Nonaqueous electrolyte storage element and method for producing the same

Abstract

To provide a nonaqueous electrolyte power storage device which is arranged to use lithium metal as a negative electrode active material and which has a high capacity-keeping rate after the charge / discharge cycle.SOLUTION: A nonaqueous electrolyte power storage device comprises: a negative electrode; a positive electrode; and a nonaqueous electrolyte solution containing a fluorinated solvent. In the nonaqueous electrolyte power storage device, the negative electrode has a negative electrode active material layer containing lithium metal, the fluorinated solvent contains a fluorinated phosphoric ester, and the content of the fluorinated solvent in the whole solvent of the nonaqueous electrolyte solution is 99.0 vol.% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a non-aqueous electrolyte storage element. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc., due to their high energy density. The non-aqueous electrolyte secondary batteries generally have a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring ions between the electrodes. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries.

[0003] In recent years, in order to increase the capacity of non-aqueous electrolyte storage elements, there has been a demand for high-capacity negative electrodes. Lithium metal has a significantly larger discharge capacity per active material mass than graphite, which is currently widely used as a negative electrode active material for non-aqueous electrolyte storage elements. For this reason, non-aqueous electrolyte storage elements using lithium metal as the negative electrode active material have been proposed (see JP 2011-124154 A). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-124154 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in a nonaqueous electrolyte storage element using lithium metal in the negative electrode, there is a tendency for side reactions between the highly reducing lithium metal and the electrolyte to occur significantly, and therefore, when lithium metal is used in the negative electrode, there is a risk of a decrease in the capacity retention rate after charge-discharge cycles.

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a nonaqueous electrolyte storage element that has a high capacity retention rate after charge-discharge cycles when lithium metal is used as the negative electrode active material. [Means for solving the problem]

[0007] One aspect of the present invention made to solve the above problems is a nonaqueous electrolyte storage element comprising a negative electrode, a positive electrode, and a nonaqueous electrolyte containing a fluorinated solvent, wherein the negative electrode has a negative electrode active material layer containing lithium metal, the fluorinated solvent contains a fluorinated phosphate ester, and a content of the fluorinated solvent in the total solvent of the nonaqueous electrolyte is 99.0 vol % or more. Effect of the Invention

[0008] According to the present invention, it is possible to provide a nonaqueous electrolyte storage element that has a high discharge capacity retention rate after charge-discharge cycles when lithium metal is used as the negative electrode active material. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is an external perspective view showing a nonaqueous electrolyte storage element according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A nonaqueous electrolyte storage element according to one embodiment of the present invention comprises a negative electrode, a positive electrode, and a nonaqueous electrolyte containing a fluorinated solvent, the negative electrode having a negative electrode active material layer containing lithium metal, the fluorinated solvent containing a fluorinated phosphate ester, and a content of the fluorinated solvent in the total solvent of the nonaqueous electrolyte being 99.0% by volume or more.

[0011] According to the nonaqueous electrolyte storage element, when lithium metal is used as the negative electrode active material, the nonaqueous electrolyte contains a fluorinated solvent containing a fluorinated phosphate ester, and the content of the fluorinated solvent in the total solvent of the nonaqueous electrolyte is 99.0% by volume or more, so that the discharge capacity retention rate after charge and discharge cycles is high. The reason for this is unclear, but is presumed to be as follows. In a nonaqueous electrolyte storage element using lithium metal, when the nonaqueous electrolyte comes into contact with the lithium metal, the nonaqueous electrolyte is reductively decomposed, and a coating is formed on the surface of the lithium metal, thereby suppressing further continuous reductive decomposition of the nonaqueous electrolyte on the surface of the lithium metal. However, if the coating is insufficiently formed, it is considered that the coating is fragile and therefore does not sufficiently function to suppress the continuous reductive decomposition of the electrolyte. In the nonaqueous electrolyte storage element, the nonaqueous electrolyte contains a fluorinated solvent including a fluorinated phosphate ester, and the content of the fluorinated solvent in the total solvent of the nonaqueous electrolyte is 99.0% by volume or more. Therefore, when the nonaqueous electrolyte is reductively decomposed, LiF or a compound having a fluorinated phosphate ester structure represented by the following formula ((LiO) l (CF3(CH2O) m ) n PO, where in the above formula, l is an integer of 0 or more and 3 or less. n is 3-l. m is an integer of 1 or more. However, when n is 2 or 3, multiple m's may be the same or different.) is formed. Therefore, the nonaqueous electrolyte storage element has an increased discharge capacity retention rate after charge-discharge cycles.

