Lithium secondary battery and method for manufacturing lithium secondary battery

Abstract

Provided is a technology that suppresses a decrease in cell capacity while suppressing a short circuit between a positive electrode and a negative electrode. The present invention relates to a lithium secondary battery comprising a positive electrode and a negative electrode that are facing with a separator interposed therebetween, wherein the positive electrode comprises a positive electrode current collector that is configured by sandwiching a resin layer between a first metal layer and a second metal layer, and a positive electrode active material layer that is provided on the positive electrode current collector, the first metal layer comprises a first section where the positive electrode active material layer is not provided, the second metal layer comprises a second section where the positive electrode active material layer is not provided, and the first section and the second section have different dimensions in both the width direction and the length direction.

Description

Lithium secondary battery and method of manufacturing the same

[0001] SUMMARY OF THE INVENTION Exemplary embodiments of the present disclosure relate to lithium secondary batteries and methods for manufacturing lithium secondary batteries.

[0002] Patent Document 1 describes providing an insulating coating on the positive electrode to prevent short circuits between the positive electrode and the negative electrode.

[0003] International Publication No. 2017 / 057762

[0004] The present disclosure provides a technique for suppressing a decrease in cell capacity while suppressing a short circuit between a positive electrode and a negative electrode in a lithium secondary battery.

[0005] In one exemplary embodiment of the present disclosure, there is provided a lithium secondary battery including a positive electrode and a negative electrode facing each other with a separator interposed therebetween, wherein the positive electrode includes a positive electrode current collector formed by sandwiching a resin layer between a first metal layer and a second metal layer, and a positive electrode active material layer provided on the positive electrode current collector, wherein the first metal layer includes a first portion where the positive electrode active material layer is not provided, and the second metal layer includes a second portion where the positive electrode active material layer is not provided, and the first portion and the second portion have different dimensions in both the width direction and the length direction.

[0006] According to one exemplary embodiment of the present disclosure, it is possible to provide a technology that suppresses a decrease in cell capacity while suppressing a short circuit between a positive electrode and a negative electrode.

[0007] 1 is a perspective view illustrating an example of the configuration of a lithium secondary battery according to an embodiment; FIG. 2 is a diagram illustrating an example of a negative electrode; FIG. 3 is a diagram illustrating another example of a negative electrode; FIG. 4 is a diagram illustrating another example of a negative electrode; FIG. 5 is a diagram illustrating another example of a negative electrode; FIG. 6 is a diagram illustrating an example of a positive electrode 30; FIG. 7 is a diagram illustrating a first metal layer 312a; FIG. 8 is a diagram illustrating a second metal layer 312b; FIG. 9 is a diagram illustrating an example of an arrangement of a positive electrode and a negative electrode; FIG. 10 is a diagram illustrating another example of an arrangement of a positive electrode and a negative electrode; FIG. 11 is a diagram illustrating another example of a first portion 33; FIG. 12 is a flowchart illustrating an example of a manufacturing method of a secondary battery 1; FIG. 13 is a diagram illustrating a process of forming a positive electrode of a secondary battery 1; FIG. 14 is a diagram illustrating a process of forming a positive electrode of a secondary battery 1; FIG. 15 is a diagram illustrating another example of a cutout in a positive electrode material; FIG. 16 is a diagram illustrating another example of a cutout in a positive electrode material; FIG. 17 is a diagram illustrating an example of an effect of employing a cutout line L1; and FIG. 18 is a diagram illustrating the configurations and results of examples and comparative examples.

[0008] Hereinafter, each embodiment of the present disclosure will be described.

[0009] In one exemplary embodiment, there is provided a lithium secondary battery comprising a positive electrode and a negative electrode facing each other with a separator interposed therebetween, wherein the positive electrode comprises a positive electrode current collector formed by sandwiching a resin layer between a first metal layer and a second metal layer, and a positive electrode active material layer provided on the positive electrode current collector, the first metal layer comprising a first portion where the positive electrode active material layer is not provided, and the second metal layer comprising a second portion where the positive electrode active material layer is not provided, and the first portion and the second portion have different dimensions in both the width direction and the length direction.

[0010] In one exemplary embodiment, the first portion has one end and the other end in the length direction, the one end of the first portion overlaps with the negative electrode in a planar view and the other end of the first portion does not overlap with the negative electrode in a planar view, and the second portion has one end and the other end in the length direction, the one end of the second portion overlaps with the negative electrode in a planar view and the other end of the second portion does not overlap with the negative electrode in a planar view.

[0011] In one exemplary embodiment, one end of the first portion and one end of the second portion have different width dimensions.

[0012] In one exemplary embodiment, the other end of the first portion and the other end of the second portion have the same width dimension.

[0013] In one exemplary embodiment, one end of the first portion has the same width as the portion of the first metal layer where the positive electrode active material layer is provided.

[0014] In one exemplary embodiment, one end of the second portion has a width dimension smaller than that of the portion of the second metal layer where the positive electrode active material layer is provided.

[0015] In one exemplary embodiment, the first portion comprises a first rectangular region having a first width dimension and a second rectangular region having a second width dimension that is smaller than the first width dimension.

[0016] In one exemplary embodiment, the first width dimension is the same as the width dimension of the portion of the first metal layer where the positive electrode active material layer is provided.

[0017] In one exemplary embodiment, the second portion comprises a rectangular area that is the same shape as the second rectangular area.

[0018] In one exemplary embodiment, the first portion has one end and the other end in the length direction, the second portion has one end and the other end in the length direction, the negative electrode has one end and the other end in the length direction, and one end of the negative electrode is arranged between one end of the first portion and the other end of the first portion in a planar view, and is also arranged between one end of the second portion and the other end of the second portion in a planar view.

[0019] In one exemplary embodiment, the distance from one end of the first portion to one end of the negative electrode in a plan view is longer than the distance from one end of the second portion to one end of the negative electrode in a plan view.

[0020] In one exemplary embodiment, the distance from one end of the first portion to one end of the negative electrode in a plan view is 3 mm or less.

[0021] In one exemplary embodiment, the distance from one end of the second portion to one end of the negative electrode in a plan view is 0.25 mm or more.

[0022] In one exemplary embodiment, there is provided a lithium secondary battery comprising a positive electrode and a negative electrode facing each other with a separator interposed therebetween, the positive electrode comprising: a positive electrode current collector configured by sandwiching a resin layer between a first metal layer and a second metal layer; and a positive electrode active material layer provided on the positive electrode current collector, the first metal layer comprising a first portion where the positive electrode active material layer is not provided, the first portion comprising a first region and a second region, the first region having one end and the other end in the length direction and having a first width dimension, and the second region extending in the length direction from a portion of the other end of the first region and having a second width dimension smaller than the first width dimension.

[0023] In one exemplary embodiment, the first region completely overlaps with the negative electrode in a plan view, and the second region partially overlaps with the negative electrode in a plan view and partially does not overlap with the negative electrode.

[0024] In one exemplary embodiment, the second metal layer has a second portion where the positive electrode active material layer is not provided, and the second portion has a region having the same shape as the second region.

[0025] In one exemplary embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0026] In one exemplary embodiment, the negative electrode comprises a negative electrode current collector formed by sandwiching a resin layer between a pair of metal layers.

[0027] In one exemplary embodiment, a stack is provided in which multiple sets of positive electrodes, separators, and negative electrodes are stacked.

