Non-aqueous electrolyte power storage element

Abstract

A non-aqueous electrolyte power storage element according to one aspect of the present invention includes an electrode body having a positive electrode and a negative electrode, a non-aqueous electrolyte, and a container that houses the electrode body and the non-aqueous electrolyte. The positive electrode has a positive electrode active material layer containing a positive electrode active material, and the negative electrode has a negative electrode active material layer containing a negative electrode active material. The positive electrode active material contains a tungsten element, and the negative electrode active material contains graphite. The non-aqueous electrolyte contains a first additive with a reduction decomposition potential of 1.5 V (vs. Li / Li+) or higher, and a ratio (A1 / B) of a molar amount (A1) of the first additive contained in the non-aqueous electrolyte to a surface area (B) of the negative electrode active material layer is 2.0×10-7mol / m2 or higher.

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] Positive electrode active materials for non-aqueous electrolyte storage elements include lithium transition metal composite oxides and polyanion compounds. Various elements may be added to the positive electrode active material to improve the performance of non-aqueous electrolyte storage elements. 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] Incorporating tungsten into the positive electrode active material has the advantage of improving the initial input power of a nonaqueous electrolyte storage element. However, nonaqueous electrolyte storage elements using a positive electrode active material containing tungsten are prone to a decrease in input power after storage in a high-temperature environment. Note that input power refers to the energy (W) that can be absorbed per unit time during charging. In other words, a large input power means that a large amount of power (W) can be absorbed during charging. A large input power can also be referred to as excellent input power performance. When the input power retention rate is high, the decrease in input power, i.e., the decrease in input power performance, is suppressed.

[0006] An object of the present invention is to provide a nonaqueous electrolyte storage element that uses a positive electrode active material containing elemental tungsten and that has a high input power retention rate after storage in a high-temperature environment.

[0007] A non-aqueous electrolyte storage element according to one aspect of the present invention includes an electrode assembly having a positive electrode and a negative electrode, and a non-aqueous electrolyte and a container for accommodating the electrode assembly and the non-aqueous electrolyte, wherein the positive electrode has a positive electrode active material layer containing a positive electrode active material, the negative electrode has a negative electrode active material layer containing a negative electrode active material, the positive electrode active material contains elemental tungsten, and the negative electrode active material contains graphite, and the non-aqueous electrolyte has a reduction decomposition potential of 1.5 V (vs. Li / Li ＋ ) or more, and the ratio (A1 / B) of the amount of substance (A1) of the first additive contained in the non-aqueous electrolyte to the surface area (B) of the negative electrode active material layer is 2.0 × 10 －７ mol / m ２ That's all.

[0008] According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte storage element that uses a positive electrode active material containing elemental tungsten, and that has a high input power retention rate after storage in a high-temperature environment.

[0009] Fig. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte storage element, and Fig. 2 is a schematic view showing one embodiment of an electricity storage device formed by assembling a plurality of nonaqueous electrolyte storage elements.

[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 an electrode assembly having a positive electrode and a negative electrode, and a container for accommodating a nonaqueous electrolyte and the electrode assembly and the nonaqueous electrolyte, wherein the positive electrode has a positive electrode active material layer containing a positive electrode active material, the negative electrode has a negative electrode active material layer containing a negative electrode active material, the positive electrode active material contains elemental tungsten, and the negative electrode active material contains graphite, and the nonaqueous electrolyte has a reduction decomposition potential of 1.5 V (vs. Li / Li ＋ ) or more, and the ratio (A1 / B) of the amount of substance (A1) of the first additive contained in the non-aqueous electrolyte to the surface area (B) of the negative electrode active material layer is 2.0 × 10 －７ mol / m ２ That's all.

[0012] The nonaqueous electrolyte storage element described in (1) above is a nonaqueous electrolyte storage element that uses a positive electrode active material containing elemental tungsten, and has a high input power retention rate after storage in a high-temperature environment. The reason for this is unclear, but the following reason is presumed. When a nonaqueous electrolyte storage element that uses a positive electrode active material containing elemental tungsten is stored in a high-temperature environment, elemental tungsten dissolves from the positive electrode active material into the nonaqueous electrolyte, and the dissolved elemental tungsten precipitates on the surface of the negative electrode active material layer. As a result, it is thought that the resistance of the negative electrode increases and the input power of the nonaqueous electrolyte storage element decreases. Therefore, a nonaqueous electrolyte having a reductive decomposition potential of 1.5 V (vs. Li / Li ＋ ) or more, and the ratio (A1 / B) of the amount of substance (A1) of the first additive to the surface area (B) of the negative electrode active material layer is 2.0 × 10 －７ mol / m ２ By doing so, the coating formed on the surface of the negative electrode active material layer by the reaction of the first additive can be sufficiently maintained even during storage in a high-temperature environment, and it is believed that such a coating suppresses a decrease in input power due to the deposition of tungsten element on the surface of the negative electrode active material layer.

