Energy storage devices

Abstract

Provided is an electricity storage device in which the occurrence of metal deposition is suppressed. [Solution] The power storage device disclosed herein includes an electrode assembly group 20 including three or more electrode assemblies 20a, 20b, 20c arranged along an arrangement direction X. The electrode assemblies 20a, 20b, 20c are composed of a pair of end electrode assemblies 20a, 20c and an intermediate electrode assemblies 20b, each of which includes a first electrode, a second electrode, and a separator, and the first electrode and the separator are bonded together by a first adhesive layer. The adhesive strength between the first electrode and the separator of each of the pair of end electrode assemblies 20a, 20c is greater than that of the intermediate electrode assemblies 20b.

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 electric storage device is known that includes an electrode assembly group including a plurality of electrode assemblies arranged along a predetermined arrangement direction (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-77529 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the investigations of the present inventors, it has been newly discovered that in an electrode body group including three or more electrode bodies, metal deposition (for example, Li deposition in a lithium ion secondary battery) is likely to occur, particularly in the electrode bodies arranged at both ends in 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 group including three or more electrode assemblies arranged along an arrangement direction, and a battery case accommodating the electrode assembly group. The three or more electrode assemblies are composed of a pair of end electrode assemblies arranged at both ends of the arrangement direction, and at least one intermediate electrode assembly arranged between the pair of end electrode assemblies, each including a first electrode, a second electrode, and a separator interposed between the first electrode and the second electrode, and the first electrode and the separator are bonded together by a first adhesive layer. The adhesive strength between the first electrode and the separator of each of the pair of end electrode assemblies is greater than that of the at least one intermediate electrode assembly.

[0007] According to the above configuration, it is possible to suppress the occurrence of metal deposition (for example, Li deposition in a lithium ion secondary battery) particularly in the pair of end electrode bodies respectively arranged at both ends in the arrangement direction. [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 an electrode assembly according to one embodiment. [Figure 6] FIG. 6 is a schematic diagram showing the configuration of an electrode assembly according to one embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view showing the configuration of a separator according to one embodiment. 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 but necessary for implementing the present invention (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 a person skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. In this specification, the expression "A to B" indicating a range includes the meaning of "greater than A" and "smaller than B" as well as the meaning of "greater than A" and "smaller than B."

[0010] In this specification, the term "electricity storage device" refers to a general electricity storage device that can be repeatedly charged and discharged by the movement of charge carriers between a first electrode and a second electrode. The concept of electricity 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.

[0011] <Electricity storage device 100> FIG. 1 is a perspective view of an electricity storage device (hereinafter also simply referred to as a battery) 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 L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, 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 and long side directions, 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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).

[0016] 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).

[0017] 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).

[0018] 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 aluminum or an aluminum alloy, for example. 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.

[0019] 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.

[0020] 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 arranged along the short side direction X (arrangement direction). 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 20a, 20b, and 20c. However, the number N of electrode bodies arranged inside one battery case 10 is not particularly limited and may be four or more.

[0021] The electrode assemblies 20a, 20b, and 20c are arranged along the short-side direction X. The short-side direction X is an example of an arrangement direction. The electrode assemblies 20a, 20b, and 20c are composed of a pair of end electrode assemblies 20a and 20c arranged at both ends of the short-side direction X (arrangement direction), and at least one intermediate electrode assemblies 20b arranged between the pair of end electrode assemblies 20a and 20c. The pair of end electrode assemblies 20a and 20c face a pair of long side surfaces 12b (side surfaces with larger areas) of the case body 12, respectively. Note that when the number N of electrode assemblies arranged inside one battery case 10 is four or more, the number of intermediate electrode assemblies 20b is multiple, specifically (N-2). The electrode assemblies 20a, 20b, and 20c are electrically connected in parallel here. The electrode assembly group 20 may be arranged inside the battery case 10 while covered by an insulating electrode assembly holder. In other words, an electrode assembly holder may be interposed between the electrode assembly group 20 and the battery case 10 (specifically, the case body 12).

[0022] FIG. 5 is a perspective view schematically illustrating one electrode assembly 20a. FIG. 6 is a schematic diagram illustrating the configuration of the electrode assembly 20a. Note that the electrode assembly 20a will be described in detail below as an example, but the electrode assemblies 20b and 20c may also have a similar configuration. As shown in FIG. 6, the electrode assembly 20a includes a positive electrode 22, a negative electrode 24, and a separator 26 interposed between the positive electrode 22 and the negative electrode 24. One of the positive electrode 22 and the negative electrode 24 is an example of a "first electrode," and the other is an example of a "second electrode."

