the positive electrode active material-containing layer was applied to the current collector, the inclination of the slurry coating film was controlled by adjusting the reduction in the coating area in the long side direction each time the slurry was applied again to be small, so that the ratio _dm1 of the first basis weight difference to the central basis weight shown in Table 1 below was obtained.

(Comparative Example 6)
In Comparative Example 6, a secondary battery was produced in the same manner as in Comparative Example 2, except for the following change: When the slurry for forming the positive electrode active material-containing layer was applied to the current collector, the number of times the slurry was reapplied was increased so that the ratio _dm1 of the difference in first basis weight to the median basis weight shown in Table 1 below was obtained, and the coating range in the long side direction, which was reduced with each reapplication of the slurry, was further reduced to control the inclination of the slurry coating film.

<Evaluation>
The secondary batteries obtained in the above Examples , Reference Examples , and Comparative Examples were subjected to an initial charge/discharge cycle, and the initial discharge capacity was measured. Specifically, the initial discharge capacity was determined as follows.

Charging and discharging were performed under conditions of a potential range of 1.5V to 3.0V, a charge/discharge current value of 3A, and an ambient temperature of 45°C. The battery was first charged to 3.0V and then discharged to 1.5V. This charging and discharging was performed on 50 cells. The discharge capacity of each cell was measured, and the average was taken as the initial discharge capacity.

The measurement results are shown in Table 1 below.

Table 1 summarizes the details of the positive electrode active material-containing layer for the secondary batteries produced in each Example , Reference Example , and Comparative Example, the reduced pressure conditions when the electrode group was impregnated with the nonaqueous electrolyte, the pressurization conditions when the pressure impregnation was performed, and the initial discharge capacity. The details of the positive electrode active material-containing layer include the ratio of the difference in basis weight between the end and center in the long side direction (d _{m1 )} , the ratio of the difference in density (d _{d1 )} , and the aspect ratio. In addition, when pressure impregnation was not performed as in Reference Example 1, the pressure conditions are not applicable and are therefore indicated as "-".

As shown in Table 1, in the positive electrodes prepared in Reference Examples 1-3, Examples 4-5, Reference Examples 6, Examples 7-9, and Reference Examples 10-20, the ratio _dm1 of the difference in first basis weight between the minimum basis weight at the end and the center basis weight relative to the maximum basis weight (center basis weight) at the center in the long side direction of the active material-containing layer was greater than 1% and less than 10%. In the secondary batteries obtained in Reference Examples 1-3, Examples 4-5, Reference Examples 6, Examples 7-9, and Reference Examples 10-20, an initial discharge capacity substantially equal to the design capacity (3A) was obtained. From this, it can be seen that in Reference Examples 1-3, Examples 4-5, Reference Examples 6, Examples 7-9, and Reference Examples 10-20, impregnation of the electrolyte into the electrode group was promoted, and the designed capacity was achieved.

In contrast, in Comparative Example 1-6, the ratio _dm1 of the first basis weight difference was 1% or less or 10% or more, which was outside the above range. In Comparative Example 1-6, the initial discharge capacity was lower than the design capacity.

In Comparative Examples 1-5, the difference in basis weight between the edge and center of the positive electrode active material-containing layer was small, and the electrolyte impregnation was insufficient, preventing the design capacity from being achieved. As shown in Comparative Examples 3-5, the electrolyte impregnation was insufficient even after the pressurized impregnation process. Among Comparative Examples 1-5, Comparative Example 5, in which the basis weight was nearly constant along the long side of the positive electrode active material-containing layer, had the lowest initial discharge capacity despite having undergone pressurized impregnation.

In Comparative Example 6, there was a large difference in basis weight between the edges and center of the positive electrode active material-containing layer, which is thought to have promoted electrolyte impregnation. However, on the other hand, the basis weight in the center was extremely thick, which is thought to have increased the diffusion resistance in the thickness direction of the positive electrode, preventing the design capacity from being achieved.

According to at least one of the embodiments and examples described above, an electrode including an active material-containing layer is provided. The active material-containing layer includes a first end portion and a central portion adjacent to the first end portion in a first direction. The first basis weight of the active material-containing layer at the first end portion is less than the central basis weight of the active material-containing layer at the central portion, and the ratio _dm1 of the difference in first basis weight between the first basis weight and the central basis weight to the central basis weight is in the range of 1% < _dm1 < 10%. An electrode having the above configuration can realize a battery and a battery pack that can demonstrate a design capacity, and a vehicle equipped with this battery pack can be provided.