[0013] "Graphite" refers to a graphite material that has an average lattice spacing (d ００２ The term "discharged state" refers to a carbon material having a particle size of 0.33 nm or more and less than 0.34 nm. Here, the term "discharged state" of a carbon material refers to a state in which the carbon material, which is a negative electrode active material, is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released. For example, this refers to a state in which the open circuit voltage is 0.6 V or more 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.

[0014] In the present invention, the "reductive decomposition potential" refers to the potential (vs. Li / Li) at the reduction peak (the most noble reduction peak 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: EC:EMC = 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 "amount of substance of the first additive contained in the nonaqueous electrolyte" refers to the amount of substance of the first additive contained in the nonaqueous electrolyte provided in the nonaqueous electrolyte storage element, and is not the amount of substance of the first additive contained in the nonaqueous electrolyte used in the manufacture of the nonaqueous electrolyte storage element (so-called "charged amount"). A nonaqueous electrolyte storage element according to one embodiment of the present invention is completed through initial charge / discharge and subsequent aging treatment, and a portion of the first additive contained in the nonaqueous electrolyte used in the manufacture decomposes during the initial charge / discharge and subsequent aging treatment to form a coating on the surface of the negative electrode active material layer. Therefore, the amount of substance of the first additive contained in the nonaqueous electrolyte used in the manufacture of the nonaqueous electrolyte storage element and the amount of substance of the first additive contained in the nonaqueous electrolyte provided in the nonaqueous electrolyte storage element completed after initial charge / discharge, etc., are not unrelated, but are not the same. In other words, the "amount of substance of the first additive contained in the nonaqueous electrolyte" is the amount of substance of the first additive remaining in the nonaqueous electrolyte provided in the nonaqueous electrolyte storage element. The same applies to the "amount of substance of the second additive contained in the nonaqueous electrolyte" described below. The "amount of substance of the first additive contained in the nonaqueous electrolyte" is measured by the following method. The same applies to the "amount of substance of the second additive contained in the nonaqueous electrolyte" described below. The mass (X1) of the nonaqueous electrolyte storage element is then measured. The nonaqueous electrolyte storage element is then disassembled, and the nonaqueous electrolyte is collected. All parts other than the nonaqueous electrolyte are washed with dimethyl carbonate and thoroughly vacuum dried. The mass (X2) of all parts other than the nonaqueous electrolyte after vacuum drying is measured. The difference between mass (X1) and mass (X2) is taken as the mass (X3) of the nonaqueous electrolyte contained in the container of the nonaqueous electrolyte storage element. All operations from disassembling the nonaqueous electrolyte storage element to measuring the mass of all components other than the nonaqueous electrolyte after vacuum drying are carried out in a dry air atmosphere with a dew point of -30°C or below. Meanwhile, the nonaqueous electrolyte sampled during disassembly is used to determine the concentration (mass%) of the first additive in the nonaqueous electrolyte by ion chromatography analysis (IC analysis) or gas chromatography mass spectrometry (GC-MS analysis). When the first additive is an ionic compound such as a salt, the concentration determined by IC analysis is used. When the first additive is a nonionic compound, the concentration determined by GC-MS analysis is used.The mass (X4) of the first additive contained in the non-aqueous electrolyte solution is calculated from the concentration of the first additive in the non-aqueous electrolyte solution and the mass (X3) of the non-aqueous electrolyte solution. The amount of substance (A1) of the first additive contained in the non-aqueous electrolyte solution is determined by dividing the mass (X4) of the first additive contained in the non-aqueous electrolyte solution by the molecular weight of the first additive.

