Non-aqueous electrolyte power storage element and method for manufacturing the same

Abstract

To provide a non-aqueous electrolyte power storage element which can repeatedly perform excellent discharges and charges, and a method for manufacturing the non-aqueous electrolyte power storage element.SOLUTION: The non-aqueous electrolyte power storage element according to an aspect of the present invention has a non-aqueous electrolyte having an electrolyte salt, an ionic liquid, and polyvinylidene fluoride. The mass mol concentration of the electrolyte salt in the non-aqueous electrolyte is at least 1.0 mol / kg and less than 2.5 mol / kg. The content of the ionic liquid to the total amount of the ionic liquid and the polyvinylidene fluoride is at least 20 mass% and less than 40 mass%.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a non-aqueous electrolyte electricity storage element and a method for producing the same. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc., due to their high energy density. Non-aqueous electrolyte secondary batteries generally have a pair of electrically isolated electrodes and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring ions between the 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 recent years, non-aqueous electrolytes using ionic liquids, polymers, etc. have been attracting attention as non-aqueous electrolytes, instead of general non-aqueous electrolyte solutions in which an electrolyte salt is dissolved in an organic solvent. Patent Document 1 describes a lithium ion secondary battery having an electrolyte composition containing basic inorganic particles, an ionic liquid, a supporting electrolyte salt, and a polymer material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2011 / 037060 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional nonaqueous electrolyte storage elements that use an ionic liquid and a polymer as the nonaqueous electrolyte may not be able to perform satisfactory repeated charging and discharging due to the occurrence of internal short circuits and increases in overvoltage that accompany repeated charging and discharging.

[0006] An object of the present invention is to provide a nonaqueous electrolyte electricity storage element capable of satisfactorily repeating charge and discharge cycles, and a method for producing such a nonaqueous electrolyte electricity storage element. [Means for solving the problem]

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention has a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and polyvinylidene fluoride, wherein the electrolyte salt in the nonaqueous electrolyte has a molar concentration of 1.0 mol / kg or more and less than 2.5 mol / kg, and the content of the ionic liquid relative to the total of the ionic liquid and the polyvinylidene fluoride is 20 mass% or more and less than 40 mass%.

[0008] A method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention includes assembling a non-charged / discharged nonaqueous electrolyte storage element having a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and polyvinylidene fluoride, wherein the mass molar concentration of the electrolyte salt in the nonaqueous electrolyte is equal to or greater than 1.0 mol / kg and less than 2.5 mol / kg, and the content of the ionic liquid relative to the total of the ionic liquid and the polyvinylidene fluoride is equal to or greater than 20 mass% and less than 40 mass%. Effect of the Invention

[0009] According to any one of the aspects of the present invention, it is possible to provide a nonaqueous electrolyte electricity storage element capable of sufficiently repeatedly carrying out charge and discharge with good results, and a method for manufacturing such a nonaqueous electrolyte electricity storage element. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. [Diagram 3] FIG. 3 is an X-ray diffraction diagram of the PVDF films obtained in Production Examples 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] First, an outline of the nonaqueous electrolyte storage element and the method for producing the nonaqueous electrolyte storage element disclosed in this specification will be described.

[0012] (1) A nonaqueous electrolyte storage element according to one aspect of the present invention has a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and polyvinylidene fluoride, wherein the mass molar concentration of the electrolyte salt in the nonaqueous electrolyte is equal to or greater than 1.0 mol / kg and less than 2.5 mol / kg, and the content of the ionic liquid relative to the total of the ionic liquid and the polyvinylidene fluoride is equal to or greater than 20 mass% and less than 40 mass%.

[0013] The nonaqueous electrolyte storage element described in (1) above can be sufficiently repeatedly charged and discharged. The reason for this is unclear, but the following reason is presumed. Since a polymer electrolyte containing polyvinylidene fluoride (PVDF) has low ionic conductivity, a nonaqueous electrolyte storage element using such a polymer electrolyte has a very large overvoltage. On the other hand, a nonaqueous electrolyte containing an ionic liquid has high ionic conductivity, but the resistance to reduction of the cations of the ionic liquid is usually low. For this reason, in a nonaqueous electrolyte storage element using an ionic liquid as a nonaqueous electrolyte, the cations of the ionic liquid may be reduced and decomposed on the surface of the negative electrode, causing an increase in overvoltage. Therefore, by containing an ionic liquid and PVDF in a suitable mixing ratio in the nonaqueous electrolyte, a coating derived from PVDF is preferentially formed on the surface of the negative electrode, thereby suppressing the reduction and decomposition of the cations of the ionic liquid, and thus suppressing the increase in overvoltage. In addition, as described above, when the ionic conductivity of the non-aqueous electrolyte is low, the overvoltage becomes large, and when the strength of the non-aqueous electrolyte is low, the contact between the two electrodes is likely to occur, so that an internal short circuit is likely to occur, and when the flexibility of the non-aqueous electrolyte is low, a sufficient interface between the non-aqueous electrolyte and the positive and negative electrodes may not be formed. On the other hand, when the mixing ratio of the ionic liquid and PVDF and the mass molar concentration of the electrolyte salt are in a moderate range, the non-aqueous electrolyte can have good ionic conductivity, strength, and flexibility, and the increase in overvoltage and the occurrence of internal short circuits are suppressed. For this reason, according to the non-aqueous electrolyte storage element described in (1) above, the increase in overvoltage and the occurrence of internal short circuits due to repeated charging and discharging are suppressed, and good charging and discharging can be sufficiently repeated.

[0014] The "molar concentration" of an electrolyte salt in a non-aqueous electrolyte refers to the amount of substance (mol) of the electrolyte salt contained in the non-aqueous electrolyte relative to the mass (kg) of components other than the electrolyte salt contained in the non-aqueous electrolyte.

