Lithium secondary battery

Abstract

Provided is a lithium secondary battery having both high safety and excellent performance stability at high temperatures. The present invention relates to a lithium secondary battery having a positive electrode having a positive electrode current collector and a positive electrode active material layer, a negative electrode having a negative electrode current collector, an electrolyte solution, and a separator, the positive electrode current collector and / or the negative electrode current collector having a current collector film, the current collector film is provided with a resin layer containing polyethylene terephthalate and metal layers provided on both surfaces of the resin layer, and the positive electrode active material layer contains one or more compounds represented by the general formula LizNixCoyM1-x-yO2 + [alpha] (wherein 0.5 < = x < = 1.0, 0 < = y < = 0.35, 0.9 < = z < = 1.3,-0.2 < = [alpha] < = 0.15, M represents one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B, and n represents an integer of 1-3). The electrolyte solution contains a chain carbonate and / or a chain ether, vinylene carbonate, and lithium difluorophosphate.

Description

TECHNICAL FIELD

[0001] The present application relates to a lithium secondary battery. BACKGROUND

[0002] In recent years, technologies for converting natural energy such as solar energy or wind energy into electric energy have been attracting attention. Along with this, various secondary batteries have been developed as power storage devices that are high in safety and capable of storing a large amount of electric energy.

[0003] Among them, a lithium secondary battery, which performs charge and discharge by moving lithium ions between a positive electrode and a negative electrode, is known to exhibit high voltage and high energy density. As a typical lithium secondary battery, a lithium-ion secondary battery (LIB) is known in which active materials capable of holding lithium elements are provided in the positive electrode and the negative electrode, and charge and discharge are performed by intercalating and deintercalating lithium ions between the positive electrode active material and the negative electrode active material.

[0004] For example, Patent Literature 1 discloses a power storage device characterized by including an anode, a cathode, at least one separator provided between the anode and the cathode, an electrolyte, at least one thin film-shaped current collector in contact with at least one of the anode and the cathode, and at least one tab attached to the at least one thin film-shaped current collector, the tab being attached to the current collector via a connection unit, the connection unit electrically connecting between an exposed surface of the tab and the thin film-shaped current collector, either of the anode and the cathode being interposed between at least a part of the thin film-shaped current collector and the separator, the current collector including a conductive material covering a non-conductive material substrate; the current collector ceasing to conduct at the time of short circuit at a working voltage of the power storage device, the voltage being at least 2.0 volts.

[0005] In addition, Patent Literature 2 discloses a current collector characterized by having a multilayer structure in which an insulating layer is sandwiched by conductive layers, the current collector having a folded-back region obtained by folding back an end portion of the current collector two or more times in the same direction, the conductive layers sandwiching the insulating layer being electrically connected to each other in the folded-back region, and inner surfaces of the end portions of the current collector forming the folded-back region being separated from each other or partially in contact with each other.

[0006] In addition, Patent Literature 3 discloses a lithium-ion secondary battery characterized in that, in a lithium-ion secondary battery including a positive electrode and a negative electrode each formed by adhering an active material to a current collector via an adhesive material, the current collector of at least one of the positive electrode and the negative electrode includes a low-melting-point layer composed of a resin that melts at the time of abnormal heat generation of the battery, and a metal layer interposed between the low-melting-point layer and the active material and performing exchange of the active material and electric charges.

[0007] Prior Art Documents

[0008] Patent Literature

[0009] Patent Literature 1: Japanese Patent Application Laid-Open No. 2022-527140

[0010] Patent Literature 2: Japanese Patent Application Laid-Open No. 2013-016321

[0011] Patent Literature 3: Japanese Patent Application Laid-Open No. H11-102711 SUMMARY

[0012] PROBLEMS TO BE SOLVED BY THE INVENTION

[0013] From the viewpoint of safety and lightness, in the current collector described in Patent Literatures 1 to 3, a current collector film in which metal layers are formed on both surfaces of a resin film is used, and as the material of the resin film, polyethylene terephthalate (PET) which is excellent in mechanical properties and processability is preferred.

[0014] However, it has been found that when a lithium secondary battery in a charged state is stored at a high temperature, a chain carbonate and / or a chain ether as an electrolyte component chemically reacts with PET, and a problem of performance deterioration of the lithium secondary battery occurs. It has been found that the above-mentioned deterioration becomes significant particularly in the case where a positive electrode active material having a nickel ratio higher than a certain value is used.

[0015] The present application has been made in view of the above-mentioned problems, and an object thereof is to provide a lithium secondary battery which has high safety and excellent performance stability at a high temperature.

[0016] SOLUTION TO THE PROBLEMS

[0017] A lithium secondary battery of one embodiment of the present application includes a positive electrode including a positive electrode current collector and a positive electrode active material layer, a negative electrode including a negative electrode current collector, an electrolyte, and a separator. The positive electrode current collector and / or the negative electrode current collector include a current collector film including a resin layer including polyethylene terephthalate and metal layers provided on both surfaces of the resin layer. The positive electrode active material layer includes one or more compounds represented by the general formula: Li z Ni x Co y M 1-x-y O 2+α where 0.5 ≤ x ≤ 1.0, 0 ≤ y ≤ 0.35, 0.9 ≤ z ≤ 1.3, and -0.2 ≤ α ≤ 0.15, M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B, and the electrolyte contains a chain carbonate and / or a chain ether, vinylene carbonate, and lithium difluorophosphate.

[0018] The present inventors have found that in a lithium secondary battery, by the positive electrode current collector and / or the negative electrode current collector having a current collector film, and the current collector film having a resin layer containing polyethylene terephthalate, and metal layers provided on both surfaces of the resin layer, high safety is achieved. In addition, it has been found that even when the positive electrode active material layer contains one or more compounds represented by the general formula: Li z Ni x Co y M 1-x-y O 2+α where 0.5≤x≤1.0, 0≤y≤0.35, 0.9≤z≤1.3, -0.2≤α≤0.15, M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B, and the electrolyte contains a chain carbonate and / or a chain ether, by the electrolyte containing vinylene carbonate and lithium difluorophosphate, even when a lithium secondary battery in a charged state is stored at high temperature, chemical reaction of the chain carbonate and / or the chain ether as an electrolyte component with PET is suppressed, and high performance of the lithium secondary battery can be maintained. Therefore, it is presumed that the above components allow high safety and excellent performance stability at high temperature of the lithium secondary battery to be balanced. However, the main reason is not limited to the above.

[0019] In the lithium secondary battery of one embodiment of the present application, preferably, the positive electrode active material layer contains one or more compounds represented by the general formula: Li z Ni x Co y M 1-x-y O 2+α where 0.7≤x≤1.0, 0≤y≤0.35, 0.9≤z≤1.3, -0.2≤α≤0.15, M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B. According to this scheme, the lithium secondary battery is in a tendency to have excellent performance stability at high temperature.

[0020] In the lithium secondary battery of one embodiment of the present application, preferably, the electrolyte contains the above chain carbonate, and the chain carbonate includes ethyl methyl carbonate and / or dimethyl carbonate. According to this scheme, the lithium secondary battery is in a tendency to have excellent performance stability at high temperature.

[0021] In the lithium secondary battery of one embodiment of the present application, preferably, the content of the above-described vinylene carbonate is 0.1 to 5.0 mass% with respect to the total amount of the above-described electrolyte solution, and the content of the above-described lithium difluorophosphate is 0.1 to 5.0 mass% with respect to the total amount of the above-described electrolyte solution. According to this scheme, the lithium secondary battery is in a tendency to have high stability of performance at high temperature.

[0022] In the lithium secondary battery of one embodiment of the present application, preferably, the above-described electrolyte solution further contains lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide. According to this scheme, the lithium secondary battery is in a tendency to have higher stability of performance at high temperature.

[0023] Effects of Invention

[0024] According to the present application, a lithium secondary battery which has both high safety and high stability of performance at high temperature can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 FIG. 1 is one example of a schematic cross-sectional view of a lithium secondary battery of one embodiment of the present application.

[0026] Figure 2 FIG. 3 is one example of a schematic cross-sectional view of a positive electrode of one embodiment of the present application.

[0027] Figure 3 FIG. 5 is one example of a schematic cross-sectional view of a negative electrode of one embodiment of the present application.

[0028] Figure 4 FIG. 7 is another example of a schematic cross-sectional view of a lithium secondary battery of one embodiment of the present application.

[0029] Figure 5 FIG. 9 is another example of a schematic cross-sectional view of a negative electrode of one embodiment of the present application. DETAILED DESCRIPTION

[0030] Hereinafter, an embodiment of the present application (hereinafter, referred to as "this embodiment") will be described in detail, as needed, with reference to drawings, but the present application is not limited thereto and can be modified in various ways without departing from the spirit thereof. Note that the same elements are denoted by the same reference numerals in the drawings, and repetitive description is omitted. In addition, unless otherwise specified, the positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings. Moreover, the dimensional ratio of the drawings is not limited to the ratio shown in the drawings.