[0028] In one exemplary embodiment, there is provided a method for manufacturing a lithium secondary battery, the method including: a step of preparing a positive electrode material, the positive electrode material including a positive electrode current collector formed by sandwiching a resin layer between a first metal layer and a second metal layer, and a positive electrode active material layer provided on the positive electrode current collector; and a step of cutting out the positive electrode material to form a positive electrode, the positive electrode including a first portion of the first metal layer where no positive electrode active material layer is provided, and a second portion of the second metal layer where no positive electrode active material layer is provided, the first portion and the second portion having different dimensions in both the width direction and the length direction.

[0029] Hereinafter, each embodiment of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or similar elements are designated by the same reference numerals, and redundant explanations will be omitted. Unless otherwise specified, the positional relationships, such as up, down, left, and right, will be described based on the positional relationships shown in the drawings. The dimensional ratios in the drawings do not represent actual ratios, and the actual ratios are not limited to the ratios shown in the drawings.

[0030] <Configuration Example of Secondary Battery> FIG. 1 is a perspective view illustrating a configuration example of a lithium secondary battery 1 (hereinafter also referred to as "secondary battery 1") according to one embodiment. As shown in FIG. 1, in one embodiment, the secondary battery 1 includes a negative electrode 10, a separator 20, and a positive electrode 30. The negative electrode 10, the separator 20, and the positive electrode 30 are arranged in this order along the z direction of FIG. 1 (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 negative electrode 10 and the positive electrode 30 face each other with the separator 20 sandwiched between them. The negative electrode 10, the separator 20, and the positive electrode 30 each have a main surface extending in the length direction (y direction) and the width direction (x direction).

[0031] In one embodiment, the secondary battery 1 may be configured by stacking multiple sets of negative electrodes 10, separators 20, and positive electrodes 30 in a stacking direction. The number of stacked electrodes 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 30 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 30 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 30 included in the secondary battery 1 may be 50 or less, 40 or less, or 30 or less. In one embodiment, the energy density of the secondary battery 1 may be 300 Wh / kg or more. In one embodiment, the rated capacity of the secondary battery 1 may be 1.5 Ah or more, or 5 Ah or more. Each component of the secondary battery 1 will be described in detail below.

[0032] 1. Negative Electrode As shown in FIG. 1 , the negative electrode 10 has a negative electrode end portion 13. The negative electrode end portion 13 extends in the length direction (y direction) parallel to the main surface of the negative electrode 10. The negative electrode 10 is electrically connected to an external circuit via the negative electrode end portion 13. When the secondary battery 1 includes a plurality of negative electrodes 10, the negative electrode end portions 13 are electrically connected to one another. The negative electrode end portions 13 may be joined to one another by, for example, welding.

[0033] FIG. 2A is a diagram illustrating an example of a negative electrode. As shown in FIG. 2A , in one embodiment, the negative electrode 10 includes a negative electrode current collector 11 and a negative electrode active material layer 12 disposed on the negative electrode current collector 11. In one embodiment, the negative electrode current collector 11 may include a negative electrode resin layer 111 and a pair of negative electrode metal layers 112 disposed so as to sandwich the negative electrode resin layer 111. In one embodiment, the negative electrode resin layer 111 may be formed of a sheet-like (film-like) or fibrous resin. In one embodiment, the negative electrode metal layer 112 is formed of at least one metal 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 negative electrode metal layer 112 is Cu. By including the negative electrode resin layer 111, the negative electrode 10 can ensure the thickness (rigidity) required for the negative electrode 10 while being lighter than when the negative electrode 10 is formed only with the negative electrode metal layer 112. In one embodiment, the negative electrode current collector 11 may not include the negative electrode resin layer 111 and may be composed of only the negative electrode metal layer 112 .

[0034] The negative electrode active material layer 12 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.

[0035] The content of the negative electrode active material may be 60.0 mass % or more and 100 mass % or less with respect to the total amount of the negative electrode active material layer 12 .

[0036] The negative electrode active material layer 12 may contain, in addition to the negative electrode active material, a binder, a conductive aid, and other additives.

[0037] 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.

[0038] 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 12 .

[0039] 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.

[0040] 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 12 .

[0041] In one embodiment, the thickness of the negative electrode 10 may be 3.0 μm or more and 300.0 μm or less.

[0042] In one embodiment, the thickness of the negative electrode active material layer 12 may be 3.0 μm or more and 150.0 μm or less.

[0043] 2A , the negative electrode active material layer 12 is not formed on the negative electrode end portion 13. The negative electrode end portion 13 is made of the same material as the negative electrode current collector 11. In one embodiment, the negative electrode end portion 13 may be made of a separate material from the negative electrode current collector 11.

[0044] 2B to 2D are diagrams illustrating other examples of a negative electrode. In one embodiment, as shown in FIG. 2B , the negative electrode 10 may be configured with a negative electrode current collector 11 that includes a negative electrode resin layer 111 and a pair of negative electrode metal layers 112 that are arranged to sandwich the negative electrode resin layer 111. In one embodiment, as shown in FIG. 2C , the negative electrode 10 may be configured with a negative electrode current collector 11 that does not include the negative electrode resin layer 111 and is configured only with the negative electrode metal layer 112. In one embodiment, as shown in FIG. 2D , the negative electrode 10 may be configured with a negative electrode current collector 11 that does not include the negative electrode resin layer 111 and is configured only with the negative electrode metal layer 112, and a negative electrode active material layer 12 that is arranged on the negative electrode current collector 11.

[0045] 2B and 2C , the negative electrode 10 may be composed of a negative electrode metal layer 112, or may be composed of a negative electrode resin layer 111 and a negative electrode metal layer 112. In this case, the negative electrode metal layer 112 may be composed of at least one selected from the group consisting of Cu, Ni, Ti, Fe, and other metals that do not react with Li, alloys thereof, and stainless steel (SUS). The "metal that does not react with Li" may be a metal that does not react with lithium ions or lithium metal to form an alloy when the secondary battery 1 is in operation.

[0046] In one embodiment, as shown in FIGS. 2B and 2C , the negative electrode 10 is substantially free of the negative electrode active material layer 12. For example, the thickness of the negative electrode active material layer 12 deposited on the negative electrode 10 at the end of discharge (e.g., when the open-circuit voltage of the battery is 2.5 V or more and 3.6 V or less) may be 25 μm or less. In one embodiment, the thickness of the negative electrode active material layer 12 at the end of discharge may be 20 μm or less, 15 μm or less, 10 μm or less, or 5 μm or less, or even 0 μm. The negative electrode 10 being substantially free of the negative electrode active material layer 12 can improve not only the weight energy density but also the energy density per volume. In this case, the secondary battery 1 can also be referred to as an "anode-free lithium battery," a "zero-anode lithium battery," or an "anodeless lithium battery." In one embodiment, the negative electrode 10 may have the negative electrode active material layer 12 as shown in FIGS. 2A and 2D .

[0047] In one embodiment, as shown in FIGS. 2B and 2C , the negative electrode 10 does not have a negative electrode active material layer 12 before the initial charge of the battery (the state from the assembly of the battery to the first charge). That is, after the initial charge, the secondary battery 1 may be charged and discharged by depositing lithium metal on the negative electrode and electrolytically dissolving the deposited lithium metal. In this case, the volume and mass occupied by the negative electrode active material are reduced, the volume and mass of the entire battery are reduced, and the energy density is, in principle, increased. Note that "lithium metal deposited on the negative electrode" not only refers to lithium metal being deposited on the surface of the negative electrode, but also includes lithium metal being deposited on the surface of the solid electrolyte interface (SEI) layer or on or inside the buffer functional layer. Note that the buffer functional layer has a solid portion (including a gel-like portion) having ionic conductivity and electrical conductivity and a pore portion formed by gaps in this solid portion. In this case, lithium metal can be deposited on the surface of the negative electrode 10 (the interface between the negative electrode 10 and the buffer functional layer) and / or inside the buffer functional layer (the surface of the solid portion of the buffer functional layer).

