Lithium secondary battery

Abstract

Provided is a way to suppress reductions in the output characteristics and producibility of a lithium secondary battery. The present invention provides a lithium secondary battery. A lithium secondary battery according to the present invention includes (a) a first laminate that comprises a first end part, (b) an intermediate laminate, (c) a second laminate that comprises a second end part, (d) a metal sheet that includes a first portion that overlaps the first end part and the second end part as seen from the layering direction and a second portion that does not overlap the first end part and the second end part as seen from the layering direction, and (e) an electrode tab that is electrically connected to the first laminate and the second laminate. The electrode tab has a first junction mark and a second junction mark. The first junction mark is from the joining of the electrode tab and the first end part, the first portion of the metal sheet, and the second end part. The second junction mark is from the joining of the electrode tab and the second portion of the metal sheet.

Description

[Technical Field]

[0001] Exemplary embodiments of the present disclosure relate to lithium secondary batteries. [Background technology]

[0002] Patent Document 1 discloses that the safety of a battery cell is improved by using a current collector in which metal layers are formed on both sides of a resin film. The front and back of the resin film are separated by an insulating resin layer, preventing electrical continuity. Therefore, when connecting an electrode film to an electrode tab for drawing out wiring, electrical continuity cannot be achieved between the front and back of the electrode, or between multiple electrodes and the electrode tab. In this regard, Patent Document 2 discloses that multiple current collectors are folded and stacked on each metal layer in order to connect each metal layer separated by a resin layer to the electrode tab for drawing out wiring. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-102711 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-016321 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a technique for suppressing a decrease in output characteristics and productivity of lithium secondary batteries. [Means for solving the problem]

[0005] In one exemplary embodiment of the present disclosure, there is provided a lithium secondary battery comprising: (a) a first laminate including a first current collector having a first insulating layer sandwiched between a pair of first conductive layers; and a first electrode disposed on the first current collector, the first current collector having a first end where the first electrode is not disposed; (b) an intermediate laminate including an electrode having a polarity different from that of the first electrode and a separator; and (c) a second laminate disposed in a stacking direction apart from the first laminate via the intermediate laminate, the second current collector having a second insulating layer sandwiched between a pair of second conductive layers; and a second electrode disposed on the second current collector and having the same polarity as the first electrode, the second current collector being disposed on the second current collector. (d) a metal sheet arranged alongside the first end and the second end in the stacking direction, the metal sheet including a first portion overlapping the first end and the second end as viewed from the stacking direction, and a second portion not overlapping the first end and the second end as viewed from the stacking direction; and (e) an electrode tab electrically connected to the first stack and the second stack, the electrode tab having a first bonding mark and a second bonding mark, the first bonding mark being a bonding mark between the electrode tab and the first end, the first portion and the second end of the metal sheet, and the second bonding mark being a bonding mark between the electrode tab and the second portion of the metal sheet. [Effects of the Invention]

[0006] According to one exemplary embodiment of the present disclosure, it is possible to provide a technique for suppressing a decrease in the output characteristics and productivity of a lithium secondary battery. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is an exploded perspective view illustrating an example of the configuration of a secondary battery 1. FIG. [Figure 2A] FIG. 2 is a perspective view showing an example of a negative electrode 10. [Figure 2B] FIG. 2 is a perspective view showing another example of the negative electrode 10. [Figure 3] FIG. 2 is a perspective view showing an example of a positive electrode laminate 30 and a metal sheet MS. [Figure 4A] FIG. 10 is a diagram illustrating an example of a joining mark. [Figure 4B] 10A and 10B are diagrams for explaining other examples of bonding marks. [Figure 4C] 10A and 10B are diagrams for explaining other examples of bonding marks. [Figure 4D] 10A and 10B are diagrams for explaining other examples of bonding marks. [Figure 5] 10 is a diagram for explaining the joining state of the positive electrode tab 40, the end P, and the metal sheet MS. FIG. [Figure 6] FIG. 10 is a diagram for explaining a first bonding mark. [Figure 7] 1 is a flowchart showing an example of the present manufacturing method. [Figure 8A] FIG. 8 is a diagram for explaining step ST1 in FIG. 7. [Figure 8B] FIG. 8 is a diagram for explaining step ST1 in FIG. 7. [Figure 9A] FIG. 8 is a diagram for explaining step ST2 in FIG. 7. [Figure 9B] FIG. 8 is a diagram for explaining step ST2 in FIG. 7. [Figure 9C] FIG. 8 is a diagram for explaining step ST2 in FIG. 7. [Figure 9D] FIG. 8 is a diagram for explaining step ST2 in FIG. 7. [Figure 10] FIG. 8 is a diagram for explaining step ST3 in FIG. 7. [Figure 11] FIG. 2 is a perspective view showing another example of the negative electrode 10. [Figure 12] FIG. 2 is a perspective view showing another example of the negative electrode 10. [Figure 13] FIG. 10 is a cross-sectional view of a main part for explaining another example of the configuration of a lithium secondary battery. [Figure 14] FIG. 10 is a cross-sectional view of a main part for explaining another example of the configuration of a lithium secondary battery. [Figure 15] FIG. 10 is a perspective view illustrating another example of the configuration of the positive electrode laminate. [Figure 16] FIG. 10 is a perspective view illustrating another example of the configuration of the positive electrode laminate. DETAILED DESCRIPTION OF THE INVENTION

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

[0009] In one exemplary embodiment, a lithium secondary battery includes: (a) a first laminate including a first current collector having a first insulating layer sandwiched between a pair of first conductive layers; and a first electrode disposed on the first current collector, the first current collector having a first end where the first electrode is not disposed; (b) an intermediate laminate including an electrode having a polarity different from that of the first electrode and a separator; and (c) a second laminate disposed in a stacking direction apart from the first laminate via the intermediate laminate, the second laminate including a second current collector having a second insulating layer sandwiched between a pair of second conductive layers; and a second electrode disposed on the second current collector and having the same polarity as the first electrode, the second current collector having a first end where the second electrode is not disposed. A lithium secondary battery is provided, comprising: (d) a second laminate having a second end; (e) a metal sheet arranged in parallel with the first end and the second end in the stacking direction, the metal sheet including a first portion overlapping the first end and the second end as viewed from the stacking direction, and a second portion not overlapping the first end and the second end as viewed from the stacking direction; and (f) an electrode tab electrically connected to the first laminate and the second laminate, the electrode tab having a first bonding mark and a second bonding mark, the first bonding mark being a bonding mark between the electrode tab and the first end, the first portion and the second end of the metal sheet, and the second bonding mark being a bonding mark between the electrode tab and the second portion of the metal sheet.

[0010] In one exemplary embodiment, the first bond mark is a weld mark.

[0011] In one exemplary embodiment, the first bonding mark is in the form of one or more lines.

[0012] In one exemplary embodiment, the first bonding marks are in the form of one or more dots.

[0013] In one exemplary embodiment, the first bonding marks include, in a cross section in the stacking direction, a region where the pair of first conductive layers, the metal sheet, and the pair of second conductive layers are integrated.

[0014] In one exemplary embodiment, the second bond mark is a weld mark.

[0015] In one exemplary embodiment, the second bonding marks are in the form of one or more lines.

[0016] In one exemplary embodiment, the second bonding marks are in the form of one or more dots.

[0017] In one exemplary embodiment, the first portion of the metal sheet further has a preliminary joining mark formed by joining to either the first end or the second end.

[0018] In one exemplary embodiment, the first bonding marks are located at different positions from the preliminary bonding marks when viewed in the stacking direction.

[0019] In one exemplary embodiment, a plurality of first stacks and second stacks are arranged alternately in the stacking direction with an intermediate stack sandwiched between them.

[0020] In one exemplary embodiment, the first laminate is formed from a flat sheet, and the second laminate is formed from a flat sheet separate from the first laminate.

[0021] In one exemplary embodiment, the first and second laminates are constructed by folding or rolling a single sheet.

[0022] In one exemplary embodiment, the metal sheet is provided on at least one of the plurality of first ends and the plurality of second ends.