[0023] The electrode assembly 20a here is a wound electrode assembly. The electrode assembly 20a is configured by stacking a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 in an insulated state with a strip-shaped separator 26 interposed therebetween, and winding the stack around a winding axis WL. The electrode assembly 20a is preferably a wound electrode assembly. When the electrode assembly 20a is a wound electrode assembly, it is particularly effective to apply the technology disclosed herein. However, in other embodiments, the electrode assembly 20a may be a stacked electrode assembly in which multiple square-shaped (typically rectangular) positive electrodes and multiple square-shaped (typically rectangular) negative electrodes are stacked in an insulated state.

[0024] 2 and 6, the electrode body 20a is disposed inside the battery case 10 so that the winding axis WL is aligned with the long side direction Y. Here, the direction of the winding axis WL coincides with the long side direction Y. The electrode body 20a is 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.

[0025] As shown in Fig. 5, the electrode body 20a has a flat outer shape. The electrode body 20a has a pair of flat portions 20f and a pair of curved portions (R portions) 20r connecting the pair of flat portions 20f. The flat portions 20f have a flat outer surface (the YZ plane in Fig. 5). The curved portions 20r have a curved outer surface. In this specification, the term "flat outer surface" is not limited to a completely flat surface, and includes cases where, for example, when viewed microscopically, there are slight steps, curves, recesses, protrusions, etc.

[0026] As can be seen from FIGS. 2 and 5, in this embodiment, the pair of flat portions 20f face the pair of long side surfaces 12b of the case body 12. The flat portions 20f extend along the long side surfaces 12b of the case body 12. As can be seen from FIGS. 4 and 5, the flat portions 20f of the electrode bodies 20a, 20b, and 20c adjacent to each other in the short side direction X (arrangement direction) face each other. Specifically, the flat portions 20f of the pair of end electrode bodies 20a and 20c face the flat portion 20f of the intermediate electrode body 20b, respectively. The pair of curved portions 20r face the bottom surface 12a and the sealing plate 14 of the case body 12. As in this embodiment, the electrode body 20a is preferably arranged inside the battery case 10 such that the stacking direction of the positive electrode 22 (see FIG. 6) and the negative electrode 24 (see FIG. 6) in the flat portions 20f coincides with the short side direction X (the direction perpendicular to the long side surfaces 12b of the case body 12).

[0027] 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 so that their outer ends are aligned. When the positive electrode tabs 22t are bent, Li deposition is likely to occur near the base of the positive electrode tabs 22t, making it particularly effective to apply the technology disclosed herein. A positive electrode second current collecting portion 52 (described later) of the positive electrode current collecting portion 50 is attached to (more specifically, joined to) the positive electrode tab group 23. The positive electrode tabs 22t are connected to the positive electrode second current collecting portion 52. The positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collecting portion 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. Here, the positive electrode active material layer 22a constitutes the outermost surface of the positive electrode 22. 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. As the conductive material, for example, a carbon material such as acetylene black (AB) can be used. As the binder, for example, polyvinylidene fluoride (PVdF) is preferable.

[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] 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 , multiple 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 multiple negative electrode tabs 24t are stacked and bent and curved so that their outer ends are aligned. When multiple negative electrode tabs 24t are bent and curved, Li deposition is likely to occur near the base of the negative electrode tabs 24t, making it particularly effective to apply the technology disclosed herein. A negative electrode second current collecting portion 62 (described later) of the negative electrode current collecting portion 60 is attached to (more specifically, joined to) the negative electrode tab group 25. The multiple negative electrode tabs 24t are connected to the negative electrode second current collecting portion 62. The negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collecting portion 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. Here, the negative electrode active material layer 24a constitutes the outermost surface of the negative electrode 24. 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. Rubbers such as styrene butadiene rubber (SBR) are preferred as binders. Celluloses such as carboxymethyl cellulose (CMC) can be used as dispersants.

[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 equal to or longer than the length La of the negative electrode active material layer 24a in the long side direction Y. The separator 26 is preferably a porous sheet made of a resin such as 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. Although not particularly limited, the total thickness (average) of the separator 26 is preferably 3 to 25 μm, more preferably 3 to 18 μm, and even more preferably 5 to 14 μm.

