Electric storage device and stack

Abstract

To provide a power storage device in which variation of an inner resistance in each power storage device is mitigated by mitigating variation of pressurization load with respect to thickness variation of an electrode body.SOLUTION: A power storage device 100 disclosed here, comprises: a flat electrode body 20 including a pair of rectangular-like width surfaces 20a and 20b; and a pair of pressuring members 70 that elastically compresses the electrode body 20 to a thickness direction. Here, each pressuring force member 70 includes: a first convex portion 71a that projects toward each width surface 20a of the flat electrode body 20; and a second convex portion 71b that further projects to a wide surface of the electrode body from the first convex portion 71a. Each pressuring force member 70 is formed in such a manner that it is elastically deformed by a reference pressuring force Fa. A second spring constant of each pressuring force member 70 after the elastic deformation is smaller than a first spring constant of each pressuring force member 70 before being elastically deformed.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a power storage device and a stack.

Background Art

[0002] Conventionally, in a power storage device, a technique of reducing the resistance of the power storage device by stacking a plurality of power storage devices (cells) in a predetermined direction and applying a restraint load (pressing load) by compressing them in the arrangement direction with a restraint jig is known. For example, Patent Document 1 discloses a battery pack (stack) in which a plurality of rectangular battery cells (power storage devices) accommodating electrode wound bodies (electrode bodies) and a plurality of spacers are alternately stacked in the thickness direction, and a plurality of ribs arranged in a comb shape and contacting the surface of the battery cell are formed on the surface of the spacer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, it has been difficult to apply the technique of applying a pressing load to a stack (a plurality of power storage devices) as described above to a single power storage device. In addition, there is some variation in the thickness of the electrode body used in the power storage device. According to the intensive study by the present inventor, it has been found that when the thickness of the electrode body is small, the pressing load applied in the thickness direction of the electrode body becomes small, while when the thickness of the electrode body is large, the pressing load applied in the thickness direction of the electrode body becomes large. As a result, when the conventional pressing load application technique is adopted, variations in the pressing load occur for each power storage device, and it has been found that variations in the internal resistance occur for each power storage device.

[0005] The technology disclosed herein has been made in view of the above circumstances, and its object is to provide a power storage device in which variations in internal resistance for each power storage device are reduced by alleviating variations in pressing load with respect to variations in the thickness of the electrode body in the power storage device.

Means for Solving the Problem

[0006] The power storage device disclosed herein is 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 wide surfaces, and a pair of pressing members facing the electrode body and elastically compressing each of the pair of wide surfaces of the electrode body in the thickness direction of the electrode body. Here, at least one of the pair of pressing members has a first convex portion protruding toward the wide surface of the electrode body and a second convex portion protruding further toward the wide surface of the electrode body than the first convex portion, and the pressing member is formed so as to elastically deform at a reference pressing load Fa. When the spring constant of the pressing member before the elastic deformation is defined as a first spring constant and the spring constant of the pressing member after the elastic deformation is defined as a second spring constant, the second spring constant is smaller than the first spring constant.

[0007] According to such a configuration, the pressing member is formed so as to elastically deform at the reference pressing load Fa. And, before and after the elastic deformation of the pressing member, the spring constant after the elastic deformation (second spring constant) is configured to be smaller than the spring constant before the elastic deformation (first spring constant). Thereby, variations in the pressing load with respect to variations in the thickness of the electrode body in the power storage device can be alleviated.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments according to the technology disclosed herein will be described with reference to the drawings. Matters not mentioned in this specification and necessary for the implementation of the technology disclosed herein can be grasped as design matters of 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 the common general knowledge in the relevant field. In the following drawings, members and parts having the same function are denoted by the same reference numerals for explanation. Also, the dimensional relationships (length, width, thickness, etc.) in each figure do not reflect the actual dimensional relationships. In this specification, a numerical range expressed as "A to B" includes A and B, and also includes the meaning of "preferably greater than A" and "preferably less than B".