[0023] In one exemplary embodiment, the metal sheet is provided on one side of at least one edge.

[0024] In one exemplary embodiment, the metal sheets are provided one on each side of at least one edge.

[0025] In one exemplary embodiment, the number of metal sheets is no more than three times the total number of first ends and second ends.

[0026] In one exemplary embodiment, the metal sheet is constructed from the same material as the first and second conductive layers.

[0027] In one exemplary embodiment, the first electrode and the second electrode are positive electrodes.

[0028] In one exemplary embodiment, the first electrode and the second electrode are negative electrodes.

[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] As mentioned above, Patent Document 2 proposes folding the current collector multiple times and stacking it on each metal layer to connect each metal layer separated by a resin layer to an electrode tab for wiring. However, this method requires a new device mechanism for stacking the current collector while folding back the end of the current collector for each metal layer. Furthermore, the end of the current collector must be folded back in conjunction with the stacking, significantly reducing productivity. Furthermore, even if this method can mechanically join the electrode tab, the current collector, and each metal layer, the resistance of the joint increases, resulting in reduced output characteristics. A lithium secondary battery 1 (hereinafter also referred to as "secondary battery 1") according to one embodiment can solve these problems.

[0031] <Example of secondary battery configuration> Fig. 1 is an exploded perspective view illustrating an example configuration of a secondary battery 1. As shown in Fig. 1, the secondary battery 1 includes a negative electrode 10, a separator 20, a first positive electrode laminate 30A, a second positive electrode laminate 30B, a metal sheet MS, a positive electrode tab 40, and a negative electrode tab 42. Each component will be described in detail below.

[0032] (Negative electrode 10) 2A is a perspective view showing an example of a negative electrode 10. In one embodiment, the negative electrode 10 includes a negative electrode current collector 12 and a negative electrode active material 14 disposed on the negative electrode current collector 12.

[0033] 2A, the negative electrode active material 14 is disposed on each of both sides of the negative electrode current collector 12. In one embodiment, the negative electrode active material 14 may be disposed on only one side of the negative electrode current collector 12.

[0034] In one embodiment, the negative electrode current collector 12 is 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.

[0035] The negative electrode active material 14 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 14 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.

[0036] 2B is a perspective view showing another example of the negative electrode 10. As shown in FIG. 2B, the negative electrode 10 may be configured to include a negative electrode current collector 16 and a negative electrode active material 14 disposed on each of both sides of the negative electrode current collector 16. The material of the negative electrode active material 14 may be the same as that described in FIG. 2A. The negative electrode current collector 16 may be configured to include a negative electrode insulating layer 160 and a pair of negative electrode conductive layers 162 disposed so as to sandwich the negative electrode insulating layer 160 therebetween.

[0037] In one embodiment, the negative electrode insulating layer 160 may be made of a sheet-like (film-like) or fibrous resin. The negative electrode conductive layer 162 is made of 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 negative electrode conductive layer 162 is made of Cu. By including the negative electrode insulating layer 160, the negative electrode current collector 16 can be made lighter than when the negative electrode current collector 16 is made of only a conductive layer, while still maintaining the thickness (rigidity) required for the negative electrode current collector 16.

[0038] As shown in FIGS. 2A and 2B , the negative electrode current collector (12, 16) has a negative electrode end Q. In one embodiment, the negative electrode end Q is configured as a part of the negative electrode current collector, extending outward (in the x direction) from the side surface of the negative electrode current collector. No negative electrode active material 14 is formed on the negative electrode end Q. A first bonding mark WL1 with the negative electrode tab 42 is formed on the negative electrode end Q.

[0039] (Negative electrode tab 42) 1, the negative electrode tabs 42 are arranged to be aligned in the stacking direction (z direction) with respect to each negative electrode end Q. In one embodiment, the negative electrode tabs 42 may be arranged above or below each negative electrode end Q. In one embodiment, the negative electrode tabs 42 may be arranged between a certain negative electrode end Q and an adjacent negative electrode end Q.

[0040] The negative electrode tab 42 is joined to each negative electrode end Q. The negative electrode end 42 is electrically connected to each negative electrode 10 via each negative electrode end Q. A first joining mark WL1 is formed on the negative electrode tab 42 by joining with each negative electrode end Q. The first joining mark WL1 may be one or more points (spots), or may be a continuous line or surface. In one embodiment, the negative electrode tab 42 and each negative electrode end Q may be joined by welding. In this case, the first joining mark WL1 is a weld mark. The welding may be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding.

[0041] (Separator 20) The separator 20 is disposed on the negative electrode 10. In the example shown in FIG. 1, the separators 20 are disposed on both sides of the negative electrode 10. The separator 20 physically and / or electrically isolates the negative electrode 10 from the positive electrode laminate 30 and ensures 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 material alone or a combination of two or more materials.

[0042] 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.

[0043] 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 styrene butadiene rubber-carboxymethyl cellulose mixture (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.

[0044] 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 allows the negative electrode 10 and the positive electrode laminate 30 to be separated while reducing the volume occupied by the separator 20. 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.

[0045] (Intermediate laminate LM) As shown in FIG. 1, in one embodiment, the negative electrode 10 and the separator 20 constitute an intermediate laminate LM. The intermediate laminate LM may have a structure in which the separator 20, the negative electrode 10, and the separator 20 are stacked in this order in the stacking direction (z direction). The secondary battery 1 includes a plurality of intermediate laminates LM. In one embodiment, the plurality of intermediate laminates LM may each be configured as a single flat sheet, as shown in FIG. 1. In one embodiment, the plurality of intermediate laminates LM may be configured as a single sheet (an example of this embodiment will be described later using FIGS. 13 and 14).

[0046] (Positive electrode laminate 30 and metal sheet MS) As shown in FIG. 1, the first positive electrode laminate 30A includes a current collector 32A and a positive electrode 34A. The first positive electrode laminate 30A is an example of a first laminate. In one embodiment, the first positive electrode laminate may have a structure in which a positive electrode 34A, a current collector 32A, and a positive electrode 34A are stacked in this order in the stacking direction. The current collector 32A has a first end P1 exposed from the positive electrode 34A. In other words, the positive electrode 34A is not formed on the first end P1. The first end P1 extends outward (in the x direction) from the side surface of the current collector 32A as part of the current collector 32A.

[0047] The second positive electrode laminate 30B includes a current collector 32B and a positive electrode 34B. The second positive electrode laminate 30B is an example of a second laminate. In one embodiment, the second positive electrode laminate 30B may have a structure in which a positive electrode 34B, a current collector 32B, and a positive electrode 34B are stacked in this order in the stacking direction. The current collector 32B has a second end P2 exposed from the positive electrode 34B. In other words, the positive electrode 34B is not formed on the second end P2. The second end P2 extends outward (in the x direction) from the side surface of the current collector 32B as part of the current collector 32B.

[0048] The first positive electrode laminate 30A and the second positive electrode laminate 30B are alternately stacked in the stacking direction with intermediate laminates LM interposed therebetween (hereinafter, when there is no need to distinguish between the first positive electrode laminate 30A and the second positive electrode laminate 30B, they are collectively referred to as the "positive electrode laminate 30"). In one embodiment, the multiple positive electrode laminates 30 may each be configured as a single flat sheet, as shown in FIG. 1. In another embodiment, the multiple positive electrode laminates 30 may be configured as a single sheet (an example of this embodiment will be described later with reference to FIGS. 15 and 16).

[0049] In one embodiment, the total number of positive electrode laminates 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 electrode laminates 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 may be 5 Ah or more.

[0050] As shown in FIG. 1, a metal sheet MS is placed on a first end P1 and a second end P2 (hereinafter, when there is no need to distinguish between the two, they will be collectively referred to as "ends P"). In one embodiment, a metal sheet MS may be placed on all of the ends P. In another embodiment, a metal sheet MS may be placed on some of the ends P, and no metal sheet MS may be placed on the remaining ends P. For example, a metal sheet MS may be placed every few ends P.

