Power storage device

Abstract

To provide a power storage device capable of more enhancing sealing performance of a sealing body while preferably holding an interval between collectors.SOLUTION: In a power storage device 1, a sealing body 3 includes: a plurality of frame-like seal members 32 welded to an edge part 21c of each collector 21; and a plurality of frame-like spacers 31 that is arranged between the seal members 32 and 32 which are adjacent to a lamination direction D. By welding an outer edge part 31a expanded to an outer side from an edge part 21a of each collector 21 in each spacer 31 and an outer edge part 32a expanded to the outer side from an edge part 21c of each collector 21 in the seal members 32 which is adjacent to the lamination direction D to each spacer 31 respectively, an outer front surface of the sealing body 3 is formed. A melt mass flow rate of a resin material constructing the spacer 31 is larger than that of the resin material constructing the seal members 32.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] An example of a conventional power storage device is the bipolar battery described in Patent Document 1. This conventional bipolar battery has multiple bipolar electrodes, each of which has a positive electrode active material layer formed on one side of a current collector and a negative electrode active material layer formed on the other side. The bipolar battery is constructed by stacking these bipolar electrodes with a gel electrolyte layer sandwiched between them.

[0003] In this conventional bipolar battery, a sealing member is disposed between adjacent current collectors in the stacking direction, surrounding the periphery of each unit cell layer, which includes a positive electrode active material layer, a gel electrolyte layer, and a negative electrode active material layer. The sealing member extends to the exterior of the current collectors and is heat-sealed to the exterior of the current collectors. The sealing member is made of an insulating heat-sealing resin such as polyethylene or polypropylene, and is heat-sealed to the current collectors or end current collectors before stacking the bipolar electrodes. These sealing members seal each unit cell layer, preventing leakage from the unit cell layers and short circuits due to contact between the current collectors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-319210 Summary of the Invention [Problem to be solved by the invention]

[0005] In the conventional bipolar battery described above, the portions of the sealing member that are heat-sealed to the current collectors are sandwiched between the current collectors to prevent short circuits due to contact between the current collectors, and the portions of the sealing member that are heat-sealed to each other outside the current collectors seal each cell layer.

[0006] In such a configuration, when a material with a low melt mass-flow rate is used as the resin material for the sealing member, the shape in the thickness direction is likely to be stable at the portion heat-sealed to the current collector when heat-sealed to the current collector, and short circuits due to contact between the current collectors can be suitably prevented. On the other hand, when a material with a low melt mass-flow rate is used as the resin material for the sealing member, the fluidity of both adjacent sealing members in the stacking direction is low at the portion heat-sealed to each other outside the current collector, and therefore there is a risk that the sealing members will not adequately seal each unit cell layer.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an electricity storage device that can more appropriately maintain the spacing between current collectors while further improving the sealing performance of the sealing body. [Means for solving the problem]

[0008] An energy storage device according to one aspect of the present disclosure includes an electrode stack formed by stacking a plurality of bipolar electrodes, each of which includes a pair of electrodes formed by a current collector and active material layers provided on a first surface and a second surface of the current collector, and a sealing body that seals the side surfaces of the bipolar electrodes in the electrode stack extending in the stacking direction, wherein the sealing body has a plurality of frame-shaped sealing members welded to the edges of the current collectors and a plurality of frame-shaped spacers arranged between adjacent sealing members in the stacking direction, and the outer edge of each spacer that protrudes outward beyond the edge of the current collector is welded to the outer edge of each sealing member adjacent to each spacer in the stacking direction, thereby forming an outer surface of the sealing body, and the melt mass flow rate of the resin material constituting the spacers is greater than the melt mass flow rate of the resin material constituting the sealing members.

[0009] The melt mass flow rate is a measure of the fluidity of a resin material when melted. In this energy storage device, the melt mass flow rate of the resin material constituting the spacers is greater than the melt mass flow rate of the resin material constituting the sealing members. Increasing the melt mass flow rate of the resin material constituting the spacers increases the fluidity of each spacer when welding the outer edge of each spacer to the outer edge of each sealing member. This improves the compatibility between the spacers and the sealing members, thereby further improving the hermeticity of the sealed body. Meanwhile, in this energy storage device, the melt mass flow rate of the sealing members welded to the current collectors is reduced, thereby preventing the resin material from spreading toward the active material layer on the surface of the current collector when welding the sealing members to the current collectors. Therefore, in this energy storage device, the thickness dimension of the sealing members after welding can be stabilized, and the spacing between the current collectors in the stacking direction can be more appropriately maintained.