[0015] The type and content of salts (electrolyte salt and ionic liquid) contained in the non-aqueous electrolyte are identified by ion chromatography (IC). However, the type and content of cations of the ionic liquid contained in the non-aqueous electrolyte are identified by liquid chromatography-mass spectrometry (LC-MS). Specifically, the following is performed. The IC and LC-MS measurements are performed consecutively under the same conditions. 1. Collection of non-aqueous electrolyte First, the nonaqueous electrolyte storage element is disassembled to remove the nonaqueous electrolyte. An appropriate amount of dimethyl sulfoxide is poured into the nonaqueous electrolyte storage element, and the nonaqueous electrolyte dissolved in the dimethyl sulfoxide is removed. 2.IC analysis The components of the collected non-aqueous electrolyte (cations of the electrolyte salt and anions of the electrolyte salt and ionic liquid) are analyzed by IC. The IC analysis is performed in the following order: qualitative analysis and quantitative analysis. (qualitative analysis) A measurement sample (non-aqueous electrolyte) is subjected to IC analysis. The components contained in the measurement sample are predicted from the peak positions of each peak in the obtained ion chromatogram. A known sample of the predicted components (hereinafter referred to as "predicted components") is subjected to IC analysis. The retention times of the peaks corresponding to each predicted component in the measurement sample are compared with the retention times of the peaks of known samples of each predicted component, and if they match, the prediction is presumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. First, a known sample of the predicted component with a known concentration is measured, and a calibration curve is created. The calibration curve is calculated using the coefficient of determination (r 2 ) is between 0.999 and 1. The amount of the predicted component in the measurement sample is calculated from the calibration curve and the area of ​​the peak of the predicted component in the measurement sample. The above process is carried out for all peaks detected in the IC analysis of the measurement sample, and the amount of each predicted component is calculated. 3.LC-MS analysis The components of the collected non-aqueous electrolyte (cations of the ionic liquid) are analyzed by LC-MS. The LC-MS analysis is performed in the following order of qualitative analysis and quantitative analysis. The LC-MS analysis is performed using Waters' "Acquity H" and "Xevo G2-5QTof" instruments. Water is used as the eluent. (qualitative analysis) A measurement sample (non-aqueous electrolyte) is subjected to LC-MS analysis. The components contained in the measurement sample are predicted from the MS spectrum of each peak. A known sample of the predicted components (hereinafter referred to as "predicted components") is subjected to LC-MS analysis. The retention times and MS spectrum of the peaks corresponding to each predicted component in the measurement sample are compared with the retention times and MS spectrum of the peaks of known samples of each predicted component, and if they match, the prediction is presumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. First, a known sample of the predicted component with a known concentration is measured by LC-MS, and a calibration curve is created by calculating the peak area. The calibration curve is calculated using the coefficient of determination (r 2 ) is created so that it is between 0.999 and 1. The amount of the predicted component in the measurement sample is calculated from the calibration curve and the area of ​​the peak of the predicted component in the measurement sample. The above process is performed for all peaks detected in the LC-MS analysis of the measurement sample, and the amount of each predicted component is calculated.

[0016] The presence or absence of PVDF in the non-aqueous electrolyte is confirmed by X-ray diffraction (XRD), infrared spectroscopy (IR) and nuclear magnetic resonance (NMR), and the content of PVDF in the non-aqueous electrolyte is determined by NMR. These analyses are performed on the non-aqueous electrolyte dissolved in dimethyl sulfoxide and collected by the method described above in "1. Collection of non-aqueous electrolyte", after removing the dimethyl sulfoxide.

[0017] (2) The nonaqueous electrolyte electricity storage element according to (1) above may further include a negative electrode containing metallic lithium.

[0018] The nonaqueous electrolyte storage element described in (2) above has an advantage of having a high energy density because it further has a negative electrode containing metallic lithium. In addition, a nonaqueous electrolyte storage element having a negative electrode containing metallic lithium is usually prone to internal short circuiting due to repeated charging and discharging. Therefore, the nonaqueous electrolyte storage element described in (2) above having a negative electrode containing metallic lithium has a particularly remarkable advantage of being able to perform satisfactory repeated charging and discharging.

[0019] The negative electrode of the nonaqueous electrolyte storage element described in (2) above may contain metallic lithium at least in a charged state, and may not contain metallic lithium in a discharged state. For example, the nonaqueous electrolyte storage element may be configured such that metallic lithium is deposited on at least a partial region of the negative electrode surface during charging, so that the negative electrode contains metallic lithium in a charged state, and substantially all of the metallic lithium on the negative electrode surface is dissolved into the nonaqueous electrolyte during discharging, so that the negative electrode does not substantially contain metallic lithium in a discharged state.

[0020] (3) In the nonaqueous electrolyte storage element according to (1) or (2) above, the electrolyte salt may be a lithium salt.

[0021] The nonaqueous electrolyte electricity storage element described in (3) above can perform satisfactory repeated charging and discharging more sufficiently.

[0022] (4) In the nonaqueous electrolyte storage element according to any one of (1) to (3) above, the electrolyte salt may be an imide salt.

[0023] The nonaqueous electrolyte electricity storage element described in (4) above can perform satisfactory repeated charging and discharging more sufficiently.

[0024] (5) In the nonaqueous electrolyte storage element according to (4) above, the imide salt may be at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide.

[0025] The nonaqueous electrolyte electricity storage element described in (5) above can be sufficiently repeatedly charged and discharged with good results.

[0026] (6) In the nonaqueous electrolyte storage element according to any one of (1) to (5) above, the ionic liquid may have a quaternary ammonium cation.

[0027] The nonaqueous electrolyte electricity storage element described in (6) above can perform satisfactory repeated charging and discharging more sufficiently.

[0028] (7) In the nonaqueous electrolyte storage element according to any one of (1) to (6) above, the ionic liquid may contain at least one selected from the group consisting of imidazolium-based cations and pyrrolidinium-based cations.

[0029] The nonaqueous electrolyte electricity storage element described in (7) above can perform satisfactory repeated charging and discharging.

[0030] (8) In the nonaqueous electrolyte storage element according to any one of (1) to (7) above, the ionic liquid may contain at least one selected from the group consisting of 1-ethyl-3-methylimidazolium and 1-methyl-1-propylpyrrolidinium.

[0031] The nonaqueous electrolyte electricity storage element described in (8) above can perform good repeated charging and discharging more sufficiently.

[0032] (9) In the nonaqueous electrolyte storage element according to any one of (1) to (8) above, the ionic liquid may have an imide anion.

[0033] The nonaqueous electrolyte electricity storage element described in (9) above can perform satisfactory repeated charging and discharging more sufficiently.

[0034] (10) In the nonaqueous electrolyte storage element according to (9) above, the imide anion may be at least one selected from the group consisting of bis(trifluoromethanesulfonyl)imide and bis(fluorosulfonyl)imide.

[0035] The nonaqueous electrolyte electricity storage element described in (10) above can perform satisfactory repeated charging and discharging.

[0036] (11) In the nonaqueous electrolyte storage element according to any one of (1) to (10) above, the polyvinylidene fluoride may have a β-type or γ-type crystal structure.

[0037] The nonaqueous electrolyte storage element described in (11) above can perform good repeated charging and discharging. Although the reason for this is unclear, it is speculated that the dissociation of the electrolyte salt is enhanced by the β-type or γ-type crystal structure of PVDF having polarity, and that a good interface can be formed between PVDF and the active material, etc.

