JP2023045567A - power storage device - Google Patents

Abstract

To provide a power storage device capable of mitigating deterioration of a battery performance due to temperature changes.SOLUTION: A power storage device includes: a stacked body in which a plurality of current collectors is stacked, each current collector including electrode active material layers provided on a first side and a second side thereof, respectively; and a sealing part sealing a periphery of the stacked body as viewed from a stacking direction of the current collectors. The sealing part has a sealing layer at the periphery of each of the current collectors. The active material layer includes a groove extending linearly. The sealing layer has a belt-shaped portion. The belt-shaped portion includes a notched part and a body part other than the notched part. The notched part has a length in a width direction shorter than a length of the body part in the width direction, and the notched part is provided in a position crossing the extension line of the groove.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to power storage devices.

Patent Document 1 discloses a bipolar battery. This bipolar battery is composed of a bipolar electrode having a positive electrode on one side of a current collector and a negative electrode on the other side, a gel electrolyte sandwiched between the positive electrode and the negative electrode, and the positive electrode, the negative electrode, and the gel electrolyte. and a sealing layer surrounding the cell and between the current collectors.

Japanese Patent Application Laid-Open No. 2004-158343

In the battery described in Patent Document 1, a rectangular active material layer is provided on a rectangular current collector made of metal foil, and a seal layer made of resin is attached to the current collector. located on the periphery. In such a battery, when the active material layer expands and contracts during charging and discharging, stress is concentrated on the corners of the active material layer, and the corners of the current collector may be greatly deformed. If the current collector is repeatedly deformed, the current collector may be damaged and the battery performance may be degraded.

An object of the present disclosure is to provide a power storage device that suppresses deterioration in battery performance.

A power storage device according to one aspect of the present disclosure has a first surface serving as a positive electrode, a second surface facing the first surface serving as a negative electrode, and a rectangular active material layer provided on each of the first surface and the second surface. A laminate in which a plurality of rectangular current collectors are laminated, and a rectangular frame-shaped sealing portion that seals the periphery of the laminate when viewed from the stacking direction of the current collectors, wherein the sealing portion is , a sealing layer welded to at least one of the first surface and the second surface at the periphery of each current collector, and the active material layer provided on at least one of the first surface and the second surface comprises the active material The sealing layer includes grooves extending linearly from one side of a pair of sides facing each other to the other side of the four sides defining the outer periphery of the layer, and the sealing layer is formed on each side of the rectangular current collector. The belt-shaped portion is composed of a notch-shaped portion and a main body portion other than the notch-shaped portion, and when viewed from the stacking direction, the belt-shaped portion extends in the notch-shaped portion The length in the width direction that intersects the direction is shorter than the length in the width direction of the main body portion, and the notched portion is provided at a position that intersects the extension line of the groove when viewed from the stacking direction.

In the power storage device, since the groove is formed in the active material layer, the stress generated by the expansion and contraction of the active material during charging and discharging can be dispersed in the groove. A notch-like portion is formed in the belt-like portion of the sealing layer welded to the peripheral edge of the current collector. In the notched portion, the joint area with the current collector is partially reduced, so that the rigidity of the electrode unit constituted by the current collector and the seal layer is partially reduced. In this case, the stress that tends to concentrate on the corners of the active material layer can be dispersed to the notch-shaped portions via the grooves, for example. As described above, the stress concentrated on the corners of the active material layer is dispersed, so that the deformation of the corners of the current collector is alleviated. Therefore, deterioration of battery performance can be suppressed.

The active material layer may not be provided in the groove. With this configuration, when the current collector is distorted along the groove, damage to the active material layer caused by the distortion is suppressed.

The strip-shaped portion has long side portions and short side portions extending along the long side and short side of the current collector, respectively, and a plurality of cutout portions may be formed at least along the long side portions. In this configuration, the stress is properly controlled on the long sides, which are more susceptible to contraction of the active material layer than on the short sides.

At least one of the first surface and the second surface may be a roughened surface, and the notched portion may be formed only in the seal layer welded to the roughened surface. In this configuration, the seal layer is strongly bonded by the anchoring effect of the roughened surface, so even if the current collector is wrinkled, the current collector and the seal layer are less likely to separate.

It further comprises a pair of rectangular restraint plates that sandwich the laminate in the stacking direction, and a fastening member that fastens the pair of restraint plates together. It may be provided at a position avoiding the extension line. In this configuration, the notch-shaped portion and the fastening member are arranged at positions separated from each other, thereby suppressing a strong binding force of the fastening member from acting on the periphery of the notch-shaped portion.

According to the present disclosure, it is possible to provide a power storage device that suppresses deterioration in battery performance.

FIG. 1 is a schematic side view showing an example power storage device. FIG. 2 is a schematic cross-sectional view showing an example power storage module. FIG. 3 is a schematic plan view of an example electrode unit viewed from the positive electrode side. FIG. 4 is a plan view of an example power storage device viewed from the constraining plate side. FIG. 5 is a schematic plan view of another example of the electrode unit viewed from the positive electrode side.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and overlapping descriptions are omitted. In the description, reference may be made to a Cartesian coordinate system defined by X, Y and Z axes.