[0051] In one embodiment, the number and thickness of metal sheets to be placed on an end P may be set based on the position of the end P in the stacking direction. For example, two or more metal sheets MS may be placed on the end P in the center of the stacking direction of the secondary battery 1, and one metal sheet MS may be placed on each of the end Ps at the top and bottom in the stacking direction. Also, for example, the thickness of the metal sheet MS placed on the end P in the center of the stacking direction of the secondary battery 1 may be made larger than the thickness of the metal sheets placed on the end Ps at the top and bottom in the stacking direction. This can suppress variations in resistance between the end Ps at the center.

[0052] In one embodiment, the number of metal sheets MS may be three times or less than the total number of end parts P. In one embodiment, the number of metal sheets MS may be the same as the total number of end parts P, or may be less than the total number of end parts P, for example, half or less of the total number of end parts P.

[0053] 3 is a perspective view showing an example of a positive electrode laminate 30 and a metal sheet MS. In one embodiment, the positive electrode laminate 30 may have a current collector 32 and positive electrodes 34 disposed on both sides of the current collector 32. The current collector 32 has an insulating layer 320 and conductive layers 322 formed so as to sandwich the insulating layer 320.

[0054] The insulating layer 320 of the current collector 32 may be made of, for example, a sheet-like (film-like) or fibrous resin. The resin may be, for example, at least one of polyolefin resins such as polyethylene terephthalate (PET), polyethylene, and polypropylene, and thermoplastic resins such as polystyrene, polyvinyl chloride, and polyamide. The insulating layer 320 may be made by laminating at least one of the resins. In one embodiment, the insulating layer 320 is made of a material having a melting point of 150°C or higher and 300°C or lower. In one embodiment, the thickness of the insulating layer 320 may be 3 μm or higher and 10 μm or lower, or 4 μm or higher and 8 μm or lower.

[0055] The insulating layer 320 can melt in the event of abnormal heat generation due to overcharge or high temperature conditions, damaging the positive electrode laminate 30 and interrupting short-circuit current inside the battery. This can suppress a sudden temperature rise inside the secondary battery 1 and prevent the battery from catching fire. In other words, the insulating layer 320 can contribute to improving the safety of the secondary battery 1.

[0056] The conductive layers 322 of the current collector 32 are formed on both sides of the insulating layer 320 so as to sandwich the insulating layer 320. The conductive layers 322 are in physical and / or electrical contact with the positive electrode 34 and function to donate and receive electrons to and from the positive electrode 34. The conductive layers 322 are made of a conductor that does not react with lithium ions in a battery. In one embodiment, the conductive layers 322 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 conductive layers 322 are aluminum or aluminum alloys. In one embodiment, the conductive layers 322 are formed by vapor deposition, sputtering, electroplating, or laminating the above materials on both surfaces of the insulating layer 320. 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.

[0057] The positive electrodes 34 are formed on both sides of the current collector 32. A known material may be appropriately selected for the positive electrodes 34 depending on the application. The thickness of the positive electrodes 34 may be appropriately adjusted depending on the desired capacity and rate characteristics of the battery. In one embodiment, the thickness of each positive electrode 34 is, for example, 20 μm or more and 150 μm or less.

[0058] In one embodiment, the cathode 34 includes a cathode active material. The cathode active material is a material for holding a carrier metal in the cathode 34 and can also be referred to as a host material for the carrier metal. The cathode active material may be a material for holding lithium ions in the cathode 34, in which case lithium ions are loaded into and deloaded from the cathode active material as the battery is charged and discharged. 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(x+y+z=1), LiNi x Co y Al z O(x+y+z=1), LiNi x Mn y The positive electrode active material may be at least one selected from the group consisting of LiFePO (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 34 may be 50% by mass or more and 100% by mass or less with respect to the entire positive electrode 34.

[0060] In one embodiment, positive electrode 34 may include one or more components other than the positive electrode active material.

[0061] In one embodiment, the positive electrode 34 may include a sacrificial positive electrode material, which 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 34 may include a gel electrolyte. The gel electrolyte may improve adhesion between the positive electrode 34 and the current collector 32. 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 34 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.

[0064] In one embodiment, the positive electrode 34 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 of the total positive electrode 34.

[0065] 3 , the metal sheet MS may be bonded to one surface of the end P of the current collector 32 (one surface of the pair of conductive layers 322). In one embodiment, the metal sheet MS may be bonded to the other surface of the end P of the current collector 32 (the other surface of the pair of conductive layers 322). In one embodiment, one or more metal sheets MS may be provided at the end P. For example, one metal sheet MS may be bonded to one surface and one metal sheet MS to the other surface of the end P of the current collector 32.

[0066] 3, the metal sheet MS includes a first portion MSa and a second portion MSb. The first portion MSa is a portion that overlaps with the end P when viewed from the stacking direction (z direction). The second portion MSb is a portion that does not overlap with the end P when viewed from the stacking direction (z direction). In one embodiment, the second portion MSb is a portion that extends outward (x direction) from the first portion MSa.

[0067] As shown in FIG. 3 , by joining the metal sheet MS and the end P, a preliminary joining mark WP is formed between the first portion MSa of the metal sheet MS and the end P. In one embodiment, the preliminary joining mark WP may be a joining mark formed by welding, i.e., a welding mark. The welding may be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding. In one example, the welding is ultrasonic welding. In one embodiment, the metal sheet MS and the conductive layer 322 of the end P may be partially or completely fused together at the preliminary joining mark WP by heat or the like.

[0068] 3, a first bonding mark WR1 is formed in the first portion MSa and the end P of the metal sheet MS. Furthermore, a second bonding mark WR2 is formed in the second portion MSb of the metal sheet MS. As will be described in detail later, the first bonding mark WR1 is a bonding mark between the end P and the metal sheet MS and the positive electrode tab 40, and the second bonding mark WR2 is a bonding mark between the metal sheet MS and the positive electrode tab 40. The preliminary bonding mark WP, the first bonding mark WR1, and the second bonding mark WR2 are each formed at different positions from each other when viewed from the stacking direction (z direction).

[0069] In one embodiment, as shown in FIG. 3 , the metal sheet MS may be configured to cover only a portion of the end P of the current collector 32, rather than the entire end P. For example, the metal sheet MS may be positioned a predetermined distance away from the positive electrode 34. In this case, an insulating layer may be provided on the conductive layer 322 at the end P in a region where the metal sheet MS is not disposed. In this case, if the separator 20 is damaged, a short circuit between the negative electrode 10 and the positive electrode 34 via the conductive layer 322 at the end P and / or the metal sheet MS is suppressed, thereby improving the safety of the secondary battery 1. The insulating layer may be, for example, a sheet-shaped (film-shaped) 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. Note that in one embodiment, the metal sheet MS may be configured to cover the entire end P of the current collector.

[0070] In one embodiment, the metal sheet MS is composed of at least one material selected from the group consisting of aluminum, titanium, stainless steel, nickel, and alloys thereof. In one example, the metal sheet MS is a hard aluminum foil. In one example, the metal sheet MS is a soft aluminum foil. The soft aluminum foil may be formed by subjecting the hard aluminum foil to a heat treatment at a high temperature (around 400°C). In one embodiment, the metal sheet MS may be composed of the same material as the conductive layer 322.

[0071] In one embodiment, the thickness of the metal sheet MS may be set based on the thickness of the insulating layer 320 and the thickness of the conductive layer 322. For example, when the sum of the total thickness (A) of each metal sheet MS and the total thickness (B) of each conductive layer 322 is X (= A + B), and the total thickness of each insulating layer 320 is Y, the thickness of the metal sheet MS may be set such that the relationship 0.85 < X / Y < 2.3 holds. In one embodiment, 1.0 < X / Y < 2.0 may also be satisfied. In one embodiment, the thickness of the metal sheet MS may be greater than the thickness of the insulating layer 320. In one embodiment, all of the metal sheets MS may have the same thickness, or some of them may have different thicknesses. In one embodiment, the thickness of the metal sheet MS may be 3 μm or more, 5 μm or more, or 7 μm or more. In one embodiment, the thickness of the metal sheet MS may be 15 μm or less, 12 μm or less, or 10 μm or less.

