Non-aqueous electrolyte and non-aqueous electrolyte energy storage element

Abstract

To provide a non-aqueous electrolyte that is a water soluble liquid and can suppress an expansion caused by use of a non-aqueous electrolyte storage element, and can reduce an initial low temperature resistance, and provide the non-aqueous electrolyte storage element having such as a non-aqueous electrolyte.SOLUTION: A non-aqueous electrolyte according to one aspect of the present invention, is a water soluble liquid containing an electrolyte salt and a non-aqueous solvent. The non-aqueous solvent contains: a cyclic carbonate solved in water; a chain-like carbonate solved in water; and a chain-like carbonate which is not solved in water. A content amount of the electrolyte salt exceeds 1.0 mol / dm3, and a content amount of the cyclic carbonate solved in water in the non-aqueous solvent is 35 volume% or more and 45 volume% or less. The content amount of the chain-like carbonate solved in water in the non-aqueous solvent is 15 volume% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

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

[0003] The non-aqueous electrolyte of a non-aqueous electrolyte storage element widely uses a non-aqueous electrolyte solution containing a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent. In this non-aqueous electrolyte solution, various non-aqueous solvents, additives, etc. are selected and used for performance improvement. For example, a non-aqueous electrolyte solution using a mixed solvent of a chain carbonate and a cyclic carbonate as the non-aqueous solvent is known (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The non-aqueous electrolyte for non-aqueous electrolyte energy storage devices usually falls under Class 4 Dangerous Goods (flammable liquids) in the Fire Service Act of Japan. Due to regulations under the Fire Service Act, in Japan, quantities of dangerous goods exceeding the specified amount cannot be stored outside of storage facilities, nor can they be handled outside of manufacturing plants, storage facilities, and handling facilities. Among dangerous goods, for Class 4 Dangerous Goods, namely the First Petroleum Products, Second Petroleum Products, and Third Petroleum Products, the specified amounts differ between water-insoluble liquids and water-soluble liquids, and the specified amount for water-soluble liquids is twice that of the water-insoluble liquid of the same product name. For example, in a non-aqueous electrolyte containing a mixed solvent of the above-mentioned chain carbonate and cyclic carbonate, a non-aqueous solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 30:70, and lithium hexafluorophosphate (LiPF6) is dissolved as an electrolyte salt at a content of 1.2 mol / dm 3 falls under the Second Petroleum Products water-insoluble liquid with a specified amount of 1000 L. Here, when the non-aqueous electrolyte corresponding to the Second Petroleum Products is a water-soluble liquid, the specified amount becomes 2000 L, and since it can be stored outside of storage facilities and handled outside of manufacturing plants, storage facilities, and handling facilities, it is industrially beneficial.

[0006] According to the findings of the inventors, the non-aqueous electrolyte tends to meet the above-mentioned criteria for water-soluble liquids by mixing a chain carbonate that dissolves in water, such as dimethyl carbonate (DMC). However, a non-aqueous electrolyte energy storage device equipped with such a non-aqueous electrolyte is prone to swelling of the non-aqueous electrolyte energy storage device when used at high voltages. Also, when the composition is made to meet the criteria for water-soluble liquids without mixing a chain carbonate that dissolves in water, such as DMC, in the non-aqueous electrolyte, the initial low-temperature resistance of the non-aqueous electrolyte energy storage device may increase.

[0007] The present invention has been made based on the above circumstances, and its object is to provide a non-aqueous electrolyte that is a water-soluble liquid and can suppress swelling associated with the use of a non-aqueous electrolyte energy storage device and lower the initial low-temperature resistance, and a non-aqueous electrolyte energy storage device equipped with such a non-aqueous electrolyte.

Means for Solving the Problems

[0008] A non-aqueous electrolyte according to one aspect of the present invention is a water-soluble liquid containing an electrolyte salt and a non-aqueous solvent, wherein the non-aqueous solvent includes a water-soluble cyclic carbonate, a water-soluble linear carbonate, and a water-insoluble linear carbonate, and the electrolyte salt content is 1.0 mol / dm³. 3 The non-aqueous solvent contains 35% to 45% by volume of cyclic carbonates soluble in water, and the non-aqueous solvent contains 15% or less by volume of chain-like carbonates soluble in water.