[0039] FIG. 7 is a schematic cross-sectional view illustrating the configuration of a separator 26 according to one embodiment. As shown in FIG. 7, in this embodiment, the separator 26 includes a substrate 26s made of the porous sheet and a first adhesive layer 26b1 provided on a first surface of the substrate 26s. The first adhesive layer 26b1 forms the outermost surface of the first surface of the separator 26 and is in contact with one of the positive electrode 22 and the negative electrode 24 (the first electrode). The separator 26 further includes a second adhesive layer 26b2 provided on a second surface (the surface opposite the first surface) of the substrate 26s. The second adhesive layer 26b2 forms the outermost surface of the second surface of the separator 26 and is in contact with the positive electrode 22 or the negative electrode 24 (the second electrode) that is not the first electrode. However, the second adhesive layer 26b2 is not essential and may be omitted in other embodiments. In the following, the first adhesive layer 26b1 and the second adhesive layer 26b2 may be collectively referred to as "adhesive layers." Furthermore, the first electrode and the second electrode may be collectively referred to as "electrodes."

[0040] The adhesive layer may be provided directly on the surface of the base material 26s, or may be provided on another layer (e.g., a heat-resistant layer) that is interposed between the adhesive layer and the base material 26s. Here, the first adhesive layer 26b1 is provided over the entire area of ​​the first surface of the separator 26. Similarly, the second adhesive layer 26b2 is provided over the entire area of ​​the second surface of the separator 26. However, the adhesive layer does not necessarily have to be provided over the entire area of ​​the first surface and / or the second surface of the separator 26. The first surface and / or the second surface of the separator 26 may have an area where no adhesive layer is formed (an adhesive layer-unformed area).

[0041] The adhesive layer may have a flat surface (so-called solid coating), or may have an uneven surface with a predetermined pattern. In plan view, the adhesive layer may have a pattern such as dots, stripes, waves, bands (streaks), broken lines, or a combination of these. The basis weight of the adhesive layer (the total amount formed per unit area of ​​the first adhesive layer 26b1 and the second adhesive layer 26b2) is 0.5 to 7.5 g / m 2is preferred, and 2.0 to 6.0 g / m 2 is more preferred.

[0042] The adhesive layer is a layer containing a resin binder. Resin materials conventionally used for this type of application can be used as the resin binder without any particular restrictions. Examples of such resin materials include fluorine-based resins, acrylic resins, epoxy resins, urethane resins, and ethylene vinyl acetate resins. Among these, fluorine-based resins and acrylic resins are preferred because they have high flexibility and can more suitably exhibit adhesiveness to electrodes. Examples of fluorine-based resins include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). The content of the resin binder relative to the total mass of the adhesive layer is preferably 25% by mass or more, more preferably 50% by mass or more, and even more preferably 80% by mass or more.

[0043] In addition to the resin binder, the adhesive layer may contain an inorganic filler such as alumina, silica, boehmite, magnesia, or titania. The adhesive layer may also serve as a heat resistance layer (HRL). When the adhesive layer contains an inorganic filler, the content of the inorganic filler relative to the total mass of the adhesive layer is preferably 75% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less.

[0044] In the electrode assembly 20a, the first electrode (one of the positive electrode 22 and the negative electrode 24) and the separator 26 are bonded together by a first adhesive layer 26b1. In this embodiment, the second electrode (the other of the positive electrode 22 and the negative electrode 24) and the separator 26 are further bonded together by a second adhesive layer 26b2. The adhesive layer is bonded to the electrode by, for example, conventionally known methods such as heating or pressing (typically, press molding). The first adhesive layer 26b1 and the second adhesive layer 26b2 of the separator 26 have the same configuration. That is, the adhesive layers have the same composition (e.g., binder type and content) and properties (e.g., basis weight, thickness, formation area, and formation pattern). However, in other embodiments, the first adhesive layer 26b1 and the second adhesive layer 26b2 may have different configurations. Furthermore, when the separator 26 does not have the second adhesive layer 26b2, the second electrode (the one of the positive electrode 22 and the negative electrode 24 that is not the first electrode) and the separator 26 do not need to be bonded together.

