Nonaqueous electrolytic solution power storage element

Abstract

The nonaqueous electrolytic solution power storage element according to one aspect of the present invention comprises a positive electrode, a negative electrode, and a nonaqueous electrolyte. This positive electrode contains a positive electrode active substance containing elemental tungsten. The negative electrode contains a carbon material as the negative electrode active substance. The BET specific surface area of the negative electrode active substance is at least 4.4 m2 / g. The nonaqueous electrolytic solution contains a carboxylic acid ester and a compound having a reductive decomposition potential of no less than 0.5 V (vs. Li / Li+) but no greater than 2.0 V (vs. Li / Li+).

Description

Non-aqueous electrolyte storage element

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

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

[0003] Various elements are sometimes added to the positive electrode active material in order to improve the performance of non-aqueous electrolyte storage elements, etc. Patent Document 1 describes a non-aqueous electrolyte secondary battery that uses a lithium-nickel-cobalt-manganese composite oxide containing tungsten and niobium as the positive electrode active material.

[0004] Japanese Patent Application Publication No. 2009-140787

[0005] The inclusion of tungsten in the positive electrode active material has the advantage of improving the initial output of the nonaqueous electrolyte storage element. Furthermore, from the viewpoint of improving the output of the nonaqueous electrolyte storage element, it is desirable to use a negative electrode active material with a large specific surface area. However, when a negative electrode active material with a large specific surface area is used in a nonaqueous electrolyte storage element using a positive electrode active material containing tungsten, the discharge capacity after charge-discharge cycles is significantly reduced.

[0006] An object of the present invention is to improve the disadvantage that in a nonaqueous electrolyte storage element using a positive electrode active material containing elemental tungsten, when a negative electrode active material with a large specific surface area is used, the discharge capacity after charge-discharge cycling becomes significantly smaller.

[0007] A non-aqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains a positive electrode active material containing elemental tungsten, the negative electrode contains a carbon material as a negative electrode active material, and the BET specific surface area of ​​the negative electrode active material is 4.4 m ２ / g or more, and the non-aqueous electrolyte has a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) and a carboxylic acid ester.

[0008] According to one aspect of the present invention, in a nonaqueous electrolyte storage element using a positive electrode active material containing elemental tungsten, the disadvantage that the discharge capacity after charge-discharge cycling becomes significantly smaller when a negative electrode active material with a large specific surface area is used can be improved.

[0009] Fig. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte storage element. Fig. 2 is a schematic diagram showing one embodiment of a storage device formed by assembling a plurality of nonaqueous electrolyte storage elements. Fig. 3 is a graph showing the relationship between the BET specific surface area and the initial output ratio of the negative electrode active material in the examples. Fig. 4 is a graph showing the relationship between the BET specific surface area and the discharge capacity ratio after charge-discharge cycling of the negative electrode active material in the examples.

[0010] First, an outline of the nonaqueous electrolyte storage element disclosed in this specification will be described.

[0011] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode contains a positive electrode active material containing elemental tungsten, the negative electrode contains a carbon material as a negative electrode active material, and the BET specific surface area of ​​the negative electrode active material is 4.4 m ２ / g or more, and the non-aqueous electrolyte has a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) and a carboxylic acid ester.

[0012] The nonaqueous electrolyte storage element described in [1] above can improve the disadvantage that in nonaqueous electrolyte storage elements using a tungsten-containing positive electrode active material, when a negative electrode active material with a large specific surface area is used, the discharge capacity after charge / discharge cycles is significantly reduced. While the reason for this is unclear, the following is presumed. In nonaqueous electrolyte storage elements using a tungsten-containing positive electrode active material, tungsten elutes from the positive electrode active material into the nonaqueous electrolyte as charge / discharge cycles are repeated, and the eluted tungsten precipitates on the surface of the negative electrode active material. In particular, when the negative electrode active material has a large specific surface area, the effect of the tungsten precipitation coating is significant, resulting in an increase in the resistance of the negative electrode and inhibition of the charge / discharge reaction. Therefore, it is believed that in nonaqueous electrolyte storage elements using a tungsten-containing positive electrode active material, when a negative electrode active material with a large specific surface area is used, the discharge capacity after charge / discharge cycles is significantly reduced. Meanwhile, when the reduction decomposition potential is 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) or less (hereinafter also referred to as "compound (X)") is an additive for a non-aqueous electrolyte that is effective in protecting the negative electrode active material. However, because it decomposes with charge and discharge, if the amount remaining in the non-aqueous electrolyte is small, it does not exhibit sufficient effects. In contrast, when a carboxylic acid ester is contained in a non-aqueous electrolyte together with compound (X), the carboxylic acid ester is preferentially decomposed during the initial charge and discharge due to the relative ease of reductive decomposition of the carboxylic acid ester, and decomposition of compound (X) is suppressed. Therefore, compound (X) can remain sufficiently in the non-aqueous electrolyte even after the initial charge and discharge. Then, during subsequent repeated charge and discharge, compound (X) is gradually reductively decomposed to protect the negative electrode active material, thereby suppressing tungsten deposition over a long period of time. For these reasons, it is presumed that the non-aqueous electrolyte storage element described in [1] above can improve the disadvantage of the significantly reduced discharge capacity after the above-mentioned charge and discharge cycles.

[0013] The "BET specific surface area" of the negative electrode active material is measured by the following method. The nonaqueous electrolyte storage element is disassembled to remove the negative electrode, which is then washed with dimethyl carbonate and vacuum dried at room temperature to collect the negative electrode active material. The collected negative electrode active material is used to measure the BET specific surface area by nitrogen adsorption. This measurement is performed using an "autosorb iQ" manufactured by Quantachrome. Five points are extracted from the region of P / P0 = 0.06 to 0.3 of the obtained adsorption isotherm, and a BET plot is performed. The BET specific surface area is calculated from the y-intercept and slope of the line. Note that all operations from disassembling the nonaqueous electrolyte storage element to collecting the negative electrode active material are performed in a dry air atmosphere with a dew point of -30°C or below.

[0014] The "reduction decomposition potential" is the potential (vs. Li / Li) at the reduction peak (the reduction peak with the most noble potential observed in the first cycle) confirmed from the measurement results by cyclic voltammetry (CV). ＋ The CV method is performed under the following measurement conditions. [Measurement conditions] Working electrode: graphite Reference electrode: Li metal Solvent composition: ethylene carbonate: ethyl methyl carbonate = 3:7 (volume ratio) Electrolyte salt: LiPF ６ (1 mol / dm ３ ) Temperature: Room temperature Scanning speed: 1 mV / sec Number of scans: 3 cycles Scanning range: 0 V (vs. Li / Li ＋ )-3.0V (vs.Li / Li ＋ )

[0015] The types of compound (X) and carboxylic acid ester (hereinafter also referred to as "compound (X) etc.") contained in the nonaqueous electrolyte solution and their amounts described below are specified by the following method. Note that the amount of compound (X) etc. contained in the nonaqueous electrolyte solution refers to the amount of compound (X) etc. contained in the nonaqueous electrolyte solution provided in the nonaqueous electrolyte storage element, and is not the amount of compound (X) etc. contained in the nonaqueous electrolyte solution used in the manufacture of the nonaqueous electrolyte storage element (so-called charge amount). The nonaqueous electrolyte storage element according to one embodiment of the present invention is completed after initial charge and discharge, and a portion of compound (X) etc. contained in the nonaqueous electrolyte solution used in the manufacture decomposes during the initial charge and discharge. Therefore, the amount of compound (X) etc. contained in the nonaqueous electrolyte solution used in the manufacture of the nonaqueous electrolyte storage element and the amount of compound (X) etc. contained in the nonaqueous electrolyte solution provided in the nonaqueous electrolyte storage element completed after initial charge and discharge are not unrelated, but are not the same. In other words, the amount of compound (X) etc. contained in the nonaqueous electrolyte is the amount of compound (X) etc. remaining in the nonaqueous electrolyte provided in the nonaqueous electrolyte storage element. Specific procedures for measuring the type and amount (amount of substance) of compound (X) etc. contained in the nonaqueous electrolyte will be described below.

