Lithium secondary battery

Abstract

Provided is a technique for suppressing a reduction in output characteristics and productivity of a lithium secondary battery. A lithium secondary battery is provided. The lithium secondary battery includes: (a) a first laminate having a first end portion; (b) an intermediate laminate; (c) a second laminate having a second end portion; (d) a metal sheet disposed so as to be aligned in the lamination direction with respect to the first end portion and the second end portion, and having a first bonding trace formed by bonding with either the first end portion or the second end portion; and (e) an electrode sheet electrically connected to the first laminate and the second laminate. The electrode sheet has a second bonding trace formed by bonding with the first end portion, the metal sheet, and the second end portion. The second bonding trace is located at a different position from the first bonding trace when viewed from the lamination direction.

Description

Technical Field

[0001] Exemplary embodiments of the present disclosure relate to a lithium secondary battery. Background Art

[0002] Patent Document 1 discloses improving the safety of battery cells by using a current collector with metal layers formed on both sides of a resin film. The surface and back sides of the resin film are separated by an insulating resin layer, making electrical conduction impossible. Therefore, when connecting the electrode sheet and the electrode film for lead-out wiring, there is no electrical conduction between the surface and back sides of the electrode, and between the multiple electrodes and the electrode sheet. In this regard, Patent Document 2 discloses that in order to connect each metal layer separated by the resin layer to the electrode sheet for lead-out wiring, the current collector is folded multiple times and stacked on each metal layer.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 11-102711

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-016321 Summary of the Invention

[0007] Technical issues to be solved by the invention

[0008] The present disclosure provides a technology for suppressing a decrease in output characteristics and productivity of a lithium secondary battery.

[0009] Means for solving problems

[0010] In an exemplary embodiment of the present disclosure, a lithium secondary battery is provided, which comprises: (a) a first stack including a first current collector composed of a pair of first conductive layers separated by a first insulating layer, and a first electrode arranged on the first current collector, the first current collector having a first end portion on which the first electrode is not arranged; (b) an intermediate stack including an electrode having a polarity different from that of the first electrode and a separator; (c) a second stack arranged separately in a stacking direction relative to the first stack via the intermediate stack and including a second current collector composed of a pair of second conductive layers separated by a second insulating layer, and a second electrode arranged on a second current collector and having the same polarity as the first electrode, the second current collector having a second end portion at which the second electrode is not arranged; (d) a metal sheet arranged to be arranged along a stacking direction relative to the first end portion and the second end portion, and having a first joining mark formed by joining to either the first end portion and the second end portion; and (e) an electrode sheet electrically connected to the first stack and the second stack, and having a second joining mark formed by joining to the first end portion, the metal sheet and the second end portion, the second joining mark being located at a position different from the first joining mark when viewed from the stacking direction.

[0011] Effects of the Invention

[0012] According to an exemplary embodiment of the present disclosure, it is possible to provide a technology for suppressing reduction in output characteristics and production capacity of a lithium secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is an exploded perspective view for explaining a configuration example of the secondary battery 1 .

[0014] Figure 2A It is a perspective view showing an example of the negative electrode 10 .

[0015] Figure 2B It is a perspective view showing another example of the negative electrode 10 .

[0016] Figure 3 It is a perspective view showing an example of the positive electrode laminate 30 and the metal sheet MS.

[0017] Figure 4A This is a diagram for explaining an example of a joining trace.

[0018] Figure 4B It is a diagram for explaining another example of the joining trace.

[0019] Figure 4C It is a diagram for explaining another example of the joining trace.

[0020] Figure 4D It is a diagram for explaining another example of the joining trace.

[0021] Figure 5 It is a diagram for explaining the joining state of the positive electrode tab 40 , the end portion P, and the metal sheet MS.

[0022] Figure 6 It is a diagram for explaining the second joining mark WR2.

[0023] Figure 7 This is a flowchart showing an example of the present production method.

[0024] Figure 8A Is used to illustrate Figure 7 FIG. 1 is a diagram of step ST1.

[0025] Figure 8B Is used to illustrate Figure 7 FIG. 1 is a diagram of step ST1.

[0026] Figure 9A Is used to illustrate Figure 7 FIG. 1 is a diagram of step ST2.

[0027] Figure 9B Is used to illustrate Figure 7 FIG. 1 is a diagram of step ST2.

[0028] Figure 9C Is used to illustrate Figure 7 FIG. 1 is a diagram of step ST2.

[0029] Figure 9D Is used to illustrate Figure 7 FIG. 1 is a diagram of step ST2.

[0030] Figure 10 Is used to illustrate Figure 7 FIG. 3 is a diagram of step ST3.

[0031] Figure 11 It is a perspective view showing another example of the negative electrode 10 .

[0032] Figure 12 It is a perspective view showing another example of the negative electrode 10 .

[0033] Figure 13 It is a cross-sectional view of main parts for explaining another structural example of a lithium secondary battery.

[0034] Figure 14 It is a cross-sectional view of main parts for explaining another structural example of a lithium secondary battery.

[0035] Figure 15 It is a perspective view for explaining another configuration example of the positive electrode stack.

[0036] Figure 16 It is a perspective view for explaining another configuration example of the positive electrode stack.

[0037] Figure 17 It is a figure which shows the structure and results of an Example and a comparative example.

[0038] Figure 18 It is a figure which shows the lamination pattern of the metal sheet in Example and Comparative Example. DETAILED DESCRIPTION

[0039] Hereinafter, each embodiment of the present disclosure will be described.

[0040] In one exemplary embodiment, a lithium secondary battery is provided, the lithium secondary battery comprising: (a) a first stack including a first current collector composed of a pair of first conductive layers with a first insulating layer interposed therebetween, 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 stack including an electrode having a polarity different from that of the first electrode and a separator; (c) a second stack disposed in a stacking direction separated from the first stack via the intermediate stack and including a second current collector composed of a pair of second conductive layers with a second insulating layer interposed therebetween, and a second electrode arranged on a second current collector and having the same polarity as the first electrode, the second current collector having a second end portion at which the second electrode is not arranged; (d) a metal sheet arranged to be arranged along a stacking direction relative to the first end portion and the second end portion, and having a first joining mark formed by joining to either the first end portion and the second end portion; and (e) an electrode sheet electrically connected to the first stack and the second stack, and having a second joining mark formed by joining to the first end portion, the metal sheet and the second end portion, the second joining mark being located at a position different from the first joining mark when viewed from the stacking direction.

[0041] In one exemplary embodiment, the first bonding trace is a welding trace.

[0042] In an exemplary embodiment, the first bonding trace is in the form of one or more lines.

[0043] In an exemplary embodiment, the first joining mark is in the shape of one or more dots.

[0044] In an exemplary embodiment, the second bonding mark is a welding mark.

[0045] In an exemplary embodiment, the second joining mark is in the form of one or more lines.

[0046] In an exemplary embodiment, the second joining mark is in the shape of one or more dots.

[0047] In one exemplary embodiment, the second bonding trace includes a region in which the pair of first conductive layers, the metal sheet, and the pair of second conductive layers are integrated in a cross section in the stacking direction.

[0048] In an exemplary embodiment, the first bonding trace and the second bonding trace do not overlap with each other when viewed in the stacking direction.

[0049] In one exemplary embodiment, a plurality of first stacked bodies and second stacked bodies are alternately arranged in a stacking direction with intermediate stacked bodies interposed therebetween.

[0050] In one exemplary embodiment, the first stacked body is composed of a flat sheet, and the second stacked body is composed of a flat sheet separate from the first stacked body.

[0051] In one exemplary embodiment, the first stack and the second stack are constructed by folding or rolling one sheet.

[0052] In one exemplary embodiment, the first stack and the second stack are configured in 10 or more layers in total.

[0053] In an exemplary embodiment, the metal sheet is provided at at least one of the plurality of first end portions and the plurality of second end portions.

[0054] In an exemplary embodiment, the metal sheet is provided on a single surface of at least one end portion.

[0055] In an exemplary embodiment, one metal sheet is provided on each side of at least one end portion.

