Nonaqueous electrolyte electricity storage element

Abstract

A non-aqueous electrolyte electricity storage element according to one embodiment of the present invention is provided with a negative electrode having a negative electrode active material layer, and a non-aqueous electrolyte containing an unsaturated cyclic carbonate and a fluorophosphate having a P-O bond. The BET specific surface area of the negative electrode active material layer is 0.80 m2 / g to 1.5 m2 / g, and the ratio of the content of the unsaturated cyclic carbonate to the total content of the unsaturated cyclic carbonate and the fluorophosphate having a P-O bond is 0.60 or more and less than 1.0 on a molar basis.

Description

Technical Field

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

[0002] Non-aqueous electrolyte secondary batteries represented by lithium-ion non-aqueous electrolyte secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. due to their high energy density. The above non-aqueous electrolyte secondary battery generally includes an electrode body having a pair of electrodes electrically insulated by a separator and a non-aqueous electrolyte interposed between the electrodes, and is configured to charge and discharge by receiving and discharging charge carrier ions between the two electrodes. In addition, as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double layer capacitors have also been widely popularized.

[0003] Generally, the non-aqueous electrolyte of the above non-aqueous electrolyte storage element contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. In this non-aqueous electrolyte, various additives and solvents are selected and used to improve its performance.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-162304 Summary of the Invention

[0007] In recent years, there has been a demand for a non-aqueous electrolyte storage element having a further high capacity retention rate after charge and discharge cycles and further excellent output performance in a low-temperature environment. In the above Patent Document 1, an improvement in the capacity retention rate after charge and discharge cycles was proposed by making efforts on the components contained in the electrolyte solution. However, even with such a technique, it is still insufficient to meet the required levels regarding the capacity retention rate after charge and discharge cycles or the output performance in a low-temperature environment, and there is still room for improvement.

[0008] An object of the present invention is to provide a non-aqueous electrolyte storage element having excellent capacity retention rate after charge and discharge cycles and output performance in a low-temperature environment.

[0009] A non-aqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode and a non-aqueous electrolyte. The negative electrode has a negative electrode active material layer. The non-aqueous electrolyte contains an unsaturated cyclic carbonate and a fluorophosphate having a P—O bond. The BET specific surface area of the negative electrode active material layer is 0.80 m 2 / g to 1.5 m 2 / g, and the proportion of the content of the unsaturated cyclic carbonate relative to the total content of the unsaturated cyclic carbonate and the fluorophosphate having a P—O bond is 0.60 or more and less than 1.0 on a molar basis.

[0010] A non-aqueous electrolyte storage element according to one aspect of the present invention can provide a non-aqueous electrolyte storage element having excellent capacity retention rate after charge-discharge cycles and output performance in a low-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a perspective three-dimensional view showing an embodiment of a non-aqueous electrolyte storage element.

[0012] Figure 2 is a schematic view showing an embodiment of a storage device formed by aggregating a plurality of non-aqueous electrolyte storage elements. DETAILED DESCRIPTION OF THE INVENTION

[0013] First, an outline of the non-aqueous electrolyte storage element disclosed in this specification will be described.

[0014] [1] A non-aqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode and a non-aqueous electrolyte. The negative electrode has a negative electrode active material layer. The non-aqueous electrolyte contains an unsaturated cyclic carbonate and a fluorophosphate having a P—O bond. The BET specific surface area of the negative electrode active material layer is 0.80 m 2 / g to 1.5 m 2 / g. The proportion of the content of the unsaturated cyclic carbonate relative to the total content of the unsaturated cyclic carbonate and the fluorophosphate having a P—O bond is 0.60 or more and less than 1.0 on a molar basis.

[0015] The non-aqueous electrolyte storage element described in the above [1] has excellent capacity retention rate after charge-discharge cycles and output performance in a low-temperature environment by making the BET specific surface area of the negative electrode active material layer and the molar ratio of the unsaturated cyclic carbonate and the fluorophosphate having a P—O bond within specific ranges. Although the reason is not clear, it is presumed as follows.

[0016] In the non-aqueous electrolyte of the non-aqueous electrolyte storage element, in order to improve the capacity retention rate after charge-discharge cycles, an unsaturated cyclic carbonate that forms a film on the surface of the negative electrode active material particles by decomposition during charging is sometimes used for the non-aqueous electrolyte. However, since the unsaturated cyclic carbonate forms a uniform and dense film on the surface, there is a tendency that charge carrier ions (lithium ions in the case of a lithium-ion secondary battery) are difficult to penetrate through the film, and the output performance in a low-temperature environment sometimes becomes low. On the other hand, since the fluorophosphate having a P—O bond forms a rough film on the surface, there is a tendency that charge carrier ions are easily permeable through the film. Therefore, by combining the unsaturated cyclic carbonate and the fluorophosphate having a P—O bond, the permeability of the charge carrier ions through the film can be improved, and thus the output performance in a low-temperature environment can be enhanced.

[0017] Regarding the non-aqueous electrolyte storage element described in the above [1], the BET specific surface area of the negative electrode active material layer is set to 0.80 m 2 / g to 1.5 m 2 / g, and the ratio (molar ratio) of the content of the above unsaturated cyclic carbonate to the total content of the above unsaturated cyclic carbonate and the above oxyfluorophosphate is set to 0.60 or more and less than 1.0. Thus, on the particle surface of the negative electrode active material, the above unsaturated cyclic carbonate and the above oxyfluorophosphate can be decomposed evenly to form a film, so that the permeability of the charge carrier ions to the film is improved and the surface of the negative electrode active material layer can be sufficiently covered with a proper, uniform and dense film without becoming too thick, thereby improving the output performance in a low-temperature environment. In addition, if as the charge-discharge cycle progresses, the film on the particle surface cannot follow the expansion and contraction of the particles of the negative electrode active material and breaks, thus generating a new surface of the negative electrode active material, the above unsaturated cyclic carbonate and the above oxyfluorophosphate remaining in the non-aqueous electrolyte will further decompose and grow into a film. Even in such a case, the above unsaturated cyclic carbonate and the above oxyfluorophosphate can be decomposed evenly and the film will not grow too thick, so that an increase in resistance can be suppressed, and thus a decrease in the capacity retention rate after the charge-discharge cycle can be suppressed. It is considered that this helps to improve the capacity retention rate after the charge-discharge cycle and the output performance in a low-temperature environment.

[0018] Here, the "BET specific surface area" is obtained as follows: Nitrogen molecules are physically adsorbed on the particle surface by immersing in liquid nitrogen and supplying nitrogen, and the pressure and adsorption amount at that time are measured accordingly. As a specific measurement method, the nitrogen adsorption amount (m 2 ) of the sample is obtained by the one-point method. The value obtained by dividing the obtained nitrogen adsorption amount by the mass (g) of the sample is used as the BET specific surface area (m 2 / g).

[0019] [2] In the non-aqueous electrolyte storage element described in the above [1], the content of the above unsaturated cyclic carbonate in the above non-aqueous electrolyte can be 1.4×10 -4 mol / dm 3 to 2.8×10 -4 mol / dm 3 . By making the content of the above unsaturated cyclic carbonate in the above range, the non-aqueous electrolyte storage element described in the above [2] can further improve the capacity retention rate after the charge-discharge cycle of the non-aqueous electrolyte storage element. The content of the unsaturated cyclic carbonate in the non-aqueous electrolyte is obtained by gas chromatography-mass spectrometry (GC-MS).