[0072] FIG. 4A is a diagram for explaining an example of a joining mark. FIG. 4A is a plan view of the vicinity of the end portion P of the positive electrode laminate 30 shown in FIG. 3. As shown in FIG. 3, the preliminary joining marks WP may be formed in a plurality of rows (for example, two rows) in a line along the width direction (y direction) of the end portion P. As shown in FIG. 4A, the preliminary joining marks WP are formed at positions different from those of the first joining mark WR1 and the second joining mark WR2 when viewed from the lamination direction. The preliminary joining marks WP, the first joining mark WR1, and the second joining mark WR2 do not overlap each other in a plan view.

[0073] 4B to 4D are diagrams illustrating other examples of bonding marks. In one embodiment, the first bonding marks WR1 may be formed in a line along the width direction (y direction) of the end P, as shown in FIG. 4B. In one embodiment, the first bonding marks WR1 may be in the form of multiple dots, as shown in FIGS. 4C and 4D, and may be formed in a line (FIG. 4C) or multiple lines (FIG. 4D) along the width direction (y direction) of the end P. In all of FIGS. 4B to 4D, the preliminary bonding marks WP are positioned at different positions from the first bonding marks WR1 and the second bonding marks WR2 when viewed from the stacking direction. That is, in all of FIGS. 4B to 4D, the preliminary bonding marks WP, the first bonding marks WR1, and the second bonding marks WR2 do not overlap each other in a plan view.

[0074] (Positive electrode tab 40) As shown in FIG. 1 , the positive electrode tabs 40 are arranged to align with each end P (P1, P2) of the current collectors 32 (32A, 32B) and each metal sheet MS in the stacking direction (z direction). In one embodiment, the positive electrode tabs 40 may be arranged above or below the end P of each current collector 32 and each metal sheet MS. In one embodiment, the positive electrode tabs 40 may be arranged between an end P and an adjacent end P.

[0075] The positive electrode tab 40 is made of a conductive material. For example, the positive electrode tab 40 may be made of aluminum or an aluminum alloy. In one example, the positive electrode tab 40 may be made of hard aluminum. In one embodiment, the thickness of the positive electrode tab 40 may be 0.05 mm or more and 1 mm or less, or 0.1 mm or more and 0.5 mm or less.

[0076] The positive electrode tab 40 is joined to each end P of each current collector 32 and each metal sheet MS. As a result, the positive electrode tab 40 is electrically connected to each positive electrode 34 via each end P. A first bonding mark WR1 and a second bonding mark WR2 are formed on the positive electrode tab 40.

[0077] The first bonding mark WR1 is a bonding mark formed by bonding the positive electrode tab 40 to each end P and the first portion MSa of each metal sheet MS. The first bonding mark WR1 may be one or more points (spots) in plan view, or may be a continuous line or surface. In one embodiment, the first bonding mark WR1 may be a bonding mark formed by welding, i.e., a welding mark. The welding may be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding. In one example, the welding is ultrasonic welding.

[0078] The second bonding mark WR1 is a bonding mark formed by bonding the positive electrode tab 40 to the second portion MSb of each metal sheet MS. The second bonding mark WR2 may be one or more points (spots) in plan view, or may be a continuous line or surface. In one embodiment, the second bonding mark WR2 may be a bonding mark formed by welding, i.e., a welding mark. The welding may be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding. In one example, the welding is ultrasonic welding.

[0079] Fig. 5 is a diagram for explaining the bonding state of the positive electrode tab 40, the end P, and the metal sheet MS. Fig. 5 schematically shows a cross section of the end P taken along the xz plane at a location including the preliminary bonding mark WP, the first bonding mark WR1, and the second bonding mark WR2.

[0080] As shown in FIG. 5, the preliminary bonding mark WP, the first bonding mark WR1, and the second bonding mark WR2 are provided at different positions from each other when viewed from the stacking direction. The preliminary bonding mark WP is formed for each end P. In other words, one preliminary bonding mark WP is not formed across multiple end Ps. In contrast, the first bonding mark WR1 is formed over the positive electrode tab 40, each end P, and the entire first portion MSa of each metal sheet MS. That is, the first bonding mark WR1 is formed continuously in the stacking direction from the positive electrode tab 40 to the end P of the lowest layer. Furthermore, the second bonding mark WR2 is formed over the positive electrode tab 40 and the entire second portion MSb of each metal sheet MS. That is, the second bonding mark WR2 is formed continuously from the positive electrode tab 40 to the second portion MSb of the lowest metal sheet MS.

[0081] As shown in FIG. 5, the second portion MSb of each metal sheet MS extends outward (in the x direction) beyond the first portion MSa of the metal sheet MS joined to the end portion P. The thermal conductivity of the metal sheet MS tends to be higher than that of the end portion P, which includes an insulating layer 320 (e.g., resin, etc.). Therefore, heat from the end portion P (current collector 32) is transferred from the first portion MSa of the metal sheet MS to the second portion MSb located outside it, and can be released from the second portion MSb directly or via the electrode tab 40 to the outside. This allows heat generated inside the secondary battery 1 to be efficiently released to the outside. In other words, the heat dissipation performance of the secondary battery 1 can be improved.

[0082] Furthermore, the second portions MSb of the metal sheets MS are joined to each other at the second bonding marks WR2 without passing through the end portions P (unlike the first portions MSa at the first bonding marks WR1). That is, the bonding region (second bonding marks WR2) between the electrode tab 40 and the second portions MSb does not include the insulating layer 320 and is made of metal only. Therefore, the resistance at the second bonding marks WR2 can be kept low. This can improve the output characteristics of the secondary battery 1.

[0083] 6 is a diagram illustrating the first bonding mark WR1. FIG. 6 schematically shows a cross section of the first bonding mark WR1 taken along the yz plane (cross section AA in FIG. 5). As shown in FIG. 6, the cross section of the first bonding mark WR1 includes a first region R1 and a second region R2. In one embodiment, the cross section of the first bonding mark WR1 may have a recess recessed on one side in the stacking direction.

[0084] In the first region R1, the conductive layer 322 and the metal sheet MS (first portion MSa) are integrally stacked and joined to the positive electrode tab 40. Here, being integrally stacked includes a state in which the conductive layers 322 and the metal sheet MS (first portion MSa) are partially or entirely fused together by heat or the like (a state in which the individual layers are indistinguishable).

[0085] In one embodiment, the first region R1 may be substantially free of the insulating layer 320 along the stacking direction, and provides a physical path for electrical connection between the electrode tab 40 and each conductive layer 322 and the metal sheet MS.

[0086] In one embodiment, the first region R1 may be configured between two second regions R2. In one embodiment, the maximum thickness of the first region R1 may be half or less of the maximum thickness of the second region R2.

[0087] In the second region R2, a pair of conductive layers 322 and the metal sheet MS are stacked, sandwiching the insulating layer 320. That is, the second region R2 is a region that includes the insulating layer 320 along the stacking direction.

[0088] In one embodiment, the first bonding mark WR1 may be formed by welding. In this case, the first bonding mark WR1 is a welding mark. During welding, the positive electrode tab 40, the end P, and the first portion MSa of the metal sheet MS may be pressed along the stacking direction. This softens the insulating layer 320 at the welded location and pushes it outward in the width direction (left and right direction in FIG. 6) from the welded location. Furthermore, at the welded location, each conductive layer 322 and the metal sheet MS are thermally fused and integrated. This can form the first region R1 and the second region R2.

[0089] As described above, the insulating layer 320 can prevent a sudden temperature rise inside the secondary battery 1 and prevent the battery from catching fire in the event of abnormal heat generation due to overcharge or high temperature conditions. In a current collector sandwiching insulating layers between conductive layers, the bonding between the current collector end and the electrode tab and ensuring stable bonding quality (controlling variations) at each layer become more difficult as the number of current collectors increases or the thickness of the insulating layers increases. For example, if a strong pressure is applied to weld all of the electrode tabs to the end, the conductive layer at the end may be damaged or broken if the conductive layer is thin. On the other hand, welding the electrode tab with a force that does not damage the conductive layer may result in an insufficient bond, increasing the resistance between the end of the current collector and the electrode tab.