[0016] The mass (a) of the nonaqueous electrolyte storage element is measured. The nonaqueous electrolyte storage element is then disassembled, and the nonaqueous electrolyte is collected. All components other than the nonaqueous electrolyte are washed with dimethyl carbonate and thoroughly vacuum-dried at room temperature. The mass (b) of all components other than the nonaqueous electrolyte after vacuum drying is measured. The difference between mass (a) and mass (b) is the mass (c) of the nonaqueous electrolyte contained in the container of the nonaqueous electrolyte storage element. All operations from disassembly of the nonaqueous electrolyte storage element to measurement of the mass of all components other than the nonaqueous electrolyte after vacuum drying are performed in a dry air atmosphere with a dew point of -30°C or below. The nonaqueous electrolyte collected during disassembly is then subjected to ion chromatography analysis (IC analysis) or gas chromatography-mass spectrometry (GC-MS analysis) to determine the content (mass %) of compound (X) or the like in the nonaqueous electrolyte. If compound (X) or the like is an ionic compound such as a salt, the content determined by IC analysis is used. When the compound (X) or the like is a nonionic compound, the content determined by GC-MS analysis is used. The mass (d) of the compound (X) or the like contained in the nonaqueous electrolyte solution is calculated from the content of the compound (X) or the like in the nonaqueous electrolyte solution and the mass (c) of the nonaqueous electrolyte solution. The amount (amount of substance) of the compound (X) or the like contained in the nonaqueous electrolyte solution is determined by dividing the mass (d) of the compound (X) or the like contained in the nonaqueous electrolyte solution by the molecular weight of the compound (X). Note that when only a qualitative analysis of the compound (X) or the like contained in the nonaqueous electrolyte solution is performed, the nonaqueous electrolyte storage element may be disassembled and the nonaqueous electrolyte sampled may be used for qualitative analysis by IC analysis or GC-MS analysis, without measuring the mass (a) of the nonaqueous electrolyte storage element.

[0017] [IC Analysis] Specifically, the IC analysis is performed in the following order: qualitative analysis and quantitative analysis. The IC analysis device used is a "Dionex ICS-5000+" manufactured by Thermo Fisher Scientific. Water is used as the eluent. IC measurements are performed continuously under the same conditions. (Qualitative Analysis) The measurement sample (non-aqueous electrolyte) is subjected to IC analysis. The components contained in the measurement sample are predicted from the peak positions of each peak in the obtained ion chromatogram. A known sample of the predicted components (hereinafter referred to as "predicted components") is subjected to IC analysis. The retention times of the peaks corresponding to each predicted component in the measurement sample are compared with the retention times of the peaks in a known sample of each predicted component. If they match, the prediction is assumed to be correct. (Quantitative Analysis) Quantitative analysis is performed using the calibration curve method. First, a known sample of the predicted component whose content (concentration) is known is subjected to IC analysis, and the peak areas are determined to create a calibration curve. The calibration curve is based on the coefficient of determination (r ２ The calibration curve is created so that the difference (ratio) is between 0.999 and 1. The content of the predicted component in the measurement sample is determined from the calibration curve and the peak area of ​​the predicted component in the measurement sample. The above procedure is performed for all peaks detected in the IC analysis of the measurement sample, and the content of each predicted component is determined.

[0018] [GC-MS Analysis] Specifically, the GC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The GC-MS analyzer is an Agilent 5975C. Argon is used as the carrier gas. GC-MS measurements are performed continuously under the same conditions. (Qualitative Analysis) The measurement sample (non-aqueous electrolyte) is subjected to GC-MS analysis. The components contained in the sample are predicted from the MS spectrum of each peak in the obtained gas chromatogram. A known sample of the predicted components is subjected to GC-MS analysis. The retention time and MS spectrum of the peak corresponding to each predicted component in the measurement sample are compared with the retention time and MS spectrum of the peak in a known sample of each predicted component. If they match, the prediction is assumed to be correct. (Quantitative Analysis) Quantitative analysis is performed using the calibration curve method. First, a known sample of the predicted component with a known content (concentration) is subjected to GC-MS analysis, and the peak area is determined to create a calibration curve. The calibration curve is based on the coefficient of determination (r ２) is created so that it is 0.999 or more and 1 or less. The content of the predicted component in the measurement sample is determined from the calibration curve and the peak area of ​​the predicted component in the measurement sample. The above procedure is performed for all peaks detected in the GC-MS analysis of the measurement sample, and the content of each predicted component is determined.

[0019] [2] In the nonaqueous electrolyte storage element according to [1] above, the compound (X) may comprise at least one selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, vinylethylene carbonate, ethylene sulfate, 4,5-pentene sulfate, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, 1,3-propene sultone, 1,3-propane sultone, lithium bis(oxalate)borate, lithium difluoro(oxalate)borate, and lithium difluorobis(oxalate)phosphate.

[0020] According to the nonaqueous electrolyte storage element described in [2] above, the use of the specified compound (X) makes it possible to particularly sufficiently improve the above-mentioned disadvantage that the discharge capacity after charge-discharge cycles becomes significantly smaller.

[0021] [3] In the nonaqueous electrolyte storage element according to [1] or [2] above, the molar ratio of the amount of the carboxylic acid ester contained in the nonaqueous electrolyte to the amount of the tungsten element contained in the positive electrode active material may be 2.0 or more and 7.0 or less.

[0022] According to the nonaqueous electrolyte storage element described in [3] above, the molar ratio of the amount of carboxylic acid ester contained in the nonaqueous electrolyte to the amount of tungsten element contained in the positive electrode active material is within the above range, thereby making it possible to increase the output retention rate after charge-discharge cycles.

[0023] The amount of tungsten element contained in the positive electrode active material is measured by the following procedure. First, the nonaqueous electrolyte storage element is discharged at a constant current of 0.05 C to the lower limit voltage for normal use. The nonaqueous electrolyte storage element is disassembled, the positive electrode is removed, and a test battery is assembled using metallic lithium as the counter electrode. The positive electrode potential is measured at a discharge current of 10 mA per 1 g of positive electrode active material until the positive electrode potential reaches 3.0 V (vs. Li / Li ＋) to adjust the positive electrode to a fully discharged state. The test battery is then disassembled, and the positive electrode is removed. Components (such as the nonaqueous electrolyte) adhering to the removed positive electrode are thoroughly washed using dimethyl carbonate, and the removed positive electrode is vacuum-dried at room temperature for 24 hours, after which the positive electrode is collected. The positive electrode active material layer is peeled from the removed positive electrode substrate using a solvent capable of dissolving the binder, such as N-methylpyrrolidone (NMP), to collect the positive electrode active material layer constituent components. The process from disassembling the nonaqueous electrolyte storage element to collecting the positive electrode active material layer constituent components for measurement is carried out in an argon atmosphere with a dew point of −60°C or lower. The obtained positive electrode active material layer constituent components are calcined at 800°C in an air atmosphere, and the conductive agent and binder are removed as necessary to collect the positive electrode active material. The positive electrode active material collected by the above method is completely dissolved in an acidic solution capable of dissolving the positive electrode active material by microwave decomposition. Next, this acidic solution is diluted with pure water to a certain amount to obtain a measurement solution. Then, using a multi-type inductively coupled plasma optical emission spectrometer ICPE-9820 (manufactured by Shimadzu Corporation), the concentration of elemental tungsten in the measurement solution is measured by inductively coupled plasma optical emission spectroscopy (ICP). From the obtained concentration of elemental tungsten, the content (mass%) of elemental tungsten in the positive electrode active material is calculated. The amount (moles) of elemental tungsten contained in the positive electrode active material is determined from the content (mass%) of elemental tungsten in the positive electrode active material, the mass of the positive electrode active material, and the atomic weight of elemental tungsten (183.84). To calculate the concentration of elemental tungsten in the measurement solution, a calibration curve method is used, in which a calibration curve is created from solutions of known concentrations of elemental tungsten to determine the concentration of elemental tungsten in the measurement solution. "During normal use" means when the non-aqueous electrolyte storage element is used under the charge / discharge conditions recommended or specified for the non-aqueous electrolyte storage element, and when equipment for using the non-aqueous electrolyte storage element is available, the non-aqueous electrolyte storage element is used using that equipment.

[0024] [4] In the nonaqueous electrolyte storage element according to any one of [1] to [3] above, the molar ratio of the amount of the carboxylic acid ester contained in the nonaqueous electrolyte to the amount of the tungsten element contained in the positive electrode active material may be 4.8 or more.

[0025] According to the nonaqueous electrolyte storage element described in [4] above, the molar ratio of the amount of carboxylic acid ester contained in the nonaqueous electrolyte to the amount of tungsten element contained in the positive electrode active material is within the above range, so that the output after charge-discharge cycles can be increased.

[0026] [5] In the nonaqueous electrolyte storage element according to any one of [1] to [4] above, the molar ratio of the amount of the carboxylic acid ester contained in the nonaqueous electrolyte to the amount of the compound (X) contained in the nonaqueous electrolyte may be 4.0 or more and 14.4 or less.

[0027] According to the nonaqueous electrolyte storage element described in [5] above, when the molar ratio of the amount of the carboxylic acid ester contained in the nonaqueous electrolyte to the amount of the compound (X) contained in the nonaqueous electrolyte is within the above range, the output retention rate after charge-discharge cycles can be increased.

[0028] [6] In the nonaqueous electrolyte storage element according to any one of [1] to [5] above, the molar ratio of the amount of the carboxylic acid ester contained in the nonaqueous electrolyte to the amount of the compound (X) contained in the nonaqueous electrolyte may be 9.9 or more.

[0029] According to the nonaqueous electrolyte storage element described in [6] above, when the molar ratio of the amount of the carboxylic acid ester contained in the nonaqueous electrolyte to the amount of the compound (X) contained in the nonaqueous electrolyte is within the above range, the output after charge-discharge cycles can be increased.

