Lithium secondary battery, battery assembly, and electric vehicle

Abstract

According to one exemplary embodiment of the present disclosure, it is possible to provide a technology for suppressing an increase in resistance in a lithium secondary battery. The present invention relates to a lithium secondary battery comprising: a current collector comprising a resin layer and a pair of conductive layers provided on both sides of said resin layer, said current collector comprising a body with a pair of long sides and a pair of short sides, at least one first end part extending from one of the pair of short sides of the body, and at least one second end part extending from the other of the pair of short sides of the body; a first electrode tab connected to the at least one first end part; a second electrode tab connected to the at least one second end part; and a sealed container. The sealed container is configured to seal an electrode laminate including the current collector while also bringing out a portion of the first electrode tab and a portion of the second electrode tab to the outside of the sealed container.

Description

Lithium secondary battery, battery assembly and electric vehicle

[0001] Exemplary embodiments of the present disclosure relate to a lithium secondary battery, a battery assembly, and an electric vehicle.

[0002] Patent Document 1 describes a lithium secondary battery comprising a current collector, an electrode assembly in which electrode plates provided with active material and tabs and separators are alternately stacked, leads electrically connected to the tabs, and a battery case, wherein the leads are divided into a positive electrode lead and a negative electrode lead, and at least one positive electrode lead and one negative electrode lead are provided.

[0003] Special Publication No. 2013-543228

[0004] The present disclosure provides a technique for suppressing an increase in resistance in a lithium secondary battery.

[0005] In one exemplary embodiment of the present disclosure, there is provided a lithium secondary battery comprising: a current collector including a resin layer and a pair of conductive layers provided on both sides of the resin layer, the current collector including a main body having a pair of long sides and a pair of short sides, at least one first end extending from one of the pair of short sides of the main body, and at least one second end extending from the other of the pair of short sides of the main body; a first electrode tab connected to the at least one first end; and a second electrode tab connected to the at least one second end; and a sealed container configured to enclose an electrode stack including the current collector while allowing a portion of the first electrode tab and a portion of the second electrode tab to be taken out of the sealed container.

[0006] According to one exemplary embodiment of the present disclosure, a technique for suppressing an increase in resistance in a lithium secondary battery can be provided.

[0007] 1 is a cross-sectional view showing an example of the configuration of a secondary battery; a top view showing an example of the configuration of a secondary battery; a three-dimensional perspective view showing an example of the configuration of a secondary battery; a cross-sectional view showing an example of the configuration of a positive electrode; a top view showing an example of the configuration of a positive electrode; a cross-sectional view showing an example of the configuration of a negative electrode; a top view showing an example of the configuration of a negative electrode; a top view showing an example of the configuration of a positive electrode and a negative electrode in a secondary battery; a top view showing an example of the configuration of a secondary battery; a top view showing another example of the configuration of a secondary battery; an exploded perspective view showing an example of the configuration when a plurality of secondary batteries are electrically connected in series; an exploded perspective view showing another example of the configuration when a plurality of secondary batteries are electrically connected in series; a three-dimensional perspective view showing an example of manufacturing a secondary battery; a cross-sectional view showing an example of manufacturing a secondary battery; a top view showing an example of manufacturing a secondary battery; a perspective view showing an example of the configuration of a battery assembly; a perspective view showing an example of the configuration of a secondary battery of an example; a top view showing an example of the configuration of a secondary battery of a comparative example.

[0008] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary. However, the present invention is not limited to this embodiment, and various modifications are possible without departing from the spirit of the present invention. In the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0009] 1A to 1C are cross-sectional views, top views, and a three-dimensional perspective view illustrating an example of the configuration of a lithium secondary battery 1 (hereinafter also referred to as "secondary battery 1") according to one embodiment. As shown in FIG. 1A, in one embodiment, the secondary battery 1 includes an electrode stack 10 and a sealed container 16 in which the electrode stack 10 is sealed. The electrode stack 10 includes a positive electrode 11, a separator 13, and a negative electrode 12. The positive electrode 11, the separator 13, and the negative electrode 12 are arranged in this order along the Z direction in FIG. 1A (hereinafter also referred to as the "stacking direction"; also, viewing the secondary battery 1 from the stacking direction is also referred to as a "planar view"). That is, the positive electrode 11 and the negative electrode 12 face each other with the separator 13 interposed therebetween. The positive electrode 11 includes a positive electrode tab 115 extending outside the sealed container 16. The negative electrode 12 includes a negative electrode tab 125 extending outside the sealed container 16.

[0010] The positive electrode 11 includes a positive electrode current collector 110, and the negative electrode 12 includes a negative electrode current collector 120. At least one of the positive electrode current collector 110 of the positive electrode 11 and the negative electrode current collector 120 of the negative electrode 12 is a current collector including a resin layer and a pair of conductive layers provided on both sides of the resin layer. In one embodiment, both the positive electrode current collector 110 and the negative electrode current collector 120 may be current collectors including a resin layer and a pair of conductive layers provided on both sides of the resin layer.

[0011] In one embodiment, the electrode stack 10 may be configured by stacking multiple sets of positive electrodes 11, separators 12, and negative electrodes 13 in the stacking direction. The number of stacked layers may be 10 or more and 30 or less, or 15 or more and 25 or less. In one embodiment, the total number of negative electrodes 12 included in the secondary battery 1 may be 5 or more, 10 or more, or 20 or more. In one embodiment, the total number of positive electrodes 11 included in the secondary battery 1 may be 5 or more, 10 or more, or 20 or more. In one embodiment, the total number of negative electrodes 12 included in the secondary battery 1 may be 50 or less, 40 or less, or 30 or less. In one embodiment, the total number of positive electrodes 11 included in the secondary battery 1 may be 50 or less, 40 or less, or 30 or less.

[0012] When the electrode stack 10 is configured by stacking multiple sets of positive electrodes 11, separators 12, and negative electrodes 13 in the stacking direction, the electrode stack 10 includes multiple positive electrode current collectors 110 and negative electrode current collectors 120. In this case, at least one of the multiple positive electrode current collectors 110 and negative electrode current collectors 120 is a current collector including a resin layer and a pair of conductive layers provided on both sides of the resin layer. In one embodiment, all of the multiple positive electrode current collectors 110 and negative electrode current collectors 120 may be current collectors including a resin layer and a pair of conductive layers provided on both sides of the resin layer.

[0013] 1B , the positive electrode 11 includes a first positive electrode tab 115a and a second positive electrode tab 115b that are taken out to the outside of the sealed container 16. The negative electrode 12 includes a first negative electrode tab 125a and a second negative electrode tab 125b that are taken out to the outside of the sealed container 16.

[0014] The first positive electrode tab 115a, the second positive electrode tab 115b, the first negative electrode tab 125a, and the second negative electrode tab 125b may each be present independently in plural, or only one may be present. The first positive electrode tab 115a, the second positive electrode tab 115b, the first negative electrode tab 125a, and the second negative electrode tab 125b do not overlap with each other in a plan view. In this embodiment, when there is no need to distinguish between the first positive electrode tab 115a and the second positive electrode tab 115b, they are also simply referred to as "positive electrode tab 115." The same applies to other configurations.

[0015] In one embodiment, the sealed container 16 has a pair of long sides and a pair of short sides. The short side direction is the X direction, and the long side direction is the Y direction. The sealed container 16 may be rectangular in plan view. The first positive electrode tab 115a extends from one of the pair of short sides of the sealed container 16, and the second positive electrode tab 115b extends from the other of the pair of short sides of the sealed container 16. Furthermore, the first negative electrode tab 125a extends from one of the pair of short sides of the sealed container 16, and the second negative electrode tab 125b extends from the other of the pair of short sides of the sealed container 16.

[0016] When there is one each of the first positive electrode tab 115a and the second positive electrode tab 115b, the distance D1 from one long side of the sealed container 16 to the first positive electrode tab 115a may be the same as or different from the distance D2 from that long side to the second positive electrode tab 115b, and in one embodiment, the distance D1 and the distance D2 may be different. When D1 and D2 are different, polarization within the positive electrode 11 tends to be reduced, and the resistance of the positive electrode 11 tends to be reduced. Furthermore, from the viewpoint of reducing the polarization of the positive electrode 11 and reducing the resistance of the positive electrode 11, when the sealed container 16 or the positive electrode 11 is divided into an upper half and a lower half in the X direction, one of the first positive electrode tab 115a and the second positive electrode tab 115b may be present in the upper half and the other in the lower half. Furthermore, the first electrode tab 115 a and the second electrode tab 115 b may be located diagonally opposite each other along the long side of the sealed container 16 .