[0010] As used herein, the "power storage device" refers to a device capable of charging and discharging. Power storage devices generally include batteries such as lithium-ion batteries and lithium secondary batteries, as well as lithium polymer batteries, lithium-ion capacitors, and the like. A secondary battery generally refers to a battery capable of repeated charging and discharging with the movement of charge carriers between the positive and negative electrodes. Here, as one form of the power storage device, a lithium-ion secondary battery is exemplified.

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

[0012] As shown in FIGS. 1 and 2, the power storage device 100 includes a case 10, an electrode body 20, a positive electrode terminal 30, and a negative electrode terminal 40. Although not shown, the power storage device 100 further includes an electrolytic solution here. The power 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 body 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 more preferably made of, for example, aluminum, an aluminum alloy, SUS, or the like. The case 10 according to the present embodiment is made of aluminum here.

[0014] The case body 12 is, for example, the main body of the case 10 that houses the electrode body 20 inside. 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 is a wide rectangular shape and faces the opening 12h. The pair of second surfaces 12b and 12c extend from the peripheral edges of the 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 constitutes the bottom surface of the power storage device 100. The upper second surface 12b is the upper surface facing this bottom surface, and here it is the mounting surface for the positive electrode terminal 30 and the negative electrode terminal 40. The pair of third surfaces 12d and 12e extend from the peripheral edges of the pair of opposing short sides of the first surface 12a, and the third surfaces 12d and 12e face each other. The shape and size of the case body 12 can be appropriately changed according to, for example, the size of the electrode body 20 housed in the case body 12. In this specification, the "rectangular shape" includes a shape in which a straight long side and a short side are joined to each other via a curve, a shape in which at least one of the long side and the short side is not straight, but is curved, has irregularities, or is bent and composed of a plurality of straight lines or curves, etc. Although details will be described later, in this embodiment, a second pressing member 72 is provided on a part (here, the surface) of the first surface 12a of the case body 12.

[0015] The opening 12h is, for example, a part where the sealing plate 14 is mounted. Here, the opening 12h is formed by being surrounded by the upper edges of the pair of second surfaces 12b and 12c and the upper edges of the pair of third surfaces 12d and 12e, and is a wide rectangular shape. By fitting the sealing plate 14 into the opening 12h of the case body 12 and welding the peripheral edge of the sealing plate 14, the case body 12 and the sealing plate 14 are integrated, and the case 10 is hermetically sealed.

[0016] As shown in FIG. 2, on the second surface 12b, a discharge valve 15, a liquid injection hole 16, and through holes 18 and 19 are provided. The discharge valve 15 is, for example, a thin-walled portion. Here, the discharge valve 15 is configured to break when the pressure inside the case 10 reaches a predetermined value or more and discharge the gas inside the case 10 to the outside. The liquid injection hole 16 is a through hole for injecting an electrolytic solution into the case 10 after assembling the sealing plate 14 to the case body 12. Here, the liquid injection hole 16 is sealed by a sealing member 16a after the injection of the electrolytic solution. The through hole 18 is a portion where the positive electrode terminal 30 is attached (inserted). The through hole 19 is a portion where the negative electrode terminal 40 is attached (inserted).

[0017] The sealing plate 14 is a flat plate member that seals the opening 12h. Therefore, the shape of the sealing plate 14 is preferably a shape corresponding to the shape of the opening 12h. Here, the sealing plate 14 is 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. Although details will be described later, in the present embodiment, a first pressing member 71 is provided on a part (here, the surface) of the sealing plate 14.

[0018] As the electrolytic solution, those conventionally known and used can be used without particular limitation. As an example, a non-aqueous electrolytic solution in which a supporting salt (electrolyte salt) is dissolved in a non-aqueous solvent (organic solvent) is preferably used. As an example of the non-aqueous solvent, carbonate solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate can be mentioned. As an example of the supporting salt, fluorine-containing lithium salts such as LiPF6 can be mentioned. The electrolytic solution may contain additives as necessary.

[0019] The positive electrode terminal 30 is a member 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 outside the case body 12. Here, the positive electrode terminal 30 is connected to the positive electrode current collector 50 by caulking. The positive electrode terminal 30 is preferably made of metal, and more preferably made of, for example, aluminum or an aluminum alloy.