[0020] [3] In the non-aqueous electrolyte storage element described in [1] or [2] above, the content of the fluorophosphate having a P-O bond in the non-aqueous electrolyte may be 1.1×10 -4 mol / dm 3 or less. By making the content of the fluorophosphate having a P-O bond in the non-aqueous electrolyte within the above range, the non-aqueous electrolyte storage element described in [3] can further improve the output performance in a low-temperature environment. The content of the fluorophosphate having a P-O bond in the non-aqueous electrolyte is determined by ion chromatography analysis.

[0021] [4] In the non-aqueous electrolyte storage element described in any one of [1] to [3] above, the unsaturated cyclic carbonate may be vinylene carbonate, and the fluorophosphate having a P-O bond may be lithium difluorophosphate. By making the unsaturated cyclic carbonate vinylene carbonate and the fluorophosphate having a P-O bond lithium difluorophosphate, the non-aqueous electrolyte storage element described in [4] can further improve the capacity retention rate after charge and discharge cycles and the output performance in a low-temperature environment.

[0022] The configuration of the non-aqueous electrolyte storage element, the configuration of the storage device, the manufacturing method of the non-aqueous electrolyte storage element, and other embodiments of the present invention will be described in detail. It should be noted that the names of the constituent members (each constituent element) used in each embodiment may be different from the names of the constituent members (each constituent element) used in the background art.

[0023] <Configuration of Non-aqueous Electrolyte Storage Element>

[0024] A non-aqueous electrolyte storage element (hereinafter, also simply referred to as "storage element") according to an embodiment of the present invention includes: an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated via a separator, or a wound type in which the positive electrode and the negative electrode are wound in a state of being laminated via a separator. The non-aqueous electrolyte exists in a state of being contained in the positive electrode, the negative electrode, and the separator. As an example of the non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as "secondary battery") will be described.

[0025] (Positive Electrode)

[0026] The positive electrode has a positive electrode substrate and a positive electrode active material layer directly disposed or disposed on the positive electrode substrate via an intermediate layer.

[0027] The positive electrode substrate has electrical conductivity. Whether it has "electrical conductivity" is determined with a volume resistivity of 10 7 Ω·cm measured in accordance with JIS-H-0505 (1975) as the threshold. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, stainless steel, or their alloys can be used. Among these, from the viewpoints of potential resistance, high electrical conductivity, and cost, aluminum or aluminum alloy is preferred. As the positive electrode substrate, foil, vapor deposition film, net, porous material, etc. can be cited, and from the viewpoint of cost, foil is preferred. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. As the aluminum or aluminum alloy, A1085, A3003, A1N30, etc. specified in JIS-H-4000 (2014) or JIS-H-4160 (2006) can be exemplified.

[0028] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, further preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By making the average thickness of the positive electrode substrate within the above range, both the strength of the positive electrode substrate and the energy density per unit volume of the secondary battery can be improved.

[0029] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer reduces the contact resistance between the positive electrode substrate and the positive electrode active material layer by containing a conductive agent such as carbon particles. The constitution of the intermediate layer is not particularly limited, and for example, it contains a binder and a conductive agent.

[0030] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer may contain optional components such as a conductive agent, a binder, a thickener, a filler, etc. as needed.

[0031] As the positive electrode active material, it can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium-ion secondary battery, generally, a material capable of inserting and extracting lithium ions can be used. As the positive electrode active material, for example, a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, a lithium transition metal composite oxide having a spinel-type crystal structure, a polyanion compound, an oxygen group element compound, sulfur, etc. can be cited. As the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, for example, 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. As the lithium transition metal composite oxide having a spinel-type crystal structure, Li x Mn2O4, Li x Ni γ Mn (2-γ) O4, etc. As the polyanion compound, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. can be cited. As the chalcogen element compound, titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. can be cited. A part of the atoms or polyanions in these materials can be replaced by atoms or anion species composed of other elements. The surfaces of these materials can be covered with other materials. In the positive electrode active material layer, one of these materials can be used alone, or two or more of them can be used in combination.

[0032] The positive electrode active material is usually particles (powder). The average particle diameter of the positive electrode active material is preferably, for example, 0.1 μm to 20 μm. By making the average particle diameter of the positive electrode active material equal to or greater than the above lower limit, the manufacture or operation of the positive electrode active material becomes easy. By making the average particle diameter of the positive electrode active material equal to or less than the above upper limit, the electron conductivity of the positive electrode active material layer is improved. It should be noted that in the case of using a composite of the positive electrode active material and other materials, the average particle diameter of the composite is taken as the average particle diameter of the positive electrode active material. The "average particle diameter" means the value at which the volume-based cumulative distribution is 50% based on the particle size distribution measured by the laser diffraction / scattering method for the dilution obtained by diluting the particles with a solvent in accordance with JIS-Z-8825 (2013) and calculated in accordance with JIS-Z-8819-2 (2001).

[0033] In order to obtain a powder with a predetermined particle size, a pulverizer, a classifier, etc. can be used. As a pulverization method, for example, a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, an air flow pulverizer, a jet-type air flow pulverizer, a vortex-type air flow pulverizer, or a sieve can be cited. During pulverization, wet pulverization in which an organic solvent such as water or hexane coexists can also be used. As a classification method, a sieve, a wind classifier, etc. can be used together with a dry method or a wet method as needed.

[0034] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and further preferably 80% to 95% by mass. By making the content of the positive electrode active material within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0035] The conductive agent is not particularly limited as long as it is a material with conductivity. As such a conductive agent, for example, carbonaceous materials, metals, conductive ceramics, etc. can be cited. As carbonaceous materials, graphite, non-graphite carbon, graphene-based carbon, etc. can be cited. As non-graphite carbon, carbon nanofibers, pitch-based carbon fibers, carbon black, etc. can be cited. As carbon black, furnace black, acetylene black, Ketjen black, etc. can be cited. As graphene-based carbon, graphene, carbon nanotubes (CNT), fullerene, etc. can be cited. As the shape of the conductive agent, powder, fiber, etc. can be cited. As the conductive agent, one of these materials can be used alone, or two or more can be mixed and used. In addition, these materials can also be composited and used. For example, a material composited with carbon black and CNT can be used. Among these, from the viewpoint of electronic conductivity and coating properties, carbon black is preferred, and acetylene black is preferred.

[0036] The content of the conductive agent in the positive electrode active material layer is preferably 1% to 10% by mass, more preferably 3% to 9% by mass. When the content of the conductive agent is within the above range, the energy density of the secondary battery can be increased.

[0037] As the binder, for example, there can be mentioned thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic acid, polyimide, etc.; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, etc.; polysaccharide polymers, etc.

[0038] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, and more preferably 3% by mass to 9% by mass. When the content of the binder is within the above range, the positive electrode active material can be stably retained.

[0039] As a thickener, for example, polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose can be mentioned. When the thickener has a functional group that reacts with lithium or the like, the functional group can be inactivated in advance by methylation or the like.

[0040] The filler is not particularly limited. As the filler, polyolefins such as polypropylene and polyethylene can be mentioned; inorganic oxides such as silica, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; carbonates such as calcium carbonate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate; nitrides such as aluminum nitride and silicon nitride; substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof, etc.