[0012] It is preferable that the fluorinated solvent contains a fluorinated carbonate, and the volume ratio of the total content of the fluorinated phosphate ester and the fluorinated carbonate to the total fluorinated solvent is 75.0 volume % or more. When the volume ratio of the total content of the fluorinated phosphate ester and the fluorinated carbonate to the total fluorinated solvent is in the above range, the short circuit suppression effect of the nonaqueous electrolyte storage element can be further improved.

[0013] It is preferable that the fluorinated solvent does not contain a fluorinated ether, or the fluorinated solvent contains a fluorinated ether and the content of the fluorinated ether in the fluorinated solvent is less than 25.0 volume %. When the fluorinated solvent does not contain a fluorinated ether or the content of the fluorinated ether in the fluorinated solvent is within the above range, the short circuit suppression effect of the nonaqueous electrolyte storage element can be enhanced.

[0014] Hereinafter, a nonaqueous electrolyte storage element according to an embodiment of the present invention will be described in detail. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0015] <Non-aqueous electrolyte storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention includes a negative electrode, a positive electrode, and a nonaqueous electrolyte. Hereinafter, a nonaqueous electrolyte secondary battery will be described as an example of a nonaqueous electrolyte storage element. The positive electrode and the negative electrode are usually stacked or wound alternately with a separator interposed therebetween to form an electrode body. This electrode body is housed in a case, and the case is filled with a nonaqueous electrolyte. In the nonaqueous electrolyte secondary battery, the nonaqueous electrolyte described above is used as the nonaqueous electrolyte. The nonaqueous electrolyte is interposed between the positive electrode and the negative electrode. In addition, as the case, a known metal case, a resin case, or the like that is usually used as a case for a nonaqueous electrolyte secondary battery can be used.

[0016] [Negative electrode] The negative electrode includes a negative electrode substrate and a negative electrode active material layer laminated directly or indirectly on at least one surface of the negative electrode substrate. The negative electrode may include an intermediate layer disposed between the negative electrode substrate and the negative electrode active material layer.

[0017] (Negative electrode substrate) The negative electrode substrate has electrical conductivity. Metals such as copper, nickel, stainless steel, and nickel-plated steel, or alloys thereof, and carbonaceous materials are used as the material of the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils and vapor-deposited films, and foils are preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil. The term "electrically conductive" refers to a material having a volume resistivity of 1×10 measured in accordance with JIS-H0505 (1975). 7 "Non-conductive" means that the volume resistivity is 1×10 7 This means that the resistance is greater than Ω·cm.

[0018] The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, even more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte secondary battery. Here, the "average thickness" refers to the average value obtained by measuring the thickness at 10 arbitrary points.

[0019] (Negative electrode active material layer) The negative electrode active material layer contains lithium metal as a negative electrode active material. The negative electrode active material contains lithium metal, which can improve the discharge capacity per active material mass. The lithium metal includes lithium alone as well as lithium alloys. Examples of the lithium alloy include lithium silver alloys, lithium zinc alloys, lithium calcium alloys, lithium aluminum alloys, lithium magnesium alloys, lithium tin alloys, lithium silicon alloys, and lithium indium alloys. The lithium alloy may contain a plurality of metal elements other than lithium. The negative electrode active material layer containing lithium metal can be manufactured by cutting foil-like lithium metal into a predetermined shape or forming it into a predetermined shape by rolling, vapor deposition, or the like.

[0020] The lower limit of the lithium metal content in the negative electrode active material is preferably 80 mass %, more preferably 90 mass %, and even more preferably 95 mass %, while the upper limit of this content may be 100 mass %.

[0021] The intermediate layer is a coating layer on the surface of the negative electrode substrate, and contains conductive particles such as carbon particles to reduce the contact resistance between the negative electrode substrate and the negative electrode active material layer. The configuration of the intermediate layer is not particularly limited, and it can be formed, for example, from a composition containing a resin binder and conductive particles.

[0022] [Positive electrode] The positive electrode has a positive electrode substrate and a positive electrode active material layer. The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer is laminated directly or via an intermediate layer along at least one surface of the positive electrode substrate.

[0023] The positive electrode substrate has electrical conductivity. As the material of the substrate, metals such as aluminum, titanium, tantalum, stainless steel, etc., or alloys thereof are used. Among these, aluminum and aluminum alloys are preferred in terms of the balance between potential resistance, high electrical conductivity, and cost. In addition, the form of the positive electrode substrate may be foil, vapor deposition film, etc., and foil is preferred in terms of cost. That is, aluminum foil is preferred as the positive electrode substrate. In addition, examples of aluminum or aluminum alloys include A1085, A3003, etc., as specified in JIS-H4160 (2006) or JIS-H4000 (2014).