[0010] The thickness of the spacer may be greater than that of the seal member. By making the thickness of the spacer, which has a higher melt mass flow rate than the seal member, greater than that of the seal member, the compatibility between the seal member and the spacer can be more sufficiently ensured. This facilitates welding between the outer edges of the spacer and the outer edges of the seal member, thereby further improving the hermeticity of the sealed body.

[0011] The sealing member may be welded to each of the first and second surfaces of the current collector. In this case, the electrolyte can be prevented from seeping onto the other surface of the current collector, thereby suppressing the occurrence of electrolytic corrosion. Even when sealing members are placed on each of the first and second surfaces of the current collector and then welded by applying pressure and heat from both the first and second surfaces, the melt mass-flow rate of the sealing member welded to the current collector is smaller than the melt mass-flow rate of the resin material constituting the spacer, thereby sufficiently suppressing the spread of the resin material when welding the sealing member to the current collector. Therefore, the dimensional stability of the sealing member in the thickness direction after welding can be more suitably maintained. [Effects of the Invention]

[0012] According to the present disclosure, the gap between the current collectors can be more appropriately maintained while the sealing performance of the sealing body can be further improved. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic cross-sectional view illustrating an electricity storage device according to an embodiment of the present disclosure. [Figure 2] 2 is a schematic enlarged cross-sectional view of a main part of the electricity storage device shown in FIG. 1. FIG. [Figure 3] 1(a) is a schematic cross-sectional view showing the state of welding of the sealing member to the current collector, (b) shows the state in the comparative example, and (c) shows the state in the example. [Figure 4] 10 is a schematic cross-sectional view showing a state in which a seal member and a spacer are welded together. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, preferred embodiments of an electricity storage device according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0015] FIG. 1 is a schematic cross-sectional view showing an energy storage device according to an embodiment of the present disclosure. The energy storage device 1 shown in FIG. 1 is a device used in batteries for various vehicles such as forklifts, hybrid vehicles, and electric vehicles. The energy storage device 1 is a secondary battery such as a nickel-metal hydride secondary battery or a lithium-ion secondary battery. The energy storage device 1 may be an electric double layer capacitor or an all-solid-state battery. In this embodiment, the energy storage device 1 is illustrated as a lithium-ion secondary battery.

[0016] The energy storage device 1 includes an electrode stack 2 formed by stacking a plurality of bipolar electrodes 14, and a sealing body 3 that seals the side surfaces 2a of the electrode stack 2 that extend in a stacking direction D of the bipolar electrodes 14. As shown in Fig. 1, the electrode stack 2 includes a plurality of cells 4. Each cell 4 has a positive electrode 11, a negative electrode 12, and a separator 13.

[0017] The positive electrode 11 and the negative electrode 12 have, for example, a rectangular shape when viewed from the stacking direction. The positive electrode 11 and the negative electrode 12 are disposed facing each other with a separator 13 interposed therebetween. The facing direction of the positive electrode 11 and the negative electrode 12 coincides with the stacking direction D of the bipolar electrode 14. The positive electrode 11 is composed of a current collector 21 and a positive electrode active material layer 23 provided on a first surface 21a of the current collector 21. The negative electrode 12 is composed of a current collector 21 and a negative electrode active material layer 24 provided on a second surface 21b of the current collector 21.

[0018] The current collector 21 is a chemically inactive electrical conductor that continues to pass current through the positive electrode active material layer 23 and the negative electrode active material layer 24 during discharge or charge of the lithium ion secondary battery. In this embodiment, the current collector 21 has a two-layer structure formed by stacking a first current collector 21A for the positive electrode 11 and a second current collector 21B for the negative electrode 12. The first surface 21Aa of the first current collector 21A corresponds to the first surface 21a of the current collector 21 formed by combining the first current collector 21A and the second current collector 21B. The first surface 21Ba of the second current collector 21B corresponds to the second surface 21b of the current collector 21 formed by combining the first current collector 21A and the second current collector 21B.

