Electrode, battery, battery pack, and vehicle

Abstract

To provide an electrode capable of realizing a battery capable of exhibiting its designed capacity, a battery and a battery pack capable of exhibiting its designed capacity, and a vehicle equipped with this battery pack.SOLUTION: An electrode according to an electrode embodiment includes an active material-containing layer including a first end and a central portion adjacent to the first end in the first direction. The first basis weight of the active material-containing layer at the first end is smaller than the central basis weight of the active material-containing layer at the center. The ratio dm1 of the first basis weight difference between the first basis weight and the central basis weight with respect to the center basis weight is in the range of 1%<dm1<10%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to an electrode, a battery, a battery pack, and a vehicle. [Background technology]

[0002] In recent years, research and development of high-energy density secondary batteries, such as lithium-ion secondary batteries and nonaqueous electrolyte secondary batteries, has been actively 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 for uninterruptible power supplies in 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.

[0003] Rapid charging and discharging is possible when lithium ions and electrons move rapidly between a positive electrode and a negative electrode, which are capable of absorbing and releasing lithium ions and electrons, via an electrolyte and an external circuit, respectively. Such batteries capable of 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 power performance of the vehicle and also enable efficient recovery of regenerative energy.

[0004] To improve the energy density per volume, for example, the density of the material composing the electrode can be increased. However, as the 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 not contribute much to charging and discharging. In addition, uneven distribution of charge and discharge within the electrode can cause partial deterioration of the electrode, potentially compromising its long-term reliability.

[0005] In order to efficiently impregnate electrodes with an electrolyte (liquid electrolyte) during the manufacturing process of secondary batteries, a method of injecting an electrolyte into the exterior material of the secondary battery and then allowing the electrolyte to penetrate into the battery elements, including the electrodes, in a reduced-pressure atmosphere has been proposed. However, because the constituent materials of the electrodes are packed at a high density, it is difficult to consistently achieve stable impregnation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-58247 [Patent Document 2] Special Publication No. 2015-511389 [Patent Document 3] Japanese Patent Application Publication No. 10-50339 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-28290 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide an electrode that can realize a battery that can demonstrate its designed capacity, a battery and battery pack that can demonstrate its designed capacity, and a vehicle equipped with this battery pack. [Means for solving the problem]

[0008] According to an embodiment, there is provided an electrode having 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 electrode being 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 center, or a portion where the density is lower than that of the center. 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 d of the first basis weight difference between the first basis weight and the central basis weight to the central basis weight is m1 But 1% <d m1The active material-containing layer has a first density distribution in which the density varies along a first direction. A ratio d 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 d1 5% <d d1 in the range of <20%.

[0009] According to another embodiment, there is provided a battery comprising a negative electrode, a positive electrode, and an electrolyte, wherein at least one of the negative electrode and the positive electrode comprises an electrode according to the above embodiments.

[0010] According to yet another embodiment, a battery pack including the battery according to the above embodiment is provided.

[0011] According to yet another embodiment, a vehicle including the battery pack according to the above embodiment is provided. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view schematically illustrating an example of an electrode according to the embodiment. [Figure 2] FIG. 10 is a cross-sectional view schematically illustrating another example of an electrode according to the embodiment. [Figure 3] FIG. 2 is a plan view schematically illustrating an example of an electrode according to the embodiment. [Figure 4] FIG. 10 is a plan view schematically illustrating another example of an electrode according to the embodiment. [Figure 5] FIG. 1 is a cross-sectional view schematically illustrating an example of a preferred mode of an electrode according to an embodiment. [Figure 6] FIG. 10 is a cross-sectional view schematically illustrating another example of a preferred aspect of the electrode according to the embodiment. [Figure 7] FIG. 1 is a cross-sectional view schematically illustrating an example of a conventional electrode. [Figure 8] FIG. 1 is a cross-sectional view schematically illustrating an example of a battery according to an embodiment. [Figure 9] An enlarged cross-sectional view of part A of the battery shown in Figure 8. [Figure 10] FIG. 10 is a partially cutaway perspective view schematically showing another example of a battery according to an embodiment. [Figure 11]FIG. 11 is an enlarged cross-sectional view of part B of the battery shown in FIG. [Figure 12] FIG. 1 is a perspective view schematically illustrating an example of a battery pack according to an embodiment. [Figure 13] FIG. 1 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. [Figure 14] FIG. 14 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. [Figure 15] 1 is a partially see-through view schematically illustrating an example of a vehicle according to an embodiment. [Figure 16] 1 is a diagram illustrating an example of a control system for an electrical system in a vehicle according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes embodiments with reference to the drawings. Note that common components throughout the embodiments are designated by the same reference numerals, and redundant explanations will be omitted. Each figure is a schematic diagram for explaining and facilitating understanding of the embodiments. While the shapes, dimensions, and ratios may differ from those of actual devices, these may be appropriately modified in design, taking into consideration the following explanation and known techniques.

[0014] [First embodiment] According to a first embodiment, an electrode is provided. 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 in which the first basis weight at the first end portion is less than the central basis weight at the central portion. The ratio d of the first basis weight difference between the first basis weight and the central basis weight to the central basis weight is m1 But 1% <d m1 in the range of <10%.

[0015] 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.

[0016] The active material-containing layer contains an electrode active material. The electrode active material may be, for example, an oxide or a sulfide. The active material-containing layer may optionally further contain a conductive agent and a binder in addition to the active material.

[0017] The electrode may further include a current collector. The active material-containing layer may be provided, for example, on at least one main surface of the current collector. The active material-containing layer may be provided on one main surface of the current collector. Alternatively, the active material-containing layer may be provided on both main surfaces of the current collector, for example, on both the front and rear surfaces of a foil-shaped current collector.

[0018] The current collector may include a portion on the surface of which no active material-containing layer is formed, and this portion can function as a current collecting tab.

[0019] In this electrode, the active material-containing layer has a basis weight distribution between a first end portion and a central portion adjacent to the 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 at the central portion adjacent to the end portion. By providing such a basis weight distribution to the active material-containing layer, the impregnation of the electrode with a liquid electrolyte can be improved. For example, the in-plane direction of the electrode along the first direction may be the direction along the main surface of the current collector.

[0020] The basis weight distribution of the active material-containing layer in this embodiment is not limited to a configuration having a basis weight distribution between the end portions and the central portion adjacent to the end portions, and may be a configuration in which the basis weight differs between the end portions and the central portion, or a configuration in which the basis weight changes stepwise, or a gradient (slope) is provided 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.

[0021] 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 assemblies constructed by stacking multiple electrodes and counter electrodes with an insulating member interposed therebetween, and wound electrode assemblies 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 the main surface is almost entirely unexposed, the electrolyte is mostly impregnated into the electrode via the edge of the electrode, i.e., the end in the in-plane direction. In other words, the surface of the active material-containing layer accessible to the electrolyte is small.

[0022] 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 gradient that increases from the first end to the center, it is possible to provide a region on the electrode main surface that is not in close contact with the insulating material, etc., from the first end to the center. Since the electrolyte can penetrate into the electrode from this region in addition to the end face of the electrode, impregnation of the electrolyte is promoted. In addition to providing such a gradient, a similar effect can be achieved even if the basis weight is distributed by density.

[0023] 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 the ratio d m1 1% <d m1By setting the distribution within the range of <10% (0.01 < [first basis weight difference / median basis weight] <0.1), the electrolyte can be easily impregnated without increasing the diffusion resistance of the carrier (for example, lithium ions) in the thickness direction of the electrode (towards the counter electrode). If the electrolyte is not impregnated enough, there will be parts of the electrode that are not used for charging and discharging, and the battery will not achieve the designed capacity. However, if the electrolyte is well impregnated into the electrode, the designed capacity can be achieved even if the time spent on battery production is shortened.

[0024] The region having a smaller basis weight from the first end portion to the center portion along the first direction, preferably the inclined region, is desirably provided over a length of 5% to 40% of the length of the active material-containing layer in the first direction. 、 A first width of the first end in a first direction is Both ends of the active material-containing layer along the first direction It is desirable that the width of the first width / first distance be 5% or more and 40% or less (0.05≦[first width / first distance]≦0.4) of the first distance between the first width and the first distance. The first distance may be, for example, 150 mm or more.