[0056] In an exemplary embodiment, the number of the metal pieces is 3 times or less the total number of the first end portion and the second end portion.

[0057] In one exemplary embodiment, the metal sheet is composed of the same material as the first conductive layer and the second conductive layer.

[0058] In one exemplary embodiment, the first electrode and the second electrode are positive electrodes.

[0059] In one exemplary embodiment, the first electrode and the second electrode are cathodes.

[0060] The following describes various embodiments of the present disclosure in detail with reference to the accompanying drawings. Identical or similar elements are denoted by the same reference numerals throughout the drawings, and duplicate descriptions are omitted. Unless otherwise specified, positional relationships, such as up, down, left, and right, are described based on the positional relationships shown in the drawings. The dimensional ratios in the drawings do not represent actual ratios, and actual ratios are not limited to those shown in the drawings.

[0061] As described above, in Patent Document 2, in order to connect each metal layer through a resin layer to an electrode sheet for lead-out wiring, a scheme is proposed in which a current collector is folded multiple times and stacked on each metal layer. However, in this method, a new device mechanism is required to stack each metal layer while folding back the end of the current collector. In addition, it is necessary to fold back the end of the current collector in conjunction with the stacking, which significantly deteriorates production capacity. In addition, in this method, even if the electrode sheet can be mechanically joined to the current collector and each metal layer, the resistance of the joint will increase and the output characteristics will decrease. In one embodiment of the lithium secondary battery 1 (hereinafter also referred to as "secondary battery 1"), such a problem can be solved.

[0062] <Example of Secondary Battery Configuration>

[0063] Figure 1 1 is an exploded perspective view for explaining a configuration example of the secondary battery 1. Figure 1 As shown, 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 sheet 40, and a negative electrode sheet 42. Each component will be described in detail below.

[0064] (Negative electrode 10)

[0065] Figure 2A 1 is a perspective view showing an example of the 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.

[0066] In one embodiment, Figure 2A As shown, the negative electrode active material 14 is disposed on 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.

[0067] In one embodiment, the negative electrode current collector 12 is formed 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.

[0068] The negative electrode active material 14 is a substance that undergoes electrode reactions, namely, oxidation and reduction reactions, in the negative electrode. Examples of the negative electrode active material 14 include lithium metal and alloys containing lithium metal, carbon-based materials, metal oxides, and metals alloyed with lithium and alloys containing such metals. Examples of the carbon-based materials include graphene, graphite, hard carbon, and carbon nanotubes. Examples of the metal oxides include titanium oxide compounds and cobalt oxide compounds. Examples of the metals alloyed with lithium include silicon, silicon oxide, germanium, tin, lead, aluminum, and gallium, as well as materials pre-doped with lithium.

[0069] Figure 2B 1 is a perspective view showing another example of the negative electrode 10. Figure 2B As shown, the negative electrode 10 may include a negative electrode current collector 16 and negative electrode active materials 14 disposed on both sides of the negative electrode current collector 16. The material of the negative electrode active material 14 may be Figure 2A The negative electrode current collector 16 may be composed of 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 .

[0070] In one embodiment, the negative electrode insulating layer 160 may be formed of a sheet (film) or fibrous resin. The negative electrode conductive layer 162 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, their alloys, and stainless steel. In one example, the negative electrode conductive layer 162 is Cu. The inclusion of the negative electrode insulating layer 160 in the negative electrode current collector 16 ensures the thickness (rigidity) required for the negative electrode current collector 16 while achieving a lighter weight compared to a negative electrode current collector 16 composed solely of a conductive layer.

[0071] like Figure 2A and Figure 2B As shown, the negative electrode current collector (12, 16) has a negative terminal Q. In one embodiment, the negative terminal Q is formed as a portion of the negative electrode current collector, extending outward (in the x-direction) from the side surface of the negative electrode current collector. The negative electrode active material 14 is not formed on the negative terminal Q. A bonding mark WL2 with the negative electrode tab 42 is formed on the negative terminal Q.

[0072] (Negative electrode sheet 42)

[0073] like Figure 1 As shown, the negative electrode tabs 42 are arranged in the stacking direction (z direction) relative to the negative terminals Q. In one embodiment, the negative electrode tabs 42 can be arranged above or below the negative terminals Q. In one embodiment, the negative electrode tabs 42 can be arranged between a negative terminal Q and an adjacent negative terminal Q.

[0074] The negative electrode sheet 42 is joined to each negative terminal Q. Furthermore, the negative terminal 42 is electrically connected to each negative electrode 10 via each negative terminal Q. A joining mark WL2 formed by joining with each negative terminal Q is formed on the negative electrode sheet 42. The joining mark WL2 can be one or more spots, or a continuous line or surface. In one embodiment, the negative electrode sheet 42 and each negative terminal Q can be joined by welding. In this case, the joining mark WL2 is a welding mark. Welding can be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding.

[0075] (Partition 20)

[0076] The separator 20 is disposed on the negative electrode 10. Figure 1 In the example shown, separators 20 are disposed on both sides of the negative electrode 10. The separators 20 physically and / or electrically separate the negative electrode 10 from the positive electrode stack 30 and ensure lithium ion conductivity. In one embodiment, the separators 20 may be at least one member selected from the group consisting of an insulating porous member, a polymer electrolyte, a gel electrolyte, and an inorganic solid electrolyte. Separators 20 may be formed of a single member or a combination of two or more members.

[0077] When the separator 20 comprises an insulating porous member, the pores of the porous member are filled with an ionically conductive substance (electrolyte, polymer electrolyte, and / or gel electrolyte, etc.). This allows the separator 20 to exhibit ion conductivity. The material constituting the insulating porous member is not particularly limited; examples include insulating polymer materials, specifically polyethylene (PE) and polypropylene (PP). Specifically, the separator 20 may be a porous polyethylene (PE) film, a porous polypropylene (PP) film, or a laminated structure thereof.

[0078] In one embodiment, one or both sides of the separator 20 may be coated with a separator coating layer. Thereby, the cycle characteristics of the secondary battery 1 can be improved. In one embodiment, the separator coating layer may be a continuous film with a uniform thickness in an area of ​​more than 50% of the surface of the separator 20. In one embodiment, the separator coating layer may be a layer comprising a binder such as polyvinylidene fluoride (PVDF), a composite 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, titanium oxide, zirconium oxide or magnesium hydroxide to the above-mentioned binder.

[0079] In one embodiment, the thickness of the separator 20 (including the coating layer if the separator 20 includes one) can be 3.0 μm or more and 40 μm or less. This allows the volume occupied by the separator 20 to be reduced while isolating the negative electrode 10 from the positive electrode stack 30. In one embodiment, the thickness of the separator 20 can 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 can be 30 μm or less, 20 μm or less, or 10 μm or less.

[0080] (Middle Laminated Body LM)

[0081] like Figure 1As shown, in one embodiment, the negative electrode 10 and the separator 20 constitute an intermediate laminate LM. The intermediate laminate LM can be a structure in which the separator 20, the negative electrode 10, and the separator 20 are stacked in the stacking direction (z direction). The secondary battery 1 includes a plurality of intermediate laminates LM. In one embodiment, as shown Figure 1 As shown, the plurality of intermediate stacks LM can be constituted as a flat sheet. In one embodiment, the plurality of intermediate stacks LM can be constituted by a sheet (for an example of this solution, using Figure 13 and Figure 14 described later).

[0082] (Positive Electrode Laminated Body 30 and Metal Sheet MS)

[0083] like Figure 1 As shown, the first positive electrode stack 30A includes a current collector 32A and a positive electrode 34A. The first positive electrode stack 30A is an example of a first stack. In one embodiment, the first positive electrode stack can be a structure in which the positive electrode 34A, the current collector 32A, and the positive electrode 34A are stacked in sequence in the stacking direction. The current collector 32A has a first end P1 exposed from the positive electrode 34A. That is, the positive electrode 34A is not formed on the first end P1. The first end P1, as a part of the current collector 32A, extends outward (in the x direction) from the side of the current collector 32A.

