Electricity storage device

Abstract

To provide a power storage device in which occurrence of metal deposition is suppressed.SOLUTION: The energy storage apparatus includes electrode-assembly side 20a, electrode-assembly side 20b, and electrode-assembly side 20c. The electrode-assembly 20a is disposed between the electrode-assembly 20b and the electrode-assembly 20c. In the vertical direction Z, the length 1f of the first flat outer surface region L1 of the electrode-assembly 20a is smaller than the length L2 of the second flat outer surface region 2f of the electrode-assembly 20b, and is smaller than the length 20c of the third flat outer surface region 3f of the electrode-assembly. L3. The upper-end 1u of the first flat outer surface region 1f is located below the upper-end 2u of the second flat outer surface region 2f and below the upper-end 3u of the third flat outer surface region 3f. A lower end 1f of the first flat outer surface region 1d is located above a lower end 2f of the second flat outer surface region 2d and above a lower end 3f of the third flat outer surface region 3d.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an electricity storage device. [Background technology]

[0002] BACKGROUND ART Conventionally, from the viewpoint of increasing capacity and the like, an electricity storage device including a plurality of electrode bodies arranged along a predetermined arrangement direction is known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-004633 Summary of the Invention [Problem to be solved by the invention]

[0004] The electrode bodies may have individual size differences (variations within an acceptable range) during manufacturing. According to the study by the present inventors, it has been newly discovered that in an electricity storage device including three or more electrode bodies in one battery case, if the heights of the electrode bodies are different, metal deposition (Li deposition in lithium ion secondary batteries) is more likely to occur, particularly in the electrode body located in the middle of the arrangement direction.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide an electricity storage device that includes three or more electrode assemblies and in which the occurrence of metal deposition is suppressed. [Means for solving the problem]

[0006] The present invention provides an electricity storage device comprising an electrode assembly including a first electrode assembly, a second electrode assembly, and a third electrode assembly, and a rectangular battery case that houses the electrode assembly. The first electrode assembly, the second electrode assembly, and the third electrode assembly are each flat wound electrode assemblies in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. The first electrode assembly is disposed between the second electrode assembly and the third electrode assembly. The first electrode assembly has a first flat outer surface region and a pair of first curved outer surface regions located at both ends of the first flat outer surface region. The second electrode assembly has a second flat outer surface region and a pair of second curved outer surface regions located at both ends of the second flat outer surface region. The third electrode assembly has a third flat outer surface region and a pair of third curved outer surface regions located at both ends of the third flat outer surface region. The first electrode body, the second electrode body, and the third electrode body are arranged so that the first flat outer surface region is disposed between the second flat outer surface region and the third flat outer surface region, and the first flat outer surface region, the second flat outer surface region, and the third flat outer surface region are stacked. A length L1 of the first flat outer surface region in a direction connecting the pair of first curved outer surface regions is shorter than a length L2 of the second flat outer surface region in a direction connecting the pair of second curved outer surface regions, and is shorter than a length L3 of the third flat outer surface region in a direction connecting the pair of third curved outer surface regions. One end of the first flat outer surface region in a direction connecting the pair of first curved outer surface regions is located closer to the center than one end of the second flat outer surface region in a direction connecting the pair of second curved outer surface regions, and is also located closer to the center than one end of the third flat outer surface region in a direction connecting the pair of third curved outer surface regions. The other end of the first flat outer surface region in the direction connecting the pair of first curved outer surface regions is located closer to the center than the other end of the second flat outer surface region in the direction connecting the pair of second curved outer surface regions, and is located closer to the center than the other end of the third flat outer surface region in the direction connecting the pair of third curved outer surface regions.

[0007] According to the above configuration, the occurrence of metal deposition (Li deposition in lithium ion secondary batteries) can be suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view schematically illustrating an electricity storage device according to one 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 cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a perspective view that schematically shows an electrode assembly attached to a sealing plate. [Figure 5] FIG. 5 is a perspective view schematically showing a second electrode body according to one embodiment. [Figure 6] FIG. 6 is a schematic diagram showing the configuration of a second electrode body according to one embodiment. [Figure 7] FIG. 7 is a side view schematically showing the electrode assembly of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, some preferred embodiments of the technology disclosed herein will be described with reference to the drawings. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein (for example, the general configuration and manufacturing process of an electricity storage device that do not characterize the technology disclosed herein) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field.

[0010] In this specification, the expression "A to B" indicating a range includes not only the meaning of A or more and B or less, but also the meanings of "greater than A" and "smaller than B." Furthermore, in this specification, terms such as "first," "second," and "third" are used to distinguish between configurations with similar names, and do not represent the order or importance of the configurations.

[0011] In this specification, the term "electrical energy storage device" refers to a general device that can be repeatedly charged and discharged by the movement of charge carriers between a positive electrode and a negative electrode. The concept of an electric energy storage device encompasses not only secondary batteries such as lithium-ion secondary batteries, but also capacitors that utilize chemical reactions, such as lithium-ion capacitors and pseudo-capacitor capacitors.

[0012] <Electricity storage device 100> FIG. 1 is a perspective view of the electricity storage device 100. 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 F, Rr, L, R, U, and D in the drawings represent front, rear, left, right, top, and bottom, and the symbols X, Y, and Z in the drawings represent the short side direction of the electricity storage device 100, the long side direction perpendicular to the short side direction, and the up-down direction perpendicular to the short side direction and the long side direction, respectively. 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.

[0013] As shown in Fig. 2, the electricity storage device 100 includes a battery case 10 and an electrode assembly 20. Here, the electricity storage device 100 further includes a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collector 50, a negative electrode current collector 60, and a non-aqueous electrolyte (not shown). Here, the electricity storage device 100 is a lithium ion secondary battery. The electricity storage device 100 is preferably a lithium ion secondary battery.

[0014] The battery case 10 is a housing that houses the electrode assembly 20. Here, it is a housing that houses the electrode assembly 20 and a nonaqueous electrolyte. As shown in FIG. 1, the battery case 10 has a flat, bottomed, rectangular parallelepiped (rectangular) outer shape. The material of the battery case 10 may be the same as that conventionally used, and is not particularly limited. The battery case 10 is preferably made of metal, and more preferably made of, for example, aluminum, an aluminum alloy, iron, an iron alloy, or the like. As shown in FIG. 2, the battery case 10 here includes a case body 12 having an opening 12h and a sealing plate (lid) 14 that closes the opening 12h.