[0031] 1. Lithium Secondary Battery

[0032] As the kind of the lithium secondary battery of the present embodiment, there is no particular limitation as long as it is a battery that performs charge and discharge through oxidation and reduction of lithium, and for example, a non-anode-type lithium secondary battery, a lithium-ion battery, a lithium metal battery, a lithium-sulfur battery, a lithium-oxygen battery, a lithium-air battery, and the like can be exemplified.

[0033] The battery shape of the lithium secondary battery of the present embodiment is not particularly limited, and for example, a sheet type, a laminated sheet type, a thin type shape, a bottomed cylindrical shape, a bottomed square shape, and the like can be exemplified. From the viewpoint of further effectively and reliably exerting the effects of the present embodiment, a sheet type, a laminated sheet type, or a thin type shape is preferable.

[0034] Hereinafter, the lithium secondary battery of the present embodiment will be described in detail, as needed, taking a non-anode-type lithium secondary battery (hereinafter, also simply referred to as a "non-anode-type battery" or "AFB") as one example of the lithium secondary battery of the present embodiment.

[0035] [Non-anode-type lithium secondary battery]

[0036] Figure 1 is a drawing illustrating one example of the cross-sectional structure of the non-anode-type lithium secondary battery of one embodiment of the present application.

[0037] Figure 1 The non-anode-type lithium secondary battery 100A of one embodiment of the present application illustrated in FIG. 1A includes a positive electrode 30B including a positive electrode current collector 32 and a positive electrode active material layer 34, a negative electrode 10C including a negative electrode current collector 12, an electrolyte, and a separator 20, in which the positive electrode current collector 32 and / or the negative electrode current collector 12 has a current collector film including a resin layer containing polyethylene terephthalate and metal layers provided on both surfaces of the resin layer, and the positive electrode active material layer 34 contains one or more compounds represented by the general formula: Li z Ni x Co y M 1-x-y O 2+α where 0.5 ≤ x ≤ 1.0, 0 ≤ y ≤ 0.35, 0.9 ≤ z ≤ 1.3, -0.2 ≤ α ≤ 0.15, M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B, and the electrolyte contains a chain carbonate and / or a chain ether, vinylene carbonate, and lithium difluorophosphate. Note that the lithium secondary battery of the present embodiment including the non-anode-type lithium secondary battery 100A is referred to as a lithium secondary battery 100.

[0038] As Figure 2As shown, a positive electrode active material layer 34 can be formed on at least one side of the positive electrode current collector 32 to become a positive electrode 30B. Although not shown, a positive electrode active material layer 34 can also be formed on both sides of the positive electrode current collector 32 to become a positive electrode 30. Furthermore, in this specification, the positive electrode of this embodiment, including the positive electrode 30B, is referred to as the positive electrode 30.

[0039] In this embodiment, the negative electrode, including the negative electrode 10C, is referred to as negative electrode 10, such as... Figure 3 As shown, the negative electrode 10C does not have a negative electrode active material layer 14, but is only composed of a negative electrode current collector 12.

[0040] exist Figure 2 In this embodiment, the positive current collector 32 includes a resin layer 320 and metal layers 322 disposed on both sides of the resin layer 320. However, the positive current collector 32 may also have a metal layer 322 but not a resin layer 320. Additionally, in... Figure 3 In this embodiment, the negative current collector 12 includes a resin layer 120 and metal layers 122 disposed on both sides of the resin layer 120. However, the negative current collector 12 may also have metal layers 122 but not resin layers 120. In addition, at least one of the positive current collector 32 and the negative current collector 12 has a current collector film, which includes a resin layer and metal layers disposed on both sides of the resin layer (hereinafter also simply referred to as "current collector film").

[0041] When the positive and / or negative current collectors have a current collector film, the resin layer melts under conditions such as overcharging or abnormal heating at high temperatures, allowing it to function by blocking short-circuit current inside the battery. This suppresses a rapid rise in internal battery temperature, inhibits battery fire, and contributes to high safety.

[0042] In addition, compared with the case where the positive current collector and / or negative current collector only have a metal layer, the specific gravity is smaller when a current collector film is present, thus tending to increase the energy density per unit weight.

[0043] In lithium-ion secondary batteries, current collector films are frequently used due to the aforementioned advantages. Furthermore, polyethylene terephthalate (PET), with its excellent mechanical properties and processability, is often used as the material for the resin layer. Additionally, chain carbonates and / or chain ethers are frequently used as the electrolyte to improve the performance of lithium-ion secondary batteries (energy density, cycle characteristics, residual capacity, etc.).

[0044] However, when lithium-ion batteries are stored in a charged state at high temperatures, the chain carbonates and / or chain ethers, which are components of the electrolyte, react chemically with PET, leading to a tendency for the performance of the lithium-ion batteries to deteriorate. This deterioration becomes particularly pronounced when using positive electrode active materials with a nickel ratio exceeding a certain value.

[0045] As a result of intensive studies by the present inventors, it has been found that, by including vinylene carbonate and lithium difluorophosphate, even in the case of a lithium secondary battery that is stored in a charged state at a high temperature, it is possible to suppress a chemical reaction of a chain carbonate and / or a chain ether as an electrolyte component with PET, and it is possible to maintain high performance of the lithium secondary battery. The main reason is presumed as follows, but is not limited thereto.

[0046] It is presumed that PET and dimethyl carbonate, which is one example of a chain carbonate as an electrolyte component, undergo the redox shuttle reaction shown below at the positive electrode and the negative electrode.

[0047] [Chemical Formula 1]

[0048]

[0049] It is presumed that the above-described redox shuttle reaction becomes significant particularly when a lithium secondary battery that is stored in a charged state at a high temperature. In addition, it is presumed that the above-described redox shuttle reaction becomes more significant when the positive electrode active material is a compound represented by the general formula: Li z Ni x Co y M 1-x-y O 2+α (wherein 0.5≤x≤1.0, 0≤y≤0.35, 0.9≤z≤1.3, -0.2≤α≤0.15, and M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B).

[0050] Through the above-described redox shuttle reaction, the composition of the electrolyte component changes, and the mass of the electrolyte component decreases, and thus it is presumed that the performance of the lithium secondary battery, such as the capacity retention rate, deteriorates. Furthermore, the above-described redox shuttle reaction is not limited to dimethyl carbonate, and it is presumed that it also occurs in chain carbonates such as ethyl methyl carbonate and vinylene carbonate, and chain ethers such as dimethoxyethane, diethoxyethane, dimethoxypropane, dimethoxybutane, and diethylene glycol dimethyl ether.

[0051] Here, it is presumed that, by adding vinylene carbonate as an additive to the electrolyte, the vinylene carbonate is decomposed at the negative electrode, a coating film is generated at the negative electrode, and the above-described redox shuttle reaction at the negative electrode is suppressed. In addition, it is presumed that, by adding lithium difluorophosphate as an additive to the electrolyte, the lithium difluorophosphate is decomposed at the positive electrode, a coating film is generated at the positive electrode, and the above-described redox shuttle reaction at the positive electrode is suppressed. As a result, it is presumed that the composition of the electrolyte component changes, and the mass decrease is suppressed. Thus, it is presumed that, even in the case of a lithium secondary battery that is stored in a charged state at a high temperature, it is possible to maintain the high performance of the lithium secondary battery, such as the capacity retention rate.

[0052] Therefore, it is considered that the lithium secondary battery of the present embodiment can have both high safety and excellent performance stability at high temperatures. However, the main reason is not limited to the above.

[0053] 1.1. Positive electrode

[0054] The positive electrode 30 of the present embodiment has a positive electrode current collector 32 and a positive electrode active material layer 34.

[0055] The average thickness of the positive electrode 30 of the anodeless battery is not particularly limited, and is, for example, 20 μm or more and 100 μm or less, 30 μm or more and 80 μm or less, 40 μm or more and 70 μm or less. However, the average thickness of the positive electrode 30 can be appropriately adjusted depending on the desired battery capacity.

[0056] 1.1.1. Positive electrode current collector

[0057] The positive electrode current collector 32 of the present embodiment can have a current collector film having a resin layer 320 containing polyethylene terephthalate and metal layers 322 provided on both surfaces of the resin layer 320, or can have the metal layers 322 without the resin layer 320. In the case of having the current collector film, the metal layers 322 are formed by evaporation, sputtering, electrolytic plating on both surfaces of the resin layer 320, or adhesion with an adhesive or the like.

[0058] 1.1.1.1. Resin layer

[0059] The resin layer 320 of the positive electrode current collector 32 of the present embodiment is an insulator that prevents the metal layers 322 provided on both surfaces of the resin layer 320 from being in conduction with each other. The resin constituting the resin layer 320 is not particularly limited, and can be constituted by, for example, a sheet-shaped (film-shaped) or fiber-shaped resin. As the resin, polyethylene terephthalate (PET) is included, and other resins can be further included. As the other resins, polyethylene, polypropylene, polystyrene, polyvinyl chloride, or polyamide, or the like, a thermoplastic resin can be exemplified. The other resins can be used alone or in combination of two or more.