FIG. 1 is a side view schematically showing an example power storage device. The power storage device 1 can be used, for example, as a battery for various vehicles such as forklifts, hybrid vehicles, and electric vehicles. The electricity storage device 1 includes a module laminate 2 including an electricity storage module 11 , connecting members 3 and 4 electrically connected to the module laminate 2 , and a pair of ends for restraining the module laminate (laminate) 2 . It has plates (restraining plates) 5, 5 and a fastening member 6 for fastening the end plates 5, 5 together.

The module laminate 2 is configured by stacking a plurality of power storage modules 11 and a plurality of conductive plates P in the Z-axis direction. In the example of FIG. 1, the module laminate 2 includes two power storage modules 11 and three conductive plates P. In the example of FIG. The three conductive plates P are arranged between the power storage modules 11 and at both ends of the module stack 2 in the stacking direction. These conductive plates P are electrically connected to electrodes that constitute the storage module 11 . Here, the two power storage modules 11 are connected in series by a conductive plate P. As shown in FIG.

Inside the conductive plate P, a plurality of flow paths (not shown) for circulating a cooling medium such as air may be provided. By circulating the cooling medium in the flow paths in the conductive plate P, the conductive plate P functions as a connection member that electrically connects the plurality of power storage modules 11 to each other, and also dissipates heat generated in the power storage modules 11. It also has a function as a heat sink that dissipates heat. In the example of FIG. 1 , the area of the conductive plate P is one size smaller than the area of the power storage module 11 . From the viewpoint of improving heat dissipation, the area of the conductive plate P may be equal to the area of the power storage module 11 or may be slightly larger than the area of the power storage module 11 .

The connection members 3 and 4 are conductive members (bus bars) that function as a positive terminal and a negative terminal of the power storage device 1 . The connecting member 3 is electrically connected to the conductive plate P on the positive electrode side, and the connecting member 4 is electrically connected to the conductive plate P on the negative electrode side. The connecting members 3 and 4 are made of, for example, metal material or alloy material. Examples of metal materials include copper, aluminum, titanium, and nickel. Examples of alloy materials include stainless steel plates (SUS301, SUS304, etc.) and alloys of the above metal materials. At least one of the connection members 3 and 4 may be attached with heat radiation fins (not shown) having excellent thermal conductivity. In this case, the heat generated in the power storage module 11 can be effectively dissipated through the conductive plate P, the connection members 3 and 4, and the heat dissipation fins.

The pair of end plates 5, 5 and the fastening member 6 constitute a restraining member that applies a restraining load to the module stack 2 in the stacking direction. A pair of end plates 5, 5 are provided so as to sandwich the module stack 2 in the stacking direction. The end plate 5 is made of, for example, a metal plate. Materials for forming the end plate 5 include, for example, alloys such as copper, aluminum, titanium, nickel, and stainless steel. As shown in FIGS. 1 and 2, the end plate 5 has a rectangular shape that is one size larger than the shape (here, rectangular shape) when the module stack 2 is viewed from the stacking direction. The end plate 5 is arranged concentrically with the module stack 2 when viewed in the stacking direction. As a result, the edges of the four sides of the end plate 5 form overhanging portions 5a that overhang the sandwiched portion of the module stack 2 to the outside.

The fastening member 6 is composed of, for example, a bolt 6A and a nut 6B. The bolt 6A is passed through an insertion hole 5b provided in each overhanging portion 5a of the pair of end plates 5, 5, and the pair of end plates 5, 5 are fastened by screwing a nut 6B. As a result, a binding load is applied to the module stack 2 in the stacking direction via the pair of end plates 5 , 5 . In this embodiment, when viewed from the stacking direction, the fastening members 6 are arranged at equal intervals along the four edges of the overhanging portion 5a of the end plate 5 so as to include the positions corresponding to the corners of the end plate 5. are placed.

FIG. 2 is a schematic cross-sectional view showing the layer structure of the power storage module 11. As shown in FIG. The power storage module 11 is a single cell having a rectangular parallelepiped shape flattened in the Z-axis direction. In this embodiment, a bipolar lithium ion secondary battery is exemplified as the power storage module 11 . The power storage module 11 includes an electrode laminate (laminate) 12 including a plurality of bipolar electrodes 14 and a sealing portion 30 . The bipolar electrodes 14 in the electrode laminate 12 are laminated along the Z-axis direction. The stacking direction of the bipolar electrodes 14 is along the Z-axis direction and coincides with the stacking direction of the power storage modules 11 in the module stack 2 .

The bipolar electrode 14 includes a current collector 21, a positive electrode active material layer (active material layer) 22 provided on the first surface 21a of the current collector 21, and a negative electrode provided on the second surface 21b of the current collector 21. and an active material layer (active material layer) 23 . The current collector 21 and the positive electrode active material layer 22 provided on the first surface 21 a of the current collector 21 constitute the positive electrode of the bipolar electrode 14 . The negative electrode active material layer 23 provided on the second surface 21 b constitutes the negative electrode of the bipolar electrode 14 . The positive electrode active material layer 22 is formed in a rectangular shape at the center of the first surface 21a so that the peripheral edge 21c of the current collector 21 is exposed. The negative electrode active material layer 23 is formed in a rectangular shape at the center of the second surface 21b so that the peripheral edge 21c of the current collector 21 is exposed. In one example, the cathode active material layer 22 is contained within the area of the anode active material layer 23 when viewed in the stacking direction. That is, the outer edge of the positive electrode active material layer 22 is one size smaller than the outer edge of the negative electrode active material layer 23 .

