Nonaqueous electrolyte, nonaqueous electrolyte energy storage device, and capacitor

Abstract

To provide a nonaqueous electrolyte having high tensile strength, and a nonaqueous electrolyte power storage element and a capacitor using such a nonaqueous electrolyte.SOLUTION: The nonaqueous electrolyte contains an electrolyte salt, an ionic liquid, and polyvinylidene fluoride, and the polyvinylidene fluoride has a β - type or γ - type crystal structure. Further, it is preferable that the content of the ionic liquid to the total of the ionic liquid and the polyvinylidene fluoride is 20 mass% or more and less than 40 mass%, and the molality of the electrolytic salts is 1. 0mol / kg or more and less than 2. 5mol / kg.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] In recent years, non-aqueous electrolytes using ionic liquids, polymers, etc. have been attracting attention as non-aqueous electrolytes, instead of typical 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] Non-aqueous electrolytes containing ionic liquids and polymers may have insufficient tensile strength. Non-aqueous electrolytes with low tensile strength are difficult to handle due to the tendency for cracking, etc. Furthermore, non-aqueous electrolyte storage elements containing such non-aqueous electrolytes may not be able to perform satisfactory charging and discharging due to the occurrence of internal short circuits and increased overvoltage caused by repeated charging and discharging.

[0006] An object of the present invention is to provide a non-aqueous electrolyte having high tensile strength, and a non-aqueous electrolyte storage element and capacitor using such a non-aqueous electrolyte. [Means for solving the problem]

[0007] A non-aqueous electrolyte according to one aspect of the present invention contains an electrolyte salt, an ionic liquid, and polyvinylidene fluoride, and the polyvinylidene fluoride has a β-type or γ-type crystal structure.

[0008] A non-aqueous electrolyte according to another aspect of the present invention contains an electrolyte salt, an ionic liquid, polyvinylidene fluoride, and dimethyl sulfoxide.

[0009] A nonaqueous electrolyte storage element according to another aspect of the present invention includes the nonaqueous electrolyte according to the aspect of the present invention.

[0010] A capacitor according to another aspect of the present invention includes a non-aqueous electrolyte containing an ionic liquid and polyvinylidene fluoride, the polyvinylidene fluoride having a β-type or γ-type crystal structure. [Effects of the Invention]

[0011] According to any one aspect of the present invention, it is possible to provide a nonaqueous electrolyte having high tensile strength, and a nonaqueous electrolyte storage element and a capacitor using such a nonaqueous electrolyte. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an electricity storage device including a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. [Figure 3] FIG. 3 is an X-ray diffraction diagram of the polyvinylidene fluoride films obtained in Production Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] First, an overview of the nonaqueous electrolyte, nonaqueous electrolyte storage element, and capacitor disclosed in this specification will be provided.

[0014] (1) A nonaqueous electrolyte according to one aspect of the present invention contains an electrolyte salt, an ionic liquid, and polyvinylidene fluoride, and the polyvinylidene fluoride has a β-type or γ-type crystal structure.

[0015] The non-aqueous electrolyte described in (1) above has high tensile strength. While the reason for this is unclear, the following reason is presumed. Polyvinylidene fluoride (PVDF) is known to have three types of crystal structures, typically α-type, β-type, and γ-type. While α-type is a non-polar crystal, β-type and γ-type are polar crystals. When PVDF has a β-type or γ-type crystal structure in a non-aqueous electrolyte, the interaction between PVDF and the electrolyte salt and ionic liquid is enhanced, presumably resulting in an increase in the tensile strength of the non-aqueous electrolyte.

