Power storage device

Abstract

This power storage device (10) comprises a laminate (10a) in which a plurality of electrodes (11) are laminated, and a sealing body (15). The sealing body (15) has sealing parts (40) made of resin and spacer parts (50) made of resin. The sealing parts (40) have, in a current collector (12) of each of the plurality of electrodes (11), a first sealing portion (41) welded to a first surface (12a), and a second sealing portion (42) welded to a second surface (12b). The spacer parts (50) have, between current collectors (12) adjacent in a lamination direction X, a first spacer portion (51) and a second spacer portion (52) sandwiched by the first sealing portion (41) welded to one current collector (12) among the adjacent current collectors (12), and the first sealing portion (41) welded to the other current collector (12). The second sealing portion (42) and the second spacer portion (52) are welded to each other, thereby forming a sealing part (16) for sealing an inner space (S). The degree of crystallinity of the resin constituting the spacer parts (50) is higher than the degree of crystallinity of the resin constituting the sealing parts (40).

Description

[Technical Field]

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

[0002] The electricity storage device described in Patent Document 1 includes a laminate in which a plurality of positive electrodes and a plurality of negative electrodes are stacked, and a sealant. The positive electrode includes a current collector and a positive electrode active material layer provided on one side of the current collector. The negative electrode includes a current collector and a negative electrode active material layer provided on one side of the current collector. The sealant is disposed so as to surround the periphery of the positive electrode active material layer and the negative electrode active material layer, and seals the gap between adjacent current collectors. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-16904 Summary of the Invention [Problem to be solved by the invention]

[0004] When a seal made of a resin material is welded to a current collector, thermal shrinkage occurs in the portion of the seal welded to the current collector during welding of the seal to the current collector. The seal is required to suppress deformation of the current collector due to thermal shrinkage of the seal when welded to the current collector, while also suppressing moisture penetration between adjacent current collectors that it seals. [Means for solving the problem]

[0005] According to a first aspect of the present invention, there is provided an energy storage device including a laminate and a sealing body. The laminate is formed by stacking multiple electrodes each composed of a current collector having a positive electrode active material layer on a first surface and a negative electrode active material layer on a second surface. The multiple electrodes are stacked such that the first surface of the current collector of one of the multiple electrodes adjacent to each other in the stacking direction of the multiple electrodes faces the second surface of the current collector of the other electrode. The sealing body is disposed to surround the positive electrode active material layer and the negative electrode active material layer, and seals the gap between the current collectors adjacent to each other in the stacking direction. The sealing body has a sealing portion and a spacer portion made of resin. The resins constituting the sealing portion and the spacer portion are resins having the same main component. The sealing portion has a first sealing portion welded to the first surface and the second surface of the current collector of each of the multiple electrodes, and a second sealing portion extending from the first sealing portion outward beyond the outer edge of the current collector. The spacer portion includes a first spacer portion sandwiched between the first seal portion welded to one of the adjacent current collectors in the stacking direction and a second spacer portion welded to the other of the adjacent current collectors, and a second spacer portion extending from the first spacer portion outward beyond the outer edge of the current collector. The second seal portion and the second spacer portion are welded to each other to form a sealing portion for sealing the internal space between the adjacent current collectors in the stacking direction. The crystallinity of the resin constituting the spacer portion is higher than the crystallinity of the resin constituting the sealing portion.

[0006] Resins with high crystallinity tend to have lower water vapor transmission rates than resins with low crystallinity, so when a resin with high crystallinity is used for the sealant, the penetration of moisture into the internal space can be further suppressed compared to when a resin with low crystallinity is used for the sealant.

[0007] On the other hand, resins with high crystallinity tend to have a higher Young's modulus than resins with low crystallinity. When a resin with high crystallinity is used for the sealant, the thermal contraction of the sealant that occurs when welding it to the current collector increases the contraction force transmitted to the current collector, making the current collector more susceptible to deformation, compared to when a resin with low crystallinity is used for the sealant.

[0008] In the above configuration, the crystallinity of the resin constituting the spacer portion is higher than the crystallinity of the resin constituting the seal portion. The first seal portion of the seal portion is welded to the first and second surfaces of the current collector. By using a resin with a crystallinity lower than that of the resin constituting the spacer portion as the resin constituting the seal portion, the contraction force transmitted to the current collector due to thermal contraction of the seal portion when the seal portion is welded to the current collector can be reduced compared to when the same resin as the resin constituting the spacer portion is used. Therefore, deformation of the current collector due to thermal contraction of the seal portion when the seal portion is welded to the current collector can be suppressed.

[0009] The sealing portion, which is composed of a portion of the sealing portion and a portion of the spacer portion welded together, prevents leakage of electrolyte and infiltration of moisture. By using a resin with a higher crystallinity than the resin that constitutes the sealing portion as the resin that constitutes the spacer portion, the proportion of resin with a higher crystallinity in the resin that constitutes the sealing portion can be increased compared to when the resin that constitutes the spacer portion and the resin that constitutes the sealing portion are the same. Therefore, it is possible to prevent moisture from penetrating between adjacent current collectors sealed by the seal.

[0010] In the above-mentioned energy storage device, the dimension in the stacking direction of the spacer portion arranged between adjacent current collectors in the stacking direction may be larger than the dimension in the stacking direction of the seal portion arranged between adjacent current collectors.

