Nonaqueous electrolyte electricity storage element

Abstract

A non-aqueous electrolyte electricity storage element according to one aspect of the present invention is provided with a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and is characterized in that: the non-aqueous electrolyte contains a non-aqueous solvent containing a chain carboxylic acid ester and an additive that is reductively decomposed on the surface of the negative electrode; when the volume of the non-aqueous electrolyte is Ve, the void volume of the positive electrode is Vp, the void volume of the negative electrode is Vn, and the void volume of the separator is Vs, formula 1 is satisfied. (Vp + Vn + Vs) * 1.1 < = Ve... 1.

Description

Technical Field

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

[0002] Non-aqueous electrolyte secondary batteries, represented by lithium-ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as in automobiles, due to their high energy density. These non-aqueous electrolyte secondary batteries generally comprise a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes. Charge and discharge are achieved by the transfer of charge ions between the two electrodes. As non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors are also widely used.

[0003] In order to improve the performance of non-aqueous electrolyte storage devices, the addition of various additives to non-aqueous electrolytes has been studied (see Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2004-319212 Summary of the Invention

[0007] Among the additives, there are substances that can increase the input of the non-aqueous electrolyte storage element if they are moderately reduced and decomposed on the negative electrode surface. However, in non-aqueous electrolyte storage elements using such additives, the initial input is sometimes reduced due to excessive reduction and decomposition of the additive on the negative electrode surface. It should be noted that input refers to the energy (power: W) that the non-aqueous electrolyte storage element can absorb per unit time during charging. In other words, input refers to the input power during charging, which is an indicator of performance that can be effectively charged.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte energy storage device having a large initial input.

[0009] A non-aqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains a non-aqueous solvent comprising a chain carboxylic acid ester and an additive that undergoes reductive decomposition on the surface of the negative electrode. When the volume of the non-aqueous electrolyte is set to Ve, the void volume of the positive electrode is set to Vp, the void volume of the negative electrode is set to Vn, and the void volume of the separator is set to Vs, the following formula 1 is satisfied.

[0010] (Vp+Vn+Vs)×1.1≤Ve···1

[0011] The nonaqueous electrolyte electricity storage element according to one aspect of the present invention has a large initial input. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a perspective view showing one embodiment of a non-aqueous electrolyte electricity storage device.

[0013] Figure 2 This is a schematic diagram showing one embodiment of an electricity storage device composed of a plurality of nonaqueous electrolyte electricity storage elements assembled together. DETAILED DESCRIPTION

[0014] First, the outline of the nonaqueous electrolyte electricity storage device disclosed in this specification will be described.

[0015] (1) One aspect of the present invention relates to a non-aqueous electrolyte storage element comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains a non-aqueous solvent comprising a chain carboxylic acid ester and an additive that undergoes reduction and decomposition on the surface of the negative electrode. When the volume of the non-aqueous electrolyte is set to Ve, the void volume of the positive electrode is set to Vp, the void volume of the negative electrode is set to Vn, and the void volume of the separator is set to Vs, the following formula 1 is satisfied.

[0016] (Vp+Vn+Vs)×1.1≤Ve···1

[0017] The initial input of the non-aqueous electrolyte storage element described in (1) above is large. The reason has not yet been determined, but it is speculated to be the following. In the non-aqueous electrolyte storage element described in (1) above, the non-aqueous electrolyte contains an additive that undergoes reduction and decomposition on the surface of the negative electrode. According to the opinions of the inventors, in the past, when such non-aqueous electrolyte storage elements were initially charged, the additives were excessively reduced and decomposed on the surface of the negative electrode, and thus a thick film was sometimes formed on the surface of the negative electrode. This thick film is an important factor in reducing the initial input of the non-aqueous electrolyte storage element. In contrast, the non-aqueous electrolyte of the non-aqueous electrolyte storage element described in (1) above contains a chain carboxylate. The chain carboxylate is reduced and decomposed on the surface of the negative electrode before the additives during initial charging. As a result, the excessive reduction and decomposition of the additives is suppressed, and thus a film from the additives is appropriately formed on the surface of the negative electrode. Therefore, the initial input of the non-aqueous electrolyte storage element described in (1) above is large.

[0018] In addition, when the amount of non-aqueous electrolyte in the non-aqueous electrolyte storage element is small, as described above, if the reduction decomposition of the above-mentioned additives is suppressed by containing chain carboxylic acid esters, the amount of chain carboxylic acid esters and the amount of the above-mentioned additives in the non-aqueous electrolyte are small, and the films from the chain carboxylic acid esters and the above-mentioned additives are not fully formed on the negative electrode surface. Other components in the non-aqueous electrolyte (non-aqueous solvent, etc.) are reduced and decomposed on the negative electrode surface, and it is easy to form films from the other components. Such films from other components usually have high resistance and may reduce the initial input of the non-aqueous electrolyte storage element. In this regard, in the non-aqueous electrolyte storage element described in (1), by satisfying the above formula 1, the amount of non-aqueous electrolyte in the non-aqueous electrolyte storage element can be kept large. As a result, the reduction decomposition of the above-mentioned additives is not excessively suppressed, and it is difficult to form films from other components in the non-aqueous electrolyte. Therefore, the initial input of the non-aqueous electrolyte storage element described in (1) is large.

[0019] It should be noted that, according to the non-aqueous electrolyte storage element described in (1), as described above, excessive reductive decomposition of the additive is suppressed by containing a chain carboxylate, so that a sufficient amount of the additive may remain in the non-aqueous electrolyte even after the initial charge and discharge. The residual additive is gradually reductively decomposed during the charge and discharge cycle to maintain the film. Therefore, the non-aqueous electrolyte storage element described in (1) may have a large input after the charge and discharge cycle.

[0020] (2) In the non-aqueous electrolyte storage element described in (1), the reduction potential of the additive may be 0.5 V (vs. Li / Li + )above.

[0021] In the non-aqueous electrolyte storage element described in (2) above, the additive is easily reduced and decomposed on the surface of the negative electrode, and thus the effects of the present invention can be significantly exhibited.

[0022] (3) In the non-aqueous electrolyte storage element described in (1) or (2) above, the above-mentioned additive can also be at least one selected from unsaturated cyclic carbonates, fluorinated cyclic carbonates, oxalates containing phosphorus or boron elements, sulfonates containing fluorine elements, phosphates containing fluorine elements and oxygen elements, sulfates and sulfonates.

[0023] The nonaqueous electrolyte electricity storage element described in (3) above can easily increase the initial input.

[0024] (4) In the nonaqueous electrolyte storage element described in any one of (1) to (3), the additive may be at least one of an unsaturated cyclic carbonate and an oxalate containing phosphorus or boron.

[0025] The nonaqueous electrolyte energy storage device described in (4) above can further increase the initial input.

[0026] (5) In the non-aqueous electrolyte storage element described in (4) above, the ratio (C / (A+B)) of the content C of the above-mentioned chain carboxylic acid ester in the above-mentioned non-aqueous electrolyte to the total content A of the above-mentioned unsaturated cyclic carbonate and the content B of the above-mentioned oxalate containing phosphorus or boron element can be 6.4 to 14.4 on a molar basis.

[0027] In the nonaqueous electrolyte storage element described in (5), during the charge-discharge cycle, the unsaturated cyclic carbonate, the oxalate containing phosphorus or boron, and the chain carboxylate are uniformly reduced and decomposed, so that the coating maintains a moderate thickness on the negative electrode surface, thereby suppressing the increase in resistance during the charge-discharge cycle. Therefore, the nonaqueous electrolyte storage element described in (5) has a high input retention rate after the charge-discharge cycle.

[0028] (6) In the non-aqueous electrolyte storage element described in (4) above, the ratio (C / (A+B)) of the content C of the above-mentioned chain carboxylic acid ester in the above-mentioned non-aqueous electrolyte to the total content A of the above-mentioned unsaturated cyclic carbonate and the content B of the above-mentioned oxalate containing phosphorus or boron element can be 9.7 or more on a molar basis.

[0029] In the nonaqueous electrolyte storage element described in (6), during the charge-discharge cycle, the unsaturated cyclic carbonate, the oxalate containing phosphorus or boron, and the chain carboxylate are uniformly reduced and decomposed, and the coating maintains a moderate thickness on the negative electrode surface, thereby suppressing the increase in resistance during the charge-discharge cycle. Therefore, the nonaqueous electrolyte storage element described in (5) has a large input after the charge-discharge cycle.

[0030] In the present invention, the “additive” refers to compounds other than the chain carboxylic acid ester, each of which is contained in an amount of 10% by mass or less in the non-aqueous electrolyte before initial charge and discharge.

[0031] In the present invention, the "volume of the non-aqueous electrolyte" refers to the volume of the non-aqueous electrolyte measured at 25°C and 1 atmosphere [cm 3 When a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the volume of the non-aqueous electrolyte is measured by the following method.