[0060] The resin layer 320 can appropriately include other additives in addition to the above-described resin depending on the desired properties. The additives are not particularly limited, and can be exemplified by, for example, a coloring agent, a flame retardant, a surfactant, or the like.

[0061] The content of the resin is not particularly limited, and can be, for example, 60% by mass or more and 100% by mass or less, can be 80% by mass or more and 100% by mass or less, can be 90% by mass or more and 100% by mass or less, can be 95% by mass or more and 100% by mass or less, or can be 100% by mass, with respect to the total amount of the resin layer 320.

[0062] The content of PET is not particularly limited, and for example, can be 60% by mass or more and 100% by mass or less, can be 80% by mass or more and 100% by mass or less, can be 90% by mass or more and 100% by mass or less, can be 95% by mass or more and 100% by mass or less, or can be 100% by mass, with respect to the total amount of the resin layer 320.

[0063] The content of PET is not particularly limited, and for example, can be 80% by mass or more and 100% by mass or less, can be 85% by mass or more and 100% by mass or less, can be 90% by mass or more and 100% by mass or less, can be 95% by mass or more and 100% by mass or less, can be 98% by mass or more and 100% by mass or less, or can be 100% by mass, with respect to the total amount of the resin.

[0064] The thickness of the resin layer 320 is not particularly limited, and for example, can be 2 μm or more and 15 μm or less, 3 μm or more and 12 μm or less, or 4 μm or more and 10 μm or less.

[0065] 1.1.1.2, Metal Layer

[0066] The metal layer 322 of the positive electrode current collector 32 of the present embodiment makes physical and / or electrical contact with the positive electrode active material layer 34, and functions to accept and deliver electrons to and from the positive electrode active material layer 34. The metal layer 322 is composed of an electrically conductive body such as a metal that does not react with lithium in a battery. As the metal that constitutes the metal layer 322, there is no particular limitation, and it is at least one selected from the group consisting of aluminum, titanium, stainless steel, nickel, and alloys thereof. Among them, aluminum or an aluminum alloy is preferable, and aluminum is particularly preferable. As the metal, one kind alone or two or more kinds in combination can be used. In the present specification, the "metal that does not react with lithium" means a metal that does not undergo alloying with lithium ions or lithium metal under the working conditions of a lithium secondary battery.

[0067] When the positive electrode current collector 32 has a current collector film, the thickness of the metal layer 322 is not particularly limited, and for example, can be 0.1 μm or more and 4.0 μm or less, 0.2 μm or more and 3.0 μm or less, 0.3 μm or more and 2.5 μm or less, or 0.4 μm or more and 2.0 μm or less.

[0068] When the positive electrode current collector 32 has the metal layer 322 and does not have the resin layer 320, the thickness of the metal layer 322 is not particularly limited, and for example, can be 4.0 μm or more and 20.0 μm or less, 6.0 μm or more and 17.5 μm or less, or 8.0 μm or more and 15.0 μm or less.

[0069] 1.1.2, Positive Electrode Active Material

[0070] The positive electrode active material of the present embodiment is not particularly limited, and for example, is contained in a positive electrode active material composition containing a binder, a conductive aid, a sacrificial positive electrode agent, and other additives, and the positive electrode active material layer 34 is provided on at least one side or both sides of the positive electrode current collector 32 by coating the positive electrode active material composition on at least one side or both sides of the positive electrode current collector 32 and compression molding.

[0071] As a method of providing the positive electrode active material layer 34 on the positive electrode current collector 32, compression molding is not limited, and for example, a method of containing a thermosetting compound in the positive electrode active material composition and curing it by heating, a method of containing a photocurable compound in the positive electrode active material composition and curing it by light irradiation, a method of curing the positive electrode active material composition as a two-component curable composition by two-component mixing, and the like can be exemplified.

[0072] The positive electrode active material layer 34 of the present embodiment contains one or more compounds represented by the general formula: Li z Ni x Co y M 1-x-y O 2+α wherein 0.5≤x≤1.0, 0≤y≤0.35, 0.9≤z≤1.3, -0.2≤α≤0.15, and M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B.

[0073] In addition, preferably, the positive electrode active material layer 34 contains one or more compounds represented by the general formula: Li z Ni x Co y M 1-x-y O 2+α wherein 0.7≤x≤1.0, 0≤y≤0.35, 0.9≤z≤1.3, -0.2≤α≤0.15, and M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B. By containing the above compound having a high nickel ratio as the positive electrode active material, the energy density of the lithium secondary battery is in a tendency to further increase. In addition, if the nickel ratio becomes high, the above redox shuttle reaction is more likely to occur, but by containing an additive described below in the electrolyte, the reaction is suppressed, and a tendency to have excellent performance stability at high temperatures is exhibited.

[0074] As the positive electrode active material, other positive electrode active materials than the above-mentioned compounds can be contained. The positive electrode active material refers to a material that undergoes electrode reactions, i.e., oxidation and reduction reactions, in the positive electrode. Specifically, as the other positive electrode active material of the present embodiment, a host material of lithium element (typically, lithium ion) can be exemplified. The other positive electrode active material is not particularly limited, and for example, metal oxides and metal phosphates can be exemplified. The above-mentioned metal oxides are not particularly limited, and for example, cobalt oxide-based compounds, manganese oxide-based compounds, and nickel oxide-based compounds, etc. can be exemplified. The above-mentioned metal phosphates are not particularly limited, and for example, iron phosphate-based compounds and cobalt phosphate-based compounds can be exemplified. As typical other positive electrode active materials, LiCoO2, LiNi x Mn y O (x+y=1), LiNiO2, LiMn2O4, LiFePO, LiCoPO, LiFeOF, LiNiOF, and TiS2 can be exemplified. The other positive electrode active material can be used alone or in combination of two or more.

[0075] The content of the positive electrode active material is not particularly limited with respect to the total amount of the positive electrode active material composition, and for example, is 60% by mass or more and 100% by mass or less, 70% by mass or more and 99% by mass or less, 80% by mass or more and 98% by mass or less, 85% by mass or more and 97% by mass or less, or 90% by mass or more and 96% by mass or less.

[0076] 1.1.3. Binder

[0077] The positive electrode active material composition of the present embodiment can contain a binder. By containing the binder, the positive electrode active material layer 34 is more easily adhered to the positive electrode current collector 32, and in addition, the softness is improved after the positive electrode active material layer 34 is disposed on the positive electrode current collector 32.

[0078] The binder of the present embodiment is not particularly limited, and for example, polyvinylidene fluoride; modified polyvinylidene fluoride obtained by introducing a functional group such as a hydroxyl group, an amino group, a carbonyl group, a carboxyl group, a phenyl group, or a methyl group into polyvinylidene fluoride; polytetrafluoroethylene; modified polytetrafluoroethylene obtained by introducing a functional group such as a hydroxyl group, an amino group, a carbonyl group, a carboxyl group, a phenyl group, or a methyl group into polytetrafluoroethylene; a block copolymer, a random copolymer, or a graft copolymer having tetrafluoroethylene as a constituent unit; styrene butadiene rubber; carboxymethyl cellulose; acrylic resin; polyimide resin, etc. can be exemplified. The binder can be used alone or in combination of two or more.

[0079] The content of the binder is not particularly limited with respect to the total amount of the positive electrode active material composition, and for example, is 0.5% by mass or more and 10.0% by mass or less, 1.0% by mass or more and 8.0% by mass or less, or 2.0% by mass or more and 6.0% by mass or less.

[0080] 1.1.4, Conductive assistant

[0081] The positive electrode active material composition of the present embodiment can contain a conductive assistant. The conductive assistant is not particularly limited, and examples thereof include carbon black, single-walled carbon nanotube (SWCNT), multi-walled carbon nanotube (MWCNT), carbon nanofiber (CF), and acetylene black. The conductive assistant can be used alone or in combination of two or more.

[0082] The content of the conductive assistant is not particularly limited, and is, for example, 0.5% by mass or more and less than 30.0% by mass, relative to the total amount of the positive electrode active material composition.

[0083] 1.1.5, Sacrificial positive electrode agent

[0084] The positive electrode active material composition of the present embodiment can further contain a sacrificial positive electrode agent. The sacrificial positive electrode agent of the present embodiment refers to a lithium-containing compound that undergoes oxidation reaction within the charge-discharge potential range of the positive electrode active material and substantially does not undergo reduction reaction. In the case where the positive electrode contains the sacrificial positive electrode agent, when the lithium secondary battery provided with the positive electrode is subjected to the first charge, the positive electrode active material and the sacrificial positive electrode agent release lithium ions and undergo oxidation reaction, and release electrons to the negative electrode through the external circuit. As a result, the lithium ions from the positive electrode active material and the sacrificial positive electrode agent are deposited on the surface of the negative electrode. In addition, when such lithium secondary battery is subjected to discharge after the first charge (i.e., first discharge), the lithium metal deposited on the surface of the negative electrode is electrolytically dissolved, and the electrons move from the negative electrode to the positive electrode through the external circuit. Subsequently, the positive electrode active material receives the lithium ions and undergoes reduction reaction, on the other hand, the sacrificial positive electrode agent substantially does not undergo reduction reaction within the discharge potential range of the positive electrode active material, and substantially cannot return to the state before the oxidation reaction. Therefore, when the above-described lithium secondary battery is subjected to discharge after the first charge, the lithium metal from the positive electrode active material is electrolytically dissolved from the negative electrode, and in contrast, most of the lithium metal from the sacrificial positive electrode agent remains on the negative electrode, and even after the battery is completely discharged, a part of the lithium metal remains on the negative electrode. This remaining lithium metal becomes the basis for further deposition of lithium metal on the negative electrode in the charging step after the first discharge, and thus the lithium metal is easily and uniformly deposited on the negative electrode in the charging step after the first discharge. As a result, the lithium secondary battery is in a tendency to have more excellent cycle characteristics.