[0011] With this configuration, the ratio of resin with a high degree of crystallinity in the resin constituting the sealing portion can be further increased between adjacent current collectors in the stacking direction compared to when the dimension of the spacer portion in the stacking direction is equal to or less than the dimension of the seal portion in the stacking direction, thereby further suppressing moisture penetration between adjacent current collectors sealed by the seal.

[0012] In the above-described electricity storage device, the sealing portion may be made of acid-modified polyethylene, and the spacer portion may be made of polyethylene. In the above-described electricity storage device, the current collector may include a positive electrode current collector and a negative electrode current collector, and the current collector may be configured by integrating the positive electrode current collector and the negative electrode current collector. [Effects of the Invention]

[0013] According to this invention, it is possible to suppress the occurrence of deformation of the current collector when the seal is welded to the current collector, and also to suppress the permeation of moisture between adjacent current collectors sealed by the seal. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing a part of the electricity storage device. [Figure 3] 10A and 10B are cross-sectional views illustrating a method for welding a seal precursor to an electrode. [Figure 4] FIG. 10 is a cross-sectional view showing an electrode with an integrated sealing portion. [Figure 5] 10A and 10B are cross-sectional views illustrating a method for welding a seal portion and a spacer portion together. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, one embodiment of the electricity storage device will be described with reference to FIGS. <Electricity storage device> 1, the energy storage device 10 includes a stack 10a in which a plurality of electrodes 11, a positive terminal electrode 36, and a negative terminal electrode 37 are stacked, and a sealing body 15. The energy storage device 10 in this embodiment is a lithium ion secondary battery. Hereinafter, the stacking direction of the plurality of electrodes 11 will be simply referred to as the stacking direction X.

[0016] <Electrode> Each of the multiple electrodes 11 includes a current collector 12, a positive electrode active material layer 23, and a negative electrode active material layer 33. The current collector 12 is sheet-shaped. The current collector 12 has a first surface 12a facing one side of the stacking direction X and a second surface 12b facing the other side of the stacking direction X. Each of the multiple electrodes 11 is a bipolar electrode composed of a current collector 12 having a positive electrode active material layer 23 provided on the first surface 12a and a negative electrode active material layer 33 provided on the second surface 12b. In the laminate 10a, the multiple electrodes 11 are stacked such that the first surface 12a of the current collector 12 of one electrode 11 faces the second surface 12b of the current collector 12 of the other electrode 11, among the electrodes 11 adjacent to each other in the stacking direction X.

[0017] In a plan view seen from the stacking direction X (hereinafter simply referred to as a plan view), the positive electrode active material layer 23 is formed in the central portion of the first surface 12a of the current collector 12. In the plan view, the peripheral portion of the first surface 12a of the current collector 12 is a positive electrode uncoated portion 12c where the positive electrode active material layer 23 is not provided. The positive electrode uncoated portion 12c is arranged so as to surround the periphery of the positive electrode active material layer 23 in the plan view. In the plan view, the negative electrode active material layer 33 is formed in the central portion of the second surface 12b of the current collector 12. In the plan view, the peripheral portion of the second surface 12b of the current collector 12 is a negative electrode uncoated portion 12d where the negative electrode active material layer 33 is not provided. The negative electrode uncoated portion 12d is arranged so as to surround the periphery of the negative electrode active material layer 33 in the plan view.

[0018] The positive electrode active material layer 23 and the negative electrode active material layer 33 are disposed so as to face each other in the stacking direction X. The negative electrode active material layer 33 is formed, for example, to be slightly larger than the positive electrode active material layer 23. In a plan view, the entire formation region of the positive electrode active material layer 23 is located within the formation region of the negative electrode active material layer 33.

[0019] <Positive electrode current collector and negative electrode current collector> In this embodiment, the current collector 12 is formed by integrating a sheet-shaped positive electrode current collector 22 and a sheet-shaped negative electrode current collector 32. The first surface 12a of the current collector 12 is formed by one surface of the positive electrode current collector 22, and the second surface 12b is formed by one surface of the negative electrode current collector 32. The integration of the positive electrode current collector 22 and the negative electrode current collector 32 may be achieved by bonding the surface of the positive electrode current collector 22 opposite the first surface 12a to the surface of the negative electrode current collector 32 opposite the second surface 12b.

[0020] The positive electrode current collector 22 and the negative electrode current collector 32 are chemically inactive electrical conductors that allow current to continue to flow through the positive electrode active material layer 23 and the negative electrode active material layer 33 during discharging or charging of the lithium-ion secondary battery. Materials that may be used to form the positive electrode current collector 22 and the negative electrode current collector 32 include, for example, metal materials, conductive resin materials, and conductive inorganic materials.

[0021] Examples of conductive resin materials include resins obtained by adding a conductive filler to a conductive polymer material or a non-conductive polymer material as needed. The positive electrode current collector 22 and the negative electrode current collector 32 may have multiple layers, including one or more layers containing a metal material or a conductive resin material. The surfaces of the positive electrode current collector 22 and the negative electrode current collector 32 may be coated with a known protective layer. The surfaces of the positive electrode current collector 22 and the negative electrode current collector 32 may be metal-plated by a known method such as plating.