[0084] The second positive electrode stack 30B includes a current collector 32B and a positive electrode 34B. The second positive electrode stack 30B is an example of a second stack. In one embodiment, the second positive electrode stack 30B can be a structure in which a positive electrode 34B, a current collector 32B, and a positive electrode 34B are stacked in sequence in the stacking direction. The current collector 32B has a second end portion P2 exposed from the positive electrode 34B. That is, the positive electrode 34B is not formed on the second end portion P2. The second end portion P2, as a part of the current collector 32B, extends outward (in the x direction) from the side of the current collector 32B.

[0085] A plurality of first positive electrode stacks 30A and second positive electrode stacks 30B are alternately stacked in the stacking direction via intermediate stacks LM (hereinafter, when there is no need to distinguish between the first positive electrode stack 30A and the second positive electrode stack 30B, the two are collectively referred to as the "positive electrode stack 30"). Figure 1 As shown, the plurality of positive electrode stacks 30 are each formed as a flat sheet. In one embodiment, the plurality of positive electrode stacks 30 may also be formed from a single sheet (for example, the embodiment of the present invention is described in detail in the accompanying drawings). Figure 15 and Figure 16 described later).

[0086] In one embodiment, the total number of positive electrode stacks 30 contained 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 stacks 30 contained 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.

[0087] like Figure 1 As shown, metal sheets MS are disposed on the first end portion P1 and the second end portion P2 (hereinafter, collectively referred to as "end portions P" when there is no need to distinguish between the two). In one embodiment, metal sheets MS may be disposed on all end portions P. In another embodiment, metal sheets MS may be disposed on some end portions P while not being disposed on the remaining end portions P. For example, metal sheets MS may be disposed on every other end portion P.

[0088] In one embodiment, the number and thickness of the metal sheets disposed at the end P can be set based on the position of the end P in the stacking direction. For example, two or more metal sheets MS can be disposed at the end P in the center of the stacking direction of the secondary battery 1, and one metal sheet MS can be disposed at the end P in the upper and lower portions of the stacking direction. Furthermore, for example, the thickness of the metal sheet MS disposed at the end P in the center of the stacking direction of the secondary battery 1 can be greater than the thickness of the metal sheet disposed at the end P in the upper and lower portions of the stacking direction. This can suppress resistance variations between the central end P.

[0089] In one embodiment, the number of metal sheets MS may be less than or equal to three times, or less than or equal to two times, the total number of end portions P. In one embodiment, the number of metal sheets MS may be the same as or less than the total number of end portions P, for example, less than or equal to half of the total number of end portions P.

[0090] Figure 3 This is a perspective view showing an example of a positive electrode stack 30 and a metal sheet MS. In one embodiment, the positive electrode stack 30 may include a current collector 32 and positive electrodes 34 disposed on both sides of the current collector 32. The current collector 32 includes an insulating layer 320 and a conductive layer 322 formed so as to sandwich the insulating layer 320.

[0091] The insulating layer 320 of the current collector 32 can be composed of, for example, a sheet (film) or fiber-shaped resin. The resin can 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, or polyamide. The insulating layer 320 can be composed of a multilayer stack of at least one of the resins. In one embodiment, the insulating layer 320 is formed 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 can be 3 μm or higher and 10 μm or lower, or 4 μm or higher and 8 μm or lower.

[0092] In the event of overcharge or abnormal heat generation at high temperatures, the insulating layer 320 melts, damaging the positive electrode stack 30 and acting to block short-circuit current within the battery. This prevents a rapid temperature rise within the secondary battery 1 and prevents battery fires. In other words, the insulating layer 320 contributes to improving the safety of the secondary battery 1.

[0093] The conductive layer 322 of the current collector 32 is formed on both sides thereof with the insulating layer 320 interposed therebetween. The conductive layer 322 is in physical contact and / or electrical contact with the positive electrode 34 to act in a manner of donating and accepting electrons to the positive electrode 34. The conductive layer 322 is composed of a conductor that does not react with lithium ions in the battery. In one embodiment, the conductive layer 322 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 conductive layer 322 is aluminum or an aluminum alloy. In one embodiment, the conductive layer 322 is formed by evaporating, sputtering, electrolytically plating or adhering the above-mentioned material to the surfaces on both sides of the insulating layer 320. In one embodiment, the thickness of each conductive layer 322 can be greater than 0.5 μm and less than 5 μm, greater than 0.7 μm and less than 3 μm, or greater than 0.8 μm and less than 2.0 μm.

[0094] Positive electrodes 34 are formed on both sides of current collector 32. A known material can be appropriately selected for positive electrode 34 depending on the intended application. The thickness of positive electrode 34 can be adjusted appropriately based on the desired battery capacity and rate characteristics. In one embodiment, the thickness of each positive electrode 34 is, for example, not less than 20 μm and not more than 150 μm.

[0095] In one embodiment, the positive electrode 34 includes a positive electrode active material. The positive electrode active material is a substance used to retain the carrier metal in the positive electrode 34 and can also be referred to as the host material of the carrier metal. The positive electrode active material can be a substance used to retain lithium ions in the positive electrode 34. In this case, lithium ions are added to and removed from the positive electrode active material during the battery's charge and discharge cycles. This can improve battery stability and output voltage.

[0096] In one embodiment, the positive electrode active material is a metal oxide or a metal phosphate. The metal oxide can be, for example, a cobalt oxide compound, a manganese oxide compound, or a nickel oxide compound. The metal phosphate can be, for example, an iron phosphate compound or a cobalt phosphate compound. In one embodiment, the positive electrode active material can be selected from LiCoO2, 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 At least one of the group consisting of O(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 relative to the total amount of the positive electrode 34.

[0097] In one embodiment, the positive electrode 34 may include one or more components other than the positive electrode active material.

[0098] In one embodiment, the positive electrode 34 may include a sacrificial positive electrode material. The sacrificial positive electrode material is a lithium-containing compound that undergoes an oxidation reaction within the charge and discharge potential range of the positive electrode active material and substantially does not undergo a reduction reaction.

[0099] In one embodiment, the positive electrode 34 may include a gel electrolyte. The gel electrolyte can improve the 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.

[0100] 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), etc. In one example, the binder is polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, acrylic resin, polyimide resin, etc. In one embodiment, the content of the conductive additive is 0.5% by mass and 30% by mass or less relative to the positive electrode 34 as a whole. In one embodiment, the content of the binder can be 0.5% by mass and 30% by mass or less relative to the positive electrode 34 as a whole.

[0101] In one embodiment, the positive electrode 34 may include a polymer electrolyte. In one example, the polymer electrolyte is a solid polymer electrolyte primarily comprising a polymer and an electrolyte, or a semi-solid polymer electrolyte primarily comprising a polymer, an electrolyte, and a plasticizer. In one embodiment, the total content of the polymer electrolyte relative to the total amount of the positive electrode 34 may be 0.5% by mass and 30% by mass or less.

[0102] In one embodiment, Figure 3 As shown, the metal sheet MS may be bonded to one side of the end portion P of the current collector 32 (the surface of one of the pair of conductive layers 322). In one embodiment, the metal sheet MS may be bonded to the other side of the end portion P of the current collector 32 (the surface of the other of the pair of conductive layers 322). In one embodiment, more than one metal sheet MS may be provided at the end portion P. For example, one metal sheet MS may be bonded to one side and the other side of the end portion P of the current collector 32.

[0103] like Figure 3 As shown, by joining the metal sheet MS to the end portion P, a first joining mark WR1 is formed between the metal sheet MS and the end portion P. In one embodiment, the first joining mark WR1 may be a joining mark formed by welding, i.e., a welding mark. 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 portion P may be integrated at the first joining mark WR1 in part or in whole by fusion such as heat. In addition, a second joining mark WR2 is also formed between the metal sheet MS and the end portion P. The second joining mark WR2 is a joining mark between the end portion P and the metal sheet MS and the positive electrode sheet 40, details of which will be described later.