[0015] As shown in Fig. 1, the case body 12 has a substantially rectangular bottom surface 12a having long and short sides, a pair of long side surfaces 12b extending from the long side of the bottom surface 12a and facing each other, and a pair of short side surfaces 12c extending from the short side of the bottom surface 12a and facing each other. The bottom surface 12a faces the opening 12h. The area of ​​the long side surfaces 12b is larger than the area of ​​the short side surfaces 12c. In this specification, the term "substantially rectangular" is intended to encompass not only a perfect rectangular shape (rectangular shape), but also shapes in which the corners connecting the long and short sides of the rectangle are rounded or have notches at the corners.

[0016] As shown in FIG. 1, the sealing plate 14 is a plate-like member extending along the XY plane. The sealing plate 14 has a substantially rectangular shape in plan view. As shown in FIG. 2, the sealing plate 14 is attached to the case body 12 so as to close the opening 12h of the case body 12. The sealing plate 14 faces the bottom surface 12a of the case body 12. The battery case 10 is integrated by joining (for example, welding) the sealing plate 14 to the periphery of the opening 12h of the case body 12. The battery case 10 is hermetically sealed (sealed).

[0017] As shown in FIG. 2, the sealing plate 14 is provided with a liquid inlet 15, a gas release valve 17, and two terminal holes 18 and 19. The liquid inlet 15 is for injecting nonaqueous electrolyte after the sealing plate 14 is assembled to the case body 12. The sealing plate 14 preferably has the liquid inlet 15. The liquid inlet 15 is sealed with a sealing member 16. The gas release valve 17 is configured to break when the pressure inside the battery case 10 reaches or exceeds a predetermined value, thereby releasing gas inside the battery case 10 to the outside. The terminal holes 18 and 19 are formed at both ends of the sealing plate 14 in the long side direction Y (the left and right ends in FIG. 2). The terminal holes 18 and 19 penetrate the sealing plate 14 in the thickness direction (the vertical direction Z). The terminal pull-out holes 18, 19 have inner diameters large enough to allow the positive electrode terminal 30 and the negative electrode terminal 40 to be inserted therethrough before being attached to the sealing plate 14 (before being crimped).

[0018] The positive electrode terminal 30 and the negative electrode terminal 40 are each fixed to the sealing plate 14 of the battery case 10. The positive electrode terminal 30 is disposed on one side of the sealing plate 14 in the long side direction Y (the left side in FIGS. 1 and 2). The negative electrode terminal 40 is disposed on the other side of the sealing plate 14 in the long side direction Y (the right side in FIGS. 1 and 2). As shown in FIG. 2, the positive electrode terminal 30 extends from the inside to the outside of the sealing plate 14 through the terminal lead-out hole 18. The negative electrode terminal 40 extends from the inside to the outside of the sealing plate 14 through the terminal lead-out hole 19. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are crimped to the peripheral portions of the sealing plate 14 surrounding the terminal lead-out holes 18 and 19 by crimping. The positive electrode terminal 30 and the negative electrode terminal 40 have crimping portions 30c, 40c formed at their ends on the case body 12 side (lower ends in FIG. 2).

[0019] As shown in FIG. 2, the positive electrode terminal 30 is electrically connected to the positive electrode 22 (see FIG. 6, specifically, the positive electrode tab group 23) of the electrode assembly 20 inside the battery case 10 via a positive electrode current collector 50. The positive electrode terminal 30 is insulated from the sealing plate 14 by a positive electrode insulating member 70 and a gasket 90. The positive electrode terminal 30 is preferably made of metal, and more preferably made of, for example, aluminum or an aluminum alloy. The negative electrode terminal 40 is electrically connected to the negative electrode 24 (see FIG. 6, specifically, the negative electrode tab group 25) of the electrode assembly 20 inside the battery case 10 via a negative electrode current collector 60. The negative electrode terminal 40 is insulated from the sealing plate 14 by a negative electrode insulating member 80 and a gasket 90. The negative electrode terminal 40 is preferably made of metal, and more preferably made of, for example, copper or a copper alloy.

[0020] As shown in FIGS. 1 and 2 , a plate-shaped positive electrode external conductive member 32 and a plate-shaped negative electrode external conductive member 42 are attached to the outer surface of the sealing plate 14. The positive electrode external conductive member 32 and the plate-shaped negative electrode external conductive member 42 are members to which conductive members such as bus bars are attached when electrically connecting multiple electricity storage devices 100 to each other. The positive electrode external conductive member 32 is electrically connected to the positive electrode terminal 30. The negative electrode external conductive member 42 is electrically connected to the negative electrode terminal 40. The positive electrode external conductive member 32 and the plate-shaped negative electrode external conductive member 42 are insulated from the sealing plate 14 by an external resin member 92. The positive electrode external conductive member 32 and the plate-shaped negative electrode external conductive member 42 are preferably made of metal, more preferably aluminum or an aluminum alloy. However, the positive electrode external conductive member 32 and the plate-shaped negative electrode external conductive member 42 are not essential and may be omitted in other embodiments.

[0021] As shown in FIG. 2, the electrode assembly group 20 is housed inside the battery case 10 (more specifically, inside the case main body 12). The electrode assembly group 20 of this embodiment includes three or more electrode bodies. FIG. 4 is a perspective view that schematically shows the electrode assembly group 20 attached to the sealing plate 14. As shown in FIGS. 3 and 4, the electrode assembly group 20 here has three electrode bodies, namely, a first electrode body 20b, a second electrode body 20a, and a third electrode body 20c. However, the number N of electrode bodies arranged inside one battery case 10 is not particularly limited and may be four or more. Note that, hereinafter, when there is no need to distinguish between the three electrode bodies, they may be simply referred to as "electrode bodies 20a, 20b, 20c."

[0022] The electrode bodies 20a, 20b, and 20c are arranged along the short side direction X (arrangement direction). In the short side direction X (arrangement direction), the first electrode body 20b is arranged between the second electrode body 20a and the third electrode body 20c. The second electrode body 20a and the third electrode body 20c each face a pair of long side surfaces 12b (side surfaces with larger areas) of the case body 12. When the number N of electrode bodies arranged inside one battery case 10 is four or more, another electrode body may be interposed between the first electrode body 20b and the second electrode body 20a and / or between the first electrode body 20b and the third electrode body 20c.

[0023] As will be described in more detail below, the electrode assemblies 20a, 20b, and 20c are electrically connected in parallel here. The electrode assembly 20 may be placed inside the battery case 10 while covered with an insulating electrode assembly holder. In other words, an electrode assembly holder may be interposed between the electrode assembly 20 and the battery case 10 (more specifically, the case body 12). The configuration of the electrode assemblies 20a, 20b, and 20c is not particularly limited and may be the same as conventional ones.