[0041] The positive electrode active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, and I; typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0042] (Negative electrode)

[0043] The negative electrode has a negative electrode substrate and a negative electrode active material layer directly disposed or disposed on the negative electrode substrate via an intermediate layer. The constitution of the intermediate layer is not particularly limited, and can be selected, for example, from the constitutions exemplified in the above positive electrode.

[0044] The negative electrode substrate has conductivity. As the material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or their alloys, carbonaceous materials, etc. can be used. Among these, copper or a copper alloy is preferred. As the negative electrode substrate, a foil, a vapor deposition film, a net, a porous material, etc. can be mentioned, and from the viewpoint of cost, a foil is preferred. Therefore, as the negative electrode substrate, a copper foil or a copper alloy foil is preferred. As an example of the copper foil, a rolled copper foil, an electrolytic copper foil, etc. can be mentioned.

[0045] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, further preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By making the average thickness of the negative electrode substrate within the above range, both the strength of the negative electrode substrate and the energy density per unit volume of the secondary battery can be improved.

[0046] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer may contain, as needed, any components such as a conductive agent, a binder, a thickener, a filler, etc. Any components such as a conductive agent, a binder, a thickener, a filler, etc. can be selected from the materials exemplified in the above positive electrode.

[0047] The negative electrode active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, I, etc.; typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, etc.; transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W, etc. as components other than the negative electrode active material, the conductive agent, the binder, the thickener, and the filler.

[0048] As the negative electrode active material, it can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium ion secondary battery, generally, a material capable of inserting and extracting lithium ions can be used. As the negative electrode active material, for example, metallic Li; metals or semi-metals such as Si, Sn; metal oxides or semi-metal oxides such as Si oxides, Ti oxides, Sn oxides; titanium-containing oxides such as Li4Ti5O 12 , LiTiO2, TiNb2O7, etc.; polyphosphoric acid compounds; silicon carbide; carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or hardly graphitizable carbon). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials can be used alone, or two or more can be used in combination.

[0049] "Graphite" refers to a carbon material having an average lattice plane spacing (d 002 ) of 0.33 nm or more and less than 0.34 nm as determined by X-ray diffraction before charge and discharge or in the discharged state. As graphite, natural graphite and artificial graphite can be cited. From the viewpoint of materials with stable physical properties, artificial graphite is preferred.

[0050] "Non-graphitic carbon" refers to a carbon material having an average lattice plane spacing (d 002 ) of 0.34 nm to 0.42 nm as determined by X-ray diffraction before charge and discharge or in the discharged state. As non-graphitic carbon, hardly graphitizable carbon and easily graphitizable carbon can be cited. As non-graphitic carbon, for example, materials from resins, petroleum pitch or materials from petroleum pitch, petroleum coke or materials from petroleum coke, materials from plants, materials from alcohols, etc. can be cited.

[0051] Here, the "discharge state" refers to a state in which the lithium ions that can be inserted and removed during charging and discharging are fully removed from the carbon material as the negative electrode active material to complete the discharge. For example, in a monopolar battery using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metal Li as a counter electrode, the open circuit voltage is 0.7V or more.

[0052] "Non-graphitizable carbon" refers to the above-mentioned 002 It is a carbon material with a diameter of 0.36nm to 0.42nm.

[0053] "Graphitizable carbon" refers to the above-mentioned 002 A carbon material having a diameter of 0.34 nm or more and less than 0.36 nm.

[0054] The negative electrode active material is usually a particle (powder). The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm. When the negative electrode active material is a carbon material, a titanium-containing oxide or a polyphosphate compound, the average particle size can be 1 μm to 100 μm. When the negative electrode active material is Si, Sn, Si oxide or Sn oxide, etc., the average particle size can be 1 nm to 1 μm. By making the average particle size of the negative electrode active material above the above lower limit, the manufacture or handling of the negative electrode active material becomes easy. By making the average particle size of the negative electrode active material below the above upper limit, the electronic conductivity of the active material layer is improved. In order to obtain a powder with a specified particle size, a pulverizer, a classifier, etc. can be used. The pulverization method and the classification method can be selected, for example, from the methods exemplified in the above-mentioned positive electrode. When the negative electrode active material is a metal such as metal Li, the negative electrode active material can be in the form of foil.

[0055] The negative electrode active material content of the negative electrode active material layer is preferably 60 to 99 mass %, more preferably 90 to 98 mass %. When the negative electrode active material content is within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0056] The lower limit of the BET specific surface area of ​​the negative electrode active material layer is 0.80 m 2 / g, preferably 0.85m 2 / g, more preferably 0.90m 2 In several ways, the BET specific surface area of ​​the negative electrode active material layer can be 0.95 m 2 / g or more, and can also be 1.00m 2 By making the BET specific surface area of ​​the negative electrode active material layer above the lower limit, the output performance in a low temperature environment can be improved. The upper limit of the BET specific surface area of ​​the negative electrode active material layer is 1.50 m 2 / g, preferably 1.30m2 / g, more preferably 1.20 m 2 / g. In several ways, the BET specific surface area of the negative electrode active material layer can be 1.15 m 2 / g or less, or can be 1.10 m 2 / g or less. By making the BET specific surface area of the above-mentioned negative electrode active material layer be below the above upper limit, the capacity retention rate after charge and discharge cycling can be improved. The above BET specific surface area can be above any of the above lower limits and below any of the above upper limits.

[0057] Although not particularly limited, the surface area of the above-mentioned negative electrode active material layer can be, for example, 1.6×10 2 m 2 or more, preferably 1.7×10 2 m 2 or more, more preferably 1.8×10 2 m 2 or more. In addition, the surface area of the above-mentioned negative electrode active material layer can be, for example, 2.9×10 2 m 2 or less, preferably 2.6×10 2 m 2 or less, more preferably 2.4×10 2 m 2 or less. The surface area of the above-mentioned negative electrode active material layer is calculated by the product of the BET specific surface area of the above-mentioned negative electrode active material layer and the mass of the above-mentioned negative electrode active material layer. The above surface area can be above any of the above lower limits and below any of the above upper limits. In a non-aqueous electrolyte storage element having a negative electrode active material layer with such a surface area, the above-mentioned effects (at least one of the effect of improving the capacity retention rate after charge and discharge cycling and the effect of improving the output performance in a low-temperature environment, preferably both) can be further favorably exerted.

[0058] In the present application specification, the BET specific surface area of the negative electrode active material layer is measured by the following method. Using a specific surface area measuring device manufactured by YUASA IONICS Co., Ltd. (trade name: MONOSORB), the nitrogen adsorption amount (m 2 ) of the sample is obtained by the one-point method. The value obtained by dividing the obtained adsorption amount by the mass (g) of the sample is used as the BET specific surface area (m 2 / g). During the measurement, gas adsorption is carried out under cooling using liquid nitrogen. In addition, preheating is performed at 120 °C for 15 minutes before cooling. The input amount of the measurement sample is 0.5 g ± 0.1 g.

[0059] (Separator)

[0060] The separator can be appropriately selected from known separators. As the separator, for example, a separator composed only of a base material layer can be used, or a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one or both surfaces of the base material layer can be used. As the form of the base material layer of the separator, for example, woven fabric, non-woven fabric, porous resin film, etc. can be cited. Among these forms, from the viewpoint of strength, a porous resin film is preferred; from the viewpoint of the liquid retention property of the non-aqueous electrolyte, non-woven fabric is preferred. As the material of the base material layer of the separator, from the viewpoint of the cutting function, for example, polyolefins such as polyethylene and polypropylene are preferred; from the viewpoint of antioxidant decomposition resistance, for example, polyimide, aromatic polyamide, etc. are preferred. As the base material layer of the separator, a material obtained by compounding these resins can also be used.