[0019] In this embodiment, multiple cells 4 are stacked such that the second surface 21Ab of the first current collector 21A of one cell 4 and the second surface 21Bb of the second current collector 21B of another cell 4 are in contact with each other. This electrically connects the multiple cells 4 in series to form the electrode stack 2 described above. In adjacent cells 4, 4 in the stacking direction D, a pseudo-bipolar electrode 14 is formed in which the mutually contacting first current collector 21A and second current collector 21B form a single current collector 21. A terminal electrode (positive terminal electrode) including the first current collector 21A is disposed at one end of the electrode stack 2 in the stacking direction D. A terminal electrode (negative terminal electrode) including the second current collector 21B is disposed at the other end of the electrode stack 2 in the stacking direction D.

[0020] Examples of materials constituting the first current collector 21A and the second current collector 21B include metal materials, conductive resin materials, and conductive inorganic materials. Examples of conductive resin materials include resins in which conductive fillers are added to conductive polymer materials or non-conductive polymer materials. The first current collector 21A and the second current collector 21B may have multiple layers including one or more layers containing the above-mentioned metal materials or conductive resin materials. A coating layer may be formed on the surfaces of the first current collector 21A and the second current collector 21B by a known method such as plating or spray coating.

[0021] The first current collector 21A and the second current collector 21B may be formed in the form of, for example, a plate, foil, sheet, film, mesh, or the like. When the first current collector 21A and the second current collector 21B are made of metal foil, for example, aluminum foil, copper foil, nickel foil, titanium foil, or stainless steel foil is used. The first current collector 21A and the second current collector 21B may also be an alloy foil or clad foil of the above metals. When the first current collector 21A and the second current collector 21B are made of foil, the thickness of the first current collector 21A and the second current collector 21B may be in the range of 1 μm to 100 μm.

[0022] In this embodiment, the first current collector 21A is an aluminum foil, and the second current collector 21B is a copper foil. The first current collector 21A and the second current collector 21B may be integrated together by, for example, copper plating one side of an aluminum foil. The first current collector 21A and the second current collector 21B may also be integrated together by bonding the aluminum foil and the copper foil together.

[0023] The positive electrode active material layer 23 is provided in a rectangular shape on the first surface 21Aa of the rectangular first current collector 21A, with dimensions smaller than the first surface 21Aa. The negative electrode active material layer 24 is provided in a rectangular shape on the first surface 21Ba of the rectangular second current collector 21B, with dimensions slightly smaller than the first surface 21Ba. In other words, at the edge portion 21c of the current collector 21, a region where the positive electrode active material layer 23 is not provided is formed on the first surface 21Aa side, and a region where the negative electrode active material layer 24 is not provided is formed on the first surface 21Ba side. The negative electrode active material layer 24 is formed slightly larger than the positive electrode active material layer 23. When viewed from the stacking direction D, the entire region where the positive electrode active material layer 23 is formed is located in the region where the negative electrode active material layer 24 is formed.

[0024] The positive electrode active material layer 23 includes a positive electrode active material capable of absorbing and releasing charge carriers such as lithium ions. Examples of the positive electrode active material include composite oxides, metallic lithium, and sulfur. The composite oxides include lithium and at least one of iron, manganese, titanium, nickel, cobalt, and aluminum. Examples of the composite oxides include olivine-type lithium iron phosphate (LiFePO4), LiCoO2, and LiNiMnCoO2.

[0025] The negative electrode active material layer 24 includes a negative electrode active material capable of absorbing and releasing charge carriers such as lithium ions. Examples of the negative electrode active material include graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, soft carbon, and other carbons, metal compounds, elements or compounds thereof that can be alloyed with lithium, and boron-doped carbon. Examples of elements that can be alloyed with lithium include silicon and tin.

[0026] In addition to the active material, the positive electrode active material layer 23 and the negative electrode active material layer 24 may contain a binder and a conductive additive. The binder serves to connect the active material or conductive additive to each other and maintain the conductive network within 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 such as polyacrylic acid and polymethacrylic 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 may be used alone or in combination. The conductive additive is, for example, a conductive material such as acetylene black, Kern black, or graphite, which can enhance electrical conductivity. Examples of viscosity-adjusting solvents include N-methyl-2-pyrrolidone.

[0027] The positive electrode active material layer 23 and the negative electrode active material layer 24 can be formed on the current collector 21 by a conventionally known method, such as roll coating, die coating, dip coating, doctor blade coating, spray coating, or curtain coating. Specifically, an active material, a solvent, and, if necessary, a binder and a conductive additive are mixed to produce a slurry-like active material layer-forming composition, which is then applied to the current collector 21 and dried. Examples of solvents that can be used include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The dried active material layer-forming composition may be compressed to increase electrode density.