[0024] FIG. 5 is a perspective view schematically illustrating the second electrode body 20a. FIG. 6 is a schematic diagram illustrating the configuration of the second electrode body 20a. Note that, although the second electrode body 20a will be described in detail below in some cases, the first electrode body 20b and the third electrode body 20c may also have a similar configuration. As can be seen from FIG. 6, the electrode bodies 20a, 20b, and 20c are wound electrode bodies in which a positive electrode 22 and a negative electrode 24 are wound with a separator 26 interposed therebetween. The electrode bodies 20a, 20b, and 20c are configured by stacking a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 in a state of being insulated via the strip-shaped separator 26, and winding the stack around a winding axis WL.

[0025] Although not particularly limited, the number of windings (number of turns) of the electrode bodies 20a, 20b, 20c is preferably 20 turns or more, more preferably 30 turns or more, and can be, for example, 150 turns or less, or 100 turns or less.

[0026] The electrode bodies 20a, 20b, and 20c are disposed inside the battery case 10 so that the winding axis WL (see FIG. 6) is aligned with the long side direction Y. The direction of the winding axis WL here coincides with the long side direction Y. The electrode bodies 20a, 20b, and 20c are disposed inside the battery case 10 so that the winding axis WL is parallel to the bottom surface 12a of the case body 12 and perpendicular to the short side surface 12c of the case body 12.

[0027] The positive electrode 22 is not particularly limited and may be the same as a conventional positive electrode. As shown in FIG. 6, the positive electrode 22 includes a positive electrode current collector 22c, a positive electrode active material layer 22a, and a positive electrode protective layer 22p adhered to at least one surface of the positive electrode current collector 22c. However, the positive electrode protective layer 22p is not essential and may be omitted in other embodiments. The positive electrode current collector 22c is strip-shaped here. The positive electrode current collector 22c is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. Here, the positive electrode current collector 22c is a metal foil, specifically, an aluminum foil.

[0028] A plurality of positive electrode tabs 22t are provided at one end (the left end in FIG. 6) in the long side direction Y (the direction of the winding axis WL) of the positive electrode current collector 22c. Each of the plurality of positive electrode tabs 22t is convex and protrudes toward one side in the long side direction Y (the left side in FIG. 6). The plurality of positive electrode tabs 22t extend further in the long side direction Y than the separator 26. The plurality of positive electrode tabs 22t are provided at intervals (intermittently) along the longitudinal direction of the positive electrode 22. Here, the positive electrode tabs 22t are part of the positive electrode current collector 22c and are made of metal foil (aluminum foil).

[0029] As shown in FIG. 3, the positive electrode tabs 22t are stacked at one end in the long side direction Y (the left end in FIG. 3) to form a positive electrode tab group 23. The positive electrode tabs 22t are stacked and bent and curved so that their outer ends are aligned. A positive electrode second current collecting member 52 (described later) of the positive electrode current collecting part 50 is attached (more specifically, joined) to the positive electrode tab group 23. The positive electrode tabs 22t are connected to the positive electrode second current collecting member 52. The positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collecting part 50.

[0030] As shown in Fig. 6, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the strip-shaped positive electrode current collector 22c. The positive electrode active material layer 22a contains a positive electrode active material (e.g., a lithium transition metal composite oxide such as a lithium nickel cobalt manganese-containing composite oxide) that can reversibly store and release charge carriers. The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, such as a conductive material, a binder, and various additives. For example, a carbon material such as acetylene black (AB) can be used as the conductive material. For example, polyvinylidene fluoride (PVdF) can be used as the binder.

[0031] Although not particularly limited, in a high-capacity electricity storage device 100 used in a vehicle or the like, the length Lc (average value, excluding the portion formed in the positive electrode tab 22t) in the long side direction Y (winding axis WL direction) of the positive electrode active material layer 22a is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 250 mm or more, as shown in Fig. 6. The length Lc is preferably the same as or shorter than the length La in the long side direction Y of the negative electrode active material layer 24a described below.

[0032] As shown in FIG. 6, the positive electrode protective layer 22p is provided between the positive electrode current collector 22c and the positive electrode active material layer 22a in the long side direction Y. Here, the positive electrode protective layer 22p is provided at one end of the positive electrode current collector 22c in the long side direction Y (the left end in FIG. 6). The positive electrode protective layer 22p is provided in a strip shape along the positive electrode active material layer 22a. The positive electrode protective layer 22p contains an inorganic filler (e.g., alumina). The positive electrode protective layer 22p may contain optional components other than the inorganic filler, such as a conductive material, a binder, various additive components, etc. The conductive material and binder may be the same as those exemplified as those that may be contained in the positive electrode active material layer 22a.

[0033] The negative electrode 24 is not particularly limited and may be the same as a conventional negative electrode. As shown in FIG. 6, the negative electrode 24 includes a negative electrode current collector 24c and a negative electrode active material layer 24a fixed to at least one surface of the negative electrode current collector 24c. The negative electrode current collector 24c is strip-shaped. The negative electrode current collector 24c is made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. The negative electrode current collector 24c preferably contains copper or a copper alloy. The negative electrode current collector 24c is a metal foil, specifically a copper foil.

[0034] A plurality of negative electrode tabs 24t are provided at one end (the right end in FIG. 6) in the long side direction Y (the direction of the winding axis WL) of the negative electrode current collector 24c. Each of the plurality of negative electrode tabs 24t is convex and protrudes toward one side in the long side direction Y (the right side in FIG. 6). The plurality of negative electrode tabs 24t extend further in the long side direction Y than the separator 26. The plurality of negative electrode tabs 24t are provided at intervals (intermittently) along the longitudinal direction of the negative electrode 24. Here, the negative electrode tabs 24t are part of the negative electrode current collector 24c and are made of metal foil (copper foil).

[0035] As shown in FIG. 3, the negative electrode tabs 24t are stacked at one end in the long side direction Y (the right end in FIG. 3) to form a negative electrode tab group 25. The negative electrode tabs 24t are stacked and bent so that their outer ends are aligned. A negative electrode second current collecting member 62 (described later) of a negative electrode current collecting part 60 is attached (more specifically, joined) to the negative electrode tab group 25. The negative electrode tabs 24t are connected to the negative electrode second current collecting member 62. The negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collecting part 60.

[0036] As shown in Fig. 6, the negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of a strip-shaped negative electrode current collector 24c. The negative electrode active material layer 24a contains a negative electrode active material (e.g., a carbon material such as graphite) that can reversibly store and release charge carriers. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as a binder, a dispersant, and various additives. For example, rubbers such as styrene butadiene rubber (SBR) can be used as the binder. For example, celluloses such as carboxymethyl cellulose (CMC) can be used as the dispersant.