[0016] [IC Analysis] Specifically, the IC analysis is performed in the following order of 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. (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 component (hereinafter referred to as "predicted component") is subjected to IC analysis. The retention time of the peak corresponding to the predicted component in the measurement sample is compared with the retention time of the peak in a known sample of the predicted component, and if they match, the prediction is presumed 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 concentration is subjected to IC analysis, and the peak area is determined to create a calibration curve. The calibration curve is created using 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.

[0017] [GC-MS Analysis] Specifically, the GC-MS analysis is performed in the following order of qualitative analysis and quantitative analysis. The GC-MS analysis is performed using an Agilent "5975C" analyzer. Argon is used as the carrier gas. (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 the predicted component in the measurement sample are compared with the retention time and MS spectrum of the peak in a known sample of the predicted component, and if they match, the prediction is presumed 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 concentration is subjected to GC-MS analysis, and the peak area is determined to create a calibration curve. The calibration curve is calculated using 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.

[0018] The "surface area of ​​the negative electrode active material layer" refers to the area of ​​all surfaces, taking into account the surfaces of voids in the negative electrode active material layer, and is measured by the following method. A predetermined area of ​​the negative electrode active material layer is sampled from the negative electrode of the nonaqueous electrolyte storage element that was disassembled, washed, and vacuum-dried when measuring the "amount of substance of the first additive contained in the nonaqueous electrolyte." The mass per unit area of ​​the negative electrode active material layer is determined by measuring the mass of the sampled negative electrode active material layer. The mass (Y) of the negative electrode active material layer is determined from the mass per unit area of ​​the negative electrode active material layer and the area of ​​the negative electrode active material layer provided on the negative electrode. Here, the "area of ​​the negative electrode active material layer provided on the negative electrode" is defined as the area of ​​the portion facing the positive electrode active material layer directly or via a separator. Meanwhile, a portion of the negative electrode active material layer not used to determine the mass (Y) of the negative electrode active material layer is sampled, and its BET specific surface area is measured by a nitrogen adsorption method. This measurement is performed using an "autosorb iQ" manufactured by Quantachrome. Five points are extracted from the region of the resulting adsorption isotherm where P / P0 = 0.06 to 0.3, and a BET plot is performed. The BET specific surface area is calculated from the y-intercept and slope of the resulting line. The surface area (B) of the negative electrode active material layer is determined as the product of the BET specific surface area of ​​the negative electrode active material layer and the mass (Y) of the negative electrode active material layer. All operations from disassembly of the nonaqueous electrolyte storage element to extraction of the negative electrode active material layer are performed in a dry air atmosphere with a dew point of -30°C or lower.

[0019] (2) In the nonaqueous electrolyte capacitor element described in (1), the ratio (A1 / B) is 5.0×10 ―６ mol / m ２ It may be the following:

[0020] When the ratio (A1 / B) is large, the amount of the first additive contained in the nonaqueous electrolyte used in the production of the nonaqueous electrolyte storage element also tends to be large, and therefore, with the nonaqueous electrolyte storage element described in (2) above, the formation of an excessively thick coating derived from the first additive is suppressed, thereby making it possible to increase the initial input power, etc.

[0021] (3) In the nonaqueous electrolyte capacitor element according to (1) or (2), the graphite may be natural graphite.

[0022] Natural graphite has higher crystallinity than artificial graphite. Therefore, the nonaqueous electrolyte storage element described in (3) above tends to have a larger discharge capacity per mass of the negative electrode active material, and also tends to have a larger input power initially and after storage in a high-temperature environment.

[0023] Natural graphite is a general term for graphite extracted from natural resources. Natural graphite may exhibit four peaks at a diffraction angle 2θ ranging from 40° to 50° in an X-ray diffraction pattern using CuKα radiation measured before and after charging and discharging or in a discharged state. These four peaks are believed to be two peaks derived from a hexagonal crystal structure and two peaks derived from a rhombohedral crystal structure. In the case of artificial graphite, it is generally believed that only two peaks derived from a hexagonal crystal structure appear. In the X-ray diffraction pattern, the ratio of the peak intensity derived from the (012) plane to the peak intensity derived from the (100) plane ((012) / (100)) is preferably 0.3 or more, more preferably 0.4 or more. The peak intensity ratio ((012) / (100)) is preferably 0.6 or less. Here, the (100) plane is derived from a hexagonal crystal structure, and the (012) plane is derived from a rhombohedral crystal structure.