[0028] The separator 13 is disposed between the positive electrode 11 and the negative electrode 12 in the stacking direction D. The separator 13 is a component that allows charge carriers such as lithium ions to pass through while preventing an electrical short circuit due to contact between the electrodes by isolating the positive electrode 11 and the negative electrode that are adjacent to each other in the electrode stack 2. The separator 13 is disposed between the positive electrode active material layer 23 and the negative electrode active material layer 24 that face each other in the stacking direction D.

[0029] When viewed from the stacking direction D, the separator 13 has a rectangular shape that is slightly larger than the positive electrode active material layer 23 and the negative electrode active material layer 24 and slightly smaller than the current collector 21. When viewed from the stacking direction D, the end portion 13a of the separator 13 is located outside the positive electrode active material layer 23 and the negative electrode active material layer 24, and is welded to a sealing member 32 (described later) on the first surface 21a side of the current collector 21.

[0030] The separator 13 is formed, for example, in a sheet shape. The separator 13 is made of, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains electrolyte. Examples of materials that constitute the separator 13 include polypropylene, polyethylene, polyolefin, and polyester. The separator 13 may have a single-layer structure or a multi-layer structure. In the case of a multi-layer structure, the separator 13 may include, for example, a substrate layer and a pair of adhesive layers, and may be bonded and fixed to the positive electrode active material layer 23 and the negative electrode active material layer 24 by the pair of adhesive layers. The separator 13 may also include a ceramic layer that serves as a heat-resistant layer. The separator 13 may also be reinforced with a vinylidene fluoride resin compound.

[0031] Examples of the electrolyte impregnated into the separator 13 include a liquid electrolyte (electrolytic solution) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, and a polymer gel electrolyte containing an electrolyte held in a polymer matrix. When the separator 13 is impregnated with an electrolyte, known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2 can be used as the electrolyte salt. Known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, and ethers can be used as the non-aqueous solvent. Two or more of these known solvent materials may be used in combination.

[0032] The sealing body 3 is a member that seals the side surfaces 2a of the bipolar electrodes 14 in the electrode stack 2, which extend in the stacking direction D. The sealing body 3 seals the space S between the current collectors 21, 21 adjacent to each other in the stacking direction D. The space S is defined by the sealing body 3 and the current collectors 21, 21 adjacent to each other in the stacking direction D. An electrolyte is accommodated in the space S.

[0033] The sealing body 3 is composed of a plurality of frame-shaped spacers 31 and a plurality of frame-shaped sealing members 32. The spacers 31 are disposed between the current collectors 21, 21 adjacent to each other in the stacking direction D. The spacers 31 are also disposed between the sealing members 32, 32 adjacent to each other in the stacking direction D. The sealing members 32 are welded to the edge portions 21c of the current collectors 21. In this embodiment, as shown in FIG. 2, the sealing members 32 are provided so as to cover the edge portions 21c of the current collectors 21. That is, the sealing members 32 are located on both the first surface 21a side and the second surface 21b side of the edge portions 21c of the current collectors 21, and are also located on the side end surfaces 21d of the current collectors 21 so as to connect these surfaces.

[0034] The sealing member 32 is welded to the first surface 21a over the entire overlapping portion with the first surface 21a, and is welded to the second surface 21b over the entire overlapping portion with the second surface 21b. The sealing member 32 may be welded to the entire side end surface 21d of the current collector 21, or may be welded to only a portion of it. The sealing member 32 does not necessarily have to be welded to the side end surface 21d. In this case, the sealing member 32 may be in contact with the side end surface 21d, or may be slightly spaced from the side end surface 21d.

[0035] The spacer 31 also functions as a member for maintaining the distance between the current collectors 21, 21 adjacent to each other in the stacking direction D. The spacer 31 is disposed between the sealing members 32, 32 that cover the edge portions 21c of the current collectors 21, 21 adjacent to each other in the stacking direction D. A thickness T2 of the spacer 31 is greater than a thickness T1 of the sealing member 32.

[0036] In this embodiment, the sealing member 32 is provided to cover the edge portion 21c of the current collector 21, and the thickness T1 of the sealing member 32 is defined by the thickness of the portion located on the first surface 21a of the current collector 21 (or the thickness of the portion located on the second surface 21b of the current collector 21). The thickness T2 of the spacer 31 is defined by the thickness of the portion located between the sealing members 32, 32 adjacent to each other in the stacking direction D. The ratio of the thickness T2 of the spacer 31 to the thickness T1 of the sealing member 32 is, for example, 1:2 to 1:4.