[0085] The sacrificial positive electrode agent is not particularly limited, and examples thereof include lithium oxides such as Li2O2; lithium nitrides such as Li3N; lithium sulfide-based solid solutions such as Li2S-P2S5, Li2S-LiCl, Li2S-LiBr, and Li2S-LiI; Li 1+x (Ti 1- y Fey ) 1-x O2(0 < x < 0.25, 0.4 < y < 0.9), Li 2-x Ti 1-z Fe z O 3-y (0 < x < 2, 0 < y < 1, 0.05 < z < 0.95), Li5FeO4, and the like. The sacrificial cathode agent can be used alone or in combination of two or more.

[0086] The content of the sacrificial cathode agent is not particularly limited, and is, for example, 1.0 mass% or more and 30.0 mass% or less, 2.0 mass% or more and 20.0 mass% or less, 3.0 mass% or more and 15.0 mass% or less, with respect to the total amount of the cathode active material composition.

[0087] In addition, the total amount of the cathode active material and the sacrificial cathode agent is not particularly limited, and is, for example, 60 mass% or more and 100 mass% or less, 70 mass% or more and 99 mass% or less, 80 mass% or more and 98 mass% or less, 85 mass% or more and 97 mass% or less, 90 mass% or more and 96 mass% or less, with respect to the total amount of the cathode active material composition.

[0088] 1.1.6, Method for manufacturing the cathode

[0089] The cathode 30 of the present embodiment is manufactured, for example, by the following operation, without particular limitation. A metal layer 322 is formed by evaporation, sputtering, electrolytic plating, or adhesion using an adhesive on both surfaces of a resin layer 320, thereby forming a current collector film to obtain a cathode current collector 32 of the present embodiment. Then, the above-mentioned cathode active material, binder, sacrificial cathode agent, and other additives are mixed as necessary to obtain a cathode active material composition. The cathode active material or the obtained cathode active material composition is coated on both surfaces or one surface of the above-mentioned cathode current collector 32, and is subjected to press molding to form a cathode active material layer 34 on both surfaces or one surface of the cathode current collector 32, thereby obtaining a molded body. The obtained molded body is subjected to blanking processing to be punched to a predetermined size, thereby obtaining the cathode 30 of the present embodiment.

[0090] In the above-mentioned manufacturing method, a cathode current collector 32 having the metal layer 322 without the resin layer 320 can also be used instead of the cathode current collector 32 having the current collector film.

[0091] 1.2, Anode

[0092] The anode 10 of the present embodiment has an anode current collector 12.

[0093] 1.2.1, Anode current collector

[0094] The negative electrode current collector 12 of the present embodiment can have a current collector film including a resin layer 120 containing polyethylene terephthalate and metal layers 122 provided on both surfaces of the resin layer 120, and can have the metal layers 122 without the resin layer 120. In the case of having the current collector film, the metal layers 122 are formed by evaporation, sputtering, electrolytic plating on the surfaces of both sides of the resin layer 120, or adhesion with an adhesive or the like.

[0095] 1.2.1.1, Resin layer

[0096] The resin layer 120 of the negative electrode current collector 12 of the present embodiment is an insulator, and prevents the metal layers 122 provided on both surfaces of the resin layer 120 from being in conduction with each other. The resin constituting the resin layer 120 is not particularly limited, and can be constituted by a sheet-shaped (film-shaped) or fiber-shaped resin, for example. As the resin, polyethylene terephthalate (PET) is contained, and other resins can be further contained. As the other resins, the same resins as the resin layer 320 of the positive electrode current collector 32 can be listed. In addition, the resin layer 120 can appropriately contain other additives in addition to the above-described resins according to desired physical properties, and the same additives as the resin layer 320 of the positive electrode current collector 32 can be listed as the other additives.

[0097] The content of the resin and the content of PET can be the same as the content of the resin and the content of PET in the positive electrode current collector 32.

[0098] The thickness of the resin layer 120 can be the same as the thickness of the resin layer 320 in the positive electrode current collector 32.

[0099] 1.2.1.2, Metal layer

[0100] As the metal constituting the metal layer 122 of the negative electrode current collector 12 of the present embodiment, any metal that can be used as a current collector can be used without particular limitation, and for example, a metal constituted by at least one selected from the group consisting of copper, nickel, titanium, iron, other metals that do not react with lithium, and alloys thereof, and stainless steel (SUS) can be listed, and preferably, a metal constituted by at least one selected from the group consisting of copper, nickel, and alloys thereof, and SUS can be listed.

[0101] When the negative electrode current collector 12 has the current collector film, the thickness of the metal layer 122 can be the same as the thickness of the metal layer 322 in the positive electrode current collector 32 having the current collector film.

[0102] When the negative electrode current collector 12 has the metal layer 122 without the resin layer 120, the thickness of the metal layer 122 can be the same as the thickness of the metal layer 322 in the positive electrode current collector 32 having the metal layer 322 without the resin layer 320.

[0103] 1.2.2, Negative electrode active material

[0104] The negative electrode active material refers to a substance in which an electrode reaction, i.e., an oxidation reaction and a reduction reaction, occurs at the negative electrode. Specifically, as the negative electrode active material of the present embodiment, lithium metal, and a host substance of lithium element (lithium ion or lithium metal) can be exemplified. The host substance of lithium element refers to a substance provided to hold lithium ion or lithium metal at the negative electrode. As such a holding mechanism, for example, intercalation, alloying, and insertion of metal clusters, etc. can be exemplified, and intercalation is typical.

[0105] The negative electrode active material is not particularly limited, and for example, lithium metal and an alloy containing lithium metal, a carbon-based substance, a metal oxide, and a metal alloyed with lithium and an alloy containing the metal, etc. can be exemplified. The carbon-based substance is not particularly limited, and for example, graphene, graphite, hard carbon, carbon nanotube, etc. can be exemplified. The metal oxide is not particularly limited, and for example, titanium oxide-based compounds, cobalt oxide-based compounds, etc. can be exemplified. The metal alloyed with lithium is not particularly limited, and for example, silicon, germanium, tin, lead, aluminum, and gallium can be exemplified.

[0106] The anode-free lithium secondary battery of the present embodiment is configured such that the negative electrode 10 is composed of the negative electrode current collector 12 having no negative electrode active material, and uses the electrolyte described later as the electrolyte.

[0107] The anode-free battery is configured such that the negative electrode 10 has no negative electrode active material and is composed only of the negative electrode current collector 12 before the first charge of the battery. Therefore, after the first charge thereof, the lithium metal is deposited on the negative electrode 10, and the deposited lithium metal is electrolytically dissolved to perform charge and discharge. Therefore, in the anode-free battery, the volume occupied by the negative electrode active material and the mass of the negative electrode active material are reduced, and the volume and the mass of the entire battery are small, and thus the energy density is high in principle.

[0108] In the anode-free battery of the present specification, the negative electrode "having no negative electrode active material" means that the negative electrode has no or substantially no negative electrode active material. The negative electrode substantially has no negative electrode active material means that the content of the negative electrode active material in the negative electrode is 10.0 mass% or less with respect to the entire negative electrode. The content of the negative electrode active material in the negative electrode 10 of the anode-free battery is preferably 5.0 mass% or less, 1.0 mass% or less, 0.1 mass% or less, 0.0 mass% with respect to the entire negative electrode 10. By the negative electrode 10 having no negative electrode active material or the content of the negative electrode active material in the negative electrode 10 being within the above range, the energy density of the lithium secondary battery is increased.

[0109] In addition, in the anodeless battery of the present specification, the battery "before the first charge" means a state from when the battery is assembled to the first charge. In addition, the battery "at the end of discharge" means a state in which the voltage of the battery is preferably 1.0 V or more and 3.8 V or less, 1.0 V or more and 3.0 V or less.

[0110] The anodeless battery of the present embodiment can have a content of lithium metal of 10.0 mass% or less (preferably 5.0 mass% or less, 1.0 mass% or less) with respect to the entire negative electrode 10, in the case where the voltage of the battery is 1.0 V or more and 3.5 V or less; 10.0 mass% or less (preferably 5.0 mass% or less, 1.0 mass% or less) with respect to the entire negative electrode 10, in the case where the voltage of the battery is 1.0 V or more and 3.0 V or less; or 10.0 mass% or less (preferably 5.0 mass% or less, 1.0 mass% or less) with respect to the entire negative electrode 10, in the case where the voltage of the battery is 1.0 V or more and 2.5 V or less.

