Energy storage device and stack

Abstract

To provide a power storage device in which an increase of an inner resistance between electrode bodies is suppressed, by uniformly pressurizing each of the electrode body.SOLUTION: A power storage device 100 of the present disclosure, includes: a flat electrode body 20 that includes a first main surface 20a and a second main surface 20b; a first pressurizing member 71 that pressurizes the electrode body 20 to a thickness direction; and a second pressurizing member 72. The first pressurizing member 71 comprises: a plurality of first projecting portions 71a that project toward the first main surface 20a in a surface opposite to the first main surface 20a, and pushes against the first main surface 20a; and a first base portion 71f. The second pressurizing member 72 comprises: a plurality of second projecting portions 72a that projects toward the second main surface 20b in the surface opposite to the second main surface 20b, and pushes against the second main surface 20b; and a second base portion 72f. Here, at least a part of the first pressurizing member 71 includes a first convex portion 71a at a position which is not overlapped with each second convex portion 72a when viewing it in the thickness direction of the electrode body 20.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to an electricity storage device and a stack. [Background technology]

[0002] Conventionally, in the field of electricity storage devices, a technique is known in which a plurality of electricity storage devices (cells) are stacked in a predetermined direction and compressed in the arrangement direction using a restraining jig to apply a restraining load (pressure load), thereby reducing the resistance of the electricity storage device, as shown in Patent Documents 1 and 2. For example, Patent Document 1 discloses a battery assembly (stack) in which a plurality of rectangular battery cells (electricity storage devices) containing electrode windings (electrode bodies) and a plurality of spacers are alternately stacked in the thickness direction, and the surfaces of the spacers are formed with a plurality of ribs arranged in a comb-like pattern and abutting the surfaces of the battery cells, for the purpose of providing flow paths for cooling air. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-32581 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-189960 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it has been difficult to apply the above-described technology of applying a pressure load to a stack (multiple electricity storage devices) to a single electricity storage device. Furthermore, according to the inventor's intensive studies, it has been found that when the electrode body is pressed with a rib as disclosed in Patent Document 1, the electrode body is not pressed uniformly only by the rib portion, which causes unevenness in the thickness of the electrode body (unevenness in the distance between the electrodes), and as a result, the internal resistance between the electrode bodies increases.

[0005] The technology disclosed herein has been developed in consideration of the above circumstances, and its purpose is to provide an energy storage device in which the electrode bodies are uniformly pressed, thereby suppressing an increase in internal resistance between the electrode bodies. [Means for solving the problem]

[0006] The disclosed power storage device includes an electrode assembly having a positive electrode and a negative electrode, the electrode assembly being a flat electrode assembly having a pair of opposing rectangular first and second main surfaces, and a pressing member that presses the electrode assembly in a thickness direction. The pressing member has a first pressing member arranged to face the first main surface of the electrode assembly and a second pressing member arranged to face the second main surface of the electrode assembly, the first pressing member having, on a surface facing the first main surface of the electrode assembly, a plurality of first protrusions that protrude toward the first main surface and press against the first main surface, and a first base portion. The second pressing member having, on a surface facing the second main surface of the electrode assembly, a plurality of second protrusions that protrude toward the second main surface and press against the second main surface, and a second base portion. At least a portion of the first pressing member has the first protrusions at positions that do not overlap with the second protrusions when viewed in the thickness direction of the electrode assembly.

[0007] The first pressing member 71 and the second pressing member 72 described above have regions where the multiple first protrusions and the multiple second protrusions are not arranged overlapping each other. When the electrode body is pressed in the thickness direction by the first pressing member 71 and the second pressing member 72 configured in this way, the electrode body is pressed uniformly. Therefore, the laminated portion of the electrode body can be pressed uniformly. Furthermore, the inter-electrode distance (thickness of the electrode body) in the laminated portion of the electrode body 20 becomes uniform. This realizes the provision of an electricity storage device in which an increase in the internal resistance of the electrode body is suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view schematically showing an electricity storage device according to a first embodiment. [Figure 2] FIG. 2 is a schematic vertical cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a schematic vertical cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a schematic diagram of the electrode assembly according to the first embodiment. [Figure 5] FIG. 5 is a plan view of the sealing plate (first pressing member) according to the first embodiment, as viewed from the inner surface side of the case. [Figure 6] FIG. 6 is a plan view of the case main body (second pressing member) according to the first embodiment, viewed from the front in the short side direction. [Figure 7] FIG. 7 is a diagram showing a pressure distribution obtained by CAE analysis on the electricity accumulation device according to the first embodiment, where (a) shows the first main surface side and (b) shows the second main surface side. [Figure 8] FIG. 8 is a schematic diagram showing how the electrode body is housed inside the case according to the first embodiment. [Figure 9] FIG. 9 is a diagram showing a pressure distribution obtained by CAE analysis on the electricity accumulation device according to the second embodiment, where (a) shows the first main surface side and (b) shows the second main surface side. [Figure 10] FIG. 10 is a perspective view schematically illustrating a stack according to an embodiment. [Figure 11] FIG. 11 is a diagram showing a pressure distribution obtained by CAE analysis on a conventional electricity storage device, where (a) shows the first main surface side and (b) shows the second main surface side. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the technology disclosed herein will be described with reference to the drawings. Matters not mentioned in this specification but necessary for implementing the technology disclosed herein can be understood as design matters for those skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. In the following drawings, components and parts that perform the same function are denoted by the same reference numerals. Furthermore, dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships. In this specification, a numerical range expressed as "A to B" includes A and B, and also encompasses the meanings of "preferably greater than A" and "preferably smaller than B."