[0025] It is preferable that a distribution of low basis weight is provided not only at one end along the first direction but also at both end portions of the active material-containing layer. That is, the ratio d m1 is within the above range, and In the active material-containing layer, an end portion adjacent to the center portion at a position opposite to the first end portion in the first direction and a second end portion are provided, 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 of the second basis weight difference between the second basis weight and the central basis weight is m2 1% <d m2 It is preferable that the difference in basis weight between the first and second ends is within the range of <10% (0.01<[second basis weight difference / center basis weight]<0.1). When introducing an electrolyte into a battery, for example, the electrolyte is poured into an exterior member housing a battery element such as an electrode group including electrodes. Here, the battery element is immersed in the electrolyte when the electrolyte is impregnated into the electrode. Therefore, the electrolyte penetrates into the electrode 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.

[0026] Regarding the second end side as well, it is desirable to provide a distribution with a low basis weight similar to that of the first end. Also in this case, it is desirable that a region with a low basis weight and preferably inclined is provided over a length of 5% or more and 40% or less of the length of the active material-containing layer in the first direction. Therefore, the second width of the second end in the first direction is Both ends of the active material-containing layer along the first direction It is desirable that it be 5% or more and 40% or less (0.05 ≤ [second width / first distance] ≤ 0.4) with respect to the first distance between

[0027] In the electrodes of a specific example, the average basis weight at each of the first end and the second end of the active material-containing layer is 120 g / m 2 and the average basis weight at the central portion between those ends is 160 g / m 2 and the average basis weight of the entire active material-containing layer along the first direction is 150 g / m 2 is.

[0028] The electrode may have a shape in which one dimension in one direction in its plane and another dimension in a direction intersecting that direction are not equal. For example, the electrode may have a plate shape having a rectangular main surface including a long side and a short side. For example, in the active material-containing layer, the direction intersecting the first direction is defined as the second direction In addition, Ends that are adjacent to the central portion of the active material-containing layer and are respectively located at both ends of the active material-containing layer in the second direction are defined as the third end and the fourth end. The distance between Both ends of the active material-containing layer along the second direction is defined as the second distance. Active material-containing layer Both ends in the first direction of the first distance between Between the two ends of the second direction and the aspect ratio r (r = longer distance / shorter distance) of the longer distance to the shorter distance of the second distance may be within the range of 1 < r < 50. For example, in an electrode having a rectangular shape, the ratio of the longer side length to the shorter side length of the rectangular shape (longer side / shorter side) may be greater than 1 and less than 50.

[0029] The shape of the electrode is not limited to a rectangular shape. For example, it may have a quadrilateral or polygonal surface shape with one or more chamfered corners, or an elliptical surface shape. Also, the outer peripheral sides defining the shape of the electrode main surface do not have to be straight lines. For example, they may be arc-shaped or wavy.

[0030] In an electrode that is long in one direction, the long side direction is 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. both ends The distance from the center to the short side is both ends Since the first distance is longer than the distance from the electrode, it is effective to reduce the basis weight at the end of the long side direction to promote impregnation of the electrolyte along the long side direction. Specifically, in this type of electrode, the long side direction is the first direction, and the first distance is longer than the second distance.

[0031] 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 laminate including a strip-shaped electrode is wound with the winding axis aligned with the short side direction of the strip to form a wound electrode group, the long side of the strip is wound to form a wound end surface that intersects with the winding axis. When an electrolyte is impregnated into a wound electrode group, the electrolyte mainly penetrates through the wound end surface. Therefore, in this type of electrode, 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.

[0032] The shape of the electrode main surface is not limited to a shape including a long dimension and a short dimension, and may be, for example, a square or a circle. 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.

[0033] In addition to the basis weight distribution along the first direction of the active material-containing layer, it is preferable to have 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 at both ends of the active material-containing layer 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 can be further obtained. Specifically, the third basis weight of the active material-containing layer at the third end is less than the central basis weight, and the ratio d of the third basis weight difference between the third basis weight and the central basis weight to the central basis weight is m3 1% <d m3 <10% (0.01<[third basis weight difference / central basis weight]<0.1). Alternatively, the fourth basis weight of the active material-containing layer at the fourth end is less than the central basis weight, and the ratio d of the fourth basis weight difference between the fourth basis weight and the central basis weight to the central basis weight is m4 1% <d m4 <10% (0.01<[fourth basis weight difference / center basis weight]<0.1). Alternatively, both the distribution from the third end to the center and the distribution from the fourth end to the center are provided.

[0034] At each of the third end and the fourth end, it is desirable that a region having a lower basis weight than the central portion be provided over a length of 5% to 40% of the length of the active material-containing layer in the second direction. That is, 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).

[0035] The density of the active material-containing layer at the first end portion may be different from that at the central portion. Alternatively, the density at the first end portion may be equal to that at the central portion. Preferably, the density at the first end portion is lower than that at the central portion. A lower density at the first end portion can further promote impregnation of the electrolyte from the first end portion.

[0036] Similarly, the density of the active material-containing layer at the second end portion may be different from that at the central portion. Alternatively, the density at the second end portion may be equal to that at the central portion. Preferably, the density at the second end portion is lower than that at the central portion. A lower density at the second end portion can further promote impregnation of the electrolyte from the second end portion.

[0037] That is, the active material-containing layer may have a first density distribution in which the density varies along a first direction. When the maximum and minimum densities in the first density distribution are defined as a first maximum density and a first minimum density, respectively, and the difference between the first maximum density and the first minimum density is defined as a first density difference, the ratio d d1 5% <d d1 It is preferable that the density is within the range of <20% (0.05<[(first maximum density-first minimum density) / first maximum density]<0.2). Here, the first maximum density is the average density in the center. If the average densities of the first end and second end are different, the smaller value is used as the first minimum density. If the average densities of the first end and second end are equal, that value is used as the first minimum density.

[0038] 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, since this further promotes impregnation of the electrolyte 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 of the second density difference to the second maximum density is d2 5% <d d2It is preferable that the density is within the range of <20% (0.05<[(second maximum density - second minimum density) / second maximum density]<0.2). Here, the second maximum density is the average density in the center. If the average densities of the third end and fourth end are different, the second minimum density is the smaller one. If the average densities of the third end and fourth end are equal, that value is taken as the second minimum density.

[0039] Next, the electrode according to the first embodiment will be described in detail with respect to both the negative electrode and the positive electrode.

[0040] (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.

[0041] As the negative electrode active material, for example, lithium titanate having a ramsdellite structure (e.g., Li 2+y Ti3O7, 0≦y≦3), lithium titanates with spinel structure (e.g., Li 4+x Ti5O 12 , 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.

[0042] As an example of orthorhombic titanium-containing composite oxide, Li 2+a M(I) 2-b Ti 6-c M(II) d O 14+σExamples of compounds represented by the formula (I) include compounds represented by the formula (I) above. 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. Specific examples of orthorhombic titanium-containing composite oxides include Li 2+a Na2Ti6O 14 (0≦a≦6).

[0043] As an example of the monoclinic niobium titanium composite oxide, 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. Specific examples of monoclinic niobium titanium composite oxides include Li x Examples include Nb2TiO7 (0≦x≦5).

[0044] Another example of monoclinic niobium titanium composite oxide is Li x Ti 1-y M3 y+z Nb 2-z O 7-δ Here, 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.

[0045] The conductive agent is blended 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 surfaces of the active material particles may be coated with carbon or an electronically conductive inorganic material.

[0046] The binder is blended to fill gaps between the dispersed active materials and to bind the active materials 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. These may be used alone or in combination.

[0047] The blending ratios of the negative electrode active material, conductive agent, and binder in the negative electrode active material-containing layer can be appropriately changed 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 adjusting the amount of conductive agent to 2% by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved. Furthermore, by adjusting the amount of binder to 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 adjust the amount of conductive agent and binder to 30% by mass or less each in order to achieve high capacity.

[0048] 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 thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector with such a thickness can balance the strength and weight of the electrode.

[0049] The negative electrode current collector may also include a portion on the surface of which the negative electrode active material-containing layer is not formed, and this portion can function as a negative electrode current collecting tab.

[0050] The overall average density of the negative electrode active material-containing layer (excluding the current collector) is 1.8 g / cm 3 More than 2.8g / cm 3 A negative electrode having a density of the negative electrode active material-containing layer as a whole within this range is excellent in energy density and electrolyte retention. The overall average density of the negative electrode active material-containing layer is preferably 2.1 g / cm or less. 3 More than 2.6g / cm 3 More preferably, it is:

[0051] (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.