[0022] The positive electrode current collector 22 and the negative electrode current collector 32 may have the form of, for example, a foil, a sheet, a film, a wire, a rod, a mesh, or a clad material. When the positive electrode current collector 22 and the negative electrode current collector 32 are metal foils, the positive electrode current collector 22 and the negative electrode current collector 32 may be, for example, aluminum foil, copper foil, nickel foil, titanium foil, or stainless steel foil. The positive electrode current collector 22 and the negative electrode current collector 32 may be alloy foils of the above metals. When the positive electrode current collector 22 and the negative electrode current collector 32 are metal foils, the thickness of the positive electrode current collector 22 and the negative electrode current collector 32 is, for example, 1 to 100 μm. The positive electrode current collector 22 of this embodiment is aluminum foil. The negative electrode current collector 32 of this embodiment is copper foil. In order to improve the structural stability of the laminate 10a, for example, the current collectors 12 of the positive terminal electrode 36 and the negative terminal electrode 37, and some of the current collectors 12 of the multiple electrodes 11 consisting of bipolar electrodes, may have a thickness of 100 μm or more.

[0023] The current collector 12 is not limited to a configuration in which the positive electrode current collector 22 and the negative electrode current collector 32 are integrated, and may be configured as a single sheet-like current collector made of a metal material, a conductive resin material, a conductive inorganic material, or the like. Furthermore, the current collector 12 may be configured as a single plated current collector, in which a coating is formed on one surface of the single sheet-like current collector by plating. In these cases, the single current collector 12 functions as the positive electrode current collector 22 and the negative electrode current collector 32.

[0024] <Details of the positive electrode active material layer and the negative electrode active material layer> The positive electrode active material layer 23 includes a positive electrode active material capable of absorbing and releasing lithium ions as a charge carrier. Examples of the positive electrode active material include polyanion compounds such as olivine-type lithium iron phosphate (LiFePO4), lithium composite metal oxides having a layered rock salt structure, and metal oxides having a spinel structure. The positive electrode active material used is one that can be used as a positive electrode active material for the power storage device 10, such as a lithium-ion secondary battery.

[0025] The negative electrode active material layer 33 includes a negative electrode active material capable of absorbing and releasing charge carriers such as lithium ions. The negative electrode active material is not particularly limited as long as it is an element, alloy, or compound capable of absorbing and releasing charge carriers such as lithium ions. For example, the negative electrode active material may be Li, carbon, a metal compound, an element or compound thereof that can be alloyed with lithium, or the like. Examples of carbon include natural graphite, artificial graphite, hard carbon (non-graphitizable carbon), and soft carbon (easily graphitizable carbon). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Examples of elements that can be alloyed with lithium include silicon and tin.

[0026] The positive electrode active material layer 23 and the negative electrode active material layer 33 may contain other components, such as a conductive additive for improving electrical conductivity, a binder, an electrolyte (polymer matrix, ion-conductive polymer, liquid electrolyte, etc.), an electrolyte supporting salt (lithium salt) for improving ion conductivity, etc. The types and blending ratios of other components contained in the positive electrode active material layer 23 and the negative electrode active material layer 33 are not particularly limited.

[0027] Examples of conductive additives include acetylene black, carbon black, and graphite. Examples of binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber; thermoplastic resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamideimide; alkoxysilyl group-containing resins; acrylic resins such as poly(meth)acrylic acid; styrene-butadiene rubber; carboxymethyl cellulose; alginates such as sodium alginate and ammonium alginate; water-soluble cellulose ester crosslinked bodies; and starch-acrylic acid graft polymers. These binders can be used alone or in combination. Examples of solvents or dispersion media include water and N-methyl-2-pyrrolidone.

[0028] <separator> The electricity storage device 10 includes a separator 35. The separator 35 is disposed between the positive electrode active material layer 23 and the negative electrode active material layer 33. The separator 35 is a member that separates the positive electrode active material layer 23 and the negative electrode active material layer 33 to prevent a short circuit due to contact between the two electrodes, while allowing charge carriers such as lithium ions to pass through.

[0029] The separator 35 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains an electrolyte. Examples of the electrolyte impregnated into the separator 35 include a liquid electrolyte containing a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent, or a polymer gel electrolyte containing an electrolyte retained in a polymer matrix. In this embodiment, a liquid electrolyte is used. Examples of the electrolyte salt for the liquid electrolyte include known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2. Examples of the nonaqueous solvent include known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, and ethers. Two or more of these known solvent materials may be used in combination. Examples of materials constituting the separator 35 include polypropylene, polyethylene, polyolefin, and polyester. The separator 35 may have a single-layer or multilayer structure. The multilayer structure may include, for example, an adhesive layer, a ceramic layer as a heat-resistant layer, and the like.

[0030] <Positive and negative terminal electrodes> In the stacking direction X, the multiple electrodes 11 are located between a positive terminal electrode 36 and a negative terminal electrode 37. The positive terminal electrode 36 has a current collector 12 and a positive electrode active material layer 23 provided on a first surface 12a of the current collector 12, and is configured similarly to the electrode 11 except that it does not have the negative electrode active material layer 33. The negative terminal electrode 37 has a current collector 12 and a negative electrode active material layer 33 provided on a second surface 12b of the current collector 12, and is configured similarly to the electrode 11 except that it does not have the positive electrode active material layer 23. The current collector 12 of the positive terminal electrode 36 is located at one end of the stack 10a in the stacking direction X. The current collector 12 of the negative terminal electrode 37 is located at the other end of the stack 10a in the stacking direction X.