[0038] (12) In the nonaqueous electrolyte storage element according to any one of (1) to (11) above, the total content of the electrolyte salt, the ionic liquid, and the polyvinylidene fluoride in the nonaqueous electrolyte may be 90 mass % or more.

[0039] The nonaqueous electrolyte storage element described in (12) above can perform good repeated charging and discharging. Although the reason for this is unclear, it is presumed that the nonaqueous electrolyte is mainly composed of an electrolyte salt, an ionic liquid, and PVDF, which results in more optimal ionic conductivity, strength, flexibility, and the like of the nonaqueous electrolyte.

[0040] (13) A method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention includes assembling a non-charged / discharged nonaqueous electrolyte storage element having a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and polyvinylidene fluoride, wherein a molar concentration of the electrolyte salt in the nonaqueous electrolyte is equal to or greater than 1.0 mol / kg and less than 2.5 mol / kg, and a content of the ionic liquid relative to a total of the ionic liquid and the polyvinylidene fluoride is equal to or greater than 20 mass% and less than 40 mass%.

[0041] According to the method for producing a nonaqueous electrolyte electricity storage element described above in (13), it is possible to produce a nonaqueous electrolyte electricity storage element that is capable of satisfactorily repeating charge and discharge.

[0042] A nonaqueous electrolyte electricity storage element, an electricity storage device, a method for manufacturing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, and other embodiments will be described in detail. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0043] <Non-aqueous electrolyte electricity storage element> A nonaqueous electrolyte storage element (hereinafter, also simply referred to as "storage element") according to one embodiment of the present invention includes an electrode assembly having a positive electrode, a negative electrode, and an isolating layer containing a nonaqueous electrolyte, and a container that accommodates the electrode assembly. The electrode assembly is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated with an isolating layer interposed therebetween, or a wound type in which a positive electrode and a negative electrode are laminated with an isolating layer interposed therebetween and wound. A part of the nonaqueous electrolyte may be present in a state in which it is infiltrated into the voids of the positive electrode and the negative electrode. The isolating layer may be a layer consisting of only the nonaqueous electrolyte, or may be a layer containing other components other than the nonaqueous electrolyte. The isolating layer may have a porous separator. For example, the isolating layer may be a layer in which the nonaqueous electrolyte is infiltrated into a porous separator. As an example of a nonaqueous electrolyte storage element, a nonaqueous electrolyte secondary battery (hereinafter, also simply referred to as "secondary battery") will be described.

[0044] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0045] The positive electrode substrate is conductive. Whether or not it has "conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 -2 The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. The positive electrode substrate may be a foil, a vapor deposition film, a mesh, a porous material, etc., and a foil is preferred from the viewpoint of cost. Therefore, aluminum foil or an aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or an aluminum alloy include A1085, A3003, A1N30, etc., as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0046] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, further preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate and to increase the energy density per volume of the nonaqueous electrolyte storage element.

[0047] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0048] The positive electrode active material layer includes a positive electrode active material. The positive electrode active material layer includes optional components such as a conductive agent, a binder, a thickener, and a filler, as necessary. The positive electrode active material layer may be formed from a positive electrode mixture including the positive electrode active material and other optional components.

[0049] The positive electrode active material can be appropriately selected from known positive electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the positive electrode active material for a lithium ion secondary battery. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, lithium transition metal composite oxides having a spinel type crystal structure, polyanion compounds, chalcogen compounds, and sulfur-based active materials. Examples of the lithium transition metal composite oxides having an α-NaFeO2 type crystal structure include 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 Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), Li[Li x Ni γ Co β Al (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β). Lithium transition metal composite oxides with spinel crystal structure include Li x Mn2O4, Li x Ni γ Mn (2-γ)O4, etc. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be mixed and used.

[0050] In one embodiment of the present invention, the positive electrode active material may contain a sulfur-based active material. The sulfur-based active material may be sulfur alone or a sulfur compound. Examples of sulfur compounds include metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds. The sulfur-based active material has the advantages of a high theoretical capacity and low cost. In particular, a nonaqueous electrolyte storage element having a positive electrode containing a sulfur-based active material and a negative electrode containing metal lithium is prone to internal short circuiting due to repeated charging and discharging, and is highly prone to being unable to perform good charging and discharging repeatedly. For this reason, when the technology of the present invention is applied to such a nonaqueous electrolyte storage element, the advantage of being able to perform good charging and discharging repeatedly is particularly prominent.

[0051] The sulfur-based active material may be in the form of a complex with a conductive agent (a material having a higher conductivity than the sulfur-based active material), etc. This complex may be in the form in which the sulfur-based active material is supported on a conductive agent or the like as a carrier, and specifically, may be a complex of sulfur and porous carbon (sulfur-porous carbon composite: SPC), etc.

[0052] The positive electrode active material is usually a particle (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to the above lower limit or more, the positive electrode active material can be easily manufactured or handled. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. In addition, when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. The "average particle size" means a value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by a laser diffraction / scattering method for a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0053] In order to obtain powder with a predetermined particle size, a pulverizer, a classifier, etc. are used. Examples of the pulverization method include a method using a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, or a sieve. During pulverization, wet pulverization in the presence of water or an organic solvent such as hexane can also be used. As a classification method, a sieve, an air classifier, etc. are used as necessary for both dry and wet methods.

[0054] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 95% by mass. By setting the content of the positive electrode active material in the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0055] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, and the like. Examples of carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, and the like. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, and the like. Examples of the conductive agent include powder and fiber. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. These materials may also be used in combination. For example, a material in which carbon black and CNT are combined may be used. Among these, carbon black is preferable from the viewpoint of electronic conductivity and coatability, and acetylene black is preferable among them.

[0056] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent in the above range, the energy density of the nonaqueous electrolyte storage element can be increased. Note that, when a composite of a positive electrode active material and a conductive agent is used as the positive electrode active material, the content of the conductive agent in the composite is not included in the content of the conductive agent in the positive electrode active material layer.

[0057] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, polyimide, etc.; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, etc.; polysaccharide polymers, etc.

[0058] The content of the binder in the positive electrode active material layer is preferably from 1% by mass to 10% by mass, and more preferably from 3% by mass to 9% by mass. By setting the content of the binder in the above range, the positive electrode active material can be stably maintained.

[0059] Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. In one embodiment of the present invention, it may be preferable that the thickener is not contained in the positive electrode active material layer.

[0060] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, poorly soluble ion crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof. In one embodiment of the present invention, it may be preferable that the filler is not contained in the positive electrode active material layer.

[0061] The positive electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic 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.

[0062] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode.

[0063] The negative electrode substrate has electrical conductivity. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, carbonaceous materials, etc. are used as the material of the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor deposition films, meshes, and porous materials, and foils are preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0064] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, further preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate and to increase the energy density per volume of the nonaqueous electrolyte storage element.