[0032] First, the mass W1 of the non-aqueous electrolyte storage element (non-aqueous electrolyte storage element) is measured. The non-aqueous electrolyte storage element is disassembled and the extractable non-aqueous electrolyte is removed. Then, all the components are washed with dimethyl carbonate (DMC) and dried under reduced pressure at room temperature for 24 hours. It should be noted that all the components refer to all components other than the non-aqueous electrolyte that constitute the non-aqueous electrolyte storage element. Next, the mass W2 of all the components after drying is measured. The mass W3 of the non-aqueous electrolyte can be calculated from the difference (W1-W2) between the mass W1 of the non-aqueous electrolyte storage element and the mass W2 of all the components after drying. Furthermore, the volume of the non-aqueous electrolyte is calculated from the mass W3 of the non-aqueous electrolyte and the density of the non-aqueous electrolyte. It should be noted that the density of the non-aqueous electrolyte is the value at 25°C and is obtained by measuring the non-aqueous electrolyte removed when the non-aqueous electrolyte storage element is disassembled using a liquid density meter.

[0033] In the present invention, the "void volume" is measured by the following method.

[0034] The non-aqueous electrolyte storage element was discharged at a constant current of 0.1C to the discharge end voltage during normal use, which was considered the discharged state. Here, normal use refers to the use of the non-aqueous electrolyte storage element under the recommended or specified charge and discharge conditions for the non-aqueous electrolyte storage element. The discharged non-aqueous electrolyte storage element was disassembled, and the positive electrode, negative electrode, and separator to be measured were removed. After each was cleaned with dimethyl carbonate (DMC), it was dried under reduced pressure at room temperature for 24 hours.

[0035] The void volume of the positive electrode can be calculated as the difference between the apparent volume of the positive electrode and the sum of the actual volumes of the materials constituting the positive electrode. For example, when the positive electrode is composed of a non-porous positive electrode substrate having no voids and a porous positive electrode active material layer having voids, the void volume of the positive electrode is equal to the void volume of the positive electrode active material layer. The void volume of the positive electrode active material layer can be calculated as the difference (V1-V2) between the apparent volume (including the volume of the voids) V1 of the positive electrode active material layer and the sum of the actual volumes V2 of the materials constituting the positive electrode active material layer. The apparent volume of the positive electrode active material layer can be calculated based on the length, average thickness and width of the positive electrode active material layer. The average thickness is set as the average of the measured values at any five locations (hereinafter, the same applies to the average thickness). The sum of the actual volumes V2 of the materials constituting the positive electrode active material layer can be calculated based on the content of each material in the positive electrode active material layer and the true density of each material.

[0036] The void volume of the negative electrode can be calculated as the difference between the apparent volume of the negative electrode and the sum of the actual volumes of the materials that make up the negative electrode. Furthermore, when the negative electrode consists of a negative electrode substrate without voids and a negative electrode active material layer with voids, the void volume of the negative electrode is equal to the void volume of the negative electrode active material layer. The void volume of the negative electrode active material layer can be calculated in the same way as the void volume of the positive electrode active material layer.

[0037] The void volume of the separator is calculated based on the difference between the apparent volume and the actual volume of the separator. The apparent volume of the separator can be calculated based on the length, average thickness and width of the separator. In addition, the actual volume of the separator can be calculated based on the mass and true density of the separator. It should be noted that in the case where the separator is composed of multiple components (layers), the void volume of the separator can be calculated as the sum of the void volumes of the various components that constitute the separator. For example, in the case where the separator is composed of a porous substrate layer and a porous heat-resistant layer described later, the void volume of the separator can be calculated as the sum of the void volume of the substrate layer and the void volume of the heat-resistant layer.

[0038] In the present invention, the "reduction potential" refers to the potential (vs. Li / Li) at the reduction peak (the highest potential reduction peak observed in the first cycle) confirmed by the measurement results of the cyclic voltammetry (CV) method. + ). It should be noted that the CV method was carried out under the following measurement conditions.

[0039] [Measurement conditions]

[0040] Working electrode: graphite

[0041] Reference electrode: Li metal

[0042] Solvent composition: EC:EMC=3:7 (volume ratio)

[0043] Electrolyte salt: LiPF6 (1 mol / dm 3 )

[0044] Temperature: Room temperature

[0045] Scan speed: 1mV / s

[0046] Scan times: 2 cycles

[0047] Scan range: 0V (vs. Li / Li + )-3.2V(vs.Li / Li + )

[0048] In the present invention, the content A of the unsaturated cyclic carbonate, the content B of the oxalate containing phosphorus or boron, and the content C of the chain carboxylate in the non-aqueous electrolyte are determined based on the contents in the non-aqueous electrolyte solution removed when the non-aqueous electrolyte storage element is disassembled. The content A of the unsaturated cyclic carbonate and the content C of the chain carboxylate in the non-aqueous electrolyte are determined using gas chromatography-mass spectrometry (GC-MS). Furthermore, the content B of the oxalate containing phosphorus or boron is determined using ion chromatography (IC).

[0049] The following describes in detail a nonaqueous electrolyte energy storage element, energy storage device, and method for manufacturing a nonaqueous electrolyte energy storage element according to one embodiment of the present invention, as well as other embodiments. It should be noted that the names of the components (constituent elements) used in each embodiment may differ from the names of the components (constituent elements) used in the background art.

[0050] [Non-aqueous electrolyte storage device]

[0051] A non-aqueous electrolyte storage element (hereinafter also referred to as a "storage element") according to one embodiment of the present invention comprises: an electrode body having a positive electrode, a negative electrode, and a separator; a non-aqueous electrolyte; and a container for storing the electrode body and the non-aqueous electrolyte. The electrode body is generally a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked via a separator, or a wound type in which a positive electrode and a negative electrode are wound in a state in which they are stacked via a separator. The non-aqueous electrolyte exists in a state contained in the positive electrode, the negative electrode, and the separator. As an example of a non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter referred to as a "secondary battery") will be described.

[0052] <Positive electrode>

[0053] The positive electrode includes a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or through an intermediate layer.

[0054] The positive electrode substrate has electrical conductivity. Whether it has "electrical conductivity" is determined by the volume resistivity 10 measured in accordance with JIS-H-0505 (1975). -2Ω·cm is the threshold value for judgment. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, stainless steel, or their alloys can be used. Among them, from the viewpoints of potential resistance, high conductivity and cost, aluminum or aluminum alloys are preferred. As the positive electrode substrate, foil, vapor-deposited film, mesh, porous material, etc. can be mentioned. From the viewpoint of cost, foil is preferred. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. As aluminum or aluminum alloy, A1085, A3003, A1N30, etc. specified in JIS-H-4000 (2014) or JIS-H-4160 (2006) can be mentioned.

[0055] 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 this range, the strength of the positive electrode substrate can be increased while also increasing the energy density per unit volume of the non-aqueous electrolyte storage device.

[0056] The intermediate layer is placed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent, such as carbon particles, to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The structure of the intermediate layer is not particularly limited; for example, it may contain a binder and a conductive agent.

[0057] The positive electrode active material layer contains a positive electrode active material and optionally contains a conductive agent, a binder, a thickener, a filler, and other optional components.

[0058] As the positive electrode active material, it can be appropriately selected from known positive electrode active materials. As the positive electrode active material for lithium ion secondary batteries, materials that can absorb and release lithium ions are generally used. As the positive electrode active material, for example, lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, sulfur, etc. can be cited. As lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, for example, Li[Li x Ni (1－x) ]O2(0≤x<0.5),Li[Li x Ni γ Co (1－x－γ) ]O2 (0≤x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Co (1－x) ]O2(0≤x<0.5),Li[Li x Ni γ Mn (1－x－γ) ]O2 (0≤x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Niγ Mn β Co (1－x－γ－β) ]O2 (0≤x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), Li[Li x Ni γ Co β Al (1－x－γ－β) ]O2 (0≤x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β) etc. As lithium transition metal composite oxides having a spinel crystal structure, Li x Mn2O4、Li x Ni γ Mn (2－γ) O4, etc. Examples of polyanionic compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. Examples of chalcogenides include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. The atoms or polyanions in these materials may be partially replaced by atoms or anionic substances composed of other elements. The surfaces of these materials may also be covered with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be mixed.

[0059] As the positive electrode active material, a lithium transition metal composite oxide is preferred, more preferably one containing at least one of nickel, cobalt, and manganese, further preferably one containing at least two of nickel, cobalt, and manganese, and even more preferably one containing nickel, cobalt, and manganese. The lithium transition metal composite oxide preferably has an α-NaFeO2 crystal structure. Using such a lithium transition metal composite oxide can improve energy density, among other things.

[0060] The positive electrode active material is generally in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm to 20 μm. By making the average particle size of the positive electrode active material greater than the above lower limit, the production or handling of the positive electrode active material is facilitated. By making the average particle size of the positive electrode active material less than the above upper limit, the electrical conductivity of the positive electrode active material layer is improved. It should be noted that when a composite of the positive electrode active material and other materials 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 particle size distribution measured by the laser diffraction and scattering method based on the diluted solution after the particles are diluted in a solvent in accordance with JIS-Z-8825 (2013), and the value of the volume standard cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) as 50%.