[0048] In one embodiment, when the negative electrode 10 does not have the negative electrode active material layer 12, the mass of lithium metal deposited on the negative electrode when the voltage is 4.2 V is M ４．２ The same mass at a voltage of 3.0 V is M ３．０ In this case, M ３．０ / M ４．２ may be 40% or less, or 35% or less. ３．０ / M ４．２ may be 1.0% or more, 2.0% or more, 3.0% or more, or 4.0% or more.

[0049] In one embodiment, the thickness of the negative electrode 10 not including the negative electrode active material layer 12 may be 1.0 μm or more and 30 μm or less. This reduces the volume occupied by the negative electrode 10 in the secondary battery 1, thereby improving the energy density. The thickness of the negative electrode 10 may be 2.0 μm or more and 20 μm or less, 2.0 μm or more and 18 μm or less, or 3.0 μm or more and 15 μm or less.

[0050] 2. Separator As shown in FIG. 1 , the separator 20 is disposed between the negative electrode 10 and the positive electrode 30. The separator 20 physically and / or electrically isolates the negative electrode 10 and the positive electrode 30, while ensuring ionic conductivity of lithium ions. In one embodiment, the separator 20 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 20 may be formed of one type of material alone, or two or more types of materials in combination.

[0051] When the separator 20 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 20 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 20 may be a porous polyethylene (PE) film, a porous polypropylene (PP) film, or a laminate structure thereof.

[0052] In one embodiment, one or both surfaces of the separator 20 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 20. In one embodiment, the separator coating layer may include a binder such as polyvinylidene fluoride (PVDF), a mixture of styrene butadiene rubber and carboxymethyl cellulose (SBR-CMC), and 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.

[0053] In one embodiment, the thickness of the separator 20 (including the coating layer if the separator 20 includes the coating layer) may be 3.0 μm or more and 40 μm or less. This can reduce the volume occupied by the separator 20 while isolating the negative electrode 10 and the positive electrode stack 30. In one embodiment, the thickness of the separator 20 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 20 may be 30 μm or less, 20 μm or less, or 10 μm or less.

[0054] 3. 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.

[0055] The electrolytic solution may be, for example, a solution that fills a housing (not shown in FIG. 1 ) that houses the secondary battery 1. Furthermore, for example, the electrolytic solution may be impregnated into the separator 20, or may be held in a polymer to form a polymer electrolyte or a gel electrolyte.

[0056] The electrolyte contained in the electrolytic solution may be, for example, a lithium salt. Examples of the lithium salt include LiI, LiCl, LiBr, LiF, and LiBF. ４ , LiPF ６ , LiAsF ６ , LiSO ３ CF ３ , LiN(SO ２ F) ２ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ CF ３ CF ３ ) ２ , LiB(O ２ C ２ H ４ ) ２ , LiB(C ２ O ４ ) ２ , LiB(O ２ C２ H ４ ) F ２ , LiB(OCOCF ３ ) ４ , LiNO ３ , and Li ２ SO ４ It may be one or a combination of two or more selected from the group consisting of:

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] The electrolyte solution of the present embodiment may contain an additive. The additive is not particularly limited, but examples thereof include vinylene carbonate (VC), lithium difluorophosphate (LiPO ２ F ２ ), lithium bis(fluorosulfonyl)imide (LiFSI).

[0066] 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.

[0067] 1 , the positive electrode 30 includes a positive electrode current collector 31 and a positive electrode active material layer 32. The positive electrode 30 also has a positive electrode end portion 35. The positive electrode end portion 35 extends in the length direction (y direction) parallel to the main surface of the positive electrode 30. The positive electrode 30 is electrically connected to an external circuit via the positive electrode end portion 35. When the secondary battery 1 includes a plurality of positive electrodes 30, the positive electrode ends 35 are electrically connected to one another. The positive electrode ends 35 may be joined to one another by, for example, welding.

[0068] Fig. 3 is a diagram illustrating an example of a positive electrode 30. Fig. 3 is a cross-sectional view taken along the line A-A' in Fig. 1. In one embodiment, as shown in Fig. 3, the positive electrode 30 includes a positive electrode current collector 31 and positive electrode active material layers 32 formed on both surfaces of the positive electrode current collector 31.

[0069] The positive electrode current collector 31 has a resin layer 311, a first metal layer 312a, and a second metal layer 312b. The first metal layer 312a and the second metal layer 312b are arranged to sandwich the resin layer 311. Hereinafter, the first metal layer 312a and the second metal layer 312b will also be collectively referred to as the "metal layer 312."

[0070] The resin layer 311 of the positive electrode current collector 31 may be made of, for example, 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 311 may be made by laminating a plurality of at least one of the resins. In one embodiment, the resin layer 311 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 311 may be 3 μm or higher and 10 μm or lower, or 4 μm or higher and 8 μm or lower.

[0071] The resin layer 311 melts in the event of abnormal heat generation due to overcharge or high temperature conditions, damaging the positive electrode 30 and 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 311 can contribute to improving the safety of the secondary battery 1.

[0072] The metal layer 312 of the positive electrode current collector 31 is in physical and / or electrical contact with the positive electrode active material layer 32 and functions to donate and receive electrons to and from the positive electrode active material layer 32. The metal layer 312 is made of a conductor that does not react with lithium ions in a battery. In one embodiment, the metal layer 312 is made of at least one material selected from the group consisting of aluminum, titanium, stainless steel, nickel, and alloys thereof. In one example, the metal layer 312 is aluminum or an aluminum alloy. In one embodiment, the metal layer 312 is formed by vapor deposition, sputtering, electrolytic plating, or lamination of the above material on both surfaces of the resin layer 311. In one embodiment, the thickness of each conductive layer 322 may be 0.5 μm to 5 μm, 0.7 μm to 3 μm, or 0.8 μm to 2.0 μm.

[0073] The positive electrode active material layer 32 includes a first positive electrode active material layer 32A provided on the surface of the positive electrode current collector 31 facing the first metal layer 312a, and a first positive electrode active material layer 32B provided on the surface of the positive electrode current collector 31 facing the second metal layer 312b. In one embodiment, the positive electrode active material layer 32 may be provided on only one surface of the positive electrode current collector 31. That is, the positive electrode active material layer 32 may be provided on only the surface of the positive electrode current collector 31 facing the first metal layer 312a or the surface of the positive electrode current collector 31 facing the second metal layer 312b. The thickness of the positive electrode active material layer 32 may be adjusted appropriately depending on the desired battery capacity and rate characteristics. In one embodiment, the thickness of each positive electrode active material layer 32 is, for example, 20 μm or more and 150 μm or less.

[0074] The positive electrode active material layer 32 contains a positive electrode active material. The positive electrode active material is a material for holding the carrier metal in the positive electrode active material layer 32, 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 32. In this case, lithium ions are charged into and released from the positive electrode active material as the battery is charged and discharged. This can improve the stability and output voltage of the battery.