[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 outside the case body 12. Here, the negative electrode terminal 40 is connected to the negative electrode current collector 60 by caulking. The negative electrode terminal 40 is made of, for example, copper or a copper alloy. The negative electrode terminal 40 may have the same configuration as the positive electrode terminal 30, for example. Therefore, the description of the configuration of the negative electrode terminal 40 is omitted here.

[0021] The positive electrode current collector 50 is a member that electrically connects the positive electrode current collector foil 22c and the positive electrode terminal 30, for example. The positive electrode current collector 50 is a plate-shaped conductive member. As shown in FIG. 2, a non-positive electrode active material layer portion 22d (positive electrode current collector foil 22c) is connected to one end (the lower end in FIG. 2) of the positive electrode current collector 50. Also, the other end (the upper end in FIG. 2) of the positive electrode current collector 50 is caulked 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 a plate-shaped conductive member, for example. 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. Also, the other end (the upper end in FIG. 2) of the negative electrode current collector 60 is caulked 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] In the power storage device 100, various insulating members are used. For example, outside 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. Here, the gasket 92 insulates the case body 12 from the positive electrode terminal 30 and the negative electrode terminal 40, and has a function of sealing (closing) the through holes 18 and 19. Also, inside 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.

[0024] It is preferable that a material excellent in 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 a resin material having electrical insulation properties and capable of elastic deformation, for example, a fluorinated resin such as perfluoroalkoxy fluororesin (PFA), polyphenylene sulfide resin (PPS), aliphatic polyamide, or the like. The gasket 92 and the internal insulating member 93 may be integrated by insert molding, for example.

[0025] The electrode body 20 is a power generation element of the power storage device 100 having a positive electrode 22 and a negative electrode 24. FIG. 4 is a schematic diagram of the electrode body 20 according to one embodiment. As shown in FIG. 3, here, one electrode body 20 is disposed inside the case body 12. As shown in FIG. 4, the electrode body 20 has a flat outer shape. As shown in FIG. 4, the electrode body 20 is a so-called wound electrode body in which a long sheet-like positive electrode 22 and a long sheet-like negative electrode 24 are wound in the longitudinal direction with separators 23 (here, two sheets) interposed therebetween. The electrode body 20 can be produced, for example, by winding the positive electrode 22, the negative electrode 24, and the separator 23 into a cylindrical body and press-molding the cylindrical body. Note that the electrode body 20 may be housed inside the case 10 in a state covered with an electrode body holder (not shown) made of an insulating resin sheet.

[0026] The electrode body 20 has a first main surface 20a and a second main surface 20b which are wide surfaces having a pair of opposing rectangular shapes, and a pair of curved regions 20r provided at both ends of the first main surface 20a and the second main surface 20b and having curved outer surfaces. As shown in FIG. 3, the electrode body 20 is housed in the case body 12 such 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 (the upper side in FIG. 3) of the electrode body 20 faces the second surface 12b, and the other curved region 20r (the lower side in FIG. 3) of the electrode body 20 faces the second surface 12c. The end face of the electrode body 20 is, here, a laminated surface of the positive electrode 22, the negative electrode 24, and the separator 23 and is an open surface. The first main surface 20a and the second main surface 20b are examples of the "wide surfaces of the electrode body".

[0027] As shown in FIG. 4, the positive electrode 22 has a long strip-shaped positive electrode current collector foil 22c (for example, an aluminum foil) and a positive electrode active material layer 22a fixed on 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 of the positive electrode 22 in the winding axis direction WD as needed. Note that, as the constituent materials of the positive electrode active material layer 22a and the protective layer, those used in this type of power storage device (in this embodiment, a lithium ion secondary battery) may be used without particular limitation.

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

[0029] The positive electrode active material layer non-formation portion 22d (that is, the portion where the positive electrode current collector foil 22c is exposed without the formation of the positive electrode active material layer 22a) and the negative electrode active material layer non-formation portion 24d (that is, the portion where the negative electrode current collector foil 24c is exposed without the formation of the negative electrode active material layer 24a) are formed so as to protrude outward from both ends in the winding axis direction of the electrode body 20 (that is, the sheet width direction orthogonal to the longitudinal direction). The positive electrode current collector 50 and the negative electrode active material layer non-formation portion 24d are joined to the positive electrode active material layer non-formation portion 22d and the negative electrode active material layer non-formation portion 24d, respectively.