[0009] A non-aqueous electrolyte energy storage element according to another aspect of the present invention comprises the non-aqueous electrolyte. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide a water-soluble liquid non-aqueous electrolyte that can suppress swelling associated with the use of a non-aqueous electrolyte energy storage element and can lower the initial low-temperature resistance, and a non-aqueous electrolyte energy storage element equipped with such a non-aqueous electrolyte. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a perspective view showing one embodiment of a non-aqueous electrolyte energy storage element. [Figure 2] Figure 2 is a schematic diagram showing one embodiment of an energy storage device configured by assembling multiple non-aqueous electrolyte energy storage elements. [Modes for carrying out the invention]

[0012] First, an overview of the non-aqueous electrolytes and non-aqueous electrolyte energy storage elements disclosed herein will be provided.

[0013] A non-aqueous electrolyte according to one aspect of the present invention is a water-soluble liquid containing an electrolyte salt and a non-aqueous solvent, wherein the non-aqueous solvent includes a water-soluble cyclic carbonate, a water-soluble linear carbonate, and a water-insoluble linear carbonate, and the electrolyte salt content is 1.0 mol / dm³.3 The non-aqueous solvent contains 35% to 45% by volume of cyclic carbonates soluble in water, and the non-aqueous solvent contains 15% or less by volume of chain-like carbonates soluble in water.

[0014] The non-aqueous electrolyte is a water-soluble liquid that can suppress swelling associated with the use of non-aqueous electrolyte energy storage elements and lower the initial low-temperature resistance. The reason for this is not entirely clear, but the following reasons are speculated. The non-aqueous electrolyte is a water-soluble liquid because, in addition to water-soluble linear carbonates, it contains a sufficient amount of water-soluble cyclic carbonates and a sufficient amount of electrolyte salts. On the other hand, water-soluble linear carbonates such as DMC have low oxidation resistance, so gas is easily generated by the decomposition of the non-aqueous electrolyte, especially when non-aqueous electrolyte energy storage elements are used at high voltages, which can cause the non-aqueous electrolyte energy storage elements to swell. In contrast, the non-aqueous electrolyte contains a small amount of water-soluble linear carbonate (less than 15% by volume), so the amount of gas generated by the decomposition of the non-aqueous electrolyte is small, and it is speculated that swelling associated with the use of non-aqueous electrolyte energy storage elements can be suppressed. Furthermore, it is presumed that the viscosity of the non-aqueous electrolyte is moderately suppressed due to its composition, which allows for a lower initial low-temperature resistance of the non-aqueous electrolyte energy storage element. Moreover, since the non-aqueous electrolyte is a water-soluble liquid, the specified quantity is larger than that of a non-water-soluble liquid of the same name, making it industrially beneficial.

[0015] Furthermore, "water-soluble liquid" refers to a liquid that falls under the category of "water-soluble liquid" in Appendix 3 of the Cabinet Order Concerning the Regulation of Dangerous Goods, and means that when gently stirred with the same volume of pure water at 1 atmosphere and a temperature of 20°C, the mixture maintains a uniform appearance even after the flow has subsided. Furthermore, the Cabinet Order Concerning the Regulation of Dangerous Goods is a Cabinet Order enacted based on the provisions of the Fire Service Act. Furthermore, in this specification, "gently stirring with the same volume of pure water" means pouring 10 mL of pure water and 10 mL of non-aqueous electrolyte into a 50 mL beaker and stirring 20 times with a stirring rod at a rotation speed of 60 rpm. Furthermore, "after the flow has subsided" means after stirring, letting it stand for 30 seconds or more and confirming that no flow is visible.

[0016] Furthermore, the statement that each compound is "soluble in water" means that its solubility in water at 20°C, measured according to OECD Testing Guideline No. 105 (Solubility in Water, adopted July 27, 1995), is 114.7 g / dm³. 3 The above is what is meant. "Insoluble in water" for each compound means that its solubility in water at 20°C, measured in accordance with the above OECD Test Guideline No. 105, is 114.7 g / dm³. 3 This means less than [a certain value]. Note that the solubility of DMC in water at 20°C, measured in accordance with the above OECD Test Guideline No. 105, is 114.7 g / dm³. 3 Therefore, for each compound to be "soluble in water," it means that the solubility of that compound in water at 20°C is greater than or equal to the solubility of DMC in water at 20°C, and for each compound to be "insoluble in water," it means that the solubility of that compound in water at 20°C is less than the solubility of DMC in water at 20°C.

[0017] A non-aqueous electrolyte storage element according to another aspect of the present invention includes the non-aqueous electrolyte. Although a non-aqueous electrolyte that is a water-soluble liquid is used in the non-aqueous electrolyte storage element, swelling associated with use is suppressed and the initial low-temperature resistance is low. Further, since the non-aqueous electrolyte storage element uses a non-aqueous electrolyte that is a water-soluble liquid, the specified quantity is larger than that in the case of a non-water-soluble liquid of the same product name, which is industrially beneficial.