[0010] In this specification, the term "electricity storage device" refers to a device that can be charged and discharged. Electricity storage devices include batteries generally referred to as lithium ion batteries and lithium secondary batteries, as well as lithium polymer batteries and lithium ion capacitors. A secondary battery generally refers to a battery that can be repeatedly charged and discharged by the movement of charge carriers between the positive and negative electrodes. Here, a lithium ion secondary battery is exemplified as one form of electricity storage device.

[0011] First Embodiment FIG. 1 is a perspective view schematically showing an electricity storage device 100 according to a first embodiment. FIG. 2 is a schematic longitudinal sectional view taken along line II-II in FIG. 1. FIG. 3 is a schematic transverse sectional view taken along line III-III in FIG. 1. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom. In the drawings, the symbol X indicates the short side direction (also referred to as the thickness direction) of the electricity storage device 100, the symbol Y indicates the long side direction of the electricity storage device 100, and the symbol Z indicates the vertical direction (also referred to as the height direction). However, these directions are merely used for the convenience of description and do not limit the installation form of the electricity storage device 100 in any way.

[0012] 1 and 2, the electricity storage device 100 includes a case 10, an electrode assembly 20, a positive electrode terminal 30, and a negative electrode terminal 40. Although not shown, the electricity storage device 100 further includes an electrolyte solution. The electricity storage device 100 is preferably a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

[0013] The case 10 is, for example, a hexahedral member that houses the electrode assembly 20. As shown in FIGS. 1 and 2, the case 10 includes a case body 12 and a sealing plate 14. The case 10 is preferably made of metal, and more preferably made of, for example, aluminum, an aluminum alloy, or SUS. The case 10 according to this embodiment is made of aluminum.

[0014] The case body 12 is, for example, the main body of the case 10 that accommodates the electrode assembly 20 therein. As shown in FIGS. 1 and 2, the case body 12 has an opening 12h, a first surface 12a, a pair of opposing second surfaces 12b and 12c, and a pair of opposing third surfaces 12d and 12e. In this embodiment, the first surface 12a has a wide rectangular shape and faces the opening 12h. The pair of second surfaces 12b and 12c extend from the periphery of a pair of opposing long sides of the first surface 12a, and the second surfaces 12b and 12c face each other. As shown in FIGS. 1 and 2, the lower second surface 12c forms the bottom surface of the electricity storage device 100. The upper second surface 12b is the top surface facing the bottom surface, and in this case, is the mounting surface for the positive electrode terminal 30 and the negative electrode terminal 40. The pair of third surfaces 12d, 12e extend from the periphery of a pair of opposing short sides of the first surface 12a, and the third surfaces 12d, 12e face each other. The shape and size of the case body 12 can be changed as appropriate, for example, depending on the size of the electrode body 20 to be accommodated in the case body 12. In this specification, the term "rectangular" encompasses a shape in which linear long and short sides are joined to each other via a curve, a shape in which at least one of the long and short sides is not linear but is curved, uneven, or bent and composed of multiple straight lines or curves, and the like. As will be described in detail later, in this embodiment, a second pressing member 72 is provided on a portion (here, the surface) of the first surface 12a of the case body 12.

[0015] Opening 12h is, for example, a portion where sealing plate 14 is attached. Here, opening 12h is formed by being surrounded by the upper edges of the pair of second surfaces 12b, 12c and the upper edges of the pair of third surfaces 12d, 12e, and has a wide rectangular shape. By fitting sealing plate 14 into opening 12h of case body 12 and welding the periphery of sealing plate 14, case body 12 and sealing plate 14 are integrated, and case 10 is airtightly sealed.