[0090] In this regard, in the secondary battery 1 according to one embodiment, a metal sheet MS is disposed between at least one end P. The metal sheet MS functions as an additional conductive layer for the conductive layer 322 at the first bonding mark WR1, increasing the ratio of the conductive layer to the insulating layer 320. This can suppress an increase in resistance at the first bonding mark WR1. This can improve the output characteristics of the secondary battery 1. The metal sheet MS can also function as a protective layer for the conductive layer 322 at the end P when bonding the positive electrode tab 40 to the end P. This can suppress damage or breakage of the conductive layer 322 even when the positive electrode tab 40 is bonded to each end P by pressing it with a strong force, especially when the total number (number of stacked positive electrode bodies 30) of the secondary battery 1 is large. This can improve the production yield of the secondary battery 1. In one embodiment, the resistance of the second bonding mark WR2 may be 5.0 mΩ or less, 3.0 mΩ or less, 1.0 mΩ or less, or 0.5 mΩ or less.

[0091] (electrolyte) In one embodiment, the secondary battery 1 may contain an electrolytic solution. The electrolytic solution is a liquid containing a solvent and an electrolyte and has ion conductivity. The electrolytic solution 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 electrolytic solution, the internal resistance can be reduced, and the energy density, capacity, and cycle characteristics can be improved.

[0092] The electrolytic solution may be, for example, a solution that fills the housing (pouch) of 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.

[0093] 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(OCOCF), LiB(OCOH), LiB(OCOCF), LiNO, and LiSO.

[0094] As the solvent contained in the electrolytic solution, for example, a non-aqueous solvent containing fluorine atoms (hereinafter referred to as a "fluorinated solvent") and a non-aqueous solvent containing no fluorine atoms (hereinafter referred to as a "non-fluorinated solvent") may be added.

[0095] The fluorinated solvent may be, for example, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0096] The fluorine-free solvent may be, for example, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,2-dimethoxyethane, dimethoxyethane, dimethoxypropane, dimethoxybutane, diethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, chloroethylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, trimethyl phosphate, triethyl phosphate, and 12-crown-4.

[0097] The above fluorinated solvents and / or non-fluorinated solvents may be used alone or in any combination of two or more in any ratio. The contents of the fluorinated solvent and non-fluorinated solvent are not particularly limited, and the ratio of the fluorinated solvent to the total solvent may be 0 to 100% by volume, or the ratio of the non-fluorinated solvent to the total solvent may be 0 to 100% by volume.

[0098] <Secondary battery manufacturing method> Next, an example of a method for manufacturing the secondary battery 1 (hereinafter also referred to as "this manufacturing method") will be described with reference to Figs. 7 to 10. Fig. 7 is a flowchart showing an example of this manufacturing method. Figs. 8A and 8B are diagrams for explaining step ST1 in Fig. 7. Figs. 9A to 9D are diagrams for explaining step ST2 in Fig. 7. Fig. 10 is a diagram for explaining step ST3 in Fig. 7.

[0099] As shown in FIG. 7 , this manufacturing method includes step ST1 of preparing a positive electrode laminate sheet, step ST2 of joining metal sheets of the positive electrode laminate sheet, step ST3 of cutting out a positive electrode laminate from the positive electrode laminate sheet, step ST4 of assembling a compact, step ST5 of joining electrode tabs and current collectors, and step ST6 of sealing the compact in an airtight container.

[0100] First, in step ST1, a positive electrode laminate sheet S1 is prepared as shown in FIGS. 8A and 8B. FIG. 8A is a plan view of the positive electrode laminate sheet S1. FIG. 8B is a cross-sectional view taken along the line BB of FIG. 8A. As shown in FIG. 8A, the positive electrode laminate sheet S1 may be a strip-shaped sheet having a longitudinal direction (y direction) and a transverse direction (x direction). In one embodiment, as shown in FIGS. 8A and 8B, the positive electrode laminate sheet S1 may be composed of a current collector 32 and a positive electrode 34 applied to both sides of the current collector 32. The current collector 32 may have an insulating layer 320 and conductive layers 322 formed so as to sandwich the insulating layer 320. One end of the positive electrode laminate sheet in the transverse direction (x direction) is not formed with a positive electrode 34, and the conductive layer 322 of the current collector 32 is exposed.

[0101] Next, in step ST2, a metal sheet MS is joined to one short-side end of the positive electrode laminate sheet S1, as shown in Figures 9A to 9D. Figure 9A is a plan view of the positive electrode laminate sheet S1 joined to the metal sheet MS. Figures 9B to 9D are examples of a CC cross section of Figure 9A.

[0102] In step ST2, the metal sheet MS is joined to the positive electrode laminate sheet S1 so as to have a portion (first portion MSa) overlapping one short-side end of the positive electrode laminate sheet S1 and a portion (second portion MSb) extending in the short-side direction from the short-side end (see FIGS. 9B to 9D). The joining in step ST2 then forms preliminary joining marks WP in the longitudinal direction, for example, in the shape of a line (see FIG. 9A). In step ST2, the metal sheet MS may be joined to the positive electrode laminate sheet S1 by welding. The welding may be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding. One example of the welding is ultrasonic welding.

[0103] In one embodiment, the joining in step ST2 may be performed by pressing the metal sheet MS against the current collector 32. For example, as shown in FIGS. 9B and 9C , the preliminary joining mark WP may be formed so that the first portion MSa of the metal sheet MS is recessed toward the current collector 32. In one embodiment, the preliminary joining mark WP may be provided between the metal sheet MS and one conductive layer 322 (with which the metal sheet MS is in contact) as shown in FIG. 9B. In this case, the metal sheet MS is not electrically connected to the other conductive layer 322 at the preliminary joining mark WP. In one embodiment, the preliminary joining mark WP may be provided between the metal sheet MS and both conductive layers 322 as shown in FIG. 9C. In this case, the metal sheet MS is electrically connected to both conductive layers 322 at the preliminary joining mark WP.

[0104] In one embodiment, the bonding in step ST2 may be performed by pressing the current collector 32 against the metal sheet MS. For example, as shown in Fig. 9D, the preliminary bonding mark WP may be formed so that the current collector 32 is recessed toward the first portion MSa of the metal sheet MS. In this case, the metal sheet MS is electrically connected to both conductive layers 322 at the preliminary bonding mark WP.

[0105] Next, in step ST3, the positive electrode laminate 30 is cut out. Specifically, using a cutting blade, a laser, or the like, multiple positive electrode laminates 30 having a given shape are cut out from the positive electrode laminate sheet S1 in a state in which the metal sheet MS is joined to the positive electrode laminate sheet S1, as shown in Fig. 10. In this way, multiple positive electrode laminates 30 are obtained.

[0106] Next, in step ST4, a molded body is assembled in which positive electrode laminates 30 and intermediate laminates LM are alternately stacked. Specifically, the multiple positive electrode laminates 30 prepared in step ST3 are arranged so as to be spaced apart from one another in the stacking direction, with intermediate laminates LM interposed therebetween, as shown in Fig. 1. Note that, as will be described later, when the negative electrode 10 and separator 20 are configured in a sheet-like form, the positive electrode laminates 30 may be arranged between separators 20 formed by folding the sheet in a zigzag shape (see Fig. 9) or between separators 20 formed by rolling the sheet (see Fig. 10).

[0107] Next, in step ST5, the electrode tabs and the current collectors are joined. Specifically, the end P of each current collector 32 and the metal sheet MS are joined to the electrode tab 40 so as to form the second joining mark WR2 described above. Also, the negative electrode end Q is joined to the negative electrode tab 42 so as to form the second joining mark WL2. The joining may be performed by ultrasonic welding, laser welding, resistance welding, or spot welding.