[0104] In one embodiment, Figure 3 As shown, the metal sheet MS can be constructed in a manner that covers only a portion of the end P of the collector 32, but not all of it. For example, the metal sheet MS can be arranged at a position at a predetermined distance from the positive electrode 34. At this time, an insulating layer can be provided in an area on the conductive layer 322 of the end P where the metal sheet MS is not arranged. In this case, in the event of damage to the separator 20, etc., the negative electrode 10 can be prevented from short-circuiting with the positive electrode 34 via the conductive layer 322 of the end P and / or the metal sheet MS, thereby improving the safety of the secondary battery 1. The insulating layer can be composed of, for example, a sheet-like (film-like) or fiber-like resin. The resin can be, for example, at least one of a polyolefin resin such as polyethylene terephthalate (PET), polyethylene, polypropylene, or a thermoplastic resin such as polystyrene, polyvinyl chloride, or polyamide. In addition, in one embodiment, the metal sheet MS can be constructed in a manner that covers the entire surface of the end P of the collector.

[0105] In one embodiment, 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, metal sheet MS is a hard aluminum foil. In another example, metal sheet MS is a soft aluminum foil. Soft aluminum foil can be formed by subjecting hard aluminum foil to a high-temperature (approximately 400° C.) heat treatment. In one embodiment, metal sheet MS can be composed of the same material as conductive layer 322.

[0106] In one embodiment, the thickness of the metal sheet MS can be set according to 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 set to X (=A+B), and the total thickness of each insulating layer 322 is set to Y, the thickness of the metal sheet MS can be set to a relationship of 0.85<X / Y<2.3. In one embodiment, it can be 1.0<X / Y<2.0. In one embodiment, the thickness of the metal sheet MS can be thicker than the thickness of the insulating layer 320. In one embodiment, all the metal sheets MS can have the same thickness, and some can have different thicknesses. In one embodiment, the thickness of the metal sheet MS can be greater than 3 μm, greater than 5 μm, or greater than 7 μm. In one embodiment, the thickness of the metal sheet MS can be less than 15 μm, less than 12 μm, or less than 10 μm.

[0107] Figure 4A This is a diagram for explaining an example of a joining trace. Figure 4A yes Figure 3 FIG. 1 is a top view of the positive electrode stack 30 near the end P. Figure 3 As shown in FIG. 1 , the first bonding traces WR1 may be formed in a plurality of lines (eg, two lines) along the width direction (y direction) of the end portion P. Figure 4A As shown, the first joint trace WR1 is formed at a position different from the second joint trace WR2 when viewed from the stacking direction. That is, the first joint trace WR1 and the second joint trace WR2 do not overlap in a plan view.

[0108] Figures 4B to 4D is a diagram for explaining another example of a joining trace. Figure 4B As shown, the first bonding trace WR1 may be formed in a line along the width direction (y direction) of the end portion P. In one embodiment, as shown in FIG. Figure 4C and Figure 4D As shown, the first joint trace WR1 may be in the form of a plurality of dots, or may be formed in a row ( Figure 4C ) or multiple columns ( Figure 4C ).exist Figures 4B to 4DIn any of the figures, the first bonding trace WR1 is arranged at a position different from the second bonding trace WR2 when viewed from the stacking direction. Figures 4B to 4D In any of the figures, the first bonding trace WR1 and the second bonding trace WR2 do not overlap in the plan view.

[0109] (Positive electrode sheet 40)

[0110] like Figure 1 As shown, the positive electrode tabs 40 are arranged in the stacking direction (z direction) relative to the end portions P (P1, P2) of the current collectors 32 (32A, 32B) and the metal sheets MS. In one embodiment, the positive electrode tabs 40 may be arranged above or below the end portions P of the current collectors 32 and the metal sheets MS. In one embodiment, the positive electrode tabs 40 may be arranged between one end portion P and an adjacent end portion P.

[0111] The positive electrode sheet 40 is made of a conductive material. For example, the positive electrode sheet 40 can be made of aluminum or an aluminum alloy. In one example, the positive electrode sheet 40 can be made of hard aluminum. In one embodiment, the thickness of the positive electrode sheet 40 can be greater than 0.05 mm and less than 1 mm, or can be greater than 0.1 mm and less than 0.5 mm.

[0112] The positive electrode tab 40 is bonded to each end P of each current collector 32 and each metal sheet MS. Thus, the positive electrode tab 40 is electrically connected to each positive electrode 34 via each end P. A second bond mark WR2 is formed on the positive electrode tab 40 by bonding to each end P. The second bond mark WR2 may be one or more spots in a top view, or may be a continuous line or surface.

[0113] In one embodiment, the positive electrode sheet 40 and each end portion P and each metal sheet MS can be joined by welding. Welding can be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding. In one example, the welding is ultrasonic welding.

[0114] Figure 5 It is a diagram for explaining the joining state of the positive electrode tab 40 , the end portion P, and the metal sheet MS. Figure 5 A cross section obtained by cutting a portion of the end portion P including the first joint trace WR1 and the second joint trace WR2 along the xz plane is schematically shown.

[0115] like Figure 5As shown, the first and second joint marks WR1 and WR2 are located at different positions when viewed in the stacking direction. The first joint mark WR1 is formed for each end P. In other words, a single first joint mark WR1 does not span multiple end Ps. In contrast, the second joint mark WR2 is formed within the entirety of the positive electrode sheet 40, each end P, and each metal sheet MS. Specifically, the second joint mark WR2 is formed by continuously penetrating from the positive electrode sheet 40 to the end P of the bottommost layer along the stacking direction.

[0116] Figure 6 It is a diagram for explaining the second joining mark WR2. Figure 6 The cross section obtained by cutting the second joining mark WR2 along the zy plane is schematically shown ( Figure 5 AA section). Figure 6 As shown, the cross section of the second joint mark WR2 includes a first region R1 and a second region R2. In one embodiment, the cross section of the second joint mark WR2 may have a concave portion that is concave in one direction in the stacking direction.

[0117] In the first region R1, the conductive layer 322 is integrally laminated with the metal sheet MS and bonded to the positive electrode sheet 40. Integrally laminated here means that the conductive layer 322 and the metal sheet MS are partially or entirely fused by heat or the like (the layers are indistinguishable).

[0118] In one embodiment, the first region R1 may substantially not include the insulating layer 320 along the stacking direction. The first region R1 provides a physical path for electrically connecting the electrode sheet 40 with each conductive layer 322 and the metal sheet MS.

[0119] In one embodiment, the first region R1 may be formed between two second regions R2. In one embodiment, the maximum thickness of the first region R1 may be less than half of the maximum thickness of the second region R2.

[0120] In the second region R2, a pair of conductive layers 322 and the metal sheet MS are stacked via the insulating layer 320. That is, the second region R2 is a region including the insulating layer 320 along the stacking direction.

[0121] In one embodiment, the second joint trace WR2 can be formed by welding. In this case, the second joint trace WR2 is a welding trace. During welding, the positive electrode sheet 40, the end portion P, and the metal sheet MS are pressed along the stacking direction. As a result, the insulating layer 320 softens at the welding portion and is stretched from the welding portion to the width direction ( Figure 6 In addition, at the welding location, each conductive layer 322 is thermally fused with the metal sheet MS to form a single body. Thus, the first region R1 and the second region R2 can be formed.

[0122] However, as mentioned above, when abnormal heat generation occurs in an overcharged state or a high-temperature state, the insulating layer 320 can suppress a sharp rise in the temperature inside the secondary battery 1 and suppress a fire in the battery. For a current collector composed of a conductive layer separated by an insulating layer, it is difficult to guarantee (control deviations) the bonding between the ends of the current collector and the electrode sheet or the stable bonding quality in each layer as the number of current collectors increases or the thickness of the insulating layer increases. For example, if you want to weld the electrode sheet to all the ends and press hard, then when the conductive layer is thin, the conductive layer at the end may be damaged or broken. On the other hand, if the electrode sheet is welded with a force that does not damage the conductive layer, the bonding may be insufficient, resulting in an increase in the resistance between the end of the current collector and the electrode sheet.