[0024] (4) In the non-aqueous electrolyte storage element according to any one of (1) to (3), the non-aqueous electrolyte has a reduction decomposition potential of 0.6 V (vs. Li / Li ＋ ) or more 1.5V (vs.Li / Li ＋ ) of a second additive.

[0025] According to the nonaqueous electrolyte storage element described in (4) above, the second additive together with the first additive forms a coating on the surface of the negative electrode active material layer, thereby further increasing the input power retention rate after storage in a high-temperature environment. Furthermore, the second additive together with the first additive forms a coating on the surface of the negative electrode active material layer, which forms a stronger coating and can suppress reaction with the electrolyte, thereby further increasing the capacity retention rate after storage in a high-temperature environment.

[0026] (5) In the nonaqueous electrolyte storage element according to (4), the ratio (A2 / B) of the amount of substance (A2) of the second additive contained in the nonaqueous electrolyte to the surface area (B) of the negative electrode active material layer is 5.0 × 10―６ mol / m ２ Above 1.0 x 10 ―５ mol / m ２ It may be the following:

[0027] According to the nonaqueous electrolyte storage element described in (5) above, the amount of the second additive relative to the surface area of ​​the negative electrode active material layer is appropriate, so that at least one (preferably both) of the input power retention rate and the capacity retention rate after storage in a high-temperature environment is further improved.

[0028] (6) In the nonaqueous electrolyte storage element described in (4) or (5) above, the ratio (A1 / A2) of the amount of substance (A1) of the first additive to the amount of substance (A2) of the second additive contained in the nonaqueous electrolyte may be 0.05 or more and 1 or less.

[0029] According to the nonaqueous electrolyte storage element described in (6) above, the ratio of the amounts of the first additive and the second additive is appropriate, and a coating of particularly good composition can be formed, so that at least one (preferably both) of the input power retention rate and the capacity retention rate after storage in a high-temperature environment is further improved.

[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 a larger initial input power 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 preferred, 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 Li-type are more preferred, and 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) is more preferable. ｘ Ni γ Mn β Co （１－ｘ－γ－β） ]O ２ In the above, it is preferable that 0.1≦γ<0.9 and 0.1≦β<0.9, for example. When such a substance is used, the effect of improving the input power due to the 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%, and more preferably 0.5 mol% to 2 mol%. By setting the content of tungsten at or above the above lower limit, the effect of tungsten in the positive electrode active material is fully exerted, and the initial input, etc., is increased. On the other hand, by setting the content of tungsten element to the above upper limit or less, it is possible to increase the discharge capacity, etc.

[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 contains graphite. The graphite may be natural graphite or artificial graphite, but is preferably natural graphite. When the graphite is natural graphite, the discharge capacity per mass of the negative electrode active material tends to be large, and the input power also tends to be large initially and after storage in a high-temperature environment.

[0059] The average particle size of the graphite 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 graphite is within the above range, it is possible to improve the charge / discharge performance of the nonaqueous electrolyte storage element. In order to obtain graphite 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.

[0060] The BET specific surface area of ​​graphite is 1 m ２ / g or more 10m ２ / g or less is preferable, and 2m ２ / g or more 6m ２ / g or less is more preferable, ２ / g or more 5m ２ When the BET specific surface area of ​​the graphite is in the above range, it is possible to exhibit good charge / discharge performance.

[0061] The graphite content 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. By setting the graphite content within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved, and the input power retention rate after storage in a high-temperature environment can be further increased.

[0062] The negative electrode active material may contain a negative electrode active material other than graphite. As the other negative electrode active material, various conventionally known negative electrode active materials can be used. However, the content of graphite relative to all the negative electrode active materials contained in the negative electrode active material layer is preferably 90% by mass or more, more preferably 99% by mass or more, and may be substantially 100% by mass. In other words, it is particularly preferable that only graphite is used as the negative electrode active material. In this way, by mainly using graphite as the negative electrode active material, it is possible to further increase the input power retention rate after storage in a high-temperature environment.

[0063] The content of all the 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. By setting the content of all the negative electrode active materials within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0064] 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 above, except that graphite contained in the negative electrode active material layer is not included in the conductive agent.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] The BET specific surface area of ​​the negative electrode active material layer is 1 m ２ / g or more 10m ２ / g or less is preferable, and 2m ２ / g or more 6m ２ / g or less is more preferable, ２ / g or more 5m ２ / g or less is more preferable. When the BET specific surface area of ​​the negative electrode active material layer is in the above range, good charge / discharge performance can be exhibited, etc. The BET specific surface area of ​​the negative electrode active material layer can be adjusted by the particle size of the negative electrode active material, the pressure applied to the negative electrode active material layer, etc.