[0075] 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 ２ , LiNi ｘ Co ｙ Mn ｚ O(x+y+z=1), LiNi ｘ Co ｙ Al ｚ O(x+y+z=1), LiNi ｘ Mn ｙ O(x+y=1), LiNiO ２ , LiMn ２ O ４ , LiFePO ４ , LiCoPO ４ , LiFeOF, LiNiOF, and LiTiS ２ The positive electrode active material may be at least one selected from the group consisting of: (a) and (b) above. The positive electrode active material may be used singly 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 32 may be 50% by mass or more and 100% by mass or less with respect to the entire positive electrode active material layer 32.

[0076] In one embodiment, the positive electrode active material layer 32 may include one or more components other than the positive electrode active material.

[0077] In one embodiment, the positive electrode active material layer 32 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.

[0078] In one embodiment, the positive electrode active material layer 32 may include a gel electrolyte. The gel electrolyte may improve the adhesive strength between the positive electrode active material layer 32 and the positive electrode current collector 31. 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.

[0079] In one embodiment, the positive electrode active material layer 32 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 to 30% by mass or less with respect to the entire positive electrode 34. In one embodiment, the content of the binder may be 0.5% by mass to 30% by mass or less with respect to the entire positive electrode 34.

[0080] In one embodiment, the positive electrode active material layer 32 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 to 30% by mass or less with respect to the entire positive electrode active material layer 32.

[0081] Fig. 4A is a diagram illustrating the first metal layer 312a. Fig. 4A is a plan view of the positive electrode 30 as viewed from the direction of arrow sd in Figs. 1 and 3 (the side of the first metal layer 312a). Fig. 4B is a diagram illustrating the second metal layer 312b. Fig. 4B is a plan view of the positive electrode 30 as viewed from the direction of arrow bd in Figs. 1 and 3 (the side of the second metal layer 312b).

[0082] 4A, in one embodiment, the first metal layer 312a has a first portion 33 where no positive electrode active material layer is provided. The first portion 33 has one end 33a and the other end 33b in the length direction. The one end 33a forms the boundary with the positive electrode active material layer 32A. The width dimension W of the one end 33a of the first portion 33 ２ａ is the width W of the other end 33b ３ａ In one embodiment, the width dimension W of one end 33a is ２ａ is the width dimension W of the positive electrode active material layer 32A １ａ The positive electrode active material layer 32A may have the same width dimension W １ａmay have

[0083] The first portion 33 is composed of a first region 331 and a second region 332. The first region 331 is a region adjacent to the positive electrode active material layer 32A. The first region 331 is a region including one end 33a of the first portion described above. The first region 331 has one end 33a and the other end 331a in the longitudinal direction. In one embodiment, the other end 331a has the same width dimension W as the one end 33a. ２ａ In one embodiment, the first region 331 may be rectangular.

[0084] The second region 332 is adjacent to the first region 331. The second region 332 is a region including the other end 33b of the first portion described above. The second region 332 has one end 332a and the other end 33b along the longitudinal direction. In one embodiment, the one end 332a has the same width dimension W as the other end 33b. ３ａ (<W ２ａ ) The first end 332a constitutes a portion of the other end 331a of the first region 331. The second region 332 extends in the length direction from a portion of the other end 331a of the first region 331. In one embodiment, the second region 332 may be rectangular. In another embodiment, the second region 332 may have various shapes (e.g., triangular, trapezoidal, etc.) other than a rectangular shape.

[0085] 4B , in one embodiment, the second metal layer 312b has a second portion 34 where no positive electrode active material layer is provided. The second portion 34 has one end 34a and the other end 34b in the length direction. The one end 34a forms the boundary with the positive electrode active material layer 32B. The one end 34a of the second portion 34 has the same width dimension W as the other end 34b. ２ｂ In one embodiment, the width dimension W of the one end 34a ２ｂ is the width dimension W of the positive electrode active material layer 32B １ｂ The positive electrode active material layer 32B has the same width W １ｂ In one embodiment, the second portion 34 may have a rectangular shape. In another embodiment, the second portion 34 may have various shapes other than a rectangular shape (e.g., a triangular shape, a trapezoidal shape, etc.).

[0086] 4A and 4B, in one embodiment, the second region 332 and the second portion 34 may have the same shape. Also, in one embodiment, the second region 332 and the second portion 34 may have different shapes.

[0087] 4A and 4B, in one embodiment, the first portion 33 and the second portion 34 have different width and length dimensions. ２ａ is the width dimension W of one end 34a of the second portion ２ｂ In one embodiment, the width dimension W of the other end 33b of the first portion is larger than ３ａ is the width dimension W of the other end 34b of the second portion ２ｂ In one embodiment, the length dimension T of the first portion is equal to １ａ (the distance from one end 33a to the other end 33b) is the length dimension T of the second portion 34 １ｂ In one embodiment, the width dimension W of the positive electrode active material layer 32A is larger than the distance from one end 34a to the other end 34b. １ａ and the width dimension W of the positive electrode active material layer 32B. １ｂ is the same as

[0088] 5A and 5B are diagrams illustrating examples of the arrangement of the positive electrode and the negative electrode. FIG. 5A shows the positional relationship between the negative electrode 10 and the positive electrode 30 when viewed from the direction of arrows sd in FIGS. 1 and 3 (the surface on the first metal layer 312a side). FIG. 5B shows the positional relationship between the negative electrode 10 and the positive electrode 30 when viewed from the direction of arrows bd in FIGS. 1 and 3 (the surface on the second metal layer 312b side). In FIGS. 5A and 5B, the negative electrode 10 is shown by a dashed line, and the positive electrode 30 is shown by a solid line.

[0089] 5A and 5B, the negative electrode 10 has one end 10a and the other end 10b in the length direction (y direction). When the negative electrode 10 has a negative electrode active material layer 12 (see FIGS. 2A and 2D), the negative electrode active material layer 12 is provided between the one end 10a and the other end 10b. In one embodiment, the negative electrode 10 has a constant width dimension W from the one end 10a to the other end 10b. ｎ The negative electrode end portion 13 extends in the length direction from one end 10a. The width dimension of the negative electrode end portion 13 is width dimension Wｎ Smaller is better.

[0090] 5A , the first region 331 of the first portion 33 completely overlaps with the negative electrode 10 in a plan view. The second region 332 of the first portion 33 partially overlaps with the negative electrode 10 in a plan view and partially does not overlap with the negative electrode 10 in a plan view. In one embodiment, one end 33a of the first portion 33 overlaps with the negative electrode 10 in a plan view, and the other end 33b of the first portion does not overlap with the negative electrode 10 in a plan view. In one embodiment, one end 10a of the negative electrode 10 is disposed between one end 33a of the first portion 33 and the other end 33b of the first portion 33 in a plan view.

[0091] 5B , in one embodiment, the second portion 34 partially overlaps with the negative electrode 10 in a plan view and partially does not overlap with the negative electrode 10. In one embodiment, one end 34a of the second portion 34 overlaps with the negative electrode 10 in a plan view, and the other end 34b does not overlap with the negative electrode 10 in a plan view. In one embodiment, one end 10a of the negative electrode 10 is disposed between one end 34a and the other end 34b of the second portion 34 in a plan view.

[0092] 5A and 5B , the negative electrode 10 is disposed so as to cover the positive electrode active material layers 32A, 32B of the positive electrode 30 in a plan view. If the negative electrode 10 is not disposed at a location facing the positive electrode active material layers 32A, 32B via the separator 20, metallic lithium may be deposited at that location during charging, potentially deteriorating battery performance. In one embodiment, the negative electrode 10 and the positive electrode 30 are disposed so that the distance from one end 10 a of the negative electrode 10 to the positive electrode active material layer 32 in a plan view is equal to or greater than a predetermined distance (hereinafter also referred to as the "minimum separation distance").