[0111] In addition, in the anodeless battery of the present embodiment, the mass M 3.0 of the lithium metal deposited on the negative electrode 10 in a state where the voltage of the battery is 3.0 V 4.2 is preferably 40.0% or less, 38.0% or less, 35.0% or less, with respect to the mass M 3.0 of the lithium metal deposited on the negative electrode 10 in a state where the voltage of the battery is 4.2 V 4.2 . 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.

[0112] The average thickness of the negative electrode 10 of the anodeless battery is not particularly limited, and is, for example, 3.0 μm or more and 30.0 μm or less. From the viewpoint of reducing the volume occupied by the negative electrode 10 in the anodeless battery and improving the energy density, the average thickness of the negative electrode 10 is preferably 4.0 μm or more and 20.0 μm or less, 5.0 μm or more and 18.0 μm or less, or 6.0 μm or more and 15 μm or less.

[0113] 1.2.3, Method for manufacturing negative electrode

[0114] The negative electrode 10 of the present embodiment is manufactured, for example, by the following operation, without particular limitation. A metal layer 122 is formed by evaporation, sputtering, electrolytic plating on both surfaces of the resin layer 120, or adhesion using an adhesive, thereby forming a current collector film, to obtain the negative electrode current collector 12 of the present embodiment. In a lithium secondary battery of the anodeless type, since no negative electrode active material is present, the above-described negative electrode current collector 12 can be used as the negative electrode 10 of the present embodiment.

[0115] In addition, in the above-described manufacturing method, a negative electrode current collector 12 having the metal layer 122 and not having the resin layer 120 can be used instead of the negative electrode current collector 12 having the current collector film.

[0116] 1.3 Separator

[0117] As the separator 20 of the present embodiment, any separator having a function of physically and / or electrically separating the positive electrode 30 from the negative electrode 10 and a function of ensuring ionic conduction of lithium ions is acceptable, without particular limitation. As such a separator, for example, an insulating porous member, a polymer electrolyte, a gel electrolyte, and an inorganic solid electrolyte can be cited, and typically at least one selected from the group consisting of an insulating porous member, a polymer electrolyte, and a gel electrolyte is preferable. In addition, as the separator 20, one member alone can be used, or two or more members can be used in combination.

[0118] As the separator 20, an insulating porous member, a polymer electrolyte, or a gel electrolyte alone or in combination of two or more is preferably used. Further, in the case where an insulating porous member alone is used as the separator 20, the lithium secondary battery needs to further have an electrolyte solution.

[0119] The above-described polymer electrolyte is not particularly limited, and for example, a solid polymer electrolyte mainly containing a polymer and an electrolyte; and a semi-solid polymer electrolyte mainly containing a polymer, an electrolyte, and a plasticizer can be cited.

[0120] The above-described gel electrolyte is not particularly limited, and for example, a gel electrolyte mainly containing a polymer and a liquid electrolyte (i.e., a solvent and an electrolyte) can be cited.

[0121] The polymer contained in the polymer electrolyte and the gel electrolyte is not particularly limited, and examples thereof include polymers containing oxygen atom-containing functional groups such as ethers and esters, polar groups such as halogen groups, and cyano groups. Specifically, examples thereof include resins having an oxirane unit in the main chain and / or side chain such as polyethylene oxide (PEO), resins having an oxolane unit in the main chain and / or side chain such as polypropylene oxide (PPO), acrylic resins, vinyl resins, ester resins, nylon resins, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polysiloxane, polyphosphazene, polymethyl methacrylate, polyamide, polyimide, aromatic polyamide, polylactic acid, polyurethane, polyacetal, polysulfone, polyethylene carbonate, polypropylene carbonate, and polytetrafluoroethylene. The resins described above can be used alone or in combination of two or more.

[0122] As the electrolyte contained in the polymer electrolyte and the gel electrolyte, examples of salts of Li, Na, K, Ca, and Mg, and the like can be given. Typically, in the present embodiment, the polymer electrolyte and the gel electrolyte contain a lithium salt.

[0123] The lithium salt is not particularly limited, and examples thereof include 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, and preferably at least one selected from the group consisting of LiPF6, LiN(SO2F)2, LiN(SO2CF3)2, and LiN(SO2CF3CF3). The salt or the lithium salt described above can be used alone or in combination of two or more.

[0124] The ratio of the polymer to the lithium salt in the polymer electrolyte and the gel electrolyte can be determined depending on the ratio of the polar group possessed by the polymer to the lithium atom possessed by the lithium salt. For example, in the case where the polymer has an oxygen atom, the ratio can be determined depending on the ratio of the number of oxygen atoms possessed by the polymer to the number of lithium atoms possessed by the lithium salt ([Li] / [O]). In the polymer electrolyte and the gel electrolyte, the ratio of the polymer to the lithium salt can be adjusted so as to be, for example, 0.02 or more and 0.20 or less, 0.03 or more and 0.15 or less, or 0.04 or more and 0.12 or less, in terms of the above ratio ([Li] / [O]).

[0125] The solvent contained in the gel electrolyte is not particularly limited, and for example, one kind alone or two or more kinds in combination among the solvents that can be contained in the electrolyte solution described later can be used. Examples of the preferred solvent are also the same as the solvents in the electrolyte solution described later.

[0126] The plasticizer contained in the semi-solid polymer electrolyte is not particularly limited, and for example, the same components as the solvents that can be contained in the gel electrolyte and various oligomers can be listed.

[0127] In the case where the separator 20 contains an insulating porous member, the member exhibits ion conductivity by filling a substance having ion conductivity in the fine pores of the member. Therefore, in the present embodiment, for example, the electrolyte of the present embodiment and the gel electrolyte containing the electrolyte of the present embodiment are filled.

[0128] The material constituting the insulating porous member is not particularly limited, and for example, insulating polymeric materials, specifically, polyethylene (PE) and polypropylene (PP) can be listed. That is, the separator 20 can be a porous polyethylene (PE) film, a porous polypropylene (PP) film, or a laminated structure thereof.

[0129] The separator 20 can be covered (coated) with a separator covering layer. The separator covering layer can cover both surfaces of the separator 20, or can cover only one surface. From the viewpoint of improving the cycle characteristics of the lithium secondary battery in the present embodiment, it is preferred that both surfaces of the separator 20 be covered. Furthermore, the separator covering layer in the present embodiment is a uniform continuous film-like covering layer, for example, a uniform continuous film-like covering layer in an area of 50% or more of the surface of the separator 20.

[0130] The separator covering layer is not particularly limited, and for example, polyvinylidene fluoride (PVdF), a composite of styrene butadiene rubber and carboxymethyl cellulose (SBR-CMC), and a layer containing a binder such as polyacrylic acid (PAA) are preferred. The separator covering layer can be inorganic particles such as silica, alumina, titania, zirconia, magnesium hydroxide added to the above binder.

[0131] The average thickness of the separator 20 containing the separator covering layer is not particularly limited, and for example, 3.0 μm or more and 40.0 μm or less. In the lithium secondary battery, from the viewpoint of reliably separating the positive electrode 30 and the negative electrode 10 while reducing the volume occupied by the separator 20 in the battery, the average thickness of the separator 20 is preferably 5.0 μm or more and 30.0 μm or less, 7.0 μm or more and 10.0 μm or less, 10.0 μm or more and 20.0 μm or less.

[0132] 1.4, Electrolyte Solution

[0133] The electrolytic solution of the present embodiment contains a chain carbonate and / or a chain ether, vinylene carbonate, and lithium difluorophosphate. The electrolytic solution can be impregnated into the separator 20, or the electrolytic solution can be enclosed together with the laminate of the negative electrode 10, the separator 20, and the positive electrode 30.

[0134] 1.4.1. Electrolyte

[0135] The electrolyte of the present embodiment can be used using an electrolyte that can be contained in a polymer electrolyte and a gel electrolyte, in particular, alone or in combination of two or more of the above-described lithium salts. The preferable lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiN(SO2F)2). A lithium secondary battery using an electrolytic solution containing these electrolytes is in a tendency to have excellent battery performance such as cycle characteristics.

[0136] The concentration of the electrolyte of the present embodiment in the electrolytic solution is not particularly limited, and is, for example, 0.1 M or more and 6.0 M or less, 0.2 M or more and 5.0 M or less, 0.3 M or more and 4.0 M or less, 0.4 M or more and 3.0 M or less, or 0.5 M or more and 2.0 M or less.