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

[0031] The power storage device 100 disclosed herein is characterized by having a pressing member 70. FIG. 5 is a plan view of a sealing plate 14 (first pressing member 71) according to an embodiment as viewed from the inner surface side of the case 10. FIG. 6 is a longitudinal sectional view taken along line VI-VI in FIG. 5. FIG. 7 is a plan view of a case body 12 (second pressing member 72) according to an embodiment as viewed from the front (front side). FIG. 8 is a schematic view showing a state where an electrode body 20 is housed inside the case 10 according to an embodiment. For convenience of explanation, in FIG. 8, the electrode body 20 before being housed in the case 10 is shown by a virtual line.

[0032] The pressing member 70 is a pair of members that elastically compress each of the first main surface 20a and the second main surface 20b of the electrode body 20 in the thickness direction X of the electrode body 20. Here, as shown in FIG. 3, the pressing member 70 has a first pressing member 71 and a second pressing member 72. In the present embodiment, the pressing member 70 (first pressing member 71, second pressing member 72) is a part of the sealing plate 14 and the case 10.

[0033] The first pressing member 71 is arranged to face the first main surface 20a, which is one of the wide surfaces of the electrode body 20. The first pressing member 71 is formed at the center of the sealing plate 14 so as to protrude further toward the first main surface 20a side than the peripheral edge portion 14p of the sealing plate 14. The first pressing member 71 has a first convex portion 71a, a second convex portion 71b, and a first base portion 71f. As shown in FIGS. 5 and 6, here, among the first pressing members 71, the surface facing the first main surface 20a of the electrode body 20 (here, the rear side) has a plurality of first convex portions 71a, a plurality of second convex portions 71b, and a plurality of first base portions 71f. The first convex portion 71a, the second convex portion 71b, and the first base portion 71f are integrally formed here. As shown in FIG. 6, the first convex portion 71a protrudes from the first base portion 71f toward the first main surface 20a of the electrode body 20. In other words, the plurality of first convex portions 71a protrude from the first base portion 71f at the same height toward the first surface 12a of the case body 12. As shown in FIG. 6, the second convex portion 71b protrudes from the first convex portion 71a or the first base portion 71f toward the first main surface 20a of the electrode body 20. In other words, the plurality of second convex portions 71b protrude from the first convex portion 71a or the first base portion 71f at the same height toward the first surface 12a of the case body 12. As shown in FIG. 3, here, the first pressing member 71 is a part of the sealing plate 14. However, it is not limited thereto, and in some preferred embodiments, the first pressing member 71 may be a member independent of the sealing plate 14. In this case, the first convex portion 71a, the second convex portion 71b, and the first base portion 71f of the first pressing member 71 are arranged inside the case 10 so as to face one first main surface 20a of the electrode body 20.

[0034] The second pressing member 72 is arranged to face the second main surface 20b which is the other wide surface of the electrode body 20. As shown in FIG. 7, here, the second pressing member 72 has no convex portion and has only the second base portion 72f. The second pressing member 72 is formed at the center portion of the first surface 12a so as to protrude further toward the second main surface 20b side than the peripheral edge portion 12ap of the first surface 12a. However, it is not limited thereto, and a convex portion (for example, a comb shape or the like) may be provided. Further, it is not limited thereto, and in some preferred embodiments, the second pressing member 72 may be a member independent of the case 10. In this case, the second base portion 72f of the second pressing member 72 is arranged inside the case 10 so as to face the second main surface 20b of the electrode body 20. As shown in FIG. 3, here, the second pressing member 72 is a part of the first surface 12a. However, it is not limited thereto, and in some preferred embodiments, the second pressing member 72 may be a member independent of the first surface 12a. In this case, the second base portion 72f of the second pressing member 72 is arranged inside the case 10 so as to face one of the second main surfaces 20b of the electrode body 20.