[0061] The heat-resistant particles contained in the heat-resistant layer are preferably heat-resistant particles with a mass reduction of 5% or less when heated from room temperature to 500 °C in an air atmosphere at 1 atmosphere, and more preferably heat-resistant particles with a mass reduction of 5% or less when heated from room temperature to 800 °C. As materials with a mass reduction of less than a specified amount, inorganic compounds can be cited. As inorganic compounds, for example, oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium titanate; covalent crystals such as silicon and diamond; substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, or their artificial products, etc. As inorganic compounds, monomers or complexes of these substances can be used alone, or two or more kinds can be mixed and used. Among these inorganic compounds, from the viewpoint of the safety of the energy storage element, silicon oxide, aluminum oxide, or aluminosilicate is preferred.

[0062] From the viewpoint of strength, the porosity of the separator is preferably 80% by volume or less, and from the viewpoint of discharge performance, it is preferably 20% by volume or more. Here, the "porosity" refers to a value based on volume and is the measured value obtained using a mercury porosimeter.

[0063] As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte can be used. As the polymer, for example, polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyvinylidene fluoride, etc. can be cited. If a polymer gel is used, there is an effect of suppressing liquid leakage. As the separator, the above-mentioned porous resin film or non-woven fabric, etc. can be used in combination with the polymer gel.

[0064] (Non-aqueous electrolyte)

[0065] The non-aqueous electrolyte contains an unsaturated cyclic carbonate and a fluorophosphate having a P-O bond. In the non-aqueous electrolyte, a non-aqueous electrolytic solution can be used. The non-aqueous electrolytic solution contains, in addition to the unsaturated cyclic carbonate and the fluorophosphate having a P-O bond as additives, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0066] As the non-aqueous solvent, it can be appropriately selected from known non-aqueous solvents. Examples of the non-aqueous solvent include saturated cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonate esters, ethers, amides, nitriles, etc. As the non-aqueous solvent, a solvent in which a part of the hydrogen atoms contained in these compounds is substituted by a halogen can be used.

[0067] Examples of the saturated cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), etc. Among these, EC is preferred.

[0068] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0069] As the non-aqueous solvent, a saturated cyclic carbonate or a chain carbonate is preferably used, and more preferably a saturated cyclic carbonate and a chain carbonate are used in combination. By using the saturated cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolytic solution can be increased. By using the chain carbonate, the viscosity of the non-aqueous electrolytic solution can be suppressed to a low level. When a saturated cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the saturated cyclic carbonate to the chain carbonate (saturated cyclic carbonate: chain carbonate) is preferably in the range of 5:95 to 50:50, for example.

[0070] As the electrolyte salt, it can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, salts, etc. Among these, lithium salts are preferred.

[0071] Examples of the lithium salt include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiN(SO2F)2; lithium oxalate salts such as lithium bis(oxalato)borate (LiBOB), lithium difluorooxalate borate (LiFOB); lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, LiC(SO2C2F5)3, etc. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0072] The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / dm 3 ~2.5 mol / dm 3 at 20 °C and 1 atmosphere, more preferably 0.3 mol / dm 3 ~2.0 mol / dm 3 and even more preferably 0.5 mol / dm 3 ~1.7 mol / dm 3 and particularly preferably 0.7 mol / dm 3 ~1.5 mol / dm 3 . By making the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be improved.

[0073] In addition to the non-aqueous solvent and the electrolyte salt, the non-aqueous electrolyte further contains an unsaturated cyclic carbonate and a fluorophosphate having a P-O bond as additives. By making the non-aqueous electrolyte contain the unsaturated cyclic carbonate and the fluorophosphate having a P-O bond, an improvement in the capacity retention rate after charge and discharge cycles and the output performance in a low-temperature environment can be achieved.

[0074] A part of the unsaturated cyclic carbonate and the fluorophosphate having a P-O bond contained in the non-aqueous electrolyte used in manufacturing the non-aqueous electrolyte storage element decomposes due to forming a film on the surface of the particles of the negative electrode active material as described above during the initial charge and discharge. Therefore, the unsaturated cyclic carbonate and the fluorophosphate that are not decomposed during the initial charge and discharge remain in the non-aqueous electrolyte. That is, the content of the unsaturated cyclic carbonate and the fluorophosphate having a P-O bond in the present invention refers to the remaining amount of the unsaturated cyclic carbonate and the fluorophosphate that are not decomposed during the initial charge and discharge in the non-aqueous electrolyte.

[0075] The unsaturated cyclic carbonate is not particularly limited as long as it is a cyclic compound having a carbonate structure (-O-(C=O)-O-) and a double bond or a triple bond in the molecule, and it can be a cyclic carbonate having a carbon-carbon double bond in the molecule. The unsaturated cyclic carbonate is decomposed during the initial charge and discharge, and a uniform and dense film can be formed on the surface of the particles of the negative electrode active material by the contribution of the double bond or the triple bond in the above-mentioned molecule. As the unsaturated cyclic carbonate, a cyclic carbonate having a carbon-carbon double bond in the ring structure, a cyclic carbonate having a carbon-carbon double bond in a part other than the ring structure, etc. can be mentioned. As the unsaturated cyclic carbonate, an unsaturated cyclic carbonate having 3 to 15 carbon atoms (for example, 3 to 12, preferably 3 to 9, more preferably 3 to 6) is preferably used. As long as the number of carbon-carbon double bonds of the above-mentioned unsaturated cyclic carbonate is 1 or more, it is not particularly limited, for example, it is 1 to 3, and preferably 1 or 2 (for example, 1). The unsaturated cyclic carbonate may also be an unsaturated cyclic carbonate in which a part or all of the hydrogen atoms are substituted by other groups or atoms (for example, fluorine atoms). It should be noted that the unsaturated cyclic carbonate mentioned here is a concept including its geometric isomers.

[0076] As a preferable example of the cyclic carbonate having a carbon-carbon double bond in the ring structure, the compound represented by the following general formula (1) can be mentioned.

[0077] [Chemical formula 1]

[0078]

[0079] Here, R in the above general formula (1) 1 and R 2 each independently selected from a hydrogen atom, a fluorine atom, and an alkyl group or an aryl group which may be substituted by a fluorine atom. Or R 1 and R 2 may be bonded to each other to form an aromatic ring or an aliphatic ring. In the above compound, at least one (for example, two) of the two substituents R 1 and R 2 on the carbon atom constituting the heterocycle may be a hydrogen atom or a fluorine atom. In addition, at least one of R 1 and R 2 may be an alkyl group or an aryl group having 1 to 6 carbon atoms (for example, 1 to 4, typically 1 or 2). R 1 and R 2 may be linear or branched. In addition, one or more of the hydrogen atoms of these alkyl chain skeletons may be a group having a structure substituted by a fluorine atom (that is, a fluorinated alkyl group having 1 to 6 carbon atoms). As a preferable example of the compound represented by the above general formula (1), a structure in which one of R 1 and R 2 is a hydrogen atom and the other is a fluorine atom, R 1 and R2 has a structure in which one is a hydrogen atom and the other is an alkyl group having 4 or less carbon atoms, R 1 and R 2 has a structure in which one is a hydrogen atom and the other is a fluorinated alkyl group having 4 or less carbon atoms, R 1 and R 2 both being hydrogen atoms, etc. Specific examples of the compound represented by the above general formula (1) include vinylene carbonate (VC), fluoro vinylene carbonate, methyl vinylene carbonate, fluoromethyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, trifluoromethyl vinylene carbonate, catechol carbonate, 1-phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate, and the like.