[0137] 1.4.2. Solvent

[0138] The solvent of the electrolytic solution of the present embodiment contains a chain carbonate and / or a chain ether. The chain carbonate refers to a carbonate that does not have a cyclic structure such as an aromatic ring, an alicyclic ring, a monocyclic ring, a heterocyclic ring, and the like. The chain carbonate is not particularly limited, and examples thereof include dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, vinylene carbonate, propylene carbonate, chloroethylene carbonate, and a compound in which the hydrogen of some or all of these carbonates is replaced with fluorine. Among them, dimethyl carbonate and ethylmethyl carbonate are preferable. The chain ether refers to an ether that does not have a cyclic structure such as an aromatic ring, an alicyclic ring, a monocyclic ring, a heterocyclic ring, and the like. The chain ether is not particularly limited, and examples thereof 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, triglyme, tetraglyme, dimethoxyethane, diethoxyethane, dimethoxypropane, dimethoxybutane, and diglyme.

[0139] The solvent of the electrolytic solution of the present embodiment can further contain another solvent other than the above-described chain carbonate and chain ether. The other solvent is not particularly limited, and examples thereof include a nonaqueous solvent having a fluorine atom (hereinafter, referred to as "fluorinated solvent") and a nonaqueous solvent not having a fluorine atom (hereinafter, referred to as "non-fluorinated solvent").

[0140] The fluorinated solvent as the other solvent is not particularly limited, and examples thereof include derivatives of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, derivatives of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and derivatives of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, and the like.

[0141] The non-fluorinated solvent as the other solvent is not particularly limited, and examples thereof include acetonitrile, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, trimethyl phosphate, triethyl phosphate, and 12-crown-4, and the like.

[0142] When the solvent contains the chain carbonate and does not contain the chain ether, the content of the chain carbonate with respect to the total amount of the electrolyte solution is preferably 40 vol% or more and 100 vol% or less, 50 vol% or more and 100 vol% or less, 60 vol% or more and 100 vol% or less, or 70 vol% or more and 100 vol% or less. In addition, it is preferably 100 vol%.

[0143] When the solvent contains the chain ether and does not contain the chain carbonate, the content of the chain ether with respect to the total amount of the electrolyte solution is preferably 40 vol% or more and 100 vol% or less, 50 vol% or more and 100 vol% or less, 60 vol% or more and 100 vol% or less, or 70 vol% or more and 100 vol% or less. In addition, it is preferably 100 vol%.

[0144] When the solvent contains the chain carbonate and the chain ether, the total content of the chain carbonate and the chain ether with respect to the total amount of the electrolyte solution is preferably 40 vol% or more and 100 vol% or less, 50 vol% or more and 100 vol% or less, 60 vol% or more and 100 vol% or less, or 70 vol% or more and 100 vol% or less. In addition, it is preferably 100 vol%.

[0145] The fluorinated solvent and / or the non-fluorinated solvent as the other solvent described above can be used alone or two or more thereof can be used in any ratio. The content of the fluorinated solvent and the non-fluorinated solvent is not particularly limited, and the ratio of the fluorinated solvent with respect to the entire solvent can be 0 vol% or more and 60 vol% or less, and the ratio of the non-fluorinated solvent with respect to the entire solvent can be 0 vol% or more and 60 vol% or less.

[0146] 1.4.3, Additives

[0147] The electrolyte solution of the present embodiment contains vinylene carbonate and lithium difluorophosphate. The content of vinylene carbonate is preferably 0.1 mass% or more and 5.0 mass% or less, 0.2 mass% or more and 4.5 mass% or less, 0.3 mass% or more and 4.0 mass% or less, 0.4 mass% or more and 3.5 mass% or less, 0.5 mass% or more and 3.0 mass% or less, or 0.6 mass% or more and 2.5 mass% or less, with respect to the total amount of the solvent. By the content of vinylene carbonate being within the above range, there is a tendency to have more excellent performance stability at high temperatures.

[0148] In addition, the content of lithium difluorophosphate is preferably 0.1 mass% or more and 5.0 mass% or less, 0.2 mass% or more and 4.5 mass% or less, 0.3 mass% or more and 4.0 mass% or less, 0.4 mass% or more and 3.5 mass% or less, 0.5 mass% or more and 3.0 mass% or less, or 0.6 mass% or more and 2.5 mass% or less, with respect to the total amount of the solvent. By the content of lithium difluorophosphate being within the above range, there is a tendency to have more excellent performance stability at high temperatures.

[0149] By adding lithium bis(fluorosulfonyl)imide, the occurrence of the above-described redox shuttle reaction is also suppressed, and in the case of storing a lithium secondary battery in a charged state at high temperatures, there is a tendency to be able to maintain the high performance of the lithium secondary battery such as capacity retention rate.

[0150] The content of lithium bis(fluorosulfonyl)imide is preferably 0.1 mass% or more and 12.0 mass% or less, 0.5 mass% or more and 10.0 mass% or less, or 1.0 mass% or more and 6.0 mass% or less, with respect to the total amount of the solvent.

[0151] 1.5. Usage

[0152] A usage of the lithium secondary battery represented by the anodeless battery will be described. In the usage of the lithium secondary battery, a positive electrode terminal and a negative electrode terminal for connecting the battery to an external circuit are joined to the positive electrode current collector 32 and the negative electrode current collector 12, respectively. The lithium secondary battery is charged and discharged by connecting the negative electrode terminal to one end of the external circuit and the positive electrode terminal to the other end of the external circuit. In the positive electrode terminal and the negative electrode terminal, the lithium secondary battery is charged by applying a voltage to cause current to flow from the negative electrode terminal (negative electrode) to the positive electrode terminal (positive electrode) through the external circuit. For the lithium secondary battery after charging, the lithium secondary battery is discharged by connecting the positive electrode terminal and the negative electrode terminal via a desired external circuit.

[0153] In the anodeless battery, it is presumed that a solid electrolyte interface layer (SEI layer) is formed on the surface of the negative electrode 10 (the interface between the negative electrode 10 and the separator 20) by the first charging, but the battery can also not have the SEI layer. By charging the anodeless battery, deposition of lithium metal occurs at the interface between the negative electrode 10 and the SEI layer, the interface between the negative electrode 10 and the separator 20, and / or the interface between the SEI layer and the separator 20. In addition, the anodeless battery is discharged, and the deposition of lithium metal that occurs on the negative electrode 10 is electrolytically eluted. In the case where the SEI layer is formed in the battery, the deposition of lithium metal that occurs at at least either of the interface between the negative electrode 10 and the SEI layer and the interface between the SEI layer and the separator 20 is electrolytically eluted.

[0154] 1.6, Manufacturing method

[0155] As the manufacturing method of the anodeless battery, any method that can manufacture the lithium secondary battery having the above-described configuration is acceptable, and is not particularly limited, and for example, the following methods can be listed.

[0156] First, the positive electrode 30 of the present embodiment is obtained by the above-described manufacturing method of the positive electrode.

[0157] Next, the negative electrode 10 of the present embodiment is obtained by the above-described manufacturing method of the negative electrode. In addition, the negative electrode 10 of the anodeless battery does not have a negative electrode active material.

[0158] The positive electrode current collector 32 and the negative electrode current collector 12 of the present embodiment can each have a current collector film having a resin layer containing polyethylene terephthalate and a metal layer provided on both surfaces of the resin layer, can have only the positive electrode current collector 32 having the current collector film and the negative electrode current collector 12 having the metal layer 122 without the resin layer 120, or can have only the negative electrode current collector 12 having the current collector film and the positive electrode current collector 32 having the metal layer 322 without the resin layer 320.

[0159] Next, the separator 20 having the above-described configuration is prepared. The separator 20 can be manufactured by a publicly known method, or a commercially available product can be used. In addition, a functional buffer layer that is a fibrous or porous layer that mitigates the volume expansion / contraction accompanying the dissolution / deposition of lithium metal can be provided between the separator 20 and the negative electrode 10. The functional buffer layer preferably has ion conductivity or electrical conductivity, but can also not have them.

[0160] By sequentially stacking the positive electrode 30, the separator 20, and the negative electrode 10 obtained by the above operations with the positive electrode 30 facing the separator 20, a laminate is obtained. By enclosing the obtained laminate and an electrolyte solution in a sealed container, an anodeless battery can be obtained. The sealed container is not particularly limited, and for example, a laminated film can be listed.

[0161] Multiple positive electrodes 30 and negative electrodes 10 can be stacked alternately with a separator 20 between the positive electrode 30 and the negative electrode 10. By doing so, the battery performance, such as energy density, tends to be further improved.

[0162] [Lithium-ion battery]

[0163] For example, such as Figure 4 As shown, a lithium-ion battery 100B, as an example of a lithium secondary battery according to this embodiment, includes: a positive electrode 30 having a positive current collector 32 and a positive active material layer 34, a negative electrode 10 having a negative current collector 12 and a negative active material layer 14, an electrolyte, and a separator 20. The positive current collector 32 and / or the negative current collector 12 have a current collector film, which comprises a resin layer containing polyethylene terephthalate and metal layers disposed on both sides of the resin layer. The positive active material layer 34 contains one or more materials of the general formula: Li z Ni x Co y M 1-x-y O 2+α The compound is defined as follows: 0.5≤x≤1.0, 0≤y≤0.35, 0.9≤z≤1.3, -0.2≤α≤0.15, M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F and B, and the electrolyte contains chain carbonates and / or chain ethers, vinylene carbonate, and lithium difluorophosphate.