[0016] The type and content of salts (electrolyte salt and ionic liquid) contained in the non-aqueous electrolyte are determined by ion chromatography (IC). However, the type and content of cations in the ionic liquid contained in the non-aqueous electrolyte are determined by liquid chromatography-mass spectrometry (LC-MS). Specifically, the determination is performed as follows. Note that the IC and LC-MS measurements are performed consecutively under the same conditions. 1. Collection of non-aqueous electrolyte When the nonaqueous electrolyte is provided in a nonaqueous electrolyte storage element, first, the nonaqueous electrolyte storage element is disassembled and the nonaqueous electrolyte is removed. An appropriate amount of dimethyl sulfoxide is poured into the nonaqueous electrolyte storage element, and the nonaqueous electrolyte dissolved in dimethyl sulfoxide is removed. An appropriate amount of water is mixed with the nonaqueous electrolyte dissolved in dimethyl sulfoxide, and PVDF is precipitated and removed by filtration. The components of the nonaqueous electrolyte (electrolyte salt and ionic liquid) dissolved in a mixed solvent of dimethyl sulfoxide and water are then collected. 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 (components of a non-aqueous electrolyte) is subjected to IC analysis. The components contained in the measurement sample are predicted from the peak positions of each peak in the obtained ion chromatogram. A known sample of the predicted components (hereinafter referred to as "predicted components") is subjected to IC analysis. The retention times of the peaks corresponding to each predicted component in the measurement sample are compared with the retention times of the peaks in a known sample of each predicted component, and if they match, the prediction is assumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. First, a known sample of the predicted component with a known concentration is measured, and a calibration curve is created. 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. This process is performed 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: 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. Note that, in cases where it is not possible to perform measurements using the above-mentioned measuring instruments, other instruments that are thought to produce equivalent measurement results can be used. The same applies to other measuring instruments in this specification. (qualitative analysis) A measurement sample (components of a 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 time and MS spectrum of the peak corresponding to each predicted component in the measurement sample are compared with the retention time and MS spectrum of the peak in a known sample of each predicted component, and if they match, the prediction is assumed to be correct. (Quantitative analysis) Quantitative analysis is performed using the calibration curve method. First, a known sample of the predicted component with a known concentration is measured by LC-MS, and the peak area is calculated to create a calibration curve. 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. This 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.

[0017] 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 identified by NMR. Furthermore, the crystalline structure of PVDF is confirmed by X-ray diffraction measurement. When the non-aqueous electrolyte is contained in a non-aqueous electrolyte storage element, these analyses are performed on the non-aqueous electrolyte dissolved in dimethyl sulfoxide and extracted by the method described above in "1. Extraction of non-aqueous electrolyte," after removing the dimethyl sulfoxide. The X-ray diffraction measurement is carried out under the following conditions. X-ray diffraction equipment: Rigaku RINT-TTRIII X-ray: Cu-Kα X-ray output: 40kV-40mA Optical system: Concentration optical system Scan speed: 2θ=2 / min Scanning method: 2θ-θ Scan range: 2θ=10° to 60° Slits: Divergence slit -1 / 2°, receiving slit -0.15mm, scattering slit -1 / 2°

[0018] (2) In the nonaqueous electrolyte described in (1) above, the content of the ionic liquid may be 20% by mass or more and less than 40% by mass with respect to the total of the ionic liquid and the polyvinylidene fluoride.

[0019] The non-aqueous electrolyte described in (2) above has a higher tensile strength when the mixing ratio of the ionic liquid to PVDF is within an appropriate range. Furthermore, the nonaqueous electrolyte described in (2) above can suppress the occurrence of internal short circuits, an increase in overvoltage, and the like that occur with repeated charge and discharge of a nonaqueous electrolyte energy storage element, enabling good charge and discharge. The reason why the occurrence of internal short circuits and an increase in overvoltage can be suppressed is not clear, but it is presumed that the reason is that PVDF has a polar β-type or γ-type crystal structure and the mixing ratio of ionic liquid to PVDF is within an appropriate range, allowing the nonaqueous electrolyte to combine good ionic conductivity, strength, and flexibility, and that a coating with a good composition is formed on the surface of the negative electrode.

[0020] (3) In the nonaqueous electrolyte according to (1) or (2), the molar concentration of the electrolyte salt may be 1.0 mol / kg or more and less than 2.5 mol / kg.

[0021] The nonaqueous electrolyte described in (3) above has higher tensile strength and can suppress the occurrence of internal short circuits and increases in overvoltage that occur during repeated charge and discharge of a nonaqueous electrolyte storage element, thereby enabling good charge and discharge. The reason for this is also unclear, but it is presumed that the nonaqueous electrolyte can combine good ionic conductivity, strength, and flexibility when the molar concentration of the electrolyte salt is within the above range.