[0123] In this regard, a secondary battery 1 in one embodiment includes a metal sheet MS disposed between at least one end P. The metal sheet MS functions as an additional conductive layer to the conductive layer 322 in the second joint mark WR2, thereby increasing the ratio of the conductive layer to the insulating layer 320. Therefore, an increase in resistance in the second joint mark WR2 can be suppressed. Consequently, the output characteristics of the secondary battery 1 can be improved. Furthermore, when the positive electrode sheet 40 is joined to the end P, the metal sheet MS can also function as a protective layer for the conductive layer 322 at the end P. Consequently, even when the total number (number of stacked layers) of positive electrode stacks 30 in the secondary battery 1 is large, and strong force is applied to join the positive electrode sheet 40 to each end P, damage or breakage of the conductive layer 322 can be suppressed. Consequently, the production capacity of the secondary battery 1 can be improved. In one embodiment, the resistance of the second joint mark WR2 can be 5.0 mΩ or less, 3.0 mΩ or less, 1.0 mΩ or less, or 0.5 mΩ or less.

[0124] (Electrolyte)

[0125] In one embodiment, the secondary battery 1 may include an electrolyte. An electrolyte is a liquid containing a solvent and an electrolyte and exhibits ion conductivity. The electrolyte, also known as a liquid electrolyte, serves as a conductive path for lithium ions. Therefore, when the secondary battery 1 includes an electrolyte, internal resistance is reduced, which can improve energy density, capacity, and cycle characteristics.

[0126] The electrolyte solution may be, for example, a solution that fills the pouch of the secondary battery 1. Alternatively, the electrolyte solution may, for example, soak the separator 20 or may be retained in a polymer to form a polymer electrolyte or a gel electrolyte.

[0127] The electrolyte contained in the electrolyte solution may be, for example, a lithium salt. The lithium salt may be, for example, one selected from the group consisting of LiI, LiCl, LiBr, LiF, LiBF4, LiPF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2CF3CF3)2, LiB(O2C2H4)2, LiB(C2O4)2, LiB(O2C2H4)F2, LiB(OCOCF3)4, LiNO3, and Li2SO4, or a combination of two or more thereof.

[0128] As the solvent contained in the electrolyte solution, for example, a non-aqueous solvent having fluorine atoms (hereinafter referred to as a "fluorinated solvent") and a non-aqueous solvent not having fluorine atoms (hereinafter referred to as a "non-fluorinated solvent") can be added.

[0129] Examples of the fluorinated solvent include 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.

[0130] The non-fluorinated 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.

[0131] The above-mentioned fluorinated solvent and / or non-fluorinated solvent may be used alone or in combination of two or more in any proportion. There is no particular limitation on the content of the fluorinated solvent and the non-fluorinated solvent. The proportion of the fluorinated solvent relative to the total solvent may be 0 to 100% by volume, and the proportion of the non-fluorinated solvent relative to the total solvent may be 0 to 100% by volume.

[0132] <Method for manufacturing secondary battery>

[0133] Next, use Figures 7 to 10 An example of a method for manufacturing the secondary battery 1 (hereinafter also referred to as “this manufacturing method”) will be described. Figure 7 This is a flowchart showing an example of the present production method. Figure 8A and Figure 8B Is used to illustrate Figure 7 FIG. 1 is a diagram of step ST1. Figures 9A to 9D Is used to illustrate Figure 7 FIG. 1 is a diagram of step ST2. Figure 10 Is used to illustrate Figure 7 FIG. 3 is a diagram of step ST3.

[0134] like Figure 7 As shown, the manufacturing method includes: step ST1, preparing a positive electrode laminate sheet; step ST2, joining the metal sheet of the positive electrode laminate sheet; step ST3, cutting the positive electrode laminate from the positive electrode laminate sheet; step ST4, assembling a formed body; step ST5, joining the electrode sheet and the collector; and step ST6, sealing the formed body into a sealed container.

[0135] First, in step ST1, Figure 8A and Figure 8B As shown, a positive electrode laminate sheet S1 is prepared. Figure 8A It is a plan view of the positive electrode laminate sheet S1. Figure 8B yes Figure 8A BB cross-section diagram. Figure 8A As shown, the positive electrode laminate sheet S1 may be a strip-shaped sheet having a long side direction (y direction) and a short side direction (x direction). Figure 8A and Figure 8B As shown, the positive electrode laminate sheet S1 can be composed of a current collector 32 and positive electrodes 34 applied to both surfaces of the current collector 32. The current collector 32 can include an insulating layer 320 and a conductive layer 322 formed so as to sandwich the insulating layer 320. At one end of the positive electrode laminate sheet in the short side direction (x direction), the positive electrode 34 is not formed, and the conductive layer 322 of the current collector 32 is exposed.

[0136] Next, in step ST2, as shown in FIG. Figures 9A to 9D As shown in FIG. 1 , a metal sheet MS is bonded to one end of the positive electrode laminate sheet S1 in the short side direction. Figure 9A It is a plan view of the positive electrode laminate sheet S1 to which the metal sheet MS is joined. Figures 9B to 9D yes Figure 9A An example of CC cross section.

[0137] By joining in step ST2, as Figure 9A As shown, the first joint mark WR1 is formed in a linear shape along the longitudinal direction. The metal sheet MS can be joined to the positive electrode laminate sheet S1 by welding. Welding can be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding. In one example, the welding is ultrasonic welding.

[0138] In one embodiment, the bonding in step ST2 can be performed by pressing the metal sheet MS against the current collector 32. Figure 9B 、 Figure 9C As shown, the first joint mark WR1 may be formed in such a manner that the metal sheet MS is recessed toward the current collector 32. Figure 9BAs shown, the first bonding trace WR1 may be provided between the metal sheet MS and one conductive layer 322 (with which the metal sheet MS contacts). In this case, in the first bonding trace WR1, the metal sheet MS is not electrically connected to the other conductive layer 322. Figure 9C As shown, the first bonding trace WR1 may be provided between the metal sheet MS and the two conductive layers 322. In this case, the metal sheet MS is electrically connected to the two conductive layers 322 in the first bonding trace WR1.

[0139] In one embodiment, the bonding in step ST2 can be performed by pressing the current collector 32 against the metal sheet MS. Figure 9D As shown, the first joint trace WR1 may be formed such that the current collector 32 is recessed toward the metal sheet MS. In this case, the metal sheet MS and the two conductive layers 322 are electrically connected in the first joint trace WR1.

[0140] Next, in step ST3, the positive electrode laminate 30 is cut. Specifically, a cutter or laser is used, such as Figure 10 As shown, a plurality of positive electrode laminates 30 having the given shape are cut out from the state where the metal sheet MS and the positive electrode laminate sheet S1 are bonded together.

[0141] Next, in step ST4, a molded body is assembled in which the positive electrode stack 30 and the intermediate stack LM are alternately stacked. Figure 1 As shown in FIG. 1 , the plurality of positive electrode stacks 30 prepared in step ST3 are arranged so as to be separated from each other in the stacking direction via the intermediate stack LM. In addition, when the negative electrode 10 and the separator 20 are formed in a sheet shape as described later, the separators 20 formed by folding the sheet into a zigzag shape (see FIG. 9 ) or by winding the sheet (see FIG. 1 ) can be separated from each other in the stacking direction. Figure 10 ) each positive electrode stack 30 is configured.

[0142] Next, in step ST5 , the electrode sheet is joined to the current collector. Specifically, the end portion P of each current collector 32 and the metal sheet MS are joined to the electrode sheet 40 to form the second joining mark WR2 described above. The second joining mark WR2 is joined so as not to overlap with the first joining mark WR1 in the stacking direction.

[0143] The negative terminal Q is joined to the negative electrode tab 42 to form a joining mark WL2. The joining can be performed by ultrasonic welding, laser welding, resistance welding, or spot welding.

[0144] Next, in step ST6, the formed body prepared in step ST5 is sealed in a sealed container. In one embodiment, the electrolyte solution may be sealed in the sealed container. The sealed container may be, for example, a laminate film. The above operations complete the production of the secondary battery 1.