[0061] In order to obtain a powder of a predetermined particle size, a pulverizer, a classifier, etc. can be used. As a pulverization method, for example, methods such as using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a reverse jet mill, a rotary airflow type jet mill, or a sieve can be mentioned. During pulverization, wet pulverization in which an organic solvent such as water or hexane coexists can also be used. As a classification method, a sieve, an air classifier, etc. can be used, and either a dry method or a wet method can be used as needed.

[0062] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and even more preferably 80% to 95% by mass. By setting the content of the positive electrode active material in the above range, it is possible to achieve both high energy density and manufacturability of the positive electrode active material layer.

[0063] The conductive agent is not particularly limited as long as it is a material with conductivity. Examples of such conductive agents include carbon materials, metals, and conductive ceramics. Examples of carbon materials include graphite, non-graphite carbon, and graphene-based carbon. Examples of non-graphite carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. Examples of the shape of the conductive agent include powdered and fibrous forms. As the conductive agent, one of these materials may be used alone, or two or more may be mixed and used. In addition, these materials may be used in combination. For example, a material obtained by combining carbon black with CNTs may be used. Among these, carbon black is preferred from the viewpoint of electrical conductivity and coating properties, and acetylene black is preferred.

[0064] The content of the conductive agent in the positive electrode active material layer is preferably 1% to 10% by mass, more preferably 3% to 9% by mass. By setting the content of the conductive agent within the above range, the energy density of the nonaqueous electrolyte storage device can be increased.

[0065] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic acid, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0066] The content of the binder in the positive electrode active material layer is preferably 1% to 10% by mass, more preferably 3% to 9% by mass. When the content of the binder is within the above range, the positive electrode active material can be stably retained.

[0067] As a thickener, for example, polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose can be mentioned. When the thickener has a functional group that reacts with lithium or the like, the functional group can be deactivated in advance by methylation or the like. When a thickener is used, the content of the thickener in the positive electrode active material layer can be set to 0.1% by mass to 8% by mass, usually preferably 5% by mass or less, more preferably 2% by mass or less. The technology disclosed herein is preferably implemented in a manner that does not contain a thickener in the positive electrode active material layer.

[0068] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silica, aluminum oxide, 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; talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. When a filler is used, the content of the filler in the positive electrode active material layer can be set to 0.1% by mass to 8% by mass, preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein is preferably implemented in a manner such that the positive electrode active material layer does not contain a filler.

[0069] The positive electrode active material layer may also contain typical non-metallic elements such as B, N, P, F, Cl, Br, I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0070] Negative electrode

[0071] The negative electrode comprises a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The structure of the intermediate layer is not particularly limited and can be selected from the structures exemplified for the positive electrode described above.

[0072] The negative electrode substrate has electrical conductivity. As the material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, aluminum, or their alloys, carbon materials, etc. can be used. Among them, copper or copper alloys are preferred. As the negative electrode substrate, foil, vapor-deposited film, mesh, porous material, etc. can be mentioned. From the perspective of cost, foil is preferred. Therefore, as the negative electrode substrate, copper foil or copper alloy foil is preferred. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0073] 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 this range, the strength of the negative electrode substrate can be increased while also increasing the energy density per unit volume of the non-aqueous electrolyte storage device.

[0074] The negative electrode active material layer contains a negative electrode active material. Optionally, the negative electrode active material layer may contain a conductive agent, a binder, a thickener, a filler, and other optional components. These optional components may be selected from the materials exemplified above for the positive electrode.

[0075] The negative electrode active material layer may also contain typical non-metallic elements such as B, N, P, F, Cl, Br, I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, 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.

[0076] The negative electrode active material can be appropriately selected from known negative electrode active materials. Generally, materials that can absorb and release lithium ions can be used as negative electrode active materials for lithium ion secondary batteries. Examples of negative electrode active materials include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; Li4Ti5O 12 Titanium-containing oxides such as LiTiO2, TiNb2O7, and others; polyphosphate compounds; silicon carbide; carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Of these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, any one of these materials may be used alone, or a mixture of two or more may be used.

[0077] “Graphite” refers to the average lattice spacing (d) of the (002) plane determined by X-ray diffraction before charge or discharge or in the discharged state. 002 ) is a carbon material having a diameter of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. From the perspective of obtaining a material with stable physical properties, artificial graphite is preferred.

[0078] “Non-graphite carbon” refers to the average lattice spacing (d) of the (002) plane determined by X-ray diffraction before charge and discharge or in the discharged state. 002) is a carbon material having a diameter of 0.34 nm to 0.42 nm. Examples of non-graphite carbon include hardly graphitizable carbon and easily graphitizable carbon. Examples of non-graphite carbon include resin-derived materials, petroleum pitch or materials derived from petroleum pitch, petroleum coke or materials derived from petroleum coke, plant-derived materials, and alcohol-derived materials.

[0079] Here, the "discharge state" of a carbonaceous material refers to a state in which lithium ions, which can be stored and released, are fully released from the carbonaceous material, which serves as the negative electrode active material, during charge and discharge. For example, in a half-cell comprising a negative electrode containing a carbonaceous material as the negative electrode active material as the working electrode and metallic lithium as the counter electrode, the open circuit voltage is 0.7 V or higher.

[0080] “Non-graphitizable carbon” refers to the above-mentioned 002 It is a carbon material with a diameter of 0.36nm to 0.42nm.

[0081] “Graphitizable carbon” refers to the above-mentioned 002 A carbon material having a diameter of 0.34 nm or more and less than 0.36 nm.

[0082] The negative electrode active material is generally in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm. When the negative electrode active material is a carbon material, a titanium oxide or a polyphosphate compound, its average particle size can also be 1 μm to 100 μm. When the negative electrode active material is Si, Sn, Si oxide or Sn oxide, etc., its average particle size can also be 1 nm to 1 μm. By setting the average particle size of the negative electrode active material to be above the above lower limit, the manufacture or handling of the negative electrode active material is facilitated. By setting the average particle size of the negative electrode active material to be below the above upper limit, the electrical conductivity of the negative electrode active material layer is improved. In order to obtain powder of a specified particle size, a pulverizer, a classifier, etc. can be used. The pulverization method and the classification method can be selected, for example, from the methods exemplified in the above-mentioned positive electrode. When the negative electrode active material is a metal such as metal Li, the negative electrode active material can also be in the form of foil.

[0083] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% to 99% by mass, more preferably 90% to 98% by mass. By setting the content of the negative electrode active material to the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer. When the negative electrode active material is metallic Li, the content of the negative electrode active material in the negative electrode active material layer may be 99% by mass or more, or 100% by mass.

[0084] <Isolators>

[0085] The separator can be appropriately selected from known separators. As the separator, for example, a separator consisting only of a substrate layer, a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer, etc. can be used. As the shape of the substrate layer of the separator, woven fabrics, non-woven fabrics and porous resin films can be mentioned. Among these shapes, from the viewpoint of strength, porous resin films are preferred, and from the viewpoint of liquid retention of non-aqueous electrolytes, non-woven fabrics are preferred. As the material of the substrate layer of the separator, from the viewpoint of insulation function, for example, polyolefins such as polyethylene and polypropylene are preferred, and from the viewpoint of resistance to oxidative decomposition, polyimides, aromatic polyamides, etc. are preferred. As the substrate layer of the separator, a material composited with these resins can also be used.

[0086] The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere, and more preferably have a mass loss of 5% or less when heated from room temperature to 800°C. Materials with a mass loss below a specified value 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 aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; and sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate. Covalent crystals such as silicon and diamond are also available. Mineral-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof, can be used as inorganic compounds. These materials may be used alone or as a composite, or as a mixture of two or more. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of safety of the non-aqueous electrolyte storage device.

[0087] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" is a value based on volume and is measured using a mercury porosimeter.

[0088] As a separator, a polymer gel composed of a polymer and a non-aqueous electrolyte can be used. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinyl pyrrolidone, and polyvinylidene fluoride. Using a polymer gel can effectively suppress liquid leakage. As a separator, a porous resin film or nonwoven fabric, as described above, can be used in combination with the polymer gel.

[0089] <Non-aqueous electrolyte>

[0090] The nonaqueous electrolyte in one embodiment of the present invention comprises a nonaqueous solvent containing a chain carboxylate and an additive that undergoes reductive decomposition on the negative electrode surface. The nonaqueous electrolyte is typically a nonaqueous electrolyte solution comprising the nonaqueous solvent, an electrolyte salt dissolved in the nonaqueous solvent, and the additive.