Although several 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 embodied 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 within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.
The inventions described in the original claims of this application are set forth below.
[1] A first end portion;
a central portion adjacent to the first end portion in a first direction;
an active material-containing layer comprising
An electrode wherein a first basis weight of the active material-containing layer at the first end is less than a central basis weight of the active material-containing layer at the central portion, and a ratio dm1 of the first basis weight difference between the first basis weight and the central basis weight to the central basis weight _is within the range of 1% < dm1 _< 10%.
[2] The electrode according to [1], wherein the active material-containing layer includes a second end portion adjacent to the central portion and located on the opposite side of the first end portion in the first direction, and a first width of the first end portion in the first direction is 5% to 40% of a first distance between the first end portion and the second end portion.
[3] The electrode according to [2], wherein the second basis weight of the active material-containing layer at the second end is less than the central basis weight, and a ratio d _m2 of the second basis weight difference between the second basis weight and the central basis weight to the central basis weight is in the range of 1% < d _m2 < 10%.
[4] The electrode according to [2] or [3], wherein the active material-containing layer includes a third end and a fourth end adjacent to the central portion and positioned at both ends in a second direction intersecting with the first direction, and the first distance is longer than a second distance between the third end and the fourth end.
[5] The electrode according to [2] or [3], wherein the active material-containing layer includes a third end and a fourth end adjacent to the central portion and positioned at both ends in a second direction intersecting with the first direction, and the first distance is shorter than a second distance between the third end and the fourth end.
[6] The electrode according to [2] or [3], wherein the active material-containing layer includes a third end and a fourth end adjacent to the central portion and positioned at both ends in a second direction intersecting with the first direction, and wherein an aspect ratio r of a longer distance to a shorter distance of the first distance and a second distance between the third end and the fourth end is within a range of 1<r<50.
[7] The electrode according to any one of [1] to [6], wherein the active material-containing layer has a first density distribution in which the density varies along the first direction, and a ratio d d1 of a first density difference between the first maximum density and a first minimum density to a first maximum density in the first density _distribution is within a range of 5% < d _d1 < 20%.
[8] The electrode according to any one of [1] to [3], wherein the active material-containing layer includes a third end and a fourth end adjacent to the central portion and located at both ends in a second direction intersecting with the first direction, a third basis weight of the active material-containing layer at the third end and a fourth basis weight of the active material-containing layer at the fourth end are less than the central basis weight, a ratio d _m3 of the third basis weight difference between the third basis weight and the central basis weight to the central basis weight is within a range of 1% < d _m3 < 10%, and a ratio d _m4 of the fourth basis weight difference between the fourth basis weight and the central basis weight to the central basis weight is within a range of 1 % < d _m4 < 10%.
[9] The electrode according to [8], wherein the active material-containing layer has a second density distribution in which the density varies along the second direction, and a ratio d _d2 of a second density difference between the second maximum density and the second minimum density to a second maximum density in the second density distribution is within a range of 5% < d _d2 < 20%.
[10] a negative electrode;
A positive electrode and
Electrolytes and
A battery comprising:
A battery, wherein at least one of the negative electrode and the positive electrode includes the electrode according to any one of [1] to [9].
[11] A battery pack comprising the battery according to [10].
[12] An external terminal for supplying current;
Protection circuit and
The battery pack according to [11], further comprising:
[13] A battery comprising a plurality of the batteries,
The battery pack according to [11] or [12], wherein the batteries are electrically connected in series, in parallel, or in a combination of series and parallel.
[14] A vehicle equipped with the battery pack according to any one of [11] to [13].
[15] The vehicle according to [14], including a mechanism for converting kinetic energy of the vehicle into regenerative energy.

DESCRIPTION OF SYMBOLS 1... Electrode group, 2... Exterior member, 3... Negative electrode, 3a... Negative electrode current collector, 3b... Negative electrode active material containing layer, 3b ₀ ... Center part, 3b ₁ ... First end part, 3b ₂ ... Second end part, 3b ₃ ... Third end part, 3b ₄ ...fourth end, 3c...negative electrode current collecting tab, 4...separator, 5...positive electrode, 5a...positive electrode current collector, 5b...positive electrode active material containing layer, 6...negative electrode terminal, 7...positive electrode terminal, 21...bus bar, 22...positive electrode side lead, 22a...other end, 23...negative electrode side lead, 23a...other end, 24...adhesive tape, 31...container, 32...lid, 33...protective sheet, 34...printed wiring board, 35...wiring, 40...vehicle body, 41...vehicle power source, 42...electrical control device, 43...external terminal, 44...inverter, 45...drive motor, 100...battery, 200...assembled battery, 200a...assembled battery, 200b...assembled battery, 200c...assembled battery, 300...battery pack, 300a...battery pack, 300b...battery pack 300c...battery pack, 301a...assembled battery monitoring device, 301b...assembled battery monitoring device, 301c...assembled battery monitoring device, 342...positive side connector, 343...negative side connector, 345...thermistor, 346...protection circuit, 342a...wiring, 343a...wiring, 350...external terminal for supplying current, 352...positive side terminal, 353...negative side terminal, 348a...positive side wiring, 348b...negative side wiring, 400...vehicle, 411...battery management device, 412...communication bus, 413...positive side terminal, 414...negative side terminal, 415...switching device, 416...current detection unit, 417...negative side input terminal, 418...positive side input terminal, L1...connection line, L2...connection line, W...drive wheel.