[0018] In the non-aqueous electrolyte storage element, the positive electrode potential at the charging cut-off voltage during normal use is 4.2 V (vs. Li / Li + ) or more and 4.5 V (vs. Li / Li + ) or less. When the positive electrode potential at the charging cut-off voltage during normal use is 4.2 V (vs. Li / Li + ) or more, it can function as a high-voltage non-aqueous electrolyte storage element. Further, even when the positive electrode potential at the charging cut-off voltage during normal use of the non-aqueous electrolyte storage element is 4.2 V (vs. Li / Li + ) or more, swelling associated with use is suppressed. On the other hand, by setting the positive electrode potential at the charging cut-off voltage during normal use to 4.5 V (vs. Li / Li + ) or less, swelling associated with use can be further suppressed.

[0019] Here, normal use refers to the case where the non-aqueous electrolyte storage element is used by adopting the charging conditions recommended or specified for the non-aqueous electrolyte storage element. When a charger for the non-aqueous electrolyte storage element is prepared, it refers to the case where the non-aqueous electrolyte storage element is used by applying the charger. For example, in a non-aqueous electrolyte storage element using graphite as the negative electrode active material, depending on the design, when the charging cut-off voltage is 4.25 V, the positive electrode potential is about 4.35 V (vs. Li / Li + ).

[0020] This document describes in detail a non-aqueous electrolyte energy storage element, an energy storage device, a method for manufacturing a non-aqueous electrolyte energy storage element, and other embodiments according to one embodiment of the present invention. Note that the names of the components (parts) used in each embodiment may differ from the names of the components (parts) used in the background art.

[0021] <Nonaqueous electrolyte> A non-aqueous electrolyte according to one embodiment of the present invention is a water-soluble liquid containing an electrolyte salt and a non-aqueous solvent. This non-aqueous electrolyte is suitably used as a non-aqueous electrolyte in a non-aqueous electrolyte energy storage element.

[0022] (Non-aqueous solvent) Non-aqueous solvents include cyclic carbonates that dissolve in water, linear carbonates that dissolve in water, and linear carbonates that do not dissolve in water.

[0023] Examples of cyclic carbonates that dissolve in water include ethylene carbonate (EC) and propylene carbonate (PC). One or two types of cyclic carbonates that dissolve in water can be used simultaneously.

[0024] The content of water-soluble cyclic carbonates in the non-aqueous solvent is 35% by volume or more and 45% by volume or less, with a preferred lower limit of 36% by volume, more preferably 37% by volume, even more preferably 38% by volume, even more preferably 39% by volume, and particularly preferred at 40% by volume. By setting the content of water-soluble cyclic carbonates in the non-aqueous solvent to be above the above lower limit, the water solubility of the non-aqueous electrolyte can be increased. On the other hand, the upper limit of water-soluble cyclic carbonates in the non-aqueous solvent is preferred at 44% by volume, more preferably 43% by volume, even more preferably 42% by volume, even more preferably 41% by volume, and particularly preferred at 40% by volume. By setting the content of water-soluble cyclic carbonates in the non-aqueous solvent to be below the above upper limit, it is possible to suppress the viscosity of the non-aqueous electrolyte and lower the initial low-temperature resistance of the non-aqueous electrolyte energy storage element.

[0025] When the non-aqueous solvent contains EC as a cyclic carbonate that dissolves in water, the EC content in the non-aqueous solvent is preferably 10% to 44% by volume, more preferably 15% to 40% by volume, even more preferably 20% to 36% by volume, and in some cases even more preferably 24% to 30% by volume. When the non-aqueous solvent contains PC as a cyclic carbonate that dissolves in water, the PC content in the non-aqueous solvent is preferably 1% to 30% by volume, more preferably 3% to 25% by volume, even more preferably 4% to 20% by volume, and in some cases even more preferably 10% to 18% by volume.

[0026] Examples of water-soluble linear carbonates include dimethyl carbonate (DMC). One or more water-soluble linear carbonates can be used.

[0027] The upper limit of the content of water-soluble linear carbonate in the non-aqueous solvent is 15% by volume, preferably 12% by volume or less, and more preferably 10% by volume or less. By keeping the content of water-soluble linear carbonate in the non-aqueous solvent below the above upper limit, swelling associated with the use of the non-aqueous electrolyte energy storage element can be suppressed. The lower limit of the content of water-soluble linear carbonate in the non-aqueous solvent is preferably 0.01% by volume, more preferably 0.1% by volume, even more preferably 1% by volume, even more preferably 3% by volume, even more preferably 5% by volume, and even more preferably 7% by volume. By keeping the content of water-soluble linear carbonate in the non-aqueous solvent above the above lower limit, the water solubility of the non-aqueous electrolyte is increased, and the initial low-temperature resistance of the non-aqueous electrolyte energy storage element tends to be lower.