[0037] 6, the length La (average value, excluding the portion formed on the negative electrode tab 24t) of the negative electrode active material layer 24a in the long side direction Y (winding axis WL direction) is typically the same as or longer than the length Lc of the positive electrode active material layer 22a in the long side direction Y. Although not particularly limited, from the viewpoint of achieving high capacity, the length La of the negative electrode active material layer 24a is preferably 200 mm or more, and more preferably 250 mm or more. The length La may be, for example, 1000 mm or less, or 500 mm or less.

[0038] As shown in Fig. 6, the separator 26 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. Here, two separators 26 are used for one electrode body 20a. However, in other embodiments, a single separator 26 may be used. The length Ls of the separator 26 in the long side direction Y (winding axis WL direction) is typically the same as or longer than the length La of the negative electrode active material layer 24a in the long side direction Y.

[0039] Separator 26 is not particularly limited and may be the same as conventional separators. Separator 26 is preferably a porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP). The porous sheet may have a single layer structure or a two or more layer structure, for example a three-layer structure. Separator 26 may have a functional layer (for example, an adhesive layer or a heat-resistant layer) on the surface of the porous sheet. The adhesive layer is a layer containing a resin binder. The heat-resistant layer (HRL) is a layer containing a resin binder and an inorganic filler. The adhesive layer may also serve as a heat-resistant layer.

[0040] As shown in FIG. 4, the electrode bodies 20a, 20b, and 20c each have a flat outer shape. FIG. 7 is a side view schematically showing the electrode bodies 20a, 20b, and 20c (electrode body group 20). Note that although the electrode bodies 20a, 20b, and 20c are shown spaced apart in FIG. 7, they may actually be in contact with each other in the short side direction X (arrangement direction). Each of the electrode bodies 20a, 20b, and 20c has a flat outer surface region and a pair of curved outer surface regions. Specifically, as shown in FIG. 7, the first electrode body 20b has a first flat outer surface region 1f and a pair of first curved outer surface regions 1r located at both ends of the first flat outer surface region 1f. The second electrode body 20a has a second flat outer surface region 2f and a pair of second curved outer surface regions 2r located at both ends of the second flat outer surface region 2f. The third electrode body 20c has a third flat outer surface region 3f and a pair of third curved outer surface regions 3r disposed on both ends of the third flat outer surface region 3f.

[0041] The first flat outer surface region 1f, the second flat outer surface region 2f, and the third flat outer surface region 3f each have a flat outer surface (YZ plane in FIG. 4). In this embodiment, the first flat outer surface region 1f, the second flat outer surface region 2f, and the third flat outer surface region 3f extend along the long side surfaces 12b of the case body 12. The second flat outer surface region 2f and the third flat outer surface region 3f face a pair of long side surfaces 12b of the case body 12. In the first flat outer surface region 1f, the second flat outer surface region 2f, and the third flat outer surface region 3f, the positive electrode 22 (see FIG. 6) and the negative electrode 24 (see FIG. 6) are stacked in the short side direction X (arrangement direction). The short side direction X is also the stacking direction of the positive electrode 22 and the negative electrode 24. In this specification, the term "flat outer surface" is not limited to a completely flat surface, but also includes cases where, when viewed microscopically, there are slight steps, curves, recesses, protrusions, etc.

[0042] The pair of first curved outer surface regions 1r, the pair of second curved outer surface regions 2r, and the pair of third curved outer surface regions 3r each have a curved outer surface. Of the pair of first curved outer surface regions 1r, the pair of second curved outer surface regions 2r, and the pair of third curved outer surface regions 3r, one (lower) curved outer surface region faces the bottom surface 12a of the case body 12, and the other (upper) curved outer surface region faces the sealing plate 14 of the case body 12. As in this embodiment, the electrode bodies 20a, 20b, and 20c are preferably arranged inside the battery case 10 with the pair of curved outer surface regions oriented along the bottom surface 12a and the sealing plate 14 and the flat outer surface region oriented along the long side surface 12b.

[0043] The flat outer surface regions of the electrode assemblies 20a, 20b, and 20c adjacent to each other in the short side direction X (arrangement direction) are directly opposed to each other. The electrode assemblies 20a, 20b, and 20c are arranged in the short side direction X (arrangement direction) such that the first flat outer surface region 1f is disposed between the second flat outer surface region 2f and the third flat outer surface region 3f, and the first flat outer surface region 1f, the second flat outer surface region 2f, and the third flat outer surface region 3f are stacked.

[0044] The electrode assemblies 20a, 20b, and 20c may have individual size variations (within an acceptable range) during manufacturing. The power storage device 100 may be used with a load applied in the short-side direction X (the arrangement direction of the electrode assemblies 20a, 20b, and 20c, the stacking direction of the positive electrode 22 and the negative electrode 24). In this case, if the heights of the electrode assemblies 20a, 20b, and 20c (specifically, the lengths of the flat outer surface regions in the vertical direction Z) are different, uneven restraint may occur in the flat outer surface regions in the vertical direction Z. For example, in the first flat outer surface region 1f disposed between the second flat outer surface region 2f and the third flat outer surface region 3f, the application of a restraint load to the end in the vertical direction Z may be difficult, resulting in the end becoming an unrestrained portion. As a result, the distance between the positive electrode 22 and the negative electrode 24 (the inter-electrode distance) becomes locally large in the unrestrained portion, making metal deposition (here, Li deposition) more likely to occur.

[0045] Therefore, in the technology disclosed herein, as shown in FIG. 7, the electrode bodies 20a, 20b, and 20c have the following three characteristics: (1) The length L1 of the first flat outer surface region 1f in the direction connecting the pair of first curved outer surface regions 1r (vertical direction Z) is smaller than the length L2 of the second flat outer surface region 2f in the direction connecting the pair of second curved outer surface regions 2r (vertical direction Z), and is also smaller than the length L3 of the third flat outer surface region 3f in the direction connecting the pair of third curved outer surface regions 3r (vertical direction Z) (i.e., L1 <L2かつL1<L3); (2) One end 1u (upper end, here the end on the sealing plate 14 side) of the first flat outer surface region 1f in the direction connecting the pair of first curved outer surface regions 1r (vertical direction Z) is located closer to the center (lower) than one end 2u (upper end, here the end on the sealing plate 14 side) of the second flat outer surface region 2f in the direction connecting the pair of second curved outer surface regions 2r (vertical direction Z), and is also located closer to the center (lower) than one end 3u (upper end, here the end on the sealing plate 14 side) of the third flat outer surface region 3f in the direction connecting the pair of third curved outer surface regions 3r (vertical direction Z); (3) The other end 1d (end, lower end) of the first flat outer surface region 1f in the direction connecting the pair of first curved outer surface regions 1r (vertical direction Z) is located closer to the center (upper) than the other end 2d (end, lower end) of the second flat outer surface region 2f in the direction connecting the pair of second curved outer surface regions 2r (vertical direction Z), and is located closer to the center (upper) than the other end 3d (end, lower end) of the third flat outer surface region 3f in the direction connecting the pair of third curved outer surface regions 3r (vertical direction Z); It has all of the above.