[0017] When there is only one first negative electrode tab 125a and one second negative electrode tab 125b, the distance D3 from one long side of the sealed container 16 to the first negative electrode tab 125a may be the same as or different from the distance D4 from that long side to the second negative electrode tab 125b. In one embodiment, the distances D3 and D4 may be different. When the negative electrode 12 and the positive electrode 11 are combined to form the secondary battery 1, the difference between D3 and D4 tends to reduce polarization within the negative electrode 12 and reduce the resistance of the negative electrode 12. Furthermore, from the viewpoint of reducing the polarization of the negative electrode 12 and reducing the resistance of the negative electrode 12, when the sealed container 16 or the negative electrode 12 is divided into an upper half and a lower half in the X direction, one of the first negative electrode tab 125a and the second negative electrode tab 125b may be present in the upper half and the other in the lower half. Furthermore, the first electrode tab 125 a and the second electrode tab 125 b may be located diagonally opposite each other along the long side of the sealed container 16 .

[0018] From the viewpoint of improving the battery capacity per unit volume, the positive electrode 11 and the negative electrode 12 may have substantially the same size in a plan view. Furthermore, the sizes of the positive electrode 11 and the negative electrode 12 may be as close as possible to the size of the sealed container 16 in a plan view.

[0019] As shown in FIG. 1C , in one embodiment, the sealed container 16 has a rectangular shape in a plan view. Here, the ratio (L / W) of the long side length L (mm) to the short side length W (mm) of the sealed container 16 is preferably 1.5 < L / W < 10.0, more preferably 2.0 < L / W < 5.0, and even more preferably 2.5 < L / W < 5.0. When the ratio (L / W) is within the above range, the battery capacity of the secondary battery 1 tends to be increased while suppressing an increase in resistance. Furthermore, when the secondary battery 1 is intended for in-vehicle use, the secondary battery 1 is typically stored under the floor of the vehicle. To improve passenger accessibility, it is preferable to reduce the short side length W and lower the height of the floor. From the viewpoint of achieving both improved passenger accessibility and increased battery capacity, the ratio (L / W) is preferably within the above range.

[0020] However, the sealed container 16 is not limited to a rectangular shape and may have various shapes (e.g., a triangular shape, a trapezoidal shape, etc.). The sealed container 16 may also be deformed by having rounded or chipped corners. In one embodiment, the direction in which the long sides of the sealed container 16 extend is the Y direction, and the direction in which the short sides of the sealed container 16 extend is the X direction.

[0021] When the sealed container 16 is rectangular, the length L of the long side is preferably 200 to 600 mm, 250 to 550 mm, or 300 to 500 mm. The length W of the short side is preferably 50 to 200 mm, 50 to 150 mm, or 70 to 120 mm. When the sealed container 16 satisfies these numerical ranges, the battery capacity of the secondary battery 1 tends to be increased while suppressing an increase in resistance.

[0022] In one embodiment, the positive electrode tab 115 and the negative electrode tab 125 are taken out from the short side of the sealed container 16 to the outside.

[0023] In one embodiment, the sealed container 16 is made of a sheet such as an aluminum sheet containing aluminum. For example, it may be an aluminum laminate pouch made by sealing aluminum foil into a bag shape.

[0024] The sealed container 16 may be formed by folding one long side of a sheet and sealing the other long side of the sheet. That is, one long side of the sealed container 16 may be formed by folding a sheet, and the other long side of the sealed container 16 may be formed by sealing the edges of the folded sheet.

[0025] The components of the secondary battery 1 will be described in detail below.

[0026] 1. Separator As shown in FIG. 1 , the separator 13 is disposed between the negative electrode 12 and the positive electrode 11. The separator 13 physically and / or electrically isolates the negative electrode 12 and the positive electrode 11, while ensuring ionic conductivity of lithium ions. In one embodiment, the separator 13 may be at least one selected from the group consisting of an insulating porous material, a polymer electrolyte, a gel electrolyte, and an inorganic solid electrolyte. The separator 13 may be formed of one type of material alone, or two or more types of materials in combination.

[0027] When the separator 13 includes an insulating porous member, the pores of the porous member are filled with an ion-conductive substance (such as an electrolytic solution, a polymer electrolyte, and / or a gel electrolyte). This allows the separator 13 to exhibit ion conductivity. The material constituting the insulating porous member is not particularly limited, and examples thereof include insulating polymer materials, specifically polyethylene (PE) and polypropylene (PP). That is, the separator 13 may be a porous polyethylene (PE) film, a porous polypropylene (PP) film, or a laminate structure thereof.

[0028] In one embodiment, one or both surfaces of the separator 13 may be coated with a separator coating layer. This may improve the cycle characteristics of the secondary battery 1. In one embodiment, the separator coating layer may be a continuous film with a uniform thickness over 50% or more of the surface area of ​​the separator 13. In one embodiment, the separator coating layer may include polyvinylidene fluoride (PVDF), a mixture of styrene butadiene rubber and carboxymethyl cellulose (SBR-CMC), and a binder such as polyacrylic acid (PAA). In one embodiment, the separator coating layer may be formed by adding inorganic particles such as silica, alumina, titania, zirconia, or magnesium hydroxide to the binder.

[0029] In one embodiment, the thickness of the separator 13 (including the coating layer if the separator 13 includes the coating layer) may be 3.0 μm or more and 40 μm or less. This allows the negative electrode 12 and the positive electrode 11 to be separated while the volume occupied by the separator 20 can be reduced. In one embodiment, the thickness of the separator 13 may be 5.0 μm or more, 7.0 μm or more, or 10 μm or more. In one embodiment, the thickness of the separator 13 may be 30 μm or less, 20 μm or less, or 15 μm or less.

[0030] 2. Electrolyte In one embodiment, the secondary battery 1 may contain an electrolyte. The electrolyte is a liquid containing a solvent and an electrolyte and has ion conductivity. The electrolyte may also be referred to as a liquid electrolyte and acts as a conductive path for lithium ions. Therefore, when the secondary battery 1 contains an electrolyte, the internal resistance can be reduced, and the energy density, capacity, and cycle characteristics can be improved.

[0031] The electrolytic solution may be, for example, a solution that fills the sealed container 16. Furthermore, for example, the electrolytic solution may be impregnated into the separator 13, or may be held by a polymer to form a polymer electrolyte or a gel electrolyte.

[0032] The electrolyte contained in the electrolytic solution may be, for example, a lithium salt, which may be, for example, one or a combination of two or more selected from the group consisting of LiI, LiCl, LiBr, LiF, LiBF, LiPF, LiAsF, LiSOCF, LiN(SOF), LiN(SOCF), LiN(SOCFCF), LiB(OCOH), LiB(COOH), LiB(OCOH)F, LiB(OCOCF), LiNO, and LiSO.

[0033] The solvent contained in the electrolytic solution is not particularly limited, but examples thereof include chain carbonates, cyclic carbonates, chain ethers, and other solvents other than these solvents. The solvents may be used alone or in combination of two or more.

[0034] The chain carbonate is a carbonate that does not have a cyclic structure such as an aromatic ring, an alicyclic ring, a homocyclic ring, a heterocyclic ring, etc. The chain carbonate is not particularly limited, but examples thereof include dimethyl carbonate (DMC), diethyl carbonate, ethyl methyl carbonate (EMC), and compounds in which some or all of the hydrogen atoms in these carbonates have been substituted with fluorine atoms.

[0035] The cyclic carbonate is a carbonate having a cyclic structure such as an aromatic ring, an alicyclic ring, a homocyclic ring, a heterocyclic ring, etc. The cyclic carbonate is not particularly limited, but examples thereof include ethylene carbonate (EC), propylene carbonate, chloroethylene carbonate, and compounds in which some or all of the hydrogen atoms in these carbonates have been substituted with fluorine atoms.

[0036] The chain ether is an ether that does not have a cyclic structure such as an aromatic ring, an alicyclic ring, a homocyclic ring, a heterocyclic ring, etc. The chain ether is not particularly limited, but examples thereof include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dimethoxyethane, diethoxyethane, dimethoxypropane, dimethoxybutane, and diethylene glycol dimethyl ether.

[0037] The other solvents are not particularly limited, but examples thereof include acetonitrile, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, 12-crown-4, trimethyl phosphate, triethyl phosphate, derivatives of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, derivatives of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and derivatives of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0038] The total amount of the chain carbonate and the cyclic carbonate relative to the total amount of the solvent is not particularly limited, but is, for example, 40% by volume or more and 100% by volume or less, 60% by volume or more and 100% by volume or less, or 80% by volume or more and 100% by volume or less.

[0039] The content of the chain ether relative to the total amount of the solvent is not particularly limited, but is, for example, 5% by volume to 40% by volume, or 10% by volume to 30% by volume. In addition, the solvent may not contain a chain ether.

[0040] The content of the other solvents relative to the total amount of the solvents is not particularly limited, but is, for example, 1% by volume or more and 10% by volume or less. In addition, the solvent does not necessarily contain other solvents.

[0041] The electrolyte solution of the present embodiment may contain an additive, which is not particularly limited, but may include, for example, vinylene carbonate (VC), lithium difluorophosphate (LiPOF), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0042] The content of the additives relative to the total amount of the solvent is not particularly limited, but is, for example, 0.1% by mass or more and 5.0% by mass or less.