Claims (13)

A first end portion;
an active material-containing layer including the first end portion and a central portion adjacent to the first end portion in a first direction;
the first end portion is either a portion where the thickness of the active material-containing layer increases in a gradient from an outer edge of a cross-sectional shape of the active material-containing layer toward the central portion, or a portion where the density is lower than that of the central portion,
a first width of the first end portion in the first direction is 5% to 40% of the length of the active material-containing layer in the first direction;
a first basis weight of the active material-containing layer at the first end portion is less than a central basis weight of the active material-containing layer at the central portion, and a ratio _dm1 of a first basis weight difference between the first basis weight and the central basis weight to the central basis weight is in a range of 1%< _dm1 <10%,
An electrode for a battery containing a liquid electrolyte, wherein the active material-containing layer has a first density distribution in which the density varies along the first direction, and a ratio d _d1 of a first density difference between the first maximum density and the first minimum density to a first maximum density in the first density distribution is within the range of 5% < d _d1 < 20%. the active material-containing layer includes a second end portion adjacent to the central portion and located on the opposite side of the first end portion in the first direction,
the second end portion is either a portion where the thickness of the active material-containing layer increases in a gradient from an outer edge of the cross-sectional shape of the active material-containing layer toward the central portion, or a portion where the density is lower than that of the central portion,
a second width of the second end portion in the first direction is 5% to 40% of the length of the active material-containing layer in the first direction;
2. The electrode of claim 1, wherein the second basis weight of the active material-containing layer at the second end is less than the central basis weight, and the ratio d _m2 of the second basis weight difference between the second basis weight and the central basis weight is within the range of 1% < d _m2 < 10%. The electrode described in claim 1 or 2, wherein the length of the active material-containing layer along the first direction is longer than the length of the active material-containing layer along a second direction intersecting the first direction. The electrode described in claim 1 or 2, wherein the length of the active material-containing layer along the first direction is shorter than the length of the active material-containing layer along a second direction intersecting the first direction. The electrode described in claim 1 or 2, wherein the aspect ratio r of the longer length of the active material-containing layer along the first direction to the shorter length of the active material-containing layer along a second direction intersecting the first direction is within the range of 1 < r < 50. the active material-containing layer includes a third end portion and a fourth end portion adjacent to the central portion and located at both ends in a second direction intersecting with the first direction,
the third end portion is either a portion where the thickness of the active material-containing layer increases in a gradient from an outer edge of a cross-sectional shape of the active material-containing layer toward the central portion, or a portion where the density is lower than that of the central portion,
the fourth end portion is either a portion where the thickness of the active material-containing layer increases in a gradient from an outer edge of a cross-sectional shape of the active material-containing layer toward the central portion, or a portion where the density is lower than that of the central portion,
a third width of the third end portion in the second direction is 5% to 40% of the length of the active material-containing layer in the second direction,
a fourth width of the fourth end portion in the second direction is 5% to 40% of the length of the active material-containing layer in the second direction,
4. The electrode according to claim 1, wherein the third basis weight of the active material-containing layer at the third end and the fourth basis weight of the active material-containing layer at the fourth end are less than the central basis weight, the ratio d _m3 of the third basis weight difference between the third basis weight and the central basis weight to the central basis weight is in the range of 1% < d _m3 < 10%, and the ratio d _m4 of the fourth basis weight difference between the fourth basis weight and the central basis weight to the central basis weight is in the range of 1% < d _m4 < 10%. The electrode described in claim 6, wherein the active material-containing layer has a second density distribution in which the density varies along the second direction, and a ratio d _d2 of a second density difference between the second maximum density and the second minimum density to a second maximum density in the second density distribution is within the range of 5% < d _d2 < 20%. a negative electrode;
A positive electrode and
an electrolyte,
A battery, wherein at least one of the negative electrode and the positive electrode comprises the electrode according to claim 1 . A battery pack comprising the battery described in claim 8. An external terminal for applying current;
The battery pack according to claim 9, further comprising a protection circuit. a plurality of the batteries;
11. The battery pack according to claim 9, wherein the batteries are electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle equipped with a battery pack according to any one of claims 9 to 11. The vehicle described in claim 12, including a mechanism for converting the kinetic energy of the vehicle into regenerative energy.