[0046] That is, in the technology disclosed herein, as described in (1) above, the height (length L1 in the vertical direction Z) of the first flat outer surface region 1f is smaller than those of the second flat outer surface region 2f and the third flat outer surface region 3f. This allows the first flat outer surface region 1f to be suitably contained within the height range of the second flat outer surface region 2f and the third flat outer surface region 3f when the first flat outer surface region 1f, the second flat outer surface region 2f, and the third flat outer surface region 3f are stacked, as described in (2) and (3) above. As a result, the first flat outer surface region 1f is evenly loaded in the vertical direction Z, reducing constraint unevenness. This prevents the interelectrode distance from becoming locally large, particularly at the ends of the flat outer surface region in the vertical direction Z. This in turn prevents metal deposition (Li deposition in a lithium-ion secondary battery) from occurring, resulting in an electricity storage device 100 with excellent Li deposition resistance.

[0047] Furthermore, the technology disclosed herein allows the flat outer surface regions of the electrode assemblies 20a, 20b, and 20c to directly face each other (preferably abut) without using spacers as described in, for example, Patent Document 1, thereby making it possible to compact the electrode assembly group 20. This allows the volumetric energy density of the battery 100 to be relatively improved compared to the embodiment as disclosed in, for example, Patent Document 1.

[0048] According to the above-mentioned configuration, it is conceivable that uneven restraint occurs in the second flat outer surface region 2f and the third flat outer surface region 3f, which may result in metal deposition. However, according to the study by the present inventors, this is due to the following reasons: One surface (YZ surface) of the flat outer surface region faces the long side surface 12b of the battery case 10 and is constrained from the battery case 10 side, so that uneven constraining due to the height of the electrode bodies 20a, 20c (more specifically, the length of the flat outer surface region in the vertical direction Z) is unlikely to occur; The electrode bodies 20a and 20c are less likely to be subjected to a concentrated load than the electrode body 20b sandwiched between the electrode bodies 20a and 20c, and differences in the inter-electrode distance due to uneven restraint are less likely to occur; Therefore, the influence on the second flat outer surface region 2f and the third flat outer surface region 3f is small, and as will be shown in the examples described later, the occurrence of metal deposition (Li deposition in a lithium ion secondary battery) is suppressed overall.

[0049] In some embodiments, the difference (L2-L1) between the length L2 of the second flat outer surface region 2f and the length L1 of the first flat outer surface region 1f may be 0.05 mm or more, 0.10 mm or more, or even 0.20 mm or more. The difference (L3-L1) between the length L3 of the third flat outer surface region 3f and the length L1 of the first flat outer surface region 1f may be 0.05 mm or more, 0.10 mm or more, or even 0.20 mm or more. In such cases, applying the technology disclosed herein is particularly effective.

[0050] Furthermore, the difference (L2 - L1) between the length L2 of the second flat outer surface region 2f and the length L1 of the first flat outer surface region 1f is preferably 0.70 mm or less, more preferably 0.60 mm or less. The difference (L3 - L1) between the length L3 of the third flat outer surface region 3f and the length L1 of the first flat outer surface region 1f is preferably 0.70 mm or less, more preferably 0.60 mm or less. This allows the effects of the technology disclosed herein to be exerted at a higher level. The length L2 of the second flat outer surface region 2f and the length L3 of the third flat outer surface region 3f may be the same or different.

[0051] Although not particularly limited, in a high-capacity type electricity storage device 100 to be used in a vehicle, etc., the length L1 of the first flat outer surface region 1f, the length L2 of the second flat outer surface region 2f, and the length L3 of the third flat outer surface region 3f are each preferably 50 to 110 mm, more preferably 70 to 100 mm, and even more preferably 80 to 100 mm.

[0052] 7, in this embodiment, the first electrode body 20b located at the middle in the short side direction X (arrangement direction) has a longer length in the up-down direction Z of the upper first curved outer surface region 1r than the upper second curved outer surface region 2r of the second electrode body 20a and the upper third curved outer surface region 3r of the third electrode body 20c. In other words, the upper first curved outer surface region 1r of the first electrode body 20b has a larger curvature than the upper second curved outer surface region 2r of the second electrode body 20a and the upper third curved outer surface region 3r of the third electrode body 20c.

[0053] As a result, in this embodiment, although the position of the upper end 1u of the first flat outer surface region 1f is lower (shifted) than the position of the upper end 2u of the second flat outer surface region 2f and the position of the upper end 3u of the third flat outer surface region 3f in the vertical direction Z, as indicated by the symbol T1, the position of the upper end of the first electrode body 20b (the vertex of the upper first curved outer surface region 1r), the position of the upper end of the second electrode body 20a (the vertex of one second curved outer surface region 2r), and the position of the upper end of the third electrode body 20c (the vertex of one third curved outer surface region 3r) are approximately aligned (within ±0.05 mm). However, in other embodiments, the positions of the upper ends of the first electrode body 20b, the second electrode body 20a, and the third electrode body 20c do not have to be aligned. For example, the curvature of the upper curved outer surface regions of the electrode bodies 20a, 20b, and 20c may be the same, and the upper end of the first electrode body 20b may be positioned lower than the upper end of the second electrode body 20a and the upper end of the third electrode body 20c.

[0054] In this embodiment, the positions of the lower ends of the first electrode body 20b (the apex of the lower curved outer surface region 1r), the second electrode body 20a (the apex of the lower curved outer surface region 2r), and the third electrode body 20c (the apex of the lower curved outer surface region 3r) are not aligned in the vertical direction Z. However, in other embodiments, the positions of the lower ends of the first electrode body 20b, the second electrode body 20a, and the third electrode body 20c may be approximately aligned (within ±0.05 mm), similar to the upper ends.

[0055] The electrode assemblies 20a, 20b, and 20c described above can be manufactured by a manufacturing method including, for example, (S1) a winding step and (S2) a molding step, in this order. In the (S1) winding step, a cylindrical wound body (tubular body) is manufactured. Specifically, for example, a strip-shaped first separator 26, a strip-shaped negative electrode 24, a strip-shaped second separator 26, and a strip-shaped positive electrode 22 are first stacked in this order and wound around a substantially cylindrical winding core. This produces a cylindrical body. Next, in the (S2) molding step, the cylindrical body is crushed by, for example, press molding. This produces the flat-shaped electrode assemblies 20a, 20b, and 20c shown in FIGS. 5 and 6.