The current collector 21 is a sheet-like conductive member having a rectangular shape in plan view, and has a first surface 21a and a second surface 21b located on the opposite side of the first surface 21a. The current collector 21 is made of, for example, metal foil or alloy foil. Examples of metal foil include copper foil, aluminum foil, titanium foil, nickel foil and the like. As the alloy foil, for example, stainless steel foil (e.g. SUS304, SUS316, SUS301, etc. specified by JIS G 4305:2015), plated steel plate (e.g., JIS G 3141: Cold foil specified by 2005) rolled steel plate (SPCC, etc.), plated stainless steel plate, and the like. The alloy foil may be an alloy foil of the metals exemplified as the material of the metal foil. The current collector 21 may be formed by integrating or laminating a plurality of metal foils, or may be formed by plating the surface of a metal foil with another metal.

The current collector 21 in the illustrated example may be, for example, a clad foil in which an aluminum foil and a copper foil are joined such that the first surface 21a is an aluminum layer and the second surface 21b is a copper layer. In addition, on the first surface 21 a of the current collector 21 , the aluminum layer may be subjected to chromate treatment. In addition, on the second surface 21b of the current collector 21, the copper layer may be plated with nickel. In this case, the nickel plating layer may be a roughened surface, which is a projection-like plating surface on which fine projections are provided. The roughened surface may be formed by roughening such as etching or electroplating, as long as the surface is rougher than the unprocessed metal foil.

The positive electrode active material layer 22 is a layered member containing a positive electrode active material, a conductive aid, and a binder. Examples of positive electrode active materials include composite oxides, metallic lithium, and sulfur. The composition of the composite oxide includes, for example, at least one of iron, manganese, titanium, nickel, cobalt, and aluminum, and lithium. Composite oxides include olivine-type lithium iron phosphate (LiFePO ₄ ), LiCoO ₂ , LiNiMnCoO ₂ and the like.

An example of the positive electrode active material layer 22 is provided on the first surface 21a of the current collector 21 via an adhesive layer. For example, the adhesive layer may be made of an adhesive such as acetylene black. As an example, the edge of the adhesive layer may be formed along the edge of the negative electrode active material layer 23 surrounding the positive electrode active material layer 22 when viewed in the stacking direction.

The binder serves to bind the active material or conductive aid to the surface of the current collector 21 and maintain the conductive network in the electrode. Examples of binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber; thermoplastic resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamideimide; alkoxysilyl group-containing resins; Acrylic resins containing monomer units such as acid and methacrylic acid, styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates such as sodium alginate and ammonium alginate, water-soluble cellulose ester crosslinked products, starch-acrylic acid graft polymers, etc. is mentioned. These binders can be used singly or in combination. Examples of conductive aids include acetylene black, carbon black, and graphite. A viscosity adjusting solvent such as N-methyl-2-pyrrolidone (NMP) may be used for the positive electrode active material layer 22 .

The negative electrode active material layer 23 is a layered member containing a negative electrode active material, a conductive aid, and a binder. Examples of the negative electrode active material include graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, carbon such as hard carbon and soft carbon, metal compounds, elements that can be alloyed with lithium or compounds of such elements, and boron-added carbon. etc. Elements that can be alloyed with lithium include silicon (silicon) and tin. As the conductive aid and the binder, the same ones as those used for the positive electrode active material layer 22 can be used.

In order to form the positive electrode active material layer 22 and the negative electrode active material layer 23 on the current collector 21, conventionally known methods such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, a curtain coating method, and the like can be used. method is used. Specifically, an active material, a solvent, and, if necessary, a binder and a conductive aid are mixed to produce a slurry composition for forming an active material layer, and the composition for forming an active material layer is prepared in the first step. After being applied to the first surface 21a and the second surface 21b, it is dried. Solvents are, for example, N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, water. After drying, they may be compressed to increase electrode density.

In the electrode laminate 12, the bipolar electrodes 14, 14 adjacent in the stacking direction are arranged such that the positive electrode active material layer 22 and the negative electrode active material layer 23 face each other. A separator 15 is arranged between the bipolar electrodes 14 , 14 . In this embodiment, the separator 15 is a sheet-like member having a rectangular shape in plan view, and prevents a short circuit between the bipolar electrodes 14, 14 adjacent in the stacking direction.

The separator 15 has a rectangular shape that is one size larger than the positive electrode active material layer 22 and the negative electrode active material layer 23 and one size smaller than the current collector 21 when viewed in the stacking direction. The end portion 15a of the separator 15 is located outside the positive electrode active material layer 22 and the negative electrode active material layer 23 when viewed in the stacking direction. The end portion 15a of the separator 15 overlaps neither the positive electrode active material layer 22 nor the negative electrode active material layer 23 when viewed from the stacking direction.