[0045] In the present embodiment, the first adhesive layer 26b1 and the second adhesive layer 26b2 are provided on the separator 26. However, the position of the first adhesive layer is not particularly limited as long as it can bond the first electrode and the separator 26. Furthermore, the position of the second adhesive layer is not particularly limited as long as it can bond the second electrode and the separator 26. In other embodiments, the first adhesive layer and / or the second adhesive layer may not be provided on the separator 26. For example, the first adhesive layer may be provided on the outermost surface of the first electrode (the surface facing the separator 26), and the second adhesive layer may be provided on the outermost surface of the second electrode (the surface facing the separator 26). Alternatively, when two separators 26 are used for one electrode assembly 20a, as in the present embodiment, the first adhesive layer 26b1 may be provided on one surface of one separator 26, and the second adhesive layer 26b2 may be provided on one surface of the other separator 26.

[0046] Incidentally, according to the study by the present inventor, the electrode body group 20 expands typically in the stacking direction of the positive electrode 22 and the negative electrode 24 during charge and discharge. At this time, when the electrode body group 20 includes three or more electrode bodies 20a, 20b, 20c arranged along the short side direction X (arrangement direction) as in the present embodiment, the expansion amounts during charge and discharge may be different between the pair of end electrode bodies 20a, 20c and the intermediate electrode body 20b. More specifically, since the intermediate electrode body 20b is pressed by the pair of end electrode bodies 20a, 20c from the short side direction X, the expansion in the short side direction X is relatively suppressed. On the other hand, since the pair of end electrode bodies 20a, 20c expand while crushing the intermediate electrode body 20b, the expansion amount in the short side direction X tends to be relatively large. As a result, in the pair of end electrode bodies 20a, 20c, the distance (inter-pole distance) between the positive electrode 22 and the negative electrode 24 becomes relatively large, and所谓, metal deposition (here, Li deposition) is likely to occur due to gas biting.

[0047] Therefore, in the technology disclosed herein, the adhesion strength Pe between the first electrode (positive electrode 22 or negative electrode 24) and the separator 26 in the pair of end electrode bodies 20a, 20c is made larger than the adhesion strength Pm between the first electrode (positive electrode 22 or negative electrode 24) and the separator 26 in the intermediate electrode body 20b (Pm < Pe). That is, each of the pair of end electrode bodies 20a, 20c is configured such that the adhesion strength between the first electrode (positive electrode 22 or negative electrode 24) and the separator 26 is larger than that of the intermediate electrode body 20b. Thereby, the pair of end electrode bodies 20a, 20c can be constrained more strongly than the intermediate electrode body 20b, and the expansion in the short side direction X during charge and discharge can be suppressed. As a result, the difference in the expansion amounts between the pair of end electrode bodies 20a, 20c and the intermediate electrode body 20b becomes smaller, and an increase in the inter-pole distance in the pair of end electrode bodies 20a, 20c can be suppressed. Consequently, the occurrence of metal deposition (here, Li deposition) in the pair of end electrode bodies 20a, 20c can be suppressed, and a power storage device 100 excellent in Li deposition resistance can be realized.

[0048] In this specification, "adhesion strength" can be evaluated by the "90° peel test" specified in Japanese Industrial Standard JIS K6854-1:1999. Detailed evaluation methods are described in the Examples section. The adhesive strength between an electrode (positive electrode 22 or negative electrode 24) and a separator 26 can be adjusted, for example, by the composition of the adhesive layer (e.g., the type and content of the binder) or the properties of the adhesive layer (e.g., the basis weight, thickness, formation area, and formation pattern). Alternatively, the adhesive strength can be adjusted by the processing conditions when adhering the adhesive layer to the electrode, such as the load and temperature during press molding to form the electrode body into a flat shape.

[0049] To achieve the effects of the technology disclosed herein at a high level, the adhesive strength Pe of the pair of end electrode bodies 20a, 20c is preferably at least 1.2 times the adhesive strength Pm of at least one intermediate electrode body 20b. That is, (Pe / Pm) ≥ 1.2 is preferable. Here, when there are two or more intermediate electrode bodies 20b, the adhesive strength Pm refers to the arithmetic mean of the adhesive strengths of the two or more intermediate electrode bodies 20b. The ratio (Pe / Pm) is more preferably 1.3 or greater, and even more preferably 1.5 or greater. There is no particular upper limit to the ratio (Pe / Pm), but it is preferably, for example, 5.0 or less, 3.0 or less, or 2.0 or less.