[0028] Examples of water-insoluble linear carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. Among these, EMC is preferred. One or more water-insoluble linear carbonates can be used.

[0029] The content of water-insoluble linear carbonates in the non-aqueous solvent is preferably 35% to 64% by volume, more preferably 40% to 60% by volume, and even more preferably 45% to 55% by volume. By setting the content of water-insoluble linear carbonates in the non-aqueous solvent above the lower limit, it is possible to suppress the viscosity of the non-aqueous electrolyte and lower the initial low-temperature resistance of the non-aqueous electrolyte energy storage element. On the other hand, by setting the content of water-insoluble linear carbonates in the non-aqueous solvent below the upper limit, it is possible to increase the water solubility of the non-aqueous electrolyte.

[0030] The non-aqueous solvent may further contain other non-aqueous solvents other than water-soluble cyclic carbonates, water-soluble linear carbonates, and water-insoluble linear carbonates. Examples of other non-aqueous solvents include water-insoluble cyclic carbonates, esters, ethers, amides, sulfones, lactones, nitriles, etc. However, the lower limit of the total content of water-soluble cyclic carbonates, water-soluble linear carbonates, and water-insoluble linear carbonates in the non-aqueous solvent is preferably 90% by volume, and more preferably 99% by volume. Similarly, the lower limit of the total content of all carbonates in the non-aqueous solvent is preferably 90% by volume, and more preferably 99% by volume. The non-aqueous solvent may consist substantially only of water-soluble cyclic carbonates, water-soluble linear carbonates, and water-insoluble linear carbonates, or it may consist substantially only of carbonates. By adopting this composition, the water solubility, viscosity, and oxidation resistance of the non-aqueous electrolyte are improved, which further suppresses swelling associated with the use of non-aqueous electrolyte energy storage elements and lowers the initial low-temperature resistance.

[0031] (Electrolyte salts) The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred.

[0032] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2; lithium oxalate salts such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); and lithium salts having halogenated hydrocarbon groups such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0033] The electrolyte salt content in the non-aqueous electrolyte is 1.0 mol / dm³ at 20°C and 1 atm. 3 It is greater than 1.1 mol / dm³ 3 The above is preferable, 1.2 mol / dm 3 The above is more preferable. By setting the electrolyte salt content in the non-aqueous electrolyte above the lower limit, the water solubility of the non-aqueous electrolyte can be increased. The upper limit of the electrolyte salt content in the non-aqueous electrolyte is 1.6 mol / dm³. 3 Preferably, 1.5 mol / dm 3 More preferably, 1.4 mol / dm 3 A more preferable is 1.3 mol / dm 3 In some cases, this is even more preferable. By keeping the electrolyte salt content in the non-aqueous electrolyte below the above upper limit, it is possible to suppress the viscosity of the non-aqueous electrolyte and lower the initial low-temperature resistance of the non-aqueous electrolyte energy storage element.

[0034] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and electrolyte salt. Examples of additives include: aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halides of the aforementioned 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; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; and ethyl sulfite. Examples include propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethylsulfone, dimethyl sulfoxide, 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, 1,3-propensultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butensultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakithrimethylsilyl titanate, etc. These additives may be used individually or in combination of two or more.

[0035] The additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass, relative to the total mass of the non-aqueous electrolyte. By setting the additive content within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

[0036] The non-aqueous electrolyte can be manufactured by known methods. It can be prepared by mixing an electrolyte salt, a non-aqueous solvent, and, if necessary, additives in predetermined amounts.

[0037] <Non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element (hereinafter also simply referred to as "energy storage element") according to one embodiment of the present invention comprises 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 stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with a separator in between, or a wound type in which the positive electrode and negative electrode are wound in a stacked state with a separator in between. The non-aqueous electrolyte exists in a state impregnated with the positive electrode, negative electrode, and separator. As an example of a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0038] (positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode active material layer disposed directly on the positive electrode substrate or via an intermediate layer.

[0039] The positive electrode substrate is conductive. Whether or not it is conductive is determined by the volume resistivity measured in accordance with JIS-H-0505 (1975), which is 10 7The determination is made using Ω·cm as the threshold. The positive electrode substrate material can be a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoint of high potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30 as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0040] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte energy storage element.