The separator 15 is formed in a sheet shape, for example. The separator 15 is, for example, a porous sheet or non-woven fabric containing a polymer that absorbs and retains electrolyte. Examples of materials that constitute the separator 15 include polypropylene, polyethylene, polyolefin, and polyester. The separator 15 may have a single layer structure or a multilayer structure. In the case of a multilayer structure, the separator 15 may include, for example, a base material layer and a pair of adhesive layers, and may be adhered and fixed to the positive electrode active material layer 22 and the negative electrode active material layer 23 by the pair of adhesive layers. The separator 15 may include a ceramic layer that serves as a heat resistant layer. The separator 15 may be reinforced with a vinylidene fluoride resin compound.

Examples of the electrolyte impregnated in the separator 15 include a liquid electrolyte (electrolytic solution) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, or a polymer gel electrolyte containing an electrolyte held in a polymer matrix. is mentioned. When the separator 15 is impregnated with an electrolyte, known electrolyte salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(FSO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ and the like are used. can be used. As the non-aqueous solvent, known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters and ethers can be used. Two or more of these known solvent materials may be used in combination.

In addition to the bipolar electrode 14, the electrode laminate 12 has a positive terminal electrode 16 and a negative terminal electrode 17. The positive terminal electrode 16 includes a current collector 21 and a and the positive electrode active material layer 22 provided. The positive terminal electrode 16 is arranged on one end side of the electrode stack 12 in the stacking direction so that the positive electrode active material layer 22 on the first surface 21 a faces the negative electrode active material layer 23 of the terminal bipolar electrode 14 . In the positive terminal electrode 16, the second surface 21b of the current collector 21 is not provided with the negative electrode active material layer 23, and the second surface 21b is electrically connected to the adjacent conductive plate P. there is

The negative terminal electrode 17 is composed of a current collector 21 and a negative electrode active material layer 23 provided on the second surface 21 b of the current collector 21 . The negative terminal electrode 17 is arranged on the other end side of the electrode laminate 12 in the stacking direction such that the negative electrode active material layer 23 on the second surface 21b faces the positive electrode active material layer 22 of the terminal bipolar electrode 14 . In the negative terminal electrode 17, the positive electrode active material layer 22 is not provided on the first surface 21a of the current collector 21, and the first surface 21a is electrically connected to the adjacent conductive plate P. there is

In addition to the bipolar electrodes 14 , 14 adjacent in the stacking direction, the separators 15 described above are arranged between the bipolar electrode 14 and the positive terminal electrode 16 and between the bipolar electrode 14 and the negative terminal electrode 17 . The placement of the separator 15 prevents short circuits between the bipolar electrode 14 and the positive terminal electrode 16 and short circuits between the bipolar electrode 14 and the negative terminal electrode 17 .

The sealing portion 30 is a member that seals the space S between the current collectors 21 adjacent in the stacking direction. The sealing portion 30 has electrical insulation. The sealing portion 30 is adhered (bonded) to the edge of the current collector 21 . The sealing portion 30 is separated from the positive electrode active material layer 22 and the negative electrode active material layer 23 when viewed in the stacking direction. The sealing portion 30 has a frame shape when viewed in the stacking direction, and is arranged between the current collectors 21 adjacent to each other in the stacking direction so as to surround the positive electrode active material layer 22 and the negative electrode active material layer 23 . In the electric storage module 11, a space S is defined by the current collector 21 and the sealing portion 30 that are adjacent to each other in the stacking direction. The space S accommodates an electrolyte (not shown). The sealing portion 30 is arranged between the current collectors adjacent to each other in the stacking direction, and thus functions as a spacer that maintains the interval between the adjacent current collectors.

An example seal 30 includes a first sealing layer 31 , a second sealing layer 32 and a spacer layer 33 . The first seal layer 31, the second seal layer 32, and the spacer layer 33 each have a frame shape when viewed from the stacking direction. The first sealing layer 31 is bonded to the first surface 21a along the peripheral edge 21c of the current collector 21 . In one example, the outer edge 31 b of the first seal layer 31 is larger than the edge 21 d of the current collector 21 and surrounds the current collector 21 when viewed in the stacking direction. Further, when viewed from the stacking direction, the edge 21d of the current collector 21 is larger than the inner edge 31a of the first seal layer 31 and surrounds the inner edge 31a of the first seal layer 31 . The first seal layer 31 and the current collector 21 are bonded to each other in overlapping regions when viewed in the stacking direction. That is, the first sealing layer 31 and the current collector 21 are bonded to each other in the region from the inner edge 31a of the first sealing layer 31 to the edge 21d of the current collector 21 . The inner edge 31 a of the first seal layer 31 is separated from the positive electrode active material layer 22 when viewed from the stacking direction.

The second sealing layer 32 is bonded to the second surface 21b along the peripheral edge 21c of the current collector 21. As shown in FIG. In one example, the outer edge 32b of the second seal layer 32 is larger than the edge 21d of the current collector 21 and surrounds the current collector 21 when viewed in the stacking direction. For example, the second sealing layer 32 and the current collector 21 are bonded to each other in the overlapping regions. In other words, the second sealing layer 32 and the current collector 21 are joined together in the region from the inner edge 32a of the second sealing layer 32 to the edge 21d of the current collector 21 . The inner edge 32 a of the second seal layer 32 is separated from the negative electrode active material layer 23 when viewed from the stacking direction.

