JP2022077634A - Power storage device - Google Patents

Abstract

To suppress copper elution from a negative electrode collector into an electrolyte filling a space.SOLUTION: A seal member 50 is disposed between a positive electrode surface 32a of a positive electrode collector 32 and a negative electrode surface 22a of a negative electrode collector 22. In a first direction X and a second direction Y, the seal member 50 surrounds a positive electrode active material layer 33 and a negative electrode active material layer 23. The negative electrode collector 22 is made of copper. In plan view from a lamination direction Z, the negative electrode surface 22a is covered with the negative electrode active material layer 23 and the seal member 50. The negative electrode active material layer 23 and the seal member 50 are in contact with each other.SELECTED DRAWING: Figure 1

Description

The present invention relates to a power storage device.

The power storage device, which is a lithium ion secondary battery described in Patent Document 1, includes a plurality of stacked current collectors, a positive electrode active material layer, a negative electrode active material layer, and a sealing member. The positive electrode active material layer is arranged on one surface of the current collector in the stacking direction of the current collector. The negative electrode active material layer is arranged on the other surface of the current collector in the stacking direction. The sealing member is arranged between two current collectors adjacent to each other in the stacking direction, and tightly seals the periphery of the positive electrode active material layer and the negative electrode active material layer. The electrolytic solution is injected into the space partitioned by the current collector and the sealing member.

Further, as a current collector, a current collector including a negative electrode current collector made of copper is known. In this case, the negative electrode active material layer is arranged on one surface of the negative electrode current collector in the stacking direction.

Japanese Unexamined Patent Publication No. 2020-61221

By the way, a part of one surface of the negative electrode current collector in the stacking direction may be an exposed surface on which the negative electrode active material layer is not arranged and is exposed in the electrolytic solution in the space. In this case, electrolysis that fills the space when the potential of the negative electrode current collector rises from the injection of the electrolytic solution into the space to the initial charge or when an overdischarge occurs to the potential at which copper elutes in the electrolytic solution. Copper may elute from the exposed surface in the liquid. If copper elutes in the electrolytic solution, various problems such as short circuit, gas generation, and deterioration of sealing property due to the sealing member may occur, which is not preferable.

The power storage device that solves the above problems includes a current collector that is laminated in the stacking direction, a positive electrode active material layer that is arranged on the first surface that is one surface of the current collector in the stacking direction, and a positive electrode active material layer that is arranged in the stacking direction. The negative electrode active material layer arranged on the second surface which is the other surface of the current collector, and the first surface of the current collector of the two adjacent current collectors in the stacking direction. A seal member is provided between the second surface of the other current collector and surrounding the positive electrode active material layer and the negative electrode active material layer in an orthogonal direction orthogonal to the stacking direction. A power storage device for a lithium ion secondary battery in which the inside of a space partitioned by two adjacent current collectors adjacent to each other in the stacking direction and the sealing member is filled with an electrolytic solution, and the current collector is a power storage device. The second surface is one surface of the negative electrode current collector in the stacking direction, and the negative electrode active material layer and the sealing member in a plan view from the stacking direction. The negative electrode active material layer and the sealing member are in contact with each other.

According to the above configuration, the second surface does not have a negative electrode active material layer and has no exposed surface exposed to the electrolytic solution in the space. Therefore, it is possible to suppress the elution of copper from the negative electrode current collector into the electrolytic solution that fills the space during the period from the injection of the electrolytic solution into the space to the initial charge or when an overdischarge occurs.

In the power storage device, it is preferable that the boundary position between the negative electrode active material layer and the sealing member does not overlap with the positive electrode active material layer when the second surface is viewed in a plan view in the stacking direction.

As a means of covering one surface of the negative electrode current collector with the negative electrode active material layer and the seal, a molten sealing material is arranged around the negative electrode active material layer with respect to the negative electrode current collector having the negative electrode active material layer arranged on one surface. There is a way. In such a method, when the molten sealing material comes into contact with the peripheral edge portion of the negative electrode active material layer, the peripheral edge portion of the negative electrode active material layer may receive heat transfer from the sealing material to change the component.

According to the above configuration, the boundary position between the negative electrode active material layer and the sealing member does not overlap with the positive electrode active material layer when the second surface is viewed in a plan view in the stacking direction. Therefore, the peripheral edge of the negative electrode active material layer does not face the positive electrode active material layer in the stacking direction. Therefore, even if the component changes due to the influence of heat when the seal member is formed so as to abut on the peripheral edge of the negative electrode active material layer, the influence on the battery performance can be suppressed.

In the power storage device, it is preferable that the seal member covers the second surface with an area larger than the area covering the first surface.
According to the above configuration, the second surface has a larger area covered by the sealing member than the first surface. That is, by increasing the covering area of the sealing member on the second surface, the second surface does not have an exposed surface on which the negative electrode active material layer is not arranged and is exposed. Therefore, on the second surface, elution of copper from the negative electrode current collector into the electrolytic solution can be further suppressed as compared with the case where the covering area by the negative electrode active material layer containing the electrolytic solution inside is increased.

In the power storage device, it is preferable that the first surface includes an exposed surface that is not covered by either the positive electrode active material layer or the sealing member.
According to the above configuration, the space inside the power storage device can be increased by the amount that the first surface includes the exposed surface. Therefore, even if gas is generated during the use of the power storage device, the increase in the internal pressure of the power storage device can be reduced by the amount of the large space.

In the power storage device, the seal member includes a first seal portion joined to the first surface of the one of the current collectors and the second surface of the other of the current collectors, and the other of the current collectors. The negative electrode active material layer comprises a second seal portion that is joined only to the second surface of the body and extends from the first seal portion toward the negative electrode active material layer in the orthogonal direction. It may be in contact with the second seal portion.

In the power storage device, the dimension of the second seal portion in the stacking direction is preferably smaller than that of the negative electrode active material layer.
According to the above configuration, the space can be increased by the amount that the dimension of the second seal portion in the stacking direction is made smaller than that of the negative electrode active material layer. Therefore, when gas is generated during the use of the power storage device, the increase in the internal pressure of the power storage device can be further reduced.