[0016] As shown in FIG. 2, the second surface 12b is provided with a drain valve 15, a liquid inlet 16, and through-holes 18 and 19. The drain valve 15 is, for example, a thin-walled portion. Here, the drain valve 15 is configured to break when the pressure inside the case 10 reaches a predetermined value or higher, thereby discharging gas inside the case 10 to the outside. The liquid inlet 16 is a through-hole for injecting electrolyte into the case 10 after the sealing plate 14 is assembled to the case body 12. Here, the liquid inlet 16 is sealed with a sealing member 16a after the electrolyte is injected. The through-hole 18 is a portion into which the positive electrode terminal 30 is attached (inserted). The through-hole 19 is a portion into which the negative electrode terminal 40 is attached (inserted).

[0017] The sealing plate 14 is a flat plate-like member that seals the opening 12h. Therefore, the shape of the sealing plate 14 should correspond to the shape of the opening 12h. Here, the sealing plate 14 has a wide rectangular shape. Here, when the sealing plate 14 is attached to the opening 12h, the sealing plate 14 faces the first surface 12a. As will be described in detail later, in this embodiment, a first pressing member 71 is provided on a portion of the sealing plate 14 (here, the front surface).

[0018] As the electrolyte, any known electrolyte may be used without any particular limitation. For example, a non-aqueous electrolyte in which a supporting salt (electrolyte salt) is dissolved in a non-aqueous solvent (organic solvent) is preferably used. Examples of non-aqueous solvents include carbonate-based solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of supporting salts include fluorine-containing lithium salts such as LiPF6. The electrolyte may contain additives as needed.

[0019] The positive electrode terminal 30 is a member that is electrically connected to the positive electrode 22 of the electrode body 20. As shown in FIG. 2, the positive electrode terminal 30 is inserted into the through-hole 18 and exposed to the outside of the case body 12. Here, the positive electrode terminal 30 is connected to the positive electrode current collector 50 by crimping. The positive electrode terminal 30 is preferably made of metal, and more preferably made of aluminum or an aluminum alloy, for example.

[0020] The negative electrode terminal 40 is a member electrically connected to the negative electrode 24 of the electrode body 20. As shown in FIG. 2, the negative electrode terminal 40 is inserted into the through-hole 19 and exposed to the outside of the case body 12. Here, the negative electrode terminal 40 is connected to the negative electrode current collector 60 by crimping. The negative electrode terminal 40 is made of, for example, copper or a copper alloy. The negative electrode terminal 40 may have a configuration similar to that of the positive electrode terminal 30. Therefore, a description of the configuration of the negative electrode terminal 40 will be omitted here.

[0021] The positive electrode current collector 50 is, for example, a member that electrically connects the positive electrode current collector foil 22c and the positive electrode terminal 30. The positive electrode current collector 50 is a plate-shaped conductive member. As shown in FIG. 2, one end (the lower end in FIG. 2) of the positive electrode current collector 50 is connected to the positive electrode active material layer non-forming portion 22d (the positive electrode current collector foil 22c). The other end (the upper end in FIG. 2) of the positive electrode current collector 50 is crimped to the lower end of the positive electrode terminal 30. The positive electrode current collector 50 is made of, for example, aluminum or an aluminum alloy.

[0022] The negative electrode current collector 60 is a member that electrically connects the negative electrode current collector foil 24c and the negative electrode terminal 40. The negative electrode current collector 60 is, for example, a plate-shaped conductive member. As shown in FIG. 2, the negative electrode current collector foil 24c is connected to one end (the lower end in FIG. 2) of the negative electrode current collector 60. The other end (the upper end in FIG. 2) of the negative electrode current collector 60 is crimped to the lower end of the negative electrode terminal 40. The negative electrode current collector 60 is made of, for example, copper or a copper alloy.

[0023] Various insulating members are used in the electricity storage device 100. For example, on the outside of the case 10, a gasket 92 is disposed between the positive electrode terminal 30 and the second surface 12b and between the negative electrode terminal 40 and the second surface 12b. On the inside of the case 10, an internal insulating member 93 is disposed between the positive electrode current collector 50 and the second surface 12b and between the negative electrode current collector 60 and the second surface 12b. Here, the gasket 92 serves to insulate the case 10 from the positive electrode terminal 30 and the negative electrode terminal 40, and also to seal (close) the through-holes 18 and 19.

[0024] It is preferable that a material having excellent chemical resistance and weather resistance be used for the gasket 92 and the internal insulating member 93. The gasket 92 and the internal insulating member 93 may be made of an electrically insulating and elastically deformable resin material, for example, a fluorinated resin such as perfluoroalkoxy fluorine resin (PFA), polyphenylene sulfide resin (PPS), aliphatic polyamide, etc. The gasket 92 and the internal insulating member 93 may be integrated by, for example, insert molding.