[0041] The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The composition of the intermediate layer is not particularly limited and may include, for example, a binder and a conductive agent.

[0042] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer may optionally contain conductive agents, binders, thickeners, fillers, and other optional components.

[0043] The positive electrode active material can be appropriately selected from known positive electrode active materials. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used as positive electrode active materials. Examples of positive electrode active materials include lithium transition metal composite oxides having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanionic compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having an α-NaFeO2 crystal structure include Li[Lix 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, 0<1-x-γ), 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, 0<1-x-γ), 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, 0<1-x-γ-β), Li[Li x Ni γ Co β Al (1-x-γ-β) Examples include ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), etc. As a lithium transition metal composite oxide having a spinel-type crystal structure, Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples include O4. 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. Some atoms or polyanions in these materials may be substituted with atoms or anions 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 may be used in mixture form.

[0044] As the positive electrode active material, a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure is preferred, and 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, 0<1-x-γ-β) is more preferable. By using such a positive electrode active material, the positive electrode potential at the charging termination voltage during normal use is 4.2V(vs.Li / Li + The non-aqueous electrolyte energy storage element can be used effectively even under conditions such as those described above.

[0045] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material above the lower limit makes it easier to manufacture or handle the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When a composite material of the positive electrode active material and other materials is used, the average particle size of the composite material is used as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering method on a dilution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013), becomes 50%.

[0046] To obtain powder with a predetermined particle size, grinders and classifiers are used. Examples of grinding methods include using mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counter-jet mills, swirling airflow jet mills, or sieves. Wet grinding, which involves the coexistence of water or organic solvents such as hexane, can also be used during grinding. For classification, sieves and wind classifiers are used as needed, both dry and wet.

[0047] 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 even more preferably 80% to 95% by mass. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0048] The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent can take the form of powder or fiber. One of these materials may be used alone as the conductive agent, or two or more may be used in mixture form. These materials may also be used in composite form. For example, a composite material of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coating properties, and acetylene black is particularly preferred.

[0049] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the non-aqueous electrolyte energy storage element can be increased.

[0050] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0051] The binder content in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By keeping the binder content within the above range, the active material can be stably maintained.

[0052] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickening agent has a functional group that reacts with lithium or the like, this functional group may be deactivated beforehand by methylation or the like.

[0053] The filler is not particularly limited. Examples of fillers 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, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof.

[0054] The positive electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic 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.

[0055] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer disposed directly on the negative electrode substrate or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from, for example, the configurations exemplified in the positive electrode.

[0056] The negative electrode substrate is electrically conductive. Suitable materials for the negative electrode substrate include metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, as well as carbonaceous materials. Among these, copper or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials, with foil being preferred from a cost perspective. 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.

[0057] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte energy storage element.

[0058] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer optionally contains conductive agents, binders, thickeners, fillers, and other optional components. These optional components can be selected from the materials exemplified above for the positive electrode.

[0059] The negative electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0060] The negative electrode active material can be appropriately selected from known negative electrode active materials. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used as negative electrode active materials. Examples of negative electrode active materials include: metallic Li; metals or metalloids such as Si and Sn; metal oxides or metalloid oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 LiTiO 2、Examples of materials include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or poorly graphitizable carbon). Among these materials, graphite and non-graphitizable carbon are preferred, with graphite being more preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be used in mixture form.

[0061] "Graphite" refers to the average lattice plane spacing (d) of the (002) plane, determined by X-ray diffraction before charging or discharging, or during the discharge state. 002 ) refers to carbon materials with a n-scale between 0.33 nm and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the standpoint of obtaining materials with stable physical properties.

[0062] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging or during the discharge state. 002 This refers to carbon materials with a nautical radius of 0.34 nm or more and 0.42 nm or less. Non-graphitized carbons include poorly graphitizable carbons and easily graphitizable carbons. Examples of non-graphitized carbons include resin-derived materials, petroleum pitch or materials derived from petroleum pitch, petroleum coke or materials derived from petroleum coke, plant-derived materials, and alcohol-derived materials.

[0063] Here, "discharge state" refers to a state in which sufficient lithium ions that can be absorbed and released during charging and discharging are released from the carbon material, which is the negative electrode active material. For example, in a half-cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode, this is the state in which the open-circuit voltage is 0.7V or higher.

[0064] "Non-graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength between 0.36 nm and 0.42 nm.

[0065] "Easily graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.34 nm or more and less than 0.36 nm.