[0145] In this manufacturing method, in step ST2, the metal sheet MS is previously joined to the positive electrode laminate sheet MS. Therefore, in step ST3, the metal sheet MS can be cut simultaneously in accordance with the shape of the end P of the positive electrode laminate sheet S1. That is, there is no need for another step of cutting the metal sheet MS in accordance with the shape of the end P. In addition, in step ST5, there is no need to align the metal sheet MS with the end P of the current collector 32, so the joining of the positive electrode sheet 40 to the end P becomes easy. Moreover, in step ST5, in principle, the second joining mark WR2 can be set so as not to overlap with the first joining mark WR1 in the stacking direction. By setting the second joining mark WR2 so as not to overlap with the first joining mark WR1 in the stacking direction, the joining state of the second joining mark WR2 can be improved compared to the case where the two are set to overlap, and the increase in resistance of the second joining mark WR2 can be suppressed.

[0146] How to use secondary batteries

[0147] The secondary battery 1 is charged and discharged by connecting the positive electrode sheet 40 to one end of an external circuit and the negative electrode sheet 42 to the other end of the external circuit. The external circuit may be, for example, a resistor, a power supply, a device, a component, another battery, or a potentiostat. Each end P of the plurality of positive electrode stacks 30 may be connected to the external circuit at the same potential. In addition, each negative terminal Q of the plurality of negative electrodes 10 may be connected to the external circuit at the same potential.

[0148] When a voltage is applied between the positive electrode sheet 40 and the negative electrode sheet 42 so that current flows from the negative electrode sheet 42 to the positive electrode sheet 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 sheet 40 and the negative electrode sheet 42 are connected via a desired external circuit to the charged secondary battery 1, the secondary battery 1 is discharged, and the lithium metal in the negative electrode 10 is electrolytically dissolved.

[0149] In one embodiment, the secondary battery 1 forms a solid electrolyte interface layer (SEI layer) 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 battery 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 greater than 1.0 nm and less than 10 μm. When the 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 through charging and discharging.

[0150] According to the secondary battery 1 described above, the output characteristics and productivity of the battery can be improved.

[0151] Modifications

[0152] The secondary battery 1 can be modified in various ways without departing from the scope and spirit of the present disclosure.

[0153] (Negative electrode 10)

[0154] Figure 11 1 is a perspective view showing another example of the negative electrode 10. In one embodiment, a metal piece may be provided at the negative terminal Q of the negative electrode 10. Figure 11 The example shown is in Figure 2B The negative electrode 10 is shown as having a negative electrode metal sheet MS2 provided on one surface of the negative terminal Q. In one embodiment, the negative electrode metal sheet MS2 can 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.

[0155] like Figure 11 As shown, the joining of the negative electrode metal sheet MS2 and the negative terminal Q forms a first joining mark WL1 therebetween. Furthermore, the joining of the negative terminal Q and the negative electrode metal sheet MS2 to the negative electrode tab 42 forms a second joining mark WL2. The joining configuration and positional relationship of the first joining mark WL1 and the second joining mark WL2 of the negative terminal Q are similar to those of the first joining mark WR1 and the second joining mark WR2 of the end portion P, and their description is omitted.

[0156] Figure 12 is a perspective view showing another example of the negative electrode 10. In one embodiment, the negative electrode 10 may not substantially contain a negative electrode active material. Figure 12 In the example shown, negative electrode 10 is composed of at least one material selected from the group consisting of Cu, Ni, Ti, Fe, other metals that do not react with lithium, their alloys, and stainless steel (SUS). A "metal that does not react with lithium" refers to a metal that does not react with lithium ions or lithium metal to form an alloy during the operation of secondary battery 1. Negative electrode 10 also functions as a current collector.

[0157] In addition, the negative electrode 10 "does not substantially have a negative electrode active material", for example, includes: at the end of discharge (for example, the state where the open circuit voltage of the battery is greater than 2.5V and less than 3.6V), the layer thickness of the negative electrode active material precipitated on the negative electrode 10 is 25μm or less. In one embodiment, the layer thickness of the negative electrode active material at the end of discharge can be less than 20μm, less than 15μm, less than 10μm or less than 5μm, and can also be 0μm. By having substantially no negative electrode active material in the negative electrode 10, in addition to increasing the weight energy density, the energy density per unit volume can also be increased. In addition, in this case, the secondary battery 1 can also be referred to as an "anode-free lithium battery", "zero anode lithium battery" or "anode-less lithium battery".

[0158] In one embodiment, the negative electrode 10 does not have a negative electrode active material before the initial charging of the battery (the state from after the battery is assembled to the first charging). That is, the secondary battery 1 can be charged and discharged by precipitating lithium metal on the negative electrode after the initial charging, and the precipitated lithium metal is electrolytically dissolved. In this case, the volume and mass occupied by the negative electrode active material are suppressed, the overall volume and mass of the battery become smaller, and in principle the energy density becomes higher. In addition, "lithium metal precipitates on the negative electrode" not only refers to the precipitation of lithium metal on the surface of the negative electrode, but also includes the precipitation of lithium metal on the surface of the solid electrolyte interface (SEI) layer described later, the surface or inside of the buffer functional layer.

[0159] In one embodiment, the mass of lithium metal deposited on the negative electrode at a voltage of 4.2 V is M 4.2 , set the same mass at 3.0V to M 3.0 In the case of M 3.0 / M 4.2 It can be 40% or less or 35% or less. In one embodiment, the ratio of M 3.0 / M 4.2 It may be 1.0% or more, 2.0% or more, 3.0% or more, or 4.0% or more.

[0160] In one embodiment, the thickness of the negative electrode 10 can be 1.0 μm to 30 μm. This reduces the volume occupied by the negative electrode 10 in the secondary battery 1 and improves the energy density. The thickness of the negative electrode 10 can be 2.0 μm to 20 μm, 2.0 μm to 18 μm, or 3.0 μm to 15 μm.

[0161] In one embodiment, the negative electrode 10 may be coated with a compound containing an aromatic ring (hereinafter also referred to as a "negative electrode coating agent") on at least a portion of the surface facing the positive electrode stack 30, wherein the aromatic ring is formed by independently bonding two or more elements selected from the group consisting of N, S, and O. The negative electrode coating agent can be retained on the negative electrode 10 by the coordination bonding between the above-mentioned elements and the metal atoms constituting the negative electrode 10. According to this solution, the uneven precipitation reaction of lithium metal on the surface of the negative electrode 10 can be suppressed, and the dendritic growth of lithium metal precipitated on the negative electrode 10 can be suppressed.

[0162] 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 at least 10% of the surface area, or may be applied to at least 20%, at least 40%, at least 60%, or at least 80% of the surface area.

[0163] In one embodiment, the aromatic ring contained in the negative electrode coating agent can be an aromatic hydrocarbon such as benzene, naphthalene, azulene, anthracene, and pyrene, as well as 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 another example, the aromatic ring is benzene.

[0164] In one embodiment, the negative electrode coating agent may be composed of 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 independently bonded. Using a compound having a nitrogen atom bonded to an aromatic ring as the negative electrode coating agent can improve the cycling characteristics of the battery.

[0165] The negative electrode coating agent may be, for example, at least one selected from the group consisting of benzotriazole, benzimidazole, benzimidazolethiol, benzoxazole, benzoxazolethiol, benzothiazole, 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, mercaptobenzothiazole, and derivatives thereof.

[0166] (Buffer functional layer)

[0167] In one embodiment, a porous or fibrous buffer layer may be provided between the negative electrode 10 and the separator 20. The buffer layer comprises a solid portion (including a gel-like portion) with ionic and electrical conductivity, and a porous portion formed by the gaps between the 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 layer) and / or within the buffer layer (the surface of the solid portion of the buffer layer).

[0168] (Intermediate laminate)

[0169] Figure 13 and Figure 14 Each of them is a cross-sectional view of a main part for explaining another configuration example of a lithium secondary battery. In one embodiment, the negative electrode 10 and the separators 20 disposed on both sides of the negative electrode 10 can be configured as a single sheet SH.