[0164] A lithium-ion battery (hereinafter also referred to as "LIB") has lithium (lithium ions or lithium metal) as the main material in its negative electrode. The battery is charged to fill this material with lithium, and discharged by releasing lithium from the main material. LIBs differ from anode-less batteries, particularly in that the negative electrode has a lithium-based main material. The materials, composition, and preferred embodiments of the positive electrode 30, electrolyte, separator 20, and negative electrode 10 are the same as described above, except as otherwise provided below.

[0165] As the negative electrode 10 of LIB, any material containing lithium elements (lithium ions or lithium metal) as the main negative electrode active material can be used; there are no particular limitations, and the materials and structures described above can be used.

[0166] like Figure 5 As shown, a negative electrode active material layer 14 can be formed on at least one side of the negative electrode current collector 12 to become a negative electrode 10B. Although not shown, a negative electrode active material layer 14 can also be formed on both sides of the negative electrode current collector 12 to become a negative electrode 10.

[0167] The average thickness of the negative electrode 10 of the LIB is not particularly limited and is, for example, 5.0 μm or more and 100.0 μm or less. From the viewpoint of improving the capacity and / or energy density of the battery, it is preferable to be 8.0 μm or more and 50.0 μm or less, 10.0 μm or more and 40.0 μm or less, or 10.0 μm or more and 20.0 μm or less.

[0168] The LIB can be produced using known materials and known production methods, and can be produced in the same manner as the production method of the anodeless battery described above, except that the lithium element main body is used in the negative electrode 10.

[0169] The production method of the negative electrode 10 having the negative electrode active material is not particularly limited and is, for example, as follows. The negative electrode active material described above, the binder described below, the conductive aid, and other additives are mixed as necessary to obtain a negative electrode active material composition. The negative electrode active material or the obtained negative electrode active material composition is coated on both surfaces or one surface of the negative electrode current collector 12 described above, and is subjected to press molding to form a negative electrode active material layer 14 on both surfaces or one surface of the negative electrode current collector 12, thereby obtaining a molded body. The obtained molded body is punched to a predetermined size by punching processing, thereby obtaining the negative electrode 10 of the present embodiment.

[0170] In addition, in the production method described above, the negative electrode current collector 12 composed only of the metal layer 122 can be used instead of the negative electrode current collector 12 having the current collector film.

[0171] The content of the negative electrode active material with respect to the total amount of the negative electrode active material composition is not particularly limited and is, for example, 60 mass% or more and 100 mass% or less, 70 mass% or more and 99 mass% or less, or 80 mass% or more and 98 mass% or less.

[0172] The binder of the negative electrode active material composition of the present embodiment is not particularly limited and is, for example, the same binder as the binder of the positive electrode active material composition. In addition, the content of the binder of the negative electrode active material composition is not particularly limited and is, for example, the same degree as the content of the binder of the positive electrode active material composition.

[0173] The conductive aid of the negative electrode active material composition of the present embodiment is not particularly limited and is, for example, the same conductive aid as the conductive aid of the positive electrode active material composition. In addition, the content of the conductive aid of the negative electrode active material composition is not particularly limited and is, for example, the same degree as the content of the conductive aid of the positive electrode active material composition.

[0174] The method of depositing the negative electrode active material layer 14 on the negative electrode current collector 12 is not limited to compression molding. Examples include: a method of containing a thermosetting compound in the negative electrode active material composition and curing it by heating; a method of containing a photocurable compound in the negative electrode active material composition and curing it by light irradiation; and a method of curing the negative electrode active material composition as a two-component curable composition by mixing the two components.

[0175] [Lithium metal battery]

[0176] A lithium metal battery (hereinafter also referred to as "LMB"), as an example of a lithium secondary battery in this embodiment, is manufactured using an electrode with lithium metal or a lithium metal alloy on its surface, or elemental lithium metal, as the negative electrode. Similar to an anode-less battery, the LMB is charged and discharged by electrolyzing and dissolving lithium metal deposited on the surface of the negative electrode.

[0177] Unlike anode-less batteries, LMB batteries have lithium metal as the active material at the negative electrode before the first charge.

[0178] The lithium metal battery of this embodiment includes: a positive electrode 30, a negative electrode 10 containing lithium metal opposite to the positive electrode 30, a separator 20 disposed between the positive electrode 30 and the negative electrode 10, and an electrolyte. The materials, structures, and preferred embodiments of the positive electrode 30, electrolyte, separator 20, and negative electrode 10 are the same as those described above, except for the aspects described later.

[0179] As the negative electrode 10 of the LMB, any negative electrode containing lithium metal or a lithium metal alloy as the negative electrode active material is acceptable; there are no particular limitations, and the aforementioned materials and structures can be used. LMBs using a negative electrode 10 containing lithium metal or a lithium metal alloy that has a high specific capacity and low redox potential typically result in batteries with higher energy density than lithium-ion batteries. Examples of such a negative electrode 10 include: a lithium metal electrode; an electrode in which a rolled lithium metal foil is bonded to the surface of a conductive metal foil such as copper to form a coating material; an electrode obtained by pre-electrochemically depositing lithium metal on the surface of a metal foil such as copper; and an electrode in which lithium metal is vacuum-deposited. From the viewpoint of further improving the effect of this embodiment, an electrode formed by bonding a lithium metal foil to the surface of a conductive metal such as copper or an electrode obtained by electrochemically depositing lithium metal is preferred; an electrode formed by bonding a lithium metal foil to the surface of a conductive metal such as copper is more preferred.

[0180] like Figure 5 As shown, a negative electrode active material layer 14 can be formed on at least one side of the negative electrode current collector 12 to become a negative electrode 10B. Although not shown, a negative electrode active material layer 14 can also be formed on both sides of the negative electrode current collector 12 to become a negative electrode 10.

[0181] The average thickness of the negative electrode 10 of the LMB is not particularly limited, and is, for example, 5.0 μm or more and 100.0 μm or less. From the viewpoint of improving the capacity and / or energy density of the battery, it is preferable to be 8.0 μm or more and 50.0 μm or less, 10.0 μm or more and 40.0 μm or less, or 10.0 μm or more and 20.0 μm or less.

[0182] The LMB can be produced using a publicly known material and a publicly known production method, and can be produced in the same manner as the production method of the above-described anodeless battery, except that lithium metal or a lithium metal alloy is used as the negative electrode active material in the negative electrode 10.

[0183] The production method of the negative electrode 10 having the negative electrode active material is not particularly limited, and is, for example, as described below. The above-described negative electrode active material, the binder described below, the conductive aid, and other additives are mixed as necessary to obtain a negative electrode active material composition. The negative electrode active material or the obtained negative electrode active material composition is coated on both surfaces or one surface of the above-described negative electrode current collector 12, and is subjected to press molding to form a negative electrode active material layer 14 on both surfaces or one surface of the negative electrode current collector 12, thereby obtaining a molded body. The obtained molded body is punched to a predetermined size by a punching process, thereby obtaining the negative electrode 10 of the present embodiment.

[0184] In addition, in the above-described production method, a negative electrode current collector 12 composed only of the metal layer 122 can be used instead of the negative electrode current collector 12 having the current collector film.

[0185] The content of the negative electrode active material with respect to the total amount of the negative electrode active material composition is not particularly limited, and is, for example, 60 mass% or more and 100 mass% or less, 70 mass% or more and 99 mass% or less, or 80 mass% or more and 98 mass% or less.

[0186] The binder of the negative electrode active material composition of the present embodiment is not particularly limited, and is, for example, the same binder as the binder of the positive electrode active material composition. In addition, the content of the binder of the negative electrode active material composition is not particularly limited, and is, for example, the same degree as the content of the binder of the positive electrode active material composition.

[0187] The conductive aid of the negative electrode active material composition of the present embodiment is not particularly limited, and is, for example, the same conductive aid as the conductive aid of the positive electrode active material composition. In addition, the content of the conductive aid of the negative electrode active material composition is not particularly limited, and is, for example, the same degree as the content of the conductive aid of the positive electrode active material composition.

[0188] As a method of disposing the negative electrode active material layer 14 on the negative electrode current collector 12, not limited to press molding, for example, a method of containing a thermosetting compound in the negative electrode active material composition and curing it by heating, a method of containing a photocurable compound in the negative electrode active material composition and curing it by light irradiation, a method of curing the negative electrode active material composition as a two-component curable composition by two-component mixing, and the like can be exemplified.

[0189] Example

[0190] Hereinafter, the present application will be more specifically described using examples and comparative examples. The present application is not limited by the examples below. In addition, unless otherwise specifically noted, at room temperature (25°C), 10 5 Pa.

[0191] 1. Production of lithium ion secondary battery

[0192] The lithium ion secondary batteries of the examples and comparative examples were produced by the following operations.