[0043] 3. Positive Electrode FIG. 2A is a cross-sectional view showing an example of the configuration of the positive electrode 11, and FIG. 2B is a top view showing an example of the configuration of the positive electrode 11. As shown in FIGS. 2A and 2B , in one embodiment, the positive electrode 11 includes a positive electrode current collector 110 and a positive electrode active material layer 113 disposed on the positive electrode current collector 110. In one embodiment, the positive electrode current collector 110 includes a positive electrode resin layer 111 (hereinafter also simply referred to as "resin layer 111") and a pair of positive electrode conductive layers disposed so as to sandwich the positive electrode resin layer 111. The pair of positive electrode conductive layers includes a first positive electrode conductive layer 112a and a second positive electrode conductive layer 112b.

[0044] Alternatively, in one embodiment, the positive electrode current collector 110 does not include a resin layer, but includes a positive electrode conductive layer.

[0045] In one embodiment, the thickness of the positive electrode 11 may be 3 μm or more and 300 μm or less.

[0046] In one embodiment, the positive electrode resin layer 111 may be composed of a sheet-like (film-like) or fibrous resin. The resin may be, for example, at least one of a polyolefin resin such as polyethylene terephthalate (PET), polyethylene, or polypropylene, or a thermoplastic resin such as polystyrene, polyvinyl chloride, or polyamide. The positive electrode resin layer 111 may be composed of a plurality of layers of at least one of the resins. In one embodiment, the positive electrode resin layer 111 is formed from a material having a melting point of 150°C or higher and 300°C or lower. In one embodiment, the thickness of the positive electrode resin layer 111 may be 3 μm or higher and 10 μm or lower, or 4 μm or higher and 8 μm or lower.

[0047] The positive electrode resin layer 111 can function to melt and damage the positive electrode 11 in the event of abnormal heat generation due to overcharge or high temperature conditions, thereby interrupting short-circuit current within the battery. This can suppress a sudden temperature rise within the secondary battery 1 and prevent the battery from catching fire. In other words, the positive electrode resin layer 111 can contribute to improving the safety of the secondary battery 1. Furthermore, since resins tend to have a smaller specific gravity than metals, use of the positive electrode current collector 110 including the positive electrode resin layer 111 tends to reduce the weight per unit volume of the secondary battery 1 and increase the energy density per unit weight of the secondary battery 1.

[0048] The pair of positive electrode conductive layers are in physical and / or electrical contact with the positive electrode active material layer 113 and function to donate and receive electrons to and from the positive electrode active material layer 113. The pair of positive electrode conductive layers are made of a conductor that does not react with lithium ions in a battery. In one embodiment, the pair of positive electrode conductive layers are made of at least one material selected from the group consisting of aluminum, titanium, stainless steel, nickel, and alloys thereof. In one example, the pair of positive electrode conductive layers is aluminum or an aluminum alloy. In one embodiment, the pair of positive electrode conductive layers are formed by vapor deposition, sputtering, electrolytic plating, or lamination of the above material on both surfaces of the positive electrode resin layer 111. In one embodiment, the thickness tp of each pair of positive electrode conductive layers may be 0.5 μm or more and 5 μm or less, 0.7 μm or more and 3 μm or less, or 0.8 μm or more and 2.0 μm or less.

[0049] The thickness tp (μm) of at least one of the pair of positive electrode conductive layers preferably satisfies 1.0<L / (W×tp)<5.0, more preferably 1.5<L / (w×tp)<4.5, and further preferably 1.5<L / (w×tp)<4.0, where L (mm) is the length of the long side and W (mm) of the sealed container 16. In addition, the thickness t p1 (μm) and the thickness t of the second positive electrode conductive layer 112b p2 (μm) is 1.0<L / (W×t p1 ) < 5.0 and 1.0 < L / (W × t p2 ) < 5.0, and 1.5 < L / (W × t p1) < 4.5 and 1.5 < L / (W × t p2 ) < 4.5, and more preferably 1.5 < L / (W × t p1 ) < 4.0 and 1.5 < L / (W × t p2 )<4.0. When the above formula is satisfied in the secondary battery 1, the battery capacity of the secondary battery 1 tends to be increased while the increase in resistance can be suppressed.

[0050] The positive electrode current collector 110 includes a main body 110a on which the positive electrode active material layer 113 is provided, a positive electrode first end 114a (hereinafter also referred to as the "first end 114a") on which the positive electrode active material layer 113 is not provided, and a positive electrode second end 114b (hereinafter also simply referred to as the "second end 114b"). The main body 110a has a pair of long sides and a pair of short sides. In one embodiment, the main body 110a is rectangular in plan view.

[0051] When the main body 110a is rectangular in plan view, the length of the long side lp (mm) is preferably 200 to 600 mm, and the length of the short side wp (mm) is preferably 50 to 200 mm. When the main body 110a satisfies these numerical ranges, the battery capacity of the secondary battery 1 tends to be increased while suppressing an increase in resistance.

[0052] When the main body 110a is rectangular, the ratio (lp / wp) of the long side length lp (mm) to the short side length wp (mm) is preferably 1.5 < lp / wp < 10.0, more preferably 2.0 < lp / wp < 5.0, and even more preferably 2.5 < lp / wp < 5.0. When the ratio (lp / wp) is within the above range, the battery capacity of the secondary battery 1 tends to be increased while suppressing an increase in resistance.

[0053] The thickness tp (μm) of at least one of the pair of positive electrode conductive layers preferably satisfies 1.0<lp / (wp×tp)<5.0, more preferably 1.5<lp / (wp×tp)<4.5, and further preferably 1.5<lp / (wp×tp)<4.0, where wp (mm) is the length of the short side and lp (mm) is the length of the long side. p1(μm) and the thickness t of the second positive electrode conductive layer 112b p2 (μm) is 1.0<lp / (wp×t p1 ) < 5.0 and 1.0 < lp / (wp x t p2 ) < 5.0, and 1.5 < lp / (wp × t p1 ) < 4.5 and 1.5 < lp / (wp x t p2 ) < 4.5, and more preferably 1.5 < lp / (wp × t p1 ) < 4.0 and 1.5 < lp / (wp x t p2 )<4.0. When the above formula is satisfied in the secondary battery 1, the battery capacity of the secondary battery 1 tends to be increased while the increase in resistance can be suppressed.

[0054] In one embodiment, the first end 114a and the second end 114b are configured as parts of the positive electrode current collector 110, extending in the Y direction, which is a direction different from the stacking direction, from the side surface of the main body 110a of the positive electrode current collector 110. Note that in one embodiment, the Y direction is the direction in which the long sides of the positive electrode current collector 110 extend, and the X direction is the direction in which the short sides of the positive electrode current collector 110 extend.

[0055] The first end 114a and the second end 114b are electrically connected to the first positive electrode tab 115a and the second positive electrode tab 115b, respectively. The first positive electrode tab 115a and the second positive electrode tab 115b may be made of the same material as the first end 114a and the second end 114b, or may be made of a different material. However, from the viewpoint of suppressing an increase in resistance, they may be made of the same material. The thickness of the first positive electrode tab 115a and the second positive electrode tab 115b may be 0.1 to 1.0 mm, 0.2 to 0.9 mm, or 0.3 to 0.8 mm.

[0056] The first end 114a and the first positive electrode tab 115a may be joined to each other via the first positive electrode metal sheet 116a. The second end 114b and the second positive electrode tab 115b may be joined to each other via the second positive electrode metal sheet 116b. The entire first end 114a and the second end 114b may be joined to the positive electrode metal sheet 116, or only a portion of the first end 114a and the second end 114b may be joined to the positive electrode metal sheet 116. The first positive electrode metal sheet 116a and the second positive electrode metal sheet 116b may be made of the same material as the first end 114a and the second end 114b, or may be made of different materials. However, from the viewpoint of suppressing an increase in resistance, they may be made of the same material. In one embodiment, the thickness of the positive electrode metal sheet 116 may be 3 to 15 μm, 5 to 14 μm, or 7 to 13 μm.

[0057] The positive electrode active material layer 113 may be provided on both sides or one side of the positive electrode current collector 110. The thickness of the positive electrode active material layer 113 may be adjusted appropriately depending on the desired capacity and rate characteristics of the battery. In one embodiment, the thickness of the positive electrode active material layer 113 is, for example, 20 μm or more and 150 μm or less.

[0058] The positive electrode active material layer 113 includes a positive electrode active material. The positive electrode active material is a material for holding a carrier metal in the positive electrode active material layer 113, and can also be called a host material for the carrier metal. The positive electrode active material may be a material for holding lithium ions in the positive electrode active material layer 113. In this case, lithium ions are charged into and released from the positive electrode active material by charging and discharging the battery. This can improve the stability and output voltage of the battery.