[0108] Next, in step ST6, the molded body prepared in step ST5 is sealed in a sealed container. In one embodiment, an electrolyte may be sealed in the sealed container. The sealed container may be, for example, a laminate film. In this way, the secondary battery 1 is manufactured.

[0109] In this manufacturing method, in step ST2, a metal sheet MS is bonded to a positive electrode laminate sheet MS in advance. Therefore, in step ST3, the metal sheet MS can be simultaneously cut out to match the shape of the end P of the positive electrode laminate sheet S1. That is, a separate step of cutting out the metal sheet MS to match the shape of the end P is not required. Furthermore, in step ST5, it is not necessary to align the metal sheet MS with the end P of the current collector 32, facilitating bonding of the positive electrode tab 40 to the end P. Furthermore, in principle, in step ST5, the first bonding mark WR1 can be provided so as not to overlap with the preliminary bonding mark WP in the stacking direction. By providing the first bonding mark WR1 so as not to overlap with the preliminary bonding mark WP in the stacking direction, the bonding state of the first bonding mark WR1 is improved compared to when the two are provided overlapping, and an increase in the resistance of the first bonding mark WR1 can be suppressed.

[0110] <How to use secondary batteries> The secondary battery 1 is charged and discharged by connecting the positive electrode tab 40 to one end of an external circuit and the negative electrode tab 42 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. The ends P of the multiple positive electrode laminates 30 may be connected to the external circuit at the same potential. The negative electrode ends Q of the multiple negative electrodes 10 may be connected to the external circuit at the same potential.

[0111] When a voltage is applied between the positive electrode tab 40 and the negative electrode tab 42 such that a current flows from the negative electrode tab 42 to the positive electrode tab 40 through an external circuit, the secondary battery 1 is charged and lithium metal is deposited on the negative electrode 10. When the positive electrode tab 40 and the negative electrode tab 42 of the charged secondary battery 1 are connected via a desired external circuit, the secondary battery 1 is discharged and the lithium metal in the negative electrode 10 is electrolytically dissolved.

[0112] 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 the secondary battery 1 is assembled. 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 deposited or dissolved at the interface between the negative electrode 10 and / or the separator 20 and the SEI layer during charge and discharge.

[0113] According to the secondary battery 1 described above, the output characteristics and productivity of the battery can be improved.

[0114] <Modification> The secondary battery 1 can be modified in various ways without departing from the scope and spirit of the present disclosure.

[0115] (Negative electrode 10) FIG. 11 is a perspective view showing another example of the negative electrode 10. In one embodiment, a metal sheet may be provided at the negative electrode end Q of the negative electrode 10. The example shown in FIG. 11 is an example in which a negative electrode metal sheet MS2 is provided on one surface of the negative electrode end Q of the negative electrode 10 shown in FIG. 2B. In one embodiment, the negative electrode metal sheet MS2 may be made of the same material as the negative electrode conductive layer 162. In one example, the negative electrode metal sheet MS2 is made of Cu.

[0116] 11 , a preliminary bonding mark WP may be formed between the negative electrode metal sheet MS2 and the negative electrode end Q by joining the negative electrode metal sheet MS2 and the negative electrode end Q. Furthermore, a first bonding mark WL1 may be formed by joining the negative electrode end Q and the negative electrode metal sheet MS2 to the negative electrode tab 42. A second bonding mark WL2 may be formed by joining the negative electrode metal sheet MS2 to the negative electrode tab 42. The bonding form and positional relationship of the preliminary bonding mark WP, first bonding mark WL1, and second bonding mark WL2 at the negative electrode end Q may be similar to those of the preliminary bonding mark WP, first bonding mark WR1, and second bonding mark WR2 at the end P described above, and therefore will not be described again.

[0117] FIG. 12 is a perspective view showing another example of the negative electrode 10. In one embodiment, the negative electrode 10 may be substantially free of a negative electrode active material. In the example shown in FIG. 12, the negative electrode 10 is made of at least one material 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. The negative electrode 10 also functions as a current collector.

[0118] Note that the negative electrode 10 being "substantially free of negative electrode active material" includes, for example, that the thickness of the layer of negative electrode active material deposited on the negative electrode 10 at the end of discharge (e.g., a state in which the open circuit voltage of the battery is 2.5 V or more and 3.6 V or less) is 25 μm or less. In one embodiment, the thickness of the layer of negative electrode active material 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 may even be 0 μm. When the negative electrode 10 is substantially free of negative electrode active material, the energy density per volume can be improved in addition to the energy density per weight. Note that 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."

[0119] In one embodiment, the negative electrode 10 does not have a negative electrode active material before the initial charge of the battery (the state from the time the battery is assembled until 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 then electrolytically dissolving the deposited lithium metal. In this case, the volume and mass occupied by the negative electrode active material are reduced, reducing the volume and mass of the entire battery and, in principle, increasing the energy density. Note that "lithium metal deposited on the negative electrode" refers not only to lithium metal being deposited on the surface of the negative electrode, but also to lithium metal being deposited on the surface of a solid electrolyte interface (SEI) layer or on or within a buffer functional layer, which will be described later.

[0120] In one embodiment, 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. In one embodiment, the ratio M 3.0 / M 4.2 may be 1.0% or more, 2.0% or more, 3.0% or more, or 4.0% or more.

[0121] In one embodiment, the thickness of the negative electrode 10 may be 1.0 μm or more and 30 μm or less, which can reduce the volume occupied by the negative electrode 10 in the secondary battery 1 and improve 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.

[0122] In one embodiment, the negative electrode 10 may be coated on at least a portion of the surface facing the positive electrode laminate 30 with a compound (hereinafter also referred to as "negative electrode coating agent") containing an aromatic ring to which two or more elements selected from the group consisting of N, S, and O are independently bonded. The negative electrode coating agent can be held on the negative electrode 10 by the above elements being coordinately bonded to metal atoms constituting the negative electrode 10. According to this embodiment, a non-uniform deposition reaction of lithium metal on the surface of the negative electrode 10 can be suppressed, and the lithium metal deposited on the negative electrode 10 can be suppressed from growing in a dendritic form.

[0123] In one embodiment, the negative electrode coating agent is applied to at least a portion of the surface of the negative electrode 10. In one embodiment, the negative electrode coating agent may be applied to 10% or more of the surface area, or may be applied to 20% or more, 40% or more, 60% or more, or 80% or more of the surface area.

[0124] In one embodiment, the aromatic ring contained in the negative electrode coating agent may be an aromatic hydrocarbon such as benzene, naphthalene, azulene, anthracene, and pyrene, or a heteroaromatic compound such as furan, thiophene, pyrrole, imidazole, pyrazole, pyridine, pyridazine, pyrimidine, and pyrazine. In one example, the aromatic ring is an aromatic hydrocarbon. In one example, the aromatic ring is benzene or naphthalene. In one example, the aromatic ring is benzene.

[0125] In one embodiment, the negative electrode coating agent may be configured with one or more nitrogen atoms bonded to an aromatic ring. In one embodiment, the negative electrode coating agent may be a compound having a structure in which a nitrogen atom is bonded to an aromatic ring and, in addition to the nitrogen atom, one or more elements selected from the group consisting of N, S, and O are each independently bonded. Using a compound in which a nitrogen atom is bonded to an aromatic ring as the negative electrode coating agent can improve the cycle characteristics of the battery.

[0126] The negative electrode coating agent may be, for example, at least one selected from the group consisting of benzotriazole, benzimidazole, benzimidazole thiol, benzoxazole, benzoxazole thiol, benzothiazole, and mercaptobenzothiazole, and derivatives thereof. In one example, the negative electrode coating agent is at least one selected from the group consisting of benzotriazole, benzimidazole, benzoxazole, and mercaptobenzothiazole, and derivatives thereof.

[0127] (buffer layer) In one embodiment, a porous or fibrous buffer functional layer may be provided between the negative electrode 10 and the separator 20. The buffer functional layer has a solid portion (including a gel portion) that has ionic conductivity and electrical conductivity, and a pore portion formed by gaps between the solid portion. In this case, lithium metal may precipitate 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).