[0052] The positive electrode active material may be, for example, an oxide or a sulfide. The positive electrode may contain one type of compound alone or two or more types of compounds in combination as the positive electrode active material. Examples of oxides and sulfides include compounds that can insert and extract Li or Li ions.

[0053] Examples of such compounds include, for example, manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (e.g., Li x Mn2O4 or Li x MnO2; 0 < x ≦ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium phosphate having an olivine structure (e.g., Li x FePO4; 0 < x ≦ 1, Li x Fe 1-y Mn y PO4; 0 < x ≦ 1, 0 < y < 1, Li x CoPO4; 0 < x ≦ 1), iron sulfate (Fe2(SO4)3), vanadium oxide (e.g., V2O5), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≦ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included.

[0054] Among the above, examples of more preferred compounds as the positive electrode active material include lithium manganese composite oxide having a spinel structure (e.g., Li x Mn2O4; 0 < x ≦ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), a lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), a lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), lithium iron phosphate (e.g., Li x FePO4; 0 < x ≤ 1), and a lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included. When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

[0055] When a room temperature molten salt is used as the electrolyte of the battery, it is preferable to use a positive electrode active material containing lithium iron phosphate, Li x VPO4F (0 ≤ x ≤ 1), a lithium manganese composite oxide, a lithium nickel composite oxide, a lithium nickel cobalt manganese composite oxide, or a mixture thereof. Since these compounds have low reactivity with the room temperature molten salt, the cycle life can be improved. Details of the room temperature molten salt will be described later.

[0056] The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. A positive electrode active material with a primary particle size of 1 μm or less can allow the solid-state diffusion of lithium ions to proceed smoothly.

[0057] The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less. A positive electrode active material having a specific surface area of 0.1 m 2 / g or more can sufficiently secure the occlusion / discharge sites of Li ions. A specific surface area of 10 m 2A positive electrode active material having a specific surface area of ​​0.15g / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0058] The binder is blended to fill gaps between the dispersed positive electrode active material and to bind the positive electrode active material and 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 CMC salts. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0059] The conductive agent is blended 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 as the conductive agent. The conductive agent may also be omitted.

[0060] In the positive electrode active material-containing layer, the positive electrode active material and the binder are preferably mixed in proportions of 80% by mass to 98% by mass and 2% by mass to 20% by mass, respectively.

[0061] By using a binder amount of 2% by mass or more, sufficient electrode strength can be obtained. Furthermore, the binder can 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.

[0062] When a conductive agent is added, the positive electrode active material, binder, and conductive agent are preferably mixed 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.

[0063] By setting the amount of conductive agent to 3% by mass or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This low proportion can reduce decomposition of the electrolyte during high-temperature storage.

[0064] The positive electrode current collector is preferably an aluminum foil or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

[0065] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, 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.

[0066] The positive electrode current collector may also include a portion on the surface of which the positive electrode active material-containing layer is not formed, and this portion can function as a positive electrode current collecting tab.

[0067] <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.

[0068] When applying the slurry, the amount of the slurry applied to at least one end is reduced. For example, when applying the slurry using a die coater, slowing the liquid feed rate in a portion of the die head can reduce the amount of the slurry applied to the corresponding portion of the coating width. Specifically, by applying the slurry using the following die head, the direction intersecting the coating direction is defined as the first direction, and the amount of the slurry applied to both ends of the coating width can be reduced. This reduces the amount of the slurry applied to the first and second ends of the active material-containing layer obtained after drying, resulting in 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. In such a die head, the liquid 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 ends of the coating width.

[0069] 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 having an active material-containing layer with a lower basis weight at the edges. In one example, the use of the trapezoidal shim described above, combined with control of the slurry flow rate and current collector transport, can result in an electrode with a gradient in basis weight distribution in both the first and second directions.

[0070] 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 varies depending on the desired gradient in basis weight and the amount of coating per coat, but for example, the coating width can be narrowed by 1 cm.

[0071] By pressing a laminate including a dried coating film with locally different basis weights along the surface of a current collector coated with a slurry, an active material-containing layer with a density distribution that varies locally can be obtained. For example, if the entire coating film of the dried slurry is uniformly pressed, the density after pressing will naturally be high in the areas with a high basis weight and low in the areas with a low basis weight. In addition, the density distribution can be further controlled by performing roll pressing using a roller with steps or inclinations to perform partial pressing according to the areas where the coating film contacts the roll.

[0072] <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.

[0073] When measuring electrodes that are installed in a battery, remove the electrodes from the battery using the following procedure.

[0074] First, the battery is placed in a discharged state. Here, "discharged state" 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, for example, a glove box filled with argon gas. Next, the target electrode is removed from the battery in the glove box. Specifically, in the glove box, the battery exterior is cut open while paying careful attention not to short-circuit the positive and negative electrodes. From the battery, for example, if the electrode used as the negative electrode is used as the measurement sample, the electrode connected to the negative terminal is cut out. Alternatively, if the electrode used as the positive electrode is used as the measurement sample, the electrode connected to the positive terminal is cut out. The removed electrode is washed with, for example, ethyl methyl ether solvent and dried.

[0075] (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.

[0076] For the electrode used as the measurement sample, multiple circular sample pieces with a diameter of 15 mm are punched out from both ends in one arbitrary direction and in another direction intersecting the arbitrary direction, as well as from the center where the two 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, the long side direction and the short side direction are selected. The number of sample pieces to be collected is determined by dividing the electrode from the end to the center at equal intervals, and collecting sample pieces from the center of each divided area. For example, the electrode is divided into five or more parts, i.e., five or more sample pieces are collected.

[0077] 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 fills 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 itself is measured. The current collector is also placed in the liquid in the container, and the volume of the current collector is determined based on the increase in the liquid level.

[0078] The mass of the active material-containing layer was 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 was multiplied 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 of the basis weights of the active material-containing layers of the obtained sample pieces is calculated for each sampling point, and this is taken as the average basis weight for each sampling point.

[0079] 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 of the densities of the active material-containing layers of the obtained sample pieces is calculated for each sampling point, and this is taken as the average density of each sampling point.

[0080] 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, with the central portion sandwiched between them, 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, aligned across the central portion along a direction intersecting the first direction, are arbitrarily deemed to be the third end and the fourth end, respectively.

[0081] The first basis weight difference is calculated by subtracting the average basis weight (first basis weight) at the first end portion specified as above from the average basis weight (center basis weight) of the center portion. Then, the first basis weight difference is divided by the average basis weight (center basis weight) of the center portion to calculate the ratio d of the first basis weight difference to the center basis weight. m1 Calculate (d m1 = [(average basis weight of the center part - average basis weight of the first end part) / average basis weight of the center part] × 100%). Similarly, for the second end part to the fourth end part, the ratio d m2 ,d m3 , and d m4 Calculate.

[0082] The average densities of the first end and second end identified as above and the central portion are compared. The largest value among them is set as the first maximum density in the first density distribution along the first direction. The smallest value is set 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 the first maximum density, and the average density of either or both of the first end and second end is the first minimum density. The first density difference is calculated by subtracting the first minimum density from the first maximum density. Then, the ratio d of the first density difference to the first maximum density is calculated by dividing the first density difference by the first maximum density. d1 Calculate (d d1 = [(first maximum density - first minimum density) / first maximum density] × 100%). Based on the average densities of the third end, fourth end, and center, the ratio d of the second density difference to the second maximum density in the second direction is d2 is calculated in the same manner.

[0083] (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.

[0084] The length of the active material-containing layer is measured along the first direction specified when measuring the basis weight distribution and density distribution. 、 The first distance is determined by defining the direction along the line connecting the third end and the fourth end as the second direction, and measuring the length of the active material-containing layer along that direction. in The second distance is calculated. The aspect ratio is calculated by dividing the longer of the first distance and the second distance by the shorter one.

[0085] Next, the electrode according to the first embodiment will be described in more detail with reference to the drawings.

[0086] A specific example of an electrode according to an embodiment is shown in Fig. 1. Fig. 1 is a cross-sectional view that schematically shows one example of an electrode according to an embodiment. In the example shown in Fig. 1, an embodiment of the electrode as a negative electrode of a battery is described. Fig. 1 is a schematic cross-sectional view that shows a cross section that intersects with the main surface of a negative electrode 3.