[0170] In one embodiment, Figure 13 As shown, the sheet SH is alternately bent multiple times at acute angles to form an intermediate stack, and each positive electrode stack 30 ( 30A, 30B) can be arranged between the separators 20 facing each other in the intermediate stack.

[0171] In one embodiment, Figure 14 As shown, the sheet SH is wound multiple times to form an intermediate stack, and each positive electrode stack 30 (30A, 30B) can be respectively arranged between the separators 20 facing each other in the intermediate stack. Figure 14 In the example shown, each positive electrode laminate 30 may be formed by winding a sheet as described later (see Figure 15 ).

[0172] exist Figure 13 、 Figure 14 In the example shown, even when the negative electrode 10 and separator 20 are extremely thin, they can be handled integrally as a sheet SH, thereby improving battery productivity. Furthermore, because physical pressure is applied from both sides of the sheet SH to the negative electrode 10 sandwiched between the separator 20, the negative electrode 10 is less likely to wrinkle when the sheets SH are stacked, thereby improving battery cycle performance.

[0173] (Positive Electrode Laminated Body)

[0174] Figure 15 and Figure 16 are three-dimensional diagrams for explaining other configuration examples of the positive electrode stack. Figure 15 As shown, each positive electrode stack 30 may be formed by winding a sheet SH2 multiple times. Figure 16As shown in FIG, each positive electrode stack 30 may be formed by alternately bending a sheet SH2 multiple times at acute angles. The sheet SH2 may be formed to include, for example, a current collector 32 and positive electrodes 34 disposed on both sides of the current collector 32. Figure 15 、 Figure 16 In the example shown, even when the current collector 32 and the positive electrode 34 are extremely thin, they can be handled integrally as the sheet SH2 , thereby improving the productivity of the battery.

[0175] <Example>

[0176] Next, examples and comparative examples will be described. The present disclosure is not limited in any way by the following examples and comparative examples.

[0177] Figure 17 It is a figure which shows the structure and results of an Example and a comparative example. Figure 18 It is a figure which shows the lamination pattern of the metal sheet in Example and Comparative Example. Figure 18 "Pattern 1" to "Pattern 4" correspond to Figure 17 "Pattern 1" to "Pattern 4" shown in the "Layered Pattern".

[0178] (Example 1)

[0179] As Example 1, a Figure 1 First, prepare a lithium secondary battery having the structure shown in FIG. Figure 2B The negative electrode 10 of the structure shown. 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 evaporated as the negative electrode conductive layer 162. As the negative electrode active material 14, the following mixed material was used: 97 parts by mass of graphite, 0.5 parts by mass of carbon black as a conductive aid, and 1.5 parts by mass of carboxymethyl cellulose (CMC), 1.0 parts by mass of styrene-butadiene rubber (SBR) as a binder were mixed in water as a solvent. Through the above operations, 21 negative electrodes 10 were prepared. Then, the end Q of each negative electrode 10 was ultrasonically welded to install the negative electrode metal sheet MS2 (copper foil with a thickness of 4 μm) to form Figure 11 Next, a sheet (thickness: 15 μm) coated with a mixture of polyvinylidene fluoride (PVDF) and Al2O3 was prepared as a separator 20. Then, both sides of the negative electrode 10 were sandwiched and pressed with the separators 20 to obtain an intermediate laminate LM.

[0180] As the current collector 32 of the positive electrode stack 30, a current collector was used in which 1.0 μm of Al (conductive layer 322) was deposited on both sides of a 6 μm thick film of polyethylene terephthalate (PET, insulating layer 320). As the positive electrode 34, 96 parts by mass of LiNi was mixed in N-methyl-pyrrolidone (NMP) as a solvent. 0.8 Co 0.15 Al 0.05 A mixture of O2 as the positive electrode active material, 2 parts by mass of carbon black as the conductive additive, and 2 parts by mass of polyvinylidene fluoride (PVDF) as the binder was prepared by coating both sides of the current collector 32 with a unit area weight of 23 mg / cm 2 The positive electrode 34 was applied to obtain a positive electrode laminate 30. Twenty positive electrode laminates 30 were prepared. Then, the ends P of the current collectors 32 of ten positive electrode laminates 30 were ultrasonically welded to attach the positive electrode laminates 30. Figure 17 The metal sheet MS (12 μm hard aluminum) of the structure shown in "Example 1" is prepared. Figure 17 The positive electrode sheet 40 (thickness 0.2 mm) was made of the material (hard aluminum) shown in "Example 1". As the negative electrode sheet 42, nickel-plated copper with a thickness of 0.2 mm was used.

[0181] Next, the intermediate stacks LM and the positive electrode stacks 30 are alternately stacked. At this time, the positive electrode stacks 30 with the metal sheet MS attached to the end P and the positive electrode stacks 30 without the metal sheet MS are appropriately selected to form Figure 18 The stacking pattern (pattern 1) shown. Then, each end P of the collector 32 is overlapped with the metal sheet MS and joined to the positive electrode sheet 40 by ultrasonic welding. In addition, the negative terminal Q and the negative electrode metal sheet MS2 are overlapped and joined to the negative electrode sheet 42 by ultrasonic welding. This structure is inserted into a laminated outer body and sealed with an electrolyte to obtain a lithium secondary battery. The electrolyte used is the following electrolyte: 2 parts by weight of vinylene carbonate (VC) is added to an electrolyte in which lithium hexafluorophosphate (LiPF6) is dissolved, so that it reaches a 1M electrolyte in a solvent prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a ratio of 30:35:35 parts by mass.

[0182] (Examples 2 to 8)

[0183] like Figure 17 and Figure 18 As shown, Examples 2 to 8 were similar to Example 1, except for the material and thickness of the metal sheet MS, the material of the positive electrode sheet 40 , and the stacking pattern of the metal sheet MS, to produce lithium secondary batteries.

[0184] (Comparative Example 1)

[0185] In Comparative Example 1, a lithium secondary battery was produced in the same manner as in Example 1 except that the metal sheet MS was not used.

[0186] Figure 17 Here, "X / Y" refers to the value obtained by dividing X by Y, where the sum of the total thickness (A) of each metal sheet MS and the total thickness (B) of each conductive layer 322 in Examples 1 to 8 is X (=A+B), and the total thickness of each insulating layer 320 is Y. In Comparative Example 1, no metal sheet MS is used, so X is the total thickness of each conductive layer.

[0187] Figure 17 In the figure, "resistance [mΩ]" is the resistance in the second joint trace WR2. The lithium secondary batteries of the embodiment and the comparative example were disassembled and measured using the four-terminal method. Specifically, the positive electrode of the clip-type lead of the resistance meter BT3561 manufactured by HIOKI was connected to the positive electrode sheet 40, and the negative electrode was clamped with a clip to the part of one of the 20 positive electrode stacks 30 that was not coated with the positive electrode active material, and the resistance at 1kHz was measured using a four-terminal lead. Next, the negative electrode was connected to another positive electrode stack for measurement, and the average value of the 20 was calculated. The average value is Figure 17 The "Resistance (mΩ)" is shown. Figure 17 As shown in FIG. 1 , the resistance in the second joint trace WR2 in Examples 1 to 8 is significantly lower than that in Comparative Example 1.

[0188] Furthermore, no fire or explosion occurred in the nail penetration test of the lithium secondary batteries of Examples 1 to 8 and Comparative Example 1. The nail penetration test involves penetrating each battery with a nail to simulate an internal short circuit and confirming whether the battery will catch fire or rupture.

[0189] (Comparative Example 2)

[0190] In Comparative Example 2, a lithium secondary battery was produced in the same manner as in Example 1 except that the negative electrode metal sheet MS2 was not used.

[0191] In Example 1 and Comparative Example 2, the resistance of the junction region between the negative electrode tab 42 and the negative terminal Q was measured in the same manner as described above. In Comparative Example 2, the resistance was 19.4 mΩ. In contrast, in Example 1, the resistance was 0.88 mΩ, significantly lower than that in Comparative Example 2.