[0022] 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.

[0023] (4) In the nonaqueous electrolyte according to any one of (1) to (3), the electrolyte salt may be a lithium salt.

[0024] (5) In the nonaqueous electrolyte according to any one of (1) to (4) above, the electrolyte salt may be an imide salt.

[0025] (6) In the nonaqueous electrolyte described in (5) above, the imide salt may be at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide.

[0026] (7) In the nonaqueous electrolyte according to any one of (1) to (6) above, the ionic liquid may contain at least one cation selected from the group consisting of imidazolium-based cations and pyrrolidinium-based cations.

[0027] (8) In the nonaqueous electrolyte according to any one of (1) to (7), the ionic liquid may have at least one cation selected from the group consisting of a 1-ethyl-3-methylimidazolium cation and a 1-methyl-1-propylpyrrolidinium cation.

[0028] (9) In the nonaqueous electrolyte according to any one of (1) to (8), the ionic liquid may have an imide anion.

[0029] (10) In the nonaqueous electrolyte described in (9) above, the imide anion may be at least one selected from the group consisting of bis(trifluoromethanesulfonyl)imide anion and bis(fluorosulfonyl)imide anion.

[0030] (11) In the nonaqueous electrolyte according to any one of (1) to (10) above, the total content of the electrolyte salt, the ionic liquid, and the polyvinylidene fluoride may be 90 mass % or more.

[0031] (12) In the non-aqueous electrolyte according to any one of (1) to (11) above, the non-aqueous electrolyte may not have substantially any fluidity.

[0032] "Substantially no fluidity" means that the viscosity at 20°C is 10 8 The viscosity is 10 Pa·s or more. 9 Pa·s or more, 10 10 It may be Pa·s or more.

[0033] Each of the non-aqueous electrolytes described in (4) to (12) above has a higher tensile strength.

[0034] (13) A nonaqueous electrolyte according to another aspect of the present invention contains an electrolyte salt, an ionic liquid, polyvinylidene fluoride, and dimethyl sulfoxide.

[0035] The non-aqueous electrolyte described in (13) above has high tensile strength.

[0036] (14) A nonaqueous electrolyte storage element according to another aspect of the present invention includes the nonaqueous electrolyte according to any one of (1) to (13) above.

[0037] The nonaqueous electrolyte storage element described in (14) above has good handleability because it contains a nonaqueous electrolyte with high tensile strength. In addition, the nonaqueous electrolyte storage element described in (14) above can be charged and discharged satisfactorily.

[0038] (15) The nonaqueous electrolyte storage element according to (14) above may further include a negative electrode containing metallic lithium.

[0039] The nonaqueous electrolyte storage element described in (15) above has advantages such as high energy density because it further includes a negative electrode containing metallic lithium. Furthermore, nonaqueous electrolyte storage elements having a negative electrode containing metallic lithium are generally prone to the occurrence of internal short circuits due to repeated charge and discharge. Therefore, the nonaqueous electrolyte storage element described in (15) above, which has a negative electrode containing metallic lithium, significantly exhibits the advantages of the nonaqueous electrolyte described in (2) above, such as suppressing the occurrence of internal short circuits and increases in overvoltage due to repeated charge and discharge of the nonaqueous electrolyte storage element, thereby enabling good charge and discharge.

[0040] The negative electrode of the nonaqueous electrolyte storage element described in (15) 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 that substantially all of the metallic lithium on the negative electrode surface is eluted into the nonaqueous electrolyte during discharge, so that the negative electrode does not substantially contain metallic lithium in a discharged state.

[0041] (16) A capacitor according to another aspect of the present invention includes a non-aqueous electrolyte containing an ionic liquid and polyvinylidene fluoride, the polyvinylidene fluoride having a β-type or γ-type crystal structure.

[0042] The capacitor described in (16) above has good handling properties because it includes a non-aqueous electrolyte with high tensile strength. Also, the capacitor described in (16) above can be charged and discharged well.