[0024] The positive electrode active material layer is formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode mixture forming the positive electrode active material layer further contains optional components such as a conductive agent, a binder, a thickener, and a filler as necessary.

[0025] The positive electrode active material can be appropriately selected from, for example, known positive electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as a positive electrode active material for a lithium ion secondary battery. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, lithium transition metal composite oxides having a spinel type crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of the lithium transition metal composite oxides having an α-NaFeO2 type crystal structure include Li[Li x Ni 1-x ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β≦1), Li[Li x Ni γ Co β Al (1-x-γ-β) ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), etc. Lithium transition metal composite oxides with spinel crystal structure include Li x Mn2O4, Li x Ni γ Mn (2-γ)O4, etc. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used. In the positive electrode active material layer, one of these compounds may be used alone, or two or more of them may be mixed and used. The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but the lower limit is preferably 50 mass%, more preferably 80 mass%, and even more preferably 90 mass%. On the other hand, the upper limit of this content is preferably 99% by mass, more preferably 98% by mass.

[0026] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, and the like. Examples of carbonaceous materials include graphitized carbon, non-graphitized carbon, graphene-based carbon, and the like. Examples of non-graphitized carbon include carbon nanofibers, pitch-based carbon fibers, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, and the like. Examples of the shape of the conductive agent include powder and fiber. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. In addition, these materials may be used in a composite form. For example, a material in which carbon black and CNT are composited may be used. Among these, carbon black is preferable from the viewpoint of electronic conductivity and coatability, and acetylene black is preferable among them.

[0027] The content of the conductive agent in the positive electrode active material layer is preferably from 1 to 10% by mass, more preferably from 3 to 9% by mass. By setting the content of the conductive agent in the above range, the energy density of the nonaqueous electrolyte storage element can be increased.

[0028] Examples of the binder include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyimide, etc.; elastomers such as ethylene propylene diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, etc.; polysaccharide polymers, etc. The content of the binder in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less.

[0029] Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. In addition, when the thickener has a functional group that reacts with lithium, it is preferable to deactivate this functional group in advance by methylation or the like.

[0030] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, poorly soluble ion crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, and mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof.

[0031] The intermediate layer is a coating layer on the surface of the positive electrode substrate, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. As with the negative electrode, the configuration of the intermediate layer is not particularly limited, and can be formed, for example, from a composition containing a resin binder and conductive particles.

[0032] [Nonaqueous electrolyte] The nonaqueous electrolyte contains a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolyte contains a fluorinated solvent. The fluorinated solvent contains a fluorinated phosphate ester. The nonaqueous electrolyte is not limited to a liquid. That is, the nonaqueous electrolyte is not limited to a liquid, but also includes a solid or gel.

[0033] (Fluorinated Solvents) The fluorinated solvent includes a fluorinated phosphate ester. Note that the term "fluorinated solvent" refers to a non-aqueous solvent having a fluorine atom in the molecule, such as a fluorinated ester, a fluorinated ether, or a fluorinated carbonate (a fluorinated chain carbonate or a fluorinated cyclic carbonate).

[0034] As the fluorinated phosphate, fluoroalkyl phosphate is preferred, and trisfluoroalkyl phosphate is more preferred. Specific examples of the fluorinated phosphate include tris(2,2-difluoroethyl)phosphate, tris(2,2,3,3-tetrafluoropropyl)phosphate, tris(2,2,3,3,4,4-hexafluorobutyl)phosphate, tris(1H,1H,5H-octafluoropentyl)phosphate, tris(2,2,2-trifluoroethyl)phosphate, tris(2,2,3,3,3-pentafluoropropyl)phosphate, tris(1H,1H-perfluorobutyl)phosphate, tris(1H,1H-perfluoropentyl)phosphate, and tris(1,1,1,3,3,3-hexafluoro-2-propyl)phosphate. As the fluorinated phosphate, tris(2,2,2-trifluoroethyl)phosphate (TFEP) is preferred.

[0035] The lower limit of the content of the fluorinated phosphate in the fluorinated solvent is preferably 5% by volume, more preferably 10% by volume, and even more preferably 15% by volume. Meanwhile, the upper limit is preferably 70% by volume, more preferably 60% by volume, and even more preferably 50% by volume. By setting the content of the fluorinated phosphate in the above range, the discharge capacity retention rate after charge-discharge cycles can be further increased.

[0036] The fluorinated solvent preferably contains a fluorinated carbonate, such as a fluorinated cyclic carbonate or a fluorinated chain carbonate.