[0025] The electrode assembly 20 is a power generating element of the electricity storage device 100, and has a positive electrode 22 and a negative electrode 24. FIG. 4 is a schematic diagram of the electrode assembly 20 according to the first embodiment. As shown in FIG. 4, the electrode assembly 20 has a flat outer shape. As shown in FIG. 4, the electrode assembly 20 is a so-called wound electrode assembly, in which a long sheet-like positive electrode 22 and a long sheet-like negative electrode 24 are wound in the longitudinal direction with a separator 23 (two sheets in this case) interposed therebetween. The electrode assembly 20 can be produced, for example, by winding the positive electrode 22, the negative electrode 24, and the separator 23 to form a cylindrical body, and then press-molding the cylindrical body. The number of electrode assemblies 20 arranged inside one case body 12 is not particularly limited, and may be one or two or more (plural). As shown in FIG. 3, one electrode assembly 20 is arranged inside the case body 12.

[0026] The electrode body 20 has a pair of opposing rectangular wide surfaces, namely, a first main surface 20a and a second main surface 20b, and a pair of curved regions 20r, each having a curved outer surface, provided at both ends of the first main surface 20a and the second main surface 20b. As shown in FIG. 3, the electrode body 20 is housed in the case body 12 so that the first main surface 20a of the electrode body 20 faces the sealing plate 14 and the second main surface 20b faces the first surface 12a. One curved region 20r of the electrode body 20 (upper side in FIG. 2) faces the second surface 12b, and the other curved region 20r (lower side in FIG. 2) faces the second surface 12c. The electrode body 20 may be housed inside the case 10 covered with an electrode body holder (not shown) made of an insulating resin sheet. In this case, the end face of the electrode assembly 20 is the surface where the positive electrode 22, the negative electrode 24, and the separator 23 are stacked, and is an open surface.

[0027] 4, the positive electrode 22 has a long, strip-shaped positive electrode current collector foil 22c (e.g., aluminum foil) and a positive electrode active material layer 22a fixed to at least one surface of the positive electrode current collector foil 22c. Although not particularly limited, a protective layer (not shown) may be provided on one side edge portion in the winding axis direction WD of the positive electrode 22, as necessary. Note that, as the constituent materials of the positive electrode active material layer 22a and the protective layer, materials used in this type of electricity storage device (in this embodiment, a lithium ion secondary battery) may be used without particular limitation.

[0028] 4, the negative electrode 24 has a long, strip-shaped negative electrode current collector foil 24c (e.g., copper foil) and a negative electrode active material layer 24a fixed to at least one surface of the negative electrode current collector foil 24c. Note that, as a constituent material of the negative electrode active material layer 24a, any material used in this type of electricity storage device (in this embodiment, a lithium ion secondary battery) may be used without any particular limitation.

[0029] The positive electrode active material layer-free portion 22d (i.e., a portion where the positive electrode active material layer 22a is not formed and the positive electrode current collector foil 22c is exposed) and the negative electrode active material layer-free portion 24d (i.e., a portion where the negative electrode active material layer 24a is not formed and the negative electrode current collector foil 24c is exposed) are formed so as to protrude outward from both ends in the winding axis direction (i.e., the sheet width direction perpendicular to the longitudinal direction) of the electrode body 20. The positive electrode active material layer-free portion 22d and the negative electrode active material layer-free portion 24d are joined to the positive electrode current collector 50 and the negative electrode active material layer-free portion 24d, respectively.

[0030] The separator 23 is a member that insulates the positive electrode active material layer 22a of the positive electrode 22 from the negative electrode active material layer 24a of the negative electrode 24. In this embodiment, the separator 23 forms the outer surface of the electrode body 20. The separator 23 is, for example, a porous sheet made of a resin such as a polyolefin resin, such as polyethylene (PE) or polypropylene (PP).

[0031] The electricity storage device 100 disclosed herein is characterized by having a first pressing member 71 and a second pressing member 72. FIG. 5 is a plan view of the sealing plate 14 according to the first embodiment, viewed from the inside surface of the case 10. FIG. 6 is a plan view of the case body 12 according to the first embodiment, viewed from the front side (F side) in the short side direction X. In this embodiment, the first pressing member 71 is a part of the sealing plate 14, and the second pressing member 72 is a part of the first surface 12a of the case body 12.

[0032] The pressing member 70 is a member that presses the electrode body 20 in the thickness direction. The pressing member has a first pressing member 71 and a second pressing member 72.