[0030] A nonaqueous electrolyte storage element, a storage device, a method for manufacturing a nonaqueous electrolyte storage element according to one embodiment of the present invention, and other embodiments will be described in detail below. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0031] <Non-aqueous Electrolyte Storage Element> A non-aqueous electrolyte storage element (hereinafter also simply referred to as "storage element") according to one embodiment of the present invention includes an electrode assembly having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container that accommodates the electrode assembly and the non-aqueous electrolyte. The electrode assembly is typically a stacked type in which multiple positive electrodes and multiple negative electrodes are stacked with separators interposed therebetween, or a wound type in which positive electrodes and negative electrodes are stacked with separators interposed therebetween and wound. At least a portion of the non-aqueous electrolyte is present in a state of being impregnated into the positive electrode, negative electrode, and separator. A portion of the non-aqueous electrolyte may be present outside the electrode assembly, i.e., between the electrode assembly and the container, as excess electrolyte. The container may be made of a metal such as aluminum or stainless steel, or may be made of a resin. As an example of a non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0032] (Positive Electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0033] The positive electrode substrate has electrical conductivity. Whether or not it has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 －２ The resistance is determined using Ω cm as a threshold value. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate 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).

[0034] 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, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0035] The intermediate layer is a layer disposed 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 configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0036] The positive electrode active material layer contains a positive electrode active material and, if necessary, optional components such as a conductive agent, a binder, a thickener, and a filler.

[0037] The positive electrode active material contains tungsten element. The tungsten element can be, for example, an oxide (WO ３The tungsten-containing compound may be present in the form of a compound such as a tungsten-containing compound. The tungsten-containing compound may, for example, coat at least a portion of the surface of particles of a material capable of absorbing and releasing charge transport ions such as lithium ions. In other words, the positive electrode active material may contain a material capable of absorbing and releasing charge transport ions and a tungsten-containing compound. The positive electrode active material may essentially consist of a material capable of absorbing and releasing charge transport ions and a tungsten-containing compound. The material capable of absorbing and releasing charge transport ions may itself contain tungsten. The tungsten-containing compound may, for example, be present on the surface of the positive electrode active material particles. The tungsten-containing compound may also be present inside the positive electrode active material particles. By including tungsten in the positive electrode active material, side reactions at the positive electrode can be suppressed and the conductivity of charge transport ions such as lithium ions can be improved, resulting in an increase in the initial output of the nonaqueous electrolyte storage element. As a method for incorporating tungsten element into the positive electrode active material, a method of coating a compound containing tungsten element on the particle surface of a material capable of absorbing and releasing charge transport ions can be mentioned.Also, a method of adding tungsten element during the synthesis of a material capable of absorbing and releasing charge transport ions and then calcining the material, thereby supporting the compound containing tungsten element on the particle surface of the positive electrode active material or incorporating it into the particle.As the positive electrode active material containing tungsten element, a commercially available product can be used.

[0038] As the material capable of absorbing and releasing charge transport ions, a material capable of absorbing and releasing lithium ions is preferable, and conventionally known materials can be used. Examples of such materials include α-NaFeO ２ Examples of suitable lithium transition metal composite oxides include those having a α-type crystal structure, those having a spinel type crystal structure, polyanion compounds, chalcogen compounds, and sulfur. ２ As the lithium transition metal composite oxide having a crystalline structure, for example, Li[Li ｘ Ni （１－ｘ） ]O ２(0≦x<0.5), Li[Li ｘ Ni γ Co （１－ｘ－γ） ]O ２ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li ｘ Co （１－ｘ） ]O ２ (0≦x<0.5), Li[Li ｘ Ni γ Mn （１－ｘ－γ） ]O ２ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li ｘ Ni γ Mn β Co （１－ｘ－γ－β） ]O ２ (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） ]O ２ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1−x−γ−β), etc. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li ｘ Mn ２ O ４ , Li ｘ Ni γ Mn （２－γ） O ４ Examples of polyanion compounds include LiFePO ４ , LiMnPO ４ , LiNiPO ４ , LiCoPO ４ , Li ３ V ２ (P.O. ４ ) ３ , Li ２ MnSiO ４ , Li ２ CoPO ４ Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. The atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. These materials may be used singly or in combination of two or more.

[0039] Among these, lithium transition metal composite oxides are preferred as materials capable of absorbing and releasing charge transport ions, and α-NaFeO ２ Lithium transition metal composite oxides having a crystalline structure of the type α-NaFeO are more preferred, and contain at least one element selected from the group consisting of nickel, cobalt, and manganese. ２ More preferred is a lithium transition metal composite oxide having a crystalline structure of the type α-NaFeO ２ Lithium transition metal composite oxides having a crystalline structure such as Li[Li ｘ Ni γ Mn β Co （１－ｘ－γ－β） ]O ２ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1−x−γ−β), and the above Li[Li ｘ Ni γ Mn β Co （１－ｘ－γ－β） ]O ２ In the above formula, it is preferable that 0.1≦γ<0.9 and 0.1≦β<0.9 are satisfied. When such a substance is used, the output improving effect of tungsten element is particularly sufficiently exhibited.

[0040] The positive electrode active material preferably further contains a transition metal element other than tungsten. When a lithium-transition metal composite oxide, a polyanion compound, or the like is used as the material capable of absorbing and releasing charge transport ions, the positive electrode active material further contains a transition metal element other than tungsten. Examples of transition metal elements other than tungsten include nickel, manganese, cobalt, and iron. The positive electrode active material preferably contains at least one element selected from the group consisting of nickel, manganese, and cobalt, and more preferably contains nickel, manganese, and cobalt. The content of tungsten relative to all transition metal elements other than tungsten in the positive electrode active material is preferably 0.2 mol% to 3 mol%, more preferably 0.5 mol% to 2 mol% (e.g., 0.8 mol% to 2 mol%, 1 mol% to 2 mol%). By setting the content of elemental tungsten to the above lower limit or more, the effect of elemental tungsten in the positive electrode active material is fully exhibited, and initial output, etc. can be increased. On the other hand, by setting the content of elemental tungsten to the above upper limit or less, discharge capacity, etc. can be increased.

[0041] 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. By setting the average particle size of the positive electrode active material to the above-mentioned lower limit or more, the positive electrode active material is easily manufactured or handled. By setting the average particle size of the positive electrode active material to the above-mentioned upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0042] To obtain powders with a predetermined particle size, grinders, classifiers, etc. are used. Grinding methods include, for example, methods using a mortar, ball mill, sand mill, vibration ball mill, planetary ball mill, jet mill, counter jet mill, swirling airflow jet mill, or sieves. Wet grinding in the presence of water or an organic solvent such as hexane can also be used during grinding. As classification methods, sieves, air classifiers, etc. are used as needed for both dry and wet methods.

[0043] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 95% by mass. By setting 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.

[0044] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbon materials, metals, conductive ceramics, etc. Examples of carbon materials include graphite, non-graphitic carbon, graphene-based carbon, etc. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, carbon black, etc. Examples of carbon black include furnace black, acetylene black, ketjen black, etc. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, etc. The conductive agent may be in the form of powder, fiber, etc. As the conductive agent, one of these materials may be used alone, or two or more may be mixed and used. These materials may also be used in combination. For example, a composite material of carbon black and CNT may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0045] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the content of the conductive agent in this range, the energy density of the nonaqueous electrolyte storage element can be increased.

[0046] 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.

[0047] The content of the binder in the positive electrode active material layer is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 9% by mass, inclusive. By setting the binder content within this range, the positive electrode active material can be stably maintained.

[0048] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0049] The content of the thickener in the positive electrode active material layer may be, for example, 0.1% by mass to 6% by mass, or 0.5% by mass to 3% by mass, or 1% by mass or less, or the positive electrode active material layer may not contain a thickener.

[0050] The filler is not particularly limited, and examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, 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, and artificial products thereof.

[0051] The content of the filler in the positive electrode active material layer may be, for example, 0.1% by mass to 8% by mass, or 0.5% by mass to 5% by mass, 3% by mass or less, or 1% by mass or less, or the positive electrode active material layer may not contain a filler.

[0052] The positive electrode active material layer may contain typical non-metallic 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, and Nb as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0053] The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above, for example.

[0054] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, and nickel-plated steel, alloys thereof, and carbonaceous materials are used as the material of the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0055] 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, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0056] The negative electrode active material layer contains a negative electrode active material and, if necessary, optional components such as a conductive agent, a binder, a thickener, and a filler.

[0057] The negative electrode active material layer may contain typical non-metallic 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, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0058] The negative electrode active material includes a carbon material. The carbon material refers to a material containing carbon as a main constituent element. The main constituent element refers to the element that is most abundant on a mass basis. For example, the carbon content in the carbon material may be 80 mass% or more, 90 mass% or more, 95 mass% or more, or 99 mass% or more. Examples of carbon materials used as the negative electrode active material include graphite and non-graphitic carbon, with graphite being preferred. The surface of graphite may be coated with another material such as non-graphitic carbon. One or more carbon materials may be used as the negative electrode active material.