[0037] Examples of the fluorinated cyclic carbonate include fluoroethylene carbonate (FEC), 4,5-difluoroethylene carbonate (including trans isomer, cis isomer and a mixture thereof: DFEC), 4,4-difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, 4-(fluoromethyl)-1,3-dioxolan-2-one, 4-(difluoromethyl)-1,3-dioxolan-2-one, 4-(trifluoromethyl)-1,3-dioxolan-2-one, 4,5-bis(fluoromethyl)ethylene carbonate (including trans isomer, cis isomer and a mixture thereof), 4,5-bis(difluoromethyl)ethylene carbonate (including trans isomer, cis isomer and a mixture thereof), and 4,5-bis(difluoromethyl)ethylene carbonate (including trans isomer, cis isomer and a mixture thereof). Examples of the fluorinated cyclic carbonate include 4,4-bis(difluoromethyl)ethylene carbonate, 4,5-(trifluoromethyl)ethylene carbonate (including trans, cis and mixtures thereof), 4,4-(trifluoromethyl)ethylene carbonate, (fluoroethyl)ethylene carbonate, (difluoroethyl)ethylene carbonate, (trifluoroethyl)ethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate (including trans, cis and mixtures thereof), 4,4-difluoro-5-methylethylene carbonate, 4,5-difluoro-4,5-dimethylethylene carbonate, etc. Among these, the fluorinated cyclic carbonate is preferably fluorinated ethylene carbonate, and more preferably fluoroethylene carbonate (FEC). The above-mentioned fluoroethylene carbonate has high oxidation resistance and is highly effective in suppressing side reactions (such as oxidative decomposition of non-aqueous solvents) that may occur during charging and discharging of a non-aqueous electrolyte storage element.

[0038] Examples of the fluorinated chain carbonate include (2-fluoroethyl)methyl carbonate, (2,2-difluoroethyl)methyl carbonate, (2,2,2-trifluoroethyl)methyl carbonate, ethyl-(2-fluoroethyl)carbonate, ethyl-(2,2-difluoroethyl)carbonate, bis(2-fluoroethyl)carbonate, ethyl-(2,2,2-trifluoroethyl)carbonate, 2,2-difluoroethyl-2'-fluoroethyl carbonate, bis(2,2-difluoroethyl)carbonate, 2,2,2-trifluoroethyl-2'-fluoroethyl carbonate, 2,2,2-trifluoroethyl-2',2'-difluoroethyl carbonate, bis(2,2,2-trifluoroethyl)carbonate, and (3,3,3-trifluoropropyl)methyl carbonate. ester, (2,2,3,3-tetrafluoropropyl)methyl carbonate, (2,2,3,3,3-pentafluoropropyl)methyl carbonate, ethyl-(3,3,3-trifluoropropyl)carbonate, ethyl-(2,2,3,3-tetrafluoropropyl)carbonate, ethyl-(2,2,3,3,3-pentafluoropropyl)carbonate, (3,3,3-trifluoropropyl)n-propyl carbonate, (2,2,3,3-tetrafluoropropyl)n-propyl carbonate, (2,2,3,3,3-pentafluoropropyl)propyl carbonate, bis(3,3,3-trifluoropropyl)carbonate, bis(2,2,3,3-tetrafluoropropyl)carbonate, bis(2,2,3,3-pentafluoropropyl)carbonate, and the like. Among these, (2,2,2-trifluoroethyl)methyl carbonate and bis(2,2,2-trifluoroethyl)carbonate are preferred.

[0039] The above-mentioned fluorinated carbonates can be used alone or in combination of two or more, but it is preferable to use a fluorinated cyclic carbonate and a fluorinated chain carbonate in combination. When a fluorinated cyclic carbonate and a fluorinated chain carbonate are used in combination, the volume ratio of the fluorinated cyclic carbonate to the fluorinated chain carbonate (fluorinated cyclic carbonate:fluorinated chain carbonate) is preferably 5:95 to 90:10, more preferably 10:90 to 30:70.

[0040] The lower limit of the volume ratio of the total content of the fluorinated phosphate ester and the fluorinated carbonate to the total fluorinated solvent is preferably 75.0 volume %, more preferably 80.0 volume %, further preferably 90.0 volume %, and may be 100 volume %. When the volume ratio of the total content of the fluorinated phosphate ester and the fluorinated carbonate to the total fluorinated solvent is within the above range, the short circuit suppression effect after charge and discharge cycles can be further improved.