[0056] The height of the electrode bodies 20a, 20b, and 20c (the length of the flat outer surface region in the vertical direction Z) can be changed by the diameter (circumferential length) of the winding core used in the (S1) winding step and the press conditions (pressure, etc.) in the (S2) molding step. For example, if it is desired to increase the height of the electrode bodies 20a, 20b, and 20c (the length of the flat outer surface region in the vertical direction Z), it is preferable to increase the diameter of the winding core used in the (S1) winding step. Furthermore, the curvature of the curved outer surface region of the electrode bodies 20a, 20b, and 20c can be changed by the press conditions (pressure, etc.) in the (S2) molding step.

[0057] 2, the positive electrode current collecting part 50 forms a conductive path that electrically connects the positive electrode tab group 23 consisting of multiple positive electrode tabs 22t to the positive electrode terminal 30. The positive electrode current collecting part 50 may be made of the same metal type as the positive electrode current collector 22c, such as a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The positive electrode current collecting part 50 has a positive electrode first current collecting member 51 electrically connected to the positive electrode terminal 30, and three or more positive electrode second current collecting members 52.

[0058] The positive electrode second current collecting member 52 extends along the short side surface 12c of the case body 12. In this embodiment, the number of positive electrode second current collecting members 52 is the same as the number N of electrode bodies (three). The three positive electrode second current collecting members 52 are respectively connected to the positive electrode tab groups 23 of the electrode bodies 20a, 20b, and 20c. More specifically, the first positive electrode tab group 23 of the first electrode body 20b is connected to the first positive electrode second current collecting member 52, the second positive electrode tab group 23 of the second electrode body 20a is connected to the second positive electrode second current collecting member 52, and the third positive electrode tab group 23 of the third electrode body 20c is connected to the third positive electrode second current collecting member 52. The three positive electrode second current collecting members 52 are respectively attached to the positive electrode tab groups 23 of the electrode bodies 20a, 20b, and 20c.

[0059] 3, each of the three positive electrode second current collecting members 52 has a joint J formed with the positive electrode tab group 23. The joint J is a welded joint formed by welding, such as ultrasonic welding, resistance welding, or laser welding, with the multiple positive electrode tabs 22t stacked on top of each other. The joint J is arranged such that the multiple positive electrode tabs 22t are closer to one side (the front side in FIG. 3) in the short side direction X of the electrode bodies 20a, 20b, and 20c.

[0060] As shown in Fig. 7, the three positive electrode second current collecting members 52 have approximately the same length (within ±0.05 mm) extending along the short side surface 12c of the case body 12 (length in the vertical direction Z). The three positive electrode second current collecting members 52 have approximately the same lower end positions (within ±0.05 mm), as indicated by the reference symbol T2. Note that Fig. 7 shows the positive electrode second current collecting members 52 in a simplified form.

[0061] The positive electrode first current collecting member 51 is attached to the inner surface of the sealing plate 14. Here, there is one positive electrode first current collecting member 51. The first positive electrode second current collecting member 52, the second positive electrode second current collecting member 52, and the third positive electrode second current collecting member 52 are connected to one positive electrode first current collecting member 51. This allows stable current collection even if, for example, the height (length in the up-down direction Z) of each positive electrode tab group 23 is shortened, thereby realizing space savings.

[0062] 7, the positions of one end (upper end, vertex of the upper first curved outer surface region 1r) of the first electrode body 20b in the direction connecting the pair of first curved outer surface regions 1r (vertical direction Z), one end (upper end, vertex of the upper second curved outer surface region 2r) of the second electrode body 20a in the direction connecting the pair of second curved outer surface regions 2r (vertical direction Z), and one end (upper end, vertex of the upper third curved outer surface region 3r) of the third electrode body 20c in the direction connecting the pair of third curved outer surface regions 3r (vertical direction Z) are substantially aligned (within ±0.05 mm). This allows the three positive electrode second current collecting members 52, each connected to a positive electrode tab group 23, to be stably connected to one positive electrode first current collecting member 51.

[0063] As shown in FIG. 2 , the negative electrode current collector 60 forms a conductive path that electrically connects the negative electrode tab group 25 consisting of multiple negative electrode tabs 24t to the negative electrode terminal 40. The negative electrode current collector 60 may be made of the same metal as the negative electrode current collector 24c, such as a conductive metal such as copper, a copper alloy, nickel, or stainless steel. The negative electrode current collector 60 has a negative electrode first current collector 61 electrically connected to the negative electrode terminal 40 and three or more negative electrode second current collectors 62. The configurations and arrangements of the negative electrode first current collector 61 and the negative electrode second current collector 62 may be similar to those of the positive electrode first current collector 51 and the positive electrode second current collector 52 of the positive electrode current collector 50.

[0064] The negative electrode second current collecting member 62 extends along the short side surface 12c of the case body 12. In this embodiment, the number of negative electrode second current collecting members 62 is the same as the number N of electrode bodies (three). The three negative electrode second current collecting members 62 are respectively connected to the negative electrode tab groups 25 of the electrode bodies 20a, 20b, and 20c. More specifically, the first negative electrode tab group 25 of the first electrode body 20b is connected to the first negative electrode second current collecting member 62, the second negative electrode tab group 25 of the second electrode body 20a is connected to the second negative electrode second current collecting member 62, and the third negative electrode tab group 25 of the third electrode body 20c is connected to the third negative electrode second current collecting member 62. The three negative electrode second current collecting members 62 are each attached to the negative electrode tab group 25 of the electrode body 20a.

[0065] 3, a joint J is formed on each of the three negative electrode second current collecting members 62 with the negative electrode tab group 25. As with the positive electrode side, the joint J is a welded joint formed by welding, such as ultrasonic welding, resistance welding, or laser welding, with the multiple negative electrode tabs 24t stacked on top of each other. The joint J is arranged such that the multiple negative electrode tabs 24t are closer to one side (the front side in FIG. 3) in the short side direction X of the electrode bodies 20a, 20b, and 20c.

[0066] The negative electrode first current collecting part 61 is attached to the inner surface of the sealing plate 14. Here, there is one negative electrode first current collecting part 61. The first negative electrode second current collecting member 62, the second negative electrode second current collecting member 62, and the third negative electrode second current collecting member 62 are connected to one negative electrode first current collecting part 61. This allows stable current collection even if, for example, the height (length in the up-down direction Z) of each negative electrode tab group 25 is shortened, thereby realizing space savings.