[0059] "Graphite" refers to a graphite material that has an average lattice spacing (d ００２ ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite.

[0060] "Non-graphitic carbon" refers to a carbon material that has an average lattice spacing (d ００２ ) is 0.34 nm or more and 0.42 nm or less. Non-graphitizable carbon includes non-graphitizable carbon and graphitizable carbon. "Non-graphitizable carbon" refers to a carbon material having the above d ００２ The term "easily graphitizable carbon" refers to a carbon material having a particle size of 0.36 nm or more and 0.42 nm or less. ００２ The term "carbon material" refers to a carbon material having a particle size of 0.34 nm or more and less than 0.36 nm.

[0061] Here, the "discharged state" of the carbon material means a state in which the carbon material, which is a negative electrode active material, is discharged so that charge-transporting ions that can be absorbed and released during charging and discharging are sufficiently released from the carbon material. For example, this refers to a state in which the open circuit voltage is 0.6 V or higher in a half cell using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metallic lithium as a counter electrode.

[0062] The average particle size of the carbon material as the negative electrode active material is preferably, for example, 1 μm or more and 30 μm or less, and more preferably 3 μm or more and 20 μm or less. When the average particle size of the carbon material is within the above range, it is possible to improve the charge / discharge performance of the nonaqueous electrolyte storage element. In order to obtain the carbon material with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and the classification method can be selected, for example, from the methods exemplified for the positive electrode above.

[0063] The negative electrode active material may contain other negative electrode active materials together with the carbon material. As the other negative electrode active materials, conventionally known negative electrode active materials may be used. However, in one embodiment of the present invention, the content of the carbon material relative to the total negative electrode active materials is preferably 90% by mass or more, more preferably 99% by mass or more, and may be 100% by mass.

[0064] The lower limit of the BET specific surface area of ​​the negative electrode active material is 4.4 m ２ / g, and 4.6 m ２ / g, 4.8m ２ / g, 5.0 m ２ / g, 5.2 m ２ / g or 5.4m ２ When the BET specific surface area of ​​the negative electrode active material is equal to or greater than the lower limit, the initial output can be increased. The upper limit of the BET specific surface area of ​​the negative electrode active material is, for example, 10.0 m ２ / g, and 9.0m ２ / g, 8.0 m ２ / g, 7.0 m ２ / g, 6.0 m ２ / g, 5.5m ２ / g, 5.2 m ２ / g or 5.0m ２The BET specific surface area of ​​the negative electrode active material may be a combination of any of the above-mentioned lower limits and any of the above-mentioned upper limits (with the proviso that the upper limit is greater than the lower limit).

[0065] The content of the carbon material in the negative electrode active material layer is preferably 60% by mass or more and 99.5% by mass or less, and more preferably 90% by mass or more and 99% by mass or less (for example, 95% by mass or more and 99% by mass or less). The content of all negative electrode active materials in the negative electrode active material layer is preferably 60% by mass or more and 99.5% by mass or less, and more preferably 90% by mass or more and 99% by mass or less (for example, 95% by mass or more and 99% by mass or less). By setting the content of the carbon material or all negative electrode active materials within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0066] The optional components in the negative electrode active material layer, such as a conductive agent, binder, thickener, and filler, can be selected from the materials exemplified for the positive electrode, except that the carbon material contained in the negative electrode active material layer is not included in the conductive agent.

[0067] The content of the conductive agent in the negative electrode active material layer may be 3% by mass or less, or 1% by mass or less, and the negative electrode active material layer may not contain any conductive agent.

[0068] The content of the binder in the negative electrode active material layer is preferably 0.5% by mass or more and 5% by mass or less, and more preferably 0.8% by mass or more and 3% by mass or less.

[0069] The content of the thickener in the negative electrode active material layer is, for example, preferably 0.1% by mass or more and 6% by mass or less, and more preferably 0.5% by mass or more and 3% by mass or less.

[0070] The content of the filler in the negative electrode active material layer may be, for example, 0.1% by mass to 8% by mass, or 0.5% by mass to 5% by mass, 3% by mass or less, or 1% by mass or less, or the negative electrode active material layer may not contain a filler.

[0071] (Separator) The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin films are preferred from the viewpoint of strength, and nonwoven fabrics are preferred from the viewpoint of non-aqueous electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used as the substrate layer of the separator.

[0072] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C under an air atmosphere at 1 atmosphere, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. 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 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 fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of safety of the nonaqueous electrolyte storage element.

[0073] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0074] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0075] (Non-aqueous electrolyte) The non-aqueous electrolyte contains Compound (X) (having a reduction decomposition potential of 0.5 V (vs. Li / Li) ＋ ) or more 2.0V (vs.Li / Li ＋ ) and a carboxylic acid ester.

[0076] Compound (X) is vinylene carbonate (reductive decomposition potential 0.64 V (vs. Li / Li ＋ )), fluoroethylene carbonate, vinylethylene carbonate, ethylene sulfate, 4,5-pentene sulfate (reducing decomposition potential 0.95 V (vs. Li / Li ＋ )), 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane) (reductive decomposition potential 0.60 V (vs. Li / Li ＋ )), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, 1,3-propene sultone (reductive decomposition potential 1.09 V (vs. Li / Li ＋ )), 1,3-propane sultone, lithium bis(oxalato)borate (reduction decomposition potential 1.70 V (vs. Li / Li ＋ )), lithium difluoro(oxalato)borate and lithium difluorobis(oxalato)phosphate (reduction decomposition potential 1.90 V (vs. Li / Li ＋)), more preferably at least one selected from the group consisting of vinylene carbonate and lithium bis(oxalate)borate, and even more preferably vinylene carbonate and lithium bis(oxalate)borate. By using these compounds as compound (X), the disadvantage of a significantly reduced discharge capacity after charge-discharge cycles can be particularly sufficiently improved. Incidentally, even for compounds for which the reductive decomposition potential is not described among the above-mentioned compounds exemplified as compound (X), the reductive decomposition potential is 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) It has been confirmed that

[0077] Compound (X) has a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) or less, a cyclic carbonate having a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) or less, sulfates having a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) or less, and a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) or less, or a lithium oxalate having a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ The compound (X) may be a lithium imide salt having a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) or less and a cyclic carbonate having a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) or less.

[0078] The reduction decomposition potential is 0.5 V (vs. Li / Li ＋) or more 2.0V (vs.Li / Li ＋ Examples of cyclic carbonates having a reduction decomposition potential of 0.5 V (vs. Li / Li) or less include vinylene carbonate, fluoroethylene carbonate, and vinylethylene carbonate. ＋ ) or more 2.0V (vs.Li / Li ＋ Examples of sulfates having a reduction decomposition potential of 0.5 V (vs. Li / Li) or less include ethylene sulfate, 4,5-pentene sulfate, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, etc. ＋ ) or more 2.0V (vs.Li / Li ＋ Examples of sultones having a reduction decomposition potential of 0.5 V (vs. Li / Li) or less include 1,3-propene sultone and 1,3-propane sultone. ＋ ) or more 2.0V (vs.Li / Li ＋ ) or less, examples of the lithium oxalate salt include lithium bis(oxalate)borate, lithium difluoro(oxalate)borate, and lithium difluorobis(oxalate)phosphate. One or more types of compound (X) can be used.

[0079] In a preferred embodiment, the compound (X) has a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 1.2V (vs.Li / Li ＋ In another preferred embodiment, the compound (X) may include a compound (X1) having a reduction decomposition potential of less than 1.2 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ In another preferred embodiment, the compound (X) may contain a compound (X2) having a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 1.2V (vs.Li / Li ＋ ) and a compound (X1) having a reductive decomposition potential of less than 1.2 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋The compound (X1) may include a compound (X2) having a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 1.2V (vs.Li / Li ＋ Among them, the compound (X1) is preferably a cyclic carbonate, a sulfate, a sultone, or the like having a reduction decomposition potential of less than 0.5 V (vs. Li / Li ＋ ) or more 1.2V (vs.Li / Li ＋ The reduction decomposition potential of the compound (X1) is preferably less than 0.5 V (vs. Li / Li ＋ ) or more 0.8V (vs.Li / Li ＋ The compound (X2) may have a reduction decomposition potential of 1.2 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ Among them, the compound (X2) is preferably a lithium oxalate salt, a lithium imide salt, or the like, having a reduction decomposition potential of 1.2 V (vs. Li / Li) or less. ＋ ) or more 2.0V (vs.Li / Li ＋ The reduction decomposition potential of the compound (X2) is 1.5 V (vs. Li / Li ＋ ) or more 2,0V (vs.Li / Li ＋ ) or less. When compound (X) contains both compound (X1) and compound (X2), the lower limit of the molar ratio (X1 / X2) of the amount of compound (X2) contained in the non-aqueous electrolyte to the amount of compound (X1) contained in the non-aqueous electrolyte may be, for example, 0.5, or may be 1.0, 1.5, 2.0, or 2.5. On the other hand, the upper limit of the molar ratio (X1 / X2) may be, for example, 10.0, or may be 9.0, 8.0, 7.0, 6.0, 5.0, or 4.0. The molar ratio (X1 / X2) may be a combination of any of the above-mentioned lower limits and any of the above-mentioned upper limits (with the proviso that the upper limit is greater than the lower limit).