[0128] (Intermediate laminate) 13 and 14 are cross-sectional views of a main part for explaining other structural examples of a lithium secondary battery. In one embodiment, the negative electrode 10 and the separators 20 arranged on both sides of the negative electrode 10 may be configured as a single sheet SH.

[0129] In one embodiment, as shown in FIG. 13, a sheet SH may be folded multiple times at acute angles to form an intermediate laminate, and each positive electrode laminate 30 (30A, 30B) may be disposed between opposing separators 20 of the intermediate laminate.

[0130] In one embodiment, as shown in Fig. 14, a sheet SH may be wound multiple times to form an intermediate laminate, and each positive electrode laminate 30 (30A, 30B) may be disposed between opposing separators 20 of the intermediate laminate. Note that in the example shown in Fig. 14, each positive electrode laminate 30 may also be formed by winding a single sheet, as described below (see Fig. 15).

[0131] 13 and 14, even if the negative electrode 10 and separator 20 are very thin, they can be handled as a single sheet SH, which can improve the productivity of the battery. Furthermore, in the sheet SH, physical pressure is applied from both sides to the negative electrode 10 sandwiched between the separators 20, so wrinkles are less likely to occur in the negative electrode 10 when the sheets SH are stacked, which can improve the cycle characteristics of the battery.

[0132] (Positive electrode laminate) 15 and 16 are perspective views illustrating other configuration examples of the positive electrode laminate. In one embodiment, each positive electrode laminate 30 may be formed by winding a single sheet SH2 multiple times, as shown in FIG. 15. In one embodiment, each positive electrode laminate 30 may be formed by alternately folding a single sheet SH2 multiple times at acute angles, as shown in FIG. 16. The sheet SH2 may include, for example, a current collector 32 and positive electrodes 34 disposed on both sides of the current collector 32. In the examples shown in FIGS. 15 and 16, even if the current collector 32 and the positive electrodes 34 are very thin, they can be handled as a single sheet SH2, which can improve battery productivity.

[0133] <Example> Next, examples and comparative examples will be described. The present disclosure is not limited in any way by the following examples and comparative examples.

[0134] Fig. 17 shows the configurations and results of the examples and comparative examples. Fig. 18 shows the lamination patterns of the metal sheets in the examples and comparative examples. "Pattern 1" to "Pattern 4" in Fig. 18 correspond to "Pattern 1" to "Pattern 4" shown in "Lamination Pattern" in Fig. 17.

[0135] Example 1 As Example 1, a lithium secondary battery having the structure shown in FIG. 1 was fabricated. First, a negative electrode 10 having the structure shown in FIG. 2B was prepared. A 6 μm-thick polyethylene terephthalate (PET) was used as the negative electrode insulating layer 160 of the negative electrode current collector 16, and 1.0 μm of Cu was vapor-deposited as the negative electrode conductive layer 162. The negative electrode active material 14 was a mixture of 97 parts by mass of graphite, 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, mixed with water as a solvent. As a result, 21 negative electrodes 10 were prepared. Then, 21 metal sheets MS2 (4 μm-thick copper foil) for the negative electrode were prepared and attached to the negative electrode end Q of each negative electrode 10 by ultrasonic welding, resulting in the structure shown in FIG. 11. Next, a sheet (thickness: 15 μm) whose surface was coated with a mixture of polyvinylidene fluoride (PVDF) and Al2O3 was prepared as the separator 20. Then, both sides of the negative electrode 10 were sandwiched between the separators 20 and pressed together to obtain an intermediate laminate LM.

[0136] The current collector 32 of the positive electrode laminate 30 was a 6 μm-thick polyethylene terephthalate (PET) film with an insulating layer 320 and 1.0 μm of Al (conductive layer 322) deposited on both sides. The positive electrode 34 was made of N-methyl-pyrrolidone (NMP) as a solvent and LiNi as a positive electrode active material. 0.8 Co 0.15 Al 0.05 A mixture of 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 was used. This positive electrode 34 was applied to both sides of the current collector 32 with a basis weight of 23 mg / cm. 2 The positive electrode laminate 30 was obtained by applying the paste to the positive electrode laminate 30. Twenty positive electrode laminates 30 were prepared. Twenty metal sheets MS (12 μm hard aluminum) were also prepared and attached to the end P of the current collector 32 of each positive electrode laminate 30 by ultrasonic welding.

[0137] Next, intermediate laminates LM and positive electrode laminates 30 were alternately stacked. Then, each end P of the current collector 32 was overlapped with a metal sheet MS and joined to a positive electrode tab 40 by ultrasonic welding. The positive electrode tab 40 was made of 0.2 mm thick hard aluminum. The negative electrode end Q was overlapped with a negative metal sheet MS2 and joined to a negative electrode tab 42 by ultrasonic welding. The negative electrode tab 42 was made of 0.2 mm thick nickel-plated copper. This structure was inserted into a laminate outer casing and sealed together with an electrolyte to obtain a lithium secondary battery. The electrolyte used was a 1 M electrolyte solution prepared by dissolving lithium hexafluorophosphate (LiPF6) in a solvent containing a 30:35:35 mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a ratio of 30:35:35 by mass, to which 2 parts by weight of vinylene carbonate (VC) was added.

[0138] (Comparative Example 1) In Comparative Example 1, a lithium secondary battery was produced in the same manner as in Example 1, except that the metal sheet MS and the metal sheet MS2 for the negative electrode were not used.

[0139] In Comparative Example 2, metal sheets having only the first portion MSa (i.e., no second portion MSb extending outward from the first portion MSa) were used at the end P and the negative electrode end Q. In addition, metal sheets were provided at every other end (i.e., one for every two end Ps and one for every two negative electrode end Qs) (i.e., the total number of metal sheets was half that of Example 1). In other respects, a lithium secondary battery was fabricated in the same manner as in Example 1.

[0140] For each of Example 1, Comparative Example 1, and Comparative Example 2, the resistance between the positive electrode tab 40 and the positive electrode laminate 30 (hereinafter referred to as "positive electrode resistance") was measured. Specifically, the lithium secondary batteries according to the Examples and Comparative Examples were disassembled and measured using a four-terminal method. The positive electrode of a clip-type lead of a resistance meter BT3561 manufactured by HIOKI Corporation was connected to the positive electrode tab 40, and the negative electrode of one of the 20 positive electrode laminates 30 was clipped with a clip at a location on the positive electrode laminate where the positive electrode active material was not applied, and the impedance at 1 kHz was measured using the four-terminal lead. Next, the negative electrode was connected to another positive electrode laminate and measurements were repeated, and the average value of the 20 measurements was calculated. Similarly, the resistance between the negative electrode tab 42 and the negative electrode 10 (hereinafter referred to as "negative electrode resistance") was measured.

[0141] The positive electrode resistance and negative electrode resistance of Example 1 were 0.48 mΩ and 0.62 mΩ, respectively. In contrast, the positive electrode resistance and negative electrode resistance of Comparative Example 1 were 22.3 mΩ and 19.4 mΩ, respectively. The positive electrode resistance and negative electrode resistance of Comparative Example 2 were 0.92 mΩ and 0.88 mΩ, respectively. The positive electrode resistance and negative electrode resistance of Example 1 were lower than those of Comparative Example 2 and significantly lower than those of Comparative Example 1.

[0142] Furthermore, when a nail penetration test was performed on the lithium secondary batteries according to Example 1, Comparative Example 1, and Comparative Example 2, no fire or explosion occurred in any of them. Here, the nail penetration test is a test in which a nail is penetrated into each battery to simulate an internal short circuit and check whether the battery will fire or explode.

[0143] Embodiments of the present disclosure further include the following aspects.