[0192] The embodiments of the present disclosure also include the following aspects.

[0193] (Note 1)

[0194] A lithium secondary battery having:

[0195] (a) a first stack including a first current collector formed of a pair of first conductive layers with a first insulating layer interposed therebetween, 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;

[0196] (b) an intermediate stack comprising an electrode having a polarity different from that of the first electrode and a separator;

[0197] (c) a second stack disposed in a stacking direction separated from the first stack via the intermediate stack, the second stack including a second current collector formed of a pair of second conductive layers with a second insulating layer interposed therebetween, 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 at which the second electrode is not disposed;

[0198] (d) a metal sheet arranged in the stacking direction relative to the first end portion and the second end portion, and having a first bonding mark formed by bonding to either the first end portion or the second end portion; and

[0199] (e) an electrode sheet electrically connected to the first stack and the second stack, and having a second bonding mark formed by bonding to the first end portion, the metal sheet, and the second end portion, the second bonding mark being located at a position different from that of the first bonding mark when viewed in the stacking direction.

[0200] (Note 2)

[0201] The lithium secondary battery according to Supplementary Note 1, wherein the first joining trace is a welding trace.

[0202] (Note 3)

[0203] The lithium secondary battery according to Supplementary Note 1 or 2, wherein the first joining trace is in the form of one or more lines.

[0204] (Note 4)

[0205] The lithium secondary battery according to Supplementary Note 1 or 2, wherein the first joining mark is in the form of one or more dots.

[0206] (Note 5)

[0207] The lithium secondary battery according to any one of Supplementary Notes 1 to 4, wherein the second joining trace is a welding trace.

[0208] (Note 6)

[0209] The lithium secondary battery according to any one of Supplementary Notes 1 to 5, wherein the second joining trace is in the form of one or more lines.

[0210] (Note 7)

[0211] The lithium secondary battery according to any one of Supplementary Notes 1 to 5, wherein the second joining mark is in the form of one or more dots.

[0212] (Note 8)

[0213] The lithium secondary battery according to any one of Supplementary Notes 1 to 7, wherein the second joining trace includes a region formed by integrating the pair of first conductive layers, the metal sheet, and the pair of second conductive layers in a cross section in the stacking direction.

[0214] (Note 9)

[0215] The lithium secondary battery according to any one of Supplementary Notes 1 to 8, wherein the first joining trace and the second joining trace do not overlap with each other when viewed in the stacking direction.

[0216] (Note 10)

[0217] The lithium secondary battery according to any one of Supplementary Notes 1 to 9, wherein a plurality of the first stack and the second stack are alternately arranged in the stacking direction with the intermediate stack interposed therebetween.

[0218] (Note 11)

[0219] The lithium secondary battery according to Supplementary Note 10, wherein the first stack is formed of a flat sheet, and the second stack is formed of a flat sheet separate from the first stack.

[0220] (Note 12)

[0221] The lithium secondary battery according to Supplementary Note 10, wherein the first stack and the second stack are formed by folding or rolling one sheet.

[0222] (Note 13)

[0223] The lithium secondary battery according to any one of Supplementary Notes 10 to 12, wherein the first stack and the second stack are arranged in a total of 10 or more layers.

[0224] (Note 14)

[0225] The lithium secondary battery according to any one of Supplementary Notes 10 to 13, wherein the metal sheet is provided at at least one of the plurality of first end portions and the plurality of second end portions.

[0226] (Note 15)

[0227] The lithium secondary battery according to Supplementary Note 14, wherein the metal sheet is provided on a single surface of the at least one end portion.

[0228] (Note 16)

[0229] The lithium secondary battery according to Supplementary Note 14, wherein the metal sheet is provided on each side of the at least one end portion.

[0230] (Note 17)

[0231] The lithium secondary battery according to any one of Supplementary Notes 10 to 16, wherein the number of the metal pieces is 3 times or less the total number of the first end portion and the second end portion.

[0232] (Note 18)

[0233] The lithium secondary battery according to any one of Supplementary Notes 1 to 17, wherein the metal sheet is made of the same material as the first conductive layer and the second conductive layer.

[0234] (Note 19)

[0235] The lithium secondary battery according to any one of Supplementary Notes 1 to 18, wherein the first electrode and the second electrode are positive electrodes.

[0236] (Note 20)

[0237] The lithium secondary battery according to any one of Supplementary Notes 1 to 18, wherein the first electrode and the second electrode are negative electrodes.

[0238] Description of Reference Numerals

[0239] 1...lithium secondary battery; 10...negative electrode; 20...separator; 30...positive electrode laminate; 32...current collector; 320...insulating layer; 322...conductive layer; 34...positive electrode; 40...positive electrode sheet; 42...negative electrode sheet; MS...metal sheet; LM...intermediate laminate; WR1...first joint mark; WR2...second joint mark.

Claims

1. A lithium secondary battery, wherein: The lithium secondary battery has: (a) a first stack including a first current collector formed of a pair of first conductive layers with a first insulating layer interposed therebetween, 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 stack comprising an electrode having a polarity different from that of the first electrode and a separator; (c) a second stack disposed in a stacking direction separated from the first stack via the intermediate stack, the second stack including a second current collector formed of a pair of second conductive layers with a second insulating layer interposed therebetween, 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 at which the second electrode is not disposed; (d) a metal sheet arranged in the stacking direction relative to the first end portion and the second end portion, and having a first bonding mark formed by bonding to either the first end portion or the second end portion; and (e) an electrode sheet electrically connected to the first stack and the second stack, and having a second bonding mark formed by bonding to the first end portion, the metal sheet, and the second end portion, the second bonding mark being located at a position different from that of the first bonding mark when viewed in the stacking direction.

2. The lithium secondary battery according to claim 1, wherein The first bonding trace is a welding trace.

3. The lithium secondary battery according to claim 2, wherein The first joining trace is in the form of one or more lines.

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

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

6. The lithium secondary battery according to claim 5, wherein The second bonding trace is in the form of one or more lines.

7. The lithium secondary battery according to claim 5, wherein The second joining marks are in the form of one or more dots.

8. The lithium secondary battery according to claim 1, wherein The second bonding trace includes a region formed by integrating the pair of first conductive layers, the metal sheet, and the pair of second conductive layers in a cross section in the stacking direction.

9. The lithium secondary battery according to claim 1, wherein The first bonding trace and the second bonding trace do not overlap with each other when viewed in the stacking direction.

10. The lithium secondary battery according to any one of claims 1 to 9, wherein A plurality of the first stacked bodies and the second stacked bodies are alternately arranged in the stacking direction with the intermediate stacked body interposed therebetween.

11. The lithium secondary battery according to claim 10, wherein The first stacked body is formed of a flat sheet, and the second stacked body is formed of a flat sheet separate from the first stacked body.

12. The lithium secondary battery according to claim 10, wherein The first stacked body and the second stacked body are constructed by folding or rolling one sheet.

13. The lithium secondary battery according to claim 10, wherein The first stack and the second stack are arranged in 10 or more layers in total.

14. The lithium secondary battery according to claim 10, wherein The metal sheet is provided at at least one of the plurality of first end portions and the plurality of second end portions.

15. The lithium secondary battery according to claim 14, wherein The metal sheet is provided on a single surface of the at least one end portion.

16. The lithium secondary battery according to claim 14, wherein The metal sheets are respectively provided on both sides of the at least one end portion.

17. The lithium secondary battery according to claim 10, wherein The number of the metal pieces is less than or equal to three times the total number of the first end portion and the second end portion.

18. The lithium secondary battery according to any one of claims 1 to 9, wherein The metal sheet is made of the same material as the first conductive layer and the second conductive layer.

19. The lithium secondary battery according to any one of claims 1 to 9, wherein The first electrode and the second electrode are positive electrodes.

20. The lithium secondary battery according to any one of claims 1 to 9, wherein The first electrode and the second electrode are cathodes.

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