[0059] In one embodiment, the positive electrode active material is a metal oxide or a metal phosphate. The metal oxide may be, for example, a cobalt oxide-based compound, a manganese oxide-based compound, or a nickel oxide-based compound. The metal phosphate may be, for example, an iron phosphate-based compound or a cobalt phosphate-based compound. In one embodiment, the positive electrode active material is LiCoO, LiNi x Co y Mn z O ２ (x+y+z=1), LiNi x Coy Al z O ２ (x+y+z=1), LiNi x Mn y O ２ (x+y=1), LiNiO2, LiMn2O4, LiFePO4, LiCoPO4, LiFeOF, LiNiOF, and LiTiS2. The positive electrode active material may be used alone or in combination of two or more. In one embodiment, the content of the positive electrode active material in the positive electrode active material layer 113 may be 50% by mass or more and 100% by mass or less with respect to the entire positive electrode active material layer 113.

[0060] In one embodiment, the positive electrode active material layer 113 may include one or more components other than the positive electrode active material.

[0061] In one embodiment, the positive electrode active material layer 113 may include a sacrificial positive electrode material. The sacrificial positive electrode material is a lithium-containing compound that undergoes an oxidation reaction and does not substantially undergo a reduction reaction in the charge / discharge potential range of the positive electrode active material.

[0062] In one embodiment, the positive electrode active material layer 113 may include a gel electrolyte. The gel electrolyte may improve the adhesion between the positive electrode active material layer 113 and the positive electrode current collector 110. In one example, the gel electrolyte includes a polymer, an organic solvent, and a lithium salt. The polymer in the gel electrolyte may be, for example, a copolymer of polyethylene and / or polyethylene oxide, polyvinylidene fluoride, or a copolymer of polyvinylidene fluoride and hexafluoropropylene.

[0063] In one embodiment, the positive electrode active material layer 113 may include a conductive additive and / or a binder. In one example, the conductive additive is carbon black, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), carbon nanofibers (CF), or the like. In one example, the binder is polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, acrylic resin, polyimide resin, or the like. In one embodiment, the content of the conductive additive is 0.5% by mass or more and 30% by mass or less with respect to the entire positive electrode 11. In one embodiment, the content of the binder may be 0.5% by mass or more and 30% by mass or less with respect to the entire positive electrode 11.

[0064] In one embodiment, the positive electrode active material layer 113 may include a polymer electrolyte. For example, the polymer electrolyte may be a solid polymer electrolyte primarily containing a polymer and an electrolyte, or a semi-solid polymer electrolyte primarily containing a polymer, an electrolyte, and a plasticizer. In one embodiment, the total content of the polymer electrolyte may be 0.5% by mass or more and 30% by mass or less with respect to the entire positive electrode active material layer 113.

[0065] 2B , the first end 114a extends from one of a pair of short sides of the main body 110a, and the second end 114b extends from the other of the pair of short sides of the main body 110a. There may be multiple first ends 114a or just one. There may also be multiple second ends 114b or just one.

[0066] The first end 114a and the second end 114b may each independently be rectangular. However, the first end 114a and the second end 114b may not be rectangular but may have various shapes (e.g., triangular, trapezoidal, etc.). Furthermore, the first end 114a and the second end 114b may be deformed by having rounded or chipped corners.

[0067] In one embodiment, when there is one each of the first end 114a and the second end 114b, there is also one each of the first positive electrode tab 115a and the second positive electrode tab 115b. In another embodiment, when there is one each of the first positive electrode tab 115a and the second positive electrode tab 115b, there is also one each of the first end 114a and the second end 114b.

[0068] The first end 114a and the second end 114b do not overlap with each other in a plan view.

[0069] 4. Negative Electrode FIG. 3A is a cross-sectional view showing an example of the configuration of the negative electrode 12, and FIG. 3B is a top view showing an example of the configuration of the negative electrode 12. As shown in FIGS. 3A and 3B , in one embodiment, the negative electrode 12 includes a negative electrode current collector 120 and a negative electrode active material layer 123 disposed on the negative electrode current collector 120. In one embodiment, the negative electrode current collector 120 includes a negative electrode resin layer 121 (hereinafter also simply referred to as "resin layer 121") and a pair of negative electrode conductive layers disposed so as to sandwich the resin layer 121. The pair of negative electrode conductive layers includes a first negative electrode conductive layer 122a and a second negative electrode conductive layer 122b.

[0070] Alternatively, in one embodiment, the negative electrode current collector 120 does not include a resin layer, but includes a negative electrode conductive layer.

[0071] In one embodiment, the thickness of the negative electrode 12 may be 3 μm or more and 300 μm or less.

[0072] In one embodiment, the resin layer 121 may be composed of a sheet-like (film-like) or fibrous resin. The resin may be, for example, at least one of a polyolefin resin such as polyethylene terephthalate (PET), polyethylene, or polypropylene, or a thermoplastic resin such as polystyrene, polyvinyl chloride, or polyamide. The resin layer 121 may be composed of a plurality of layers of at least one of the resins. In one embodiment, the negative electrode resin layer 121 is formed from a material having a melting point of 150°C or higher and 300°C or lower. In one embodiment, the thickness of the resin layer 121 may be 3 μm or higher and 10 μm or lower, or 4 μm or higher and 8 μm or lower.

[0073] The resin layer 121 can function to melt and damage the negative electrode 12 in the event of abnormal heat generation due to overcharge or high temperature conditions, thereby interrupting short-circuit current within the battery. This can suppress a sudden temperature rise within the secondary battery 1 and prevent the battery from catching fire. In other words, the resin layer 121 can contribute to improving the safety of the secondary battery 1. Furthermore, since resins tend to have a smaller specific gravity than metals, using the negative electrode current collector 120 including the resin layer 121 tends to reduce the weight per unit volume of the secondary battery 1 and increase the energy density per unit weight of the secondary battery 1.

[0074] In one embodiment, the pair of negative electrode conductive layers are formed from at least one selected from the group consisting of metals that do not react with Cu, Ni, Ti, Fe, and Li, alloys thereof, and stainless steel. In one example, the pair of negative electrode conductive layers is Cu. In one embodiment, the pair of negative electrode conductive layers are formed by vapor deposition, sputtering, electrolytic plating, or lamination of the above-mentioned material on both surfaces of the resin layer 121. In one embodiment, the thickness tn of each pair of negative electrode conductive layers may be 0.5 μm or more and 5 μm or less, 0.7 μm or more and 3 μm or less, or 0.8 μm or more and 2.0 μm or less.

[0075] The thickness tn (μm) of at least one of the pair of negative electrode conductive layers preferably satisfies 1.0<L / (W×tn)<5.0, more preferably 1.5<L / (W×tn)<4.5, and further preferably 1.5<L / (W×tn)<4.0, where L (mm) is the length of the long side and W (mm) of the sealed container 16. In addition, the thickness t n1 (μm) and the thickness t of the second negative electrode conductive layer 122b n2 (μm) is 1.0<L / (W×t n1 ) < 5.0 and 1.0 < L / (W × t n2 ) < 5.0, and 1.5 < L / (W × t n1 ) < 4.5 and 1.5 < L / (W × t n2 ) < 4.5, and more preferably 1.5 < L / (W × t n1 ) < 4.0 and 1.5 < L / (W × t n2)<4.0. When the above formula is satisfied in the secondary battery 1, the battery capacity of the secondary battery 1 tends to be increased while the increase in resistance can be suppressed.

[0076] The negative electrode current collector 120 includes a main body 120a having a pair of long sides and a pair of short sides, a first end 124a (hereinafter also referred to as the "first end 124a") of the negative electrode extending from one of the pair of short sides of the main body 120a, and a second end 124b (hereinafter also simply referred to as the "second end 124b") extending from the other of the pair of short sides of the main body 120a. When the negative electrode 12 includes a negative electrode active material layer 123, the negative electrode active material layer 123 is provided on the main body 120a, and the negative electrode active material layer 123 is not provided on the first end 124a or the second end 124b. In one embodiment, the main body 120a is rectangular in a plan view.

[0077] When the main body 120a is rectangular in plan view, the length ln (mm) of the long side is preferably 200 to 600 mm, and the length wn (mm) of the short side is preferably 50 to 200 mm. When the main body 120a satisfies these numerical ranges, the battery capacity of the secondary battery 1 tends to be increased while suppressing an increase in resistance.

[0078] When the main body 120a is rectangular, the ratio (ln / wn) of the long side length ln (mm) to the short side length wn (mm) is preferably 1.5 < ln / wn < 10.0, more preferably 2.0 < ln / wn < 5.0, and even more preferably 2.5 < ln / wn < 5.0. When the ratio (ln / wn) is within the above range, the battery capacity of the secondary battery 1 tends to be increased while suppressing an increase in resistance.

[0079] The thickness tn (μm) of at least one of the pair of negative electrode conductive layers preferably satisfies 1.0<ln / (wn×tn)<5.0, more preferably 1.5<ln / (wn×tn)<4.5, and further preferably 1.5<ln / (wn×tn)<4.0, where wn (mm) is the length of the short side and ln (mm) is the length of the long side. n1 (μm) and the thickness t of the second negative electrode conductive layer 122b n2(μm) is 1.0<ln / (wn×t n1 ) < 5.0 and 1.0 < ln / (wn × t n2 ) < 5.0, and 1.5 < ln / (wn × t n1 ) < 4.5 and 1.5 < ln / (wn × t n2 ) < 4.5, and more preferably 1.5 < ln / (wn × t n1 ) < 4.0 and 1.5 < ln / (wn × t n2 )<4.0. When the above formula is satisfied in the secondary battery 1, the battery capacity of the secondary battery 1 tends to be increased while the increase in resistance can be suppressed.