[0041] The fluorinated solvent may contain other fluorinated solvents in addition to the fluorinated phosphate ester and the fluorinated carbonate, such as fluorinated ethers, fluorinated esters, and fluorinated hydrocarbons.

[0042] The above-mentioned fluorinated ether may be either a fluorinated chain ether or a fluorinated cyclic ether.The above-mentioned fluorinated ether may be bis(2-fluoroethyl)ether, bis(2,2-difluoroethyl)ether, bis(2,2,2-trifluoroethyl)ether, ethyl-2-fluoroethylether, ethyl-2,2,2-trifluoroethylether, ethyl-1,1,2,2-tetrafluoroethylether, 2-fluoroethyl-2,2,2-trifluoroethylether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethylether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether, 1,1,2,2-tetrafluoroethyl-2,2,3,3,3-pentafluoropropylether, 2,2,3,3-tetrafluoropropyl-1,1,2,3,3,3-hexafluoropropylether, etc.

[0043] Examples of the fluorinated ester include methyl 3,3,3-trifluoropropionate, ethyl 3,3,3-trifluoropropionate, ethyl trifluoroacetate, and 2,2,2-trifluoroethyl acetate.

[0044] The fluorinated hydrocarbon may be a fluorinated aliphatic hydrocarbon such as a fluorinated alkane or a fluorinated cycloalkane, or may be a fluorinated aromatic hydrocarbon such as hexafluorobenzene.

[0045] The fluorinated solvent does not contain a fluorinated ether, or the fluorinated solvent contains a fluorinated ether, and the content of the fluorinated ether in the fluorinated solvent is preferably less than 25.0 volume %, more preferably 20.0 volume % or less. When the fluorinated solvent does not contain a fluorinated ether, or the content of the fluorinated ether in the fluorinated solvent is within the above range, the short circuit suppression effect of the nonaqueous electrolyte storage element can be improved. When the fluorinated solvent contains a fluorinated ether, the upper limit of the content of the fluorinated phosphate ester in the fluorinated solvent is preferably 40.0 volume %, more preferably 30.0 volume %, and even more preferably 20.0 volume %.

[0046] The non-aqueous solvent may contain an organic solvent other than the fluorinated solvent. Examples of the other organic solvent include carbonates other than fluorinated carbonates, esters other than fluorinated esters, ethers other than fluorinated ethers, amides, lactones, nitriles, etc. Also, the non-aqueous solvent may contain an organic solvent containing sulfur, such as sulfones and sulfites.

[0047] Examples of carbonates other than the above-mentioned fluorinated carbonates include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate, and chain carbonates such as diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diphenyl carbonate. Examples of esters other than the above-mentioned fluorinated esters include methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), and ethyl propionate (EP). Examples of the above-mentioned sulfones include sulfolane (SL), ethyl isopropyl sulfone (EiPSO2), and ethyl methyl sulfone (EMSO2). Examples of the sulfite include diethyl sulfite (DES) and dimethyl sulfite (DMS).

[0048] The lower limit of the content of the fluorinated solvent in the total nonaqueous solvent of the nonaqueous electrolyte is 99.0 vol%, preferably 99.5 vol%, more preferably 99.9 vol%, and even more preferably 100 vol%. When the content of the fluorinated solvent is within the above range, the discharge capacity retention rate after charge-discharge cycles of the nonaqueous electrolyte storage element can be further increased.

[0049] (Electrolyte salt) The electrolyte salt may be any known electrolyte salt commonly used in general non-aqueous electrolyte solutions, including lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts, with lithium salts being preferred.

[0050] Examples of the lithium salt include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, LiN(SO2F)2, and LiSO3CF3, imide lithium salts such as LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9), and lithium salts having a fluorohydrocarbon group such as LiC(SO2CF3)3 and LiC(SO2C2F5)3, etc. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0051] The lower limit of the content of the electrolyte salt in the nonaqueous electrolyte solution is 0.1 mol dm -3 is preferred, and 0.3 mol dm -3 is more preferred, and 0.5 mol dm -3 On the other hand, the upper limit is not particularly limited, but is preferably 3 mol dm -3 is preferred, and 2 mol dm -3 is more preferred.

[0052] (Other additives, etc.) The non-aqueous electrolyte may contain other additives as long as they do not impair the effects of the present invention. Examples of the other additives include various additives contained in general non-aqueous electrolytes. Examples of the additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, and dibenzofuran; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, dimethyl sulfate, and ethylene sulfate. Examples of the additives include dimethylsulfone, sulfolane, dimethylsulfone, diethylsulfone, dimethylsulfoxide, diethylsulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, tetrakistrimethylsilyl titanate, etc. These additives may be used alone or in combination of two or more.