[0193] 1.1. Production of negative electrode

[0194] As the negative electrode current collector 12, a current collector film obtained by vapor-depositing 1.0 μm of Cu as a metal layer 122 on both sides of a 6 μm thick film-like polyethylene terephthalate (PET) as a resin layer 120 was prepared. Then, a negative electrode active material composition obtained by mixing 97.0 parts by mass of graphite as a negative electrode active material, 0.5 parts by mass of carbon black as a conductive aid, and 1.5 parts by mass of carboxymethyl cellulose (CMC) as a binder, 1.0 parts by mass of styrene-butadiene rubber (SBR) as a solvent were prepared. The negative electrode active material composition was coated and pressed on one side of the negative electrode current collector 12 so that the weight per unit area was 15 mg / cm 2 of the negative electrode active material layer 14 on one side of the negative electrode current collector 12, and a molded body was obtained. The molded body was cut into a predetermined size (4 x 4 cm). Thus, the negative electrode 10 was obtained. In Table 1, the negative electrode 10 is referred to as "current collector film type".

[0195] Alternatively, as the negative electrode current collector 12, a 8 μm thick copper foil was prepared, and the negative electrode active material composition was coated and pressed on one side thereof in the same manner as described above, and a molded body was obtained in which the negative electrode active material layer 14 was formed on one side of the negative electrode current collector 12. The molded body was cut into a predetermined size (4 x 4 cm). Thus, the negative electrode 10 was obtained. In Table 1, the negative electrode 10 is referred to as "metal type".

[0196] 1.2. Production of positive electrode

[0197] As the positive electrode current collector 32, a current collector film was obtained by vapor-depositing Al as a 1.0 μm metal layer 322 on both sides of a 6.0 μm thick film-like PET as a resin layer 320. Then, 96 parts by mass of LiNi as the positive electrode active material were prepared by mixing it in N-methylpyrrolidone (NMP) as a solvent. 0.8 Co 0.15 Al 0.05 A positive electrode active material composition was obtained by comprising O2, 2 parts by mass of carbon black as a conductive additive, and 2 parts by mass of polyvinylidene fluoride (PVDF) as a binder. This positive electrode active material composition was prepared such that its weight per unit area was 23 mg / cm². 2 The material is coated and pressed onto one side of the positive electrode current collector 32 in a specific manner, forming a positive electrode active material layer 34 on one side of the positive electrode current collector 32, thus obtaining a molded body. The molded body is then cut into a predetermined size (4×4cm). This yields the positive electrode 30. Furthermore, in Table 1, this positive electrode 30 is referred to as the "current collector film type".

[0198] 1.3 Preparation of partitions

[0199] A sheet of polyethylene microporous membrane (thickness: 15 μm, 4 × 4 cm) coated with a mixture of polyvinylidene fluoride (PVDF) and Al2O3 was prepared as a separator 20.

[0200] 1.4 Electrolyte Preparation

[0201] In a solvent obtained by mixing one or more of the group consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in the volume ratios shown in Table 1, one or more of the group consisting of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) are dissolved at the concentrations shown in Table 1. Furthermore, one or more of the group consisting of lithium difluorophosphate (LiPO2F2) and vinylene carbonate (VC) are added to the solvent in such a manner that the content ratio relative to the total amount of the solvent (excluding LiPF6 and LiFSI, the total mass of one or more of the group consisting of EC, DMC, and EMC) is the value shown in Table 1. The electrolyte is adjusted by performing this operation.

[0202] 1.5 Battery Assembly

[0203] The positive electrode 30, the separator 20, and the negative electrode 10 obtained by the above operations were stacked in this order in such a manner that the positive electrode 30 was in contact with the separator 20, thereby obtaining a laminate. Further, 100 μm of an Al terminal and 100 μm of a Ni terminal were joined to the positive electrode current collector 32 and the negative electrode current collector 12, respectively, by ultrasonic welding, and then inserted into the laminated outer body. Then, the electrolyte obtained by the above operations was injected into the above-mentioned outer body. The outer body was sealed, thereby obtaining the lithium ion secondary batteries of the examples and the comparative examples.

[0204] 2. Evaluation

[0205] 2.1. Capacity retention rate (stability of performance at high temperature)

[0206] The lithium ion secondary batteries of the examples and the comparative examples were subjected to CC charging at 6 mA until the voltage became 4.2 V in a thermostat at 25°C, and then CV charging until the charge current became 3 mA while maintaining at 4.2 V. Thereafter, CC discharging was performed at 6 mA until the voltage became 2.7 V, and the obtained discharge capacity was taken as the rated capacity (mAh). In addition, CC charging means charging at a constant current value, CC discharging means discharging at a constant current value, and CV charging means charging at a constant voltage.

[0207] Next, the lithium ion secondary batteries of the examples and the comparative examples were subjected to CC charging at 6 mA until the voltage became 4.2 V in a thermostat at 25°C, and then CV charging until the charge current became 3 mA while maintaining at 4.2 V. Thereafter, a tape for preventing short circuit was adhered to the terminals, and the lithium ion secondary batteries of the examples and the comparative examples were taken out of the thermostat at 25°C and put into a thermostat at 60°C. After being left to stand in the thermostat at 60°C for two weeks, the lithium ion secondary batteries of the examples and the comparative examples were taken out of the thermostat at 60°C, and subjected to CC discharging at 6 mA until the voltage became 2.7 V. The obtained discharge capacity was taken as the residual capacity (mAh), and the capacity retention rate (%) after the high-temperature storage was calculated as [residual capacity] / [rated capacity] x 100, and recorded in the column of capacity retention rate in Table 1.

[0208] [Table 1]

[0209]

[0210] 3. Evaluation results

[0211] As is apparent from Table 1, even in the case of a lithium secondary battery which has a positive electrode 30 having a positive electrode current collector 32 and a positive electrode active material layer 34, a negative electrode 10 having a negative electrode current collector 12, an electrolyte, and a separator 20, and in which the positive electrode current collector 32 and / or the negative electrode current collector 12 has a current collector film having a resin layer containing polyethylene terephthalate and metal layers provided on both surfaces of the resin layer, and the positive electrode active material layer 34 contains one or more compounds represented by the general formula: Li z Ni x Co y M 1-x-y O 2+α wherein 0.5≤x≤1.0, 0≤y≤0.35, 0.9≤z≤1.3, -0.2≤α≤0.15, and M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B, and the electrolyte contains a chain carbonate and / or a chain ether, a vinylene carbonate, and lithium difluorophosphate, and even in the case of a lithium secondary battery which is stored at a high temperature in a charged state, the lithium secondary battery exhibits an excellent capacity retention rate.

[0212] Industrial applicability

[0213] The lithium secondary battery of the present application exhibits an excellent capacity retention rate even in the case of storage at a high temperature, and thus has industrial applicability as a power storage device for various uses.

[0214] Explanation of reference numerals

[0215] 100, 100A, 100B lithium secondary battery; 10, 10B, 10C negative electrode; 12 negative electrode current collector; 120 resin layer; 122 metal layer; 14 negative electrode active material layer; 20 separator; 30, 30B positive electrode; 32 positive electrode current collector; 320 resin layer; 322 metal layer; 34 positive electrode active material layer.

Claims

1. A lithium secondary battery, characterized by comprising: having: a positive electrode having a positive electrode current collector and a positive electrode active material layer; a negative electrode having a negative electrode current collector; an electrolyte solution; and a separator, the positive electrode current collector and / or the negative electrode current collector has a current collector film having a resin layer containing polyethylene terephthalate and a metal layer provided on both surfaces of the resin layer, the electrolyte solution contains a chain carbonate and / or a chain ether, a vinylene carbonate, and lithium difluorophosphate. The positive electrode active material layer contains one or more compounds represented by the general formula: Li z Ni x Co y M 1-x-y O 2+α wherein 0.5≤x≤1.0, 0≤y≤0.35, 0.9≤z≤1.3, -0.2≤α≤0.15, and M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B.

2. The lithium secondary battery according to claim 1, wherein 3. The lithium secondary battery according to claim 1, wherein The positive electrode active material layer contains one or more compounds represented by the general formula: Li z Ni x Co y M 1-x-y O 2+α wherein 0.7≤x≤1.0, 0≤y≤0.35, 0.9≤z≤1.3, -0.2≤α≤0.15, and M is one or more elements selected from the group consisting of Mn, Al, V, Mg, Mo, Nb, Ti, Zr, Fe, Cu, Cr, Zn, F, and B. the electrolyte solution contains the chain carbonate, the chain carbonate contains ethyl methyl carbonate and / or dimethyl carbonate.

4. The lithium secondary battery according to claim 1, wherein the content of the vinylene carbonate is 0.1 mass% or more and 5.0 mass% or less with respect to the total amount of the solvent contained in the electrolyte solution, the content of the lithium difluorophosphate is 0.1 mass% or more and 5.0 mass% or less with respect to the total amount of the solvent contained in the electrolyte solution.

5. The lithium secondary battery according to claim 1, wherein the electrolyte solution further contains lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide. ​

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