[0050] Although not particularly limited, in the intermediate electrode body 20b, from the viewpoint of favorably bonding the first electrode (positive electrode 22 or negative electrode 24) and the separator 26, the adhesive strength Pm is preferably 0.5 N / m or more. The adhesive strength Pm is more preferably 1.0 N / m or more, and even more preferably 1.5 N / m or more. Although there are no particular limitations on the upper limit of the adhesive strength Pm, from the viewpoint of increasing the ratio (Pe / Pm) and achieving a high level of the effects of the technology disclosed herein, for example, it is preferably 4.0 N / m or less, 3.0 N / m or less, or 2.5 N / m or less.

[0051] Although not particularly limited, in the pair of end electrode bodies 20a and 20c, from the viewpoint of increasing the above ratio (Pe / Pm) and achieving the effects of the technology disclosed herein at a high level, etc., the adhesive strength Pe is preferably 1.0 N / m or more, more preferably 1.5 N / m or more, and even more preferably 2.0 N / m or more for each. The upper limit of the adhesive strength Pe is not particularly limited, but from the viewpoint of enhancing the electrolyte impregnation property of the pair of end electrode bodies 20a and 20c, etc., for example, 5.0 N / m or less, 4.0 N / m or less, and 3.0 N / m or less are preferable.

[0052] In some embodiments, the pair of end electrode bodies 20a and 20c preferably contain a type of resin binder (e.g., fluorine-based resin or acrylic resin) having a greater adhesive strength (peeling strength) than the intermediate electrode body 20b in the first adhesive layer 26b1 facing the first electrode (positive electrode 22 or negative electrode 24). Also, in some other embodiments, the pair of end electrode bodies 20a and 20c preferably have a higher content ratio of the resin binder in the first adhesive layer 26b1 facing the first electrode (positive electrode 22 or negative electrode 24) than the intermediate electrode body 20b. This makes it easier to realize the above-described magnitude relationship of the adhesive strength (Pm < Pe) and the preferable ratio (Pe / Pm) range.

[0053] Also, in some embodiments, the pair of end electrode bodies 20a and 20c preferably have a greater basis weight (average per side) of the first adhesive layer 26b1 facing the first electrode (positive electrode 22 or negative electrode 24) than the intermediate electrode body 20b. Also, in some other embodiments, the pair of end electrode bodies 20a and 20c preferably have a greater thickness T (see FIG. 7, average thickness per side, the same hereinafter) of the first adhesive layer 26b1 facing the first electrode (positive electrode 22 or negative electrode 24) than the intermediate electrode body 20b. This makes it easier to realize the above-described magnitude relationship of the adhesive strength (Pm < Pe) and the preferable ratio (Pe / Pm) range.

[0054] In some embodiments, the thickness T of the first adhesive layer 26b1 in the pair of end electrode bodies 20a, 20c is preferably 1.25 times or more the thickness T of the first adhesive layer 26b1 in at least one intermediate electrode body 20b. This makes it easier to achieve the above-mentioned range of the ratio (Pe / Pm). The above thickness ratio may be 2 times or less, or 1.5 times or less. Note that, when there are two or more intermediate electrode bodies 20b, the phrase "the thickness of the first adhesive layer in at least one intermediate electrode body" refers to the arithmetic average of the thicknesses of the first adhesive layer 26b1 in the two or more intermediate electrode bodies 20b.

[0055] In some embodiments, in the pair of end electrode bodies 20a, 20c, the thickness T of the first adhesive layer 26b1 facing the first electrode (positive electrode 22 or negative electrode 24) is preferably 0.5 μm or more, more preferably 1 μm or more, even more preferably 2 μm or more, and particularly preferably 4 μm or more. This makes it easier to achieve the above-mentioned suitable adhesive strength Pe and / or the above-mentioned ratio (Pe / Pm) within the range. In the pair of end electrode bodies 20a, 20c, the thickness T of the first adhesive layer 26b1 is preferably approximately 15 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less, from the viewpoint of battery performance, etc.