[0080] In one embodiment, the first end 124a and the second end 124b are configured as parts of the negative electrode current collector 120, extending in the Y direction, which is a direction different from the stacking direction, from the side surface of the main body 120a of the negative electrode current collector 120. Note that in one embodiment, the Y direction is the direction in which the long sides of the negative electrode current collector 120 extend, and the X direction is the direction in which the short sides of the negative electrode current collector 120 extend.

[0081] The first end 124a and the second end 124b are electrically connected to the first negative electrode tab 125a and the second negative electrode tab 125b, respectively. The first negative electrode tab 125a and the second negative electrode tab 125b may be made of the same material as the first end 124a and the second end 124b, or may be made of a different material; however, from the viewpoint of suppressing an increase in resistance, they may be made of the same material. The thickness of the first negative electrode tab 125a and the second negative electrode tab 125b may be 0.1 to 1.0 mm, 0.2 to 0.9 mm, or 0.3 to 0.8 mm.

[0082] The first end 124a and the first negative electrode tab 125a may be joined to each other via a first negative electrode metal sheet 126a. The second end 124b and the second negative electrode tab 125b may be joined to each other via a second negative electrode metal sheet 126b. The entire first end 124a and the second end 124b may be joined to the negative electrode metal sheet 126, or only a portion of the first end 124a and the second end 124b may be joined to the negative electrode metal sheet 126. The first negative electrode metal sheet 126a and the second negative electrode metal sheet 126b may be made of the same material as the first end 124a and the second end 124b, or may be made of different materials. However, from the viewpoint of suppressing an increase in resistance, they may be made of the same material. In one embodiment, the thickness of the negative electrode metal sheet 116 may be 2 to 15 μm, 3 to 12 μm, or 4 to 10 μm.

[0083] The anode active material layer 123 may be provided on both sides or one side of the anode current collector 120. Alternatively, the anode active material layer 123 may not be provided. When the anode active material layer 123 is provided, the thickness of the anode active material layer 123 may be adjusted appropriately depending on the desired capacity and rate characteristics of the battery. In one embodiment, the thickness of the anode active material layer 123 is, for example, 20 μm or more and 150 μm or less.

[0084] The negative electrode active material layer 123 includes a negative electrode active material. The negative electrode active material is a material that causes an electrode reaction, i.e., an oxidation reaction and a reduction reaction, at the negative electrode. The negative electrode active material may be, for example, lithium metal, an alloy containing lithium metal, a carbon-based material, a metal oxide, a metal that alloys with lithium, or an alloy containing such a metal. The carbon-based material may be, for example, graphene, graphite, hard carbon, carbon nanotubes, or the like. The metal oxide may be, for example, a titanium oxide-based compound, a cobalt oxide-based compound, or the like. The metal that alloys with lithium may be, for example, silicon, silicon oxide, germanium, tin, lead, aluminum, gallium, or any of these pre-doped with lithium.

[0085] The content of the negative electrode active material may be 60.0% by mass or more and 100% by mass or less with respect to the total amount of the negative electrode active material layer 123 .

[0086] The negative electrode active material layer 123 may contain a binder, a conductive aid, and other additives in addition to the negative electrode active material.

[0087] The binder is not particularly limited, but examples thereof include polyvinylidene fluoride; modified polyvinylidene fluoride obtained by introducing functional groups such as hydroxyl groups, amino groups, carbonyl groups, carboxyl groups, phenyl groups, and methyl groups into polyvinylidene fluoride; polytetrafluoroethylene; modified polytetrafluoroethylene obtained by introducing functional groups such as hydroxyl groups, amino groups, carbonyl groups, carboxyl groups, phenyl groups, and methyl groups into polytetrafluoroethylene; block copolymers, random copolymers, and graft copolymers having tetrafluoroethylene as a constituent unit; styrene butadiene rubber; carboxymethyl cellulose; acrylic resins; polyimide resins, etc. The binders may be used alone or in combination of two or more.

[0088] The content of the binder may be 0.5% by mass or more and 10.0% by mass or less with respect to the total amount of the negative electrode active material layer 123 .

[0089] The conductive additive is not particularly limited, but examples thereof include carbon black, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), carbon nanofibers (CF), and acetylene black. The conductive additives may be used alone or in combination of two or more.

[0090] The content of the conductive additive may be 0.0 mass % or more and 30.0 mass % or less with respect to the total amount of the negative electrode active material layer 123 .

[0091] 3B , the first end 124a extends from one of a pair of short sides of the main body 120a, and the second end 124b extends from the other of the pair of short sides of the main body 120a. There may be multiple first ends 124a or just one. There may also be multiple second ends 124b or just one.

[0092] The first end 124a and the second end 124b may each independently be rectangular. However, the first end 124a and the second end 124b may not be rectangular but may have various shapes (e.g., triangular, trapezoidal, etc.). Furthermore, the first end 124a and the second end 124b may be deformed by having rounded or chipped corners.

[0093] In one embodiment, when there is one each of the first end 124a and the second end 124b, there is also one each of the first negative electrode tab 125a and the second negative electrode tab 125b. In another embodiment, when there is one each of the first negative electrode tab 125a and the second negative electrode tab 125b, there is also one each of the first end 124a and the second end 124b.

[0094] The first end 124a and the second end 124b do not overlap with each other in a plan view.

[0095] 4 is a top view showing an example of the configuration of the positive electrode 11 and the negative electrode 12 in the secondary battery 1. When the positive electrode 11 and the negative electrode 12 are configured in combination, the first end 114a of the positive electrode, the second end 114b of the positive electrode, the first end 124a of the negative electrode, and the second end 124b of the negative electrode do not overlap with each other in a plan view.

[0096] When there is one each of the positive electrode first end 114a, the positive electrode second end 114b, the negative electrode first end 124a, and the negative electrode second end 124b, an imaginary line L1 connecting the positive electrode first end 114a and the positive electrode second end 114b and an imaginary line L2 connecting the negative electrode first end 124a and the negative electrode second end 124b may intersect on the secondary battery 1. In other words, the positive electrode first end 114a and the positive electrode second end 114b, and the negative electrode first end 124a and the negative electrode second end 124b may be located diagonally opposite each other along the long sides of the sealed container 16. In this case, the distance from one of the long sides of the sealed container 16 to the first end 114a of the positive electrode is different from the distance from that long side to the second end 114b of the positive electrode, and the distance from that long side to the first end 124a of the negative electrode is different from the distance from that long side to the second end 124b of the negative electrode.

[0097] Fig. 5A is a top view showing an example configuration of the secondary battery 1, and Fig. 5B is a top view showing another example configuration of the secondary battery 1. Fig. 5A is a top view showing an example configuration of the secondary battery 1, specifically, when the imaginary line L1 and the imaginary line L2 intersect on the secondary battery 1. Fig. 5B is a top view showing an example configuration of the secondary battery 1, specifically, when the imaginary line L1 and the imaginary line L2 do not intersect on the secondary battery 1.

[0098] As will be described in detail later, the sealed container 16 is constructed by folding a sheet along one of the long sides of the sealed container 16 and sealing the sheet along the other side. The sealed portion of the long side that is constructed by the sealing is folded over, so that the sealed portion is slightly bent in the X direction and distorted in the Z direction. In the secondary battery 1 shown in Figures 5A and 5B, one of the long sides of the sealed container 16 is substantially straight, and the other long side is slightly bent in the X direction and distorted in the Z direction.

[0099] 6A is an exploded perspective view showing an example of a configuration in which multiple secondary batteries 1 shown in FIG. 5A are electrically connected in series, and FIG. 6B is an exploded perspective view showing an example of a configuration in which multiple secondary batteries 1 shown in FIG. 5B are electrically connected in series.

[0100] 6A, when multiple secondary batteries 1 are electrically connected in series, where the virtual lines L1 and L2 intersect on the secondary batteries 1, a substantially straight long side of the sealed container 16 appears on one side in the X direction (the upper side in the X direction in FIG. 6A), and a long side of the sealed container 16 that is slightly bent in the X direction or distorted in the Z direction appears on the other side in the X direction (the lower side in the X direction in FIG. 6A). In this case, the surface on one side in the X direction of the multiple secondary batteries 1 becomes substantially flat, making installation easy.

[0101] 5B , when multiple secondary batteries 1 are electrically connected in series where the virtual lines L1 and L2 do not intersect on the secondary batteries 1, the long sides of the sealed container 16 alternate between those that are substantially straight and those that are slightly bent in the X direction or distorted in the Z direction. In this case, the surfaces on both sides of the X direction of the multiple secondary batteries 1 will not be substantially flat, making installation difficult.

[0102] That is, when the imaginary line L1 and the imaginary line L2 intersect on the secondary battery 1, the secondary battery 1 can be easily installed even when a plurality of such secondary batteries 1 are electrically connected in series.