[0093] In one embodiment, the distance D1 in a planar view from one end 33a of the first portion 33 to one end 10a of the negative electrode 10 may be 3 mm or less, 0.25 mm or more and 3 mm or less, 0.5 mm or more and 2.75 mm or less, or 0.75 mm or more and 2.5 mm or less.

[0094] In one embodiment, the distance D2 in a plan view from one end 34 a of the second portion 34 to one end 10 a of the negative electrode 10 may be 0.25 mm or more, 0.25 mm or more to 2 mm or less, 0.5 mm or more to 1.75 mm or less, or 0.75 mm or more to 1.5 mm or less. The distance D2 is the minimum separation distance.

[0095] In one embodiment, a distance D1 in a plan view from one end 33 a of the first portion 33 to one end 10 a of the negative electrode 10 is longer than a distance D2 in a plan view from one end 34 a of the second portion 34 to one end 10 a of the negative electrode 10. The difference between the distance D1 and the distance D2 may be 0.25 mm or more and 2.5 mm or less, 0.5 mm or more and 2 mm or less, or 0.75 mm or more and 1.75 mm or less.

[0096] Incidentally, damage to the separator 20 or the like may cause a short circuit between the negative electrode 10 and the positive electrode current collector 31. However, as described above, in the secondary battery 1, the first metal layer 312a and the second metal layer 312b in the positive electrode current collector 31 are configured with the resin layer 311 sandwiched therebetween (see FIG. 3 ). Therefore, even if such a short circuit occurs in the secondary battery 1, the resin layer 311 of the positive electrode current collector 31 does not melt, preventing abnormal heat generation or fire. In one embodiment, an insulating member may be further provided at a location of the exposed metal surface of the positive electrode current collector 31 facing the negative electrode 10. The insulating member can suppress the above-mentioned short circuit due to damage to the separator 20 or the like.

[0097] 6A and 6B are diagrams illustrating other examples of the first portion 33. In one embodiment, the first portion 33 may have a curved outer edge, partially or entirely. For example, as shown in FIG. 6A , the first region 331 and the second region 332 may have a rectangular shape with rounded corners (in this disclosure, "rectangular" may include an embodiment in which a portion of the outer edge, such as the corners, is curved). In another embodiment, the first region 331 and the second region 332 of the first portion 33 may each have a shape other than a rectangular shape. For example, as shown in FIG. 6B , the first region 331 may be rectangular and the second region 332 may be trapezoidal. Alternatively, for example, the first region 331 may be rectangular or trapezoidal, and the second region 332 may be triangular or trapezoidal.

[0098] 7 is a flowchart showing an example of a method for manufacturing the secondary battery 1. This method includes a step ST1 of preparing a positive electrode material, a step ST2 of forming a positive electrode 30, a step ST3 of forming a negative electrode 10, and a step ST4 of sealing the positive electrode 30, the negative electrode 10, the separator 20, and, if necessary, an electrolyte solution in a sealed container.

[0099] 1. Step of Preparing Positive Electrode Material In step ST1, the positive electrode material is prepared. First, the positive electrode current collector 31 is prepared. The positive electrode current collector 31 is configured by sandwiching a resin layer 311 between a first metal layer 312a and a second metal layer 312b.

[0100] The positive electrode current collector 31 may be a commercially available product or may be made from various materials. In one embodiment, when making the positive electrode current collector 31, a metal is deposited on both surfaces of the resin layer 311 by vapor deposition, sputtering, electrolytic plating, or lamination. This results in the positive electrode current collector 31 having the metal layer 312a and the metal layer 312b formed on the resin layer 311.

[0101] Next, a positive electrode active material layer 32 is formed on the positive electrode current collector 31. 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 31. The positive electrode current collector 31 to which the positive electrode active material composition has been applied is press-molded to form positive electrode active material layers 32A and 32B on both surfaces of the positive electrode current collector 31. In this manner, the positive electrode material is formed.

[0102] 2. Step of Forming Positive Electrode Next, in step ST2, the positive electrode material is cut out to form the positive electrode 30.

[0103] The method for cutting out the positive electrode material is not particularly limited, and the material may be cut out using scissors, a cutter, or the like, or may be cut out using a mold prepared in advance.

[0104] 8A to 8C are diagrams illustrating the process of forming the positive electrode of the secondary battery 1. FIG. 8A shows an example of a plan view of one surface of the positive electrode material. FIG. 8B shows an example of a cross-sectional view of the positive electrode material. FIG. 8C shows an example of a plan view of the other surface of the positive electrode material.

[0105] When the positive electrode active material layer 32 is formed on both sides of the positive electrode current collector 31, misalignment of the formed surface in the longitudinal direction may occur due to, for example, the precision of the coating device. In the example shown in Fig. 8B, the positive electrode active material layer 32B on the second metal layer 312b is closer to the positive electrode end portion 35 than the positive electrode active material layer 32A on the first metal layer 312a. ｄｐ In this case, in step ST2, the positive electrode material is cut out along cutout line L1 shown in FIGS. 8A and 8C. Cutout line L1 is set to match the application area of ​​positive electrode active material layer 32B shown in FIG. 8A. As a result, a first portion 33 consisting of first region 331 and second region 332 is formed in first metal layer 312a (FIG. 8C). Furthermore, a second portion 34 is formed in second metal layer 312b.

[0106] 3. Step of Forming Negative Electrode Next, in step ST3, the negative electrode 10 is formed. The negative electrode 10 may have any of the forms shown in FIGS. 2A to 2D. The negative electrode current collector 11 may be a commercially available product or may be made from various materials. When making the negative electrode current collector 11, it may be made in the same manner as the positive electrode current collector 31.

[0107] When the negative electrode 10 has a negative electrode active material layer 12, the negative electrode active material layer 12 is formed on the negative electrode current collector 11 as follows. 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 11. The negative electrode current collector 11 to which the negative electrode active material composition has been applied is press-molded to form the negative electrode active material layers 12 on both surfaces of the negative electrode current collector 11. In this manner, a negative electrode material is formed. The negative electrode 10 is formed by cutting out this negative electrode material. The method for cutting out the negative electrode material is not particularly limited, and the material may be cut out with scissors, a cutter, or the like, or may be cut out using a mold prepared in advance.

[0108] 4. Step of Encapsulating in a Sealed Container Next, a separator 20 is prepared. The separator 20 may be formed by punching out a predetermined shape from the above-described material. One or more sets of the negative electrode 10, separator 20, and positive electrode 30 are then arranged so that the negative electrode 10 formed in step ST3 and the positive electrode 30 formed in step ST2 face each other with the separator 20 interposed therebetween to form a laminate, which is then enclosed in a sealed container. At this time, an electrolyte may be enclosed in the sealed container. The laminate may also be fixed by welding or the like to prevent misalignment of the components within the sealed container.

[0109] In this embodiment, the positive electrode material is cut out along the cutout line L1 for the following reason.

[0110] 9A and 9B are diagrams illustrating other examples of cutting out the positive electrode material. FIGS. 9A and 9B show examples of cutting out the positive electrode material along the cutout line L2 when the coating surface misalignment shown in FIG. 8B occurs. The cutout line L2 is set to match the coating area of ​​the positive electrode active material layer 32A shown in FIG. 9B. As a result, as shown in FIG. 9A, the positive electrode active material layer 32B on the second metal layer 312b after being cut out along the cutout line L2 has a width W ｐ and length T ｑ Rectangular area 32B １ and the same width and length T as the positive electrode end 35B. ｄｐ Rectangular area 32B ２ The positive electrode active material layer 32A on the first metal layer 312a after being cut out along the cutout line L2 has a width W ｐ and length T ｑ Rectangular area 32A １ The length of the positive electrode end 35B of the second metal layer 312b is longer than the length of the positive electrode end 35B of the first metal layer 312a by T ｄｐ Only shorter.