[0087] 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 in which the negative electrode active material-containing layer 3b is supported on both the front and back main surfaces of the negative electrode current collector 3a.

[0088] 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 portion 3b1, a central portion 3b0, and a second end portion 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 portion 3b1 and the second end portion 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 each of the first end portion 3b1 and the second end portion 3b2 toward the central portion 3b0.

[0089] 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% <d m1 <10%. In addition, 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% <d m2 <10%).

[0090] FIG. 7 is a cross-sectional view showing a schematic diagram of an example of a conventional electrode. The conventional electrode 10 shown in FIG. 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 FIG. 1, the electrode 10 has a generally uniform basis weight and a substantially constant thickness throughout the active material-containing layer 10b.

[0091] 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.

[0092] No. The proportion of the length of the negative electrode active material-containing layer 3b in the first direction 11 corresponding to one 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).

[0093] 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, but 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, while 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.

[0094] 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. In the example of Fig. 1, the density of the negative electrode active material-containing layer 3b is uniform throughout, whereas 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 obtained by uniformly pressing the negative electrode 3 of Fig. 1 over the entire first distance D1.

[0095] 2, the thickness of the negative electrode active material-containing layer 3b is approximately the same among the first end portion 3b1, the central portion 3b0, and the second end portion 3b2, but the density of the first end portion 3b1 and the second end portion 3b2 is lower than the density of the central portion 3b0, and therefore the basis weight at the first end portion 3b1 and the second end portion 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 portion 3b1 and the second end portion 3b2, which have lower density, is high.

[0096] In the first density distribution of the negative electrode active material-containing layer 3b along the first direction 11, when a first maximum density corresponding to the density in the central portion 3b0 is compared with a first minimum density corresponding to at least one of the density in the first end portion 3b1 and the density in 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%).

[0097] 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 FIGS. 3 and 4, respectively.

[0098] FIG. 3 is a plan view schematically illustrating an example of an electrode whose long side direction is the first direction. The negative electrode 3 illustrated in FIG. 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 collecting tab 3c that does not support the negative electrode active material-containing layer 3b. The negative electrode 3 illustrated in FIG. 3 may be the negative electrode 3 illustrated in FIG. 1 or the negative electrode 3 illustrated in FIG. 2. FIGS. 1 and 2 may be cross-sectional views taken along a second direction 12 corresponding to the short side direction of the negative electrode 3 illustrated in FIG. 3. The negative electrode 3 illustrated in FIG. 3 may be, for example, a negative electrode used in a stacked electrode group.

[0099] 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, but the first embodiment also includes electrodes in which the first direction 11 and the second direction 12 are reversed.

[0100] FIG. 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 FIG. 4 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 illustrated in FIG. 4 may be the negative electrode 3 illustrated in FIG. 1 or the negative electrode 3 illustrated in FIG. 2. FIGS. 1 and 2 may be cross-sectional views of the negative electrode 3 illustrated in FIG. 4 taken along a second direction 12 corresponding to the short side direction. The negative electrode 3 illustrated in FIG. 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.

[0101] 5 and 6 show examples of preferred electrodes in which the basis weight of the active material-containing layer is reduced not only at the first and second ends in the first direction but also at the third and fourth ends in the second direction. FIGS. 5 and 6 are cross-sectional views that schematically show one preferred embodiment and another preferred embodiment, respectively. The negative electrode 3 shown in each of FIGS. 5 and 6 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b provided on the negative electrode current collector 3a. Both FIGS. 5 and 6 may be cross-sectional views of the negative electrode 3 in FIG. 3 or the negative electrode 3 in FIG. 4 taken along the first direction 11.

[0102] In both the examples of FIG. 5 and FIG. 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% compared to the average basis weight of the central portion 3b0 (1% <d m3 <10%. In addition, 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% <d m4 <10%).

[0103] In the example shown in Fig. 5, the density of the negative electrode active material containing layer 3b is uniform throughout, similar to the example shown in Fig. 1. In the example shown in Fig. 6, similar to the example shown in Fig. 2, the density of the negative electrode 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. Specifically, in the second density distribution of the negative electrode 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%).

[0104] Because the third end 3b3 and the fourth end 3b4 are configured as described above, the negative electrode 3 of Figures 5 and 6 not only has improved electrolyte impregnation from both ends in the first direction 11, but also has improved electrolyte impregnation from both ends in the second direction 12.

[0105] No. The proportion of the length of the negative electrode active material containing layer 3b in the second direction 12 corresponding to the 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).

[0106] In the preferred example shown in Figures 5 and 6, the basis weight at both ends of the negative electrode active material-containing layer 3b along the second direction 12, i.e., the third end 3b3 and the fourth end 3b4, is smaller than that at the central portion 3b0, but the electrode according to the first embodiment also includes an embodiment in which the basis weight at the third end and / or the fourth end is equal to or greater than the basis weight at the central portion.

[0107] The electrode according to the first embodiment comprises 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 less 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 a ratio d m1 1% <d m1The size is within the range of <10%. By using this electrode, secondary batteries that can demonstrate their designed capacity can be manufactured in a short period of time.

[0108] [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.

[0109] The battery according to the second embodiment may further include a separator disposed between the negative electrode and the positive electrode. The negative electrode, the positive electrode, and the separator may constitute an electrode assembly. The electrolyte may be held in the electrode assembly.

[0110] The battery according to the second embodiment may further include an exterior member that houses the electrode group and the electrolyte.

[0111] 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.

[0112] 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. The secondary battery also includes a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0113] Since the battery includes the electrode according to the first embodiment as the negative electrode and / or positive electrode, the impregnation of the electrolyte into the electrode and thus into the electrode assembly is excellent. Therefore, the electrolyte can be stably impregnated into the electrode assembly, and a battery exhibiting the performance as designed can be obtained. In addition, the productivity of the battery is also high.

[0114] The impregnation of the electrodes and electrode group with the electrolyte can be further improved by introducing vacuum impregnation or pressure impregnation in the production of the battery. Vacuum impregnation and pressure impregnation are carried out, for example, as follows.

[0115] A negative electrode, a positive electrode, and a separator are prepared, and an electrode group is constructed using these components. The resulting electrode group is then housed in a housing. Next, an electrolyte (e.g., a liquid electrolyte) is poured into the housing. After the electrolyte is poured, the electrode group 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.

[0116] The impregnation under reduced pressure may be performed while the exterior member containing the electrode group and the electrolyte is restrained. For example, after the electrolyte is poured, plates are placed on both sides of the exterior member from the outside and held with a jig or the like to restrain the electrode group and the electrolyte. The plates used for restraint may be rigid plates made of metal or resin, for example.

[0117] Furthermore, before maintaining the product in a reduced pressure environment, a cycle of reducing the pressure from -60 kPa to -90 kPa and then returning it to normal pressure may be performed two or more times. After the reduced pressure-normal pressure cycle, the product is adjusted to a reduced pressure environment of -60 kPa to -90 kPa and maintained for 30 to 60 minutes to perform reduced pressure impregnation.

[0118] After the vacuum impregnation is carried out by holding the container in a vacuum environment, the exterior member is sealed while the vacuum state is maintained.

[0119] After vacuum impregnation, further pressure impregnation may be performed. After vacuum impregnation and sealing of the exterior members, the sealed battery is placed in a pressure vessel. Next, the air pressure inside the pressure vessel is set to 0.6 MPa. Pressure impregnation is performed by waiting for 3 to 12 hours in a pressurized state of 0.6 MPa. Before waiting in a pressurized state, a cycle of pressurizing to 0.6 MPa and then returning to normal pressure (0 MPa) may be performed two or more times. After performing the pressurized-normal pressure cycle, the pressure is adjusted to 0.6 MPa, and the battery is allowed to wait for 3 to 12 hours before pressure impregnation.

[0120] The negative electrode, positive electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal will be described below.

[0121] 1) Negative electrode The negative electrode may be in the form of the negative electrode of the electrode according to the first embodiment, or 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.

[0122] In the other negative electrodes, the ratio d of the first basis weight difference to the central basis weight in the first direction of the negative electrode active material-containing layer m1 1% <d m1 <10%. Otherwise, the details of the other negative electrodes are the same as those of the electrode according to the first embodiment.