[0091] The chain carboxylic acid ester contained in the non-aqueous solvent may be of the chemical formula [R 1 (COO)R 2 ] is a compound represented by. In the above chemical formula, R 1 and R 2 It is a saturated or unsaturated hydrocarbon group having 1 to 5 carbon atoms (preferably 1 to 3, more preferably 1 or 2). 1 Can be used with R 2 The same or different. 1 and R 2 It can be straight chain or branched chain. 1 and R 2 A part of the hydrogen atoms in may be substituted with a halogen atom (eg, a fluorine (F) atom, a chlorine (Cl) atom, a bromine (Br) atom) or the like.

[0092] Examples of the chain carboxylic acid ester include methyl propionate, ethyl propionate, propyl propionate, methyl acetate, ethyl acetate, propyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl acrylate, and methyl methacrylate. Among these, propionic acid esters are preferred because they are easily reductively decomposed on the negative electrode surface, and methyl propionate is more preferred. The chain carboxylic acid esters may be used alone or in combination of two or more.

[0093] The lower limit of the content of the chain carboxylate in the non-aqueous electrolyte before initial charge and discharge is preferably 1 volume %, more preferably 1.5 volume %, and further preferably 2 volume % relative to the non-aqueous solvent as a whole. From the viewpoint of improving the input after the charge and discharge cycle, as the lower limit of the above-mentioned content of the chain carboxylate, it is further preferably 3 volume %, and sometimes particularly preferably 5 volume %. In some ways, the above-mentioned content of the chain carboxylate can be greater than 5 volume %, or it can be more than 5.5 volume %. On the other hand, as the upper limit of the above-mentioned content of the chain carboxylate, it is preferably 9 volume %, more preferably 8 volume %, and further preferably 7 volume %. From the viewpoint of improving the input maintenance rate after the charge and discharge cycle, as the upper limit of the above-mentioned content of the chain carboxylate, it is sometimes further preferably 6 volume %. In some ways, the above-mentioned content of the chain carboxylate can also be less than 5 volume % (for example, less than 5 volume %, less than 4.5 volume %). If the above-mentioned content of the chain carboxylate is above the above-mentioned lower limit, it is possible to easily increase the input of the non-aqueous electrolyte storage element. Furthermore, if the content of the chain carboxylic acid ester is below the upper limit, the efficiency of the initial input effect relative to the increase in the content of the chain carboxylic acid ester is high. The content of the chain carboxylic acid ester is preferably 1% to 9% by volume, more preferably 1.5% to 8% by volume, and more preferably 2% to 7% by volume.

[0094] The lower limit of the content C (residual amount) of the chain carboxylic acid ester in the non-aqueous electrolyte after initial charge and discharge is preferably 5.0 mol / dm 3 , more preferably 10.0 mol / dm 3 , more preferably 15.0 mol / dm 3 , more preferably 17.0 mol / dm 3 The lower limit of the content C of the chain carboxylic acid ester is particularly preferably 20.0 mol / dm 3 , and sometimes particularly preferably 25.0 mol / dm 3 On the other hand, the upper limit of the content C of the chain carboxylic acid ester is preferably 100.0 mol / dm 3 , more preferably 80.0 mol / dm 3 , more preferably 60.0 mol / dm 3 , more preferably 45.0 mol / dm 3 Furthermore, from the viewpoint of increasing the input after the charge-discharge cycle, the upper limit of the content C of the chain carboxylic acid ester is sometimes particularly preferably 40.0 mol / dm 3 In some embodiments, the content C of the chain carboxylic acid ester can be 30.0 mol / dm 3 Below, it can also be 25.0 mol / dm 3The content C of the chain carboxylic acid ester after the initial charge and discharge can be greater than any of the lower limits and less than any of the upper limits. If the content C of the chain carboxylic acid ester after the initial charge and discharge is within the above range, the input after the charge and discharge cycle can be increased.

[0095] As other nonaqueous solvents beyond the linear carboxylic acid ester, can suitably select from known nonaqueous solvents.As above-mentioned other nonaqueous solvent, can enumerate cyclic carbonate, linear carbonate, cyclic carboxylic acid ester, phosphoric acid ester, ether, acid amides, nitrile etc.As nonaqueous solvent, can use the solvent after the part of the hydrogen atom that contains in these compounds is replaced by halogen atom.

[0096] Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), chloroethylene carbonate, and styrene carbonate. Among them, EC is preferred.

[0097] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. Among these, EMC and DMC are preferred.

[0098] As the above-mentioned other non-aqueous solvents other than the chain carboxylic acid ester, it is preferred to use cyclic carbonate or chain carbonate, and more preferably to use cyclic carbonate and chain carbonate simultaneously. By using cyclic carbonate, the dissociation of electrolyte salt can be promoted and the ion conductivity of non-aqueous electrolyte can be improved. By using chain carbonate, the viscosity of non-aqueous electrolyte can be controlled to be relatively low. When using cyclic carbonate and chain carbonate in combination, the volume ratio of cyclic carbonate to chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of 5:95 to 50:50, for example.

[0099] As the electrolyte salt, it can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, Among them, lithium salts are preferred.

[0100] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2; and lithium salts having a halogenated hydrocarbon group such as LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0101] The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / dm at 25°C and 1 atmosphere. 3 ~2.5mol / dm3 , more preferably 0.3 mol / dm 3 ~2.0mol / dm 3 Below, more preferably 0.5 mol / dm 3 ~1.7mol / dm 3 , particularly preferably 0.7 mol / dm 3 ~1.5mol / dm 3 By setting the content of the electrolyte salt to be within the above range, the ion conductivity of the non-aqueous electrolyte solution can be improved.

[0102] The non-aqueous electrolyte contains an additive that undergoes reduction and decomposition on the negative electrode surface as described above. The lower limit of the reduction potential of such an additive is preferably 0.5 V (vs. Li / Li + ), preferably 0.7V (vs. Li / Li + ), more preferably 0.9V (vs.Li / Li + On the other hand, the upper limit of the reduction potential of the additive is preferably 2.0 V (vs. Li / Li + ), more preferably 1.8V (vs.Li / Li + ), more preferably 1.6V (vs.Li / Li + If the reduction potential of the additive is above the lower limit, a film is easily formed on the negative electrode surface, and thus the effect of the present invention is easily exhibited. In addition, if the reduction potential of the additive is below the upper limit, the input reduction caused by the film being too thick on the negative electrode surface can be suppressed. In addition, the reduction potential of the additive is preferably 0.5 V (vs. Li / Li + )~2.0V(vs.Li / Li + ), more preferably 0.7V (vs.Li / Li + )~1.8V(vs.Li / Li + ), more preferably 0.9V (vs.Li / Li + )~1.6V(vs.Li / Li + ).

[0103] As additives that undergo reductive decomposition on the negative electrode surface, from the viewpoint of being able to exhibit the above-mentioned reduction potential and easily forming a good film on the negative electrode surface, there can be mentioned unsaturated cyclic carbonates, fluorinated cyclic carbonates, oxalates containing phosphorus or boron, sulfonates containing fluorine, phosphates containing fluorine and oxygen, sulfates, and sulfonates. These can be used alone or in combination of two or more.

[0104] Examples of the unsaturated cyclic carbonate include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1-methylvinylene carbonate, 1-ethylvinylene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Unsaturated cyclic carbonates are preferably those having a carbon-carbon unsaturated bond in the ring structure, and vinylene carbonate is more preferred.

[0105] Contain under the situation of unsaturated cyclic carbonate in nonaqueous electrolytic solution, as the lower limit of the content of the unsaturated cyclic carbonate in the nonaqueous electrolytic solution before the initial charge and discharge, with respect to the overall quality of nonaqueous electrolytic solution, be preferably 0.01 quality esters, more preferably 0.05 quality esters, further be preferably 0.10 quality esters, further be preferably 0.15 quality esters.On the other hand, as the upper limit of the content of unsaturated cyclic carbonate, sometimes be preferably 3.0 quality esters, more preferably 2.0 quality esters, further be preferably 1.0 quality esters, further be preferably 0.8 quality esters.The upper limit of the content of unsaturated cyclic carbonate is preferably 0.5 quality esters particularly, is preferably 0.3 quality esters particularly.The content of the unsaturated cyclic carbonate before the initial charge and discharge can be more than above-mentioned arbitrary lower limit and below above-mentioned arbitrary upper limit.If the content of unsaturated cyclic carbonate is in above-mentioned scope, then can better bring into play above-mentioned effect.

[0106] When the non-aqueous electrolyte contains an unsaturated cyclic carbonate, the lower limit of the content A (residual amount) of the unsaturated cyclic carbonate in the non-aqueous electrolyte after the initial charge and discharge is preferably 0.05 mol / dm 3 , more preferably 0.1 mol / dm 3 , more preferably 0.5 mol / dm 3 , more preferably 1.0 mol / dm 3 The lower limit of the content A of the unsaturated cyclic carbonate is preferably 1.2 mol / dm 3 , particularly preferably 1.4 mol / dm 3 On the other hand, the upper limit of the content A of the unsaturated carbonate is preferably 5.0 mol / dm 3 , more preferably 4.0 mol / dm 3 , more preferably 3.0 mol / dm 3 , more preferably 2.0 mol / dm 3 Furthermore, from the viewpoint of increasing the input after the charge-discharge cycle, the upper limit of the content A of the unsaturated carbonate is sometimes particularly preferably 1.6 mol / dm 3The content A of the unsaturated cyclic carbonate after the initial charge and discharge may be greater than any of the lower limits and less than any of the upper limits. If the content A of the unsaturated cyclic carbonate after the initial charge and discharge is within the above range, the input after the charge and discharge cycle can be further increased.