[0066] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, between 1 nm and 100 μm. If the negative electrode active material is a carbon material, titanium-containing oxide, or polyphosphate compound, its average particle size may be between 1 μm and 100 μm. If the negative electrode active material is Si, Sn, Si oxide, or Sn oxide, its average particle size may be between 1 nm and 1 μm. Setting the average particle size of the negative electrode active material above the lower limit makes it easier to manufacture or handle. Setting the average particle size of the negative electrode active material below the upper limit improves the electronic conductivity of the active material layer. To obtain powder with a predetermined particle size, a pulverizer or classifier is used. The pulverizing method and classification method can be selected from, for example, the methods exemplified above for the positive electrode. If the negative electrode active material is a metal such as metallic Li, the negative electrode active material may be in the form of foil.

[0067] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode active material layer.

[0068] (Separator) The separator can be appropriately selected from known separators. Examples of separators include a separator consisting only of a base layer, or a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer. Examples of the base layer shape of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. As the material for the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative degradation resistance. A composite material of these resins may also be used as the base layer of the separator.

[0069] The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere of 1 atmosphere, and more preferably have a mass loss of 5% or less when heated from room temperature to 800°C. Inorganic compounds are examples of materials with a mass loss of less than the specified amount. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; 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 fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. These inorganic compounds may be used individually or in combination, or two or more may be used as a mixture. Among these inorganic compounds, silicon dioxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for non-aqueous electrolyte energy storage elements.

[0070] The porosity of the separator is preferably 80 volume% or less from the viewpoint of strength, and preferably 20 volume% or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value and means the measurement value obtained using a mercury porosimeter.

[0071] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. Using a polymer gel has the effect of suppressing leakage. A polymer gel may also be used in combination with a porous resin film or nonwoven fabric as described above as a separator.

[0072] (Non-aqueous electrolyte) The non-aqueous electrolyte used in the non-aqueous electrolyte energy storage element is the non-aqueous electrolyte according to the embodiment of the present invention described above.

[0073] (Positive electrode potential at the charging termination voltage during normal use) The non-aqueous electrolyte energy storage element generates less gas due to the decomposition of the non-aqueous electrolyte, even when used at high voltages, and swelling during use is suppressed. Therefore, the non-aqueous electrolyte energy storage element can be used at high operating voltages. The positive electrode potential at the charging termination voltage during normal use of the non-aqueous electrolyte energy storage element is, for example, 4.0V (vs. Li / Li + ) or higher is also acceptable, but 4.2V (vs. Li / Li + ) or higher is preferable. On the other hand, the upper limit of the positive electrode potential at the charging termination voltage during normal use is, for example, 5.0V (vs.Li / Li + ) may be used, but 4.5V (vs. Li / Li + ) is preferable. By keeping the positive electrode potential at the charging termination voltage during normal use below the above upper limit, swelling associated with the use of the non-aqueous electrolyte energy storage element can be further suppressed.

[0074] The shape of the non-aqueous electrolyte energy storage element in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, etc. Furthermore, the material of the outer casing (container) of the non-aqueous electrolyte energy storage element in this embodiment is not particularly limited, and examples include metal, resin, and a metal-resin composite film in which resin layers are formed on both sides of a metal layer. Among these, it is preferable to include a metal-resin composite film in the outer casing (container). This allows for the full enjoyment of the effects of the present invention.

[0075] Figure 1 shows a non-aqueous electrolyte energy storage element 1 as an example of a rectangular battery. Note that the figure is a transparent view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound around a separator is housed in a rectangular container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via a negative electrode lead 51.

[0076] <Energy storage device> The non-aqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) formed by assembling multiple non-aqueous electrolyte energy storage elements 1 in power supplies for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power supplies for electronic devices such as personal computers and communication terminals, or power storage power supplies. In this case, it is sufficient that the technology of the present invention is applied to at least one non-aqueous electrolyte energy storage element included in the energy storage unit.

[0077] Figure 2 shows an example of an energy storage device 30 which is formed by further assembling energy storage units 20, each of which is an assembly of two or more electrically connected non-aqueous electrolyte energy storage elements 1. The energy storage device 30 may include busbars (not shown) that electrically connect two or more non-aqueous electrolyte energy storage elements 1, busbars (not shown) that electrically connect two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a condition monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte energy storage elements.

[0078] <Method for manufacturing a non-aqueous electrolyte energy storage element> The method for manufacturing the non-aqueous electrolyte energy storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and housing the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes preparing a positive electrode and a negative electrode, and forming the electrode body by stacking or winding the positive electrode and the negative electrode via a separator.