[0031] The second surface 12b of the current collector 12 of the positive terminal electrode 36 constitutes the first outer surface 32a, which is the outer surface at one end of the stacking direction X of the laminate 10a. The first surface 12a of the current collector 12 of the negative terminal electrode 37 constitutes the second outer surface 22a, which is the outer surface at the other end of the stacking direction X of the laminate 10a. The first outer surface 32a and the second outer surface 22a are flat surfaces extending perpendicular to the stacking direction X.

[0032] <Interior space> An internal space S is located between two current collectors 12 adjacent to each other in the stacking direction X. The internal space S is defined by a positive electrode current collector 22 and a negative electrode current collector 32 adjacent to each other in the stacking direction X, and a sealing body 15. One internal space S is defined for each pair of a positive electrode current collector 22 and a negative electrode current collector 32 adjacent to each other in the stacking direction X. A positive electrode active material layer 23, a negative electrode active material layer 33, a separator 35, and a liquid electrolyte (not shown) are disposed in the internal space S. The liquid electrolyte is, for example, a so-called electrolytic solution containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0033] <Positive and negative conductive plates> The energy storage device 10 includes a positive electrode current-carrying plate 38 and a negative electrode current-carrying plate 39. The positive electrode current-carrying plate 38 and the negative electrode current-carrying plate 39 are made of a material with excellent conductivity. Examples of materials that can be used to make the positive electrode current-carrying plate 38 and the negative electrode current-carrying plate 39 include metal materials such as aluminum, copper, and stainless steel. The stack 10a is disposed between the positive electrode current-carrying plate 38 and the negative electrode current-carrying plate 39 in the stacking direction X.

[0034] The positive electrode current-carrying plate 38 is electrically connected to the first outer surface 32a of the laminate 10a. The negative electrode current-carrying plate 39 is electrically connected to the second outer surface 22a of the laminate 10a. Terminals (not shown) are provided on each of the positive electrode current-carrying plate 38 and the negative electrode current-carrying plate 39. The energy storage device 10 is charged and discharged via the terminals provided on the positive electrode current-carrying plate 38 and the negative electrode current-carrying plate 39.

[0035] <Sealing body> The sealing body 15 is disposed so as to surround the periphery of the positive electrode active material layers 23 and negative electrode active material layers 33 of the multiple electrodes 11, the positive electrode terminal electrode 36, and the negative electrode terminal electrode 37, as viewed from the stacking direction X. Hereinafter, the electrodes 11, the positive electrode terminal electrode 36, and the negative electrode terminal electrode 37 may be simply referred to as electrodes 11a. The sealing body 15 seals the gaps between the current collectors 12 adjacent to each other in the stacking direction X.

[0036] As shown in FIG. 2, the sealing body 15 has a plurality of seal portions 40 welded to the current collectors 12 of the plurality of electrodes 11a. Each of the seal portions 40 is made of resin. Each seal portion 40 has a first seal portion 41 and a second seal portion 42. The first seal portion 41 is disposed between the first surface 12a of the current collector 12 of one of the electrodes 11a adjacent to each other in the stacking direction X and the second surface 12b of the current collector 12 of the other electrode 11a. That is, the first seal portion 41 is disposed inside the outer edge 12e of the current collector 12 when viewed from the stacking direction X. The first seal portion 41 is welded to the first surface 12a and the second surface 12b of the current collector 12 of each of the plurality of electrodes 11a. In other words, the seal portion 40 is welded to the first surface 12a and the second surface 12b of the current collector 12 of each of the plurality of electrodes 11a. Examples of a method for welding the seal portion 40 to the first surface 12a and the second surface 12b include known welding methods such as contact or non-contact thermal welding and ultrasonic welding. The first seal portion 41 is welded to the first surface 12a and the second surface 12b via the first weld portion 41a. The first seal portion 41 is welded to each of the positive electrode uncoated portion 12c and the negative electrode uncoated portion 12d.

[0037] The first sealing portion 41 located on the positive electrode uncoated portion 12c is arranged so as to surround the periphery of the positive electrode active material layer 23. The first sealing portion 41 located on the negative electrode uncoated portion 12d is arranged so as to surround the periphery of the negative electrode active material layer 33. The first sealing portion 41 is frame-shaped.

[0038] The second seal portion 42 extends from the first seal portion 41 located between adjacent current collectors 12 in the stacking direction X to the outside of the outer edge 12e of the current collector 12. More specifically, the second seal portion 42 is located outside the outer edge 12e of the current collector 12 when viewed from the stacking direction X. In other words, the seal portion 40 extends from between adjacent current collectors 12 in the stacking direction X to the outside of the laminate 10a.

[0039] The second sealing portion 42 is disposed so as to surround the periphery of the current collector 12 when viewed from the stacking direction X. The second sealing portion 42 is frame-shaped. The second sealing portion 42 covers the end face connecting the first surface 12a and the second surface 12b of the current collector 12, and connects, in the stacking direction X, the outer periphery of the first sealing portion 41 located on the positive electrode uncoated portion 12c and the outer periphery of the first sealing portion 41 located on the negative electrode uncoated portion 12d.