[0080] Examples of the cyclic carbonate having a carbon-carbon double bond in a part other than the ring structure include ethylene glycol vinyl carbonate (VEC), styrene carbonate, and the like.

[0081] As the unsaturated cyclic carbonate, a cyclic carbonate having a carbon-carbon double bond in the ring structure is preferred, and vinylene carbonate (VC) is more preferred. The above unsaturated cyclic carbonate can be used alone or in combination of two or more.

[0082] As the above fluorophosphate having a P-O bond, a compound in which at least one oxygen atom and at least one fluorine atom are bonded to a pentavalent phosphorus atom can be used. The number of oxygen atoms bonded to the phosphorus atom can be, for example, 1 to 4 (preferably 2 or 3). The number of fluorine atoms bonded to the phosphorus atom can be, for example, 1 to 4 (preferably 1 or 2). As the above fluorophosphate having a P-O bond, a fluorophosphate having a P=O bond is preferred, and for example, a fluorophosphate having a monofluorophosphate anion (PO3F 2- ), a difluorophosphate anion (PO2F2 -Various salts thereof. The above-mentioned fluorophosphate having a P-O bond is decomposed during the initial charge and discharge, and a rough film can be formed on the surface of the particles of the negative electrode active material by the contribution of the P-O bond and fluorine atoms in the above-mentioned molecule. The cation of the above-mentioned fluorophosphate is not particularly limited and can be an inorganic cation or an organic cation. Specific examples of the inorganic cation include cations of alkali metal elements such as Li, Na, and K; cations of alkaline earth metal elements such as Be, Mg, and Ca, etc. Specific examples of the organic cation include ammonium cations (ammonium ions), etc. Among them, lithium cations (lithium ions) are preferred. Preferred examples of such fluorophosphates include lithium monofluorophosphate, lithium difluorophosphate (LiDFP), lithium tetrafluorophosphate, sodium difluorophosphate, lithium bis(oxalate) difluorophosphate (LiFOP), etc. Among these, lithium difluorophosphate (LiDFP) is preferred.

[0083] As the lower limit of the molar ratio of the above-mentioned unsaturated cyclic carbonate to the total content of the above-mentioned unsaturated cyclic carbonate and the above-mentioned fluorophosphate having a P-O bond, it is 0.60, preferably 0.62, more preferably 0.65. In several embodiments, the molar ratio of the above-mentioned unsaturated cyclic carbonate to the total content of the above-mentioned unsaturated cyclic carbonate and the above-mentioned fluorophosphate having a P-O bond can be 0.66 or more, or can be 0.68 or more. As the upper limit of the molar ratio of the above-mentioned unsaturated cyclic carbonate, it is less than 1.0, more preferably 0.90, and further preferably 0.80. From the viewpoint of improving the output performance in a low-temperature environment, etc., the molar ratio of the above-mentioned unsaturated cyclic carbonate to the total content of the above-mentioned unsaturated cyclic carbonate and the above-mentioned fluorophosphate having a P-O bond can be 0.75 or less, or can be 0.70 or less. By making the content of the above-mentioned unsaturated cyclic carbonate within the above range, the capacity retention rate after charge and discharge cycling of the non-aqueous electrolyte storage element and the output performance in a low-temperature environment are excellent. The molar ratio of the above-mentioned unsaturated cyclic carbonate to the total content of the above-mentioned unsaturated cyclic carbonate and the above-mentioned fluorophosphate having a P-O bond can be any of the above lower limits or more and any of the above upper limits or less.

[0084] As the content (molar concentration) of the unsaturated cyclic carbonate in the above-mentioned non-aqueous electrolyte, as long as the ratio (molar ratio) of the content of the above-mentioned unsaturated cyclic carbonate to the total content of the above-mentioned unsaturated cyclic carbonate and the above-mentioned fluorophosphate having a P-O bond satisfies 0.60 or more and less than 1.0, there is no particular limitation. As the lower limit, it is preferably 1.4×10 -4 mol / dm 3 , more preferably 1.5×10 -4 mol / dm 3 , further preferably 1.6×10 -4 mol / dm 3As the upper limit of the content of the above-mentioned unsaturated cyclic carbonate, it is preferably less than 2.8×10 -4 mol / dm 3 and more preferably 2.5×10 -4 mol / dm 3 and even more preferably 2.2×10 - 4 mol / dm 3 . By making the content of the above-mentioned unsaturated cyclic carbonate within the above range, the capacity retention rate after charge and discharge cycles can be further improved. The content of the above-mentioned unsaturated cyclic carbonate can be above any of the above lower limits and below any of the above upper limits. It should be noted that the content of the unsaturated cyclic carbonate refers to the amount of substance (mole amount) of the unsaturated cyclic carbonate contained in 1 dm 3 of the non-aqueous electrolyte. In the case of containing multiple types of unsaturated cyclic carbonates, the content of the unsaturated cyclic carbonate refers to the total amount of substance (total mole amount) of the multiple unsaturated cyclic carbonates contained in 1 dm 3 of the non-aqueous electrolyte. Hereinafter, the same applies to the content of the fluorophosphate having a P-O bond.

[0085] As the content (molar concentration) of the fluorophosphate having a P-O bond in the above-mentioned non-aqueous electrolyte, as long as the ratio (molar ratio) of the content of the above-mentioned unsaturated cyclic carbonate to the total content of the above-mentioned unsaturated cyclic carbonate and the fluorophosphate having a P-O bond satisfies 0.60 or more and less than 1.0, there is no particular limitation. As the lower limit, it is preferably 6.6×10 -5 mol / dm 3 and more preferably 7.0×10 -5 mol / dm 3 and even more preferably 7.4×10 -5 mol / dm 3 . As the upper limit of the content of the fluorophosphate having a P-O bond, it is preferably 1.1×10 -4 mol / dm 3 and more preferably 9.6×10 -5 mol / dm 3 and even more preferably 8.2×10 -5 mol / dm 3 . By making the content of the fluorophosphate having a P-O bond within the above range, the output performance of the non-aqueous electrolyte storage element in a low-temperature environment can be further improved. The content of the fluorophosphate having a P-O bond can be above any of the above lower limits and below any of the above upper limits.

[0086] Regarding the difference between the content (molar concentration) of the unsaturated cyclic carbonate in the above non-aqueous electrolyte and the content (molar concentration) of the fluorophosphate having a P-O bond in the above non-aqueous electrolyte, as long as the ratio (molar ratio) of the content of the unsaturated cyclic carbonate to the total content of the unsaturated cyclic carbonate and the fluorophosphate having a P-O bond satisfies 0.60 or more and less than 1.0, there is no particular limitation, and it is preferably 7.4×10 -5 mol / dm 3 or more, more preferably 8.6×10 - 5 mol / dm 3 or more. In addition, the difference between the content of the unsaturated cyclic carbonate in the above non-aqueous electrolyte and the content of the fluorophosphate having a P-O bond in the above non-aqueous electrolyte is preferably 1.7×10 -4 mol / dm 3 or less, more preferably 1.5×10 -4 mol / dm 3 or less, still more preferably 1.4×10 -4 mol / dm 3 or less.