[0080] The content of compound (X) in the non-aqueous electrolyte is preferably 0.02% by mass or more and 5.0% by mass or less, more preferably 0.05% by mass or more and 4.0% by mass or less, even more preferably 0.1% by mass or more and 3.0% by mass or less, even more preferably 0.2% by mass or more and 2.0% by mass or less, and even more preferably 0.3% by mass or more and 1.0% by mass or less, and even more preferably 0.4% by mass or more and 0.7% by mass or less. By having the content of compound (X) in the above range, the disadvantage of the discharge capacity after charge-discharge cycles being significantly reduced can be more fully improved. When compound (X) contains compound (X1), the content of compound (X1) in the non-aqueous electrolyte may be 0.02% by mass or more and 2.0% by mass or less, 0.08% by mass or more and 1.5% by mass or less, 0.12% by mass or more and 1.0% by mass or less, or 0.15% by mass or more and 0.5% by mass or less. When compound (X) contains compound (X2), the content of compound (X2) in the non-aqueous electrolyte may be 0.03% by mass or more and 3.0% by mass or less, 0.1% by mass or more and 2.0% by mass or less, 0.2% by mass or more and 1.5% by mass or less, 0.3% by mass or more and 1.0% by mass or less, or 0.35% by mass or more and 0.8% by mass or less. When compound (X) contains both compound (X1) and compound (X2), the content of compound (X2) in the non-aqueous electrolyte may be greater than the content of compound (X1) in the non-aqueous electrolyte. The content of compound (X2) in the non-aqueous electrolyte may be 0.1% by mass or more greater than the content of compound (X1) in the non-aqueous electrolyte.

[0081] The carboxylic acid ester suppresses the consumption of compound (X) during the initial charge / discharge cycle and reduces the initial resistance of the nonaqueous electrolyte storage element by forming a coating on the surface of the negative electrode active material. Furthermore, when the positive electrode contains a positive electrode active material containing elemental tungsten, the carboxylic acid ester also increases the output after charge / discharge cycles and improves the output retention rate after charge / discharge cycles. Examples of the carboxylic acid ester include acetate esters such as methyl acetate, ethyl acetate, and propyl acetate, and propionic acid esters such as methyl propionate, ethyl propionate, and propyl propionate. As the carboxylic acid ester, propionic acid esters are preferred, with alkyl propionates being more preferred, and methyl propionate being even more preferred. The use of such a carboxylic acid ester not only sufficiently improves the disadvantage of a significantly reduced discharge capacity after charge / discharge cycles, but also tends to increase the initial output. The carboxylic acid ester is preferably an alkyl carboxylic acid ester. Furthermore, from the viewpoint of reductive decomposition potential, the carboxylic acid ester should have a reductive decomposition potential of about 0.5 V (vs. Li / Li ＋ The carboxylic acid esters may be used alone or in combination of two or more.

[0082] The content of the carboxylic acid ester in the non-aqueous electrolyte is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.3% by mass or more and 10% by mass or less, even more preferably 0.5% by mass or more and 6.0% by mass or less, and even more preferably 1.0% by mass or more and 5.0% by mass or less. By having the content of the carboxylic acid ester in the above range, it is possible to more sufficiently improve the disadvantage of a significantly reduced discharge capacity after charge-discharge cycling. The lower limit of the content of the carboxylic acid ester in the non-aqueous electrolyte may be 1.5% by mass, 2.0% by mass, 2.5% by mass, or 3.0% by mass. By having the content of the carboxylic acid ester in the non-aqueous electrolyte at or above the lower limit, the output after charge-discharge cycling tends to be higher. The upper limit of the content of the carboxylic acid ester in the non-aqueous electrolyte may be 4.0% by mass, 3.5% by mass, 3.0% by mass, 2.5% by mass, or 2.0% by mass. By having the content of the carboxylic acid ester in the non-aqueous electrolyte at or below the above upper limit, the output retention rate after charge-discharge cycling tends to be higher. The content of the carboxylic acid ester in the non-aqueous electrolyte may be a combination of any of the above-mentioned lower limits and any of the above-mentioned upper limits (provided that the upper limit is greater than the lower limit).

[0083] The lower limit of the molar ratio (CE / W) of the amount of carboxylic acid ester (CE) contained in the non-aqueous electrolyte to the amount of tungsten element (W) contained in the positive electrode active material may be, for example, 1.0, or may be 2.0, 3.0, 4.0, or 4.8. By setting the molar ratio (CE / W) to the above lower limit or higher, the output after charge / discharge cycles tends to be higher. On the other hand, the upper limit of the molar ratio (CE / W) may be, for example, 10.0, or may be 9.0, 8.0, 7.0, 6.0, 5.0, or 4.0. By setting the molar ratio (CE / W) to the above upper limit or lower, the output maintenance rate after charge / discharge cycles tends to be higher. From the viewpoint of increasing the output maintenance rate after charge / discharge cycles, the molar ratio (CE / W) may be 2.0 or higher and 7.0 or lower. Alternatively, the molar ratio (CE / W) may be a combination of any of the above lower limits and any of the above upper limits (provided that the upper limit is greater than the lower limit).

[0084] The lower limit of the molar ratio (CE / X) of the amount of carboxylic acid ester (CE) contained in the non-aqueous electrolyte to the amount of compound (X) contained in the non-aqueous electrolyte may be, for example, 2.0, or may be 4.0, 6.0, 8.0, or 9.9. By setting the molar ratio (CE / X) to the above lower limit or higher, the output after charge / discharge cycles tends to be higher. On the other hand, the upper limit of the molar ratio (CE / X) may be, for example, 20.0, or may be 15.0, 14.4, 12.0, 10.0, or 8.0. By setting the molar ratio (CE / X) to the above upper limit or lower, the output maintenance rate after charge / discharge cycles tends to be higher. From the viewpoint of increasing the output maintenance rate after charge / discharge cycles, the molar ratio (CE / X) may be 4.0 or higher and 14.4 or lower. Alternatively, the molar ratio (CE / X) may be a combination of any of the above lower limits and any of the above upper limits (provided that the upper limit is greater than the lower limit). The molar ratio (CE / X) is equal to the molar concentration of compound (X) relative to the molar concentration of compound (X) in the non-aqueous electrolyte.

[0085] The amount of elemental tungsten (amount of substance) contained in the positive electrode active material is adjusted by the content (content rate) of elemental tungsten in the positive electrode active material, the mass of the positive electrode active material contained in the positive electrode, etc. The amount of carboxylic acid ester (amount of substance) contained in the non-aqueous electrolyte is adjusted by the content (content rate) of carboxylic acid ester in the non-aqueous electrolyte, the mass of the non-aqueous electrolyte contained in the non-aqueous electrolyte storage element, etc. The amount of compound (X) contained in the non-aqueous electrolyte is adjusted by the content (content rate) of compound (X) in the non-aqueous electrolyte, the mass of the non-aqueous electrolyte contained in the non-aqueous electrolyte storage element, etc.

[0086] The non-aqueous electrolyte solution may generally further contain, in addition to the compound (X) and the carboxylic acid ester, a non-aqueous solvent other than the compound (X) and the carboxylic acid ester (hereinafter also referred to as “another non-aqueous solvent”) and an electrolyte salt other than the compound (X) (hereinafter also referred to as “another electrolyte salt”).

[0087] The other non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of the other non-aqueous solvent include cyclic carbonates, chain carbonates, phosphate esters, sulfonate esters, ethers, amides, and nitriles. As the other non-aqueous solvent, those in which some of the hydrogen atoms contained in these compounds are substituted with halogens may also be used.

[0088] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), styrene carbonate, etc. Among these, EC is preferred.

[0089] 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, DMC and EMC are preferred.

[0090] As the other non-aqueous solvent, it is preferable to use a cyclic carbonate or a chain carbonate, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0091] The other electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salt, sodium salt, potassium salt, magnesium salt, onium salt, etc. Among these, lithium salt is preferred.

[0092] The lithium salt is LiPF ６ , LiPO ２ F ２ , LiBF ４ , LiClO ４ , LiN(SO ２F) ２ Inorganic lithium salts such as LiSO ３ CF ３ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiN(SO ２ CF ３ ) (SO ２ C ４ F ９ ), LiC(SO ２ CF ３ ) ３ , LiC(SO ２ C ２ F ５ ) ３ Among these, inorganic lithium salts are preferred, and LiPF ６ is more preferred.

[0093] LiPF in non-aqueous electrolyte ６ When LiPF is contained, ６ However, HF is likely to react with small amounts of water present in the nonaqueous electrolyte to generate HF. The presence of HF in the nonaqueous electrolyte is thought to promote the elution of elemental tungsten from the positive electrode active material into the nonaqueous electrolyte. Therefore, when a nonaqueous electrolyte storage element using a nonaqueous electrolyte containing such a component is one embodiment of the present invention, the effect of improving the disadvantage of a significantly reduced discharge capacity after charge-discharge cycles is particularly pronounced.