[0033] The first pressing member 71 is disposed to face the first main surface 20a of the electrode body 20. The first pressing member 71 has a first protrusion 71a and a first base portion 71f. As shown in FIG. 5, the first pressing member 71 here has a plurality of first protrusions 71a and a plurality of first base portions 71f. The first protrusions 71a and the first base portion 71f are integrally molded here. The first protrusions 71a protrude from the first base portion 71f toward the first main surface 20a of the electrode body 20. In other words, the plurality of first protrusions 71a protrude from the plurality of first base portions 71f toward the second pressing member 72 at the same height. As shown in FIG. 3, the first pressing member 71 here is a part of the sealing plate 14. More specifically, here, the first pressing member 71 is formed in the center of the sealing plate 14 so as to protrude further toward the first main surface 20a than the peripheral edge portion 14p of the sealing plate 14. However, without being limited to this, in some preferred embodiments, the first pressing member 71 may be an independent member, in which case it is placed inside the case 10 so that the first protrusion 71a and the first base portion 71f of the first pressing member 71 face the first main surface 20a of the electrode body 20.

[0034] The second pressing member 72 is disposed to face the second main surface 20b of the electrode body 20. The second pressing member 72 has a second protrusion 72a and a second base portion 72f. As shown in FIG. 6, the second pressing member 72 has a plurality of second protrusions 72a and a plurality of second base portions 72f. The second protrusions 72a and the second base portion 72f are integrally molded here. The plurality of second protrusions 72a protrude from the plurality of second base portions 72f toward the second main surface 20b of the electrode body 20. In other words, the second protrusions 72a protrude from the second base portion 72f toward the first pressing member 71. As shown in FIG. 3, the second pressing member 72 is a part of the first surface 12a of the case body 12. More specifically, the second pressing member 72 is formed in the center of the first surface 12a so as to protrude further toward the second main surface 20b than the peripheral edge portion 12ap of the first surface 12a. However, without being limited to this, in some preferred embodiments, the second pressing member 72 may be an independent member, in which case it is disposed inside the case 10 so that the second protrusion 72a and the second base portion 72f of the second pressing member 72 face the second main surface 20b of the electrode body 20.

[0035] The first pressing member 71 and the second pressing member 72 may be made of a metal such as aluminum, aluminum alloy, or SUS, or may be made of a fluorinated resin such as PFA, PPS, or aliphatic polyamide.

[0036] The heights of the first protrusion 71a and the second protrusion 72a can be adjusted as appropriate depending on the thickness of the electrode body 20 (here, this refers to the distance in the thickness direction X between the first main surface 20a and the second main surface 20b of the electrode body 20 before insertion into the case 10), and may be, for example, 0.3 to 2 mm. In this specification, the "height of the first protrusion 71a" refers to the difference in height between the first base portion 71f and the first protrusion 71a in the short side direction X of the electricity storage device 100. In this specification, the "height of the second protrusion 72a" refers to the difference in height between the second base portion 72f and the second protrusion 72a in the short side direction X of the electricity storage device 100.

[0037] The first protrusion 71a and the second protrusion 72a are configured to abut against the first main surface 20a or the second main surface 20b of the electrode body 20 and to apply a load (press against) the abutting portion and a surrounding portion of the electrode body 20 in the thickness direction X of the electrode body 20. The shape, size, and arrangement of the first protrusion 71a and the second protrusion 72a can be determined appropriately depending on, for example, the required characteristics of the electricity storage device and the electrode body 20.

[0038] As shown in FIG. 5, the multiple first protrusions 71a are arranged substantially symmetrically about the center CL in the long side direction Y of the case 10. The multiple first protrusions 71a are arranged in a so-called comb-tooth (ridge) shape. More specifically, the first protrusion 71a arranged closest to the center CL extends toward both ends in the long side direction Y, in other words, is formed in a T-shape. The other multiple first protrusions 71a extend upward from the lower end of the sealing plate 14 near the center in the long side direction Y of the sealing plate 14. Thereafter, the first protrusions 71a curve and extend toward the ends in the long side direction Y. In some preferred embodiments, as shown in FIG. 5, the multiple first protrusions 71a are arranged at equal intervals while being spaced apart from each other. This allows the electrode body 20 to be pressed over a wider area, and airflow paths for cooling heat generated by the electrode body 20 can be suitably secured.

[0039] As shown in FIG. 6, the multiple second protrusions 72a are arranged substantially symmetrically about the center CL in the long side direction Y of the case 10. The multiple second base portions 72f are arranged in a so-called comb-tooth (ridge) shape. More specifically, the second base portion 72f arranged closest to the center CL extends toward both ends in the long side direction Y, in other words, is formed in a T-shape. The other multiple second base portions 72f extend upward from the lower end of the first surface 12a of the case main body 12 near the center of the first surface 12a in the long side direction Y. Thereafter, the second base portion 72f extends toward the ends in the long side direction Y while curving.