[0087] Regarding the total content (total molar concentration) of the above unsaturated cyclic carbonate and the fluorophosphate having a P-O bond, as long as the ratio (molar ratio) of the content of the unsaturated cyclic carbonate to the total content of the unsaturated cyclic carbonate and the fluorophosphate having a P-O bond satisfies 0.6 or more and less than 1.0, there is no particular limitation. As the lower limit thereof, it is preferably 2.1×10 -4 mol / dm 3 , more preferably 2.2×10 -4 mol / dm 3 , still more preferably 2.3×10 -4 mol / dm 3 . As the upper limit of the total content of the above unsaturated cyclic carbonate and the fluorophosphate having a P-O bond, it is preferably 3.9×10 - 4 mol / dm 3 , more preferably 3.5×10 -4 mol / dm 3 , still more preferably 3.0×10 -4 mol / dm 3The above total content may be not less than any of the above lower limits and not more than any of the above upper limits. By making the total content of the above unsaturated cyclic carbonate and the above fluorophosphate having a P-O bond within the above range, the above effects (at least one of the effect of improving the capacity retention rate after charge and discharge cycles and the effect of improving the output performance in a low-temperature environment, preferably both) can be further exerted well.

[0088] When the above unsaturated cyclic carbonate is vinylene carbonate (VC), the content of vinylene carbonate in the above non-aqueous electrolyte (by mass) may exceed 1.00% by mass, for example. The content of vinylene carbonate is preferably 1.05% by mass or more, more preferably 1.10% by mass or more. In several embodiments, the content of vinylene carbonate may be 1.15% by mass or more, or may be 1.20% by mass or more, for example. In addition, the content of vinylene carbonate in the above non-aqueous electrolyte (by mass) may be 2.00% by mass or less, for example. The content of vinylene carbonate is preferably 1.80% by mass or less, more preferably 1.70% by mass or less. In several embodiments, the content of vinylene carbonate may be 1.58% by mass or less, or may be 1.30% by mass or less, for example. The content of vinylene carbonate may be not less than any of the above lower limits and not more than any of the above upper limits. By making the content of vinylene carbonate within the above range, the above effects (at least one of the effect of improving the capacity retention rate after charge and discharge cycles and the effect of improving the output performance in a low-temperature environment, preferably both) can be further exerted well.

[0089] When the above fluorophosphate having a P-O bond is lithium difluorophosphate (LiDFP), the content of lithium difluorophosphate in the above non-aqueous electrolyte (by mass) may be less than 1.00% by mass, for example. The content of lithium difluorophosphate is preferably 0.90% by mass or less, more preferably 0.80% by mass or less. In several embodiments, the content of lithium difluorophosphate may be 0.75% by mass or less, or may be 0.72% by mass or less, for example. In addition, the content of lithium difluorophosphate in the above non-aqueous electrolyte (by mass) may be 0.10% by mass or more, for example. The content of lithium difluorophosphate is preferably 0.30% by mass or more, more preferably 0.50% by mass or more. In several embodiments, the content of lithium difluorophosphate may be 0.67% by mass or more, or may be 0.70% by mass or more, for example. The content of lithium difluorophosphate may be not less than any of the above lower limits and not more than any of the above upper limits. By making the content of lithium difluorophosphate within the above range, the above effects (at least one of the effect of improving the capacity retention rate after charge and discharge cycles and the effect of improving the output performance in a low-temperature environment, preferably both) can be further exerted well.

[0090] The non-aqueous electrolyte may contain additives other than unsaturated cyclic carbonates and fluorophosphates having a P-O bond. As such other additives, for example, oxalates such as lithium bis(oxalato)borate (LiBOB) and lithium difluorooxalate borate (LiFOB); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether, and dibenzofuran; partially halogenated products of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; vinylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, 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, dipyridyl disulfide, 1,3-propylene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, and tetrakis(trimethylsilyl) titanate, etc. These additives may be used singly or in combination of two or more. The above other components may be used singly or in combination of two or more.

[0091] The total content of the additives (unsaturated cyclic carbonates, fluorophosphates having a P-O bond, and other additives, i.e., components other than the non-aqueous solvent and the electrolyte salt) contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, still more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass with respect to the total mass of the non-aqueous electrolyte. By making the total content of the additives within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, or further improve the safety.

[0092] The shape of the non-aqueous electrolyte storage element of the present embodiment is not particularly limited, and examples thereof include cylindrical batteries, square batteries, flat batteries, coin-type batteries, button-type batteries, etc.

[0093] Figure 1This shows a non-aqueous electrolyte storage element 1 as an example of a square battery. It should be noted that this figure is a view of the interior of the container in perspective. An electrode body 2 having a positive electrode and a negative electrode wound with a separator interposed therebetween is housed in a square container 3. The positive electrode is electrically connected to the positive terminal 4 via the positive electrode lead wire 41. The negative electrode is electrically connected to the negative terminal 5 via the negative electrode lead wire 51.

[0094] <Configuration of the energy storage device>

[0095] The non-aqueous electrolyte storage element of the present embodiment can be used as a power source for vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs) that are assembled by combining multiple non-aqueous electrolyte storage elements to form an energy storage unit (battery module); a power source for electronic devices such as personal computers and communication terminals; or a power source for power storage. In this case, the technology of the present invention can be applied to at least one non-aqueous electrolyte storage element contained in the energy storage unit.

[0096] Figure 2 This shows an example of an energy storage device 30 formed by further combining energy storage units 20 formed by combining two or more electrically connected non-aqueous electrolyte storage elements 1. The energy storage device 30 may include a bus bar (not shown) for electrically connecting two or more non-aqueous electrolyte storage elements 1, a bus bar (not shown) for electrically connecting two or more energy storage units 20, and the like. The energy storage unit 20 or the energy storage device 30 may include one or more state monitoring devices (not shown) for monitoring the state of the non-aqueous electrolyte storage element 1.

[0097] <Manufacturing method of the non-aqueous electrolyte storage element>

[0098] The manufacturing method of the non-aqueous electrolyte storage element according to an embodiment of the present invention is not particularly limited. For example, the following manufacturing method can be adopted.

[0099] This manufacturing method includes: a step of preparing a negative electrode having a negative electrode active material layer, a step of preparing a non-aqueous electrolyte containing an unsaturated cyclic carbonate and a fluorophosphate having a P-O bond, and a step of performing initial charge and discharge on an uncharged and discharged storage element assembled using the above negative electrode and the above non-aqueous electrolyte.

[0100] The step of preparing the negative electrode can be performed, for example, by coating the negative electrode substrate with a negative electrode mixture and laminating the negative electrode active material layer along at least one surface of the negative electrode substrate. Specifically, for example, the negative electrode active material layer can be laminated by coating the negative electrode mixture on the negative electrode substrate and drying.

[0101] The negative electrode mixture contains a negative electrode active material. The negative electrode mixture can be a negative electrode mixture paste in a state that further contains a dispersion medium in addition to the negative electrode active material and each optional component constituting the above-mentioned negative electrode active material layer. As the dispersion medium, an organic solvent such as N-methylpyrrolidone (NMP) or toluene, water, etc. can be used.