[0037] The outer edge 32a of the seal member 32 and the outer edge 31a of the spacer 31 both slightly protrude outward beyond the edge 21c of the current collector 21. The outer edge 31a of each spacer 31 that protrudes outward beyond the edge 21c of the current collector 21 and the outer edge 32a of each seal member 32 adjacent to each spacer 31 in the stacking direction D that protrudes outward beyond the edge 21c of the current collector 21 are welded to each other to form a welded portion W, and this welded portion W forms the outer surface 3a of the sealing body 3. The outer edge 31a of the spacer 31 and the outer edge 32a of the seal member 32 can be welded to each other by techniques such as infrared welding or hot plate welding. At the welded portion W, the compatibility of the resin material constituting the seal member 32 and the resin material constituting the spacer 31 ensures sealing of the space S between the adjacent current collectors 21, 21 in the stacking direction D.

[0038] Inside the welded portion W, the spacer 31 is not welded to either the seal member 32 on the first surface 21a of one current collector 21 adjacent to the spacer 31 in the stacking direction D or the seal member 32 on the second surface 21b of the other current collector 21. In the non-welded portion, the spacer 31 and the seal member 32 on the first surface 21a of the current collector 21 may be in contact with each other or may be slightly spaced apart. Similarly, in the non-welded portion, the spacer 31 and the seal member 32 on the second surface 21b of the current collector 21 may be in contact with each other or may be slightly spaced apart. The spacer 31 is not welded to either of the current collectors 21, 21 adjacent to each other in the stacking direction D.

[0039] In this embodiment, the inner edge portion 32b of the sealing member 32 protrudes further inward (i.e., toward the active material layer) than the inner edge portion 31b of the spacer 31 toward the inside of the current collector 21 (i.e., toward the active material layer). That is, when viewed from the stacking direction D, the inner edge portion 31b of the spacer 31 is in a state where it overlaps with the sealing member 32 on the first surface 21a side of the current collector 21 and the sealing member 32 on the second surface 21b side of the current collector 21, inside the welded portion W. On the first surface 21a side of the current collector 21, the end portion 13a of the separator 13 described above is welded to the protruding portion of the inner edge portion 32b of the sealing member 32 from the inner edge portion 31b of the spacer 31.

[0040] Examples of the resin material constituting the sealing member 32 and the spacer 31 include electrolyte-resistant materials such as acid-modified polyethylene (acid-modified PE), acid-modified polypropylene (acid-modified PP), polyethylene, polypropylene, etc. The resin material constituting the sealing member 32 and the resin material constituting the spacer 31 may be the same or different.

[0041] In this embodiment, the resin material constituting the sealing member 32 is acid-modified polyethylene or acid-modified polypropylene, and the resin material constituting the spacer 31 is polyethylene or polypropylene. Acid-modified polyethylene and acid-modified polypropylene have the property of adhering more easily to metal than non-acid-modified polyethylene and non-acid-modified polypropylene. In this embodiment, in which the current collector 21 is made of a metal foil such as copper foil or aluminum foil, by forming the sealing member 32 from acid-modified polyethylene or acid-modified polypropylene, the adhesive strength (bonding strength) to the current collector 21 can be improved. For the spacer 31, which does not require adhesion to the current collector 21, inexpensive polyethylene or polypropylene is used, thereby reducing the cost of the energy storage device 1.

[0042] The melt mass flow rate of the resin material constituting the spacer 31 is greater than the melt mass flow rate of the resin material constituting the sealing member 32. The melt mass flow rate is a measure of the fluidity of a resin material when melted. In this embodiment, the melt mass flow rate is measured in accordance with JIS K 7210 (ISO 1133) at a temperature of 230°C and a load of 2.16 kg. As an example, the melt mass flow rate of the resin material constituting the sealing member 32 is 1 g / 10 min to 10 g / 10 min, and the melt mass flow rate of the resin material constituting the spacer 31 is 5 g / 10 min to 15 g / 10 min.

[0043] Generally, the melt mass flow rate of a resin material has an inverse relationship with the molecular weight of the resin material. The higher the molecular weight, the higher the boiling point and melting point of the resin material, and the lower the melt mass flow rate. The lower the molecular weight, the lower the boiling point and melting point of the resin material, and the higher the melt mass flow rate.