[0065] The negative electrode active material layer includes a negative electrode active material. The negative electrode active material layer includes optional components such as a conductive agent, a binder, a thickener, and a filler as necessary. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode. The negative electrode active material layer may be formed from a negative electrode mixture including a negative electrode active material and other optional components, and when the negative electrode active material is a metal such as metallic lithium, it may be formed from a foil or the like and may not be formed from a negative electrode mixture.

[0066] The negative electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0067] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for a lithium ion secondary battery. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、 Examples of the material include titanium-containing oxides such as TiNb2O7, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). In the negative electrode active material layer, one of these materials may be used alone, or two or more of them may be used in combination.

[0068] "Graphite" refers to a material that has an average lattice spacing (d 002 ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of availability of materials with stable physical properties.

[0069] "Non-graphitic carbon" refers to carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitizable carbon include non-graphitizable carbon and graphitizable carbon. Examples of non-graphitizable carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0070] Here, the "discharged state" refers to a state in which the negative electrode active material carbon material is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released. For example, in a single-electrode battery using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metallic lithium as a counter electrode, the state is one in which the open circuit voltage is 0.7 V or more.

[0071] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0072] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0073] The negative electrode active material is usually a particle (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to the above lower limit or more, the production or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to the above upper limit or less, the electronic conductivity of the negative electrode active material layer is improved. In order to obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. When the negative electrode active material is a metal such as metallic lithium, the negative electrode active material may be in the form of a foil.

[0074] In one embodiment of the present invention, the negative electrode active material preferably contains metallic lithium. That is, the negative electrode or the negative electrode active material layer preferably contains metallic lithium. The metallic lithium may be pure metallic lithium substantially composed of lithium element only, or may be a lithium alloy containing other metal elements. Examples of the lithium alloy include a lithium silver alloy, a lithium zinc alloy, a lithium calcium alloy, a lithium aluminum alloy, a lithium magnesium alloy, and a lithium indium alloy. The lithium alloy may contain a plurality of metal elements other than lithium.

[0075] The negative electrode active material layer may be a non-porous layer (solid layer) or a porous layer. When the negative electrode active material layer is formed from a negative electrode mixture, the negative electrode active material layer is usually a porous layer. When the negative electrode active material layer is formed from, for example, a metal foil, the negative electrode active material layer is usually a non-porous layer.

[0076] In one embodiment of the present invention, the content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material in the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer. In addition, when the negative electrode active material contains metallic lithium, the content of lithium element in the negative electrode active material layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more. The upper limit of the content of lithium element in the negative electrode active material layer may be 100% by mass.

[0077] In the case of a non-aqueous electrolyte storage element configured so that metallic lithium is precipitated on at least a portion of the negative electrode surface during charging and substantially all of the metallic lithium on the negative electrode surface is dissolved into the non-aqueous electrolyte during discharging, the negative electrode does not need to have a negative electrode active material layer in a discharged state.

[0078] (isolation layer) The separator is a layer interposed between the positive electrode and the negative electrode, and contains a non-aqueous electrolyte.

[0079] (Non-aqueous electrolyte) The non-aqueous electrolyte contains an electrolyte salt, an ionic liquid, and PVDF.

[0080] [Electrolyte salt] The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, etc. Among these, lithium salts are preferred.

[0081] The anion that constitutes the electrolyte salt is N(CF3SO2)2 - (Bis(trifluoromethanesulfonyl)imide: TFSI - ), N(SO2F)2 - (Bis(fluorosulfonyl)imide: FSI - ), N(C2F5SO2)2 -(Bis(pentafluoroethanesulfonyl)imide), N(C4F9SO2)2 - (Bis(nonafluorobutanesulfonyl)imide), N(POF2)2 - (Bis(difluorophosphonyl)imide), N(CF3SO2)(CF3CO) - ((Trifluoromethanesulfonyl)(trifluoromethanecarbonyl)imide), N(CN)2 - (dicyanoimide), CF3-SO2-N-SO2-N-SO2CF3 - , FSO2-N-SO2-C4F9 - , CF3-SO2-N-SO2-C4F9 - , CF3-SO2-N-SO2-CF2-SO2-N-SO2-CF3 2- , CF3-SO2-N-SO2-CF2-SO3 2- , CF3-SO2-N-SO2-CF2-SO2-C(-SO2CF3)2 2- Examples of the anions that make up the electrolyte salt include imide anions such as PF6 - , PO2F2 - , BF4 - , ClO4 - , NO2 - , NO3 - , I - , SO3CF3 - , C(SO2CF3)3 - , C(SO2C2F5)3 - Anions other than the imide anion such as the above can also be used.

[0082] The anion constituting the electrolyte salt is preferably an imide anion, and more preferably bis(trifluoromethanesulfonyl)imide (TFSI - ) and bis(fluorosulfonyl)imide (FSI - ), and bis(fluorosulfonyl)imide (FSI -) is more preferred. That is, the electrolyte salt is preferably an imide salt, more preferably at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), and even more preferably LiFSI. In addition, the anion constituting the electrolyte salt preferably has a fluorine atom. When the anion constituting the electrolyte salt is such an anion, the ionic conductivity of the non-aqueous electrolyte is increased, and good charge and discharge can be repeated more sufficiently. One or more electrolyte salts can be used.

[0083] The molar mass concentration of the electrolyte salt in the non-aqueous electrolyte is 1.0 mol / kg or more and less than 2.5 mol / kg. The lower limit of the molar mass concentration is preferably 1.2 mol / kg, more preferably 1.4 mol / kg, may be 1.6 mol / kg, or may be 1.8 mol / kg. The upper limit of the molar mass concentration is preferably 2.3 mol / kg, more preferably 2.1 mol / kg, may be 1.9 mol / kg, or may be 1.7 mol / kg. By setting the molar mass concentration of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte is optimized, and good charging and discharging can be sufficiently repeated. The molar mass concentration of the electrolyte salt can be set to a range that combines any of the above lower limits and any of the above upper limits (however, the upper limit is greater than the lower limit).

[0084] [Ionic liquid] An ionic liquid is an ionic compound that is at least partially liquid at room temperature (20° C.) under 1 atmospheric pressure.

[0085] Examples of the cation that constitutes the ionic liquid include a quaternary ammonium cation, a quaternary phosphonium cation, and a sulfonium cation.

[0086] Examples of cations constituting the ionic liquid include imidazolium-based cations, tetraalkylammonium-based cations, pyridinium-based cations, pyrrolium-based cations, pyrazolium-based cations, pyrrolinium-based cations, pyrrolidinium-based cations, and piperidinium-based cations.