The power storage device further includes a separator located between the positive electrode active material layer and the negative electrode active material layer in the stacking direction, and the sealing member faces the space and has an installation surface intersecting the stacking direction. It is preferable that the end portion of the separator is arranged on the installation surface.

According to the above configuration, by arranging the end portion of the separator on the installation surface of the seal member, the separator can be positioned in the orthogonal direction.

According to the present invention, it is possible to suppress the elution of copper from the negative electrode current collector into the electrolytic solution that fills the space.

Sectional drawing which shows the power storage device. FIG. 3 is a sectional perspective view showing a storage cell. Sectional drawing which shows the storage cell. FIG. 6 is a cross-sectional view showing a storage cell before being stacked as a cell stack. In another embodiment, a cross-sectional view showing a storage cell before being stacked as a cell stack. In another embodiment, a cross-sectional view showing a storage cell before being stacked as a cell stack. In another embodiment, a cross-sectional view showing a storage cell before being stacked as a cell stack.

Hereinafter, embodiments in which the power storage device is embodied will be described with reference to FIGS. 1 to 4. The power storage device is, for example, a power storage module used for batteries of various vehicles such as forklifts, hybrid vehicles, and electric vehicles. The power storage device of this embodiment is a lithium ion secondary battery.

As shown in FIG. 1, the power storage device 10 includes a cell stack 11, a positive electrode energizing plate 12b, and a negative electrode energizing plate 12a. The positive electrode energizing plate 12b and the negative electrode energizing plate 12a face each other with the cell stack 11 interposed therebetween. The positive electrode energizing plate 12b and the negative electrode energizing plate 12a are made of a metal good conductive material. The cell stack 11, the positive electrode energizing plate 12b, and the negative electrode energizing plate 12a are laminated in the stacking direction Z. The stacking direction Z is a direction perpendicular to the outer surface of the positive electrode energizing plate 12b and the negative electrode energizing plate 12a adjacent to the cell stack 11. The cell stack 11 is a laminated body in which a plurality of storage cells 20 are laminated in the stacking direction Z.

The positive electrode energizing plate 12b and the negative electrode energizing plate 12a are electrically connected to the cell stack 11, respectively. Although not shown, terminals are connected to each of the positive electrode energizing plate 12b and the negative electrode energizing plate 12a. The power storage device 10 is charged and discharged through this terminal.

The cell stack 11, the positive electrode energizing plate 12b, and the negative electrode energizing plate 12a are constrained by restraint units or the like from both sides in the stacking direction Z. As a result, the restraining load in the stacking direction Z is applied to the cell stack 11, the positive electrode energizing plate 12b, and the negative electrode energizing plate 12a.

Each storage cell 20 includes a positive electrode 31, a negative electrode 21, and a separator 40. The positive electrode 31 includes a positive electrode current collector 32 and a positive electrode active material layer 33 arranged on the positive electrode surface 32a, which is one surface of the positive electrode current collector 32. The positive electrode current collector 32 does not have the positive electrode active material layer 33 on the positive electrode back surface 32b, which is the back surface of the positive electrode surface 32a.

The negative electrode 21 includes a negative electrode current collector 22 and a negative electrode active material layer 23 arranged on the negative electrode surface 22a, which is one surface of the negative electrode current collector 22. The negative electrode current collector 22 does not have the negative electrode active material layer 23 on the negative electrode back surface 22b, which is the back surface of the negative electrode surface 22a.

In the present embodiment, the positive electrode current collector 32 and the negative electrode current collector 22 have a rectangular shape having the same area in a plan view from the stacking direction Z. The positive electrode current collector 32 and the negative electrode current collector 22 overlap each other in a plan view seen from the stacking direction Z. The positive electrode active material layer 33 has a rectangular shape smaller than that of the positive electrode current collector 32 in a plan view seen from the stacking direction Z. The negative electrode active material layer 23 has a rectangular shape that is smaller than the negative electrode current collector 22 and larger than the positive electrode active material layer 33 in a plan view from the stacking direction Z.

As shown in FIGS. 2 and 3, when the negative electrode current collector 22 is viewed from the stacking direction Z in a plan view, the direction in which the long side of the negative electrode current collector 22 extends is referred to as the first direction X, and the negative electrode current collector 22 is used. The direction in which the short side of is extended is called the second direction Y. Although not shown, in a plan view of the positive electrode current collector 32 viewed from the stacking direction Z, the long side of the positive electrode current collector 32 extends in the first direction X, and the short side of the positive electrode current collector 32. Extends in the second direction Y. The first direction X is a direction orthogonal to the stacking direction Z. The second direction Y is a direction orthogonal to both the stacking direction Z and the first direction X. The first direction X and the second direction Y correspond to orthogonal directions orthogonal to the stacking direction Z.

As shown in FIG. 1, the separator 40 is located between the positive electrode active material layer 33 and the negative electrode active material layer 23 in the stacking direction Z. The positive electrode active material layer 33 and the negative electrode active material layer 23 face each other in the stacking direction Z via the separator 40. In a plan view from the stacking direction Z, the entire positive electrode active material layer 33 overlaps with the negative electrode active material layer 23 via the separator 40.

The separator 40 has a rectangular shape larger than the positive electrode active material layer 33 and the negative electrode active material layer 23 in a plan view from the stacking direction Z. In a plan view of the separator 40 viewed from the stacking direction Z, the long side of the separator 40 extends in the first direction X, and the short side of the separator 40 extends in the second direction Y.

The separator 40 includes a separator central portion 40a located at the center and a separator end portion 40b located around the separator central portion 40a in a plan view from the stacking direction Z. In a plan view from the stacking direction Z, the separator central portion 40a overlaps the entire positive electrode active material layer 33 and the negative electrode active material layer 23. In a plan view from the stacking direction Z, the separator end portion 40b is located outside the positive electrode active material layer 33 and the negative electrode active material layer 23. One surface of the separator end portion 40b in the stacking direction Z is welded to and bonded to the positive electrode surface 32a and is arranged along the positive electrode surface 32a.