[0044] Therefore, the melt mass flow rate of the resin material constituting the sealing member 32 and the melt mass flow rate of the resin material constituting the spacer 31 can be adjusted by, for example, adjusting the molecular weight of the main component of the resin material. The melt mass flow rate can also be adjusted by adding a secondary material such as an elastomer.

[0045] In manufacturing the electricity storage device 1 as described above, a plurality of current collectors 21 each having a positive electrode active material layer 23 and a negative electrode active material layer 24 provided thereon are prepared. Next, a sealing member 32 is welded to each of the first surface 21a and the second surface 21b of the edge portion 21c of each current collector 21. Next, the current collectors 21 with the sealing members 32 welded thereto are stacked with spacers 31 interposed therebetween. Then, the outer edge portion 31a of each stacked spacer 31 and the outer edge portion 32a of each sealing member 32 are welded to each other to form a welded portion W, and a sealed body 3 is formed by the spacers 31 and the sealing members 32.

[0046] In the above process, when the sealing member 32 is fused to the current collector 21, for example, as shown in FIG. 3(a), frame-shaped sealing members 32 are placed on the first surface 21a side and the second surface 21b of the edge portion 21c of the current collector 21, and the edge portion 21c of the current collector 21 and the sealing members 32 on both sides are sandwiched between heaters 41, 41 and heated and pressurized.

[0047] When welding the seal member 32 to the current collector 21, if the melt mass flow rate of the resin material constituting the seal member 32 is equal to or greater than the melt mass flow rate of the resin material constituting the spacer 31, the seal member 32 is heated and pressurized in the stacking direction D (thickness direction of the seal member 32) by the heaters 41, 41, as shown in FIG. 3(b). This may cause the resin material to spread toward the active material layer on the surface of the current collector 21. If the resin material spreads toward the active material layer, the thickness of the seal member 32 varies depending on the degree of spreading, making the shape of the seal member 32 in the thickness direction unstable after welding. As a result, contact between adjacent current collectors 21, 21 in the stacking direction D may result in a short circuit. Furthermore, if the thickness of the seal member 32 after welding is insufficient, this may also affect the welding of the end 13a of the separator 13 to the seal member 32.

[0048] In contrast, in the electricity storage device 1, the melt mass flow rate of the sealing member 32 welded to the current collector 21 is suppressed, which prevents the resin material from spreading toward the active material layer on the surface of the current collector 21 when the sealing member 32 is welded to the current collector 21 due to heating and pressure applied in the stacking direction D by the heaters 41, 41, as shown in FIG. 3(c). Therefore, in the electricity storage device 1, the dimension of the sealing member 32 in the thickness direction after welding can be stabilized, and the distance between the current collectors 21, 21 in the stacking direction D can be suitably maintained. Therefore, short circuits due to contact between the current collectors 21, 21 can be suitably prevented. Furthermore, because the thickness of the sealing member 32 after welding is sufficiently ensured, welding of the sealing member 32 to the end 13a of the separator 13 can also be suitably performed.

[0049] In the above process, an infrared heater 42 is used to weld the outer edge portion 31a of each spacer 31 to the outer edge portion 32a of each sealing member 32, as shown in Fig. 4, for example. In the example of Fig. 4, the infrared heater 42 is disposed at a distance from the outer edge portion 31a of each spacer 31 and the outer edge portion 32a of each sealing member 32, and heats the outer edge portion 31a of each spacer 31 and the outer edge portion 32a of each sealing member 32 in a non-contact manner from a direction intersecting the stacking direction D (thickness direction of the spacer 31).

[0050] The outer edge portion 31a of each spacer 31 and the outer edge portion 32a of each sealing member 32 are heated while being constrained in the stacking direction D and in close contact with each other. In the spacers 31 and the sealing members 32 adjacent to each other in the stacking direction D, the outer edge portion 31a of each spacer 31 melted by heating and the outer edge portion 32a of each sealing member 32 melted by heating are welded to each other, forming a welded portion W.

[0051] When welding the outer edge portion 31a of each spacer 31 to the outer edge portion 32a of each sealing member 32, if the melt mass flow rate of the resin material constituting the spacer 31 is the same as or smaller than the melt mass flow rate of the resin material constituting the sealing member 32, the fluidity of both the spacer 31 and the sealing member 32 adjacent to each other in the stacking direction D will be low. As a result, compatibility between the spacer 31 and the sealing member 32 will be insufficient, and it is thought that the sealing body 3 will not be able to seal the space S between the current collectors 21, 21 sufficiently.