[0040] The sealing body 15 has a plurality of spacer portions 50. Each of the plurality of spacer portions 50 is made of resin. Each of the spacer portions 50 has a first spacer portion 51 and a second spacer portion 52. The first spacer portion 51 overlaps with the first seal portion 41 in the stacking direction X. The second spacer portion 52 overlaps with the second seal portion 42 in the stacking direction X.

[0041] The first spacer portion 51 is sandwiched between adjacent current collectors 12 in the stacking direction X, by a first seal portion 41 located on the positive electrode uncoated portion 12c and a first seal portion 41 located on the negative electrode uncoated portion 12d. As a result, the first spacer portion 51 is sandwiched between adjacent current collectors 12 in the stacking direction X, by a first seal portion 41 welded to one of the adjacent current collectors 12 and a first seal portion 41 welded to the other current collector 12. The first spacer portion 51 is arranged so as to surround the periphery of the positive electrode active material layer 23 and the negative electrode active material layer 33 when viewed from the stacking direction X. The first spacer portion 51 is frame-shaped.

[0042] Both surfaces of the first spacer portion 51 in the stacking direction X are not welded to the first seal portion 41. Therefore, the first spacer portion 51 is not welded to the current collector 12. Both surfaces of the first spacer portion 51 in the stacking direction X may be in contact with the first seal portion 41 or may be separated from the first seal portion 41.

[0043] The first seal portion 41 and the first spacer portion 51 are positioned between adjacent current collectors 12 in the stacking direction X. As a result, the first seal portion 41 and the first spacer portion 51 maintain a gap between the positive electrode current collector 22 of one of the two current collectors 12 adjacent to each other in the stacking direction X and the negative electrode current collector 32 of the other current collector 12, thereby providing insulation. In this way, the seal portion 40 and the spacer portion 50 prevent a short circuit between the positive electrode current collector 22 and the negative electrode current collector 32.

[0044] The second spacer portion 52 is sandwiched between a second seal portion 42 located around one of two current collectors 12 adjacent to each other in the stacking direction X, and a second seal portion 42 located around the other current collector 12. The second spacer portion 52 extends from the first spacer portion 51 to the outside of the stack 10a and is located so as to surround the periphery of the first spacer portion 51. More specifically, the second spacer portion 52 is located outside the outer edge 12e of the current collector 12 when viewed from the stacking direction X. The second spacer portion 52 extends from the first spacer portion 51 outside the outer edge 12e of the current collector 12. The second spacer portion 52 is frame-shaped.

[0045] The second spacer portion 52 is welded to the second seal portion 42 adjacent to the second spacer portion 52 in the stacking direction X. The second spacer portion 52 has a second weld portion 52a at the boundary between adjacent second seal portions 42 in the stacking direction X. In this embodiment, a portion of the second spacer portion 52 is welded to a portion of the adjacent second seal portion 42 in the stacking direction X. More specifically, the second weld portion 52a is not formed on the inner periphery of the second spacer portion 52 that contacts the first spacer portion 51, but is formed along the outer periphery located opposite the inner periphery. As a result, the spacer portion 50 is welded to the seal portion 40 outside the laminate 10a. Examples of a method for welding the second seal portion 42 to the second spacer portion 52 include known welding methods, such as contact or non-contact thermal welding and ultrasonic welding.

[0046] Outside the laminate 10a, the second seal portions 42 and the second spacer portions 52 are integrated with each other by the second welded portions 52a. All of the second seal portions 42 and second spacer portions 52 provided in the electricity storage device 10 are integrated with each other. By welding the second seal portions 42 and the second spacer portions 52 to each other in this manner, a sealing portion 16 is formed. The sealing portion 16 has a cylindrical shape extending in the stacking direction X. When viewed from the stacking direction X, the sealing portion 16 is positioned so as to surround the periphery of the multiple current collectors 12 from the outside of the laminate 10a.

[0047] The sealing portion 16 seals the internal space S between the current collectors 12 adjacent to each other in the stacking direction X. The sealing portion 16 can prevent moisture from entering the internal space S from the outside of the electricity storage device 10. The sealing portion 16 can prevent the liquid electrolyte accommodated in the internal space S from leaking out of the electricity storage device 10.

[0048] The dimension of the first seal portion 41 in the stacking direction X is referred to as seal dimension L1. The dimension of the first spacer portion 51 in the stacking direction X is referred to as spacer dimension L2. Between adjacent current collectors 12 in the stacking direction X, a first seal portion 41 welded to one current collector 12 and a first seal portion 41 welded to the other current collector 12 are located. Therefore, between adjacent current collectors 12 in the stacking direction X, the dimension of the seal portion 40 in the stacking direction X is seal dimension L3, which is the sum of the seal dimensions L1 of the two first seal portions 41. The seal dimension L3 corresponds to the dimension in the stacking direction X of the seal portion 40 arranged between adjacent current collectors 12 in the stacking direction X. The spacer dimension L2 corresponds to the dimension in the stacking direction X of the spacer portion 50 arranged between adjacent current collectors 12 in the stacking direction X.

[0049] The spacer dimension L2 is larger than the seal dimension L3. That is, the dimension in the stacking direction X of the spacer portion 50 arranged between adjacent current collectors 12 in the stacking direction X is larger than the dimension in the stacking direction X of the seal portion 40 arranged between adjacent current collectors 12.

[0050] Furthermore, the spacer dimension L2 may be approximately the same as or slightly smaller than the seal dimension L3. Even in such a case, the relationship in which the spacer dimension L2 is larger than the seal dimension L1 remains the same as in this embodiment in which the spacer dimension L2 is larger than the seal dimension L3.