[0123] Since the description overlaps with that in the first embodiment, detailed description will be omitted.

[0124] 2) Positive electrode The positive electrode may be in the form of the positive electrode of the electrode according to the first embodiment, or 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.

[0125] In the other positive electrodes, the ratio d of the first basis weight difference to the central basis weight in the first direction of the positive electrode active material-containing layer m1 1% <d m1 <10%. Otherwise, the other details of the positive electrode are the same as those of the electrode according to the first embodiment.

[0126] Since the description overlaps with that in the first embodiment, detailed description will be omitted.

[0127] 3) Electrolytes 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.

[0128] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoride (LiAsF), lithium trifluoromethanesulfonate (LiCFSO), and lithium bistrifluoromethylsulfonylimide (LiN(CFSO)), and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potentials, and LiPF is most preferred.

[0129] 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.

[0130] The gel-like non-aqueous electrolyte is prepared by combining a liquid non-aqueous electrolyte with a polymeric material, such as polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or a mixture thereof.

[0131] Alternatively, as the non-aqueous electrolyte, in addition to the liquid non-aqueous electrolyte and the gel non-aqueous electrolyte, a room temperature molten salt containing lithium ions (ionic melt) may be used.

[0132] Room-temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as a liquid at room temperature (15°C to 25°C). Room-temperature molten salts include those that exist as a liquid on their own, those that become liquid when mixed with an electrolyte salt, and those that become liquid when dissolved in an organic solvent, as well as mixtures of these. Generally, the melting point of room-temperature molten salts used in secondary batteries is 25°C or below. Furthermore, organic cations generally have a quaternary ammonium skeleton.

[0133] The non-aqueous electrolyte may further include a polymer solid electrolyte, an inorganic solid electrolyte, or the like.

[0134] The solid polymer electrolyte is prepared by dissolving an electrolyte salt in a polymer material and solidifying it.

[0135] The inorganic solid electrolyte is a solid material that has Li-ion conductivity.

[0136] 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 made of porous films coated with inorganic or organic compounds can also be used. From the viewpoint of safety, it is preferable to use porous films made from polyethylene or polypropylene. This is because these porous films melt at a certain temperature and are capable of interrupting current.

[0137] 5) Exterior materials The exterior member may be, for example, a container made of a laminate film or a metal container.

[0138] The thickness of the laminate film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

[0139] The laminate film is a multilayer film containing multiple resin layers and metal layers interposed between the resin layers. 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 by heat fusion.

[0140] The thickness of the wall 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.

[0141] 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. When the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content of these metals is preferably 100 ppm by mass or less. A battery equipped with such a metal container can dramatically improve long-term reliability and heat dissipation performance in high-temperature environments.

[0142] 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, button, sheet, laminated, or the like. The exterior member can be appropriately selected 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 or the like. Alternatively, the exterior member may be an exterior member for a large battery mounted in a vehicle such as a two-wheeled or four-wheeled automobile.

[0143] 6) Negative terminal The negative electrode terminal has a potential range of 0.8V to 3V relative to the redox potential of lithium (vs. Li / Li + ) and can be formed from a material that is electrically stable and conductive. Specifically, the material for the negative electrode terminal can be copper, nickel, stainless steel, aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The material for the negative electrode terminal is preferably aluminum or an aluminum alloy. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0144] 7) Positive terminal The positive electrode terminal has a potential range of 3V to 4.5V relative to the redox potential of lithium (vs. Li / Li +) and can be formed from a material that is electrically stable and conductive. 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.

[0145] Next, the battery according to the second embodiment will be described in more detail with reference to the drawings.

[0146] Fig. 8 is a cross-sectional view schematically showing an example of a battery according to Embodiment 2. Fig. 9 is an enlarged cross-sectional view of part A of the battery shown in Fig. 8.

[0147] 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 the electrolyte are housed in the bag-shaped exterior member 2. The electrolyte (not shown) is held in the electrode group 1.

[0148] The bag-shaped exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0149] As shown in Fig. 8, the electrode group 1 is a flat wound electrode group. As shown in Fig. 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.

[0150] 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-type electrode group 1, the negative electrode active material-containing layer 3b is formed only on the inner surface side of the negative electrode current collector 3a, as shown in Fig. 9. In the 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.

[0151] The positive electrode 5 includes a positive electrode current collector 5a and positive electrode active material-containing layers 5b formed on both sides of the positive electrode current collector 5a.

[0152] As shown in FIG. 8, the negative electrode terminal 6 and the 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 a portion located at the outermost shell of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to a portion located at the outermost shell of the positive electrode current collector 5a. The negative electrode terminal 6 and the positive electrode terminal 7 extend to the outside from an 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.

[0153] The battery according to the second embodiment is not limited to the battery having the configuration shown in FIGS. 8 and 9, but may also be a battery having the configuration shown in FIGS. 10 and 11, for example.

[0154] Fig. 10 is a partially cutaway perspective view schematically showing another example of the battery according to Embodiment 2. Fig. 11 is an enlarged cross-sectional view of part B of the battery shown in Fig. 10.

[0155] 10 and 11 includes an electrode group 1 shown in Fig. 10 and 11, an exterior member 2 shown in Fig. 10, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the exterior member 2. The electrolyte is held in the electrode group 1.

[0156] The exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0157] The electrode group 1 is a laminated electrode group, as shown in Fig. 11. The laminated electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately laminated with separators 4 interposed therebetween.

[0158] 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.

[0159] The negative electrode current collector 3a of each negative electrode 3 includes a portion on one side where no negative electrode active material-containing layer 3b is supported on any surface. This portion serves 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. 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 to the outside of the exterior member 2.

[0160] 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 collector tab. Like the negative electrode current collector tab 3c, the positive electrode current collector tab does not overlap with the negative electrode 3. The positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab 3c. The positive electrode current collector 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 drawn out to the outside of the exterior member 2.

[0161] Separator 4 may be, for example, a plurality of separators each disposed between a positive electrode and a negative electrode, or may be a single separator folded zigzag. In the latter case, positive electrodes and negative electrodes are alternately disposed in the spaces formed by folding separator 4.

[0162] The battery according to the second embodiment includes the electrode according to the first embodiment, and therefore the battery according to the second embodiment can achieve its designed capacity even if it is manufactured in a short period of time.

[0163] [Third embodiment] According to a third embodiment, there is provided a battery pack. The battery pack according to the third embodiment includes a plurality of batteries according to the second embodiment.

[0164] In the battery pack according to the third embodiment, the cells may be electrically connected in series or in parallel, or may be connected in a combination of series and parallel.

[0165] Next, an example of a battery pack according to a third embodiment will be described with reference to the drawings.

[0166] Fig. 12 is a perspective view schematically showing an example of a battery pack according to the third embodiment. The battery pack 200 shown in Fig. 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.

[0167] The bus bar 21 connects, for example, the negative electrode terminal 6 of one cell 100a to the positive electrode terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four bus bars 21. That is, the battery pack 200 in FIG. 12 is a five-series battery pack. Although an example is not shown, in a battery pack including a plurality of cells electrically connected in parallel, the plurality of cells can be electrically connected by, for example, connecting the negative electrode terminals to each other by a bus bar and connecting the positive electrode terminals to each other by a bus bar.

[0168] The positive electrode terminal 7 of at least one of the five cells 100a to 100e is electrically connected to a positive electrode lead 22 for external connection. Also, the negative electrode terminal 6 of at least one of the five cells 100a to 100e is electrically connected to a negative electrode lead 23 for external connection.

[0169] The battery pack according to the third embodiment includes the battery according to the second embodiment, and therefore the battery pack can achieve its designed capacity even if it is manufactured in a short period of time.

[0170] [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.

[0171] The battery pack according to the fourth embodiment may further include a protection circuit. The protection circuit has a function of controlling the charging and discharging of the battery (secondary battery). Alternatively, a circuit included in a device (e.g., electronic device, automobile, etc.) that uses the battery pack as a power source may be used as the protection circuit for the battery pack.

[0172] The battery pack according to the fourth embodiment may further include external terminals for current flow. The external terminals for current flow 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 terminals for current flow. When charging the battery pack, charging current (including regenerative energy from the power of an automobile or the like) is supplied to the battery pack through the external terminals for current flow.

[0173] Next, an example of a battery pack according to a fourth embodiment will be described with reference to the drawings.