[0053] [Separator] As the separator, for example, a woven fabric, a nonwoven fabric, a porous resin film, etc. are used. Among these, a porous resin film is preferable from the viewpoint of strength, and a nonwoven fabric is preferable from the viewpoint of the liquid retention of the nonaqueous electrolyte. As the main component of the separator, a polyolefin such as polyethylene or polypropylene is preferable from the viewpoint of strength, and a polyimide or aramid is preferable from the viewpoint of resistance to oxidation and decomposition. These resins may be combined. The "main component of the separator" refers to a component contained in an amount of 50% by mass or more based on the total mass of the separator.

[0054] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0055] As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polyethylene carbonate, polypropylene carbonate, polyvinyl carbonate, polymethyl methacrylate or polyalkyl methacrylates, polymethyl acrylate or polyalkyl acrylates, polyvinyl ethylene carbonate, polyvinyl acetate, polyvinylpyrrolidone, polymaleic acid and its derivatives, polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropylene), polytetrafluoroethylene, and copolymers and mixtures thereof. These polymers may also be combined with inorganic salts or ionic liquids. The use of a polymer gel has the effect of suppressing leakage. As the separator, a polymer gel may be used in combination with the porous resin film or nonwoven fabric as described above.

[0056] [Specific configuration of non-aqueous electrolyte storage element] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include a cylindrical battery, a pouch film battery, a square battery, a flat battery, a coin battery, and a button battery.

[0057] FIG 1 shows a square nonaqueous electrolyte secondary battery as an example of a nonaqueous electrolyte storage element 1. The figure is a see-through view of the inside of the case. An electrode body 2 having a positive electrode and a negative electrode wound with a separator sandwiched therebetween is housed in a square case 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0058] <Method of Manufacturing Nonaqueous Electrolyte Storage Element> The method for producing the nonaqueous electrolyte storage element according to the present embodiment can be appropriately selected from known methods. The method for producing the nonaqueous electrolyte storage element according to the present embodiment includes, for example, a step of preparing an electrode body, a step of preparing a nonaqueous electrolyte, and a step of housing the electrode body and the nonaqueous electrolyte in a case. The step of preparing the electrode body includes a step of preparing a positive electrode and a negative electrode, and a step of forming the electrode body by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0059] The process of housing the nonaqueous electrolyte in the case can be appropriately selected from known methods. For example, when using a liquid nonaqueous electrolyte (also called "electrolyte"), the electrolyte is injected from an injection port formed in the case, and then the injection port is sealed. Details of the other elements constituting the nonaqueous electrolyte storage element obtained by this manufacturing method are as described above.

[0060] [Other embodiments] The nonaqueous electrolyte storage element according to the present invention is not limited to the above-mentioned embodiment, and various modifications may be made without departing from the scope of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and part of the configuration of one embodiment may be replaced with the configuration of another embodiment or a well-known technique. Furthermore, part of the configuration of one embodiment may be deleted. Also, a well-known technique may be added to the configuration of one embodiment.

[0061] In the above embodiment, the nonaqueous electrolyte storage element is mainly a nonaqueous electrolyte secondary battery, but other nonaqueous electrolyte storage elements may be used. Examples of other nonaqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors), etc. Examples of nonaqueous electrolyte secondary batteries include lithium ion nonaqueous electrolyte secondary batteries.

[0062] The present invention can also be realized as an electricity storage device including a plurality of the nonaqueous electrolyte storage elements. In addition, a single or a plurality of the nonaqueous electrolyte storage elements (cells) of the present invention can be used to form an electricity storage unit, and this electricity storage unit can be used to form an electricity storage device. The electricity storage device can be used as a power source for automobiles such as electric vehicles (EVs), hybrid vehicles (HEVs), and plug-in hybrid vehicles (PHEVs). Furthermore, the electricity storage device can be used in various power sources such as engine starting power sources, auxiliary power sources, and uninterruptible power sources (UPSs).

[0063] 2 shows an example of an electricity storage device 30 in which electricity storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte storage elements 1, are further assembled. The electricity storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte storage elements 1, and a bus bar (not shown) that electrically connects two or more electricity storage units 20. The electricity storage unit 20 or the electricity storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte storage elements. EXAMPLES

[0064] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0065] [Example 1] (Preparation of non-aqueous electrolyte) Fluoroethylene carbonate (FEC), trifluoroethyl methyl carbonate (TFEMC), and tris(2,2,2-trifluoroethyl) phosphate (TFEP) were mixed in a volume ratio of 10 vol. %:70 vol. %:20 vol. %. Next, LiPF6 was added to the mixed solvent at a concentration of 1 mol dm -3 This was dissolved in water at a concentration of 100% by weight to prepare a non-aqueous electrolyte solution.