In the positive terminal electrode 16, the first sealing layer 31 is bonded to the first surface 21a of the current collector 21, and the second sealing layer 32 is not bonded to the second surface 21b. Further, in the negative terminal electrode 17, the second sealing layer 32 is bonded to the second surface 21b of the current collector 21, and the first sealing layer 31 is not bonded to the first surface 21a.

The spacer layer 33 is provided between the first sealing layer 31 and the second sealing layer 32 and welded to the first sealing layer 31 and the second sealing layer 32 . The inner edge 31 a of the first seal layer 31 and the inner edge 32 a of the second seal layer 32 are located inside the inner edge 33 a of the spacer layer 33 when viewed from the stacking direction. The inner edges 31a and 32a are located inside the inner edge 33a by, for example, 1 mm or more. That is, the inner edge 31 a of the first seal layer 31 is exposed from the spacer layer 33 so as to face the space S. An inner edge 32 a of the second seal layer 32 is exposed from the spacer layer 33 so as to face the space S.

The spacer layer 33 is welded to the first seal layer 31 outside the inner edge 31a of the first seal layer 31 when viewed in the stacking direction. The spacer layer 33 is welded to the second seal layer 32 outside the inner edge 32a of the second seal layer 32 as viewed in the lamination direction. That is, the bonding region R1 where the first sealing layer 31, the second sealing layer 32 and the spacer layer 33 are welded together is outside the inner edge 31a of the first sealing layer 31 and the inner edge 32a of the second sealing layer 32. . In one example, the bonding region R<b>1 is outside the inner edge 33 a of the spacer layer 33 . In the illustrated example, the region outside the edge 21d of the current collector 21 is the junction region R1. That is, the first seal layer 31, the second seal layer 32, and the spacer layer 33 are separated from the edge 21d of the current collector 21 when viewed from the stacking direction. They are welded together in the region up to their respective outer edges. Therefore, the portion of the spacer layer 33 inside the bonding region R1 is not welded (adhered) to the first seal layer 31 and the second seal layer 32 when viewed in the stacking direction.

An end portion 15 a of the separator 15 is fixed to the second seal layer 32 inside the inner edge 33 a of the spacer layer 33 . The end portion 15a is partially adhered (welded) to the second seal layer 32 by, for example, spot welding or the like.

The first sealing layer 31 is separated from the positive electrode active material layer 22 when viewed from the stacking direction, and the inner edge 31 a is positioned outside the positive electrode active material layer 22 . The second sealing layer 32 is separated from the negative electrode active material layer 23 when viewed from the stacking direction, and the inner edge 32 a is positioned outside the negative electrode active material layer 23 . In the present embodiment, the first sealing layer 31 is also separated from the negative electrode active material layer 23 when viewed from the stacking direction. It may overlap with the negative electrode active material layer 23 .

In the stacking direction, the thickness of the first sealing layer 31 and the thickness of the second sealing layer 32 are thinner than the thickness of the spacer layer 33, for example. The thickness of the first seal layer 31 is the thickness of the portion of the first seal layer 31 sandwiched between the current collector 21 and the spacer layer 33 . The thickness of the second seal layer 32 is the thickness of the portion of the second seal layer 32 sandwiched between the current collector 21 and the spacer layer 33 . The thickness of the spacer layer 33 is the thickness of the portion of the spacer layer 33 sandwiched between the first sealing layer 31 and the second sealing layer 32 . The thickness of the first sealing layer 31 and the second sealing layer 32 may be, for example, 1/10 or more and 1/2 or less of the thickness of the spacer layer 33 . The thicknesses of the first sealing layer 31 and the second sealing layer 32 may be equal to each other, or may be different from each other. Also, the thickness of the first sealing layer 31 and the second sealing layer 32 may be thicker than the spacer layer 33 .

The first seal layer 31, the second seal layer 32, and the spacer layer 33 are, for example, acid-denatured polyethylene (acid-denatured PE), acid-denatured polypropylene (acid-denatured PP), polyethylene, or electrolyte-resistant polyethylene or the like. It is made of a resin material. The resin materials forming the first sealing layer 31, the second sealing layer 32, and the spacer layer 33 may be the same or different. In this embodiment, the first sealing layer 31 and the second sealing layer 32 are made of acid-denatured polyethylene or acid-denatured polypropylene. The spacer layer 33 is made of polyethylene or polypropylene.

FIG. 3 is a plan view of the electrode unit 40 configured by the bipolar electrode 14, the first seal layer 31 and the second seal layer 32, viewed from the positive electrode side. In FIG. 3, the joint region R1 where the first seal layer 31, the second seal layer 32 and the spacer layer 33 are welded together is indicated by a chain double-dashed line. In one example, the position of this two-dot chain line coincides with the edge 21 d of the current collector 21 . In this case, the bonding region R2 between the current collector 21 and the first seal layer 31 extends from the inner edge 31a of the first seal layer 31 to the edge 21d of the current collector 21 (that is, the position of the two-dot chain line in FIG. 3). area. The bonding region R1 is a region outside the inner edge of the bonding region R2 when viewed from the stacking direction, and particularly in the example of FIG. 3, it is a region outside the outer edge of the bonding region R2. Note that the bonding region between the first seal layer 31 and the current collector 21 may overlap the bonding region R2 when viewed from the stacking direction. The inner edges (inner edges 31 a and 32 a in FIG. 2 ) of the bonding regions between the first sealing layer 31 and the second sealing layer 32 and the current collector 21 are located inside the inner edge 33 a of the spacer layer 33 .