[0111] 10 is a diagram illustrating an example of the effect of employing the cutout line L1. (A) and (B) of FIG. 10 show the positional relationship between the positive electrode 30 and the negative electrode 10 as viewed from one side and the other side, respectively, when a positive electrode 30 cut out along the cutout line L2 is used. (C) and (D) of FIG. 10 show the positional relationship between the positive electrode 30 and the negative electrode 10 as viewed from the side facing the first metal layer 312a and the side facing the second metal layer 312b, respectively, when a positive electrode 30 cut out along the cutout line L1 is used.

[0112] As described above, the negative electrode 10 and the positive electrode 30 are arranged so that the distance from one end 10a of the negative electrode 10 to the positive electrode active material layer 32 (32A, 32B) in a plan view is equal to or greater than the minimum separation distance (in the example shown in FIG. 10, the minimum separation distance is D2). As a result, the total area of ​​the positive electrode active material layers 32A and 32B differs between when the positive electrode 30 is fabricated along the cutout line L2 and when the positive electrode 30 is fabricated along the cutout line L1. Specifically, as shown in FIG. 10, the area (length T ｐ and width W ｐ The product of the area (region 32B) of the positive electrode active material layer 32B (FIG. 10A) defined by the cutout line L2 is １ Area and region 32B ２ The area (sum of the length T ｑ and width W ｐ and the area (length T ｑ and width W ｐ Therefore, cutting out the positive electrode material along cutout line L1 (FIGS. 8A and 8C) can increase the total area of ​​the positive electrode active material layers 32A and 32B compared to cutting out the positive electrode material along cutout line L2 (FIGS. 9A and 9B). This can increase the cell capacity of the secondary battery 1.

[0113] <Method of Using Secondary Battery> The secondary battery 1 is charged and discharged by connecting the positive electrode 30 to one end of an external circuit and the negative electrode 10 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.

[0114] When a voltage is applied between the positive electrode 30 and the negative electrode 10 such that a current flows from the negative electrode 10 to the positive electrode 30 through an external circuit, the secondary battery 1 is charged, and lithium metal is deposited on the surface of the negative electrode 10. When the positive electrode 30 and the negative electrode 10 of the charged secondary battery 1 are connected via a desired external circuit, the secondary battery 1 is discharged, and the lithium metal deposited on the surface of the negative electrode 10 is electrolytically dissolved.

[0115] In one embodiment, a solid electrolyte interface layer (SEI layer) may be formed on the surface of the negative electrode 10 or the surface of the separator 20 (i.e., the interface between the negative electrode 10 and the separator 20) 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.

[0116] The secondary battery 1 described above can have high safety and good cell capacity.

[0117] The present invention will be described in more detail below using examples and comparative examples. The present disclosure is not limited to the following examples and comparative examples. Unless otherwise specified, the following examples were carried out at room temperature (25°C) and 1 atmosphere.

[0118] 1. Fabrication of Lithium Secondary Battery In Example 1, a secondary battery 1 having the structure shown in FIG. 1 was fabricated using the method shown in FIG. 7 . First, a negative electrode 10 was prepared. Specifically, an 8 μm-thick Cu foil was prepared as a negative electrode current collector 11. Next, 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 or one side of the negative electrode current collector 11 in a basis weight of 15 mg / cm . ２The negative electrode current collector 11 on which the negative electrode active material layer 12 was formed was then cut into a shape having a predetermined size (T in FIGS. 10(C) and 10(D)). ｎ ×W ｎ The sheet was cut into pieces (42mm x 42mm).

[0119] Next, as the separator 20, polyvinylidene fluoride (PVDF) and Al ２ O ３ A sheet (thickness in the lamination direction: 15 μm, size in the width direction and length direction: 45 mm×45 mm) whose surface was coated with the mixture of the above was prepared.

[0120] Next, the positive electrode 30 was prepared. Specifically, first, a 6 μm thick film of polyethylene terephthalate (PET) was prepared as the positive electrode current collector 31, with Al deposited to a thickness of 1.0 μm on both sides. Next, LiNi was dissolved in N-methyl-pyrrolidone (NMP) as a solvent. ０．８ Co ０．１５ Al ０．０５ O ２ A mixed material was prepared by mixing 96 parts by mass of the above-mentioned cellulose acetate copolymer, 2 parts by mass of carbon black as a conductive additive, and 2 parts by mass of polyvinylidene fluoride (PVDF) as a binder. ２ This mixed material was applied to both sides of the positive electrode current collector and pressed to form the positive electrode active material layer 32. Thereafter, in the case of the cutout line L1 in FIG. 10 (FIGS. 10C and 10D), ｐ is 40 mm, T ｑ 39mm, W ｐ is 40 mm, T ｄｐ The positive electrode current collector 31 on which the positive electrode active material layer 32 was formed was cut out so that the thickness was 1 mm.

[0121] Next, a stack was formed by arranging the separator 20, the positive electrode 30, and the negative electrode 10 so that the positive electrode 30 and the negative electrode 10 faced each other with the separator 20 interposed therebetween. This stack had ten positive electrodes 30 stacked, and both ends of the stack in the stacking direction were negative electrodes 10. The negative electrodes 10 at both ends had a negative electrode active material layer 12 only on the surface facing the positive electrode 30 with the separator 20 interposed therebetween, and the negative electrodes 10 at the other ends had a negative electrode active material layer 12 on both sides. The positive electrodes 30 and the negative electrodes 10 were arranged so that D1 was 2 mm and D2 was 1 mm, as shown in FIGS. 10(C) and 10(D). This stack was then inserted into a laminate outer casing and sealed together with an electrolyte to obtain a lithium secondary battery. The electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF) in a 1M solution of a solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a ratio of 30:35:35 by mass. ６ The electrolyte used was prepared by dissolving 2 parts by mass of vinylene carbonate (VC) in the electrolyte.

[0122] Secondary batteries 1 of Examples 2 to 4 were fabricated in the same manner as in Example 1, except that the type of positive electrode current collector, the type of negative electrode current collector, and the shape of the positive electrode were changed based on FIGS. 10 and 11 .

[0123] Lithium secondary batteries of Comparative Examples 1 to 5 were fabricated in the same manner as in Example 1, except that the type of positive electrode current collector, the type of negative electrode current collector, and the shape of the positive electrode were changed based on FIGS. 10 and 11 .

[0124] 11, the Cu-deposited resin film is a 6 μm-thick polyethylene terephthalate (PET) film with 1.0 μm of Cu deposited on both sides, and the Al foil is an 8 μm-thick Al foil.

[0125] 2. Evaluation 2.1 Forced Internal Short Circuit Test The lithium secondary batteries of each Example and Comparative Example were CC charged at a current of 0.1 C in an environment at a temperature of 25°C until the voltage reached 4.2 V, and then CC discharged at a current of 0.1 C until the voltage reached 3.0 V. Next, in an environment at a temperature of 25°C, the lithium secondary batteries of each Example and Comparative Example were CC charged at a current of 0.1 C until the voltage reached 4.2 V. CC charging refers to charging at a constant current value, and CC discharging refers to discharging at a constant current value. The 1 C current is the current that can fully charge the battery in one hour, calculated based on the theoretical capacity of the battery. The 2 C current is twice the current of the 1 C current.