[0070] (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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] (Non-aqueous Electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent, and an electrolyte salt and a first additive dissolved in the non-aqueous solvent.

[0075] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used.

[0076] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0077] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0078] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a chain carbonate in combination. 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.

[0079] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0080] The lithium salt is LiPF ６ , LiPO ２ F ２ , LiBF ４ , LiClO ４ , LiN(SO ２ F) 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.

[0081] 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 a high input power retention rate after storage in a high-temperature environment is particularly pronounced.

[0082] The concentration of the electrolyte salt 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 ３ By setting the concentration of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0083] The first additive has a reduction decomposition potential of 1.5 V (vs. Li / Li ＋ The lower limit of the reductive decomposition potential of the first additive is 1.6 V (vs. Li / Li ＋ The upper limit of the reductive decomposition potential of the first additive may be, for example, 2.5 V (vs. Li / Li ＋ ), and 2.0 V (vs. Li / Li ＋ ), and 1.8V (vs. Li / Li ＋ The reductive decomposition potential of the first additive may be within a range that is a combination of any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0084] The first additive was lithium bis(oxalate)borate (LiBOB: reduction decomposition potential 1.70 V (vs. Li / Li ＋)), lithium bis(oxalate)difluorophosphate (LiFOP: reduction decomposition potential 1.90 V (vs. Li / Li ＋ )), and LiBOB is preferred. The first additive has a reduction decomposition potential of 1.5 V (vs. Li / Li ＋ The first additive may be a lithium oxalate having a molecular weight of 100 or more. One or more first additives may be used.

[0085] The concentration of the first additive in the nonaqueous electrolyte is preferably 0.001% by mass to 1% by mass, more preferably 0.01% by mass to 0.5% by mass, and even more preferably 0.02% by mass to 0.2% by mass.

[0086] The lower limit of the ratio (A1 / B) of the amount of substance (A1) of the first additive contained in the non-aqueous electrolyte to the surface area (B) of the negative electrode active material layer is 2.0 × 10 －７ mol / m ２ is 3.0 × 10 －７ mol / m ２ is preferable, and 4.0 × 10 －７ mol / m ２ More preferably, 5.0 × 10 －７ mol / m ２ The lower limit of the ratio (A1 / B) is 6.0 × 10 －７ mol / m ２ , 8.0 × 10 －７ mol / m ２ , 1.0×10 －６ mol / m ２ , 1.5 × 10 －６ mol / m ２ or 2.0 x 10 －６ mol / m ２ By setting the ratio (A1 / B) to be equal to or greater than the lower limit, the coating formed on the surface of the negative electrode active material layer can be sufficiently maintained even during storage in a high-temperature environment, and the input power retention rate can be increased. ―６ mol / m ２ is preferable, and 4.0 × 10 ―６ mol / m ２ More preferably, 3.0 × 10 ―６ mol / m ２The upper limit of the ratio (A1 / B) is 2.0 × 10 ―６ mol / m ２ , 1.0×10 ―６ mol / m ２ or 8.0 x 10 ―７ mol / m ２ By setting the ratio (A1 / B) to be equal to or less than the upper limit, it is possible to increase the initial input, etc. The ratio (A1 / B) can be set within a range that combines any of the lower limits and any of the upper limits described above (however, the upper limit is greater than the lower limit).

[0087] The amount of substance (A1) of the first additive in the nonaqueous electrolyte can be adjusted by, for example, the amount of nonaqueous electrolyte (i.e., the nonaqueous electrolyte used in the manufacture of the nonaqueous electrolyte storage element) contained in the container during the manufacture of the nonaqueous electrolyte storage element and the concentration of the first additive in the contained nonaqueous electrolyte. Furthermore, because a portion of the first additive is decomposed by initial charge / discharge and subsequent aging treatment of the assembled nonaqueous electrolyte storage element, the amount of substance (A1) of the first additive in the nonaqueous electrolyte can also be adjusted by these conditions (e.g., initial charge / discharge conditions, temperature and time of aging treatment, etc.). The surface area (B) of the negative electrode active material layer can be adjusted by, for example, the shape and amount of the negative electrode active material used, the thickness of the negative electrode active material layer, etc.