The first seal layer 31 includes a low stiffness region 31r. The low-rigidity region 31r is a region in which the peripheral rigidity of the electrode unit 40 is partially reduced. In addition, in the example of FIG. 3, the second seal layer 32 may or may not include a low-rigidity region similar to the low-rigidity region 31r of the first seal layer 31 . For example, if the second seal layer 32 does not include a low-rigidity region, the inner edge 32a of the second seal layer 32 may have a rectangular shape when viewed from the stacking direction.

An example of the low-rigidity region 31r is constituted by a cut-out portion 31k formed in the inner edge 31a of the first seal layer 31. As shown in FIG. That is, the first seal layer 31 is composed of a low-rigidity region 31r having a notch-shaped portion 31k and a portion (main body portion) other than the low-rigidity region 31r having no notch-shaped portion 31k. The body portion may be a belt-like portion in which the notch-like portion 31k is not formed. The notched portion 31k is a portion in which the straight inner edge 31a of the first seal layer 31 is recessed toward the outer edge 31b of the first seal layer 31 . The notch-shaped portion 31k in the illustrated example has an arc shape that draws a substantially semicircular shape when viewed from the stacking direction. A boundary portion between the notched portion 31k and the inner edge 31a of the first sealing layer 31 is connected with a curved locus. The notch-like portion 31k may have a notch-like shape, and does not need to be actually formed by notching. The first seal layer 31 in the illustrated example includes strip-shaped portions that form a pair of long sides 31L (long-side portions), strip-shaped portions that form a pair of short sides 31S (short-side portions), and corners at which the strip-shaped portions intersect. It is formed in a rectangular frame shape having a portion. The long sides 31L extend along the long sides of the current collector 21 and the short sides 31S extend along the short sides of the current collector 21 . When viewed from the stacking direction, in the low-rigidity region 31r, the size of the strip-shaped portion in the width direction (the direction intersecting the extending direction of the strip-shaped portion) is smaller than that of the other regions.

In addition, in the illustrated example, one low-rigidity region 31r is formed on each of the two short sides 31S and the two long sides 31L of the first sealing layer 31 . For example, the low-rigidity region 31r formed on the short side 31S is located in the longitudinal center of the short side 31S. Similarly, the low-rigidity region 31r formed on the long side 31L is located in the longitudinal center of the long side 31L. That is, the low-rigidity region 31r is formed at a position that equally divides the long side 31L or the short side 31S that constitutes the first seal layer 31 .

The first surface 21a of the current collector 21 includes grooves 22a and 22b that divide the positive electrode active material layer 22 by not forming the positive electrode active material. Grooves 22a and 22b linearly extend from one side to the other of a pair of sides facing each other among the four sides defining the outer periphery of the active material layer. In one example, the grooves 22a are parallel to the short sides of the current collector 21 when viewed from the stacking direction, and the grooves 22b are parallel to the long sides of the current collector 21 when viewed from the stacking direction. The width of groove 22a and the width of groove 22b may be the same or different. In one example, the widths of the grooves 22a and 22b are narrower than the width of the opening of the notch-shaped portion 31k. Note that the grooves 22a and 22b may be formed in a groove shape by using a thin active material layer.

The positive electrode active material layer 22 is divided into a plurality of (four in the illustrated example) regions by grooves 22a and 22b. In one example, the groove portion 22a divides the positive electrode active material layer 22 along the short side direction at the center in the long side direction. Further, the groove portion 22b divides the positive electrode active material layer 22 along the long side direction at the center in the short side direction. The low-rigidity region 31r formed in the first seal layer 31 is formed at a position that intersects the extended lines of the grooves 22a and 22b (the center lines of the grooves are indicated by dashed lines in FIG. 3). That is, in the illustrated example, the groove portion 22a extends between the low-rigidity regions 31r formed on the pair of long sides 31L facing each other, and the low-rigidity regions 31r formed on the pair of short sides 31S facing each other. A groove 22b extends therebetween. For example, when the low-rigidity region 31r is formed by an arc-shaped notch-shaped portion 31k, the center line of the groove is positioned at the center of the notch-shaped portion 31k (the center of the arc) so as to divide the notch-shaped portion 31k evenly. pass through

FIG. 4 is a plan view of an example power storage device viewed from the end plate side. As shown in FIG. 4, the fastening member 6 is provided at a position avoiding the extension of the grooves 22a and 22b when viewed from the stacking direction. That is, the fastening member 6 is provided at a position avoiding the virtual line connecting the low-rigidity regions 31r facing each other when viewed from the stacking direction. In the illustrated example, two fastening members 6 are provided along each of the long side and the short side of the end plate 5, and the two fastening members 6 are provided at positions that divide the long side and the short side into approximately three equal parts. ing. Further, in the illustrated example, the fastening members 6 are provided avoiding the four corners of the end plate 5 .