[0035] As shown in FIG. 5, in the present embodiment, the plurality of first convex portions 71a are arranged substantially line symmetrically with respect to the center CL in the long side direction Y of the case 10. The plurality of first convex portions 71a are arranged in a so-called comb tooth shape (ridge shape) here. More specifically, the first convex portion 71a arranged at the most center CL extends toward both ends in the long side direction Y. In other words, it is formed in a T shape. Then, the other plurality of first convex portions 71a extend upward from the lower end of the sealing plate 14 in the vicinity of the center in the long side direction Y of the sealing plate 14. Thereafter, the first convex portion 71a extends toward the end in the long side direction Y while curving.

[0036] In the present embodiment, as shown in FIG. 5, the second convex portion 71b is arranged substantially line symmetrically with respect to the center CL in the long side direction Y of the case 10. Here, the second convex portion 71b is arranged near the center in the long side direction Y of the case 10. The second convex portion 71b is formed in a tapered shape here. The second convex portion 71b is integrally formed with the first convex portion 71a here. The second convex portion 71b is arranged to contact the first main surface 20a of the electrode body 20 prior to the first convex portion 71a.

[0037] The height of the second convex portion 71b can be appropriately changed according to the thickness, dimensional tolerance of the electrode body 20, and the intended load. For example, it is about 0.3 to 2 mm, and preferably about 0.5 to 1.5 mm. In this specification, the "height of the second convex portion 71b" indicates the difference in height between the first convex portion 71a and the second convex portion 71b in the short side direction X of the power storage device 100.

[0038] The pressing member 70 is arranged such that the first pressing member 71 abuts on the first main surface 20a of the electrode body 20, and the second pressing member 72 abuts on the second main surface 20b. Among them, the second convex portion 71b is configured to apply a load (press) from the thickness direction X of the electrode body 20 to the portion of the first main surface 20a of the electrode body 20 where they abut and the peripheral portion thereof. The shape, size, and arrangement of the first convex portion 71a and the second convex portion 71b can be appropriately determined according to, for example, the characteristics of the required power storage device and the electrode body 20.

[0039] The target load value Fx applied to the electrode body 20 by the pressing member 70 is determined by the thickness of the electrode body 20, the performance required for the power storage device 100, and the like. Then, the width of the pressing member 70 (here, the distance from the first pressing member 71 to the second pressing member 72 in the thickness direction X) is adjusted according to the target load value Fx applied to the electrode body 20. Note that the width of the pressing member 70 (here, the inner dimension L in the thickness direction of the case 10) is set to be smaller (narrower) than the initial thickness T of the electrode body 20 (see FIG. 8). By sandwiching the electrode body 20 in the thickness direction X with respect to the pressing member 70 adjusted to such a width, the electrode body 20 is elastically compressed in the thickness direction X. Here, in the manufacturing process of the power storage device 100, there is some variation in the initial thickness T of the electrode body 20. For example, when the initial thickness T of the electrode body 20 is small, the pressing load F applied to the electrode body 20 by the pressing member 70 becomes smaller than the target load value Fx. On the other hand, when the initial thickness T of the electrode body 20 is large, the pressing load F applied to the electrode body 20 by the pressing member 70 becomes larger than the target load value Fx. That is, due to the variation in the initial thickness T of the electrode body 20, there is a variation in the actual pressing load F applied to the electrode body 20. The inventor intends to suppress the variation in the actual pressing load F applied to the electrode body 20 caused by the variation in the initial thickness T of the electrode body 20. Here, the "inner dimension L of the case 10" in this specification indicates the shortest distance from the second convex portion 71b of the first pressing member 71 to the second base portion 72f of the second pressing member 72 in the X direction. Also, the "initial thickness T of the electrode body 20" in this specification indicates 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.

[0040] Hereinafter, the pressing member 70 according to the present embodiment will be described with reference to FIG. 9. FIG. 9 is a graph for explaining the relationship between the thickness displacement of the electrode body and the change in the pressing load in the power storage device according to one embodiment. The graph shown in FIG. 9 can be obtained by designing and analyzing an evaluation sample of the power storage device using CAE (computor aided engineering) analysis. Hereinafter, specific test examples regarding FIG. 9 will be described for the technology disclosed herein, but such test examples are not intended to limit the technology disclosed herein.