[0079] The method for housing the non-aqueous electrolyte in a container can be appropriately selected from known methods. For example, the non-aqueous electrolyte can be injected through an inlet formed in the container, and then the inlet can be sealed.

[0080] <Other Embodiments> Furthermore, the non-aqueous electrolyte and non-aqueous electrolyte energy storage element of the present invention are not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. In addition, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0081] In the above embodiment, we described a case where the non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery), but the type, shape, dimensions, capacity, etc., of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, or capacitors such as lithium-ion capacitors.

[0082] In the above embodiment, an electrode body in which a positive electrode and a negative electrode are stacked with a separator in between has been described, but the electrode body does not need to have a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of either the positive electrode or the negative electrode. [Examples]

[0083] 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.

[0084] The non-aqueous solvents used in the examples and comparative examples are shown below. EC: Ethylene carbonate (a cyclic carbonate that dissolves in water) PC: Propylene carbonate (a cyclic carbonate that dissolves in water) DMC: Dimethyl carbonate (a chain-like carbonate that dissolves in water) EMC: Ethyl methyl carbonate (a chain-like carbonate that does not dissolve in water)

[0085] [Example 1] (Preparation of non-aqueous electrolyte) A non-aqueous solvent prepared by mixing EC, PC, DMC, and EMC in a volume ratio of 35:5:10:50, containing 1.20 mol / dm³ 3 LiPF6 was dissolved in the specified amount to obtain the non-aqueous electrolyte of Example 1.

[0086] (Fabrication of the positive electrode) LiNi 6 / 10 Mn 2 / 10 Co 2 / 10 A positive electrode mixture paste was prepared by mixing O2, acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium. The mass ratio of the positive electrode active material, AB, and PVDF was 93:4:3 (on a solid content basis). The positive electrode mixture paste was applied to both sides of an aluminum foil substrate and dried. After that, a roll press was performed to obtain the positive electrode.

[0087] (Fabrication of the negative electrode) A negative electrode mixture paste was prepared by mixing graphite, the negative electrode active material; styrene-butadiene rubber (SBR), the binder; carboxymethylcellulose (CMC), the thickener; and water, the dispersion medium. The mass ratio of the negative electrode active material, SBR, and CMC was 97:2:1 (on a solid content basis). The negative electrode mixture paste was applied to both sides of a copper foil, which served as the negative electrode substrate, and dried. Subsequently, a roll press was performed to obtain the negative electrode.

[0088] (Fabrication of non-aqueous electrolyte energy storage elements) A microporous membrane made of polyolefin was used as a separator. An electrode body was fabricated by stacking the positive electrode and the negative electrode with this separator in between. This electrode body was housed in a rectangular aluminum container, and positive electrode terminals and negative electrode terminals were attached. After pouring the non-aqueous electrolyte into the container (rectangular container), it was sealed to obtain the non-aqueous electrolyte energy storage element of Example 1.

[0089] [Examples 2 to 3, Comparative Examples 1 to 14] Except for the fact that the contents of the electrolyte salt and each non-aqueous solvent were as shown in Table 1 during the preparation of the non-aqueous electrolyte, the non-aqueous electrolytes and each non-aqueous electrolyte energy storage element of Examples 2 to 3 and Comparative Examples 1 to 14 were obtained in the same manner as in Example 1.

[0090] [evaluation] (Water solubility evaluation) The following water solubility evaluation was performed on each of the obtained non-aqueous electrolytes. Under an atmosphere of 1 atmosphere and 20°C, 10 mL of pure water and 10 mL of non-aqueous electrolyte were poured into a 50 mL beaker and gently stirred. Specifically, a stirring rod was used to stir 20 times at a rotation speed of 60 rpm. After stirring, the mixture was allowed to stand for 30 seconds or more, and it was confirmed that no more flow was observed visually. Non-aqueous electrolytes that maintained a uniform appearance even after the flow ceased were evaluated as water-soluble liquids, and non-aqueous electrolytes that separated into two phases were evaluated as non-water-soluble liquids. The evaluation results are shown in Table 1.

[0091] (Initial charge / discharge) Each obtained non-aqueous electrolyte energy storage element was charged with a constant current of 1.0C to 4.25V at a temperature of 25°C, and then charged with a constant voltage of 4.25V. The charging was terminated when the total charging time reached 3 hours. After a 10-minute pause, a constant current discharge was performed with a current of 1.0C to 2.75V, followed by a 10-minute pause. These charging and discharging processes constituted one cycle, and two cycles were performed.