[0051] The resins constituting the seal portion 40 and the spacer portion 50 are resins having the same main component. The seal portion 40 is made of, for example, an acid-modified polyolefin resin containing a polyolefin resin as its main component and having an acid-modified group. The spacer portion 50 is made of, for example, a non-acid-modified polyolefin resin containing the same polyolefin resin as the seal portion 40 as its main component but not having an acid-modified group. The seal portion 40 of this embodiment is made of acid-modified polyethylene. The spacer portion 50 of this embodiment is made of polyethylene. When resins have the same main component, the crystallinity of the non-acid-modified resin tends to be higher than that of the acid-modified resin. Therefore, the crystallinity of the resin constituting the spacer portion 50 is higher than that of the resin constituting the seal portion 40.

[0052] The seal portion 40 may have a sandwich structure in which unmodified polyethylene (normal polyethylene) is sandwiched between a pair of acid-modified polyethylenes. Even if the seal portion 40 has the sandwich structure described above, since the spacer portion 50 is made of normal polyethylene, the relationship of crystallinity between the seal portion 40 and the spacer portion 50 is the same as in this embodiment in which the seal portion 40 is made of acid-modified polyethylene. In other words, the crystallinity of the spacer portion 50 is higher than that of the seal portion 40.

[0053] The crystallinity refers to the weight ratio of the crystalline portion to the total weight of the polymer solid. Crystallinity can be measured by X-ray diffraction using known methods. The crystallization temperature can also be used as an index of crystallinity. The crystallization temperature is, for example, the peak exothermic temperature during cooling in differential scanning calorimetry. The higher the crystallinity of a resin, the higher the ratio of crystalline portions to the amorphous portions, such as side chains and acid-modified groups, of the resin. The seal portion 40 of this embodiment, made of acid-modified polyethylene, and the spacer portion 50 of this embodiment, made of polyethylene, were measured using differential scanning calorimetry at a heating rate of 10°C / min and a cooling rate of 30°C / min. The crystallization temperatures were 106°C for the seal portion 40 and 114°C for the spacer portion 50, respectively. In this embodiment, the crystallization of the resin constituting the spacer portion 50 is higher than that of the resin constituting the seal portion 40.

[0054] <Method of manufacturing an electricity storage device> Next, a description will be given of a method for manufacturing the electricity storage device 10. Note that, although the following description will be given using the electrode 11, the positive terminal electrode 36 and the negative terminal electrode 37 are also manufactured in the same manner.

[0055] As shown in FIG. 3, when manufacturing the electricity storage device 10, a seal precursor 140 is placed on the electrode 11. The seal precursor 140 is a precursor of the seal portion 40. The seal precursor 140 of this embodiment is made of acid-modified polyethylene. The seal precursor 140 is frame-shaped. The seal precursors 140 are placed on the first surface 12a and the second surface 12b of the current collector 12. The current collector 12 is sandwiched between the two seal precursors 140 from both sides in the thickness direction of the current collector 12. The seal precursors 140 on the first surface 12a and the second surface 12b of the current collector 12 protrude outward beyond the outer edge 12e of the current collector 12.

[0056] The seal precursor 140 disposed on the first surface 12a is also referred to as a first seal precursor 141. The first seal precursor 141 is positioned so as to surround the periphery of the positive electrode active material layer 23 when viewed from the stacking direction X. The seal precursor 140 disposed on the second surface 12b is also referred to as a second seal precursor 142. The second seal precursor 142 is positioned so as to surround the periphery of the negative electrode active material layer 33 when viewed from the stacking direction X.

[0057] Next, the seal precursor 140 is welded to the current collector 12 of the electrode 11. Welding of the seal precursor 140 to the current collector 12 may be performed by thermal welding using, for example, a pair of welding jigs 60. The welding jigs 60 are, for example, impulse sealers having heater wires. In this case, the pair of welding jigs 60 are brought into contact with the first seal precursor 141 and the second seal precursor 142 from both sides in the thickness direction of the current collector 12. The first seal precursor 141 and the second seal precursor 142 are melted by heat transferred from the welding jigs 60.

[0058] 3 and 4, when the first seal precursor 141 and the second seal precursor 142 are melted by heat transferred from the welding jig 60, the first seal precursor 141 is welded to the first surface 12a, and the second seal precursor 142 is welded to the second surface 12b. In addition, the portions of the first seal precursor 141 and the second seal precursor 142 that protrude outward beyond the outer edge 12e of the current collector 12 are welded to each other. As a result, a seal portion 40 is formed in which the outer periphery of the first seal portion 41 located on the first surface 12a and the outer periphery of the first seal portion 41 located on the second surface 12b are connected by the second seal portion 42.

[0059] 4, the first welded portion 41a is formed at the boundary between the first seal portion 41 located on the first surface 12a and the positive electrode current collector 22, and at the boundary between the first seal portion 41 located on the second surface 12b and the negative electrode current collector 32. By welding the seal portion 40 to the current collector 12, the electrode 11 and the seal portion 40 are integrated.