[0066] (Preparation of positive electrode) The positive electrode active material has an α-NaFeO2 type crystal structure and Li 1+α Me 1-αA lithium transition metal composite oxide represented by O2 (Me is a transition metal) was used. Here, the molar ratio of Li to Me, Li / Me, was 1.33, and Me was composed of Ni and Mn, and was contained in a molar ratio of Ni:Mn=1:2.

[0067] A positive electrode paste was prepared using N-methylpyrrolidone (NMP) as a dispersion solvent, containing the positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder in a mass ratio of 94.0:4.5:1.5. The positive electrode paste was applied to one side of an aluminum foil as a positive electrode substrate, and the aluminum foil was dried and pressed to prepare a positive electrode with a positive electrode active material layer. The current density was 5 mAcm at 1.0 CmA. -2 The electrode coating mass was designed so that

[0068] (Preparation of negative electrode) A lithium metal foil (100% by mass of lithium metal) was laminated as a negative electrode active material layer on one side of a copper foil as a negative electrode substrate, and then pressed to prepare a negative electrode.

[0069] (Preparation of non-aqueous electrolyte storage element) Next, the positive electrode plate and the negative electrode plate were laminated with a separator made of a polyolefin microporous film interposed therebetween to prepare an electrode assembly. The electrode assembly was housed in a case made of a metal resin composite film, and 0.5 ml of the nonaqueous electrolyte was poured into the case, which was then sealed by thermal welding to obtain a nonaqueous electrolyte storage element (nonaqueous electrolyte secondary battery) of Example 1, which was a single-layer pouch cell.

[0070] [Examples 2 to 4 and Comparative Examples 1 to 5] Non-aqueous electrolyte storage elements of Examples 2 to 4 and Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that the solvent and amount of the non-aqueous electrolyte used were as shown in Table 1. The solvents used are as follows: FEC: Fluoroethylene carbonate TFEP: Tris(2,2,2-trifluoroethyl) phosphate TFEMC: Trifluoroethyl methyl carbonate TFEE: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether EMC: Ethyl methyl carbonate EC: Ethylene carbonate In the following tables, "-" indicates that the corresponding solvent was not used.

[0071] (First charge / discharge) The obtained nonaqueous electrolyte storage elements were initially charged and discharged under the following conditions: They were charged at a constant current of 0.1 C at 25° C. up to 4.60 V, and then charged at a constant voltage of 4.60 V. The charge was terminated when the charge current reached 0.05 C. After a 10-minute pause after charging, they were discharged at a constant current of 0.1 C at 25° C. up to 2.00 V.

[0072] (Initial capacity confirmation test) After the first charge and discharge, an initial capacity confirmation test was conducted under the following conditions. The battery was charged at a constant current of 0.1C at 25°C up to 4.60V, and then charged at a constant voltage of 4.60V. The charge was terminated when the charge current reached 0.05C. After a 10-minute pause after charging, the battery was discharged at a constant current of 1.0C up to 2.00V at 25°C. The discharge capacity obtained in this test was designated the "initial discharge capacity."

[0073] (Charge-discharge cycle test) Next, the following charge-discharge cycle test was performed. At 25°C, the battery was charged at a constant current of 0.2C, and then charged at a constant voltage of 4.60V. The charge was terminated when the charge current reached 0.05C. A rest period of 10 minutes was then provided. A constant current discharge was then performed at a discharge current of 0.1C to 2.00V, and a rest period of 10 minutes was then provided. This charge-discharge cycle was performed 60 times.

[0074] Thereafter, a discharge capacity confirmation test after the charge-discharge cycle test was conducted in the same manner as the initial capacity confirmation test. The discharge capacity obtained in this test was defined as the discharge capacity after the charge-discharge cycle. The percentage of the discharge capacity after the charge-discharge cycle test to the initial discharge capacity was defined as the "discharge capacity retention rate after 60 cycles." The discharge capacity retention rate after 60 cycles is shown in Table 1.

[0075] (Number of cycles until short circuit occurs) The number of cycles until the occurrence of a short circuit was evaluated by the following procedure: Following the above-mentioned charge-discharge cycle test and the discharge capacity confirmation test after the charge-discharge cycle test, a charge-discharge cycle test was performed in the same manner as the above-mentioned charge-discharge cycle test, without setting an upper limit on the number of cycles. The occurrence of a short circuit was confirmed by a decrease in the coulombic efficiency and an increase in the amount of charged electricity during the charge-discharge cycle. Specifically, a decrease in the coulombic efficiency and an increase in the amount of charged electricity were judged to be the occurrence of a short circuit. Table 1 shows the evaluation results for the number of cycles until a short circuit occurred.