[0087] Examples of imidazolium cations include 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1,3-diethylimidazolium, 1-butyl-3-methylimidazolium, 1,2,3-trimethylimidazolium, 1,2-dimethyl-3-ethylimidazolium, 1,2-dimethyl-3-propylimidazolium, and 1-butyl-2,3-dimethylimidazolium.

[0088] Examples of the tetraalkylammonium cation include trimethylethylammonium, trimethylpropylammonium, trimethylbutylammonium, trimethylhexylammonium, and tetrapentylammonium.

[0089] Examples of pyridinium cations include 1-methylpyridinium, 1-ethylpyridinium, 1-propylpyridinium, 1-butylpyridinium, 1-ethyl-2-methylpyridinium, 1-butyl-4-methylpyridinium, and 1-butyl-2,4-dimethylpyridinium.

[0090] Examples of pyrrolium-based cations include 1,1-dimethylpyrrolium, 1-ethyl-1-methylpyrrolium, 1-methyl-1-propylpyrrolium, and 1-butyl-1-methylpyrrolium.

[0091] Examples of pyrazolium cations include 1,2-dimethylpyrazolium, 1-ethyl-2-methylpyrazolium, 1-propyl-2-methylpyrazolium, and 1-butyl-2-methylpyrazolium.

[0092] Examples of pyrrolinium cations include 1,2-dimethylpyrrolinium, 1-ethyl-2-methylpyrrolinium, 1-propyl-2-methylpyrrolinium, and 1-butyl-2-methylpyrrolinium.

[0093] Examples of pyrrolidinium cations include 1,1-dimethylpyrrolidinium, 1-ethyl-1-methylpyrrolidinium, 1-methyl-1-propylpyrrolidinium, and 1-butyl-1-methylpyrrolidinium.

[0094] Examples of piperidinium cations include 1,1-dimethylpiperidinium, 1-ethyl-1-methylpiperidinium, 1-methyl-1-propylpiperidinium, and 1-butyl-1-methylpiperidinium.

[0095] Examples of the quaternary phosphonium cation include tetramethylphosphonium, tetraethylphosphonium, trimethylethylphosphonium, trimethylpropylphosphonium, trimethylbutylphosphonium, and tetraphenylphosphonium.

[0096] Examples of the sulfonium cation include trimethylsulfonium, triethylsulfonium, and tributylsulfonium.

[0097] As the cation constituting the ionic liquid, from the viewpoint of forming a good coating on the negative electrode surface, a quaternary ammonium cation is preferable, and at least one selected from the group consisting of imidazolium-based cations and pyrrolidinium-based cations is also preferable, and at least one selected from the group consisting of 1-ethyl-3-methylimidazolium and 1-methyl-1-propylpyrrolidinium is more preferable. In addition, as the cation constituting the ionic liquid, a cation having an aromatic heterocycle such as an imidazolium-based cation or a pyridinium-based cation is also preferable. One or more of these cations may be contained.

[0098] Examples of the anion constituting the ionic liquid include the same anions as those constituting the electrolyte salt. The anion constituting the ionic liquid is preferably an imide anion, such as bis(trifluoromethanesulfonyl)imide (TFSI - ) and bis(fluorosulfonyl)imide (FSI - ), and bis(fluorosulfonyl)imide (FSI - ) is more preferable. In addition, the anion constituting the ionic liquid preferably has a fluorine atom. When the anion constituting the ionic liquid is such an anion, the ionic conductivity of the non-aqueous electrolyte is increased, and good charge and discharge can be repeated more sufficiently. One or more of these anions may be contained.

[0099] In addition, it is preferable that the anions present in the non-aqueous electrolyte are substantially only imide anions, and substantially bis(fluorosulfonyl)imide (FSI - For example, imide anion or bis(fluorosulfonyl)imide (FSI) is preferably used as the anion for all anions in the non-aqueous electrolyte. - The content of anions in the non-aqueous electrolyte is preferably 90 mol % or more, more preferably 99 mol % or more, and even more preferably 99.9 mol % or more. By configuring the anions in the non-aqueous electrolyte in this way, the ionic conductivity of the non-aqueous electrolyte is increased, and good charge and discharge can be repeated more sufficiently.

[0100] The content of the ionic liquid relative to the total of the ionic liquid and PVDF in the non-aqueous electrolyte is 20% by mass or more and less than 40% by mass. The lower limit of the content may be 22% by mass, 25% by mass, or 30% by mass. The upper limit of the content may be 38% by mass, 35% by mass, or 30% by mass. By setting the content of the ionic liquid relative to the total of the ionic liquid and PVDF in the above range, the ionic conductivity, strength, flexibility, etc. of the non-aqueous electrolyte are optimized, and good charge and discharge can be sufficiently repeated. The content can be a range that combines any of the above lower limits and any of the above upper limits (however, the upper limit is greater than the lower limit).

[0101] [PVDF] PVDF is a polymer substantially composed of vinylidene fluoride units (-CH2CF2-). "Substantially composed of vinylidene fluoride units" means that the content ratio of vinylidene fluoride units to all structural units constituting the polymer is 90 mol% or more. Examples of structural units that PVDF may have other than vinylidene fluoride units include structural units containing fluorine elements such as tetrafluoroethylene units and hexafluoropropylene units. The lower limit of the content ratio of vinylidene fluoride units to all structural units constituting PVDF is preferably 95 mol%, more preferably 99 mol%. The upper limit of the content ratio of vinylidene fluoride units to all structural units constituting PVDF is 100%. PVDF may be a polymer composed of vinylidene fluoride units only.

[0102] PVDF preferably has a crystalline structure, more preferably a β-type or γ-type crystalline structure, and even more preferably a γ-type crystalline structure. PVDF is said to have three types of crystalline structures, α-type, β-type, and γ-type. α-type is a non-polar crystal, whereas β-type and γ-type are polar crystals. When PVDF has a β-type or γ-type crystalline structure in a non-aqueous electrolyte, the ionic conductivity of the non-aqueous electrolyte is more optimized, and good charging and discharging can be repeated more sufficiently. The crystalline structure of PVDF can be confirmed by XRD measurement.

[0103] PVDF may have a plurality of crystal structures. PVDF may have a crystalline portion and an amorphous portion. PVDF preferably has a crystalline structure of 50% by mass or more, more preferably has a crystalline structure of 70% by mass or more, and even more preferably has a crystalline structure of 90% by mass or more. In the crystalline structure of PVDF, the content ratio of β-type or γ-type crystal structure is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more.