[0056] In some embodiments, in the intermediate electrode body 20b, the thickness T of the first adhesive layer 26b1 facing the first electrode (positive electrode 22 or negative electrode 24) is preferably 0.2 μm or more, more preferably 0.5 μm or more, even more preferably 1 μm or more, and particularly preferably 2 μm or more. This makes it easier to achieve the above-mentioned suitable adhesive strength Pm and / or the above-mentioned ratio (Pe / Pm) within the range. In the intermediate electrode body 20b, from the viewpoint of battery performance, etc., the thickness T of the first adhesive layer 26b1 is preferably approximately 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less.

[0057] In this embodiment, as described above, the adhesive layers (first adhesive layer 26b1 and second adhesive layer 26b2) of the separator 26 of each of the electrode assemblies 20a, 20b, and 20c have the same configuration. Therefore, the adhesive strength between the second electrode (the one of the positive electrode 22 and the negative electrode 24 that is not the first electrode) and the separator 26 of each of the pair of end electrode assemblies 20a and 20c is also greater than that of the intermediate electrode 20b. Therefore, in the above descriptions of adhesive strength and the first adhesive layer 26b1, "first adhesive layer" can be read as "second adhesive layer," and "adhesion strength between the first electrode and the separator 26" can be read as "adhesion strength between the second electrode and the separator 26." If the second electrode as well as the first electrode satisfy the above-mentioned magnitude relationship in adhesive strength, in other words, if both the positive electrode 22 and the negative electrode 24 satisfy the above-mentioned magnitude relationship in adhesive strength, the pair of end electrode assemblies 20a and 20c can be more strongly and stably constrained. Therefore, the effects of the technology disclosed herein can be exerted to a higher level. However, in other embodiments, for example, when the separator 26 does not have the second adhesive layer 26b2, the adhesive strength between the second electrode (the one of the positive electrode 22 and the negative electrode 24 that is not the first electrode) and the separator 26 of the pair of end electrode bodies 20a, 20c may be the same as that of the intermediate electrode body 20b (manufacturing errors and the like are acceptable).

[0058] In some embodiments, the electrode assemblies 20a, 20b, and 20c may have the same configuration (particularly the positive electrode 22 and the negative electrode 24) other than the separator 26. For example, by making the positive electrode 22 and the negative electrode 24 common to all of the electrode assemblies 20a, 20b, and 20c, and changing only the separator 26 (more specifically, only the adhesive layer) between the pair of end electrode assemblies 20a and 20c and the intermediate electrode assemblies 20b, efficient production of the electrode assemblies 20a, 20b, and 20c becomes possible.

[0059] As shown in FIG. 2 , the positive electrode current collecting part 50 forms a conductive path that electrically connects the positive electrode tab group 23, which is made up 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 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 includes a positive electrode first current collecting part 51 connected to the positive electrode terminal 30 and a positive electrode second current collecting part 52 connected to the positive electrode tab group 23. The positive electrode first current collecting part 51 is attached to the inner surface of the sealing plate 14.

[0060] The positive electrode second current collecting portion 52 extends along the short side surface 12c of the case body 12. The positive electrode second current collecting portion 52 is attached to the positive electrode tab group 23 of the electrode body 20a. As shown in FIG. 3, a joint J with the positive electrode tab group 23 is formed in the positive electrode second current collecting portion 52. 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.

[0061] As shown in FIG. 2 , the negative electrode current collector 60 forms a conductive path that electrically connects the negative electrode tab group 25, which is made up 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 includes a negative electrode first current collector 61 connected to the negative electrode terminal 40 and a negative electrode second current collector 62 connected to the negative electrode tab group 25. The configuration and arrangement of the negative electrode first current collector 61 and the negative electrode second current collector 62 may be the same as those of the positive electrode first current collector 51 and the positive electrode second current collector 52 of the positive electrode current collector 50.

[0062] The negative electrode second current collecting portion 62 is attached to the negative electrode tab group 25 of the electrode body 20a. As shown in Fig. 3, a joint J with the negative electrode tab group 25 is formed on the negative electrode second current collecting portion 62. 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 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.

[0063] 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 ions or sodium ions), 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.

[0064] 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).

[0065] <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 predetermined direction and a load is applied thereto using a restraining mechanism.

[0066] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to these examples.