[0102] In the process of preparing the non-aqueous electrolyte, for example, the non-aqueous electrolyte can be prepared by mixing components constituting the above-mentioned non-aqueous electrolyte such as an unsaturated cyclic carbonate, a fluorophosphate having a P-O bond, an electrolyte salt, and a non-aqueous solvent.

[0103] In this manufacturing method, in addition, it can further include: a process of preparing a positive electrode; a process of obtaining an electrode body by laminating the positive electrode and the negative electrode via a separator; a process of housing the electrode body in a container; a process of injecting the non-aqueous electrolyte into the container, etc. Then, an uncharged and discharged storage element can be obtained by sealing the injection port.

[0104] As the initial charge and discharge, the obtained uncharged and discharged storage element is charged and discharged one or more times. Thereby, a part of the above-mentioned unsaturated cyclic carbonate and the above-mentioned fluorophosphate having a P-O bond in the non-aqueous electrolyte prepared in the process of preparing the above-mentioned non-aqueous electrolyte decomposes, and a film is formed on the surface of the particles of the negative electrode active material.

[0105] In the above initial charge and discharge, for example, constant current constant voltage (CCCV) charging is performed with a charging current of 1.0C and a charging end voltage of 4.10V, and constant current (CC) discharge is performed with a discharge current of 1.0C and a discharge end voltage of 2.75V.

[0106] <Other Embodiments>

[0107] It should be noted that the non-aqueous electrolyte storage element of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. For example, the configuration of other embodiments can be added to the configuration of a certain embodiment. In addition, a part of the configuration of a certain embodiment can be replaced with the configuration of other embodiments or a known technique. Also, a part of the configuration of a certain embodiment can be deleted. In addition, a known technique can be added to the configuration of a certain embodiment.

[0108] In the above embodiments, the case where the non-aqueous electrolyte storage element is used as a non-aqueous electrolyte secondary battery (such as a lithium ion secondary battery) capable of charge and discharge has been described, but the type, shape, size, capacity, etc. of the non-aqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, double layer capacitors, or capacitors such as lithium ion capacitors.

[0109] In the above-described embodiment, an electrode body in which a positive electrode and a negative electrode are laminated via a separator has been described, but the electrode body may not include a separator. For example, the positive electrode and the negative electrode can be directly connected in a state where a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode.

[0110] Example

[0111] Hereinafter, the present invention will be described in more detail based on examples. The present invention is not limited to the following examples.

[0112] [Example 1]

[0113] (Fabrication of negative electrode)

[0114] A negative electrode mixture paste is prepared, which contains graphite as a negative electrode active material, SBR as a binder, CMC as a thickener, and water as a dispersion medium. The ratio of the negative electrode active material, the binder, and the thickener is 97:2:1 in terms of the mass ratio of solid components. The negative electrode mixture paste is coated on both sides of a copper foil with an average thickness of 10 μm as a negative electrode substrate and dried. Then, a negative electrode active material layer is formed by stamping to obtain a negative electrode. The BET specific surface area of the negative electrode active material layer of the obtained negative electrode is 1.085 m 2 / g.

[0115] (Fabrication of positive electrode)

[0116] A positive electrode mixture paste is prepared, which contains LiMn2O4 and LiNi 0.33 Co 0.33 Mn 0.33 O2 as a positive electrode active material, PVDF as a binder, and acetylene black as a conductive agent, and NMP as a dispersion medium. The ratio of the positive electrode active material, the binder, and the conductive agent is 93.5:3.5:3 in terms of the mass ratio of solid components. The ratio of LiMn2O4 and LiNi 0.33 Co 0.33 Mn 0.33 O2 is 70:30 in terms of the mass ratio. The positive electrode mixture paste is coated on both sides of an aluminum foil as a positive electrode substrate and dried. Then, stamping is performed to form a positive electrode active material layer. Thus, a positive electrode in which positive electrode active material layers are laminated on both sides of the positive electrode substrate is obtained.

[0117] (Preparation of non-aqueous electrolyte)

[0118] In a non-aqueous solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 25:75, at 1.0 mol / dm 3The content of [LiPF6] which is an electrolyte salt is mixed. To this mixed solution, vinylene carbonate (VC) which is an unsaturated cyclic carbonate as an additive and lithium difluorophosphate (LiDFP) which is a fluorophosphate having a P-O bond are mixed to prepare a non-aqueous electrolyte. The content of vinylene carbonate in the non-aqueous electrolyte is 1.5% by mass, and the content of lithium difluorophosphate is 1.0% by mass.

[0119] (Assembly of non-aqueous electrolyte storage element)

[0120] A wound electrode body is produced by laminating and winding the above positive electrode and negative electrode, and a polyethylene separator with a thickness of 30 μm. The wound electrode body is housed in a container. Then, the above non-aqueous electrolyte is injected into the container and sealed to obtain an uncharged and discharged storage element.

[0121] (Initial charge and discharge)

[0122] The obtained uncharged and discharged storage element is charged by constant current and constant voltage (CCCV) at a charging current of 1.0 C and a charging end voltage of 4.1 V in a constant temperature bath at 25 °C until the total charging time reaches 3 hours. Then, a 10-minute pause period is set. Next, constant current (CC) discharge is performed at a discharge current of 1.0 C and a discharge end voltage of 2.75 V. Through the above initial charge and discharge, the non-aqueous electrolyte storage element of Example 1 is obtained.

[0123] [Example 2 and Comparative Examples 1 - 6]

[0124] Except that the content of vinylene carbonate in the non-aqueous electrolyte is changed to 2% by mass in Example 2, 0.5% by mass in Comparative Example 1, and 1.0% by mass in Comparative Example 2, the same operations as in Example 1 are performed to obtain the non-aqueous electrolyte storage elements of Example 2, Comparative Example 1, and Comparative Example 2. Except that the content of vinylene carbonate in the non-aqueous electrolyte is changed to 0.5% by mass in Comparative Example 3, 1.0% by mass in Comparative Example 4, 1.5% by mass in Comparative Example 5, and 2.0% by mass in Comparative Example 6, and the BET specific surface area of the negative electrode active material layer is set to 0.665 m 2 / g, the same operations as in Example 1 are performed to obtain the non-aqueous electrolyte storage elements of Comparative Examples 3 to 6.

[0125] (Measurement of the content (residual amount) of the additive after the initial charge and discharge)

[0126] Using gas chromatography-mass spectrometry (GC-MS), the content (residual amount) of vinylene carbonate was measured for the non-aqueous electrolytes taken out by disassembling each non-aqueous electrolyte storage element after initial charge and discharge. In addition, the content (residual amount) of lithium difluorophosphate was measured for the non-aqueous electrolytes taken out above using ion chromatography analysis.

[0127] [Evaluation]

[0128] (Capacity retention rate after charge and discharge cycles)

[0129] (1) Initial discharge capacity confirmation test

[0130] Each non-aqueous electrolyte storage element was charged by constant current-constant voltage (CCCV) at a charging current of 1.0C and a charging end voltage of 4.10V in a constant temperature bath at 25°C until the total charging time reached 3 hours, and then a 5-minute pause period was set. Then, it was discharged by constant current (CC) at a discharge current of 1.0C and a discharge end voltage of 2.75V. The discharge capacity at this time was taken as the "initial discharge capacity".