[0043] A nonaqueous electrolyte according to one embodiment of the present invention, a method for producing a nonaqueous electrolyte, a nonaqueous electrolyte energy storage element, a capacitor, an energy storage device, a method for producing a nonaqueous electrolyte energy storage element, and other embodiments will be described in detail below.

[0044] The lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any manner.

[0045] <Non-aqueous electrolyte> A nonaqueous electrolyte according to one embodiment of the present invention contains an electrolyte salt, an ionic liquid, and PVDF. The nonaqueous electrolyte may be a nonaqueous electrolyte for a nonaqueous electrolyte storage element, a nonaqueous electrolyte for a nonaqueous electrolyte secondary battery, or a nonaqueous electrolyte for a capacitor. A nonaqueous electrolyte for a nonaqueous electrolyte storage element is a medium responsible for transporting charge-transporting ions (e.g., lithium ions) between a positive electrode and a negative electrode, and is substantially free of water. The water content in the nonaqueous electrolyte may be, for example, 10,000 ppm or less, or 5,000 ppm or less.

[0046] (electrolyte salt) The electrolyte salt may be a known electrolyte salt. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, and onium salt. Among these, lithium salt is preferred. One or more types of electrolyte salt may be used.

[0047] The anions that make up the electrolyte salt are N(CF3SO2)2 - (Bis(trifluoromethanesulfonyl)imide anion: TFSI - ), N(SO2F)2 - (Bis(fluorosulfonyl)imide anion: FSI - ), N(C2F5SO2)2 - Bis(pentafluoroethanesulfonyl)imide anion: BETI - ), N(C4F9SO2)2 - (bis(nonafluorobutanesulfonyl)imide anion), N(POF2)2 - (bis(difluorophosphonyl)imide anion), N(CF3SO2)(CF3CO) - ((Trifluoromethanesulfonyl)(trifluoromethanecarbonyl)imide anion), N(CN)2 - (dicyanoimide anion), 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 imide anions such as the above can also be used.

[0048] The anion constituting the electrolyte salt is preferably an imide anion, and more preferably a bis(trifluoromethanesulfonyl)imide anion (TFSI - ) and bis(fluorosulfonyl)imide anion (FSI - ), and bis(fluorosulfonyl)imide anion (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. Furthermore, the anion constituting the electrolyte salt preferably has a fluorine atom. When the anion constituting the electrolyte salt is such an anion, the tensile strength of the non-aqueous electrolyte is further increased, and the occurrence of internal short circuits, increases in overvoltage, and the like that occur with repeated charge and discharge of the non-aqueous electrolyte storage element can be further suppressed.

[0049] The molar concentration of the electrolyte salt in the non-aqueous electrolyte can be, for example, 0.5 mol / kg or more and less than 3.0 mol / kg, and preferably 1.0 mol / kg or more and less than 2.5 mol / kg. The lower limit of the molar concentration may be 1.2 mol / kg, 1.4 mol / kg, 1.6 mol / kg, or 1.8 mol / kg. The upper limit of the molar concentration is more preferably 2.3 mol / kg, even more preferably 2.1 mol / kg, and even more preferably 1.9 mol / kg, 1.7 mol / kg, 1.5 mol / kg, or 1.4 mol / kg. By setting the molar concentration of the electrolyte salt within the above range, and particularly by setting the molar concentration of the electrolyte salt below the above upper limit, the tensile strength tends to be further increased, and the occurrence of internal short circuits and increases in overvoltage due to repeated charging and discharging of the non-aqueous electrolyte storage element can be further suppressed.

[0050] (ionic liquid) An ionic liquid is an ionic compound that is at least partially liquid at room temperature (20°C) under 1 atmosphere.

[0051] 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, piperidinium-based cations, quaternary phosphonium cations, and sulfonium cations.

[0052] Examples of imidazolium cations include 1,3-dimethylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1,3-diethylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1,2,3-trimethylimidazolium cation, 1,2-dimethyl-3-ethylimidazolium cation, 1,2-dimethyl-3-propylimidazolium cation, and 1-butyl-2,3-dimethylimidazolium cation.

[0053] Examples of tetraalkylammonium cations include trimethylethylammonium cation, trimethylpropylammonium cation, trimethylbutylammonium cation, trimethylhexylammonium cation, and tetrapentylammonium cation.