[0040] With respect to the first pressing member 71 and the second pressing member 72, when the areas facing the first main surface 20a and the second main surface 20b of the electrode body 20 are each taken as 100%, the proportions of the first convex portions 71a of the first pressing member 71 and the second convex portions 72a of the second pressing member 72 are each preferably 20% or more, and more preferably 40% or more, from the viewpoint of suitably reducing the electrode thickness of the electrode body 20. Furthermore, the proportions of the first convex portions 71a of the first pressing member 71 and the second convex portions 72a of the second pressing member 72 are each preferably 80% or less, and more preferably 65% ​​or less, from the viewpoint of ensuring flow paths for air and electrolyte.

[0041] 3, here, at least a portion of the first pressing member 71 has first protrusions 71a at positions that do not overlap with second protrusions 72a when viewed in the thickness direction X of the electrode body 20. More specifically, at least a portion of the multiple first protrusions 71a are arranged to face the second base portion 72f across the electrode body 20, and at least a portion of the multiple second protrusions 72a are arranged to face the first base portion 71f across the electrode body 20. However, as will be described in detail later, it is sufficient that at least a portion of the first protrusions 71a and second protrusions 72a are arranged so as not to overlap when viewed in the stacking direction (X direction) of the electrode body 20.

[0042] Here, when the first pressing member 71 is viewed in the thickness direction X of the electrode body 20, if the entire first protrusions 71a are taken as 100%, typically 40% or more of the first protrusions 71a are arranged in positions that do not overlap with the second protrusions 72a, and preferably 55% or more of the first protrusions 71a are arranged in positions that do not overlap with the second protrusions 72a. More preferably, as in this embodiment, the first protrusions 71a do not overlap with any of the second protrusions 72a. With this configuration, the electrode body 20 can be pressed more uniformly.

[0043] 7A and 7B are diagrams showing pressure distributions obtained by CAE (computer-aided engineering) analysis of the power storage device 100 according to the first embodiment, where (a) shows the first main surface 20a side and (b) shows the second main surface 20b side. Fig. 11 is a diagram showing pressure distributions obtained by CAE analysis of a power storage device according to a conventional example, where (a) shows the first main surface 20a side and (b) shows the second main surface 20b side. Note that the conventional example is under the same conditions as the above-described embodiment, except that the first convex portion 71a and the second convex portion 72a are arranged so as to completely overlap each other when viewed in the thickness direction X of the electrode body 20.

[0044] Here, in the laminated portion (thickness direction X) of the electrode body 20, the region where the electrode body 20 is pressed by both the first pressing member 71 and the second pressing member 72 can be divided into a first region, a second region where the electrode body 20 is pressed by either the first pressing member 71 or the second pressing member 72, and a third region where the electrode body 20 is not pressed by either the first pressing member 71 or the second pressing member 72. The magnitude of the surface pressure for each pressed region between the electrode bodies 20 is first region > second region > third region. Therefore, the magnitude of the thickness between the electrode bodies 20 is third region > second region > first region.

[0045] In the conventional electricity storage device, when viewed in the thickness direction X of the electrode body 20, the first convex portion 71a and the second convex portion 72a are arranged to completely overlap. When the electrode body 20 is pressed in the thickness direction X using a conventional pressing member, as shown in FIGS. 11(a) and 11(b), bias in the pressing pressure occurs between the electrode bodies 20 in the thickness direction X of the electrode body 20. More specifically, the ratio of pressed regions of the electrode body 20 in the conventional example described above was determined from the pressing distribution by CAE analysis shown in FIG. 11, and was found to be first region:second region:third region = 85:0:15. That is, in the conventional electricity storage device, bias in the surface pressure occurs between the pressed and non-pressed regions of the electrode bodies 20. Therefore, differences occur in the thickness of the electrode body 20, and the internal resistance of the electrode body 20 increases.

[0046] On the other hand, when the electrode body 20 is pressed in the thickness direction using the first pressing member 71 and the second pressing member 72 having the structure according to this embodiment, as shown in FIG. 7(a), the region of the first main surface of the electrode body 20 facing the first convex portion 71a of the first pressing member 71 is pressed by the first convex portion 71a. On the other hand, as shown in FIG. 7(b), the region of the second main surface of the electrode body 20 facing the second convex portion 72a of the second pressing member 72 is pressed by the second convex portion 72a. Note that the ratio of the pressed regions of the electrode body 20 in this embodiment, as determined from FIG. 7, was first region:second region:third region = 10:80:10. This indicates that the pressed regions of the electrode body 20 are less unevenly distributed compared to the conventional example. Therefore, the laminated portion of the electrode body 20 can be pressed uniformly. Furthermore, the inter-electrode distance (thickness of the electrode body 20) in the laminated portion of the electrode body 20 becomes uniform. This makes it possible to suppress an increase in the internal resistance of the electrode body 20 of the electricity storage device 100.