[0104] The crystal structure of PVDF can be controlled by the crystallization conditions of PVDF (e.g., the type of solvent used for dissolution, the drying temperature of the solvent, etc.). According to the findings of the inventors, for example, when PVDF is dissolved using N-methyl-2-pyrrolidone (NMP) as a solvent and then dried, PVDF having an α-type crystal structure is obtained. On the other hand, when PVDF is dissolved using dimethyl sulfoxide (DMSO) as a solvent and then dried, PVDF having a γ-type crystal structure is obtained.

[0105] [Other ingredients] The non-aqueous electrolyte may further contain other components in addition to the electrolyte salt, the ionic liquid, and PVDF, such as a non-aqueous solvent, a polymer other than PVDF, and other additives.

[0106] Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, ethers, esters, amides, sulfones, lactones, nitriles, etc. When a solution of a non-aqueous electrolyte is prepared and then the solvent is dried, the solvent (e.g., NMP, DMSO, etc.) used in the preparation of the solution of the non-aqueous electrolyte may remain in the non-aqueous electrolyte. In one embodiment of the present invention, the non-aqueous electrolyte may contain DMSO.

[0107] Examples of polymers other than PVDF include polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinyl butyral, polyvinylpyrrolidone, carboxymethyl cellulose, diacetyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyacrylic acid, sodium polyacrylate, polyvinylphenol, polyvinyl methyl ether, polyvinyl alcohol, polyacrylamide, polyhydroxy(meth)acrylate, styrene-maleic acid copolymer, polyvinyl chloride, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, polybutadiene, polyester, phenolic resin, and epoxy resin.

[0108] Other additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic anhydride; ethylene sulfite, propyl sulfite, and the like. dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, and the like.

[0109] The lower limit of the total content of the electrolyte salt, ionic liquid and PVDF in the non-aqueous electrolyte may be, for example, 80% by mass, but is preferably 90% by mass, more preferably 95% by mass, even more preferably 99% by mass, and even more preferably 99.5% by mass. The upper limit of the total content may be 100% by mass, 99.9% by mass or 99% by mass. The non-aqueous electrolyte is mainly composed of the electrolyte salt, ionic liquid and PVDF, so that the ionic conductivity, strength, flexibility, etc. of the non-aqueous electrolyte are more optimized, and good charge and discharge can be sufficiently repeated. The total content can be in a range that combines any of the lower limits and any of the upper limits described above (however, the upper limit is greater than the lower limit).

[0110] The non-aqueous electrolyte in this embodiment may be one that has substantially no fluidity, or may have no fluidity at all.

[0111] A part of the non-aqueous electrolyte may be present in a state of being permeated into the voids of the positive electrode and the negative electrode. In one embodiment of the present invention, the separator may be composed of only the non-aqueous electrolyte. That is, the separator may be a non-aqueous electrolyte layer. The lower limit of the content of the non-aqueous electrolyte in the separator may be, for example, 50% by mass, 80% by mass, 90% by mass, 95% by mass, 99% by mass, or 99.5% by mass. The separator may further contain other components other than the non-aqueous electrolyte. Examples of other components other than the non-aqueous electrolyte that may be contained in the separator include a filler and a separator.

[0112] In one embodiment of the present invention, the lower limit of the total content of the electrolyte salt, ionic liquid and PVDF in the isolation layer may be, for example, 50% by mass, 80% by mass, 90% by mass, 95% by mass, 99% by mass or 99.5% by mass. The upper limit of the total content may be 100% by mass, 99.9% by mass or 99% by mass. The isolation layer is mainly composed of the electrolyte salt, ionic liquid and PVDF, so that the ionic conductivity, strength, flexibility and the like of the isolation layer are more optimized, and good charge and discharge can be sufficiently repeated. The total content may be within a range that combines any of the lower limits and any of the upper limits (however, the upper limit is greater than the lower limit).

[0113] (Separator) A separator may be used in the isolating layer. The isolating layer may be composed of only a non-aqueous electrolyte and a separator. When a separator is used, the separator can be appropriately selected from known separators. As the separator, for example, a separator composed of only a base layer, a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer, etc. can be used. Examples of the shape of the base layer of the separator include a woven fabric, a non-woven fabric, a porous resin film, etc.

[0114] 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 under 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. Examples of materials with a mass loss of a predetermined amount or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ion crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of the safety of the nonaqueous electrolyte storage element.

[0115] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0116] (Other configurations, etc.) In the nonaqueous electrolyte storage element, the electrode body may be in a pressed state. A nonaqueous electrolyte storage element in a pressed state of the electrode body has an advantage that it is less likely to shift due to vibration or the like and can exhibit good charge / discharge performance. On the other hand, when the electrode body is pressed, the separator layer interposed between the positive and negative electrodes is in a pressed state, and therefore, an internal short circuit is usually likely to occur. Therefore, when the technology of the present invention is applied to a nonaqueous electrolyte storage element in a pressed state of the electrode body, the advantage that good charge / discharge can be sufficiently repeated is particularly prominently obtained.

[0117] The electrode body accommodated in the container may be pressed from the outside of the container, i.e., via the container. The electrode body is preferably pressed in the thickness direction of the electrode body. However, a part of the electrode body (for example, a pair of curved surfaces in a flat, wound electrode body) may not be pressed. Also, only a part of the flat part of a laminated electrode body and a flat, wound electrode body may be pressed.

[0118] The electrode body can be pressed by, for example, a pressing member that presses the container from the outside. The pressing member may be a restraining member that restrains the shape of the container. The pressing member (restraining member) is provided so as to sandwich and press the electrode body from both sides in the thickness direction via the container, for example. The surface of the electrode body to be pressed is in contact with the inner surface of the container directly or via another member. Therefore, the electrode body is pressed by pressing the container. Examples of the pressing member include a restraining band and a metal frame. For example, the metal frame may be configured so that the load can be adjusted by a bolt or the like. In addition, a plurality of nonaqueous electrolyte storage elements may be arranged in the thickness direction of the electrode body, and fixed using a frame or the like in a state in which the plurality of nonaqueous electrolyte storage elements are pressed from both ends in the thickness direction.

[0119] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include a cylindrical battery, a prismatic battery, a flat battery, a coin battery, and a button battery.