[0067] The non-aqueous electrolyte typically contains a non-aqueous solvent and an electrolyte salt (supporting salt). The non-aqueous electrolyte may further contain additional components (additives). The electrolyte salt is not particularly limited as long as it contains a charge carrier (e.g., lithium ion or sodium ion), and one or more of those conventionally used for this type of application can be used. Examples of the electrolyte salt include fluorine-containing lithium salts such as LiPF6 and LiBF4. The electrolyte salt preferably contains LiPF6.

[0068] As the non-aqueous solvent, one or more of those conventionally used for this type of application can be used. Examples of non-aqueous solvents include carbonates, ethers, esters, nitriles, sulfones, lactones, etc. The non-aqueous solvent preferably contains a carbonate. Examples of carbonates include linear carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), and cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC).

[0069] <Uses of the electricity storage device 100> The electricity storage device 100 can be used for various purposes, but for example, because of its high capacity and excellent resistance to Li deposition, it can be suitably used as a power source (driving power source) for motors mounted on vehicles such as passenger cars and trucks. 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). The electricity storage device 100 can be suitably used as a battery pack in which a plurality of electricity storage devices 100 are arranged in a short side direction X (arrangement direction) and a load is applied from the short side direction X (arrangement direction) using a restraint mechanism.

[0070] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to these examples.

[0071] <Preparation of evaluation battery> First, three wound electrode assemblies (first to third electrode assemblies) were fabricated for each example. Specifically, a strip-shaped positive electrode and a strip-shaped negative electrode were stacked facing each other with a strip-shaped separator interposed therebetween, and then wound around a winding core into a cylindrical shape. This produced a cylindrical body. Next, the cylindrical body was crushed by press molding to form a flat shape. Next, the three wound electrode assemblies fabricated above were arranged in the arrangement direction in the order of the second electrode assembly, the first electrode assembly, and the third electrode assembly, with the flat outer surface regions facing each other, to produce an electrode assembly group. In the electrode assembly group, the second electrode assembly and the third electrode assembly were located at the ends in the arrangement direction, and the first electrode assembly was located in the middle in the arrangement direction (between the second electrode assembly and the third electrode assembly). The electrode assembly and non-aqueous electrolyte were then housed in a rectangular battery case to fabricate evaluation lithium-ion secondary batteries (200 Ah class, Examples 1 and 2, Comparative Examples 1-5). The height of the electrode assembly in each example, specifically the height (vertical length) L2 of the second flat outer surface region of the second electrode assembly and the height (vertical length) L1 of the first flat outer surface region of the first electrode assembly, is shown in Table 1.

[0072] In Comparative Examples 1 to 3 where the length L1 of the first flat outer surface region of the first electrode body is much larger than the length L2 of the second flat outer surface region of the second electrode body (L2≪L1), and in Comparative Examples 4 and 5 where the length L1 of the first flat outer surface region of the first electrode body is slightly larger than the length L2 of the second flat outer surface region of the second electrode body (L2<L1), the first flat outer surface region of the first electrode body protrudes in the vertical direction beyond the second flat outer surface region and the third flat outer surface region. On the other hand, in Examples 1 and 2 where the length L1 of the first flat outer surface region 1f is smaller than the length L2 of the second flat outer surface region of the second electrode body (L2>L1), the first flat outer surface region of the first electrode body is within the height range of the second flat outer surface region and the third flat outer surface region.

[0073] <Evaluation of Lithium Deposition Resistance> First, the above-prepared evaluation battery was subjected to cyclic charge and discharge under the temperature and energization conditions shown in Table 1. Specifically, in the temperature environment described in Table 1, the SOC (State of Charge) of the evaluation battery was adjusted to the state described in Table 1, and after performing constant current charging at the charging current and time described in Table 1, a 10-minute pause was taken. Then, after discharging at the same current and for the same time, a 10-minute pause was taken, and one cycle of charge and discharge was defined as such, and this was repeated 500 times. For example, in Comparative Example 1, in an environment of 25°C, the evaluation battery was adjusted to a state of SOC 80%, and charge and discharge with a charge and discharge current value of 150 A and an energization time of 50 sec were repeated 500 times. Then, the evaluation battery after the charge and discharge cycle was disassembled, and for each example, for each of the first electrode body and the second electrode body, the number of occurrence locations of Li deposition in the flat outer surface region (arithmetic mean of the first electrode body and the second electrode body) was visually confirmed. The results are shown in Table 1.

[0074]

Table 1

[0075] As shown in Table 1, in Examples 1 and 2, in which the length L1 of the first flat outer surface region 1f of the first electrode body located in the middle of the arrangement direction was made smaller than the length L2 of the second flat outer surface region of the second electrode body located at the end of the arrangement direction, the number of locations where Li deposition occurred was significantly reduced compared to Comparative Examples 1 to 5. These results demonstrate the significance of the technology disclosed herein.

[0076] Although several embodiments of the present invention have been described above, the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed in this specification and the common general 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 modifications, or to add other modifications to the above-described embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate.

[0077] <Modification> 7, the flat outer surface regions of the electrode bodies 20a, 20b, and 20c adjacent in the short side direction X (arrangement direction) directly face each other. However, this is not limited to this. A spacer may be disposed between the first flat outer surface region 1f and the second flat outer surface region 2f, or between the first flat outer surface region 1f and the third flat outer surface region 3f (preferably both).

[0078] The spacer is typically flat. The spacer has a pair of opposing surfaces that are perpendicular to the short-side direction X (arrangement direction) and extend along the YZ plane. Each of the pair of opposing surfaces faces (preferably abuts) the flat outer surface regions of the electrode bodies 20a, 20b, and 20c. The opposing surfaces are preferably substantially rectangular in plan view. The spacer is preferably configured to cover the entire flat outer surface region of each of the electrode bodies 20a, 20b, and 20c. That is, the opposing surfaces are preferably equal to or larger than the area of ​​each of the flat outer surface regions of the electrode bodies 20a, 20b, and 20c. The height of the opposing surfaces (length in the vertical direction Z) is preferably equal to or longer than the lengths L1, L2, and L3 of the first to third flat outer surface regions of the opposing electrode bodies 20a, 20b, and 20c. The length of the opposing surfaces in the long-side direction Y is preferably equal to or longer than the length La of the negative electrode active material layer 24a in the long-side direction Y. This allows the effect of the spacer to be exerted at a higher level.

[0079] The material of the spacer is not particularly limited. The spacer may be made of metal, such as aluminum, copper, or stainless steel, or may be made of resin, such as polyethylene (PE), polypropylene (PP), or polytetrafluoroethylene (PTFE). If the spacer is made of metal, it is preferable that the surface be insulating treated. In some embodiments, it is preferable that the spacer has high chemical resistance.