[0107] In the case where the non-aqueous electrolyte contains an unsaturated cyclic carbonate, the lower limit of the ratio (C / A) of the molar basis content C of the chain carboxylic acid ester in the non-aqueous electrolyte after the initial charge and discharge to the molar basis content A of the unsaturated cyclic carbonate is preferably 8.0, more preferably 10.0, and further preferably 12.0. The lower limit of the above-mentioned ratio (C / A) is sometimes particularly preferably 15.0, particularly preferably 18.0, and particularly preferably 22.0. On the other hand, as the upper limit of the above-mentioned ratio (C / A), it is preferably 50.0, more preferably 40.0, and further preferably 30.0. Furthermore, from the viewpoint of increasing the input after the charge and discharge cycle, as the upper limit of the above-mentioned ratio (C / A), it is sometimes further preferably 27.0. The above-mentioned ratio (C / A) after the initial charge and discharge can be above any of the lower limits and below any of the upper limits. If the above-mentioned ratio (C / A) in the non-aqueous electrolyte after the initial charge and discharge is within the above range, the input after the charge and discharge cycle can be further increased.

[0108] Examples of the fluorinated cyclic carbonate include fluorinated ethylene carbonate (FEC), difluorinated ethylene carbonate (DFEC), etc. Among these, fluorinated ethylene carbonate is preferred.

[0109] Contain fluorinated cyclic carbonate in the situation that nonaqueous electrolyte solution contains fluorinated cyclic carbonate, as the lower limit of the content of the above-mentioned fluorinated cyclic carbonate in the nonaqueous electrolyte solution before the initial charge and discharge, with respect to the overall quality of nonaqueous electrolyte, be preferably 0.1 quality, more preferably 0.2 quality, further preferably 0.3 quality, further preferably 0.4 quality.On the other hand, as the upper limit of the content of above-mentioned fluorinated cyclic carbonate, be preferably 5.0 quality, more preferably 3.0 quality, further preferably 2.0 quality, further preferably 1.0 quality.The content of above-mentioned fluorinated cyclic carbonate before the initial charge and discharge can be more than above-mentioned arbitrary lower limit and below above-mentioned arbitrary upper limit.If the content of fluorinated cyclic carbonate is in above-mentioned scope, then can better bring into play above-mentioned effect.

[0110] When the non-aqueous electrolyte contains a fluorinated cyclic carbonate, the lower limit of the content (residual amount) of the fluorinated cyclic carbonate in the non-aqueous electrolyte after the initial charge and discharge is preferably 0.05 mol / dm 3 , more preferably 0.1 mol / dm 3 , more preferably 0.5 mol / dm 3 , more preferably 0.7 mol / dm3 On the other hand, the upper limit of the content of the fluorinated cyclic carbonate is preferably 5.0 mol / dm 3 , more preferably 4.0 mol / dm 3 , more preferably 3.0 mol / dm 3 , more preferably 2.0 mol / dm 3 The content of the fluorinated cyclic carbonate after the initial charge and discharge may be greater than any of the lower limits and less than any of the upper limits. If the content of the fluorinated cyclic carbonate after the initial charge and discharge is within the above range, the input after the charge and discharge cycle can be further increased.

[0111] As the oxalate containing phosphorus or boron, lithium oxalate containing phosphorus or boron can be used. As specific examples of lithium oxalate containing phosphorus or boron, lithium bis(oxalate)borate (LiBOB), lithium difluorooxalatoborate (LiFOB), lithium difluorobis(oxalate)phosphate (LiFOP) and the like can be cited. Among these, lithium bis(oxalate)borate or lithium difluorobis(oxalate)phosphate are preferred, and lithium bis(oxalate)borate is more preferred.

[0112] In the case where the non-aqueous electrolyte contains an oxalate containing a phosphorus element or a boron element, the lower limit of the content of the above-mentioned oxalate in the non-aqueous electrolyte before initial charge and discharge is preferably 0.1 mass %, more preferably 0.2 mass %, more preferably 0.3 mass %, and more preferably 0.4 mass %. On the other hand, as the upper limit of the content of the above-mentioned oxalate, it is preferably 5.0 mass %, more preferably 3.0 mass %, more preferably 2.0 mass %, and more preferably 1.0 mass %. The upper limit of the content of the above-mentioned oxalate is sometimes particularly preferably 0.8 mass %, and particularly preferably 0.6 mass %. The content of the above-mentioned oxalate before initial charge and discharge can be above any lower limit and below any upper limit. If the content of the oxalate containing phosphorus element or boron element is within the above range, the above-mentioned effect can be better exerted.

[0113] When the non-aqueous electrolyte contains oxalate containing phosphorus or boron, the lower limit of the content B (residual amount) of oxalate containing phosphorus or boron in the non-aqueous electrolyte after the initial charge and discharge is preferably 0.05 mol / dm 3 , more preferably 0.1 mol / dm 3 , more preferably 0.5 mol / dm 3 , more preferably 0.7 mol / dm 3 As the lower limit of the oxalate content B, 1.0 mol / dm 3 , particularly preferably 1.3 mol / dm3 On the other hand, the upper limit of the content B of the oxalate is preferably 5.0 mol / dm 3 , more preferably 4.0 mol / dm 3 , more preferably 3.0 mol / dm 3 , more preferably 2.0 mol / dm 3 Furthermore, from the viewpoint of increasing the input after the charge-discharge cycle, the upper limit of the oxalate content B is particularly preferably 1.5 mol / dm 3 The oxalate content after the initial charge and discharge may be greater than any of the lower limits and less than any of the upper limits. If the oxalate content B after the initial charge and discharge is within the above range, the input after the charge and discharge cycle can be further increased.

[0114] In the case where the non-aqueous electrolyte contains an oxalate containing a phosphorus element or a boron element, the ratio (C / B) of the molar basis content C of the chain carboxylic acid ester in the non-aqueous electrolyte after the initial charge and discharge to the molar basis content B of the above-mentioned oxalate is preferably 8.5, more preferably 10.5, and even more preferably 12.5. The lower limit of the above-mentioned ratio (C / B) is sometimes further preferably 15.0, particularly preferably 20.0, and even more preferably 25.0. On the other hand, as the upper limit of the above-mentioned ratio (C / B), it is preferably 55.0, more preferably 45.0, and even more preferably 35.0. Furthermore, from the viewpoint of increasing the input after the charge and discharge cycle, as the upper limit of the above-mentioned ratio (C / B), it is sometimes further preferably 30.0. The above-mentioned ratio (C / B) after the initial charge and discharge may be above any of the above-mentioned lower limits and below any of the above-mentioned upper limits. If the above-mentioned ratio (C / B) in the non-aqueous electrolyte after the initial charge and discharge is within the above-mentioned range, the input after the charge and discharge cycle can be further increased.

[0115] As the sulfonate containing fluorine, a lithium sulfonate containing fluorine can be used. Specific examples of the lithium sulfonate containing fluorine include lithium fluoride sulfonate (LiSO3F) and lithium trifluoromethanesulfonate (LiSO3CF3). Among these, lithium fluoride sulfonate is preferred.

[0116] When the non-aqueous electrolyte contains a sulfonate containing the elemental fluorine, the lower limit of the content of the sulfonate containing the elemental fluorine in the non-aqueous electrolyte before initial charge and discharge is preferably 0.2% by mass, more preferably 0.4% by mass, further preferably 0.6% by mass, and further preferably 0.8% by mass, relative to the total mass of the non-aqueous electrolyte. On the other hand, the upper limit of the content of the sulfonate containing the elemental fluorine is preferably 8.0% by mass, more preferably 5.0% by mass, further preferably 2.0% by mass, and further preferably 1.5% by mass. The content of the sulfonate containing the elemental fluorine before initial charge and discharge can be above any of the above lower limits and below any of the above upper limits. If the content of the sulfonate containing the elemental fluorine is within the above range, the above effect can be more effectively exerted.

[0117] When the non-aqueous electrolyte contains a sulfonate containing a fluorine element, the lower limit of the content (residual amount) of the sulfonate containing a fluorine element in the non-aqueous electrolyte after the initial charge and discharge is preferably 0.05 mol / dm 3 , more preferably 0.1 mol / dm 3 , more preferably 0.5 mol / dm 3 , more preferably 0.7 mol / dm 3 On the other hand, the upper limit of the content of the sulfonate containing fluorine is preferably 5.0 mol / dm 3 , more preferably 4.0 mol / dm 3 , more preferably 3.0 mol / dm 3 , more preferably 2.0 mol / dm 3 The content of the sulfonate containing the fluorine element after the initial charge and discharge can be greater than any of the lower limits and less than any of the upper limits. If the content of the sulfonate containing the fluorine element after the initial charge and discharge is within the above range, the input after the charge and discharge cycle can be further increased.