[0120] A nonaqueous electrolyte storage element 1 shown in FIG. 1, which is one embodiment of the present invention, is a secondary battery in which a positive electrode 2 and a negative electrode 3 are arranged with a separator layer 4 containing a nonaqueous electrolyte interposed therebetween. The positive electrode 2 has a positive electrode substrate 5 and a positive electrode active material layer 6, and the positive electrode substrate 5 is the outermost layer of the positive electrode 2. The negative electrode 3 has a negative electrode substrate 7 and a negative electrode active material layer 8, and the negative electrode substrate 7 is the outermost layer of the negative electrode 2. In the nonaqueous electrolyte storage element 1 shown in FIG. 1, the negative electrode active material layer 8, the separator layer 4, the positive electrode active material layer 6, and the positive electrode substrate 5 are laminated in this order on the negative electrode substrate 7. An intermediate layer may be provided between the positive electrode substrate 5 and the positive electrode active material layer 6. Similarly, an intermediate layer may be provided between the negative electrode substrate 7 and the negative electrode active material layer 8. The nonaqueous electrolyte storage element according to one embodiment of the present invention may further include other members such as a container. In the nonaqueous electrolyte storage element 1 shown in FIG. 1, other members such as a container are omitted.

[0121] The nonaqueous electrolyte storage element according to one embodiment of the present invention may further include, for example, a positive electrode lead, a positive electrode external terminal, a negative electrode lead, and a negative electrode external terminal. The positive electrode lead and the negative electrode lead are housed in a container. The positive electrode external terminal and the negative electrode external terminal are provided outside the container. The positive electrode is electrically connected to the positive electrode external terminal via the positive electrode lead. The negative electrode is electrically connected to the negative electrode external terminal via the negative electrode lead.

[0122] <Electricity storage device> The nonaqueous electrolyte storage element of the present embodiment can be mounted as an electricity storage unit (battery module) comprising a plurality of nonaqueous electrolyte storage elements assembled together in automobile power sources such as electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc., power sources for electronic devices such as personal computers and communication terminals, or power storage power sources, etc. In this case, the technology of the present invention may be applied to at least one of the nonaqueous electrolyte storage elements included in the electricity storage unit.

[0123] 2 shows an example of an electricity storage device 30 in which electricity storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte electricity storage elements 1, are further assembled. The electricity storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte electricity storage elements 1, a bus bar (not shown) that electrically connects two or more electricity storage units 20, and the like. The electricity storage unit 20 or the electricity storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte electricity storage elements.

[0124] <Method of Manufacturing Nonaqueous Electrolyte Storage Element> The nonaqueous electrolyte storage element according to one embodiment of the present invention can be manufactured by a known method, but the following method is preferred. That is, the method for manufacturing a nonaqueous electrolyte storage element according to one embodiment of the present invention includes assembling a non-charged / discharged nonaqueous electrolyte storage element having a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and PVDF, wherein the molar concentration of the electrolyte salt in the nonaqueous electrolyte is 1.0 mol / kg or more and less than 2.5 mol / kg, and the content of the ionic liquid relative to the total of the ionic liquid and the PVDF is 20 mass% or more and less than 40 mass%.

[0125] Assembling the non-charged / discharged non-aqueous electrolyte storage element may include, for example, preparing a positive electrode, preparing a negative electrode, preparing a non-aqueous electrolyte solution, applying the non-aqueous electrolyte solution to a surface of the positive electrode or negative electrode and drying it to provide an isolating layer containing a non-aqueous electrolyte on the surface of the positive electrode or negative electrode, arranging the positive electrode and the negative electrode with the isolating layer therebetween to prepare an electrode body, and housing the electrode body in a container.

[0126] An electrode body may be prepared using a positive electrode, a negative electrode, and a separator, and the electrode body may be impregnated with a non-aqueous electrolyte. This forms an isolation layer composed of the separator and the non-aqueous electrolyte. The impregnation with the non-aqueous electrolyte may be performed by impregnating with a solution of the non-aqueous electrolyte and then drying, or by impregnating with a mixture of an electrolyte salt, an ionic liquid, and a monomer of PVDF and then polymerizing the mixture.

[0127] Alternatively, a film of a non-aqueous electrolyte may be prepared in advance as a separator, and an electrode assembly may be prepared using a positive electrode, a negative electrode, and the film-like non-aqueous electrolyte. In this case, the porous positive electrode active material layer and the porous negative electrode active material layer may be impregnated with the non-aqueous electrolyte in order to increase ion conductivity.

[0128] Specific and preferred forms of the nonaqueous electrolyte, positive electrode, negative electrode, etc. used in the method for producing a nonaqueous electrolyte according to one embodiment of the present invention are similar to the specific and preferred forms of the nonaqueous electrolyte, positive electrode, negative electrode, etc. provided in the nonaqueous electrolyte storage element according to one embodiment of the present invention.

[0129] The method for producing the nonaqueous electrolyte storage element may further include initially charging and discharging the assembled uncharged and discharged storage element. The initial charging and discharging may be one charge or one discharge, one charge and discharge, or two or more charge and discharges.

[0130] <Other embodiments> The nonaqueous electrolyte storage element and the method for manufacturing a nonaqueous electrolyte storage element of the present invention are not limited to the above-mentioned embodiments, and various modifications may be made without departing from the scope of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and part of the configuration of one embodiment may be replaced with the configuration of another embodiment or a well-known technique. Furthermore, part of the configuration of one embodiment may be deleted. Also, a well-known technique may be added to the configuration of one embodiment.

[0131] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors. EXAMPLES

[0132] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0133] [Production Example 1] A 15% by mass solution of PVDF was prepared using NMP as a solvent and stirred for 24 hours at 60° C. The solution was applied onto a copper foil and dried for 2 hours at 75° C. Thereafter, the foil was dried under vacuum at 75° C. for 12 hours to obtain a PVDF film (No. 1) of Production Example 1.

[0134] [Production Example 2] A PVDF film of Production Example 2 (No. 2) was obtained in the same manner as in Production Example 1, except that DMSO was used as the solvent.

[0135] XRD measurements were performed using CuKα radiation on the PVDF films obtained in Production Examples 1 and 2. The obtained X-ray diffraction patterns are shown in Figure 3. As shown in Figure 3, the PVDF film (No. 1) of Production Example 1, which used NMP as a solvent, had an α-type crystal structure, and the PVDF film (No. 2) of Production Example 2, which used DMSO as a solvent, had a γ-type crystal structure. It was confirmed that the crystal structures obtained differed depending on the type of solvent.

[0136] [Example 1] (Preparation of non-aqueous electrolyte solution) Using DMSO as a solvent, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), an ionic liquid, and PVDF were mixed in a mass ratio of 30:70, and then lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), a lithium salt, was mixed in at a mass molar concentration of 1.5 mol / kg based on the ionic liquid and PVDF to obtain a nonaqueous electrolyte solution.