[0067] <Preparation of evaluation battery> First, for each example, lithium-ion secondary batteries (Examples 1 and 2, Comparative Examples 1 and 2) including two types of wound electrode assemblies (a pair of end electrode assemblies and one intermediate electrode assembly) were fabricated. Specifically, a strip-shaped positive electrode sheet having a positive electrode active material layer on a positive electrode current collector and a strip-shaped negative electrode sheet having a negative electrode active material layer on a negative electrode current collector were prepared. Separator sheets were also prepared, each including a PE substrate and first and second adhesive layers provided over the entire area of ​​both sides of the substrate. The first and second adhesive layers had the same configuration and contained PVdF as a resin binder and alumina as an inorganic filler. For each example, two types of separator sheets were prepared, differing only in the thickness T of each adhesive layer (per side, see Table 1).

[0068] Next, the positive electrode sheet and the negative electrode sheet were opposed and laminated via the separator sheet, and wound into a cylindrical shape around a winding axis. Next, the wound electrode body (cylindrical body) was pressed into a flat shape by press molding to bond the electrode sheets (positive electrode sheet and negative electrode sheet) and the separator sheet, respectively. As a result, two types of wound electrode bodies (a pair of end electrode bodies and one intermediate electrode body) differing only in the thickness T of the adhesive layer of the separator were produced for each example. Then, the produced wound electrode bodies and the non-aqueous electrolyte were housed in a rectangular battery case to produce a plurality of evaluation batteries (200 Ah, Examples 1 and 2, Comparative Examples 1 and 2) respectively.

[0069] <Evaluation of Li precipitation resistance> First, the produced evaluation batteries were charged and discharged in an environment where Li precipitation was likely to occur. Specifically, each evaluation battery was adjusted to a state of SOC (State of Charge) of 50%, and pulsed charge and discharge at a charge and discharge rate of 0.2C for 10 seconds was repeated 500 cycles in a low temperature environment of -30°C. Then, the evaluation batteries after the charge and discharge cycles were disassembled, and for each of the two types of wound electrode bodies (a pair of end electrode bodies and one intermediate electrode body) for each example, the presence or absence (number if present) of the location of Li precipitation on the negative electrode was visually confirmed. The results are shown in Table 1. Among the two types of wound electrode bodies, no occurrence of Li precipitation was observed in all examples for the intermediate electrode body. Therefore, Table 1 shows only the number of Li precipitation locations on the end electrode body.

[0070] <Evaluation of adhesion strength> For each of the two types of wound electrode assemblies (a pair of end electrode assemblies and one intermediate electrode assembly), the adhesive strength between the first electrode and the separator and the adhesive strength between the second electrode and the separator were evaluated. Specifically, the first electrode and the separator were cut to a predetermined size, and the cut-out first electrode and the separator were stacked and pressed at 10 kN for 5 seconds to bond the first electrode and the separator. Next, in accordance with JIS-K6854-1:1999, this assembly of the first electrode and the separator was placed on a jig, and the first electrode side was fixed to the jig. Next, the separator side was grasped and pulled vertically (at a 90° angle) using an autograph. The graph was then plotted with the pulling distance on the horizontal axis and the tensile strength on the vertical axis, and the maximum tensile strength was taken as the peel strength (N / m) of the first electrode side. The peel strength (N / m) of the second electrode side was also determined in a similar manner. The results are shown in Table 1. In Table 1, the arithmetic average of the first electrode side and the second electrode side is shown as the peel strength (adhesion strength Pm, Pe), but the magnitude relationship (ratio value) is the same for both the first electrode side and the second electrode side.

[0071] [Table 1]

[0072] As shown in Table 1, in Comparative Example 1, where the adhesive strength of the separator between the pair of end electrode assemblies and the intermediate electrode assembly was the same, Li deposition occurred most frequently in the end electrode assemblies. Furthermore, in Comparative Example 2, where the adhesive strength of the separator was increased overall, Li deposition still occurred frequently. In contrast to these comparative examples, in Examples 1 and 2, where the adhesive strength Pe of the pair of end electrode assemblies was increased relative to the adhesive strength Pm of the intermediate electrode assembly, Li deposition was significantly suppressed. The reason for this is thought to be that the pair of end electrode assemblies were relatively strongly constrained, suppressing expansion during charge and discharge, thereby suppressing the increase in the interelectrode distance between the pair of end electrode assemblies. These results demonstrate the significance of the technology disclosed herein.

[0073] 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.