[0126] Next, a forced internal short circuit test was performed on the charged lithium secondary batteries of each Example and Comparative Example in accordance with the method of forced internal short circuit test described in JIS C8714:2007, and the evaluation results are shown in Fig. 10. Cases in which no change occurred as a result of the forced internal short circuit test are described as "no change," and cases in which ignition occurred are described as "ignition."

[0127] 2.2. Cell Capacity and Capacity Retention Rate The lithium secondary batteries of each Example and Comparative Example were CC-charged at a current of 0.1 C in an environment at 25°C until the voltage reached 4.2 V, and then CC-discharged at a current of 0.1 C until the voltage reached 3.0 V. Next, in an environment at 25°C and with an external pressure of 50 kPa applied, the lithium secondary batteries of each Example and Comparative Example were CC-charged at a current of 0.3 C until the voltage reached 4.2 V, and then CC-discharged at a current of 0.3 C until the voltage reached 3.0 V (first cycle). This cycle was repeated 100 times. The capacity (Ah) obtained from the 100th cycle was divided by the capacity (Ah) obtained from the first cycle to determine the capacity retention rate (%) at the 100th cycle. The capacity obtained from the first cycle is shown in the "Cell Capacity" column of FIG. 10 , and the capacity retention rate at the 100th cycle is shown in the "Capacity Retention Rate" column.

[0128] 3. Evaluation Results FIG. 10 shows the configurations and results of the Examples and Comparative Examples. It was found that the lithium secondary batteries of the Examples did not ignite, had large cell capacities, and had high capacity retention rates. On the other hand, it was found that the lithium secondary batteries of Comparative Examples 1 to 3 had high capacity retention rates but ignited and had small cell capacities. It was also found that the lithium secondary battery of Comparative Example 4 did not ignite and had large cell capacities but had a low capacity retention rate. It was also found that the lithium secondary battery of Comparative Example 5 had large cell capacity and a high capacity retention rate but ignited. That is, it was found that the lithium secondary batteries of Examples 1 to 4 had good cycle characteristics in addition to high safety and good cell capacities.

[0129] It was found that the lithium secondary batteries of Comparative Examples 1 to 3 had good cycle characteristics, but low safety and relatively small cell capacities. The reason for the low safety is not particularly limited, but is thought to be as follows: It is presumed that abnormal heat generation occurred when the positive electrode and negative electrode were short-circuited because a positive electrode current collector consisting of only a metal layer was used, rather than a positive electrode current collector consisting of a resin layer sandwiched between metal layers. In addition, the reason for the low cell capacity is not particularly limited, but is thought to be the small surface area of ​​the positive electrode active material layer.

[0130] It was found that the lithium secondary battery of Comparative Example 4 had high safety and good cell capacity, but poor cycle characteristics. The reason for this is not particularly limited, but is thought to be as follows: In a plan view of the lithium secondary battery of Comparative Example 4, the distance D2 between the positive electrode active material layer and the negative electrode active material layer on one surface was 0 mm, and it is presumed that a minute short circuit occurred between the positive electrode active material layer and the negative electrode active material layer during cycle evaluation.

[0131] The lithium secondary battery of Comparative Example 5 was found to have a good cell capacity and good cycle characteristics, but low safety. The reason for this is not particularly limited, but is thought to be as follows: It is presumed that abnormal heat generation occurred when a short circuit occurred between the positive electrode current collector and the negative electrode active material layer because a positive electrode current collector consisting of only a metal layer was used, rather than a positive electrode current collector consisting of a resin layer sandwiched between metal layers.

[0132] Embodiments of the present disclosure further include the following aspects.

[0133] (Supplementary Note 1) A lithium secondary battery comprising a positive electrode and a negative electrode facing each other with a separator interposed therebetween, wherein the positive electrode comprises a positive electrode current collector formed by sandwiching a resin layer between a first metal layer and a second metal layer, and a positive electrode active material layer provided on the positive electrode current collector, wherein the first metal layer comprises a first portion where the positive electrode active material layer is not provided, and the second metal layer comprises a second portion where the positive electrode active material layer is not provided, and wherein the first portion and the second portion have different dimensions in both the width direction and the length direction.

[0134] (Supplementary Note 2) The lithium secondary battery according to Supplementary Note 1, wherein the first portion has one end and the other end in the length direction, the one end of the first portion overlaps with the negative electrode in a planar view and the other end of the first portion does not overlap with the negative electrode in a planar view, and the second portion has one end and the other end in the length direction, the one end of the second portion overlaps with the negative electrode in a planar view and the other end of the second portion does not overlap with the negative electrode in a planar view.

[0135] (Supplementary Note 3) The lithium secondary battery according to Supplementary Note 1 or Supplementary Note 2, wherein the one end of the first portion and the one end of the second portion have different width dimensions.

[0136] (Supplementary Note 4) The lithium secondary battery according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the other end of the first portion and the other end of the second portion have the same width dimension.

[0137] (Supplementary Note 5) The lithium secondary battery according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the one end of the first portion has the same width as a portion of the first metal layer where the positive electrode active material layer is provided.

[0138] (Supplementary Note 6) The lithium secondary battery according to any one of Supplementary Note 1 to Supplementary Note 5, wherein the one end of the second portion has a width dimension smaller than that of a portion of the second metal layer where the positive electrode active material layer is provided.

[0139] (Supplementary Note 7) The lithium secondary battery according to any one of Supplementary Note 1 to Supplementary Note 6, wherein the first portion includes a first rectangular region having a first width dimension and a second rectangular region having a second width dimension smaller than the first width dimension.

[0140] (Supplementary Note 8) The lithium secondary battery according to any one of Supplementary Note 1 to Supplementary Note 7, wherein the first width dimension is the same as the width dimension of a portion of the first metal layer where the positive electrode active material layer is provided.

[0141] (Supplementary Note 9) The lithium secondary battery according to any one of Supplementary Notes 1 to 8, wherein the second portion has a rectangular area having the same shape as the second rectangular area.

[0142] (Supplementary Note 10) The lithium secondary battery according to any one of Supplementary Notes 1 to 9, wherein the first portion has one end and the other end in the length direction, the second portion has one end and the other end in the length direction, the negative electrode has one end and the other end in the length direction, and the one end of the negative electrode is disposed between the one end of the first portion and the other end of the first portion in a planar view, and is also disposed between the one end of the second portion and the other end of the second portion in a planar view.

[0143] (Supplementary Note 11) The lithium secondary battery according to any one of Supplementary Notes 1 to 10, wherein a distance from the one end of the first portion to the one end of the negative electrode in a planar view is longer than a distance from the one end of the second portion to the one end of the negative electrode in a planar view.

[0144] (Supplementary Note 12) The lithium secondary battery according to any one of Supplementary Note 1 to Supplementary Note 11, wherein the distance from the one end of the first portion to the one end of the negative electrode in a plan view is 3 mm or less.

[0145] (Supplementary Note 13) The lithium secondary battery according to any one of Supplementary Note 1 to Supplementary Note 12, wherein the distance from the one end of the second portion to the one end of the negative electrode in a plan view is 0.25 mm or more.

[0146] (Supplementary Note 14) A lithium secondary battery comprising a positive electrode and a negative electrode facing each other with a separator interposed therebetween, wherein the positive electrode comprises a positive electrode current collector configured by sandwiching a resin layer between a first metal layer and a second metal layer, and a positive electrode active material layer provided on the positive electrode current collector, wherein the first metal layer comprises a first portion where the positive electrode active material layer is not provided, the first portion comprising a first region and a second region, the first region having one end and the other end in a lengthwise direction and having a first width dimension, and the second region extending in the lengthwise direction from a part of the other end of the first region and having a second width dimension smaller than the first width dimension.