[0094] The content of other electrolyte salts in the non-aqueous electrolyte solution is 0.1 mol / dm at 20°C and 1 atmosphere. ３ 2.5mol / dm or more ３ It is preferably 0.3 mol / dm or less. ３ 2.0mol / dm or more ３ It is more preferable that it is 0.5 mol / dm or less. ３ More than 1.7mol / dm ３ It is more preferable that it is 0.7 mol / dm or less. ３ 1.5mol / dm or more ３It is particularly preferable that the content of the electrolyte salt in the non-aqueous electrolyte solution is 1% by mass or more and 35% by mass or less, more preferably 3% by mass or more and 30% by mass or less, even more preferably 5% by mass or more and 25% by mass or less, and particularly preferably 10% by mass or more and 20% by mass or less. By setting the content of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte solution can be increased.

[0095] The non-aqueous electrolyte may contain other components in addition to the compound (X), the carboxylic acid ester, other non-aqueous solvents, and other electrolyte salts. The other components may be used singly or in combination of two or more. The content of the other components contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, even more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less, relative to the total mass of the non-aqueous electrolyte.

[0096] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0097] Figure 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode assembly 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0098] <Electricity Storage Device> The nonaqueous electrolyte storage element of the present embodiment can be mounted as an electricity storage unit (battery module) comprising a plurality of nonaqueous electrolyte storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc., a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte storage element included in the electricity storage unit.

[0099] 2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte storage elements 1, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte storage elements 1, a bus bar (not shown) that electrically connects two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte storage elements.

[0100] <Method for manufacturing nonaqueous electrolyte storage element> The method for manufacturing the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode assembly, preparing a nonaqueous electrolyte, and housing the electrode assembly and the nonaqueous electrolyte in a container. Preparing the electrode assembly includes preparing a positive electrode and a negative electrode, and forming the electrode assembly by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0101] The positive electrode can be prepared, for example, by applying a positive electrode mixture paste to a positive electrode substrate directly or via an intermediate layer, and then drying. The positive electrode mixture paste contains components constituting the positive electrode active material layer, such as a positive electrode active material, and a dispersion medium. After drying, the applied positive electrode mixture paste may be pressed or the like.

[0102] The negative electrode can be prepared, for example, by applying a negative electrode mixture paste to a negative electrode substrate directly or via an intermediate layer, and then drying. The negative electrode mixture paste contains components constituting the negative electrode active material layer, such as a negative electrode active material, and a dispersion medium. After drying, the applied negative electrode mixture paste may be pressed or the like.

[0103] The term "preparing a non-aqueous electrolyte solution" may mean preparing a non-aqueous electrolyte solution. The preparation of the non-aqueous electrolyte solution can be carried out, for example, by mixing the components that constitute the non-aqueous electrolyte solution.

[0104] The non-aqueous electrolyte solution can be placed in the container by any known method, for example, by injecting the non-aqueous electrolyte solution through an inlet formed in the container and then sealing the inlet.

[0105] The method for manufacturing a nonaqueous electrolyte storage element may include initially charging and discharging the assembled nonaqueous electrolyte storage element. The initial charging and discharging may be performed once or multiple times. The initial charging and discharging causes a portion of the carboxylic acid ester, etc., in the nonaqueous electrolyte contained in the container to be reductively decomposed, forming a coating on the surface of the negative electrode active material.

[0106] <Other Embodiments> The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiments, 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, or part of the configuration of one embodiment may be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment may be deleted. Furthermore, well-known technology may be added to the configuration of one embodiment.

[0107] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (lithium ion secondary battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0108] In the above embodiment, the electrode assembly in which the positive electrode and the negative electrode are stacked with a separator interposed therebetween has been described, but the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state in which a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode.

[0109] 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.

[0110] [Example 1] (Preparation of positive electrode) LiNi １／３ Mn １／３ Co １／３ O ２A positive electrode active material was prepared by adhering tungsten oxide to the particle surfaces of the positive electrode active material. The tungsten content relative to the transition metal elements other than tungsten in this positive electrode active material was 1 mol %. A positive electrode mixture paste was prepared using the positive electrode active material, 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 93:5:2 (solid content equivalent). The positive electrode mixture paste was applied to both sides of aluminum foil as a positive electrode substrate and dried. Then, roll pressing was performed to obtain a positive electrode in which positive electrode active material layers were laminated on both sides of the positive electrode substrate. The amount of tungsten contained in the resulting positive electrode was 0.003 mol.

[0111] (Production of negative electrode) BET specific surface area: 4.4 m ２ Graphite with a porosity of 1 / g was prepared as the negative electrode active material. A negative electrode mixture paste was prepared using the negative electrode active material, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium. The mass ratio of the negative electrode active material, SBR, and CMC was 98.5:1:0.5 (solid content equivalent). The negative electrode mixture paste was applied to both sides of copper foil as the negative electrode substrate and dried. Then, roll pressing was performed to obtain a negative electrode in which negative electrode active material layers were laminated on both sides of the negative electrode substrate.

[0112] (Preparation of non-aqueous electrolyte) LiPF was added to a non-aqueous solvent prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and methyl propionate (MP), a carboxylic acid ester, in a volume ratio of 30:35:32:3. ６ to 1.2 mol / dm ３ The compound (X) is lithium bis(oxalate)borate (LiBOB: reduction decomposition potential 1.70 V (vs. Li / Li ＋ )) at a content of 0.5 mass % and vinylene carbonate (VC: reduction decomposition potential 0.64 V (vs. Li / Li ＋ )) were dissolved in a content of 0.2 mass % to prepare a non-aqueous electrolyte solution.

[0113] (Separator) A microporous polyolefin film was used as the separator.

[0114] (Assembly of Nonaqueous Electrolyte Storage Element) A wound electrode body was obtained using the positive electrode, negative electrode, and separator. The electrode body was placed in a container, and a nonaqueous electrolyte was poured into it to obtain a non-charged / discharged non-aqueous electrolyte storage element. The obtained non-charged / discharged non-aqueous electrolyte storage element was initially charged and discharged in a constant-current / constant-voltage chamber at 25°C under conditions of a charging current of 1.0 C and a charge cut-off voltage of 4.1 V for a total charge time of 3 hours. After a 10-minute pause, the element was subsequently discharged at a constant current of 1.0 C and a discharge cut-off voltage of 3.0 V to obtain the non-aqueous electrolyte storage element of Example 1. The discharged quantity of electricity was defined as the initial discharge capacity. The amount of carboxylic acid ester contained in the non-aqueous electrolyte after the initial charge / discharge was 0.010 mol, and the molar ratio (CE / W) of the amount of carboxylic acid ester contained in the non-aqueous electrolyte to the amount of tungsten element contained in the positive electrode active material was 3.0.

[0115] [Examples 2 to 4 and Comparative Example 1] The nonaqueous electrolyte storage elements of Examples 2 to 4 and Comparative Example 1 were obtained in the same manner as in Example 1, except that graphite having the BET specific surface area shown in Table 1 was used as the negative electrode active material.

[0116] [Reference Example A (Reference Examples A1 to A4)] LiNi containing no tungsten element １／３ Mn １／３ Co １／３ O ２ Each of the nonaqueous electrolyte storage elements of Reference Example A (Reference Examples A1 to A4) was obtained in the same manner as in Example 1, except that the positive electrode active material was a mixture of EC, DMC, and EMC in a volume ratio of 30:35:35 without containing a carboxylic acid ester in the nonaqueous electrolyte, and graphite having a BET specific surface area shown in Table 1 was used as the negative electrode active material.

[0117] Reference Example B (Reference Examples B1 to B4) Each of the nonaqueous electrolyte storage elements of Reference Example B (Reference Examples B1 to B4) was obtained in the same manner as in Example 1, except that the nonaqueous electrolyte did not contain a carboxylic acid ester, and a nonaqueous solvent in which EC, DMC, and EMC were mixed in a volume ratio of 30:35:35 was used, and graphite having a BET specific surface area shown in Table 1 was used as the negative electrode active material.

[0118] [Evaluation 1] (1) Initial Output For each of the obtained nonaqueous electrolyte storage elements of Examples 1 to 4, Comparative Example 1, Reference Example A, and Reference Example B, constant current charging was performed in a thermostatic chamber at 25 ° C. with a charging current of 1.0 C, with an amount of electricity of 50% of the initial discharge capacity, to bring the SOC (state of charge) to 50%. Subsequently, after storing for 4 hours in a thermostatic chamber at -30 ° C., the elements were discharged for 10 seconds at a current of 0.2 C, 0.5 C, or 1.0 C in a thermostatic chamber at -30 ° C. After each discharge, constant current charging was performed at a charging current of 1.0 C to bring the SOC to 50%. The relationship between the current and the voltage 1 second after the start of discharge in each discharge was plotted, and the DC resistance was calculated from the slope of the straight line obtained from the plot of the three points. The output 1 second after the start of discharge was calculated from the calculated DC resistance and used as the initial output. The initial output was evaluated as a relative value (initial output ratio) comparing negative electrode active materials that differed only in BET specific surface area. Specifically, in Examples 1 to 4 and Comparative Example 1, the initial output of Example 2 was used as the reference (100.0%). In Reference Example A (Reference Examples A1 to A4), the initial output of Reference Example A1 was used as the reference (100.0%). In Reference Example B (Reference Examples B1 to B4), the initial output of Reference Example B2 was used as the reference (100.0%). The results are shown in Table 1 and FIG. 3.