[0088] The non-aqueous electrolyte preferably further contains a second additive. The second additive is also usually dissolved in the non-aqueous solvent. The second additive has a reduction decomposition potential of 0.6 V (vs. Li / Li ＋ ) or more 1.5V (vs.Li / Li ＋ The upper limit of the reduction decomposition potential of the second additive is 1.2 V (vs. Li / Li ＋ ), and 1.0 V (vs. Li / Li ＋ ), and 0.8V (vs. Li / Li ＋ The reductive decomposition potential of the second additive may be within a range that is a combination of the above-mentioned lower limit and any of the above-mentioned upper limits.

[0089] The second additive was vinylene carbonate (reduction decomposition potential 0.64 V (vs. Li / Li ＋ )), 1,3-propene sultone (reductive decomposition potential 1.09 V (vs. Li / Li ＋ )), pentene glycol 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 ＋ The second additive has a carbon-carbon unsaturated double bond in the carbonate ring structure and a reduction decomposition potential of 0.6 V (vs. Li / Li ＋ ) or more 1.5V (vs.Li / Li ＋ The second additive may be a cyclic carbonate having a molecular weight of less than 1000. One or more second additives may be used.

[0090] The concentration of the second additive in the nonaqueous electrolyte is preferably 0.001% by mass to 1% by mass, more preferably 0.01% by mass to 0.5% by mass, and even more preferably 0.04% by mass to 0.2% by mass.

[0091] The lower limit of the ratio (A2 / B) of the amount of substance (A2) of the second additive contained in the non-aqueous electrolyte to the surface area (B) of the negative electrode active material layer is, for example, 1.0 × 10 ―６ mol / m ２ or 3.0 x 10 ―６ mol / m ２ may be used, but 5.0 × 10 ―６ mol / m ２ The upper limit of the ratio (A2 / B) is preferably 1.0×10 ―５ mol / m ２ is preferable, and 8.0 × 10 ―６ mol / m ２ More preferably, 7.0 × 10 ―６ mol / m ２ By setting the ratio (A2 / B) within the above range, it is possible to further increase the input power retention rate after storage in a high-temperature environment, etc. The ratio (A2 / B) may be within a range that combines any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0092] The amount of substance (A2) of the second additive in the non-aqueous electrolyte can be adjusted in the same manner as the amount of substance (A1) of the first additive in the non-aqueous electrolyte.

[0093] The lower limit of the ratio (A1 / A2) of the amount of substance (A1) of the first additive to the amount of substance (A2) of the second additive contained in the non-aqueous electrolyte solution is preferably 0.05, more preferably 0.08, and may be 0.2, 0.3, or 0.4. The upper limit of the ratio (A1 / A2) is preferably 1, more preferably 0.9, even more preferably 0.8, even more preferably 0.7, and particularly preferably 0.6. By setting the ratio (A1 / A2) within the above range, it is possible to further increase the input power retention rate after storage in a high-temperature environment. The ratio (A1 / A2) may be within a range that combines any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0094] The non-aqueous electrolyte may contain other additives in addition to the non-aqueous solvent, electrolyte salt, first additive, and second additive. The other additives may be used singly or in combination of two or more. The content of the other additives 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.

[0095] 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.

[0096] 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.

[0097] <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.

[0098] 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.

[0099] <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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] The method for manufacturing a nonaqueous electrolyte storage element may include initially charging and discharging the assembled nonaqueous electrolyte storage element before charging and discharging, and then performing an aging treatment after the initial charging and discharging. The initial charging and discharging may be performed once or multiple times. The initial charging and aging treatment decompose a part of the first additive in the nonaqueous electrolyte contained in the container, forming a coating on the surface of the negative electrode active material layer.

[0104] <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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] [Example 1] (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 content of tungsten element relative to transition metal elements other than tungsten element 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 in a mass (solid content mass) of 6 mg / cm. ２ The coating was then dried, followed by roll pressing to obtain a positive electrode in which positive electrode active material layers were laminated on both sides of the positive electrode substrate.

[0109] (Preparation of Negative Electrode) Natural graphite 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 so that the mass (solid content mass) was 4 mg / cm. ２ The coating was then roll pressed to obtain a negative electrode in which negative electrode active material layers were laminated on both sides of the negative electrode substrate. The BET specific surface area of ​​the negative electrode active material layer was 4.0 g / m ２ and the surface area is 89.3 m ２ It was.