[0076] [Table 1]

[0077] As shown in Table 1, it was confirmed that in Examples 1 to 4, which contain a fluorinated solvent containing a fluorinated phosphate ester and in which the content of the fluorinated solvent in the total solvent of the nonaqueous electrolyte is 99.0 volume % or more, the discharge capacity retention rate after charge-discharge cycles is high when lithium metal is used as the negative electrode active material. It is also found that the short circuit suppression effect can be further improved by making the volume ratio of the total content of the fluorinated phosphate ester and the fluorinated carbonate to the total fluorinated solvent 75.0 volume % or more. Furthermore, it can be seen that Example 1, in which the fluorinated solvent does not contain a fluorinated ether, and Examples 2 and 3, in which the content of fluorinated ether in the fluorinated solvent is less than 25.0% by volume, have a high short-circuit suppression effect on the nonaqueous electrolyte storage element.

[0078] In contrast, Comparative Example 1 to Comparative Example 3, in which the fluorinated solvent does not contain a fluorinated phosphate ester, show a lower discharge capacity retention rate after charge-discharge cycling than Examples 1 to 4. Moreover, Comparative Example 3, in which the content of the fluorinated solvent in the total solvent of the nonaqueous electrolyte solution is 30 vol %, showed a particularly low discharge capacity retention rate after charge-discharge cycling. Furthermore, a comparison between Example 1, Comparative Example 1, and Comparative Example 3 in which the fluorinated solvent does not contain a fluorinated ether, and a comparison between Example 2 and Comparative Example 2 in which the content of the fluorinated ether is 10% by volume, shows that Examples 1 and 2 in which the fluorinated solvent contains a fluorinated phosphate ester have a higher short-circuit suppression effect.

[0079] The above results show that the nonaqueous electrolyte storage element has a high discharge capacity retention rate after charge-discharge cycles when lithium metal is used as the negative electrode active material. [Industrial Applicability]

[0080] The present invention can be applied to nonaqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles. [Explanation of symbols]

[0081] 1. Nonaqueous electrolyte storage element 2 Electrode body 3 Cases 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy Storage Unit 30 Energy storage device

Claims

1. A negative electrode; A positive electrode and A non-aqueous electrolyte containing a fluorinated solvent; Equipped with the negative electrode has a negative electrode active material layer containing lithium metal, the fluorinated solvent comprises a fluorinated phosphate ester and a fluorinated carbonate; The fluorinated carbonate includes a fluorinated cyclic carbonate and a fluorinated linear carbonate, A non-aqueous electrolyte storage element, wherein the content of the fluorinated solvent in the total solvent of the non-aqueous electrolyte is 99.0% by volume or more.

2. A non-aqueous electrolyte storage element as described in claim 1, wherein the fluorinated solvent does not contain a fluorinated ether, or the fluorinated solvent contains a fluorinated ether and the content of the fluorinated ether in the fluorinated solvent is less than 25.0 volume %.

3. A non-aqueous electrolyte storage element as described in claim 1 or claim 2, except when the fluorinated solvent contains perfluoropolyether.

4. 4. The nonaqueous electrolyte storage element according to claim 1, wherein a volume ratio of a total content of the fluorinated phosphate ester and the fluorinated carbonate in the fluorinated solvent is 75.0 volume % or more.

5. Preparing an electrode assembly including a negative electrode having a negative electrode active material layer containing lithium metal and a positive electrode; Providing a non-aqueous electrolyte solution containing a fluorinated solvent including a fluorinated phosphate ester and a fluorinated carbonate; Equipped with The fluorinated carbonate includes a fluorinated cyclic carbonate and a fluorinated linear carbonate, A method for producing a nonaqueous electrolyte storage element, wherein the content of the fluorinated solvent in the total solvent of the nonaqueous electrolyte is 99.0 volume % or more.

6. A method for manufacturing a non-aqueous electrolyte storage element as described in claim 5, wherein the fluorinated solvent does not contain a fluorinated ether, or the fluorinated solvent contains a fluorinated ether and the content of the fluorinated ether in the fluorinated solvent is less than 25.0 volume %.

7. A method for manufacturing a non-aqueous electrolyte storage element as described in claim 5 or claim 6, except when the fluorinated solvent contains perfluoropolyether.

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