[0119] (2) Charge-Discharge Cycle Test Next, each nonaqueous electrolyte storage element was subjected to constant-current discharge in a thermostatic chamber at 25°C under conditions of a discharge current of 1.0 C and a discharge cut-off voltage of 3.0 V. After a 10-minute rest, it was subjected to constant-current / constant-voltage charging at a charging current of 1.0 C to a voltage corresponding to an SOC of 20% determined from the SOC-OCV curve, bringing the SOC to 20%. Subsequently, after storing the element in a thermostatic chamber at 55°C for 4 hours, it was subjected to constant-current charging at a charging current of 10 C to a voltage corresponding to an SOC of 80% in the thermostatic chamber at 55°C, and then constant-current discharging at a discharging current of 10 C to a voltage corresponding to an SOC of 20%. The above charge and discharge cycle was repeated for 1,000 hours, with a rest period of 72 hours or more every 250 hours.

[0120] (3) Discharge Capacity After Charge-Discharge Cycle Test After the charge-discharge cycle test, charge and discharge were performed under the same conditions as the initial charge and discharge of the non-charged / discharged non-aqueous electrolyte storage element described above. The quantity of electricity discharged at this time was defined as the discharge capacity after the charge-discharge cycle test. The discharge capacity after the charge-discharge cycle test was evaluated as a relative value (capacity ratio after charge-discharge cycle) comparing negative electrode active materials that differed only in BET specific surface area. Specifically, in Examples 1 to 4 and Comparative Example 1, the discharge capacity after the charge-discharge cycle test of Example 2 was defined as the reference (100.0%). In Reference Example A (Reference Examples A1 to A4), the discharge capacity after the charge-discharge cycle test of Reference Example A1 was defined as the reference (100.0%). In Reference Example B (Reference Examples B1 to B4), the discharge capacity after the charge-discharge cycle test of Reference Example B1 was defined as the reference (100.0%). The results are shown in Table 1 and FIG. 4.

[0121]

[0122] As shown in Table 1 and FIG. 3 , the initial output tended to increase as the BET specific surface area of ​​the negative electrode active material increased. Meanwhile, the following tendency was observed with regard to the discharge capacity after charge-discharge cycling, as shown in Table 1 and FIG. 4 . In the case of the nonaqueous electrolyte storage elements of Reference Example A, which used a positive electrode active material not containing elemental tungsten, the discharge capacity after charge-discharge cycling did not decrease significantly even when the BET specific surface area of ​​the negative electrode active material increased. In the case of the nonaqueous electrolyte storage elements of Reference Example B, which used a positive electrode active material containing elemental tungsten, the discharge capacity after charge-discharge cycling decreased significantly as the BET specific surface area of ​​the negative electrode active material increased. In contrast, in the case of the nonaqueous electrolyte storage elements of the Examples, which used a positive electrode active material containing elemental tungsten and contained compound (X) and a carboxylic acid ester in the nonaqueous electrolyte, the discharge capacity after charge-discharge cycling did not decrease significantly even when the BET specific surface area of ​​the negative electrode active material increased. As described above, in each of the nonaqueous electrolyte storage elements of the Examples, the disadvantage that the discharge capacity after charge-discharge cycles becomes significantly smaller when a negative electrode active material with a large specific surface area is used in a nonaqueous electrolyte storage element using a positive electrode active material containing elemental tungsten was improved, and the initial output was increased by increasing the BET specific surface area of ​​the negative electrode active material.

[0123] [Examples 5 to 7, Comparative Example 2] (Preparation of Positive Electrode) LiNi １／３ Mn １／３ Co １／３ O ２ A positive electrode active material was prepared by adhering tungsten oxide to the particle surfaces of the positive electrode active material. The tungsten content relative to the transition metal elements other than tungsten in this positive electrode active material was 1 mol %. A positive electrode mixture paste was prepared using the positive electrode active material, 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 93:5:2 (solid content equivalent). The positive electrode mixture paste was applied to both sides of aluminum foil as a positive electrode substrate and dried. Then, roll pressing was performed to obtain a positive electrode in which positive electrode active material layers were laminated on both sides of the positive electrode substrate. The mass of tungsten contained in the resulting positive electrode was 0.61 g.

[0124] (Production of negative electrode) BET specific surface area: 5.7 m ２ Graphite with a porosity of 1 / g was prepared as the negative electrode active material. A negative electrode mixture paste was prepared using the negative electrode active material, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium. The mass ratio of the negative electrode active material, SBR, and CMC was 98.5:1:0.5 (solid content equivalent). The negative electrode mixture paste was applied to both sides of copper foil as the negative electrode substrate and dried. Then, roll pressing was performed to obtain a negative electrode in which negative electrode active material layers were laminated on both sides of the negative electrode substrate.

[0125] (Preparation of non-aqueous electrolyte) LiPF was added to a non-aqueous solvent prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and methyl propionate (MP), a carboxylic acid ester, in a volume ratio of 30:35:32:3. ６ to 1.2 mol / dm ３ The compound (X) is lithium bis(oxalate)borate (LiBOB: reduction decomposition potential 1.70 V (vs. Li / Li ＋ )) at a content of 0.5 mass % and vinylene carbonate (VC: reduction decomposition potential 0.64 V (vs. Li / Li ＋)) were dissolved at a content of 0.2 mass%, respectively, to prepare the nonaqueous electrolyte of Example 5. The nonaqueous electrolyte of Example 6 was prepared using the same procedure as in Example 5, except that a nonaqueous solvent containing EC, DMC, EMC, and MP mixed at a volume ratio of 30:35:30:5 was used. The nonaqueous electrolyte of Example 7 was prepared using the same procedure as in Example 5, except that a nonaqueous solvent containing EC, DMC, EMC, and MP mixed at a volume ratio of 30:35:28:7 was used. The nonaqueous electrolyte of Comparative Example 2 was prepared using the same procedure as in Example 5, except that a nonaqueous solvent containing EC, DMC, and EMC mixed at a volume ratio of 30:35:35 was used without containing a carboxylic acid ester. The contents of the carboxylic acid ester and compound (X) in the nonaqueous electrolytes prepared in each Example and Comparative Example are shown in Table 2. In the table, MP is methyl propionate, VC is vinylene carbonate, and LiBOB is lithium bis(oxalate)borate.

[0126]

[0127] (Separator) A microporous polyolefin film was used as the separator.

[0128] (Assembly of Nonaqueous Electrolyte Storage Element) A wound electrode body was obtained using the positive electrode, negative electrode, and separator. The electrode body was placed in a container, and a nonaqueous electrolyte was poured into it to obtain a non-charged / discharged nonaqueous electrolyte storage element. The obtained non-charged / discharged nonaqueous electrolyte storage element was initially charged / discharged in a thermostatic chamber at 25°C under conditions of a charging current of 1.0 C and a charge cut-off voltage of 4.1 V for a total charge time of 3 hours. After a 10-minute pause, the element was subsequently discharged at a constant current of 1.0 C and a discharge cut-off voltage of 3.0 V to obtain the nonaqueous electrolyte storage elements of Examples 5 to 7 and Comparative Example 2. The discharged quantity of electricity was defined as the initial discharge capacity. Two nonaqueous electrolyte storage elements were prepared for each of Examples 5 to 7 and Comparative Example 2, one for measuring the amount of carboxylic acid ester and compound (X) in the nonaqueous electrolyte of the obtained nonaqueous electrolyte storage element and one for use in a charge / discharge cycle test.

[0129] (Measurement of the amount of carboxylic acid ester and compound (X)) For each of the obtained nonaqueous electrolyte storage elements, the content (mass%) of carboxylic acid ester and compound (X) in the nonaqueous electrolyte was measured using the method described above. Then, from the mass (0.61 g) of tungsten element contained in the positive electrode active material, the mass (45.8 g) of the nonaqueous electrolyte, the atomic weight (183.84) of tungsten element, and the molecular weight of each component, the molar ratio (CE / W) of the amount of carboxylic acid ester contained in the nonaqueous electrolyte relative to the amount of tungsten element contained in the positive electrode active material, and the molar ratio (CE / X) of the amount of carboxylic acid ester contained in the nonaqueous electrolyte relative to the amount of compound (X) contained in the nonaqueous electrolyte were calculated. In addition, the percentage of the content of each compound (X) in the nonaqueous electrolyte provided in the obtained nonaqueous electrolyte storage element relative to the content of each compound (X) in the prepared nonaqueous electrolyte (nonaqueous electrolyte before pouring into the container) was calculated as the residual rate (%). These values ​​are shown in Table 3.