[0060] As shown in FIG. 5, an electrode 11a integrated with a seal portion 40, a separator 35, and a spacer portion 50 are sequentially stacked in the stacking direction X. At this time, of two electrodes 11a adjacent to each other in the stacking direction X, a separator 35 is interposed between the positive electrode active material layer 23 of one electrode 11a and the negative electrode active material layer 33 of the other electrode 11a. This forms a laminate 10a. In addition, of two electrodes 11a adjacent to each other in the stacking direction X, a spacer portion 50 is interposed between the seal portion 40 integrated with one electrode 11a and the seal portion 40 integrated with the other electrode 11a.

[0061] The first spacer portion 51 of the spacer portion 50 overlaps with the first seal portion 41 in the stacking direction X. The second spacer portion 52 of the spacer portion 50 overlaps with the second seal portion 42 in the stacking direction X. The spacer portion 50 is disposed between adjacent seal portions 40 in the stacking direction X so that the outer peripheral edge of the spacer portion 50 overlaps with the outer peripheral edge of the seal portion 40 when viewed from the stacking direction X. This results in the second seal portion 42 and the second spacer portion 52 being located outside the stack 10a.

[0062] Next, the seal portion 40 and the spacer portion 50 are welded together. The seal portion 40 and the spacer portion 50 may be welded together by non-contact thermal welding using, for example, a welding jig 70. The welding jig 70 is, for example, an infrared heater. In this case, the welding jig 70 is positioned from the outside of the laminate 10a so as to be spaced apart from the seal portion 40 and the spacer portion 50 in a direction intersecting the stacking direction X and to face the seal portion 40 and the spacer portion 50. A portion of the second seal portion 42 and a portion of the second spacer portion 52 are heated and melted by the infrared rays irradiated from the welding jig 70. More specifically, a portion of the outer periphery of the second seal portion 42 facing the welding jig 70 and a portion of the outer periphery of the second spacer portion 52 facing the welding jig 70 are melted.

[0063] As shown in FIGS. 2 and 5 , when the second seal portion 42 and the second spacer portion 52 are melted by the welding jig 70, the second seal portion 42 and the second spacer portion 52 are welded to each other. More specifically, a portion of the melted outer periphery of the second seal portion 42 and a portion of the melted outer periphery of the second spacer portion 52 are welded to each other. As a result, the spacer portion 50 is integrated with the seal portion 40. In the stacking direction X, portions of the second seal portion 42 and the second spacer portion 52 are welded to each other via the second weld portion 52a. By welding the second seal portion 42 and the second spacer portion 52 to each other, the second seal portion 42 and the second spacer portion 52 are integrated. The integrated second seal portion 42 and second spacer portion 52 form the sealing portion 16.

[0064] [Action and effect] According to the above embodiment, the following actions and effects can be obtained. (1) Resins with high crystallinity tend to have lower water vapor permeability than resins with low crystallinity. Therefore, when a resin with high crystallinity is used for sealing body 15, the permeation of moisture into internal space S can be further suppressed compared to when a resin with low crystallinity is used for sealing body 15.

[0065] On the other hand, resins with a high degree of crystallinity tend to have a higher Young's modulus than resins with a low degree of crystallinity. When a resin with a high degree of crystallinity is used for seal 15, the thermal contraction of seal 15 that occurs when it is welded to current collector 12 increases the contraction force transmitted to current collector 12, making current collector 12 more likely to deform, compared to when a resin with a low degree of crystallinity is used for seal 15.

[0066] In the above embodiment, the crystallinity of the resin constituting the spacer portion 50 is higher than the crystallinity of the resin constituting the seal portion 40. The first seal portion 41 of the seal portion 40 is welded to the first surface 12a and the second surface 12b of the current collector 12. By using a resin with a crystallinity lower than that of the resin constituting the spacer portion 50 as the resin constituting the seal portion 40, the contraction force transmitted to the current collector 12 due to thermal contraction of the seal portion 40 when the seal portion 40 is welded to the current collector 12 can be reduced compared to when the resin constituting the seal portion 40 is the same as the resin constituting the spacer portion 50. Therefore, deformation of the current collector 12 caused by thermal contraction of the seal portion 40 when the seal portion 40 is welded to the current collector 12 can be suppressed.

[0067] The spacer portion 50 is welded to the seal portion 40 but not to the current collector 12. The sealing portion 16, which is composed of the welded seal portion 40 and a portion of the spacer portion 50, prevents electrolyte leakage and moisture penetration. By using a resin with a higher crystallinity than the resin that constitutes the seal portion 40 as the resin that constitutes the spacer portion 50, the proportion of the resin with a higher crystallinity in the resin that constitutes the sealing portion 16 can be increased compared to when the resin that constitutes the spacer portion 50 is the same as the resin that constitutes the seal portion 40. This prevents moisture from penetrating between adjacent current collectors 12 sealed by the seal 15. Furthermore, because the spacer portion 50 is not welded to the current collector 12, wrinkles and damage to the current collector 12 can be prevented.

[0068] (2) Between adjacent current collectors 12 in the stacking direction X, the dimension of the spacer portion 50 in the stacking direction X is larger than the dimension of the seal portion 40 in the stacking direction X. Therefore, the proportion of resin with a high degree of crystallinity in the resin constituting the sealing portion 16 can be further increased compared to when the dimension of the spacer portion 50 in the stacking direction X between adjacent current collectors 12 in the stacking direction X is equal to or smaller than the dimension of the seal portion 40 in the stacking direction X. Therefore, moisture permeation between adjacent current collectors 12 sealed by the seal 15 can be further suppressed.