The separator 40 separates the positive electrode 31 and the negative electrode 21. The separator 40 is a member that allows charge carriers such as lithium ions to pass through while preventing a short circuit due to contact between the positive electrode 31 and the negative electrode 21. The separator 40 may be adhered to the positive electrode active material layer 33 and the negative electrode active material layer 23 with an adhesive or the like. The separator 40 may be adhered to the positive electrode active material layer 33 and the negative electrode active material layer 23 by pressurizing the storage cell 20 by a known method such as hot pressing.

As shown in FIG. 1, the power storage device 10 includes a seal member 50. The seal member 50 is arranged between the positive electrode current collector 32 and the negative electrode current collector 22 that are adjacent to each other in the stacking direction Z. The sealing member 50 contains an insulating material and insulates between the positive electrode current collector 32 and the negative electrode current collector 22 to prevent a short circuit between the two current collectors.

As shown in FIGS. 2 and 3, the seal member 50 has a square frame shape in a plan view of the seal member 50 when viewed from the stacking direction Z. The sealing member 50 surrounds the positive electrode active material layer 33 and the negative electrode active material layer 23 by four edges. The two edges of the seal member 50 surround the positive electrode active material layer 33 and the negative electrode active material layer 23 in the first direction X. The two edges of the seal member 50 surround the positive electrode active material layer 33 and the negative electrode active material layer 23 in the second direction Y. The seal member 50 is welded to the positive electrode surface 32a of the positive electrode current collector 32 and the negative electrode surface 22a of the negative electrode current collector 22 among the positive electrode current collector 32 and the negative electrode current collector 22 adjacent to each other in the stacking direction Z. ing.

The seal member 50 is made of resin. Examples of the material constituting the seal member 50 include various resin materials such as polyethylene (PE), polystyrene (PS), polypropylene (PP), modified polypropylene (modified PP), ABS resin, and AS resin.

Inside the power storage cell 20, a space S is partitioned by a positive electrode current collector 32 and a negative electrode current collector 22 adjacent to each other in the stacking direction Z, and a seal member 50. The space S houses the positive electrode active material layer 33, the negative electrode active material layer 23, the separator 40, and the electrolytic solution.

The positive electrode current collector 32 and the negative electrode current collector 22 are chemically inert electric conductors. Copper is used as the material constituting the negative electrode current collector 22. As the material constituting the positive electrode current collector 32, for example, a metal material, a conductive resin material, a conductive inorganic material, or the like can be used. Examples of the conductive resin material include a conductive polymer material and a resin obtained by adding a conductive filler to a non-conductive polymer material as needed. The positive electrode current collector 32 may include a plurality of layers including one or more layers including a metal material or a conductive resin material.

A coating layer may be formed on the surface of the positive electrode current collector 32 by a known method such as plating treatment or spray coating. The positive electrode current collector 32 and the negative electrode current collector 22 may be formed in, for example, a plate shape, a foil shape, a sheet shape, a film shape, a mesh shape, or the like.

When the positive electrode current collector 32 is a metal foil, for example, an aluminum foil, a copper foil, a nickel foil, a titanium foil, a stainless steel foil, or the like can be used. When a stainless steel foil is used as the positive electrode current collector 32, the mechanical strength of the positive electrode current collector 32 can be ensured. Examples of the stainless steel foil include SUS316, SUS301, and SUS304 specified in JIS G4305: 2015. The positive electrode current collector 32 may be an alloy foil or a clad foil of the above metal. When the foil-shaped positive electrode current collector 32 and the negative electrode current collector 22 are used, the thickness thereof may be, for example, 1 to 100 μm.

As the material constituting the positive electrode current collector plate 12b, the same material as the material constituting the positive electrode current collector 32 can be used. As the material constituting the negative electrode current collector plate 12a, the same material as the material constituting the negative electrode current collector 22 can be used. The positive electrode current collecting plate 12b and the negative electrode current collecting plate 12a may be made of a metal plate thicker than the positive electrode current collector 32 and the negative electrode current collector 22.

The positive electrode active material layer 33 contains a positive electrode active material capable of storing and releasing charge carriers such as lithium ions. As the positive electrode active material, a material that can be used as a positive electrode active material for a lithium ion secondary battery, such as a lithium composite metal oxide having a layered rock salt structure, a metal oxide having a spinel structure, and a polyanionic compound, may be adopted. Further, two or more kinds of positive electrode active materials may be used in combination.

The negative electrode active material layer 23 can be used without particular limitation as long as it is a simple substance, an alloy, or a compound capable of storing and releasing charge carriers such as lithium ions. For example, examples of the negative electrode active material include carbon, a metal compound, an element that can be alloyed with lithium, or a compound thereof. Examples of carbon include natural graphite, artificial graphite, hard carbon (non-graphitizable carbon), and soft carbon (easy graphitizable carbon). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Examples of elements that can be alloyed with lithium include silicon and tin.

The positive electrode active material layer 33 and the negative electrode active material layer 23 are also simply referred to as an active material layer. The active material layer contains a conductive auxiliary agent, a binder, an electrolyte (polymer matrix, an ionic conductive polymer, an electrolytic solution, etc.) for enhancing electrical conductivity, and an electrolyte supporting salt for enhancing ionic conductivity, if necessary. (Lithium salt) and the like may be further contained. The components contained in the active material layer, the compounding ratio of the components, and the thickness of the active material layer are not particularly limited, and conventionally known findings regarding a lithium ion secondary battery can be appropriately referred to. The thickness of the active material layer is, for example, 2 to 150 μm. In order to form the active material layer on the surfaces of the positive electrode current collector 32 and the negative electrode current collector 22, a conventionally known method such as a roll coating method may be used.