[0052] In contrast, in the energy storage device 1, the melt mass flow rate of the resin material constituting the spacers 31 is greater than the melt mass flow rate of the resin material constituting the seal members 32. Increasing the melt mass flow rate of the resin material constituting the spacers 31 increases the fluidity of each spacer 31 when welding the outer edge portion 31a of each spacer 31 to the outer edge portion 32a of each seal member 32. Therefore, the compatibility between the spacers 31 and the seal members 32 is sufficiently improved, and the hermeticity of the sealed body 3 can be further improved.

[0053] 4, each spacer 31 is heated by an infrared heater 42 in a direction intersecting the stacking direction D (thickness direction of the spacer 31), and only the outer edge portion 31a of the spacer 31 melts and is welded to the outer edge portion 32a of the seal member 32. Therefore, even if the melt mass flow rate of the resin material constituting the spacer 31 is the same as or higher than the melt mass flow rate of the resin material constituting the seal member 32, the inner edge portion 31b of the spacer 31 located between the current collectors 21, 21 does not melt when welded to the seal member 32, and therefore, it is possible to avoid an effect on the thickness dimension of the spacer 31 for preventing a short circuit between the current collectors 21, 21 adjacent to each other in the stacking direction D.

[0054] In the energy storage device 1, the thickness T2 of the spacers 31 is greater than the thickness T1 of the seal members 32. When welding the outer edge portions 31a of each spacer 31 to the outer edge portions 32a of the seal members 32, the compatibility between the seal members 32 and the spacers 31 can be more sufficiently ensured by the spacers 31 having a greater thickness than the seal members 32, since the spacers 31 have a higher melt mass flow rate than the seal members 32. This facilitates welding between the outer edge portions 31a of the spacers 31 and the outer edge portions 32a of the seal members 32, thereby further improving the hermeticity of the sealed body 3.

[0055] In the electricity storage device 1, the sealing member 32 is welded to each of the first surface 21a and the second surface 21b of the current collector 21. This prevents the electrolyte from seeping onto other surfaces of the current collector 21, thereby suppressing the occurrence of electrolytic corrosion. Even when the sealing members 32 are disposed on each of the first surface 21a and the second surface 21b of the current collector 21 and then welded by applying pressure and heat from both the first surface 21a side and the second surface 21b side, the melt mass flow rate of the sealing member 32 welded to the current collector 21 is smaller than the melt mass flow rate of the resin material constituting the spacer 31, which sufficiently suppresses the spread of the resin material when the sealing member 32 is welded to the current collector 21. This therefore more suitably maintains the dimensional stability of the sealing member 32 in the thickness direction after welding. [Explanation of symbols]

[0056] 1...electricity storage device, 2...electrode laminate, 3...sealing body, 3a...outer surface, 21 (21A, 21B)...current collector, 14...bipolar electrode, 21a...first surface, 21b...second surface, 23...positive electrode active material layer (active material layer), 24...negative electrode active material layer (active material layer), 31...spacer, 31a...outer edge portion, 31b...inner edge portion, 32...sealing member, 32a...outer edge portion, 32b...inner edge portion, D...stacking direction, T1...thickness of sealing member, T2...thickness of spacer.

Claims

1. an electrode stack formed by stacking a plurality of bipolar electrodes, each of which includes a pair of electrodes formed by a current collector and active material layers provided on a first surface and a second surface of the current collector; a sealing body that seals a side surface of the electrode stack that extends in a stacking direction of the bipolar electrodes, the sealing body includes a plurality of frame-shaped sealing members welded to edge portions of the current collectors, and a plurality of frame-shaped spacers disposed between the sealing members adjacent to each other in the stacking direction; an outer edge portion of each spacer that protrudes outward beyond the edge portion of the current collector and an outer edge portion of each sealing member adjacent to each spacer in the stacking direction that protrudes outward beyond the edge portion of the current collector are welded to each other to form an outer surface of the sealing body, The melt mass flow rate of the resin material constituting the spacer is greater than the melt mass flow rate of the resin material constituting the sealing member.

2. 2. The electricity storage device according to claim 1, wherein the thickness of the spacer is greater than the thickness of the sealing member.

3. 3. The electricity storage device according to claim 1, wherein the sealing member is welded to each of the first surface and the second surface of the current collector.

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