As described above, the power storage device 1 of the example has the first surface 21a as a positive electrode, the second surface 21b facing the first surface 21a as a negative electrode, and the first surface 21a and the second surface 21b each having a rectangular shape. When viewed from the stacking direction of the electrode laminate 12 in which a plurality of rectangular current collectors 21 provided with active material layers (positive electrode active material layer 22, negative electrode active material layer 23) are stacked, and the current collectors 21, and a rectangular frame-shaped sealing portion 30 for sealing the peripheral edge of the electrode laminate 12 . The active material layer has a seal layer (e.g., first seal layer 31) welded to the surface and is provided on at least one of the first surface 21a and the second surface 21b. The sealing layer 31 includes grooves 22a and 22b extending linearly from one side of a pair of sides facing each other to the other side, and the seal layer 31 has a strip-like portion including a long side 31L and a short side 31S. The belt-shaped portion is composed of the notch-shaped portion 31k and the main body portion other than the notch-shaped portion 31k, and the width direction of the notch-shaped portion 31k intersects the extending direction of the belt-shaped portion when viewed from the stacking direction. The width is shorter than the length in the width direction of the main body portion other than the notched portion, and the notched portion 31k is provided at a position that intersects the extension lines of the grooves 22a and 22b when viewed from the stacking direction.

In the power storage device 1, since the grooves 22a and 22b are formed in the active material layer, the stress generated by the expansion and contraction of the active material during charge/discharge can be dispersed in the grooves 22a and 22b. A notch-like portion 31k is formed in the belt-like portion of the seal layer 31 welded to the peripheral edge of the current collector 21 . Since the joint area with the current collector 21 is partially reduced in the cutout portion 31k, the rigidity of the electrode unit 40 constituted by the current collector 21 and the seal layer 31 is reduced. In this case, the stress that tends to concentrate on the corners of the active material layer can be dispersed to the notch-like portions 31k via the grooves 22a and 22b, for example. As described above, the stress concentrated on the corners of the active material layer is dispersed, so that the deformation of the corners of the current collector 21 is alleviated. Therefore, deterioration of battery performance can be suppressed.

In addition, since the linear expansion coefficient of the seal layer is larger than that of the current collector, the power storage device as described above may be subjected to stress due to temperature changes due to use or environment. For example, when cooled from room temperature to about −40° C., it is conceivable that the current collector cannot follow the contraction of the seal layer and wrinkles are formed in the current collector. In this case, depending on the position where wrinkles are formed, it is conceivable that problems such as deterioration of battery performance may occur. However, in the power storage device 1 described above, since the low-rigidity region 31r is formed in the first seal layer 31 at a position that intersects the extension lines of the grooves 22a and 22b, the stress concentrates on the low-rigidity region 31r. At this time, the current collector 21 is easily deformed along the grooves 22a and 22b. Deformation in the grooves 22a and 22b in which no active material is formed hardly affects the battery performance, so that the electrode unit 40 is less susceptible to problems due to temperature changes.

In addition, since the notch-shaped portion 31k is formed in the sealing layer, it is conceivable that the sealing performance of the sealing layer is deteriorated. However, in the power storage device 1, the inner edge of the bonding region R1 between the sealing layer and the spacer layer 33 is located outside the inner edge of the bonding region R2 between the sealing layer and the current collector 21 when viewed from the stacking direction. there is Therefore, part of the stress applied to the sealing portion 30 is dispersed from the inner edge of the bonding region R2 between the sealing layer and the current collector 21 to the inner edge of the bonding region R1 between the sealing layer and the spacer layer 33 . Since the stress applied to the sealing portion 30 is dispersed, deterioration of sealing performance can be suppressed.

The grooves 22a and 22b may be formed only in the positive electrode active material layer 22 on the first surface 21a. With this configuration, the negative electrode active material layer 23 can be easily arranged on the first surface 21 a at a position facing the positive electrode active material layer 22 . As a result, deposition of lithium due to absence of the negative electrode active material layer 23 at a position facing the positive electrode active material layer 22 can be suppressed.

The active material layer may not be provided in the grooves 22a and 22b. In this configuration, when current collector 21 is distorted along grooves 22a and 22b, damage to the active material layer due to the distortion is suppressed.

At least one of the first surface and the second surface may be a roughened surface, and the notched portion may be formed only in the seal layer welded to the roughened surface. In this configuration, the seal layer is strongly bonded by the anchoring effect of the roughened surface, so even if the current collector is wrinkled, the current collector and the seal layer are less likely to separate.

The power storage device 1 includes a pair of rectangular end plates 5 that sandwich the electrode laminate 12 in the stacking direction, and fastening members 6 that fasten the pair of end plates 5 together. , the four corners of the end plate 5 and the extension lines of the grooves 22a and 22b. In this configuration, the notch-shaped portion 31k and the fastening member 6 are arranged at positions separated from each other, thereby suppressing a strong binding force from the fastening member 6 acting around the notch-shaped portion 31k.

Although an example form of the present disclosure has been described in detail above, the present disclosure is not limited to the above form.

FIG. 5 is a plan view of another example of the electrode unit viewed from the positive electrode side. The electrode unit 140 shown in FIG. 5 is composed of the bipolar electrode 14 , the first sealing layer 31 and the second sealing layer 32 . Note that the second sealing layer 32 is not shown in FIG. A basic configuration of an example electrode unit 140 is similar to that of the electrode unit 40 .