[0047] The ratio of the second region to the pressure region of the electrode body 20 is preferably 20% or more, and more preferably 50% or more. This ratio can be determined, for example, by obtaining a pressure distribution through CAE analysis as shown in Figure 7. It can also be determined from the surface pressure distribution obtained by measurement using a surface pressure sensor.

[0048] The load applied to the electrode body 20 by the first pressing member 71 and the second pressing member 72 is not limited as it can be adjusted appropriately depending on the thickness and size of the electrode body 20, but can be, for example, 0.5 to 15 kN or more, and preferably 1.8 to 10 kN.

[0049] In some preferred embodiments, the electricity storage device 100 includes a case body 12 and a wide, rectangular sealing plate 14, as in the first embodiment, where the first pressing member 71 is a part of the sealing plate 14 and the second pressing member 72 is a part of the first surface 12a. FIG. 8 is a schematic diagram showing how the electrode assembly 20 is housed inside the case 10 according to the first embodiment. For ease of explanation, the sealing plate 14 after sealing is shown with phantom lines. In the electricity storage device 100 of this embodiment, the first pressing member 71 and the second pressing member 72 are configured as parts of the case 10. Furthermore, the case 10 is designed so that when the sealing plate 14 is fitted into the case body 12, the inner dimension L of the case 10 in the thickness direction X of the electricity storage device 100 is smaller than the initial thickness T of the electrode assembly 20. As a result, the electrode body 20 is housed inside the case body 12, and the sealing plate 14 is welded at its periphery while being pressed into the opening 12h of the case body (indicated by the hollow arrow in FIG. 8 ) (in other words, while being pressed toward the first surface 12a), and the electrode body 20 is restrained by the second pressing member 72 of the case body 12 and the first pressing member 71 of the sealing plate 14. Here, the term "internal dimension L of the case 10" in this specification refers to the shortest distance in the X direction from the first protrusion 71a of the first pressing member 71 to the second protrusion 72a of the second pressing member 72 after the sealing plate 14 has sealed the case 10. Furthermore, the term "initial thickness T of the electrode body 20" in this specification refers to the shortest distance (in the X direction) between the first main surface 20a and the second main surface 20b of the electrode body 20 before the electrode body 20 is inserted into the case 10.

[0050] The sealing plate 14 and the case body 12 of the power storage device 100 disclosed herein may be arranged so that at least a portion of the first protrusions 71a and the second protrusions 72a do not overlap when viewed in the thickness direction X of the electrode body 20. In other words, at least a portion of the first protrusions 71a face the second base portion 72f across the electrode body 20, and at least a portion of the second protrusions 72a face the first base portion 71f across the electrode body 20. FIG. 9 shows a pressure distribution obtained by CAE analysis of the power storage device according to the second embodiment, where (a) shows the first main surface 20a side and (b) shows the second main surface 20b side. Note that the second embodiment is similar to the above-described embodiment except that, when the entire first protrusions 71a are defined as 100%, 60% of the first protrusions 71a are positioned so as not to overlap with the second protrusions 72a when viewed in the thickness direction X of the electrode body 20. The ratio of the pressed regions of the electrode assembly 20 in this embodiment, determined from Fig. 9, was first region:second region:third region = 70:20:10. Therefore, even with this configuration, the laminated portion of the electrode assembly 20 can be pressed uniformly. This makes it possible to suppress the internal resistance of the electrode assembly 20 of the electricity storage device 100.

[0051] The electricity storage device 100 can be used for various purposes, but typically can be suitably used as a power source (driving power source) for motors mounted on various vehicles, such as passenger cars, trucks, etc. The type of vehicle is not particularly limited, and examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs).

[0052] Another aspect of the technology disclosed herein provides a stack 150 formed by combining a plurality of the above-described power storage devices 100. FIG. 10 is a perspective view schematically illustrating a stack 150 according to one embodiment. In this embodiment, for example, as shown in FIG. 10 , a stack 150 may be provided in which a plurality of power storage devices 100 are electrically connected to one another via a bus bar 90. In this case, the electrical connection between the plurality of power storage devices 100 may be achieved by, for example, bridging a flat bus bar 90 between the positive electrode terminals 30 and the negative electrode terminals 40 of the plurality of power storage devices 100. The bus bar 90 may be made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The bus bar 90 may be electrically connected to the positive electrode terminals 30 and the negative electrode terminals 40 by welding, for example, laser welding. Furthermore, external connection terminals (not shown) may be further provided on the positive electrode terminals 30 and the negative electrode terminals 40 for connection with the bus bar 90. The power storage device 100 used in the stack 150 does not require a restraining jig because each case 10 is provided with the first pressing member 71 and the second pressing member 72. This allows the stack 150 to be made compact.