[0110] (Preparation of non-aqueous electrolyte) LiPF was added to a non-aqueous solvent prepared by mixing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 30:70. ６ to 1.2 mol / dm ３ The first additive, lithium bis(oxalate)borate (LiBOB: reduction decomposition potential 1.70 V (vs. Li / Li) ＋ )) at a concentration of 0.5 mass %, and vinylene carbonate (VC: reduction decomposition potential 0.64 V (vs. Li / Li ＋ )) were dissolved in a concentration of 0.2 mass % to prepare a non-aqueous electrolyte solution.

[0111] (Separator) A microporous polyolefin film was used as the separator.

[0112] (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 subjected to constant-current charging at a current of 1.0 C in a thermostatic chamber at 25°C to an SOC (state of charge) of 80%, and then aging treatment was carried out in a thermostatic chamber at 45°C. The aging treatment time was 15 hours. After aging treatment, constant-current / constant-voltage charging was carried out 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. Next, constant-current discharging was carried out under conditions of a discharge current of 1.0 C and a discharge cut-off voltage of 3.0 V, to obtain the nonaqueous electrolyte storage element of Example 1.

[0113] Example 2 A nonaqueous electrolyte capacitor element of Example 2 was obtained in the same manner as in Example 1, except that the temperature of the aging treatment was set to 65°C.

[0114] Example 3 A nonaqueous electrolyte storage element of Example 3 was obtained in the same manner as in Example 1, except that the temperature of the aging treatment was set to 70°C.

[0115] [Comparative Examples 1 and 2] The nonaqueous electrolyte storage elements of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that a natural graphite different from that used in Example 1 was used as the negative electrode active material, the BET specific surface area and the surface area of ​​the negative electrode active material layer were set to the values ​​shown in Table 1, and the nonaqueous electrolyte was prepared by dissolving LiBOB and VC at the concentrations (charge values) shown in Table 1.

[0116] [Reference Example 1] LiNi containing no tungsten element １／３ Mn １／３ Co １／３ O ２ A nonaqueous electrolyte storage element of Reference Example 1 was obtained in the same manner as in Comparative Example 1, except that the above was used as the positive electrode active material.

[0117] Two nonaqueous electrolyte storage elements were prepared for each of the Examples, Comparative Examples, and Reference Examples; one for measuring the amount of the first additive and the second additive in the nonaqueous electrolyte of the obtained nonaqueous electrolyte storage element, and the other for evaluating the input power retention rate after storage in a high-temperature environment.

[0118] (Measurement of the amount of substance of the first additive and the second additive relative to the surface area of ​​the negative electrode active material layer) For each of the obtained nonaqueous electrolyte storage elements, the amount of substance of the first additive and the second additive in the nonaqueous electrolyte was measured using the method described above, and the ratio (A1 / B) of the amount of substance of the first additive contained in the nonaqueous electrolyte (A1) to the surface area (B) of the negative electrode active material layer and the ratio (A2 / B) of the amount of substance of the second additive contained in the nonaqueous electrolyte (A2) to the surface area (B) of the negative electrode active material layer were determined. In addition, the ratio (A1 / A2) of the amount of substance of the first additive contained in the nonaqueous electrolyte (A1) to the amount of substance of the second additive (A2) was also determined. The determined values ​​of the ratios (A1 / B), (A2 / B), and (A1 / A2) are shown in Table 1.

[0119] [Evaluation] (1) Measurement of Initial Input Each of the obtained nonaqueous electrolyte storage elements was subjected to constant current charging at a current of 1.0 C in a thermostatic chamber at 25 ° C, and the SOC (state of charge) was adjusted to 50%. Subsequently, after storing the element in a thermostatic chamber at -10 ° C for 4 hours, the element was charged for 30 seconds at a constant current of 5 C, 10 C, 15 C, 20 C, or 25 C. After each charge, the element was subjected to constant current discharge at a current of 1.0 C, and the SOC was adjusted to 50%. The relationship between the current and the voltage 10 seconds after the start of charging for each charge was plotted, and the DC resistance was calculated from the slope of the straight line obtained from the five plots. The input 10 seconds after the start of charging was calculated from the calculated DC resistance and used as the initial input.