In order to improve the thermal stability of the positive electrode 31 and the negative electrode 21, a heat resistant layer may be provided on the positive electrode surface 32a or the surface of the active material layer. The heat-resistant layer may contain, for example, inorganic particles and a binder, and may also contain an additive such as a thickener.

The conductive auxiliary agent is added to increase the conductivity of the positive electrode 31 or the negative electrode 21. Conductive aids are, for example, acetylene black, carbon black, graphite and the like.
Examples of the binder include fluororesins 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 and polyacrylics. Examples thereof include acrylic resins such as acids and polymethacrylic acid, styrene-butadiene rubbers, carboxymethyl cellulose, sodium alginate, arginates such as ammonium alginate, water-soluble cellulose ester cross-linking products, and starch-acrylic acid graft polymers. These binders can be used alone or in combination. As the solvent, for example, water, N-methyl-2-pyrrolidone and the like are used.

The separator 40 may be, for example, a porous sheet or a non-woven fabric containing a polymer that absorbs and retains an electrolyte. Examples of the material constituting the separator 40 include polyolefins such as polypropylene and polyethylene, polyester and the like. The separator 40 may have a single-layer structure or a multi-layer structure. The multilayer structure may have, for example, a ceramic layer as a heat-resistant layer. The separator 40 may be impregnated with an electrolyte, or the separator 40 itself may be composed of an electrolyte such as a polymer electrolyte or an inorganic electrolyte.

Examples of the electrolyte impregnated in the separator 40 include an electrolyte solution which is a liquid electrolyte containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, a polymer gel electrolyte containing an electrolyte retained in a polymer matrix, and the like. Can be mentioned.

When the separator 40 is impregnated with an electrolytic solution, the electrolyte salts thereof include 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. Known lithium salts can be used. Further, as the non-aqueous solvent, known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, and ethers can be used. In addition, you may use two or more kinds of these known solvent materials in combination.

The positive electrode current collector 32 in this embodiment is an aluminum foil. The negative electrode current collector 22 in this embodiment is a copper foil. The positive electrode active material layer 33 in the present embodiment contains olivine-type lithium iron phosphate (LiFePO ₄ ) as a composite oxide. The negative electrode active material layer 23 in the present embodiment contains graphite as a carbon-based material. In this embodiment, the separator 40 is impregnated with an electrolytic solution.

Next, the storage cell 20 before being stacked to form the cell stack 11 will be described in more detail, focusing on the configuration of the seal member 50.
As shown in FIG. 4, the seal member 50 includes a seal body 56 and a seal end 57. The seal main body 56 is arranged between the positive electrode surface 32a of the positive electrode current collectors 32 adjacent to each other in the stacking direction Z and the negative electrode surface 22a of the negative electrode current collector 22. The seal end portion 57 extends from the seal main body 56 to the outside of the positive electrode current collector 32 and the negative electrode current collector 22.

The seal body 56 may include a first seal portion 58 and a second seal portion 59. The second seal portion 59 extends from the first seal portion 58 toward the negative electrode active material layer 23. That is, the second seal portion 59 is located inside the space S with respect to the first seal portion 58 in a plan view seen from the stacking direction Z. In the seal member 50 surrounding the positive electrode active material layer 33 and the negative electrode active material layer 23 in the first direction X, as shown in FIG. 4, the second seal portion 59 is from the first seal portion 58 in the first direction X. It extends toward the negative electrode active material layer 23. Although not shown, in the seal member 50 surrounding the positive electrode active material layer 33 and the negative electrode active material layer 23 in the second direction Y, the first seal portion 58 faces the negative electrode active material layer 23 in the second direction Y. And postpone.

The first sealing portion 58 includes a first welding surface 58a, a separator welding surface 58b, and a second welding surface 58c. The first welding surface 58a is a surface orthogonal to the stacking direction Z and is welded to the positive electrode surface 32a of the positive electrode current collector 32. When viewed in a plan view in the stacking direction Z, the first welding surface 58a has a square frame shape located along the peripheral edge of the positive electrode current collector 32.

The separator welding surface 58b is located inside the space S from the first welding surface 58a in a plan view from the stacking direction Z. The separator welding surface 58b is a surface orthogonal to the stacking direction Z and is welded to the separator end portion 40b of the separator 40. That is, the separator welding surface 58b is joined to the positive electrode surface 32a of the positive electrode current collector 32 via the separator end portion 40b. When viewed in a plan view in the stacking direction Z, the separator welding surface 58b has a square frame shape located along the separator end 40b of the separator 40.

The edge inside the space S of the separator welding surface 58b is separated from the peripheral edge of the positive electrode active material layer 33. Specifically, in the portion of the seal member 50 that surrounds the positive electrode active material layer 33 and the negative electrode active material layer 23 in the first direction X, as shown in FIG. 4, inside the space S of the separator welding surface 58b. The edge is separated from the peripheral edge of the positive electrode active material layer 33 in the first direction X. Although not shown, in the portion of the seal member 50 that surrounds the positive electrode active material layer 33 and the negative electrode active material layer 23 in the second direction Y, the edge inside the space S of the separator welding surface 58b is the first. It is separated from the peripheral edge of the positive electrode active material layer 33 in the two directions Y.

Of the positive electrode surface 32a, the portion other than the portion covered by the first welding surface 58a and the positive electrode active material layer 33 is exposed to the space S. That is, the positive electrode surface 32a includes an exposed surface 32c that is not covered by either the positive electrode active material layer 33 or the sealing member 50. The exposed surface 32c is located between the portion of the positive electrode surface 32a covered by the first welding surface 58a and the portion of the positive electrode surface 32a covered by the positive electrode active material layer 33 in a plan view seen from the stacking direction Z. It has a square frame shape.