[0053] Although several embodiments of the technology disclosed herein have been described above, the above embodiments are merely examples. The technology disclosed herein can be implemented in various other forms. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiments. For example, it is possible to replace part of the above-described embodiments with other modified embodiments, and it is also possible to add other modified embodiments to the above-described embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate.

[0054] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: An electricity storage device comprising: an electrode body having a positive electrode and a negative electrode, the electrode body being a flat electrode body having a pair of opposing rectangular first and second main surfaces; and a pressing member that presses the electrode body in a thickness direction, the pressing member having a first pressing member arranged so as to face the first main surface of the electrode body, and a second pressing member arranged so as to face the second main surface of the electrode body, the first pressing member having, on a surface facing the first main surface of the electrode body, a plurality of first protrusions that protrude toward the first main surface and press against the first main surface, and a first base portion, the second pressing member having, on a surface facing the second main surface of the electrode body, a plurality of second protrusions that protrude toward the second main surface and press against the second main surface, and a second base portion, wherein at least a part of the first pressing member has the first protrusions at positions that do not overlap with the second protrusions when viewed in the thickness direction of the electrode body. Item 2: The electricity storage device according to item 1, wherein when the first pressing member and the second pressing member are viewed in the thickness direction of the electrode body, the first convex portion and the second convex portion do not overlap. Item 3: The energy storage device according to item 1 or 2, wherein either the first convex portion or the second convex portion is arranged at equal intervals while being spaced apart from each other, and when viewed in the thickness direction of the electrode body, one of the first convex portion or the second convex portion is formed in an area where the other of the first convex portion or the second convex portion is not arranged. Item 4: The electricity storage device according to any one of items 1 to 3, further comprising a hexahedral case that houses the electrode assembly, the case comprising: a case body having a wide rectangular first surface and an opening facing the first surface, a pair of second surfaces extending from a periphery of a long side of the first surface toward the opening, and a pair of third surfaces extending from a periphery of a short side of the first surface toward the opening; and a wide rectangular sealing plate that seals the opening and faces the first surface, wherein the first pressing member is a part of the sealing plate and the second pressing member is a part of the first surface. Item 5: A stack including a plurality of the electricity storage devices according to any one of items 1 to 4. [Explanation of symbols]

[0055] 10 cases 12 Case body 12a 1st page 12b, 12c 2nd side 12d, 12e 3rd side 12h opening 14 Sealing plate 18, 19 Through holes 20 Electrode body 20a First principal surface 20b 2nd principal surface 22 Positive electrode 23 Separator 24 Negative electrode 30 Positive terminal 40 Negative terminal 70 Pressing member 71 first pressing member 71a First convex part 71f First base section 72 second pressing member 72a Second convex part 72f Second base 90 Busbar 92 Gasket 93 Internal insulating material 100 Energy storage device 150 stacks

Claims

1. an electrode body including a positive electrode and a negative electrode, the electrode body being a flat electrode body having a pair of opposing rectangular first and second main surfaces; a pressing member that presses the electrode body in a thickness direction, the pressing member includes a first pressing member arranged to face a first main surface of the electrode body, and a second pressing member arranged to face a second main surface of the electrode body, the first pressing member includes, on a surface facing the first main surface of the electrode body, a plurality of first protrusions that protrude toward the first main surface and press against the first main surface, and a first base portion; the second pressing member includes, on a surface facing the second main surface of the electrode body, a plurality of second protrusions that protrude toward the second main surface and press against the second main surface, and a second base portion; wherein the first pressing member has the first protrusion at a position that does not overlap any of the second protrusions when viewed in the thickness direction of the electrode body, With respect to the first pressing member and the second pressing member, when the area of ​​the electrode body facing the first main surface and the second main surface is taken as 100%, respectively, the proportion of the first convex portion of the first pressing member and the second convex portion of the second pressing member is 20% or more and 80% or less, respectively. Energy storage device.

2. The plurality of first protrusions are arranged in a comb-teeth shape. The electricity storage device according to claim 1 .

3. Either the first convex portion or the second convex portion is arranged at equal intervals while being spaced apart from each other, and when viewed in the thickness direction of the electrode body, one of the first convex portion or the second convex portion is formed in an area where the other of the first convex portion or the second convex portion is not arranged. The electricity storage device according to claim 1 or 2.

4. Further, a hexahedral case is provided to house the electrode assembly. The case is a case body having a wide rectangular first surface and an opening facing the first surface, a pair of second surfaces extending from the periphery of a long side of the first surface toward the opening, and a pair of third surfaces extending from the periphery of a short side of the first surface toward the opening; a wide rectangular sealing plate that seals the opening and faces the first surface, Here, the first pressing member is a part of the sealing plate, and the second pressing member is a part of the first surface. The electricity storage device according to claim 1 or 2.

5. A power storage device comprising a plurality of the power storage devices according to claim 1 or 2. stack.

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