[0041] <1. Design of Evaluation Sample> As an evaluation sample of the power storage device according to this example, a case body, a sealing plate (pressing member), and an electrode body having the shapes shown in FIGS. 1, 4, 5 to 7 were designed. Here, the material of the case was aluminum, and the plate thickness of the aluminum was 3 mm. Further, the pressing member was formed on the sealing plate, the height of the first convex portion was 3 mm, and the height of the second convex portion was 1 mm. The initial value of the thickness of the electrode body was 8 mm.

[0042] <2. Evaluation of Sample> Regarding the above-described evaluation sample, as shown in FIG. 3, the electrode body was housed inside the case, and the sealing plate and the case body were joined. Here, except for the case (pressing member) and the electrode body, nothing was designed. In the power storage device in such a state, the thickness of the electrode body was increased from the initial value without changing the conditions of the case, and the thickness displacement (mm) and the load (kN) acting on the electrode body were measured. Here, the load acting on the electrode body indicates the pressing load. The measurement results were plotted on orthogonal coordinates with the load (kN) on the vertical axis and the thickness displacement (mm) on the horizontal axis. The results are shown in FIG. 9.

[0043] <3. Spring Constant> Note that the first spring constant and the second spring constant of the pressing member 70 can be calculated based on the following formula (i) from the measurement results obtained by the above-described CAE analysis. Spring constant (kN / mm) = Δ Load displacement (kN) / Δ Electrode body thickness displacement (mm) ··· (i)

[0044] Among the pressing members 70 of the power storage device 100 according to the present embodiment, the first pressing member 71 is formed so as to elastically deform at the reference pressing load Fa. Specifically, when the electrode body 20 is pressed in the thickness direction by the pressing member 70, the second convex portion 71b applies a pressing load F to the contacted portion of the first main surface 20a of the electrode body 20 and its peripheral portion. When the pressing load F applied to the electrode body 20 from the pressing member 70 reaches the reference pressing load Fa, the periphery of the second convex portion 71b (a part of the first convex portion 71a) elastically deforms so as to bend. Such a reference pressing load Fa is set to a value smaller than the load target value Fx. The spring constant of the pressing member 70 is configured to change before and after the first pressing member 71 elastically deforms. Thereafter, until the second reference pressing load Fb is reached and the first base portion 71f deforms, the pressing load F changes with the spring constant after the elastic deformation of the first pressing member 71. Here, the pressing load F (0 ≦ F ≦ Fa) before the second convex portion 71b of the first pressing member 71 elastically deforms is defined as the first load range RF1, and the pressing load F (Fa < F ≦ Fb) after the second convex portion 71b of the first pressing member 71 elastically deforms is defined as the second load range RF2. And the spring constant of the pressing member 70 in the first load range RF1 is defined as the first spring constant, and the spring constant of the pressing member 70 in the second load range RF2 is defined as the second spring constant. At this time, the second spring constant of the pressing member 70 according to the present embodiment is configured to be smaller than the first spring constant. In other words, the spring constant of the pressing member 70 becomes smaller at the reference pressing load Fa (the variation amount of the pressing load F with respect to the thickness displacement of the electrode body 20 becomes smaller).

[0045] In the first load range RF1, the first spring constant is larger than the second spring constant. In other words, in the first load range RF1, the displacement of the pressing load F with respect to the thickness displacement of the electrode body 20 is large. Therefore, a pressing load F of a sufficient magnitude can be applied to the electrode body 20 in the thickness direction. However, when the electrode body is pressed using a configuration in which the spring constant of the pressing member is only the first spring constant as in a conventional power storage device, the variation in the pressing load F becomes large with respect to the variation in the electrode body thickness.