[0174] Fig. 13 is an exploded perspective view schematically showing an example of a battery pack according to the fourth embodiment, and Fig. 14 is a block diagram showing an example of an electric circuit of the battery pack shown in Fig. 13.

[0175] The battery pack 300 shown in FIGS. 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).

[0176] 13 is a bottomed, square container having a rectangular bottom. The 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 container 31 to accommodate the battery pack 200 and other components. Although not shown, the container 31 and the lid 32 are provided with openings or connection terminals for connection to external devices and the like.

[0177] The battery pack 200 includes a plurality of cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0178] At least one of the plurality of cells 100 is the battery according to the second embodiment. The plurality of cells 100 are electrically connected in series as shown in FIG. 14 . The plurality of cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. When the plurality of cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0179] The adhesive tape 24 fastens the plurality of cells 100 together. Heat-shrinkable tape may be used to secure the plurality of cells 100 together instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both side surfaces of the battery pack 200, and the heat-shrinkable tape is wrapped around the cells 100, and the heat-shrinkable tape is then thermally shrunk to bind the plurality of cells 100 together.

[0180] 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.

[0181] 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, wires 342a and 343a, an external terminal 350 for supplying current, a positive wire (positive wire) 348a, and a negative wire (negative wire) 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.

[0182] 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.

[0183] The thermistor 345 is fixed to one main surface of the printed wiring board 34. The thermistor 345 detects the temperature of each of the cells 100 and transmits the detection signal to the protection circuit 346.

[0184] The external terminals 350 for applying current are fixed to the other main surface of the printed wiring board 34. The external terminals 350 for applying current are electrically connected to devices located outside the battery pack 300. The external terminals 350 for applying current include a positive terminal 352 and a negative terminal 353.

[0185] 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 a positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via a negative wiring 348b. The protection circuit 346 is also electrically connected to the positive connector 342 via a wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via a wiring 343a. The protection circuit 346 is also electrically connected to each of the plurality of single cells 100 via wiring 35.

[0186] The protective sheet 33 is disposed 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 across the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0187] The protection circuit 346 controls charging and discharging of the plurality of cells 100. Furthermore, the protection circuit 346 cuts off the electrical connection between the protection circuit 346 and external terminals 350 (positive terminal 352, negative terminal 353) for supplying electricity to an external device, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from each cell 100 or the battery pack 200.

[0188] An example of the detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of the cell 100 is equal to or higher than a predetermined temperature. An example of the detection signal transmitted from each cell 100 or the battery pack 200 is a signal indicating that overcharge, overdischarge, or overcurrent of the cell 100 is detected. When detecting overcharge or the like for each cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

[0189] The protection circuit 346 may be a circuit included in a device (such as an electronic device or an automobile) that uses the battery pack 300 as a power source.

[0190] As described above, the battery pack 300 is also provided with the external terminals 350 for current application. 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 terminals 350 for current application. In other words, when the battery pack 300 is used as a power source, the current from the battery assembly 200 is supplied to the external device via the external terminals 350 for current application. When the battery pack 300 is charged, a charging current from the external device is supplied to the battery pack 300 via the external terminals 350 for current application. When the battery pack 300 is used as an in-vehicle battery, regenerative energy from the vehicle's power can be used as the charging current from the external device.

[0191] The battery pack 300 may include a plurality of assembled batteries 200. In this case, the assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 34 and the wiring 35 may 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 supplying current, respectively.

[0192] Such a battery pack is used in applications requiring excellent cycle performance when drawing a large current, for example. Specifically, this battery pack is used, for example, as a power source for electronic devices, a stationary battery, or an on-board battery for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as an on-board battery.

[0193] 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, and therefore has excellent life performance.

[0194] [Fifth embodiment] According to a fifth embodiment, a vehicle is provided, which is equipped with the battery pack according to the fourth embodiment.

[0195] In the vehicle according to the fifth embodiment, the battery pack recovers, for example, regenerative energy for powering the vehicle. The vehicle may include a mechanism (regenerator) for converting the kinetic energy of the vehicle into regenerative energy.

[0196] Examples of the vehicle according to the fifth embodiment include two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, power-assisted bicycles, and railcars.

[0197] The mounting position of the battery pack in a vehicle is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack can be mounted in the engine compartment, the rear of the vehicle body, or under the seat of the vehicle.

[0198] 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 pack, the battery packs 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.

[0199] Next, an example of a vehicle according to a fifth embodiment will be described with reference to the drawings.

[0200] FIG. 15 is a partial perspective view schematically illustrating an example of a vehicle according to the fifth embodiment.

[0201] A vehicle 400 shown in Fig. 15 includes a vehicle body 40 and a battery pack 300 according to the third embodiment. In the example shown in Fig. 15, the vehicle 400 is a four-wheeled automobile.

[0202] The vehicle 400 may be equipped with a plurality of battery packs 300. In this case, the batteries (for example, 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.

[0203] 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 described above, the battery pack 300 may be mounted, for example, at the rear of the vehicle body 40 or under a seat. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy for powering the vehicle 400.

[0204] Next, with reference to FIG. 16, an embodiment of a vehicle according to the fifth embodiment will be described.

[0205] Fig. 16 is a diagram that schematically shows an example of a control system related to an electrical system in a vehicle according to Embodiment 5. A vehicle 400 shown in Fig. 16 is an electric vehicle.

[0206] The vehicle 400 shown in Figure 16 comprises a vehicle body 40, a vehicle power supply 41, a vehicle ECU (ECU: Electric Control Unit) 42 which is a higher-level control device of 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.

[0207] Vehicle 400 has vehicle power supply 41 mounted, for example, in the engine compartment, the rear of the vehicle body, or under the seat. Note that in vehicle 400 shown in Fig. 16, the mounting location of vehicle power supply 41 is shown schematically.

[0208] Vehicle 400 has vehicle power supply 41 mounted, for example, in the engine compartment, the rear of the vehicle body, or under the seat. Note that in vehicle 400 shown in Fig. 14, the mounting location of vehicle power supply 41 is shown schematically.

[0209] The vehicle power supply 41 includes a plurality of (for example, three) battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

[0210] The battery pack 300a includes an assembled battery 200a and an assembled battery monitoring device 301a (for example, VTM: Voltage Temperature Monitoring). The battery pack 300b includes an assembled battery 200b and an assembled battery monitoring device 301b. The battery pack 300c includes an assembled battery 200c and an assembled battery monitoring device 301c. The battery packs 300a to 300c are the same as the battery pack 300 described above, and the assembled batteries 200a to 200c are the same as the assembled battery 200 described above. The assembled batteries 200a to 200c are electrically connected in series. The battery packs 300a, 300b, and 300c can each be removed independently and replaced with another battery pack 300.

[0211] Each of the assembled batteries 200a to 200c includes a plurality of unit cells connected in series. At least one of the plurality of unit cells is the secondary battery according to the second embodiment. Each of the assembled batteries 200a to 200c is charged and discharged via a positive terminal 413 and a negative terminal 414.

[0212] The battery management device 411 communicates with the assembled battery monitoring devices 301a to 301c and collects information on the voltage, temperature, etc. of each of the cells 100 included in the assembled batteries 200a to 200c included in the vehicle power supply 41. In this way, the battery management device 411 collects information on the maintenance of the vehicle power supply 41.

[0213] The battery management unit 411 and the assembled battery monitoring units 301a to 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 to 301c). The communication bus 412 is a communication bus configured based on, for example, the CAN (Control Area Network) standard.

[0214] The battery pack monitoring devices 301a to 301c measure the voltage and temperature of each of the cells constituting the battery packs 200a to 200c based on commands received through communication from the battery management device 411. However, the temperature can be measured at only a few locations per battery pack, and it is not necessary to measure the temperature of all the cells.

[0215] The vehicle power supply 41 may also have an electromagnetic contactor (for example, a switch device 415 shown in FIG. 16) that switches between electrical connection and disconnection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that is turned on when the assembled batteries 200a-200c are being charged, and a main switch (not shown) that is turned on when the output from the assembled batteries 200a-200c is being supplied to a load. Each of the pre-charge switch and the main switch includes a relay circuit (not shown) that is switched on or off by a signal supplied to a coil disposed near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 that controls the operation of the entire vehicle 400.

[0216] 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.