[0118] Examples of the phosphate containing fluorine and oxygen include lithium monofluorophosphate and lithium difluorophosphate (LiDFP), among which lithium difluorophosphate is preferred.

[0119] In the case where the non-aqueous electrolyte includes a phosphate containing fluorine and oxygen elements, the lower limit of the content of the phosphate containing fluorine and oxygen elements in the non-aqueous electrolyte before initial charge and discharge is preferably 0.2 mass %, more preferably 0.4 mass %, more preferably 0.6 mass %, and more preferably 0.8 mass %. On the other hand, the upper limit of the content of the phosphate containing fluorine and oxygen elements is preferably 8.0 mass %, more preferably 5.0 mass %, more preferably 2.0 mass %, and more preferably 1.5 mass %. The content of the phosphate containing fluorine and oxygen elements before initial charge and discharge can be above any lower limit and below any upper limit. If the content of the phosphate containing fluorine and oxygen elements is within the above range, the above effect can be better exerted.

[0120] When the non-aqueous electrolyte contains phosphate containing fluorine and oxygen, the lower limit of the content (residual amount) of phosphate containing fluorine and oxygen in the non-aqueous electrolyte after initial charge and discharge is preferably 0.05 mol / dm 3 , more preferably 0.1 mol / dm 3 , more preferably 0.5 mol / dm 3 , more preferably 0.7 mol / dm 3 On the other hand, the upper limit of the content of the phosphate containing fluorine and oxygen is preferably 5.0 mol / dm 3 , more preferably 4.0 mol / dm 3 , more preferably 3.0 mol / dm 3 , more preferably 2.0 mol / dm 3 The content of the phosphate containing fluorine and oxygen elements after the initial charge and discharge can be greater than any of the lower limits and less than any of the upper limits. If the content of the phosphate containing fluorine and oxygen elements after the initial charge and discharge is within the above range, the input after the charge and discharge cycle can be further increased.

[0121] Examples of sulfate esters include cyclic sulfate esters and chain sulfate esters. Specific examples of cyclic sulfate esters include ethylene sulfate, 1,3-propylene sulfate, 2,3-propylene sulfate, 4,5-pentene sulfate, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane. Specific examples of chain sulfate esters include dimethyl sulfate and diethyl sulfate. Among these, cyclic sulfate esters are preferred, and 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane) is more preferred.

[0122] When nonaqueous electrolyte contains sulfate, as the lower limit of the content of the above-mentioned sulfate in the nonaqueous electrolyte before initial charge and discharge, relative to the overall quality of nonaqueous electrolyte, is preferably 0.1 mass %, more preferably 0.2 mass %, more preferably 0.3 mass %, more preferably 0.4 mass %.On the other hand, as the upper limit of the content of the above-mentioned sulfate, is preferably 5.0 mass %, more preferably 3.0 mass %, more preferably 2.0 mass %, more preferably 1.0 mass %.The content of the above-mentioned sulfate before initial charge and discharge can be more than the above-mentioned arbitrary lower limit and below the above-mentioned arbitrary upper limit.If the content of sulfate is within the above range, then the above-mentioned effect can be better brought into play.

[0123] When the non-aqueous electrolyte contains sulfate esters, the lower limit of the content (residual amount) of sulfate esters in the non-aqueous electrolyte after initial charge and discharge is preferably 0.05 mol / dm 3 , more preferably 0.1 mol / dm 3 , more preferably 0.5 mol / dm 3 , more preferably 0.7 mol / dm 3 On the other hand, the upper limit of the content of the above-mentioned sulfate esters is preferably 5.0 mol / dm 3 , more preferably 4.0 mol / dm 3 , more preferably 3.0 mol / dm 3 , more preferably 2.0 mol / dm 3 The content of the sulfate esters after the initial charge and discharge can be above any of the lower limits and below any of the upper limits. If the content of the phosphate containing the sulfate esters after the initial charge and discharge is within the above range, the input after the charge and discharge cycle can be further increased.

[0124] Examples of sulfonic acid esters include cyclic sulfonic acid esters and chain sulfonic acid esters. Specific examples of cyclic sulfonic acid esters include 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, 1-methyl-1,3-propene sultone, 2-methyl-1,3-propene sultone, and 3-methyl-1,3-propene sultone. Specific examples of chain sulfonic acid esters include methyl methanesulfonate and ethyl methanesulfonate. Among these, cyclic sulfonic acid esters are preferred, and 1,3-propene sultone is more preferred.

[0125] When the non-aqueous electrolyte contains sulfonic acid esters, the lower limit of the content of the above-mentioned sulfonic acid esters in the non-aqueous electrolyte before initial charge and discharge is preferably 0.1 mass %, more preferably 0.2 mass %, more preferably 0.3 mass %, and more preferably 0.4 mass %. On the other hand, the upper limit of the content of the above-mentioned sulfate esters is preferably 5.0 mass %, more preferably 3.0 mass %, more preferably 2.0 mass %, and more preferably 1.0 mass %. The content of the above-mentioned sulfonic acid esters before initial charge and discharge can be above any lower limit and below any upper limit. If the content of the sulfonic acid esters is within the above range, the above-mentioned effect can be better exerted.

[0126] When the non-aqueous electrolyte contains sulfonic acid esters, the lower limit of the content (residual amount) of sulfonic acid esters in the non-aqueous electrolyte after initial charge and discharge is preferably 0.05 mol / dm 3 , more preferably 0.1 mol / dm 3 , more preferably 0.5 mol / dm 3 , more preferably 0.7 mol / dm 3 On the other hand, the upper limit of the content of the sulfonic acid ester is preferably 5.0 mol / dm 3 , more preferably 4.0 mol / dm 3 , more preferably 3.0 mol / dm 3 , more preferably 2.0 mol / dm 3 The content of the sulfonate ester after the initial charge and discharge can be above any of the lower limits and below any of the upper limits. If the content of the phosphate containing the sulfonate ester after the initial charge and discharge is within the above range, the input after the charge and discharge cycle can be further increased.

[0127] Among the above-mentioned additives, from the viewpoint of increasing input, unsaturated cyclic carbonates and oxalates containing phosphorus or boron are preferred. In a preferred embodiment, the non-aqueous electrolyte contains both unsaturated cyclic carbonates and oxalates containing phosphorus or boron. In the case where the non-aqueous electrolyte contains both unsaturated cyclic carbonates and oxalates containing phosphorus or boron, the content of oxalates containing phosphorus or boron in the non-aqueous electrolyte before initial charge and discharge is preferably more than the content of unsaturated cyclic carbonate. As the lower limit of the ratio (mass basis) of the content of oxalates containing phosphorus or boron in the non-aqueous electrolyte before initial charge and discharge to the content of unsaturated cyclic carbonate, it is preferably 1.1, more preferably 1.5, further preferably 2.0, and further preferably 2.5. As the upper limit of the above ratio, it is preferably 15.0, more preferably 10.0, further preferably 8.0, and particularly preferably 6.0. The above ratio before initial charge and discharge can be above any of the above lower limits and below any of the above upper limits. When the ratio (mass basis) of the content of the oxalate containing phosphorus or boron to the content of the unsaturated cyclic carbonate is within the above range, the above effects can be more effectively exhibited.

[0128] From the viewpoint that the chain carboxylic acid ester moderately suppresses the reductive decomposition of the additive on the negative electrode surface, the ratio of the molar basis content C of the chain carboxylic acid ester in the non-aqueous electrolyte after the initial charge and discharge to the molar basis content A of the unsaturated cyclic carbonate and the molar basis content B of the oxalate containing phosphorus or boron element, that is, the molar ratio (C / (A+B)) of the content in the non-aqueous electrolyte after the initial charge and discharge of the above-mentioned compound is appropriately controlled. More specifically, from the viewpoint of increasing the input maintenance rate after the charge and discharge cycle, as the lower limit of the above-mentioned molar ratio, it is preferably 3.0, more preferably 5.0, and further preferably 6.4. In addition, from the viewpoint of increasing the input after the charge and discharge cycle, as the lower limit of the above-mentioned molar ratio, it is sometimes more preferably 7.0, more preferably 8.0, and further preferably 9.7 (for example 12.0). As the upper limit of the above-mentioned molar ratio, it is preferably 25.0, more preferably 20.0, further preferably 18.0, and particularly preferably 14.4. In addition, from the viewpoint of increasing the input maintenance rate after the charge and discharge cycle, the upper limit of the above-mentioned molar ratio is sometimes more preferably 14.0, and further preferably 13.0. In some embodiments, the upper limit of the above-mentioned molar ratio may be 10.0 or 9.0. In some embodiments, from the viewpoint of increasing the input maintenance rate after the charge and discharge cycle, the above-mentioned molar ratio may be 3.0 to 20.0, 6.4 to 14.4, 6.4 to 10.0, or 6.4 to 8.0. In other embodiments, from the viewpoint of increasing the input after the charge and discharge cycle, the above-mentioned molar ratio may be 7.0 to 25.0, 8.5 to 20.0, or 9.7 to 14.4. The above-mentioned molar ratio may be above any of the above-mentioned lower limits and below any of the above-mentioned upper limits (wherein the lower limit is a value less than the upper limit).