The second welding surface 58c is a surface orthogonal to the stacking direction Z and is welded to the negative electrode surface 22a of the negative electrode current collector 22. In the first sealing portion 58, the second welding surface 58c is a surface located on the opposite side of the first welding surface 58a and the separator welding surface 58b. When viewed in a plan view in the stacking direction Z, the second welding surface 58c has a square frame shape located along the peripheral edge of the negative electrode current collector 22, and the first welding surface 58a and the separator welding surface 58b. And the whole overlaps.

In the portion of the sealing member 50 that surrounds the positive electrode active material layer 33 and the negative electrode active material layer 23 in the first direction X, as shown in FIG. 4, the dimensions of the second welding surface 58c in the first direction X are the first. 1 It is equal to the sum of the dimensions of the welding surface 58a and the separator welding surface 58b in the first direction X. Although not shown, in the portion of the sealing member 50 that surrounds the positive electrode active material layer 33 and the negative electrode active material layer 23 in the second direction Y, the dimensions of the second welding surface 58c in the second direction Y are the first. 1 It is equal to the sum of the dimensions of the welding surface 58a and the separator welding surface 58b in the second direction Y.

The first sealing portion 58 is joined to the positive electrode surface 32a of the positive electrode current collector 32 via the first welding surface 58a and the separator welding surface 58b, and is bonded to the negative electrode surface 32a of the negative electrode current collector 22 via the second welding surface 58c. It is joined to 22a. That is, in the seal member 50, when viewed in a plan view in the stacking direction Z, the joint surface between the seal member 50 and the positive electrode surface 32a of the positive electrode current collector 32, and the negative electrode surface of the seal member 50 and the negative electrode current collector 22. It can be said that the portion where the joint surface with the 22a and the joint surface overlap is the first sealing portion 58. The first seal portion 58 is joined to the positive electrode surface 32a of the positive electrode current collector 32 and the negative electrode surface 22a of the negative electrode current collector 22 among the positive electrode current collectors 32 and the negative electrode current collectors 22 adjacent to each other in the stacking direction Z. It can be said that there is.

The second sealing portion 59 is located on the opposite side of the orthogonal surface 59a that is orthogonal to the stacking direction Z and faces the space S, the contact surface 59b that abuts on the negative electrode active material layer 23, and the orthogonal surface 59a. 3 Welding surface 59c and the like. When viewed in a plan view in the stacking direction Z, the orthogonal plane 59a has a square frame shape located inside the separator welding surface 58b. The orthogonal plane 59a is separated from the positive electrode surface 32a of the positive electrode current collector 32 in the stacking direction Z. That is, the second seal portion 59 is not joined to the positive electrode surface 32a of the positive electrode current collector 32.

The contact surface 59b extends in the stacking direction Z from the inner edge of the space S of the orthogonal surface 59a when viewed from the stacking direction Z. In the portion of the sealing member 50 that surrounds the positive electrode active material layer 33 and the negative electrode active material layer 23 in the first direction X, as shown in FIG. 4, the contact surface 59b is the negative electrode active material in the first direction X. It faces the peripheral edge of the layer 23. Although not shown, in the portion of the seal member 50 that surrounds the positive electrode active material layer 33 and the negative electrode active material layer 23 in the second direction Y, the contact surface 59b is the negative electrode active material in the second direction Y. It faces the peripheral edge of the layer 23. The negative electrode active material layer 23 and the sealing member 50 are in contact with each other. Specifically, the negative electrode active material layer 23 is in contact with the second sealing portion 59. The seal member 50 is in contact with the peripheral edge portion of the negative electrode active material layer 23 via the contact surface 59b of the second seal portion 59. The dimension of the second seal portion 59 in the stacking direction Z is equal to or larger than the dimension of the negative electrode active material layer 23 in the stacking direction Z. In the present embodiment, the dimension of the second seal portion 59 in the stacking direction Z is equal to the dimension of the negative electrode active material layer 23 in the stacking direction Z. The entire peripheral edge of the negative electrode active material layer 23 is in contact with the contact surface 59b.

The third welding surface 59c is a surface orthogonal to the stacking direction Z and is welded to the negative electrode surface 22a of the negative electrode current collector 22. That is, it can be said that the second sealing portion 59 is bonded to the negative electrode current collector 22 via the third welding surface 59c. The second seal portion 59 is not bonded to the positive electrode surface 32a of the positive electrode current collector 32 among the positive electrode current collector 32 and the negative electrode current collector 22 adjacent to each other in the stacking direction Z, while the negative electrode surface of the negative electrode current collector 22. It can be said that it is joined to 22a. When viewed in a plan view in the stacking direction Z, the third welding surface 59c is located inside the space S from the second welding surface 58c of the first sealing portion 58, and is located along the peripheral edge of the negative electrode current collector 22. It has a square frame shape to be located.

In the seal member 50 surrounding the positive electrode active material layer 33 and the negative electrode active material layer 23 in the first direction X, as shown in FIG. 4, it is a joint surface between the seal member 50 and the positive electrode surface 32a of the positive electrode current collector 32. The sum of the dimensions of each of the first welding surfaces 58a arranged in the first direction X and each of the separator welding surfaces 58b arranged in the first direction X in the first direction X is referred to as the first dimension L1. Further, each of the second welding surfaces 58c arranged in the first direction X and the third welding surface 59c arranged in the first direction X, which are the joining surfaces of the sealing member 50 and the negative electrode surface 22a of the negative electrode active material layer 23, respectively. The sum of the dimensions of and in the first direction X is called the second dimension L2. Although not shown, in the seal member 50 surrounding the positive electrode active material layer 33 and the negative electrode active material layer 23 in the second direction Y, each of the first welding surfaces 58a arranged in the second direction Y and the second direction Y The sum of the dimensions in the second direction Y with each of the separator welding surfaces 58b arranged in the same direction is the same as the first dimension L1. In the seal member 50 surrounding the positive electrode active material layer 33 and the negative electrode active material layer 23 in the second direction Y, each of the second welding surfaces 58c arranged in the second direction Y and the third welding surface 59c arranged in the second direction Y. The sum of the dimensions with each in the second direction Y is the same as the second dimension L2.