[0217] The drive motor 45 is rotated by the electric power supplied from the inverter 44. The drive force generated by the rotation of the drive motor 45 is transmitted to the axles and drive wheels W via, for example, a differential gear unit.

[0218] Although not shown, the vehicle 400 also includes a regenerative braking mechanism. The regenerative braking mechanism (for example, a regenerator) rotates the drive motor 45 when the vehicle 400 is braked, and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 44 and converted into direct current. The converted direct current is input to the vehicle power supply 41.

[0219] One terminal of a 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 a negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 in the battery management device 411 is provided on the connection line L1 between the negative terminal 414 and the negative input terminal 417.

[0220] One terminal of a 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 a 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.

[0221] 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.

[0222] In response to operational inputs from the driver or the like, the vehicle ECU 42 coordinates with other management devices and control devices including the battery management device 411 to control the vehicle power supply 41, the switch device 415, the inverter 44, etc. Through the coordinated control of the vehicle ECU 42, etc., the output of power from the vehicle power supply 41 and the charging of the vehicle power supply 41 are controlled, thereby managing the entire vehicle 400. Data relating to the maintenance of the vehicle power supply 41, such as the remaining capacity of the vehicle power supply 41, is transferred between the battery management device 411 and the vehicle ECU 42 via a communication line.

[0223] The vehicle according to the fifth embodiment is equipped with the battery pack according to the fourth embodiment, and is therefore highly reliable.

[0224] [Example] Examples will be described below, but the embodiments are not limited to the examples described below.

[0225] ( reference Example 1) reference In Example 1, a secondary battery was fabricated according to the following procedure.

[0226] <Preparation of positive electrode> The positive electrode active material is LiNi with an average primary particle size of 2 μm. 0.5 Co 0.2 Mn 0.3 A slurry for forming an active material-containing layer was prepared by blending 90% by mass of O2 composite oxide, 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. The slurry was applied to the current collector in multiple recoats. The coating area in the long side direction of the current collector was reduced by 1 cm with each recoat of the slurry, creating a slope at both ends of the slurry coating. This laminate was pressed to prepare a positive electrode with a positive electrode active material-containing layer with a thickness of 40 μm.

[0227] <Preparation of negative electrode> The active material has an average particle size of 0.6 μm and a specific surface area of ​​10 m 2 / g Li4Ti5O 12Particles were prepared. 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 an NMP solvent. This dispersion was stirred for 2 hours using a ball mill (rotation speed 1000 rpm) to prepare a slurry. The obtained 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 / cm. 3 The porosity of this negative electrode excluding the current collector was 35%.

[0228] <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.

[0229] <Preparation of secondary battery> A plurality of 20 μm thick resin nonwoven fabrics 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 a separator interposed between them, to obtain a laminate. Next, the laminate was hot-pressed at 80°C to produce a stacked electrode group.

[0230] A container was prepared, consisting of a 0.1 mm-thick laminate film with a three-layer structure of nylon layer / aluminum layer / polyethylene layer. 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 under a reduced pressure of -60 kPa, thereby impregnating the electrode assembly with the nonaqueous electrolyte. Next, the open portion of the container's periphery was heat-sealed under a pressure of -60 kPa to 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.

[0231] <Measurement of the positive electrode active material-containing layer> The basis weight and density of the positive electrode active material-containing layer at the end 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 end portions 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 largest difference from the central portion were defined as the first basis weight and the first minimum density, respectively. The ratio d of the first basis weight difference to the central basis weight was calculated. m1 and the ratio d of the first density difference to the first maximum density (density at the center) d1 was calculated (d m1 = [(Center basis weight - 1st basis weight) / Center basis weight] x 100%;d d1 =[(1st maximum density - 1st minimum density) / 1st maximum density] x 100%).

[0232] The ratio of the long side length to the short side width of the positive electrode active material-containing layer was calculated to determine the aspect ratio r of the positive electrode.

[0233] The measurement results are shown in Table 1 below.

[0234] ( reference Example 2 -3, Example 4 -5) reference Example 2 Example 3 and Example 4 In -5, except for the following changes: referenceA secondary battery was fabricated in the same manner as in Example 1. When the slurry for forming the positive electrode active material-containing layer was applied to the current collector, the ratio d of the first basis weight difference to the median basis weight shown in Table 1 below was m1 The inclination of the slurry coating film was controlled by further reducing the coating area in the long side direction each time the slurry was applied so as to obtain the above-mentioned value.

[0235] ( reference Example 6) reference In Example 6, except with the following changes: reference A secondary battery was fabricated in the same manner as in Example 2. The ratio d of the first density difference to the first maximum density shown in Table 1 below was d1 In order to obtain the above, the pressing force applied to the current collector after drying the slurry for forming the active material-containing layer of the positive electrode was adjusted to be small.

[0236] Examples 7-9 In Examples 7-9, except for the following changes: reference A secondary battery was fabricated in the same manner as in Example 2. The ratio d of the first density difference to the first maximum density shown in Table 1 below was d1 In order to obtain the above, the pressing force applied to the current collector after drying the slurry for forming the active material-containing layer of the positive electrode was adjusted to be large.

[0237] ( reference Example 10-12) reference In Example 10-12, except with the following changes: reference A secondary battery was produced in the same manner as in Example 2. 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.

[0238] ( reference Example 13-15) reference In Example 13-15, except with the following changes: reference A secondary battery was produced in the same manner as in Example 2. The conditions (pressure and / or holding time) of the reduced pressure environment maintained after introducing the non-aqueous electrolyte into the container housing the electrode group in order to impregnate the electrode group with the non-aqueous electrolyte were changed as shown in Table 1 below.

[0239] ( reference Example 16) reference A secondary battery was fabricated using the same procedure as in 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. After that, the air pressure was 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.

[0240] ( reference Example 17-18) reference In Examples 17 and 18, the pressure impregnation conditions were changed as follows: reference A secondary battery was fabricated in the same manner as in Example 15. reference In Example 17, the wait time was changed to 6 hours. reference In Example 18, the wait time was changed to 12 hours.

[0241] ( reference Example 19) reference A secondary battery was fabricated using the same procedure as in 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 in this manner, with further pressure impregnation.

[0242] ( reference Example 20) reference In Example 20, the number of cycles between 0.6 MPa and atmospheric pressure was changed to 20. reference A secondary battery was fabricated in the same manner as in Example 19.

[0243] (Comparative Example 1) In Comparative Example 1, the following changes were made: referenceA secondary battery was produced using the same procedure as in Example 1. 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 so as to be small, so that the ratio dm1 of the difference in first basis weight to the central basis weight shown in Table 1 below was obtained.

[0244] (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.

[0245] (Comparative Example 3) A secondary battery was produced in the same manner as in Comparative Example 2. Pressure impregnation was further carried out under the conditions shown in Table 1 below.

[0246] (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 changes: When the slurry for forming the positive electrode active material-containing layer was applied to the current collector, the ratio d m1 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 so as to obtain the above-mentioned inclination.

[0247] (Comparative Example 6) In Comparative Example 6, a secondary battery was fabricated in the same manner as in Comparative Example 2, except for the following changes: When the slurry for forming the positive electrode active material-containing layer was applied to the current collector, the ratio d m1 The number of times the slurry was reapplied was increased so as to obtain the above-mentioned inclination of the slurry coating film, and the coating area in the long side direction, which was reduced each time the slurry was reapplied, was further reduced to control the inclination of the slurry coating film.

[0248] <Evaluation> The above example , reference exampleThe secondary batteries obtained in the comparative examples were subjected to an initial charge and discharge cycle, and the initial discharge capacities were measured. Specifically, the initial discharge capacities were determined as follows.

[0249] Charging and discharging were performed under the 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. During charging and discharging, the battery was first charged to 3.0V and then discharged to 1.5V. This charging and discharging was performed on 50 cells. The capacity at the time of discharge was measured for each cell, and the average was taken as the initial discharge capacity.

[0250] The measurement results are shown in Table 1 below.

[0251] Table 1 shows the results of each example. , reference example The details of the positive electrode active material-containing layer of the secondary batteries fabricated in the comparative examples, the reduced pressure conditions when the non-aqueous electrolyte was impregnated into the electrode group, the pressurizing conditions when the pressure was impregnated, and the initial discharge capacity are summarized below. m1 and the ratio of density difference d d1 , and the aspect ratio. reference In cases where pressurized impregnation was not performed as in Example 1, the pressurization conditions are not applicable and are therefore indicated as "-".