[0120] (2) Measurement of Input Power After Storage in a High-Temperature Environment Next, each nonaqueous electrolyte storage element was subjected to constant-current charging at a current of 1.0 C in a thermostatic chamber at 25°C to an SOC of 80%. At this SOC of 80%, each nonaqueous electrolyte storage element was stored in a thermostatic chamber at 70°C for 60 days. Thereafter, the element was stored in the thermostatic chamber at 25°C for 3 hours or more, and then subjected to constant-current discharge at a current of 1.0 C with a discharge end voltage of 3.0 V. The input power 10 seconds after the start of charging was measured in the same manner as in the "Measurement of Initial Input Power" above, and this was defined as the input power after storage in a high-temperature environment. The percentage of the input power after storage in a high-temperature environment relative to the initial input power was calculated as the input power maintenance rate. The calculated input power maintenance rates of each nonaqueous electrolyte storage element are shown in Table 1 as relative values, with the value of Example 2 set as the reference (100%).

[0121]

[0122] As shown in Table 1, the positive electrode active material contains tungsten element, and the ratio (A1 / B) is 2.0 × 10 －７ mol / m ２ In the nonaqueous electrolyte storage elements of Comparative Examples 1 and 2, in which the ratio (A1 / B) was less than 2.0×10, the input power retention rate (relative value) was 90% or less, and the input power retention rate after storage in a high-temperature environment was low. －７ mol / m ２In each of the nonaqueous electrolyte storage elements of Examples 1 to 3 described above, the input power retention rate (relative value) was 100% or more, and the input power retention rate after storage in a high-temperature environment was high. In each of the nonaqueous electrolyte storage elements of Examples 1 to 3, the input power retention rate after storage in a high-temperature environment increased as the ratio (A1 / B) increased. From these results, it can be said that the ratio (A1 / B) of the substance amount (A1) of the first additive to the surface area (B) of the negative electrode active material layer significantly contributes to improving the input power retention rate after storage in a high-temperature environment. Furthermore, in the nonaqueous electrolyte storage element of Reference Example 1, in which the positive electrode active material does not contain elemental tungsten, －７ mol / m ２ Although the input power retention rate after storage in a high-temperature environment was less than 100 kJ / s, it was confirmed that the phenomenon of input power reduction after storage in a high-temperature environment is a phenomenon that occurs significantly in nonaqueous electrolyte storage elements in which the positive electrode active material contains elemental tungsten.

[0123] 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.

[0124] 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. An electrochemical cell comprising: an electrode assembly having a positive electrode and a negative electrode; a non-aqueous electrolyte; and a container for accommodating the electrode assembly and the non-aqueous electrolyte; wherein the positive electrode has a positive electrode active material layer containing a positive electrode active material; the negative electrode has a negative electrode active material layer containing a negative electrode active material; the positive electrode active material contains tungsten element; the negative electrode active material contains graphite; and the non-aqueous electrolyte has a reduction decomposition potential of 1.5 V (vs. Li / Li ＋ ) or more, and a ratio (A1 / B) of the amount of substance (A1) of the first additive contained in the nonaqueous electrolyte to the surface area (B) of the negative electrode active material layer is 2.0×10 －７ mol / m ２ The above is the nonaqueous electrolyte storage element.

2. The above ratio (A1 / B) is 5.0 x 10 ―６ mol / m ２ 2. The nonaqueous electrolyte storage element according to claim 1, wherein:

3. The non-aqueous electrolyte storage element according to claim 1 or 2, wherein the graphite is natural graphite.

4. The non-aqueous electrolyte has a reduction decomposition potential of 0.6 V (vs. Li / Li ＋ ) or more 1.5V (vs.Li / Li ＋ 3. The nonaqueous electrolyte storage element according to claim 1, further comprising a second additive having a content of less than 100% by mass.

5. The ratio (A2 / B) of the amount of the second additive contained in the nonaqueous electrolyte (A2) to the surface area (B) of the negative electrode active material layer is 5.0×10 ―６ mol / m ２ Above 1.0 x 10 ―５ mol / m ２ The nonaqueous electrolyte storage element according to claim 4 , wherein:

6. The nonaqueous electrolyte storage element according to claim 4, wherein the ratio (A1 / A2) of the amount of substance (A1) of the first additive contained in the nonaqueous electrolyte to the amount of substance (A2) of the second additive contained in the nonaqueous electrolyte is 0.05 or more and 1 or less.

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