In the illustrated example, the low-rigidity regions 31r are formed only on the two long sides 31L of the first seal layer 31, and are not formed on the two short sides 31S. In one example, each of the two long sides 31L is formed with a plurality of (three in the illustrated example) notch-like portions 32k that constitute the low-rigidity region 31r. For example, the cut-out portion 32k may be provided at a position that divides the inner edge 31a along the long side 32L evenly. The grooves 22a formed parallel to the short sides of the current collector 21 extend between the low-rigidity regions 31r formed on the pair of long sides 31L facing each other. That is, the low-rigidity region 31r is formed at a position that intersects the extension line of the groove portion 22a (the center line of the groove portion is indicated by the dashed line in FIG. 5). Three grooves 22a are formed corresponding to the low-rigidity region 31r. The widths of the grooves 22a may be the same or different.

Since a plurality of notch-like portions 31k are formed at least on the long side 31L, stress can be properly controlled on the long side 31L, which is more susceptible to expansion and contraction of the active material layer than on the short side 31S. .

FIG. 3 shows an example in which the low-rigidity region 31r is formed in the first seal layer 31 and the low-rigidity region is not formed in the second seal layer 32. Alternatively, the first seal layer 31 may have a form in which the low-rigidity region is not formed. In this configuration, the second seal layer 32 is strongly bonded by the anchoring effect of the roughened surface, so even if the current collector 21 is wrinkled, the current collector 21 and the first seal layer 31 are less likely to separate. .

Also, although the low-rigidity region formed by the substantially semicircular notch-shaped portion is shown, the shape of the notch-shaped portion is not limited to the illustrated example. For example, the notched portion may be substantially rectangular, substantially triangular, or the like.

Moreover, although an example in which the inner edge of the bonding region R1 is aligned with the edge of the current collector has been shown, the inner edge of the bonding region R1 may be inside or outside the edge of the current collector. may be

The low-rigidity region may be formed on either one of the short sides and the long sides. Also, the number of low-rigidity regions formed in the first seal layer or the second seal layer is not particularly limited. For example, two or more low-rigidity regions may be formed on the long side or short side of the first seal layer or the second seal layer. In addition, although an example in which the low-rigidity regions are formed at positions dividing the long side or the short side of the sealing layer into equal parts has been shown, the low-rigidity regions may be formed at any position on the long side or the short side. .

Although an example in which the positive electrode active material layer is divided into a plurality of parts by the groove has been shown, for example, the negative electrode active material layer may also be divided by the groove. When the grooves are provided in the negative electrode active material layer, the grooves formed in the positive electrode active material layer and the grooves formed in the negative electrode active material layer overlap each other when viewed from the stacking direction. For example, the groove of the negative electrode active material layer is arranged in the region of the groove of the positive electrode active material layer. That is, the negative electrode active material layer is always present on the second surface at a position facing the positive electrode active material layer. Also, the active material layer may be divided into three or less, or may be divided into five or more. Note that the groove may be provided only in the negative electrode active material layer.

Reference Signs List 1 power storage device 12 electrode laminate (laminate) 21 current collector 21a first surface 21b second surface 22 positive electrode active material layer 23 negative electrode active material layer 30 sealing Stopping portion 31 First sealing layer 31k Notched portion 32 Second sealing layer 40 Electrode unit.

Claims (5)

A plurality of rectangular current collectors each having a first surface serving as a positive electrode, a second surface facing the first surface serving as a negative electrode, and a rectangular active material layer provided on each of the first surface and the second surface. a laminated body in which
A rectangular frame-shaped sealing portion that seals the periphery of the laminate when viewed from the stacking direction of the current collector,
The sealing portion has a sealing layer welded to at least one of the first surface and the second surface at the peripheral edge of each of the current collectors,
The active material layer provided on at least one of the first surface and the second surface has a pair of sides facing each other among four sides defining the outer periphery of the active material layer. Including grooves extending linearly along the sides,
The sealing layer has a strip-shaped portion extending along each side of the rectangular current collector,
The band-shaped portion is composed of a notch-shaped portion and a body portion other than the notch-shaped portion,
When viewed from the stacking direction, the length of the notch-shaped portion in the width direction that intersects with the extending direction of the strip-shaped portion is shorter than the length of the main body portion in the width direction,
The power storage device, wherein the notched portion is provided at a position that intersects with the extension line of the groove when viewed from the stacking direction. The power storage device according to claim 1, wherein said active material layer is not provided in said groove. the strip-shaped portion has a long side portion and a short side portion extending along the long side and the short side of the current collector, respectively;
3. The power storage device according to claim 1, wherein a plurality of said notch-shaped portions are formed at least on said long side portion. At least one of the first surface and the second surface is a roughened surface,
The power storage device according to any one of claims 1 to 3, wherein the notch-shaped portion is formed in the sealing layer welded to the roughened surface. Further comprising a pair of rectangular restraint plates that sandwich the laminate in the stacking direction, and a fastening member that fastens the pair of restraint plates together,
The power storage according to any one of claims 1 to 4, wherein the fastening member is provided at a position avoiding four corners of the restraining plate and an extension line of the groove when viewed from the stacking direction. Device.

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