The second dimension L2 is larger than the first dimension L1. The positive electrode current collector 32 and the negative electrode current collector 22 overlap each other in a plan view from the stacking direction Z. That is, since the second dimension L2 is larger than the first dimension L1, the area of the negative electrode surface 22a covered by the second welding surface 58c and the third welding surface 59c is the positive electrode covered by the first welding surface 58a and the separator welding surface 58b. It can be said that it is larger than the area of the surface 32a. In other words, it can be said that the seal member 50 covers the negative electrode surface 22a with an area larger than the area covering the positive electrode surface 32a.

As shown in FIG. 3, the negative electrode surface 22a is covered with the negative electrode active material layer 23 and the sealing member 50 in a plan view from the stacking direction Z. When the negative electrode surface 22a is viewed in a plan view in the stacking direction Z, the contact surface 59b of the sealing member 50 is located outside the positive electrode active material layer 33. The position where the peripheral edge portion of the negative electrode active material layer 23 and the contact surface 59b of the seal member 50 abut is corresponding to the boundary position between the negative electrode active material layer 23 and the seal member 50. That is, when the negative electrode surface 22a is viewed in a plan view in the stacking direction Z, the boundary position between the negative electrode active material layer 23 and the sealing member 50 does not overlap with the positive electrode active material layer 33.

By injecting the electrolytic solution into the space S inside the storage cell 20, the positive electrode active material layer 33 and the negative electrode active material layer 23 are impregnated with the electrolytic solution. The injection of the electrolytic solution into the space S may be performed, for example, through a liquid injection hole (not shown) formed in the seal member 50. The space S is filled with the injected electrolyte. After the space S is completely impregnated with the electrolytic solution, a plurality of the storage cells 20 are stacked to form the cell stack 11.

Next, the configuration of the storage cell 20 will be described in more detail in a state where the cell stack 11 is configured by being stacked.
As shown in FIG. 1, of the two storage cells 20 adjacent to each other in the stacking direction Z, the positive electrode back surface 32b of one storage cell 20 and the negative electrode back surface 22b of the other storage cell 20 are in contact with each other. As a result, in the two storage cells 20 adjacent to each other in the stacking direction Z, the positive electrode 31 of one storage cell 20 and the negative electrode 21 of the other storage cell 20 are in contact with each other.

A pseudo bipolar electrode 25 is formed by the positive electrode 31 and the negative electrode 21 in contact with each other. The positive electrode current collector 32 and the negative electrode current collector 22 in contact with each other function as electrode bodies of the bipolar electrode 25. One bipolar electrode 25 includes a positive electrode current collector 32 and a negative electrode current collector 22 that are in contact with each other in the stacking direction Z, and a positive electrode active material layer 33 and a negative electrode active material layer 23. The bipolar electrodes 25 are alternately laminated with the separator 40 in the stacking direction Z.

The set of the positive electrode current collector 32 and the negative electrode current collector 22 constituting one bipolar electrode 25 is referred to as one current collector 26. A plurality of current collectors 26 are stacked in the stacking direction Z. The positive electrode surface 32a is one surface of the current collector 26 in the stacking direction Z. The negative electrode surface 22a is the other surface of the current collector 26 in the stacking direction Z. Hereinafter, the positive electrode surface 32a is also referred to as a first surface 26b of the current collector 26, and the negative electrode surface 22a is also referred to as a second surface 26a of the current collector 26.

It can be said that the positive electrode active material layer 33 is arranged on the first surface 26b of the current collector 26 in the stacking direction Z. It can be said that the negative electrode active material layer 23 is arranged on the second surface 26a of the current collector 26 in the stacking direction Z.

The power storage device 10 includes a positive electrode 31 at one end in the stacking direction Z and a negative electrode 21 at the other end in the stacking direction Z. The positive electrode energizing plate 12b is electrically connected to the positive electrode current collector 32 of the positive electrode 31 located at one end in the stacking direction Z. The negative electrode current-carrying plate 12a is electrically connected to the negative electrode current collector 22 of the negative electrode 21 located at the other end in the stacking direction Z.

In the storage cells 20 adjacent to each other in the stacking direction Z, the seal end portions 57 of the seal member 50 are joined and integrated. The seal ends 57 of all the storage cells 20 to be laminated in the stacking direction Z are integrated. The integrated seal end portion 57 is referred to as a sealing body 57a.

The sealing body 57a covers the peripheral portions of the positive electrode current collector 32 and the negative electrode current collector 22. The sealing body 57a extends from the positive electrode current collector 32 arranged at one end of the cell stack 11 in the stacking direction Z to the negative electrode current collector 22 arranged at the other end of the cell stack 11 in the stacking direction Z. Examples of the joining method include heat welding, ultrasonic welding, infrared welding and the like.

The sealing member 50 also functions as a sealing portion for sealing the space S between the positive electrode 31 and the negative electrode 21. The seal member 50 can prevent the electrolytic solution contained in the space S from leaking to the outside of the power storage device 10. The seal member 50 can prevent moisture from entering the space S from the outside of the power storage device 10. Further, the seal member 50 can prevent the gas generated from the positive electrode 31 or the negative electrode 21 from leaking to the outside of the power storage device 10 due to, for example, a charge / discharge reaction.

Next, the manufacturing procedure of the storage cell 20 will be described.
As shown in FIG. 4, first, for the negative electrode current collector 22 in which the negative electrode active material layer 23 is arranged on the negative electrode surface 22a, a molten sealing material is arranged around the negative electrode active material layer 23. The mold is placed on the negative electrode surface 22a, and the melted sealing material is poured into the mold. As a result, the sealing material has a shape including the sealing main body 56 and the sealing end portion 57. The molten sealing material is brought into contact with the peripheral edge of the negative electrode active material layer 23. By fixing the sealing material in this state, the sealing member 50 is formed. Of the negative electrode surface 22a, the entire portion where the negative electrode active material layer 23 is not located is covered with the sealing member 50.