[0252] [Table 1]

[0253] As shown in Table 1, reference Example 1 -3, Examples 4-5, Reference Example 6, Examples 7-9, and Reference Example 10 In the positive electrode prepared in -20, the ratio d of the first basis weight difference between the minimum basis weight and the central basis weight at the end to the maximum basis weight (central basis weight) at the central part in the long side direction of the active material-containing layer m1 was in the range of more than 1% and less than 10%. reference Example 1 -3, Examples 4-5, Reference Example 6, Examples 7-9, and Reference Example 10 In the secondary battery obtained at -20, the initial discharge capacity was substantially the same as the design capacity (3 A). reference Example 1 -3, Examples 4-5, Reference Example 6, Examples 7-9, and Reference Example 10It can be seen that -20 promoted the impregnation of the electrolyte into the electrode group, enabling the capacity to be achieved as designed.

[0254] In contrast, in Comparative Example 1-6, the ratio d m1 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.

[0255] 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 step. Among Comparative Examples 1-5, Comparative Example 5, in which the basis weight was almost constant along the long side direction of the positive electrode active material-containing layer, had the lowest initial discharge capacity despite the pressurized impregnation.

[0256] In Comparative Example 6, the difference in basis weight between the edge and center of the positive electrode active material-containing layer was large, which is presumably why impregnation of the electrolyte was promoted. However, on the other hand, the basis weight in the center was extremely thick, which presumably increased the diffusion resistance in the thickness direction of the positive electrode, and therefore presumably prevented the design capacity from being achieved.

[0257] According to at least one of the above-described embodiments and examples, 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 d of the first basis weight difference between the first basis weight and the central basis weight is m1 1% <d m1 The electrode having the above configuration can realize a battery and a battery pack that can demonstrate the designed capacity, and a vehicle equipped with this battery pack can be provided.

[0258] 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; a central portion adjacent to the first end portion in a first direction; an active material-containing layer comprising 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 d of a first basis weight difference between the first basis weight and the central basis weight to the central basis weight m1 1% <d m1 <10% of the electrodes. [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% or more and 40% or less of a first distance between the first end portion and the second end portion. [3] The second basis weight of the active material-containing layer at the second end portion is less than the central basis weight, and a ratio d of the second basis weight difference between the second basis weight and the central basis weight to the central basis weight is m2 1% <d m2 The electrode according to [2], wherein the range is <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 active material-containing layer includes a third end portion and a fourth end portion that are adjacent to the central portion and are respectively located at both ends in a second direction intersecting the first direction, and the first distance is shorter than a second distance between the third end portion and the fourth end portion. The electrode according to [2] or [3]. [6] The active material-containing layer includes a third end portion and a fourth end portion that are adjacent to the central portion and are respectively located at both ends in a second direction intersecting the first direction. Among the first distance and the second distance between the third end portion and the fourth end portion, the aspect ratio r of the longer distance to the shorter distance is within the range of 1 < r < 50. The electrode according to [2] or [3]. [7] The active material-containing layer has a first density distribution with different densities along the first direction. The ratio d of the first density difference between the first maximum density and the first minimum density to the first maximum density in the first density distribution d1 is 5% < d d1 < 20%. The electrode according to any one of [1] to [6]. [8] The active material-containing layer includes a third end portion and a fourth end portion that are adjacent to the central portion and are respectively located at both ends in a second direction intersecting the first direction. The third basis weight of the active material-containing layer at the third end portion and the fourth basis weight of the active material-containing layer at the fourth end portion are less than the central basis weight. The ratio d of the difference in the third basis weight between the third basis weight and the central basis weight to the central basis weight m3 is 1% < d m3 < 10%. The ratio d of the difference in the fourth basis weight between the fourth basis weight and the central basis weight to the central basis weight m4 is 1% < d m4 < 10%. The electrode according to any one of [1] to [3]. [9] The active material-containing layer has a second density distribution with different densities along the second direction. The ratio d of the second density difference between the second maximum density and the second minimum density to the second maximum density in the second density distribution d2 is 5% < d d2 < 20%. The electrode according to [8].

[10] A negative electrode, A positive electrode, And an electrolyte A battery comprising: At least one of the negative electrode and the positive electrode includes the electrode according to any one of [1] to [9]. A battery.

[11] A battery pack comprising the battery according to

[10] .

[12] An external terminal for energization, And a protection circuit Further comprising. The battery pack according to

[11] .

[13] Comprising a plurality of said batteries, The batteries are electrically connected in series, in parallel, or in a combination of series and parallel. The battery pack according to

[11] or

[12] .

[14] A vehicle equipped with the battery pack according to any one of

[11] to

[13] .

[15] The vehicle described in

[14] , including a mechanism for converting the kinetic energy of the vehicle into regenerative energy. [Explanation of symbols]

[0259] REFERENCE SIGNS LIST 1...electrode group, 2...exterior member, 3...negative electrode, 3a...negative electrode current collector, 3b...negative electrode active material-containing layer, 3b0...center, 3b1...first end, 3b2...second end, 3b3...third end, 3b4...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 lead, 23a...other end, 24...adhesive tape, 31...storage container, 32...lid, 33...protective sheet, 34...printed wiring board, 35...wiring, 40...vehicle body, 41...vehicle power supply, 42...electrical control device, 43...external terminal, 44...inverter, 45...drive motor, 100...battery, 200...battery assembly, 200a...battery assembly, 200b...battery assembly, 200c... battery pack, 300... battery pack, 300a... battery pack, 300b... battery pack, 300c... battery pack, 301a... battery pack monitoring device, 301b... battery pack monitoring device, 301c... battery pack monitoring device, 342... positive electrode connector, 343... negative electrode connector, 345... thermistor, 346... protection circuit, 342a... wiring, 343a... wiring, 350... external power supply terminal, 352...positive terminal, 353...negative terminal, 348a...positive wiring, 348b...negative wiring, 400...vehicle, 411...battery management device, 412...communication bus, 413...positive terminal, 414...negative terminal, 415...switch device, 416...current detection unit, 417...negative input terminal, 418...positive input terminal, L1...connection line, L2...connection line, W...drive wheel.

Claims

1. A first end portion; a central portion adjacent to the first end portion in a first direction; an active material-containing layer comprising 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 d of a first basis weight difference between the first basis weight and the central basis weight to the central basis weight ｍ１ is 1% < d ｍ１ <10% The active material-containing layer has a first density distribution in which the density varies along the first direction, and a first density difference ratio d between the first maximum density and a first minimum density to a first maximum density in the first density distribution ｄ１ is 5% < d ｄ１ Electrodes for batteries containing a liquid electrolyte in the range of <20%.

2. 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; The second basis weight of the active material-containing layer at the second end portion is less than the central basis weight, and the ratio d of the difference in the second basis weight between the second basis weight and the central basis weight to the central basis weight ｍ２ is such that 1% < d ｍ２ < 10%, and the electrode according to claim 1.

3. 3. The electrode according to claim 1, 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.

4. 3. The electrode according to claim 1, 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.

5. 3. The electrode according to claim 1, wherein an aspect ratio r of a longer length of the active material-containing layer along the first direction to a shorter length of the active material-containing layer along a second direction intersecting the first direction is in a range of 1<r<50.

6. 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, 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, and a ratio d of a third basis weight difference between the third basis weight and the central basis weight to the central basis weight is ｍ３ is 1% < d ｍ３ < 10%, and the ratio d of the fourth basis weight difference between the fourth basis weight and the central basis weight to the central basis weight is ｍ４ is 1% < d ｍ４ 4. An electrode according to claim 1, wherein the tensile strength is in the range of <10%.

7. The active material-containing layer has a second density distribution in which the density varies along the second direction, and a second density difference ratio d between the second maximum density and the second minimum density to a second maximum density in the second density distribution ｄ２ is 5% < d ｄ２ 7. The electrode of claim 6, wherein the .lambda.

8. 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 comprises the electrode according to claim 1 .

9. A battery pack comprising the battery according to claim 8.

10. An external terminal for applying current; Protection circuit and The battery pack of claim 9 further comprising:

11. 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.

12. A vehicle comprising the battery pack according to any one of claims 9 to 11.

13. The vehicle of claim 12 , further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy.

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