[0069] Furthermore, between adjacent current collectors 12 in the stacking direction X, the dimension of the spacer portion 50 in the stacking direction X may be approximately the same as or slightly smaller than the dimension of the seal portion 40 in the stacking direction X. Even in this case, the sealing body 15 is formed by the spacer portion 50 and the seal portion 40, which are made of a material with high crystallinity. Therefore, the sealing ability of the sealing body 15 can be improved compared to when the sealing body 15 is formed by the seal portion 40 alone. Even in this configuration, the higher the ratio of the spacer dimension L2 to the seal dimension L3, the better the sealing ability of the sealing body 15. Furthermore, in the sealing body 15 of each cell, the spacer portion 50 with high crystallinity is sandwiched between a pair of seal portions 40, each of which has a thickness smaller than that of the spacer portion 50. As a result, in the sealing body 15 of each cell, the spacer portion 50 with a high degree of crystallinity is placed in the center and the sealing portions 40 are placed on both sides of it, thereby dispersing the crystallization bias that would occur, and therefore the sealing properties of the sealing body 15 on the positive electrode side and the negative electrode side of each cell can be made equal.

[0070] (3) The resins constituting the seal portion 40 and the spacer portion 50 are made of the same resin as each other. Therefore, when the seal portion 40 and the spacer portion 50 are welded to each other, the seal portion 40 and the spacer portion 50 are easily made compatible with each other. Therefore, the seal portion 40 and the spacer portion 50 can be welded to each other more firmly, thereby increasing the strength of the sealing body 15.

[0071] [Example of change] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0072] The materials of the seal portion 40 and the spacer portion 50 can be changed as long as the crystallinity of the resin constituting the spacer portion 50 is higher than the crystallinity of the resin constituting the seal portion 40 and the resins constituting the seal portion 40 and the spacer portion 50 are resins having the same main component. For example, the resin constituting the seal portion 40 may be acid-modified polypropylene. The resin constituting the spacer portion 50 may be polypropylene. For example, the molecular weight of the main component of the spacer portion 50 may be higher than the molecular weight of the main component of the seal portion 40, thereby making the crystallinity of the resin constituting the spacer portion 50 higher than the crystallinity of the resin constituting the seal portion 40. The crystallinity of the resin constituting the seal portion 40 may be lower than the crystallinity of the resin constituting the spacer portion 50 by mixing a non-crystalline additive such as an elastomer into the material of the seal portion 40.

[0073] Between adjacent current collectors 12 in the stacking direction X, the dimension of the spacer portion 50 in the stacking direction X may be equal to or smaller than the dimension of the seal portion 40 in the stacking direction X. In this case, the spacer dimension L2 is equal to or smaller than the seal dimension L3.

[0074] The energy storage device 10 may include a restraining member that restrains the stack 10a. The restraining member applies a restraining load in the stacking direction X to a region where the positive electrode active material layer 23 and the negative electrode active material layer 33 overlap when the stack 10a is viewed from the stacking direction X. An example of the restraining member includes restraining plates disposed on both ends of the stack 10a in the stacking direction X, and fastening members made of bolts and nuts that fasten the restraining plates together. In the case of this restraining member, the fastening members bias the restraining plates in directions that bring them closer to each other, thereby applying a restraining load in the stacking direction X to the stack 10a.

Claims

1. An electricity storage device, a laminate in which a plurality of electrodes are stacked, each of the electrodes being composed of a current collector having a positive electrode active material layer provided on a first surface thereof and a negative electrode active material layer provided on a second surface thereof, the plurality of electrodes being stacked such that the first surface of the current collector of one of the electrodes adjacent to each other in a stacking direction of the plurality of electrodes faces the second surface of the current collector of the other electrode; a sealant disposed so as to surround the positive electrode active material layer and the negative electrode active material layer, and sealing a gap between the current collectors adjacent to each other in the stacking direction; the sealing body has a resin seal portion and a spacer portion, the resins constituting the sealing portion and the spacer portion are resins having the same main component, the seal portion includes a first seal portion welded to the first surface and the second surface of the current collector of each of the plurality of electrodes, and a second seal portion extending from the first seal portion outward beyond an outer edge of the current collector, The spacer portion is a first spacer portion sandwiched between the current collectors adjacent in the stacking direction by the first seal portion welded to one of the adjacent current collectors and a first seal portion welded to the other current collector; a second spacer portion extending from the first spacer portion outward beyond an outer edge of the current collector, the second seal portion and the second spacer portion are welded to each other to form a sealing portion for sealing an internal space between the current collectors adjacent in the stacking direction, The energy storage device, wherein the crystallinity of the resin constituting the spacer portion is higher than the crystallinity of the resin constituting the seal portion.

2. 2. The energy storage device according to claim 1, wherein a dimension in the stacking direction of the spacer portion disposed between adjacent current collectors in the stacking direction is larger than a dimension in the stacking direction of the seal portion disposed between adjacent current collectors.

3. The sealing portion is made of acid-modified polyethylene, The power storage device according to claim 1 , wherein the spacer portion is made of polyethylene.

4. the current collector comprises a positive electrode current collector and a negative electrode current collector, The power storage device according to claim 1 , wherein the current collector is configured by integrating the positive electrode current collector and the negative electrode current collector.

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