[0129] The non-aqueous electrolyte may also contain other additives in addition to the above-mentioned additives. The above-mentioned other additives may be additives that undergo reduction decomposition at the negative electrode or additives that do not undergo reduction decomposition at the negative electrode. Examples of the above-mentioned other additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated products of terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above-mentioned aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; Halogenated anisole compounds; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, phenylene sulfide, diphenyl disulfide, dipyridyl disulfide, perfluorooctane, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tetrakis(trimethylsilyl)titanate, etc. These additives may be used alone or in combination of two or more.

[0130] The total content of all additives contained in the non-aqueous electrolyte before initial charge and discharge is preferably 0.01% to 10% by mass, more preferably 0.1% to 8% by mass, further preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass relative to the mass of the entire non-aqueous electrolyte. By making the total content of all additives within the above range, the capacity retention performance or charge and discharge cycle performance after high temperature storage can be improved, further improving safety.

[0131] In one embodiment of the present invention, the volume of the non-aqueous electrolyte is Ve [cm 3 ], the void volume of the positive electrode is set to Vp [cm 3 ], the void volume of the negative electrode is set to Vn[cm 3 ], the void volume of the separator is set to Vs [cm 3 ], the above formula 1 is satisfied. That is, the coefficient α calculated by the following formula 2 is 1.1 or more.

[0132] α=Ve / (Vp+Vn+Vs)···2

[0133] As the lower limit of the coefficient α, as described above, it is 1.1, preferably 1.12, more preferably 1.15, further preferably 1.20, and further preferably 1.30. If the coefficient α is above the above lower limit, it is possible to suppress the formation of a film of other components such as the non-aqueous solvent from the non-aqueous electrolyte at the negative electrode. Thus, the initial input of the non-aqueous electrolyte storage element can be increased. On the other hand, as the upper limit of the coefficient α, there is no particular limitation, and from the viewpoint of the energy density of the non-aqueous electrolyte storage element, for example, it can be set to 2.0 or 2.00.

[0134] Although not particularly limited, the lower limit of the volume Ve of the non-aqueous electrolyte is preferably 25.6 cm 3 , more preferably 30.2 cm 3 , more preferably 34.9cm 3 The upper limit of the volume Ve of the non-aqueous electrolyte is preferably 44.2 cm 3 , more preferably 39.5cm 3 When the volume Ve of the non-aqueous electrolyte is within the above range, the above effects can be more effectively exhibited.

[0135] Although not particularly limited, the lower limit of the void volume Vp of the positive electrode is preferably 5.0 cm 3 , more preferably 5.8 cm 3 , more preferably 6.6 cm 3 The upper limit of the volume Vp of the positive electrode is preferably 8.1 cm 3 , more preferably 7.4 cm 3 If the volume Vp of the positive electrode is within the above range, the above effects can be better exerted.

[0136] Although not particularly limited, the lower limit of the void volume Vn of the negative electrode is preferably 7.7 cm 3 , more preferably 8.8 cm 3 , more preferably 10.0 cm 3 The upper limit of the volume Vn of the negative electrode is preferably 12.2 cm 3 , more preferably 11.1 cm 3 If the volume Vn of the negative electrode is within the above range, the above effects can be better exerted.

[0137] Although not particularly limited, the lower limit of the void volume Vs of the separator is preferably 6.7 cm 3 , more preferably 6.9 cm 3 , more preferably 7.0 cm 3 The upper limit of the volume Vs of the separator is preferably 7.6 cm 3 , more preferably 7.4 cm 3If the volume Vs of the spacer is within the above range, the above effects can be better exerted.

[0138] The shape of the nonaqueous electrolyte storage element of the present embodiment is not particularly limited, and examples thereof include cylindrical batteries, square batteries, flat batteries, coin batteries, and button batteries.

[0139] Figure 1 This figure shows a nonaqueous electrolyte energy storage element 1, an example of a prismatic battery. Note that this figure also shows a perspective view of the interior of the container. An electrode assembly 2, comprising a positive electrode and a negative electrode wound with a separator, 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.

[0140] [Electricity Storage Device]

[0141] The non-aqueous electrolyte storage element of this embodiment can be used as a storage unit (battery module) composed of multiple non-aqueous electrolyte storage elements and installed in a vehicle power supply, personal computer, communication terminal, etc., such as an electric vehicle (EV), hybrid electric vehicle (HEV), or plug-in hybrid electric vehicle (PHEV). In this case, the technology of the present invention can be applied to at least one non-aqueous electrolyte storage element contained in the storage unit.

[0142] Figure 2 ] shows an example of an electricity storage device 30 formed by further assembling electricity storage cells 20, each of which is composed of two or more electrically connected non-aqueous electrolyte storage elements 1. The electricity storage device 30 may also include a bus bar (not shown) electrically connecting the two or more non-aqueous electrolyte storage elements 1, a bus bar (not shown) electrically connecting the two or more electricity storage cells 20, and the like. The electricity storage cells 20 or the electricity storage device 30 may further include a state monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte storage elements.

[0143] [Method for Manufacturing a Non-Aqueous Electrolyte Energy Storage Device]

[0144] The method for manufacturing the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. This method includes, for example, the steps of 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 the steps of 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.

[0145] The method of storing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte is used as the non-aqueous electrolyte, the non-aqueous electrolyte can be injected from an injection port formed on the container and then sealed.

[0146] [Other embodiments]

[0147] It should be noted that the nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example, the structure of another embodiment can be added to the structure of one embodiment, and a portion of the structure of one embodiment can be replaced with the structure of another embodiment or a known technology. Furthermore, a portion of the structure of one embodiment can be deleted. In addition, a known technology can be added to the structure of one embodiment.

[0148] In the above embodiment, the nonaqueous electrolyte storage element is described as being used in a rechargeable nonaqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery). However, the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention is also applicable to capacitors such as various secondary batteries, electric double layer capacitors, and lithium-ion capacitors.

[0149] Example

[0150] Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples.

[0151] <Test Example 1: Relationship between the Amount of Non-aqueous Electrolyte and Input>

[0152] To evaluate the relationship between the amount of non-aqueous electrolyte in a non-aqueous electrolyte storage element and its input, a non-aqueous electrolyte storage element containing a non-aqueous electrolyte containing methyl propionate (MP) (hereinafter referred to as a "MP-containing storage element") and a non-aqueous electrolyte storage element containing no MP (hereinafter referred to as a "MP-free storage element") were first prepared according to the following procedure. Then, using the coefficient α calculated from the above equation 2 as an indicator, the initial input of the "MP-containing storage element" and the "MP-free storage element" with different non-aqueous electrolyte amounts were evaluated.

[0153] [Fabrication of non-aqueous electrolyte storage devices]

[0154] (Production of positive electrode)

[0155] As the positive electrode active material, prepare LiNi 1 / 3 Mn 1 / 3 Co 1 / 3O2. Next, using N-methylpyrrolidone (NMP) as a dispersion medium, a positive electrode mixture paste was prepared containing the aforementioned positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder, at a mass ratio of 90:5:5 on a solids basis. The positive electrode mixture paste was directly applied to both sides of an aluminum foil serving as a positive electrode substrate, dried, and then pressed. This produced a positive electrode having positive electrode active material layers laminated on both sides of the aforementioned positive electrode substrate.

[0156] (Fabrication of negative electrode)

[0157] A negative electrode mixture paste is prepared by mixing graphite (Gr) as a 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 Gr, SBR, and CMC is set to 96:2:2 (based on solid content). The negative electrode mixture paste is applied to both sides of a copper foil serving as a negative electrode substrate, dried, and then pressed. This produces a negative electrode having negative electrode active material layers laminated on both sides of the negative electrode substrate.

[0158] (Preparation of non-aqueous electrolyte)

[0159] For the MP storage element, LiPF6 as an electrolyte salt was added at a concentration of 1.2 mol / dm in a non-aqueous solvent in which EC, DMC, EMC, and MP were mixed at a volume ratio of 30:35:32:3 (volume %). 3 In addition, in this solution, as additives, vinylene carbonate (VC) was dissolved at a content of 0.2 mass % and lithium bis(oxalato)borate (LiBOB) was dissolved at a content of 0.5 mass %. It should be noted that the reduction potential of VC is 0.6 V vs. Li / Li + , the reduction potential of LiBOB is 1.6V vs.Li / Li + .