After forming the seal member 50, the separator 40 is overlapped with the negative electrode active material layer 23 in the stacking direction Z. At this time, the separator end portion 40b is arranged on the seal member 50. Further, the positive electrode 31 is overlapped with the separator 40 in the stacking direction Z.

Subsequently, the seal member 50 is welded to the positive electrode current collector 32 and the negative electrode current collector 22. Welding of the sealing member 50 to the positive electrode current collector 32 and the negative electrode current collector 22 may be performed, for example, by abutting a welding jig on the peripheral edge portion of the positive electrode back surface 32b and the negative electrode back surface 22b. The seal member 50 is melted by receiving heat transfer from the welding jig. The first welding surface 58a is welded to the positive electrode surface 32a, and the second welding surface 58c and the third welding surface 59c are welded to the negative electrode surface 22a. Further, the separator end portion 40b is welded to the positive electrode surface 32a and welded to the seal member 50 to form a separator welding surface 58b. After that, the electrolytic solution is injected into the space S of the storage cell 20. A plurality of storage cells 20 are stacked to form a cell stack 11.

Next, the operation of this embodiment will be described.
On the second surface 26a of the current collector 26, the entire portion where the negative electrode active material layer 23 is not arranged is covered with the sealing member 50. Therefore, the second surface 26a is not exposed in the electrolytic solution of the space S. Since the second surface 26a is not exposed in the electrolytic solution of the space S even during the period from the injection of the electrolytic solution into the space S to the initial charge or when an overdischarge occurs, the second surface 26a is not exposed in the electrolytic solution of the space S from the current collector 26 to the electrolytic solution of the space S. Elution of copper to is unlikely to occur.

According to the above embodiment, the following effects can be obtained.
(1) The second surface 26a does not have an exposed surface on which the negative electrode active material layer 23 is not arranged and is exposed to the electrolytic solution in the space S. Therefore, it is possible to suppress the elution of copper from the negative electrode current collector 22 into the electrolytic solution that fills the space S during the period from the injection of the electrolytic solution into the space S to the initial charge or when an overdischarge occurs.

(2) When the second surface 26a is viewed in a plan view in the stacking direction Z, the boundary position between the negative electrode active material layer 23 and the sealing member 50 does not overlap with the positive electrode active material layer 33. Therefore, the peripheral edge of the negative electrode active material layer 23 does not face the positive electrode active material layer 33 in the stacking direction Z. Therefore, even if the component changes due to the influence of heat when the seal member 50 is formed so as to abut on the peripheral edge of the negative electrode active material layer 23, the influence on the battery performance can be suppressed.

(3) The seal member 50 covers the second surface 26a with an area larger than the area covering the first surface 26b. Therefore, the area of the second surface 26a covered by the sealing member 50 is larger than that of the first surface 26b. That is, by increasing the covering area of the sealing member 50 on the second surface 26a, the second surface 26a does not have an exposed surface on which the negative electrode active material layer 23 is not arranged and is exposed. Therefore, on the second surface 26a, the elution of copper from the negative electrode current collector 22 into the electrolytic solution can be further suppressed as compared with the case where the covering area of the negative electrode active material layer 23 containing the electrolytic solution inside is increased.

(4) The first surface 26b includes an exposed surface 32c that is not covered by either the positive electrode active material layer 33 or the sealing member 50. Therefore, since the space S inside the power storage device 10 can be increased by the amount that the first surface 26b includes the exposed surface 32c, even if gas is generated during the use of the power storage device 10, the power storage device is large by the space S. The increase in internal pressure of 10 can be reduced.

The above embodiment can be modified and implemented as follows. Each of the above embodiments and the following modifications can be implemented in combination with each other within a technically consistent range.

○ As shown in FIG. 5, the seal member 50 may have an installation surface facing the space S and intersecting the stacking direction Z. The separator end 40b of the separator 40 may be arranged on the installation surface. Specifically, the sealing member 50 of this modification does not have a separator welding surface 58b to which the separator end 40b is welded. The seal member 50 has a first welded surface 58a welded to the positive electrode surface 32a of the positive electrode current collector 32 on the entire one surface of the first sealed portion 58 in the stacking direction Z. The orthogonal surface 59a of the second seal portion 59 functions as the installation surface. The orthogonal plane 59a, which functions as an installation plane, faces the space S and intersects the stacking direction Z.

According to the above modification example, the following effects can be obtained in addition to the effects in the above embodiment.
(5) The seal member 50 has an orthogonal surface 59a as an installation surface facing the space S and orthogonal to the stacking direction Z. The separator end 40b is arranged on the orthogonal plane 59a. Therefore, by arranging the separator end portion 40b on the orthogonal surface 59a of the seal member 50, the separator 40 can be positioned in the first direction X and the second direction Y.

○ As shown in FIG. 5, the third dimension L3, which is the dimension of the second seal portion 59 in the stacking direction Z, may be smaller than the fourth dimension L4, which is the dimension of the negative electrode active material layer 23 in the stacking direction Z. .. The fourth dimension L4 is the thickness of the negative electrode active material layer 23.

According to the above modification example, the following effects can be obtained in addition to the effects in the above embodiment.
(6) The dimension of the second sealing portion 59 in the stacking direction Z is smaller than that of the negative electrode active material layer 23. Therefore, the space S can be increased by the amount that the dimension of the second seal portion 59 in the stacking direction Z is smaller than that of the negative electrode active material layer 23. Therefore, when gas is generated during the use of the power storage device 10, the increase in the internal pressure of the power storage device 10 can be further reduced.

○ As shown in FIG. 6, the area covering the first surface 26b by the seal member 50 and the area covering the second surface 26a may be the same size. That is, the seal member 50 does not have a second seal portion bonded only to the negative electrode surface 22a of the negative electrode current collector 22. In this case, the negative electrode active material layer 23 covers the second surface 26a with an area larger than that of the above embodiment. As a result, the second surface 26a is covered with the negative electrode active material layer 23 and the sealing member 50 in a plan view from the stacking direction Z.