[0144] (Appendix 1) A lithium secondary battery, (a) a first laminate including a first current collector having a first insulating layer sandwiched between a pair of first conductive layers, and a first electrode disposed on the first current collector, the first current collector having a first end portion where the first electrode is not disposed; (b) an intermediate laminate including an electrode having a polarity different from that of the first electrode and a separator; (c) a second laminate disposed apart from the first laminate in the stacking direction via the intermediate laminate, the second laminate including a second current collector configured by sandwiching a second insulating layer between a pair of second conductive layers, and a second electrode disposed on the second current collector and having the same polarity as the first electrode, the second current collector having a second end portion where the second electrode is not disposed; (d) a metal sheet arranged in the stacking direction alongside the first end and the second end, the metal sheet including a first portion that overlaps with the first end and the second end as viewed from the stacking direction, and a second portion that does not overlap with the first end and the second end as viewed from the stacking direction; (e) an electrode tab electrically connected to the first laminate and the second laminate, the electrode tab having a first bonding mark and a second bonding mark, the first bonding mark being a bonding mark between the electrode tab and the first end, the first portion and the second end of the metal sheet, and the second bonding mark being a bonding mark between the electrode tab and the second portion of the metal sheet; Lithium secondary battery.

[0145] (Appendix 2) 2. The lithium secondary battery according to claim 1, wherein the first joining mark is a welding mark.

[0146] (Appendix 3) 3. The lithium secondary battery according to claim 1, wherein the first bonding mark is in the form of one or more lines.

[0147] (Appendix 4) 3. The lithium secondary battery according to claim 1, wherein the first bonding marks are in the form of one or more dots.

[0148] (Appendix 5) 5. The lithium secondary battery according to claim 1, wherein the first bonding marks include, in a cross section in the stacking direction, an area where the pair of first conductive layers, the metal sheet, and the pair of second conductive layers are integrated.

[0149] (Appendix 6) 6. The lithium secondary battery according to claim 1, wherein the second joining marks are welding marks.

[0150] (Appendix 7) 7. The lithium secondary battery according to claim 1, wherein the second bonding mark is in the form of one or more lines.

[0151] (Appendix 8) 7. The lithium secondary battery according to claim 1, wherein the second bonding marks are in the form of one or more dots.

[0152] (Appendix 9) 9. The lithium secondary battery according to claim 1, wherein the first portion of the metal sheet further has a preliminary joining mark formed by joining the first end portion and the second end portion.

[0153] (Appendix 10) 10. The lithium secondary battery according to claim 9, wherein the first bonding marks are located at positions different from the preliminary bonding marks when viewed from the stacking direction.

[0154] (Appendix 11) 11. The lithium secondary battery according to claim 1, wherein a plurality of the first stacks and the second stacks are alternately arranged in the stacking direction with the intermediate stack sandwiched between them.

[0155] (Appendix 12) 12. The lithium secondary battery according to claim 11, wherein the first laminate is formed of a flat sheet, and the second laminate is formed of a flat sheet separate from the first laminate.

[0156] (Appendix 13) 12. The lithium secondary battery according to claim 11, wherein the first laminate and the second laminate are formed by folding or rolling a single sheet.

[0157] (Appendix 14) 14. The lithium secondary battery according to claim 11, wherein the metal sheet is provided on at least one of the first ends and the second ends.

[0158] (Appendix 15) 15. The lithium secondary battery according to claim 14, wherein the metal sheet is provided on one side of the at least one end.

[0159] (Appendix 16) 15. The lithium secondary battery according to claim 14, wherein the metal sheets are provided one on each side of the at least one end.

[0160] (Appendix 17) 17. The lithium secondary battery according to any one of claims 11 to 16, wherein the number of the metal sheets is three times or less the total number of the first end portions and the second end portions.

[0161] (Appendix 18) 18. The lithium secondary battery according to any one of claims 1 to 17, wherein the metal sheet is made of the same material as the first conductive layer and the second conductive layer.

[0162] (Appendix 19) 19. The lithium secondary battery according to any one of claims 1 to 18, wherein the first electrode and the second electrode are positive electrodes.

[0163] (Appendix 20) 19. The lithium secondary battery according to any one of claims 1 to 18, wherein the first electrode and the second electrode are negative electrodes. [Explanation of symbols]

[0164] 1...Lithium secondary battery, 10...Anode, 20...Separator, 30...Positive electrode laminate, 32...Current collector, 320...Insulating layer, 322...Conductive layer, 34...Positive electrode, 40...Positive electrode tab, 42...Anode electrode tab, MS...Metal sheet, MSa...First part, MSb...Second part, LM...Intermediate laminate, WR1...First bonding mark, WR2...Second bonding mark, WP...Preliminary bonding mark

Claims

1. A lithium secondary battery, (a) a first laminate including: a first current collector having a first insulating layer sandwiched between a pair of first conductive layers; and a first electrode disposed on the first current collector, the first current collector having a first end portion where the first electrode is not disposed; (b) an intermediate laminate including an electrode having a polarity different from that of the first electrode and a separator; (c) a second laminate disposed in a stacking direction away from the first laminate via the intermediate laminate, the second laminate including a second current collector configured by sandwiching a second insulating layer between a pair of second conductive layers, and a second electrode disposed on the second current collector and having the same polarity as the first electrode, the second current collector having a second end portion where the second electrode is not disposed; (d) a metal sheet arranged in the stacking direction alongside the first end and the second end, the metal sheet including a first portion overlapping the first end and the second end as viewed from the stacking direction, and a second portion not overlapping the first end and the second end as viewed from the stacking direction; A metal sheet; (e) an electrode tab electrically connected to the first laminate and the second laminate, the electrode tab having a first joining mark and a second joining mark, the first joining mark being a joining mark between the electrode tab and the first end, the first portion of the metal sheet, and the second end, and the second joining mark being a joining mark between the electrode tab and the second portion of the metal sheet; The first portion of the metal sheet further has a preliminary joining mark formed by joining to either the first end portion or the second end portion, a lithium secondary battery in which the first joining marks are located at a different position from the preliminary joining marks when viewed from the stacking direction, and have a recess that is recessed on one side in the stacking direction, and the recess in a cross section in the stacking direction includes an area where the pair of first conductive layers, the metal sheet, and the pair of second conductive layers are adjacent and integrated.

2. The lithium secondary battery according to claim 1 , wherein the first joining mark is a welding mark.

3. The lithium secondary battery according to claim 2 , wherein the first bonding mark has one or more line shapes.

4. The lithium secondary battery according to claim 2 , wherein the first bonding marks are in the form of one or more dots.

5. The lithium secondary battery according to claim 1 , wherein the second joining mark is a welding mark.

6. The lithium secondary battery according to claim 1 , wherein the second bonding mark has one or more line shapes.

7. The lithium secondary battery according to claim 1 , wherein the second bonding marks are in the form of one or more dots.

8. 8. The lithium secondary battery according to claim 1, wherein a plurality of the first stacked bodies and a plurality of the second stacked bodies are alternately arranged in the stacking direction with the intermediate stacked body sandwiched therebetween.

9. 9. The lithium secondary battery according to claim 8, wherein the first laminate is formed of a flat sheet, and the second laminate is formed of a flat sheet separate from the first laminate.

10. 9. The lithium secondary battery according to claim 8, wherein the first laminate and the second laminate are formed by folding or rolling a single sheet.

11. The lithium secondary battery according to claim 8 , wherein the metal sheet is provided on at least one of the first ends and the second ends.

12. 12. The lithium secondary battery according to claim 11, wherein the metal sheet is provided on one side of the at least one end portion.

13. The lithium secondary battery according to claim 11 , wherein the metal sheets are provided on both sides of the at least one end portion, one on each side.

14. The lithium secondary battery according to claim 8 , wherein the number of the metal sheets is three times or less the total number of the first end portions and the second end portions.

15. 8. The lithium secondary battery according to claim 1, wherein the metal sheet is made of the same material as the first conductive layer and the second conductive layer.

16. 8. The lithium secondary battery according to claim 1, wherein the first electrode and the second electrode are positive electrodes.

17. 8. The lithium secondary battery according to claim 1, wherein the first electrode and the second electrode are negative electrodes.

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