[0131] (2) Charge and discharge cycle test

[0132] Each non-aqueous electrolyte storage element after the "initial discharge capacity" was measured was charged by constant current-constant voltage (CCCV) at a charging current of 1.0C and a charging end voltage of 4.10V in a constant temperature bath at 0°C until the charging current became 0.01C or less, and then a 10-minute pause period was set. Then, it was discharged by constant current (CC) at a discharge current of 1.0C and a discharge end voltage of 2.75V, and then a 10-minute pause period was set. This charge and discharge cycle was carried out 2000 times. After 2000 cycles, the discharge capacity was measured under the same conditions as the initial discharge capacity confirmation test, and the discharge capacity at this time was taken as the "discharge capacity after 2000 cycles". The percentage of the "discharge capacity after 2000 cycles" relative to the "initial discharge capacity" was taken as the capacity retention rate after charge and discharge cycles.

[0133] (Initial output performance in a low-temperature environment)

[0134] According to the following steps, the initial output performance [W] in a low-temperature environment was evaluated.

[0135] After the above "initial discharge capacity" was measured, each non-aqueous electrolyte storage element was charged by constant current and constant voltage (CCCV) at a charging current of 1.0C and a charging termination voltage of 4.10V in an environment of 25°C until the total charging time reached 3 hours. Then, a 5-minute pause period was set. Then, it was discharged by constant current (CC) at a discharge current of 1.0C and a discharge termination voltage of 2.75V, and the "1.0C discharge capacity at 25°C" was measured. Next, half of the "1.0C discharge capacity at 25°C" was used as SOC50%, and it was charged by constant current from the fully discharged state until it reached SOC50% at a charging current of 1.0C. Then, after storing it in an environment of 0°C for 5 hours, it was discharged at a discharge current of 0.2C for 10 seconds, and a 5-minute pause period was set. Then, the discharge current was adjusted to 0.6C and 1.0C, and it was discharged for 10 seconds respectively, and a 5-minute pause period was set. After each discharge, it was charged by constant current at a current of 1.0C to adjust the SOC to 50%. The initial output performance [W] at 0°C low temperature was calculated from the current of each discharge and the voltage at the 10th second after the start of discharge.

[0136] The capacity retention rate after charge and discharge cycles and the initial output performance at 0°C low temperature are shown in Table 1.

[0137]

[0138] As shown in Table 1, the BET specific surface areas of the negative electrode active material layers of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are all in the range of 0.80 m 2 / g to 1.5 m 2 / g. In each non-aqueous electrolyte storage element of Example 1 and Example 2, where the BET specific surface area of the negative electrode active material layer is in the range of 0.80 m 2 / g to 1.5 m 2 / g and the ratio (molar ratio) of the content of VC to the total content of VC and LiDFP of the above-mentioned fluorophosphate having a P-O bond with respect to the unsaturated cyclic carbonate is 0.6 or more and less than 1.0, the capacity retention rate after charge and discharge cycles and the initial output performance in a low-temperature environment are relatively high values.

[0139] On the other hand, in each non-aqueous electrolyte storage element of Comparative Example 1 and Comparative Example 2, where the BET specific surface area of the negative electrode active material layer is in the range of 0.80 m 2 / g to 1.5 m 2 / g and the ratio (molar ratio) of the content of VC to the total content of VC and LiDFP is less than 0.6, compared with Example 1 and Example 2, the capacity retention rate after charge and discharge cycles and the initial output performance in a low-temperature environment are relatively low values.

[0140] In addition, the BET specific surface areas of the negative electrode active material layers in Comparative Examples 3 to 6 are all less than 0.80 m 2 / g. In these Comparative Examples 3 to 6, the initial output performance of all non-aqueous electrolyte storage elements in a low-temperature environment is a relatively low value.

[0141] Moreover, it can be observed that for each non-aqueous electrolyte storage element in Comparative Examples 3 and 4 where the ratio (molar ratio) of the content of VC to the total content of VC and LiDFP is less than 0.6, compared with Comparative Examples 5 and 6 where the ratio (molar ratio) of the content of VC is 0.6 or more and less than 1.0, the capacity retention rate after charge and discharge cycling is high, and it shows an opposite trend to that of Examples 1, 2, Comparative Example 1, and Comparative Example 2 where the BET specific surface area of the negative electrode active material layer is 0.80 m 2 / g to 1.5 m 2 / g. The reason for this is speculated as follows: In Comparative Examples 3 to 6 where the BET specific surface area of the negative electrode active material layer is less than 0.80 m 2 / g, since the reaction area of the negative electrode active material layer is small, if the ratio (molar ratio) of the content of VC to the total content of VC and LiDFP is too large, then as the charge and discharge cycling progresses, the remaining VC is consumed on the newly formed surface of the negative electrode active material, and thus the film from VC becomes thicker, accelerating the increase in resistance, and as a result, the capacity retention rate after charge and discharge cycling decreases.

[0142] From the above results, it can be seen that this non-aqueous electrolyte storage element has excellent capacity retention rate after charge and discharge cycling and output performance in a low-temperature environment.

[0143] Industrial availability

[0144] The present invention is preferably used as a non-aqueous electrolyte storage element typified by a non-aqueous electrolyte secondary battery, and the above non-aqueous electrolyte secondary battery is used as a power source requiring rapid charging for electronic devices such as personal computers and communication terminals, and vehicles such as EVs, HEVs, and PHEVs.

[0145] In addition, as a preferred application object of the present invention, a large-sized lithium-ion secondary battery can be cited. For example, a large-sized lithium-ion secondary battery of a large-capacity type with a battery capacity of 5.0 Ah or more (for example, 5.0 Ah to 100 Ah) and assumed to be used in a charge and discharge cycle including a large current discharge of 3C or more (for example, 3C to 50C) can be exemplified. Since the non-aqueous electrolyte storage element of the present invention has excellent capacity retention rate during charge and discharge cycling, it can be preferably used for the above-mentioned large-sized lithium-ion secondary battery.

[0146] Symbol description

[0147] 1 Non-aqueous electrolyte storage element

[0148] 2 electrode bodies

[0149] 3 containers

[0150] 4 positive terminals

[0151] 41 positive electrode wires

[0152] 5 negative terminals

[0153] 51 negative electrode wires

[0154] 20 energy storage units

[0155] 30 energy storage device

Claims

1. A non-aqueous electrolyte storage element comprising: a negative electrode having a negative electrode active material layer, and a non-aqueous electrolyte containing an unsaturated cyclic carbonate and a fluorophosphate having a P-O bond; The BET specific surface area of the negative electrode active material layer is 0.80 m 2 / g to 1.5 m 2 / g, The ratio of the content of the unsaturated cyclic carbonate to the total content of the unsaturated cyclic carbonate and the fluorophosphate having a P-O bond is 0.60 or more and less than 1.0 on a molar basis.

2. The non-aqueous electrolyte storage element according to claim 1, wherein, The content of the unsaturated cyclic carbonate in the non-aqueous electrolyte is 1.4×10 -4 mol / dm 3 ~2.8×10 -4 mol / dm 3 .

3. The non-aqueous electrolyte storage element according to claim 1 or 2, wherein, The content of the fluorophosphate having a P-O bond in the non-aqueous electrolyte is 1.1×10 -4 mol / dm 3 or less.

4. The non-aqueous electrolyte storage element according to claim 1 or 2, wherein, The unsaturated cyclic carbonate is vinylene carbonate, The fluorophosphate having a P-O bond is lithium difluorophosphate.

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