[0074] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: An electricity storage device comprising: an electrode assembly including three or more electrode assemblies arranged along an arrangement direction; and a battery case that houses the electrode assembly group, wherein the three or more electrode assemblies are composed of a pair of end electrode assemblies arranged at both ends of the arrangement direction, and at least one intermediate electrode assemblies arranged between the pair of end electrode assemblies, each of which includes a first electrode, a second electrode, and a separator interposed between the first electrode and the second electrode, and the first electrode and the separator are bonded together by a first adhesive layer, and the adhesive strength between the first electrode and the separator of each of the pair of end electrode assemblies is greater than that of the at least one intermediate electrode assemblies. Item 2: The energy storage device according to item 1, wherein the three or more electrode bodies each have the second electrode and the separator bonded together by a second adhesive layer, and the pair of end electrode bodies each have a greater adhesive strength between the second electrode and the separator than the at least one intermediate electrode body. Item 3: The energy storage device according to item 1 or 2, wherein the adhesive strength between the first electrode and the separator in the pair of end electrode bodies is at least 1.2 times the adhesive strength between the first electrode and the separator in the at least one intermediate electrode body (however, when there are two or more intermediate electrode bodies, the adhesive strength between the first electrode and the separator in the at least one intermediate electrode body refers to the arithmetic mean of the adhesive strengths in the two or more intermediate electrode bodies). Item 4: The electricity storage device according to any one of Items 1 to 3, wherein in the at least one intermediate electrode body, the adhesive strength between the first electrode and the separator is 0.5 N / m or more. Item 5: The electricity storage device according to any one of items 1 to 4, wherein in the at least one intermediate electrode body, the first adhesive layer has a thickness of 1 μm or more. Item 6: The electricity storage device according to any one of items 1 to 5, wherein the thickness of the first adhesive layer in the pair of end electrode bodies is at least 1.25 times the thickness of the first adhesive layer in the at least one intermediate electrode body (however, when there are two or more intermediate electrode bodies, the thickness of the first adhesive layer in the at least one intermediate electrode body refers to the arithmetic mean of the thicknesses of the first adhesive layer in the two or more intermediate electrode bodies). [Explanation of symbols]

[0075] 10 Battery case 20 Electrode group 20a, 20c electrode body (end electrode body) 20b Electrode body (intermediate electrode body) 22 Positive electrode (1st electrode / 2nd electrode) 24 Negative electrode (1st electrode / 2nd electrode) 26 Separator 100 Energy storage device X Short side direction (arrangement direction)

Claims

1. an electrode assembly including three or more electrode assemblies arranged along an arrangement direction; and a battery case that houses the electrode assembly group; The three or more electrode bodies are a pair of end electrodes disposed at both ends in the arrangement direction, and at least one intermediate electrode disposed between the pair of end electrodes; Each of the battery cells includes a first electrode, a second electrode, and a separator interposed between the first electrode and the second electrode, and the first electrode and the separator are bonded together by a first adhesive layer; The adhesive strength between the first electrode and the separator of each of the pair of end electrode bodies is greater than that of the at least one intermediate electrode body. Energy storage device.

2. In each of the three or more electrode bodies, the second electrode and the separator are bonded by a second adhesive layer, the pair of end electrode bodies each have a greater adhesive strength between the second electrode and the separator than the at least one intermediate electrode body; The electricity storage device according to claim 1 .

3. The adhesive strength between the first electrode and the separator in each of the pair of end electrode bodies is 1.2 times or more the adhesive strength between the first electrode and the separator in the at least one intermediate electrode body (however, when there are two or more intermediate electrode bodies, the adhesive strength between the first electrode and the separator in the at least one intermediate electrode body refers to the arithmetic average of the adhesive strengths in the two or more intermediate electrode bodies). The electricity storage device according to claim 1 or 2.

4. In the at least one intermediate electrode body, the adhesive strength between the first electrode and the separator is 0.5 N / m or more. The electricity storage device according to claim 3 .

5. In the at least one intermediate electrode body, the thickness of the first adhesive layer is 1 μm or more. The electricity storage device according to claim 1 or 2.

6. The thickness of the first adhesive layer in the pair of end electrode bodies is 1.25 times or more the thickness of the first adhesive layer in the at least one intermediate electrode body (however, when there are two or more intermediate electrode bodies, the thickness of the first adhesive layer in the at least one intermediate electrode body refers to the arithmetic average of the thicknesses of the first adhesive layer in the two or more intermediate electrode bodies). The electricity storage device according to claim 5 .

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