[0046] On the one hand, in the present embodiment, the spring constant of the pressing member 70 is configured to change to a second spring constant after the first pressing member 71 is elastically deformed. In the second load range RF2, the second spring constant is smaller than the first spring constant. In other words, in the second load range RF2, the displacement of the pressing load F with respect to the thickness displacement of the electrode body 20 is small. Here, by setting the load target value Fx in the second load range RF2, even when there is a variation in the initial thickness T of the electrode body 20, the variation in the pressing load F is alleviated. In other words, the error of the pressing load F with respect to the load target value Fx for each power storage device 100 can be reduced. Therefore, it is possible to provide a power storage device 100 in which the variation in the internal resistance for each power storage device 100 is reduced.

[0047] The first spring constant of the pressing member 70 can be appropriately adjusted according to the thickness and size of the electrode body 20. From the viewpoint of applying a pressing load F of sufficient magnitude to the electrode body 20 and fixing the position of the electrode body, the first spring constant of the pressing member 70 can be, for example, 0.2 kN / mm or more, preferably 0.5 kN / mm or more. The upper limit of the first spring constant of the pressing member 70 is not particularly limited, but can be, for example, 4 kN / mm or less.

[0048] The second spring constant of the pressing member 70 can be appropriately adjusted according to the thickness and size of the electrode body 20. From the viewpoint of applying a pressing load F of sufficient magnitude to the electrode body 20 and alleviating the variation in the pressing load F with respect to the variation in the initial thickness T of the electrode body 20, the second spring constant of the pressing member 70 can be, for example, 0.01 kN / mm or more, preferably 0.05 kN / mm or more. The upper limit of the second spring constant of the pressing member 70 only needs to be smaller than the first spring constant and is not particularly limited, but can be, for example, 0.5 kN / mm or less.

[0049] The target load value Fx applied to the electrode body 20 by the pressing member 70 can be appropriately adjusted according to the thickness and size of the electrode body 20. For example, it is about 0.5 to 15 kN, preferably about 1.5 to 2.5 kN. Similarly, the reference pressing load Fa and the second reference pressing load Fb can be appropriately adjusted according to the target load value Fx. In other words, the reference pressing load Fa and the second reference pressing load Fb can be appropriately set so that the target load value Fx falls within the range of the second load range RF2.

[0050] The thickness and material of the pressing member 70 can adopt a thickness and material that allows the pressing member 70 to deform at any reference pressing load Fa. As the material of the pressing member 70, for example, metals such as aluminum, aluminum alloy, and SUS can be used. Here, as shown in FIG. 6, the thicknesses of the first convex portion 71a, the second convex portion 71b, and the first base portion 71f are the same. However, it is not limited to this, and at any reference pressing load Fa, the thicknesses of the first convex portion 71a, the second convex portion 71b, and the first base portion 71f of the first pressing member 71 may be made different so that the pressing member 70 elastically deforms.

[0051] In some preferred embodiments, the power storage device 100 includes a case body 12 and a wide rectangular sealing plate 14 as 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. In the case 10 having such a configuration, the first pressing member 71 and the second pressing member 72 are configured as a part of the case 10. Also, as shown in FIG. 8, when the sealing plate 14 is fitted into the case body 12, the inner dimension of the case 10 in the thickness direction X of the power storage device 100 is designed to be smaller than the initial thickness T of the electrode body 20. Thereby, the electrode body 20 is accommodated inside the case body 12, and while the sealing plate 14 is pushed into the opening 12h of the case body (in other words, while the sealing plate 14 is pushed in the direction of the first surface 12a), the periphery of the sealing plate 14 is welded, so that the electrode body 20 is constrained by the second pressing member 72 of the case body 12 and the first pressing member 71 of the sealing plate 14. As a result, the number of parts can be reduced, and since no intervening member is required, miniaturization of the power storage device is achieved.

[0052] The power storage device 100 can be used for various applications, but typically, it 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 vehicles (PHEVs), hybrid vehicles (HEVs), battery electric vehicles (BEVs), etc.