[0103] <Method of Manufacturing Secondary Battery> In one embodiment, a method of manufacturing a secondary battery 1 includes: a current collector preparation step of preparing a current collector including a resin layer and a pair of conductive layers provided on both sides of the resin layer, the current collector including a main body having a pair of long sides and a pair of short sides, at least one first end portion extending from one of the pair of short sides of the main body, and at least one second end portion extending from the other of the pair of short sides of the main body; an electrode stack preparation step of preparing an electrode stack including the current collector; and an electrode stack encapsulation step of encapsulating the electrode stack in a sealed container configured to enclose the electrode stack while allowing a portion of the first electrode tab and a portion of the second electrode tab to be taken out of the sealed container.

[0104] Each step of the method for manufacturing the secondary battery 1 will be described in detail below.

[0105] 1. Current Collector Preparing Step In the current collector preparing step, a positive electrode current collector and a negative electrode current collector are prepared.

[0106] Although not particularly limited, for example, in preparation of the positive electrode current collector 110, a positive electrode current collector film is prepared that includes a film of polyethylene terephthalate (PET) as the resin layer 111 and aluminum layers that are a pair of conductive layers provided on both sides of the resin layer 111. Alternatively, a positive electrode current collector film that includes an aluminum layer is prepared.

[0107] The positive electrode current collector film may be a commercially available product or may be made from various materials. In one embodiment, when making the positive electrode current collector film, an aluminum layer is formed on both surfaces of a film-like PET by vapor deposition, sputtering, electrolytic plating, or lamination.

[0108] The preparation of the negative electrode current collector 120 is performed in the same manner as the preparation of the positive electrode current collector 110, except that the type of material is changed. The preparation of the negative electrode current collector 120 is not particularly limited, but for example, a copper layer is used instead of the aluminum layer.

[0109] 2. Electrode Stack Preparation Step In the electrode stack preparation step, in one embodiment, the current collector prepared in the current collector preparation step, the separator 13, and, if necessary, an active material are combined to prepare the electrode stack 10.

[0110] An example of the production of the electrode laminate 10 will be described. First, a positive electrode active material layer 113 is formed on the positive electrode current collector 110 obtained in the current collector preparation step. For example, a positive electrode active material and one or more components other than the positive electrode active material are mixed to obtain a positive electrode active material composition. The positive electrode active material composition is applied to both surfaces of the positive electrode current collector 110. The positive electrode current collector 110 to which the positive electrode active material composition has been applied is press-molded to form the positive electrode active material layers 113 on both surfaces of the positive electrode current collector 110.

[0111] Next, the positive electrode current collector 110 on which the positive electrode active material layer 113 has been formed is cut into a predetermined shape, thereby forming the positive electrode 11.

[0112] In the positive electrode 11, the first end 114a and the second end 114b are connected to the first positive electrode tab 115a and the second positive electrode tab 115b, respectively. At this time, the first positive electrode tab 115a and the second positive electrode tab 115b may be electrically connected to the first end 114a and the second end 114b by welding or the like. Alternatively, the first end 114a and the second end 114b may be electrically connected to the first positive electrode tab 115a and the second positive electrode tab 115b via the first metal sheet 116a and the second metal sheet 116b, respectively.

[0113] The predetermined shape is a shape including a main body 110a having a pair of long sides and a pair of short sides, at least one first end 114a extending from one of the pair of short sides of the main body 110a, and at least one second end 114b extending from the other of the pair of short sides of the main body 110a, and in one embodiment, the shape of the main body 110a may be rectangular. Also, the shapes of the first end 114a and the second end 114b may be rectangular.

[0114] The cutting may be done with scissors or a cutter, or may be done using a template prepared in advance.

[0115] Next, the negative electrode active material layer 123 is formed on the negative electrode current collector 120 obtained in the current collector preparation step. For example, a negative electrode active material and one or more components other than the negative electrode active material are mixed to obtain a negative electrode active material composition. The negative electrode active material composition is applied to both surfaces of the negative electrode current collector 120. The negative electrode current collector 120 to which the negative electrode active material composition has been applied is press-molded to form the negative electrode active material layer 123 on both surfaces of the negative electrode current collector 120.

[0116] Next, the negative electrode current collector 120 on which the negative electrode active material layer 123 has been formed is cut out into a predetermined shape, thereby forming the negative electrode 12. The predetermined shape is the same as the shape used to form the positive electrode 11, and the method of cutting out into the predetermined shape is also the same as the method used to form the positive electrode 11.

[0117] In the negative electrode 12, the first end 124a and the second end 124b are connected to the first negative electrode tab 125a and the second negative electrode tab 125b, respectively. At this time, the first negative electrode tab 125a and the second negative electrode tab 125b may be electrically connected to the first end 124a and the second end 124b by welding or the like. Alternatively, the first end 124a and the second end 124b may be electrically connected to the first negative electrode tab 125a and the second negative electrode tab 125b via the first negative electrode metal sheet 126a and the second negative electrode metal sheet 126b, respectively.

[0118] When the negative electrode 12 does not have the negative electrode active material layer 123, the negative electrode active material layer 123 is not formed, and the negative electrode current collector 120 is cut out into a predetermined shape.

[0119] Next, the separator 13 is prepared. The separator 13 may be made of the above-mentioned material and cut into a predetermined shape. One or more sets of the positive electrode 11, the separator 13, and the negative electrode 12 are arranged so that the positive electrode 11 and the negative electrode 12 face each other with the separator 13 interposed therebetween, thereby preparing the electrode stack 10.

[0120] When the electrode stack 10 includes multiple sets of positive electrodes 11, separators 13, and negative electrodes 12, the first ends 114a of the multiple positive electrodes, the second ends 114b of the multiple positive electrodes, the first ends 124a of the multiple negative electrodes, and the second ends 124b of the multiple negative electrodes may each be fixed together by welding or the like.

[0121] FIG. 7A is a three-dimensional perspective view showing a manufacturing example of the secondary battery 1, and FIG. 7B is a cross-sectional view showing the manufacturing example of the secondary battery 1. As shown in FIGS. 7A and 7B , in one embodiment, the separator 13 is formed by bending at acute angles at multiple bending portions, and has a zigzag structure (also referred to as a "zigzag structure") in which the bending portions and flat portions are alternately connected in the stacking direction. Here, "bending at acute angles at bending portions" means that the angle formed by the two flat portions connected to the bending portions is an acute angle. In one embodiment, the angle formed by the two flat portions connected to the bending portions at the bending portions is approximately 0 degrees. That is, in one embodiment, the separator 13 is bent so that adjacent flat portions are approximately parallel to each other. This aspect can increase the number of stacked positive electrodes 11 and negative electrodes 12 per unit length in the electrode stack 10, which tends to increase the battery capacity per unit volume of the secondary battery 1.

[0122] In the separator 13 having a zigzag structure, the positive electrode 11 and the negative electrode 12 are inserted between the opposing flat portions. At this time, the positive electrode 11 and the negative electrode 12 face each other with the separator 13 interposed therebetween. In one embodiment, the positive electrode 11 is inserted from one side of the separator 13, and the negative electrode 12 is inserted from the other side of the separator 13. For example, in FIG. 7A , the negative electrode 12 is inserted from the upper side in the X direction, and the positive electrode 11 is inserted from the lower side in the X direction.

[0123] 3. Electrode Stack Encapsulation Step In the electrode stack encapsulation step, in one embodiment, the electrode stack 10 prepared in the electrode stack preparation step is encapsulated in the sealed container 16. At this time, parts of the first positive electrode tab 115a, the second positive electrode tab 115b, the first negative electrode tab 125a, and the second negative electrode tab 125b are taken out to the outside of the sealed container 16. When current is to be extracted from the secondary battery 1, the taken-out positive electrode tab 115 and negative electrode tab 125 are connected to conductors, and the current is extracted.

[0124] 7C is a top view showing a manufacturing example of the secondary battery 1. As shown in Fig. 7C, the electrode stack 10 may be placed in the upper half of a sealed container material 161, the lower half of the sealed container material 161 may be folded over to cover the electrode stack 10, and the edge of the upper half of the sealed container material 161 and the edge of the folded-over lower half of the sealed container material 161 may be sealed to enclose the electrode stack 10 in the sealed container 16. At this time, an electrolyte may be enclosed in the sealed container 16. Furthermore, the electrode stack 10 may be fixed to the sealed container material 161 by welding or the like so that the positions of the components within the sealed container 16 do not shift.

[0125] When the electrode stack 10 is sealed in the sealed container 16 in this manner, one of the long sides of the sealed container 16 is formed by the folded portion of the sealed container material 161, and the other long side of the sealed container 16 is formed by the sealed portion of the upper and lower halves of the sealed container material 161. The sealing is not particularly limited, and may be performed by heat sealing, ultrasonic sealing, or the like.