[0080] It is preferable that the spacer has rigidity. This allows for a higher level of reduction in restraint unevenness compared to, for example, a spacer without rigidity (e.g., made of a non-flexible material such as rubber), and allows for a higher level of effectiveness of the technology disclosed herein. In this specification, "having rigidity" means that the spring constant is 80 kN / mm or more. From the viewpoint of increasing rigidity, the thickness of the spacer (average thickness in the short side direction X (arrangement direction)) is preferably 0.5 mm or more.

[0081] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: An electrode assembly including a first electrode assembly, a second electrode assembly, and a third electrode assembly, and a rectangular battery case that houses the electrode assembly; the first electrode body, the second electrode body, and the third electrode body are each a flat wound electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; the first electrode body is disposed between the second electrode body and the third electrode body, the first electrode body has a first flat outer surface region and a pair of first curved outer surface regions located at both ends of the first flat outer surface region; the second electrode body has a second flat outer surface region and a pair of second curved outer surface regions located at both ends of the second flat outer surface region; and the third electrode body has a third flat outer surface region and a pair of third curved outer surface regions located at both ends of the third flat outer surface region; the first electrode body, the second electrode body, and the third electrode body are arranged such that the first flat outer surface region is disposed between the second flat outer surface region and the third flat outer surface region, and the first flat outer surface region, the second flat outer surface region, and the third flat outer surface region are stacked; a length L1 of the first flat outer surface region in a direction connecting the pair of first curved outer surface regions is smaller than a length L2 of the second flat outer surface region in a direction connecting the pair of second curved outer surface regions, and is smaller than a length L3 of the third flat outer surface region in a direction connecting the pair of third curved outer surface regions; One end of the first flat outer surface region in a direction connecting the pair of first curved outer surface regions is located closer to the center than one end of the second flat outer surface region in a direction connecting the pair of second curved outer surface regions, and is located closer to the center than one end of the third flat outer surface region in a direction connecting the pair of third curved outer surface regions, an energy storage device in which the other end of the first flat outer surface region in the direction connecting the pair of first curved outer surface regions is located closer to the center than the other end of the second flat outer surface region in the direction connecting the pair of second curved outer surface regions, and is located closer to the center than the other end of the third flat outer surface region in the direction connecting the pair of third curved outer surface regions. Item 2: Further comprising a positive electrode current collecting unit including a positive electrode terminal, a positive electrode first current collecting member connected to the positive electrode terminal, and three or more positive electrode second current collecting members, the first electrode body has a first positive electrode tab group, the second electrode body has a second positive electrode tab group, and the third electrode body has a third positive electrode tab group; the first positive electrode tab group is connected to the first positive electrode second current collecting member, the second positive electrode tab group is connected to the second positive electrode second current collecting member, and the third positive electrode tab group is connected to the third positive electrode second current collecting member; Item 1. The electricity storage device according to item 1, wherein the first positive electrode second current collecting member, the second positive electrode second current collecting member, and the third positive electrode second current collecting member are connected to one positive electrode first current collecting member. Item 3: The energy storage device according to item 1 or 2, wherein the position of one end of the first electrode body in the direction connecting the pair of first curved outer surface regions, the position of one end of the second electrode body in the direction connecting the pair of second curved outer surface regions, and the position of one end of the third electrode body in the direction connecting the pair of third curved outer surface regions are substantially aligned. [Explanation of symbols]

[0082] 10 Battery case 20 Electrode group 20a Second electrode body 2f 2nd flat outer surface area 2r Second curved outer surface area 20b 1st electrode body 1f 1st flat outer surface area 1r First curved outer surface area 20c 3rd electrode body 3f 3rd flat outer surface area 3r 3rd curved outer surface area 22 Positive electrode 24 Negative electrode 26 Separator 30 Positive terminal 40 Negative terminal 100 Energy storage device X Short side direction (arrangement direction) Z direction (direction connecting the curved outer surface areas)

Claims

1. an electrode assembly including a first electrode assembly, a second electrode assembly, and a third electrode assembly; and a rectangular battery case that houses the electrode assembly; the first electrode body, the second electrode body, and the third electrode body are each a flat wound electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, the first electrode body is disposed between the second electrode body and the third electrode body, the first electrode body has a first flat outer surface region and a pair of first curved outer surface regions disposed on opposite ends of the first flat outer surface region; the second electrode body has a second flat outer surface region and a pair of second curved outer surface regions disposed on both ends of the second flat outer surface region; the third electrode body has a third flat outer surface region and a pair of third curved outer surface regions disposed on both ends of the third flat outer surface region; The first electrode body, the second electrode body, and the third electrode body are the first flat outer surface region is disposed between the second flat outer surface region and the third flat outer surface region; and the first flat outer surface region, the second flat outer surface region, and the third flat outer surface region are arranged to be stacked, The length L1 of the first flat outer surface region in the direction connecting the pair of first curved outer surface regions is is smaller than the length L2 of the second flat outer surface region in the direction connecting the pair of second curved outer surface regions, and is smaller than the length L3 of the third flat outer surface region in the direction connecting the pair of third curved outer surface regions, One end of the first flat outer surface region in a direction connecting the pair of first curved outer surface regions is is located closer to the center than one end of the second flat outer surface region in a direction connecting the pair of second curved outer surface regions, and a third curved outer surface region extending from the first end of the third flat outer surface region toward the center in a direction connecting the pair of third curved outer surface regions; The other end of the first flat outer surface region in the direction connecting the pair of first curved outer surface regions is is located closer to the center than the other end of the second flat outer surface region in a direction connecting the pair of second curved outer surface regions, and a third flat outer surface region located closer to the center than the other end of the third flat outer surface region in a direction connecting the pair of third curved outer surface regions; Energy storage device.

2. A positive terminal; a positive electrode current collecting portion including a positive electrode first current collecting member connected to the positive electrode terminal and three or more positive electrode second current collecting members; Furthermore, the first electrode body has a first positive electrode tab group, the second electrode body has a second positive electrode tab group, the third electrode body has a third positive electrode tab group, the first positive electrode tab group is connected to the first positive electrode second current collecting member, the second positive electrode tab group is connected to the second positive electrode second current collecting member, the third positive electrode tab group is connected to the third positive electrode second current collecting member, the first positive electrode second current collecting member, the second positive electrode second current collecting member, and the third positive electrode second current collecting member are connected to one positive electrode first current collecting member; The electricity storage device according to claim 1 .

3. a position of one end of the first electrode body in a direction connecting the pair of first curved outer surface regions, a position of one end of the second electrode body in a direction connecting the pair of second curved outer surface regions, and a position of one end of the third electrode body in a direction connecting the pair of third curved outer surface regions are substantially aligned; The electricity storage device according to claim 2 .

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