[0092] (Initial low-temperature resistance) Each non-aqueous electrolyte energy storage element that underwent initial charging and discharging was charged with a constant current of 1.0C at 25°C to bring its State of Charge (SOC) to 50%. After being stored in a -10°C constant temperature bath for 4 hours, it was discharged for 30 seconds at currents of 0.2C, 0.5C, or 1.0C. After each discharge, it was charged with a constant current of 1.0C to bring its SOC to 50%. The relationship between the current in each discharge and the voltage at 10 seconds after the start of discharge was plotted, and the initial low-temperature resistance (DC resistance) was determined from the slope of the straight line obtained from the three plots. The measurement results are shown in Table 1. In Table 1, "-" indicates that evaluation was not performed.

[0093] (Swelling after charge / discharge cycle testing) Charge-discharge cycle tests were performed on each non-aqueous electrolyte energy storage element in Examples 1 to 3, Comparative Examples 5, 6, and 9 to 14 after initial low-temperature resistance measurement, and on each non-aqueous electrolyte energy storage element in Comparative Examples 1 to 4, 7, and 8 after initial charge-discharge, according to the following procedure: At 45°C, constant current charging was performed at a current of 1.0C up to 4.25V, followed by constant voltage charging at 4.25V. The charging termination condition was when the total charging time reached 3 hours. After a 10-minute pause, constant current discharge was performed at a current of 1.0C up to 2.75V, followed by a 10-minute pause. These charging and discharging processes constituted one cycle, and a charge-discharge cycle test was performed for 1000 cycles. The thickness of the non-aqueous electrolyte energy storage element was measured before and after the charge-discharge cycle test. The degree of swelling after the charge-discharge cycle test was evaluated based on the percentage of the thickness of the non-aqueous electrolyte energy storage element after the charge-discharge cycle test relative to the thickness of the non-aqueous electrolyte energy storage element before the charge-discharge cycle test, according to the following criteria. The evaluation results are shown in Table 1. A + : 108% or less A: More than 108% and less than 110% B: More than 110% and less than 120% C: over 120%

[0094] [Table 1]

[0095] Although the non-aqueous electrolytes in Comparative Examples 1 to 5 were water-soluble liquids, they exhibited significant swelling after charge-discharge cycle testing of the non-aqueous electrolyte energy storage elements due to factors such as a high content of water-soluble linear carbonates (DMCs). The non-aqueous electrolyte in Comparative Example 6, while water-soluble and containing a high content of electrolyte salts, was water-soluble and exhibited suppressed swelling after charge-discharge cycle testing of the non-aqueous electrolyte energy storage element, it resulted in high initial low-temperature resistance. Furthermore, the non-aqueous electrolytes in Comparative Examples 7 to 14 were non-water-soluble liquids due to inappropriate compositions of electrolyte salts and non-aqueous solvents. Specifically, due to the low content of electrolyte salts (Comparative Examples 7 to 9), the low content of water-soluble cyclic carbonates (EC and PC) (Comparative Examples 7, 8, 13, and 14), and the absence of water-soluble linear carbonates (DMC) (Comparative Examples 7, 10 to 12, and 14), each of the non-aqueous electrolytes in Comparative Examples 7 to 14 was a water-insoluble liquid. On the other hand, each of the non-aqueous electrolytes in Examples 1 to 3 had an appropriate content of electrolyte salt, water-soluble cyclic carbonates (EC and PC), and water-soluble linear carbonates (DMC), resulting in a water-soluble liquid, low initial low-temperature resistance of the non-aqueous electrolyte energy storage element, and suppressed swelling after charge-discharge cycle testing. [Industrial applicability]

[0096] This invention can be applied to non-aqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, as well as automobiles and the like. [Explanation of symbols]

[0097] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage units 30 Energy storage devices

Claims

1. It is a water-soluble liquid containing an electrolyte salt and a non-aqueous solvent. The above non-aqueous solvent includes a cyclic carbonate that dissolves in water, a linear carbonate that dissolves in water, and a linear carbonate that does not dissolve in water. The electrolyte salt content is 1.0 mol / m³ ３ It is super, The content of the cyclic carbonate that dissolves in water in the above non-aqueous solvent is 36% by volume or more and 45% by volume or less. A non-aqueous electrolyte in which the content of the chain carbonate that dissolves in water in the above non-aqueous solvent is 15% by volume or less.

2. A non-aqueous electrolyte energy storage element comprising the non-aqueous electrolyte described in claim 1.

3. The positive electrode potential at the charging termination voltage during normal use is 4.2V (vs. Li / Li ＋ ) or more 4.5V (vs.Li / Li ＋ ) The non-aqueous electrolyte energy storage element according to claim 2, wherein the element is as follows:

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