[0160] For the MP-free storage element, LiPF6 as an electrolyte salt was added at a concentration of 1.2 mol / dm in a non-aqueous solvent in which EC, DMC, and EMC were mixed at a volume ratio of 30:35:35 (volume %). 3 In addition, additives are dissolved in the solution in the same manner as in the "MP-containing energy storage element".

[0161] (Fabrication of non-aqueous electrolyte storage element)

[0162] The positive electrode and negative electrode were stacked together via a separator made of a polyolefin microporous film to produce an electrode assembly. This electrode assembly was housed in a container made of a metal-resin composite film, and the non-aqueous electrolyte was injected into the container so that the coefficient α calculated using Equation 2 reached the target value. The container was then sealed by heat welding to produce an "MP-equipped" and "MP-free" energy storage element, respectively.

[0163] 〔Measurement and Evaluation〕

[0164] (Initial charge and discharge)

[0165] The obtained “electricity storage element with MP” and “electricity storage element without MP” were initially charged and discharged under the following conditions.

[0166] In a thermostatic chamber at 25°C, constant current charging was performed at a charge current of 1.0C and a charge end voltage of 4.10V, followed by constant voltage charging at 4.10V. Charging was terminated when the total charge time reached 3 hours. A 10-minute rest period was then provided. Constant current discharge was then performed at a discharge current of 1.0C and a discharge end voltage of 3.0V. The discharge capacity at this point was defined as the initial discharge capacity.

[0167] (Initial input measurement)

[0168] After the above initial charge and discharge, the initial input of the "MP storage element" and the "no MP storage element" was measured according to the following procedure.

[0169] In a thermostatic chamber at 25°C, constant current charging was performed at a charging current of 1.0C, and the SOC was adjusted to 50%. After being stored in a thermostatic chamber at -30°C for 4 hours, charging was performed at a constant voltage of 4.0V, 4.1V, 4.2V or 4.3V for 10 seconds respectively. "SOC" (State of Charge) refers to the charging state of the non-aqueous electrolyte storage element measured within the voltage range normally used for the non-aqueous electrolyte storage element based on the rated capacity. In this embodiment, the rated capacity is set to the initial discharge capacity mentioned above. After each discharge, constant current discharge was performed at a current of 0.2C to make the SOC 50%. The resistance value was calculated based on the slope of the voltage at each charge and the current 1 second after the start of charging, and "{the difference between the voltage before charging and the upper limit voltage (4.3V)} / resistance value × upper limit voltage (4.3V)" was calculated as the "initial input". The ratio of each initial input to the initial input when the coefficient α is 1.55 was calculated as the "initial input ratio". Table 1 shows the relationship between the coefficient α and the initial input ratio as the relationship between the amount of the nonaqueous electrolyte and the initial input of the nonaqueous electrolyte storage element.

[0170] [Table 1]

[0171]

[0172] (evaluate)

[0173] As shown in Table 1, the initial input ratio of the "no MP energy storage device" remained around 1.00 even when the coefficient α varied. Meanwhile, the "MP energy storage device" maintained an initial input ratio around 1.00 when the coefficient α was 1.1 or greater, but decreased when the coefficient α was less than 1.1. Therefore, it is speculated that when the amount of non-aqueous electrolyte is low, the effect of methyl propionate (MP) suppressing the reductive decomposition of the additive is excessively exerted, resulting in an increase in the resistance of the film on the negative electrode surface.

[0174] <Test Example 2: Relationship between MP Content and Input>

[0175] To evaluate the relationship between the methyl propionate (MP) content and input in a nonaqueous electrolyte storage device, a nonaqueous electrolyte storage device was first prepared according to the following procedure. Then, the input was evaluated for nonaqueous electrolyte storage devices having different MP contents.

[0176] [Fabrication of non-aqueous electrolyte storage devices]

[0177] The non-aqueous electrolyte energy storage devices of Examples 1 to 4 were prepared according to the same procedures as the "energy storage device with MP" described above, except that the methyl propionate (MP) content in the non-aqueous solvent before initial charge and discharge was changed as described in Table 2 and the non-aqueous electrolyte was injected into the container so that the coefficient α was 1.55. The EMC content in the non-aqueous solvent of each example was adjusted so that the total content of EMC and MP was 35% by volume.

[0178] 〔Measurement and Evaluation〕

[0179] Initial charge and discharge were performed on each nonaqueous electrolyte storage device using the same conditions as those for the initial charge and discharge described above. The contents of MP, VC, and LiBOB (hereinafter referred to as residual amounts) in the nonaqueous electrolyte after the initial charge and discharge are shown in Table 2. The molar ratio (C / (A+B)) of the residual amount of MP (C) to the total residual amount of VC (A) and LiBOB (B) is also shown in Table 2.

[0180] After the initial charge and discharge, the initial input of each nonaqueous electrolyte storage device was measured by the same procedure as the initial input measurement.

[0181] (Charge and discharge cycle test)

[0182] After the initial input measurement, a charge-discharge cycle test was conducted at 55°C according to the following procedures. Constant current charging was performed at a charge current of 10C and a charge end voltage of 3.9V. Then, constant current discharge was performed at a discharge current of 10C and a discharge end voltage of 3.6V. A 10-minute rest period was provided after both charge and discharge. This charge-discharge cycle was repeated for 1000 hours.

[0183] The input after the charge-discharge cycle was measured using the same procedure as the initial input. Furthermore, the percentage of the input after the charge-discharge cycle relative to the initial input was calculated as the input retention rate [%). The obtained input and input retention rates are shown in Table 2.

[0184]

[0185] As shown in Table 2, the initial input of the non-aqueous electrolyte storage element in which the MP content in the non-aqueous solvent before the initial charge and discharge is 3 volume % (Example 2), 5 volume % (Example 3), and 7 volume % (Example 4) is greater than that of the non-aqueous electrolyte storage element in which the MP content is 0 volume % (Example 1). In addition, the MP content in the non-aqueous solvent before the initial charge and discharge of the non-aqueous electrolyte storage element of Example 3 is 5 volume %, and the molar ratio (C / (A+B)) is 9.7. The input of the non-aqueous electrolyte storage element of Example 3 after the charge and discharge cycle is the largest. Therefore, from the viewpoint of improving the input after the charge and discharge cycle, the molar ratio (C / (A+B)) is preferably 9.7 or more. In addition, the MP content in the non-aqueous solvent before the initial charge and discharge of the non-aqueous electrolyte storage element of Example 2 is 3 volume %, and the molar ratio (C / (A+B)) is 6.4. The input maintenance rate of the non-aqueous electrolyte storage element of Example 2 after the charge and discharge cycle is the largest. Therefore, from the viewpoint of improving the input maintenance rate after the charge and discharge cycle, the molar ratio (C / (A+B)) is preferably 6.4 or more.

[0186] Industrial applicability

[0187] The present invention is suitable for use in non-aqueous electrolyte storage devices used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

[0188] Explanation of symbols

[0189] 1. Non-aqueous electrolyte storage element

[0190] 2 Electrode body

[0191] 3 Containers

[0192] 4 Positive terminal

[0193] 41 Positive wire

[0194] 5 Negative terminal

[0195] 51 Negative wire

[0196] 20 Power storage unit

[0197] 30 Power storage device

Claims

1. A non-aqueous electrolyte storage element comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The non-aqueous electrolyte contains a non-aqueous solvent containing a chain carboxylic acid ester and an additive that undergoes reductive decomposition on the surface of the negative electrode. When the volume of the nonaqueous electrolyte is Ve, the void volume of the positive electrode is Vp, the void volume of the negative electrode is Vn, and the void volume of the separator is Vs, the following formula 1 is satisfied: (Vp+Vn+Vs)×1.1≤Ve···1.

2. The nonaqueous electrolyte storage element according to claim 1, wherein The reduction potential of the additive is 0.5 V (vs. Li / Li + )above.

3. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein The additive is at least one selected from unsaturated cyclic carbonates, fluorinated cyclic carbonates, oxalates containing phosphorus or boron, sulfonates containing fluorine, phosphates containing fluorine and oxygen, sulfates and sulfonates.

4. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein The additive is at least one of an unsaturated cyclic carbonate and an oxalate containing phosphorus or boron.

5. The non-aqueous electrolyte storage element according to claim 4, wherein The ratio of the content C of the chain carboxylate to the total content A of the unsaturated cyclic carbonate and the content B of the oxalate containing phosphorus or boron in the non-aqueous electrolyte, namely C / (A+B), is 6.4 to 14.4 on a molar basis.

6. The nonaqueous electrolyte storage element according to claim 4, wherein The ratio of the content C of the chain carboxylate to the total content A of the unsaturated cyclic carbonate and the content B of the oxalate containing phosphorus or boron in the non-aqueous electrolyte, i.e., C / (A+B), is 9.7 or more on a molar basis.

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