[0147] (Supplementary Note 15) The lithium secondary battery according to Supplementary Note 14, wherein the first region completely overlaps with the negative electrode in a plan view, and the second region partially overlaps with the negative electrode in a plan view but not partially overlaps with the negative electrode.

[0148] (Supplementary Note 16) The lithium secondary battery according to Supplementary Note 14 or Supplementary Note 15, wherein the second metal layer has a second portion where the positive electrode active material layer is not provided, and the second portion has a region having the same shape as the second region.

[0149] (Supplementary Note 17) The lithium secondary battery according to any one of Supplementary Note 1 to Supplementary Note 16, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0150] (Supplementary Note 18) The lithium secondary battery according to any one of Supplementary Note 1 to Supplementary Note 17, wherein the negative electrode includes a negative electrode current collector formed by sandwiching a resin layer between a pair of metal layers.

[0151] (Supplementary Note 19) The lithium secondary battery according to any one of Supplementary Note 1 to Supplementary Note 18, comprising a stack of a plurality of sets of the positive electrode, the separator, and the negative electrode.

[0152] (Supplementary Note 20) A method for manufacturing a lithium secondary battery, comprising: a step of preparing a positive electrode material, the positive electrode material including a positive electrode current collector configured by sandwiching a resin layer between a first metal layer and a second metal layer, and a positive electrode active material layer provided on the positive electrode current collector; and a step of cutting out the positive electrode material to form a positive electrode, the positive electrode having a first portion of the first metal layer where the positive electrode active material layer is not provided, and a second portion of the second metal layer where the positive electrode active material layer is not provided, the first portion and the second portion having different dimensions in both width and length directions.

[0153] The above embodiments are described for the purpose of explanation and are not intended to limit the scope of the present disclosure. Various modifications can be made to the above embodiments without departing from the scope and spirit of the present disclosure. For example, some components in one embodiment can be added to other embodiments. Also, some components in one embodiment can be replaced with corresponding components in other embodiments.

[0154] REFERENCE SIGNS LIST 1...secondary battery, 10...negative electrode, 10a...one end of negative electrode, 10b...other end of negative electrode, 11...negative electrode current collector, 111...negative electrode resin layer, 112...negative electrode metal layer, 12...negative electrode active material layer, 13...negative electrode end, 20...separator, 30...positive electrode, 31...positive electrode current collector, 311...resin layer, 312a...first metal layer, 312b...second metal layer, 32...positive electrode active material layer, 33...first portion, 33a...one end of first portion, 33b...other end of first portion, 331...first region, 332...second region, 34...second portion, 34a...one end of second portion, 34b...other end of second portion, 35...positive electrode end, x...width direction, y...length direction, z...stacking direction, L1...cutout line, L2...cutout line

Claims

1. A lithium secondary battery comprising a positive electrode and a negative electrode facing each other via a separator, wherein the positive electrode includes a positive electrode current collector formed by sandwiching a resin layer between a first metal layer and a second metal layer, and a positive electrode active material layer provided on the positive electrode current collector, the first metal layer includes a first portion where the positive electrode active material layer is not provided, the second metal layer includes a second portion where the positive electrode active material layer is not provided, and the first portion and the second portion have different dimensions in both the width direction and the length direction.

2. The first portion has one end and the other end in the length direction. One end of the first portion overlaps the negative electrode in plan view, and the other end of the first portion does not overlap the negative electrode in plan view. The second portion has one end and the other end in the length direction. One end of the second portion overlaps the negative electrode in plan view, and the other end of the second portion does not overlap the negative electrode in plan view. The lithium secondary battery according to claim 1.

3. The lithium secondary battery according to claim 2, wherein one end of the first portion and one end of the second portion have different width dimensions.

4. The lithium secondary battery according to claim 3, wherein the other end of the first portion and the other end of the second portion have the same width dimension.

5. The lithium secondary battery according to claim 2, wherein one end of the first portion has the same width dimension as a portion of the first metal layer where the positive electrode active material layer is provided.

6. The lithium secondary battery according to claim 5, wherein one end of the second portion has a width dimension smaller than a portion of the second metal layer where the positive electrode active material layer is provided.

7. The first portion includes a first rectangular region having a first width dimension and a second rectangular region having a second width dimension smaller than the first width dimension. The lithium secondary battery according to claim 1.

8. The lithium secondary battery according to claim 7, wherein the first width dimension is the same as the width dimension of a portion of the first metal layer where the positive electrode active material layer is provided.

9. The lithium secondary battery according to claim 7, wherein the second portion includes a rectangular region having the same shape as the second rectangular region.

10. The first portion has one end and the other end in the length direction, the second portion has one end and the other end in the length direction, the negative electrode has one end and the other end in the length direction, and one end of the negative electrode is disposed between one end and the other end of the first portion in a plan view, and is disposed between one end and the other end of the second portion in a plan view. The lithium secondary battery according to claim 1.

11. The lithium secondary battery according to claim 10, wherein a distance in a plan view from one end of the first portion to one end of the negative electrode is longer than a distance in a plan view from one end of the second portion to one end of the negative electrode.

12. The lithium secondary battery according to claim 11, wherein a distance in a plan view from one end of the first portion to one end of the negative electrode is 3 mm or less.

13. The lithium secondary battery according to claim 12, wherein a distance in a plan view from one end of the second portion to one end of the negative electrode is 0.25 mm or more.

14. A lithium secondary battery including a positive electrode and a negative electrode facing each other with a separator therebetween, wherein the positive electrode includes a positive electrode current collector formed by sandwiching a resin layer between a first metal layer and a second metal layer, and a positive electrode active material layer provided on the positive electrode current collector. The first metal layer includes a first portion where the positive electrode active material layer is not provided, the first portion includes a first region and a second region, the first region has one end and the other end in the length direction and has a first width dimension, and the second region extends in the length direction from a part of the other end of the first region and has a second width dimension smaller than the first width dimension.

15. The lithium secondary battery according to claim 14, wherein the first region completely overlaps the negative electrode in a plan view, and the second region partially overlaps and partially does not overlap the negative electrode in a plan view.

16. The lithium secondary battery according to claim 14, wherein the second metal layer includes a second portion where the positive electrode active material layer is not provided, and the second portion includes a region having the same shape as the second region.

17. The lithium secondary battery according to any one of claims 1 to 16, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

18. The lithium secondary battery according to any one of claims 1 to 16, wherein the negative electrode includes a negative electrode current collector formed by sandwiching a resin layer between a pair of metal layers.

19. The lithium secondary battery according to any one of claims 1 to 16, comprising a laminate in which a plurality of sets of the positive electrode, the separator, and the negative electrode are laminated.

20. A method for manufacturing a lithium secondary battery, comprising: a step of preparing a positive electrode material, wherein the positive electrode material includes a positive electrode current collector formed by sandwiching a resin layer between a first metal layer and a second metal layer, and a positive electrode active material layer provided on the positive electrode current collector; and a step of cutting out the positive electrode material to form a positive electrode, wherein the positive electrode includes a first portion where the first metal layer has no positive electrode active material layer provided thereon, a second portion where the second metal layer has no positive electrode active material layer provided thereon, and the dimensions of the first portion and the second portion are different in both the width direction and the length direction.

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