[0126] One of the long sides, which is formed by the folded portion of the sealed container material 161, is substantially straight. On the other hand, the other long side, which is formed by the sealed portion where the upper and lower halves of the sealed container material 161 are joined, is wavy or curved in the Z direction or the X direction. Here, as described in detail in FIG. 6 , regarding the imaginary line L1 connecting the first end 114 a of the positive electrode and the second end 114 b of the positive electrode and the imaginary line L2 connecting the first end 124 a of the negative electrode and the second end 124 b of the negative electrode, there are two types of secondary batteries 1: one in which the imaginary line L1 and the imaginary line L2 intersect on the secondary battery 1, and one in which the imaginary line L1 and the imaginary line L2 do not intersect on the secondary battery 1. However, when considering the case where a plurality of secondary batteries 1 are electrically connected in series, the secondary battery 1 in which the imaginary line L1 and the imaginary line L2 intersect on the secondary battery 1 is preferable from the viewpoint of ease of installation of the secondary battery 1.

[0127] In one embodiment, when the lower half of the sealed container material 161 is folded back, an insulating member 15 may be disposed in the portion where the sealed container material 161 contacts the positive electrode tab 115 and the negative electrode tab 125. This makes it possible to prevent the sealed container material 161 from being electrically connected to the positive electrode tab 115 and the negative electrode tab 125.

[0128] The sealed container material 161 is not particularly limited, but may include, for example, aluminum, more specifically, aluminum foil. The sealed container 16 may be an aluminum laminate pouch formed by sealing the edge of the upper half of the sealed container material 161 and the edge of the folded lower half of the sealed container material 161.

[0129] The material of the insulating member 15 is not particularly limited as long as it can ensure insulation, and for example, the resins described in detail for the positive electrode resin layer 111 and the negative electrode resin layer 121 can be used.

[0130] <Method of Using Secondary Battery> The secondary battery 1 is charged and discharged by connecting the positive electrode 11 to one end of an external circuit and the negative electrode 12 to the other end of the external circuit. The external circuit may be, for example, a resistor, a power source, an apparatus, a device, another battery, or a potentiostat.

[0131] When a voltage is applied between the positive electrode 11 and the negative electrode 12 such that a current flows from the negative electrode 12 to the positive electrode 11 through an external circuit, the secondary battery 1 is charged, and lithium metal is deposited on the surface of the negative electrode 12. When the positive electrode 11 and the negative electrode 12 are connected to the charged secondary battery 1 via a desired external circuit, the secondary battery 1 is discharged, and the lithium metal deposited on the surface of the negative electrode 12 is electrolytically dissolved.

[0132] In one embodiment, a solid electrolyte interface layer (SEI layer) may be formed on the surface of the negative electrode 12 or the surface of the separator 13 (i.e., the interface between the negative electrode 12 and the separator 13) during the first charge (initial charge) after assembly of the secondary battery 1. The SEI layer may contain, for example, an inorganic compound containing lithium or an organic compound containing lithium. In one embodiment, the thickness of the SEI layer is 1.0 nm or more and 10 μm or less. When an SEI layer is formed in the secondary battery 1, lithium metal is precipitated or dissolved at the interface between the negative electrode 10 and / or the separator 20 and the SEI layer during charge and discharge.

[0133] Alternatively, the secondary battery 1 may be used in a battery assembly.

[0134] 1. Battery Assembly FIG. 8 is a perspective view showing an example configuration of a battery assembly. The battery assembly 2 includes a cell stack 21 and a housing 22 configured to accommodate the cell stack 21. The cell stack 21 may be detachably accommodated in the housing 22 via a restraining holder or the like. The cell stack 21 includes a plurality of secondary batteries 1. The housing 22 includes a sidewall 221 that surrounds the side of the cell stack 21 and a bottom plate 222 that supports the underside of the cell stack 21. Although not shown, the housing 22 may have a cooling channel inside the sidewall 221 that faces the cell stack 21. The cooling channel can cool the cell stack 21.

[0135] In one embodiment, the housing 22 may be configured to accommodate a plurality of cell stacks 21. In this case, the housing 22 may include a plurality of bus bars 223 that electrically connect the cell stacks 21 together. The bus bars 223 may be made of a conductive material such as copper, aluminum, nickel, or an alloy thereof. The arrangement of the bus bars 223 and the connections between the bus bars 223 can be set as appropriate, thereby defining the electrical connection relationship (series, parallel) of the cell stacks 21. In the example shown in FIG. 1 , six cell stacks 21 are connected in series. The plurality of cell stacks 21 may be arranged in an array along a horizontal plane (xy plane).

[0136] The battery assembly 2 can be applied to vehicles such as electric vehicles, hybrid vehicles (HEVs), plug-in hybrid electric vehicles (P-HEVs), electric motorcycles, and electric bicycles, as well as various mobile objects (drones, robots, power tools, ships, airplanes, etc.) and stationary systems.

[0137] <Additional Notes> Embodiments of the present disclosure include the following aspects: [1] A lithium secondary battery comprising: a current collector including a resin layer and a pair of conductive layers provided on both sides of the resin layer, the current collector including a main body having a pair of long sides and a pair of short sides, at least one first end extending from one of the pair of short sides of the main body, and at least one second end extending from the other of the pair of short sides of the main body, a first electrode tab connected to the at least one first end, a second electrode tab connected to the at least one second end, and a sealed container configured to enclose an electrode stack including the current collector while allowing a portion of the first electrode tab and a portion of the second electrode tab to be taken out of the sealed container. [2] The lithium secondary battery according to [1], wherein the sealed container has a rectangular shape in a plan view, and wherein a ratio (L / W) of a length L of a long side of the sealed container to a length W of a short side of the sealed container is 1.5<L / W<10. [3] The lithium secondary battery according to [2], wherein the ratio (L / W) is 2<L / W<5. [4] The lithium secondary battery according to any one of [1] to [3], wherein a thickness t of at least one of the pair of conductive layers satisfies 1<L / (W×t)<5. [5] The lithium secondary battery according to any one of [1] to [4], wherein there is one each of the first end and the second end, and wherein a distance from one of the long sides of the sealed container to the first electrode tab is different from a distance from one of the long sides of the sealed container to the second electrode tab. [6] The lithium secondary battery according to [5], wherein the first electrode tab and the second electrode tab are located diagonally along the long side of the sealed container. [7] The lithium secondary battery according to any one of [1] to [6], wherein the sealed container is formed by folding a sheet along one of the long sides and sealing the sheet along the other long side. [8] The lithium secondary battery according to any one of [1] to [7], wherein the first end and the first electrode tab are joined to each other via a first metal sheet, and the second end and the second electrode tab are joined to each other via a second metal sheet.[9] A battery assembly comprising: a cell stack comprising a plurality of lithium secondary batteries according to any one of [1] to [8]; and a housing configured to accommodate the cell stack, the housing comprising a side wall surrounding the periphery of the cell stack and a bottom plate supporting the cell stack, the housing having a cooling flow path inside the side wall facing the cell stack.

[10] A vehicle comprising: the battery assembly according to [9]; and a motor that is driven by receiving a supply of electric power from the battery assembly.

[0138] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited by the following examples. FIG. 9A is a perspective view showing an example of the configuration of a secondary battery of an example, and FIG. 9B is a top view showing an example of the configuration of a secondary battery of a comparative example. In FIG. 9A, only the bottom surface of the sealed container is shown, and the metal sheet, positive electrode tab, and negative electrode tab are not shown. Furthermore, unless otherwise specified, experiments for the examples and comparative examples were performed at room temperature (25°C) and 1 atmosphere.

[0139] 1. Fabrication of Lithium Secondary Battery Example 1 First, a negative electrode was prepared. That is, a negative electrode current collector was prepared by vapor-depositing Cu to a thickness of tn = 1.0 μm on both sides of a 6 μm-thick polypropylene (PP). Then, a mixed material was prepared by mixing 97 parts by mass of graphite as a negative electrode active material, 0.5 parts by mass of carbon black as a conductive additive, and 1.5 parts by mass of carboxymethyl cellulose (CMC) and 1.0 part by mass of styrene-butadiene rubber (SBR) as binders with water as a solvent. This mixed material was applied to both sides of the negative electrode current collector in a basis weight of 15 mg / cm. 2 The coating was applied, pressed, and cut out to a predetermined size. This resulted in 18 negative electrodes. The coated portion (main body) of the resulting negative electrode had a length in the Y direction (length of the long side) of 482 mm and a length in the X direction (length of the short side) of 95 mm. The negative electrode had one first end and one second end. A negative electrode metal sheet (copper foil with a thickness of 5 μm) was attached to the first end and second end of each negative electrode by ultrasonic welding.

[0140] Next, a sheet (thickness: 15 μm) whose surface was coated with a mixture of polyvinylidene fluoride (PVDF) and Al 2 O 3 was prepared as a separator.