[0137] (Preparation of test cell) Two sheets of nickel foil with a metallic lithium layer on the surface were prepared. The above non-aqueous electrolyte solution was applied onto the metallic lithium layer of each nickel foil and dried under the same conditions as in Production Example 2 to provide an isolation layer made of a non-aqueous electrolyte with a thickness of about 25 μm per layer. The two sheets of nickel foil were overlapped so that the isolation layers were in contact with each other. The reaction area (the area between the metallic lithium layers facing each other) was 441 mm 2 (=21 mm×21 mm). This was placed in a container made of a metal resin composite film, the opening was sealed by heat welding, and the container was pressurized from the outside at 1.5 kgfcm to obtain a non-charged and non-discharged nonaqueous electrolyte storage element of Example 1.

[0138] [Examples 2 to 9, Comparative Examples 1 to 5] The non-charged and discharged non-aqueous electrolyte storage elements of Examples 2 to 9 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that each component was adjusted so that the composition of the non-aqueous electrolyte was as shown in Table 1. The non-charged and discharged non-aqueous electrolyte storage element of Comparative Example 5 was obtained in the same manner as in Example 1, except that P(VDF-HFP) was used instead of PVDF. In Comparative Example 4, ethylene carbonate (EC), a non-aqueous solvent, was used instead of the ionic liquid. In addition, since DMSO was used as a solvent to prepare each non-aqueous electrolyte solution, it was presumed that the PVDF in each non-aqueous electrolyte had a γ-type crystal structure.

[0139] The components listed in Table 1 are as follows. LiTFSI: Lithium bis(trifluoromethanesulfonyl)imide LiFSI: Lithium bis(fluorosulfonyl)imide EMI-TFSI: 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide EMI-FSI: 1-Ethyl-3-methylimidazolium bis(fluorosulfonyl)imide Py13-FSI: 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide EC: Ethylene carbonate P(VDF-HFP): A copolymer consisting of vinylidene fluoride units (88 mol%) and hexafluoropropylene units (12 mol%)

[0140] (Lithium dissolution and precipitation test) A lithium dissolution and deposition test was carried out on each non-charged and discharged non-aqueous electrolyte storage element under the following conditions: 50°C, current density 0.3 mA / cm 2 and a capacity density of 3.0mAh / cm 2 After applying current for 100 s, the charge / discharge test was performed by alternately reversing the direction of the current. After each current application, a 5-minute rest period was provided. The above charge / discharge cycle was repeated 50 times, and the number of cycles was determined when the closed circuit voltage, which increases with internal short circuit or repeated charge / discharge, reached the cutoff voltage of 3.0 V. The results are shown in Table 1.

[0141] [Table 1]

[0142] As shown in Table 1, in each of the nonaqueous electrolyte storage elements of Comparative Example 1 in which the nonaqueous electrolyte did not contain ionic liquid, Comparative Example 2 in which the content of ionic liquid in the nonaqueous electrolyte was too high, Comparative Example 3 in which the mass molar concentration of the electrolyte salt in the nonaqueous electrolyte was too high, Comparative Example 4 in which a nonaqueous solvent was used instead of ionic liquid, and Comparative Example 5 in which P(VDF-HFP) was used instead of PVDF, the number of cycles at which the internal short circuit or the closed circuit voltage reached the cutoff voltage was 2 or less, and good charge and discharge could not be repeated sufficiently. In contrast, each of the nonaqueous electrolyte storage elements of Examples 1 to 9, in which the mass molar concentration of the electrolyte salt in the nonaqueous electrolyte was 1.0 mol / kg or more and less than 2.5 mol / kg and the content of the ionic liquid relative to the total of the ionic liquid and PVDF was 20 mass% or more and less than 40 mass%, had an internal short circuit or the number of cycles at which the closed circuit voltage reached the cutoff voltage was 6 or more, and was able to perform satisfactory repeated charging and discharging. Separately, a test cell was prepared in the same manner as in Example 1, except that NMP was used as a solvent to prepare the non-aqueous electrolyte solution, and a lithium dissolution and deposition test was performed. The number of cycles at which the internal short circuit or closed circuit voltage reached the cutoff voltage was less than that in Example 1. In this case, since NMP was used as a solvent to prepare the non-aqueous electrolyte solution, it is presumed that the PVDF in the non-aqueous electrolyte has an α-type crystal structure. [Industrial Applicability]

[0143] The present invention can be applied to nonaqueous electrolyte electricity storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles. [Explanation of symbols]

[0144] 1. Non-aqueous electrolyte storage element 2 Positive electrode 3 negative electrode 4 isolation layer 5. Positive electrode substrate 6 Cathode active material layer 7. Negative electrode substrate 8 Negative electrode active material layer 20 Energy Storage Unit 30 Energy storage device

Claims

1. The battery has a non-aqueous electrolyte containing an electrolyte salt, an ionic liquid, and polyvinylidene fluoride; the molar concentration of the electrolyte salt in the nonaqueous electrolyte is 1.0 mol / kg or more and less than 2.5 mol / kg; a content of the ionic liquid relative to the total content of the ionic liquid and the polyvinylidene fluoride is 20 mass % or more and less than 40 mass %;

2. The nonaqueous electrolyte storage element according to claim 1 , further comprising a negative electrode containing metallic lithium.

3. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the electrolyte salt is a lithium salt.

4. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the electrolyte salt is an imide salt.

5. 5. The nonaqueous electrolyte storage element according to claim 4, wherein the imide salt is at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide.

6. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the ionic liquid has a quaternary ammonium cation.

7. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the ionic liquid comprises at least one cation selected from the group consisting of imidazolium-based cations and pyrrolidinium-based cations.

8. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the ionic liquid comprises at least one selected from the group consisting of 1-ethyl-3-methylimidazolium and 1-methyl-1-propylpyrrolidinium.

9. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the ionic liquid has an imide anion.

10. 10. The nonaqueous electrolyte storage element according to claim 9, wherein the imide anion is at least one selected from the group consisting of bis(trifluoromethanesulfonyl)imide and bis(fluorosulfonyl)imide.

11. 3. The nonaqueous electrolyte storage element according to claim 1, wherein the polyvinylidene fluoride has a β-type or γ-type crystal structure.

12. 3. The nonaqueous electrolyte storage element according to claim 1, wherein a total content of the electrolyte salt, the ionic liquid, and the polyvinylidene fluoride in the nonaqueous electrolyte is 90 mass % or more.

13. The method includes assembling a non-charged / discharged non-aqueous electrolyte storage element having a non-aqueous electrolyte containing an electrolyte salt, an ionic liquid, and polyvinylidene fluoride; the molar concentration of the electrolyte salt in the nonaqueous electrolyte is 1.0 mol / kg or more and less than 2.5 mol / kg; A method for producing a nonaqueous electrolyte storage element, wherein the content of the ionic liquid is 20 mass % or more and less than 40 mass % based on the total of the ionic liquid and the polyvinylidene fluoride.

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