[0053] From another aspect of the technology disclosed herein, a stack 150 formed by combining a plurality of the above-described power storage devices 100 is provided. FIG. 10 is a perspective view schematically showing a stack 150 according to an embodiment. In this embodiment, for example, as shown in FIG. 10, a stack 150 can be provided in which a plurality of power storage devices 100 are electrically connected to each other via a bus bar 90. In this case, the electrical connection between the plurality of power storage devices 100 can be made by bridging, for example, 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 is made of a conductive metal such as aluminum, an aluminum alloy, nickel, stainless steel, etc. The bus bar 90 and the positive electrode terminal 30 and the negative electrode terminal 40 can be electrically connected by welding such as laser welding. Further, for the connection of the bus bar 90, external connection terminals (not shown) may be further provided on the positive electrode terminal 30 and the negative electrode terminal 40. Since each of the power storage devices 100 used in the stack 150 is provided with a first pressing member 71 and a second pressing member 72 in each case 10, a restraining jig is not required. Thereby, the provision of a miniaturized stack 150 is realized. Further, for each power storage device 100, a load corresponding to the thickness of the electrode body 20 is applied by the pressing member 70. For this reason, it is possible to provide a stack 150 with suppressed resistance variation.

[0054] Some embodiments of the technology disclosed herein have been described above, but 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 general knowledge in the art. The technology described in the claims includes various modifications and changes to the above-exemplified embodiments. For example, it is possible to replace a part of the above-described embodiments with other modified forms, and it is also possible to add other modified forms to the above-described embodiments. Also, if the technical features are not described as essential, they can be appropriately deleted.

[0055] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A power 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 wide surfaces, and having a pair of pressing members that face the electrode body and elastically compress each of the pair of wide surfaces of the electrode body in the thickness direction of the electrode body. Here, at least one of the pair of pressing members has a first convex portion that protrudes toward the wide surface of the electrode body and a second convex portion that further protrudes toward the wide surface of the electrode body from the first convex portion. The pressing member is formed to elastically deform at a reference pressing load Fa. When the spring constant of the pressing member before the elastic deformation is the first spring constant and the spring constant of the pressing member after the elastic deformation is the second spring constant, the second spring constant is smaller than the first spring constant. Power storage device. Item 2: The power storage device according to Item 1, further comprising a hexahedral case that houses the electrode body, the case including a wide rectangular first surface and an opening facing the first surface, a pair of second surfaces extending from the peripheral edge on the long side of the first surface toward the opening, and a pair of third surfaces extending from the peripheral edge on the short side of the first surface toward the opening. The case body has a sealing plate that seals the opening and is a wide rectangular sealing plate facing the first surface. Here, the pressing member is a part of the sealing plate or the first surface. Item 3: A stack comprising a plurality of the power storage devices according to Item 1 or 2.

Explanation of Signs

[0056] 10 Case 12 Case body 12a First surface 12b, 12c Second surface 12d, 12e Third surface 12h Opening 14 Sealing plate 18, 19 Through hole 20 Electrode body 20a First main surface 20b Second main surface 22 Positive electrode 23 Separator 24 Negative electrode 30 Positive electrode terminal 40 Negative electrode terminal 70 Pressing member 71 First pressing member 71a First convex portion 71b Second convex portion 71f First base portion 72 Second pressing member 72f Second base portion 90 Bus bar 92 Gasket 93 Internal insulating member 100 Power storage device 150 Stack

Claims

1. A power 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 wide surfaces, a pair of pressing members facing the electrode body and elastically compressing each of the pair of wide surfaces of the electrode body in the thickness direction of the electrode body, wherein at least one of the pair of pressing members has a first convex portion protruding toward the wide surface of the electrode body and a second convex portion protruding further toward the wide surface of the electrode body than the first convex portion, the pressing member is formed to elastically deform at a reference pressing load Fa, when the spring constant of the pressing member before the elastic deformation is defined as a first spring constant and the spring constant of the pressing member after the elastic deformation is defined as a second spring constant, the second spring constant is smaller than the first spring constant, A power storage device.

2. further comprising a hexahedral case for housing the electrode body, the case being a case body having a wide rectangular first surface, an opening facing the first surface, a pair of second surfaces extending from the peripheral edge on the long side of the first surface toward the opening, and a pair of third surfaces extending from the peripheral edge on the short side of the first surface toward the opening, and a wide rectangular sealing plate closing the opening and facing the first surface, wherein the pressing member is a part of the sealing plate or the first surface, The power storage device according to claim 1.

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

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