[0141] Next, a positive electrode was prepared. A 6 μm-thick film of polyethylene terephthalate (PET) was used as a positive electrode current collector, with Al vapor-deposited on both sides to a thickness of tp = 1.0 μm. Then, LiNi was used as a positive electrode active material in N-methyl-pyrrolidone (NMP) as a solvent. 0.6 Co 0.2 Mn 0.2 A mixed material was prepared by mixing 96 parts by mass of O2, 2 parts by mass of carbon black as a conductive additive, and 2 parts by mass of polyvinylidene fluoride (PVDF) as a binder. This mixed material was applied to both sides of a positive electrode current collector so that the basis weight was 23 mg / cm 2 The coating was applied, pressed, and cut out to a predetermined size. This resulted in 17 positive electrodes. The coated portion (main body) of the resulting positive electrode had a length in the Y direction (length of the long side) of 478 mm and a length in the X direction (length of the short side) of 93 mm. The positive electrode had one first end and one second end. Then, a positive electrode metal sheet (12 μm thick Al foil) was attached to the first end and second end of each positive electrode by ultrasonic welding.

[0142] An Al tab having a thickness of 0.5 mm and a width (length in the X direction) of 30 mm was prepared as the positive electrode tab, and a Cu tab having a thickness of 0.5 mm and a width (length in the X direction) of 30 mm was prepared as the negative electrode tab.

[0143] Next, the positive electrode, negative electrode, and separator were stacked so that the positive electrode and negative electrode faced each other with the separator interposed therebetween. Then, a first end of the positive electrode was overlapped with a positive electrode metal sheet and joined to a positive electrode tab by ultrasonic welding. A second end of the positive electrode was overlapped with a positive electrode metal sheet and joined to another positive electrode tab by ultrasonic welding. A first end of the negative electrode was overlapped with a negative electrode metal sheet and joined to a negative electrode tab by ultrasonic welding. A second end of the negative electrode was overlapped with a negative electrode metal sheet and joined to another negative electrode tab by ultrasonic welding. In this way, an electrode stack was obtained.

[0144] The electrode stack was inserted into a sealed container and sealed together with an electrolyte to obtain a lithium secondary battery. The electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF) in a solvent containing a 30:35:35 mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a concentration of 1 M, to which 2 parts by weight of vinylene carbonate (VC) was added. An insulating member was disposed between the sealed container and the positive and negative electrode metal sheets of the electrode stack.

[0145] The length L of the long side of the sealed container was 485 mm, and the length W of the short side was 97 mm. One of the long sides of the sealed container was formed by folding a sheet and was approximately straight. The other long side of the sealed container was formed by sealing the edges of a folded sheet and then folding back the sealed portion, and was slightly bent in the X direction and distorted in the Z direction. In addition, an imaginary line L1 connecting the first end of the positive electrode and the second end of the positive electrode and an imaginary line L2 connecting the first end of the negative electrode and the second end of the negative electrode intersected on the lithium secondary battery.

[0146] Examples 2 to 4 Lithium secondary batteries were fabricated in the same manner as in Example 1, except that the length L of the long side and the length W of the short side of the sealed container, the thickness tp of the Al layer of the positive electrode current collector, the thickness tn of the Cu layer of the negative electrode current collector, and the number of positive and negative electrodes were changed as shown in Table 1. The negative electrode had a length in the Y direction (long side length) of (L-3) mm and a length in the X direction (short side length) of (W-2) mm. The positive electrode had a length in the Y direction (long side length) of (L-7) mm and a length in the X direction (short side length) of (W-4) mm.

[0147] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that, as shown in Table 1, the length L of the long side and the length W of the short side of the sealed container, the thickness tp of the Al layer of the positive electrode current collector, the thickness tn of the Cu layer of the negative electrode current collector, the number of positive electrodes and negative electrodes, and the number of ends of the positive electrodes and negative electrodes were changed.

[0148] Due to the change in the number of positive electrode ends and negative electrode ends, the positive electrode ends, negative electrode ends, positive electrode tabs, and negative electrode tabs were fabricated in the arrangement shown in Figure 9B. An Al tab with a thickness of 0.5 mm and a width (length in the X direction) of 60 mm was prepared as the positive electrode tab. A Cu tab with a thickness of 0.5 mm and a width (length in the X direction) of 60 mm was prepared as the negative electrode tab.

[0149] 2. Evaluation Hereinafter, the initial CC charging of the fabricated lithium secondary battery will be referred to as "initial charging," and the initial CC discharging will be referred to as "initial discharging." CC charging is charging at a constant current value, and CC discharging is discharging at a constant current value. CV charging is charging at a constant voltage, and CV discharging is discharging at a constant voltage. A 1C current is a current calculated based on the theoretical capacity of the battery that can fully charge the battery in one hour. A 2C current is twice as large as a 1C current.

[0150] 2.1. Cell Capacity Measurement The lithium secondary batteries of each example were pressurized at 500 kPa in a thermostatic chamber at 25°C and initially charged at a current of 0.05 C until the voltage reached 4.2 V, and then initially discharged at a current of 0.1 C until the voltage reached 2.7 V. Next, the lithium secondary batteries of each example were CC charged at a current of 0.33 C without pressure in an environment at 25°C until the voltage reached 4.2 V, and then CC discharged at a current of 0.33 C until the voltage reached 2.7 V, and the cell capacity was determined from this CC discharge. The cell capacity measurement results are shown in Table 1.

[0151] 2.2. Cell Resistance Measurement The lithium secondary batteries of each example for which cell capacity measurements were performed were CC charged in a thermostatic chamber at 25°C without pressure at a current of 0.33 C until the voltage reached 4.2 V. Subsequently, while maintaining the voltage constant, they were CV charged until the current decayed to 0.05 C. Next, each lithium secondary battery was discharged in a thermostatic chamber at 25°C without pressure at a current of 0.33 C until the voltage reached 3.7 V. Subsequently, while maintaining the voltage constant, they were CV discharged until the current decayed to 0.05 C. Subsequently, to measure DC resistance, a discharge current equivalent to 3 C was passed through each lithium secondary battery for 60 seconds, and the DC resistance (mΩ) was calculated from the voltage before and after the discharge current. The DC resistance measurement results are shown in Table 1.

[0152]

[0153] REFERENCE SIGNS LIST 1... secondary battery, 10... electrode laminate, 11... positive electrode, 110... positive electrode current collector, 110a... main body, 111... resin layer, 112a... first conductive layer, 112b... second conductive layer, 113... positive electrode active material layer, 114a... first end of positive electrode, 114b... second end of positive electrode, 115a... first positive electrode tab, 115b... second positive electrode tab, 116a... first positive electrode metal sheet, 116b... second positive electrode metal sheet, 12... negative electrode, 120... negative electrode current collector, 120a... main body, 121... resin layer, 122a ...first conductive layer, 122b...second conductive layer, 123...negative electrode active material layer, 124a...first end of negative electrode, 124b...second end of negative electrode, 125a...first negative electrode tab, 125b...second negative electrode tab, 126a...first negative electrode metal sheet, 126b...second negative electrode metal sheet, 13...separator, 15...insulating member, 16...sealed container, L1, L2...phantom lines, 2...battery assembly, 21...cell stack, 22...housing, 221...side wall, 222...bottom plate, 223...bus bar

Claims

1. A lithium secondary battery comprising: a current collector having a resin layer and a pair of conductive layers provided on both sides of the resin layer, the current collector having a main body with a pair of long sides and a pair of short sides, at least one first end extending from one of the pair of short sides of the main body, and at least one second end extending from the other of the pair of short sides of the main body; a first electrode tab connected to the at least one first end; a second electrode tab connected to the at least one second end; and a sealed container configured to enclose an electrode laminate including the current collector while allowing a portion of the first electrode tab and a portion of the second electrode tab to be taken out of the sealed container.

2. The lithium secondary battery according to claim 1, wherein the sealed container is rectangular in plan view, and the ratio (L / W) of the length L of the long side of the sealed container to the length W of the short side of the sealed container is 1.5<L / W<10.

3. The lithium secondary battery according to claim 2, wherein the ratio (L / W) is 2<L / W<5.

4. The lithium secondary battery according to claim 2, wherein the thickness t of at least one of the pair of conductive layers satisfies 1<L / (W×t)<5.

5. The lithium secondary battery according to claim 1, wherein the first end and the second end are each one, and the distance from one of the long sides of the sealed container to the first electrode tab is different from the distance from one of the long sides of the sealed container to the second electrode tab.

6. The lithium secondary battery according to claim 5, wherein the first electrode tab and the second electrode tab are positioned diagonally along the long side of the sealed container.

7. The lithium secondary battery according to claim 1, wherein the sealed container is constructed by folding one of the long sides of a sheet and sealing the sheet at the other long side.

8. The lithium secondary battery according to claim 1, wherein the first end and the first electrode tab are joined to each other via a first metal sheet, and the second end and the second electrode tab are joined to each other via a second metal sheet.

9. A battery assembly comprising: a cell stack comprising a plurality of lithium secondary batteries according to claim 1; and a housing configured to accommodate the cell stack, the housing comprising a side wall surrounding the periphery of the cell stack and a bottom plate supporting the cell stack, the housing having a cooling flow path provided inside the side wall facing the cell stack.

10. A vehicle comprising: the battery assembly according to claim 9; and a motor that is driven by power supplied from the battery assembly.

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