○ As shown in FIG. 6, the seal member 50 may be divided into a plurality of parts in the stacking direction Z. FIG. 6 illustrates the seal member 50 divided into two in the stacking direction Z. The seal member 50 in this case includes a seal end portion 57 divided into two in the stacking direction Z. The seal member 50 includes a first seal main body portion 56a and a second seal main body portion 56b divided in the stacking direction Z instead of the seal main body 56. The first seal main body portion 56a is bonded only to the negative electrode surface 22a of the negative electrode current collector 22. The second seal main body portion 56b is bonded only to the positive electrode surface 32a of the positive electrode current collector 32. The first seal main body portion 56a is in contact with the negative electrode active material layer 23. The surface of the first seal main body 56a on the opposite side of the surface to be joined to the negative electrode surface 22a is joined to the surface of the second seal main body 56b on the opposite side of the surface to be joined to the positive electrode surface 32a. The separator end 40b is sandwiched between the first seal main body 56a and the second seal main body 56b. The separator end portion 40b is welded to the first seal main body portion 56a and the second seal main body portion 56b.

○ The first surface 26b does not have to include the exposed surface 32c. In this case, the first surface 26b is entirely covered with the positive electrode active material layer 33 and the sealing member 50.
○ The sealing member 50 may be arranged on the negative electrode surface 22a before the negative electrode active material layer 23. In this case, first, a portion of the negative electrode surface 22a excluding the central portion is covered with the sealing member 50 by flowing a molten sealing material onto the negative electrode surface 22a. After that, the negative electrode active material layer 23 is arranged by applying a slurry containing the negative electrode active material to the central portion of the negative electrode surface 22a on which the sealing member 50 is not arranged. As a result, the peripheral portion of the formed negative electrode active material layer 23 comes into contact with the sealing member 50. The entire negative electrode surface 22a is covered with the negative electrode active material layer 23 and the sealing member 50.

○ The current collector 26 of the bipolar electrode 25 is not limited to the one composed of a separate positive electrode current collector 32 and a negative electrode current collector 22 as in the above embodiment. For example, the current collector 26 may be a clad foil made of different metals, or the surface of the metal foil may be plated. In this case, one surface of the current collector 26 in the stacking direction Z is the first surface 26b having the positive electrode active material layer 33. The other surface of the current collector 26 in the stacking direction Z is a second surface 26a having a negative electrode active material layer 23 as well as being made of copper.

○ As shown in FIG. 7, the seal member 50 and the negative electrode active material layer 23 may overlap each other in the stacking direction Z. The seal member 50 of this modification has the same form as the modification described above with reference to FIG. In this modification, the inner peripheral end of the second seal portion 59 and the outer peripheral end of the negative electrode active material layer 23 overlap in the stacking direction Z. The outer peripheral end of the negative electrode active material layer 23 is located between the inner peripheral end of the second sealing portion 59 and the separator 40 in the stacking direction Z. The positional relationship between the seal member 50 and the negative electrode active material layer 23 in this modification is the same as in the above modification, in that the seal member 50 is arranged on the negative electrode surface 22a before the negative electrode active material layer 23. It is feasible.

S ... space, X ... first direction, Y ... second direction, Z ... stacking direction, 10 ... power storage device, 22 ... negative electrode current collector, 23 ... negative electrode active material layer, 26 ... current collector, 26a ... second Surface, 26b ... 1st surface, 32 ... Positive electrode current collector, 32c ... Exposed surface, 33 ... Positive electrode active material layer, 40 ... Separator, 40b ... Separator end, 50 ... Seal member, 58 ... First seal part, 59 ... second seal, 59a ... orthogonal plane.

Claims (7)

With a current collector that stacks multiple layers in the stacking direction,
A positive electrode active material layer arranged on the first surface, which is one surface of the current collector in the stacking direction,
A negative electrode active material layer arranged on the second surface, which is the other surface of the current collector in the stacking direction,
Of the two current collectors adjacent to each other in the stacking direction, the first surface of the current collector and the second surface of the other collector are arranged and described. A seal member surrounding the positive electrode active material layer and the negative electrode active material layer in an orthogonal direction orthogonal to the stacking direction is provided.
A power storage device for a lithium ion secondary battery in which the inside of a space partitioned by the two collectors adjacent to each other in the stacking direction and the seal member is filled with an electrolytic solution.
The current collector includes a negative electrode current collector made of copper.
The second surface is one surface of the negative electrode current collector in the stacking direction, and is covered with the negative electrode active material layer and the sealing member in a plan view from the stacking direction.
A power storage device characterized in that the negative electrode active material layer and the sealing member are in contact with each other. The power storage device according to claim 1, wherein the boundary position between the negative electrode active material layer and the sealing member does not overlap with the positive electrode active material layer when the second surface is viewed in a plan view in the stacking direction. The power storage device according to claim 1 or 2, wherein the seal member covers the second surface with an area larger than the area covering the first surface. The power storage device according to any one of claims 1 to 3, wherein the first surface includes an exposed surface that is not covered by either the positive electrode active material layer or the sealing member. The seal member includes a first seal portion joined to the first surface of the one of the current collectors and the second surface of the other of the current collectors, and the first of the other of the current collectors. It includes a second sealing portion that is joined to only two surfaces and extends from the first sealing portion toward the negative electrode active material layer in the orthogonal direction.
The power storage device according to claim 4, wherein the negative electrode active material layer is in contact with the second seal portion. The power storage device according to claim 5, wherein the dimension of the second seal portion in the stacking direction is smaller than that of the negative electrode active material layer. Further, a separator located between the positive electrode active material layer and the negative electrode active material layer in the stacking direction is further provided.
The seal member has an installation surface that faces the space and intersects the stacking direction.
The power storage device according to any one of claims 1 to 6, wherein the end portion of the separator is arranged on the installation surface.

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