[0130] [Evaluation 2] (1) Initial Output Each of the obtained nonaqueous electrolyte storage elements of Examples 5 to 7 and Comparative Example 2 was subjected to constant current charging at a charging current of 1.0 C in a thermostatic chamber at 25 ° C, with a quantity of electricity of 50% of the initial discharge capacity, to bring the SOC (state of charge) to 50%. Subsequently, after storing for 4 hours in a thermostatic chamber at -30 ° C, the element was discharged for 10 seconds at a current of 0.2 C, 0.5 C, or 1.0 C in a thermostatic chamber at -30 ° C. After each discharge, the element was subjected to constant current charging at a charging current of 1.0 C to bring the SOC to 50%. The relationship between the current and the voltage 1 second after the start of discharge in each discharge was plotted, and the DC resistance was calculated from the slope of the straight line obtained from the plot of the three points. The output 1 second after the start of discharge was calculated from the calculated DC resistance and used as the initial output.

[0131] (2) Charge-Discharge Cycle Testing Next, each nonaqueous electrolyte storage element was subjected to constant-current discharge in a thermostatic chamber at 25°C under conditions of a discharge current of 1.0 C and a discharge cut-off voltage of 3.0 V. After a 10-minute rest, it was subjected to constant-current, constant-voltage charging at a charging current of 1.0 C to a voltage corresponding to an SOC of 20% determined from the SOC-OCV curve, bringing the SOC to 20%. Subsequently, after storing the element in a thermostatic chamber at 55°C for 4 hours, it was subjected to constant-current charging at a charging current of 10 C to a voltage corresponding to an SOC of 80% in the thermostatic chamber at 55°C, followed by constant-current discharging at a discharging current of 10 C to a voltage corresponding to an SOC of 20%. The above charge and discharge cycles were repeated for 1,000 hours, with a rest period of at least 72 hours every 250 hours. (3) Output after Charge-Discharge Cycle Testing Then, the output after the charge-discharge cycle testing was determined using the same procedure as that used to determine the initial output. The percentage of the output after the charge-discharge cycle test relative to the initial output was calculated as the output maintenance rate. These results are shown in Table 3.

[0132]

[0133] As shown in Table 3, by adding compound (X) and a carboxylic acid ester to the non-aqueous electrolyte, the output after charge-discharge cycling increased and the output retention rate also increased. Furthermore, the output after charge-discharge cycling tended to increase when the molar ratio (CE / X) or the molar ratio (CE / W) was relatively large. On the other hand, the output retention rate after charge-discharge cycling tended to increase when the molar ratio (CE / X) or the molar ratio (CE / W) was relatively small. Furthermore, as can be seen from the "Residual rate of compound (X)" column in Table 3, it was found that adding a carboxylic acid ester to the non-aqueous electrolyte suppressed the consumption of compound (X) during initial charge-discharge and increased the residual rate.

[0134] [Reference Example C (Reference Examples C1 to C3)] (Preparation of Positive Electrode) LiNi １／３ Mn １／３ Co １／３ O ２A positive electrode active material was prepared by adhering tungsten oxide to the particle surfaces of the positive electrode active material. The content of tungsten relative to transition metal elements other than tungsten in this positive electrode active material was 1 mol %. A positive electrode mixture paste was prepared using the positive electrode active material, 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 93:5:2 (solid content equivalent). The positive electrode mixture paste was applied to both sides of aluminum foil as a positive electrode substrate and dried. Then, roll pressing was performed to obtain a positive electrode in which positive electrode active material layers were laminated on both sides of the positive electrode substrate.

[0135] (Production of negative electrode) BET specific surface area: 5.7 m ２ Graphite with a porosity of 1 / g was prepared as the negative electrode active material. A negative electrode mixture paste was prepared using the negative electrode active material, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium. The mass ratio of the negative electrode active material, SBR, and CMC was 98.5:1:0.5 (solid content equivalent). The negative electrode mixture paste was applied to both sides of copper foil as the negative electrode substrate and dried. Then, roll pressing was performed to obtain a negative electrode in which negative electrode active material layers were laminated on both sides of the negative electrode substrate.

[0136] (Preparation of non-aqueous electrolyte) LiPF was added to a non-aqueous solvent prepared by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and methyl propionate (MP), a carboxylic acid ester, in a volume ratio of 30:35:32:3. ６ to 1.2 mol / dm ３ The non-aqueous electrolyte solution of Reference Example C2 was prepared by dissolving 0.5% by mass of LiBOB, which is the compound (X), and 0.2% by mass of VC, which is also the compound (X). The non-aqueous electrolyte solution of Reference Example C3 was prepared in the same manner as in Reference Example C2, except that ethyl acetate (EA) was used instead of MP. The non-aqueous electrolyte solution of Reference Example C1 was prepared in the same manner as in Reference Example C2, except that a non-aqueous solvent was used in which EC, DMC, and EMC were mixed in a volume ratio of 30:35:35 without containing a carboxylic acid ester.

[0137] (Separator) A microporous polyolefin film was used as the separator.

[0138] (Assembly of Nonaqueous Electrolyte Storage Element) A wound electrode body was obtained using the positive electrode, negative electrode, and separator. The electrode body was placed in a container, and a nonaqueous electrolyte was poured into it to obtain a nonaqueous electrolyte storage element. The obtained nonaqueous electrolyte storage element was initially charged and discharged in a constant-current, constant-voltage chamber at 25°C under conditions of a charging current of 1.0 C and a cut-off voltage of 4.1 V for a total charging time of 3 hours. After a 10-minute pause, the element was subsequently discharged at a constant current of 1.0 C and a cut-off voltage of 3.0 V to obtain a nonaqueous electrolyte storage element of Reference Example C (Reference Examples C1 to C3). The quantity of electricity discharged at this time was taken as the initial discharge capacity.

[0139] [Evaluation 3] (1) Initial Resistance Each of the obtained nonaqueous electrolyte storage elements of Reference Example C was subjected to constant current charging at a charging current of 1.0 C in a thermostatic chamber at 25 °C, with a quantity of electricity of 50% of the initial discharge capacity, to bring the SOC (state of charge) to 50%. Subsequently, after storing for 4 hours in a thermostatic chamber at -10 °C, the element was discharged for 30 seconds at a current of 0.2 C, 0.5 C, or 1.0 C in a thermostatic chamber at -10 °C. After each discharge, the element was subjected to constant current charging at a charging current of 1.0 C to bring the SOC to 50%. The relationship between the current and the voltage 10 seconds after the start of discharge for each discharge was plotted, and the DC resistance (initial resistance) was calculated from the slope of the straight line obtained from the plot of the three points. The results are shown in Table 4. In the table, MP is methyl propionate, and EA is ethyl acetate.

[0140]

[0141] As shown in Table 4, it was confirmed that the initial resistance of the nonaqueous electrolyte storage element was reduced by including a carboxylic acid ester in the nonaqueous electrolyte, and that this effect was greater when the carboxylic acid ester was methyl propionate.

[0142] The present invention can be applied to non-aqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

[0143] REFERENCE SIGNS LIST 1 nonaqueous electrolyte storage element 2 electrode body 3 container 4 positive electrode terminal 41 positive electrode lead 5 negative electrode terminal 51 negative electrode lead 20 storage unit 30 storage device

Claims

1. A battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains a positive electrode active material containing elemental tungsten, the negative electrode contains a carbon material as a negative electrode active material, and the BET specific surface area of ​​the negative electrode active material is 4.4 m ２ / g or more, and the non-aqueous electrolyte has a reduction decomposition potential of 0.5 V (vs. Li / Li ＋ ) or more 2.0V (vs.Li / Li ＋ ) or below, and a carboxylic acid ester.

2. The nonaqueous electrolyte storage element according to claim 1, wherein the compound comprises at least one selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, vinylethylene carbonate, ethylene sulfate, 4,5-pentene sulfate, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, 1,3-propene sultone, 1,3-propane sultone, lithium bis(oxalate)borate, lithium difluoro(oxalate)borate, and lithium difluorobis(oxalate)phosphate.

3. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the molar ratio of the amount of the carboxylic acid ester contained in the nonaqueous electrolyte to the amount of the tungsten element contained in the positive electrode active material is 2.0 or more and 7.0 or less.

4. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the molar ratio of the amount of the carboxylic acid ester contained in the nonaqueous electrolyte to the amount of the tungsten element contained in the positive electrode active material is 4.8 or more.

5. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the molar ratio of the amount of the carboxylic acid ester contained in the nonaqueous electrolyte to the amount of the compound contained in the nonaqueous electrolyte is 4.0 or more and 14.4 or less.

6. The non-aqueous electrolyte storage element according to claim 1 or 2, wherein the molar ratio of the amount of said carboxylic acid ester contained in said non-aqueous electrolyte to the amount of said compound contained in said non-aqueous electrolyte is 9.9 or more.

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