[0054] Examples of pyridinium cations include 1-methylpyridinium cation, 1-ethylpyridinium cation, 1-propylpyridinium cation, 1-butylpyridinium cation, 1-ethyl-2-methylpyridinium cation, 1-butyl-4-methylpyridinium cation, and 1-butyl-2,4-dimethylpyridinium cation.

[0055] Examples of pyrrolium-based cations include 1,1-dimethylpyrrolium cation, 1-ethyl-1-methylpyrrolium cation, 1-methyl-1-propylpyrrolium cation, and 1-butyl-1-methylpyrrolium cation.

[0056] Examples of pyrazolium cations include 1,2-dimethylpyrazolium cation, 1-ethyl-2-methylpyrazolium cation, 1-propyl-2-methylpyrazolium cation, and 1-butyl-2-methylpyrazolium cation.

[0057] Examples of pyrrolinium-based cations include 1,2-dimethylpyrrolinium cation, 1-ethyl-2-methylpyrrolinium cation, 1-propyl-2-methylpyrrolinium cation, and 1-butyl-2-methylpyrrolinium cation.

[0058] Examples of pyrrolidinium cations include 1,1-dimethylpyrrolidinium cation, 1-ethyl-1-methylpyrrolidinium cation, 1-methyl-1-propylpyrrolidinium cation, and 1-butyl-1-methylpyrrolidinium cation.

[0059] Examples of piperidinium cations include 1,1-dimethylpiperidinium cation, 1-ethyl-1-methylpiperidinium cation, 1-methyl-1-propylpiperidinium cation, and 1-butyl-1-methylpiperidinium cation.

[0060] Examples of the quaternary phosphonium cation include a tetramethylphosphonium cation, a tetraethylphosphonium cation, a trimethylethylphosphonium cation, a trimethylpropylphosphonium cation, a trimethylbutylphosphonium cation, and a tetraphenylphosphonium cation.

[0061] Examples of the sulfonium cation include a trimethylsulfonium cation, a triethylsulfonium cation, and a tributylsulfonium cation.

[0062] The cation constituting the ionic liquid is preferably at least one selected from the group consisting of imidazolium-based cations and pyrrolidinium-based cations, and more preferably at least one selected from the group consisting of 1-ethyl-3-methylimidazolium cations and 1-methyl-1-propylpyrrolidinium cations, from the viewpoint of, for example, forming a good coating on the negative electrode surface. Furthermore, the cation constituting the ionic liquid is also preferably a cation having an aromatic heterocycle, such as an imidazolium-based cation or a pyridinium-based cation. One or more of these cations may be contained.

[0063] Examples of anions constituting the ionic liquid include the same anions as those constituting the electrolyte salt. As an anion constituting the ionic liquid, imide anions are preferred, and bis(trifluoromethanesulfonyl)imide anion (TFSI - ) and bis(fluorosulfonyl)imide anion (FSI - ), and bis(fluorosulfonyl)imide anion (FSI -) is more preferable. Furthermore, the anion constituting the ionic liquid preferably contains a fluorine atom. When the anion constituting the ionic liquid is such an anion, the tensile strength of the non-aqueous electrolyte is further increased, and the ionic conductivity of the non-aqueous electrolyte is also increased, which may enable good charge / discharge. One or more of these anions may be contained.

[0064] In addition, it is preferable that the anions present in the non-aqueous electrolyte are substantially only imide anions, and the anions present in the non-aqueous electrolyte are substantially bis(fluorosulfonyl)imide anions (FSI - For example, it is more preferable that the ratio of the imide anion or the bis(fluorosulfonyl)imide anion (FSI) to the total anions in the non-aqueous electrolyte is 1:1. - The content of ) is preferably 90 mol % or more, more preferably 99 mol % or more, and even more preferably 99.9 mol % or more.

[0065] The content of the ionic liquid relative to the total of the ionic liquid and PVDF in the non-aqueous electrolyte can be, for example, 10% by mass or more and less than 50% by mass, and preferably 20% by mass or more and less than 40% by mass. The lower limit of the content may be 22%, 25%, or 30% by mass. The upper limit of the content may be 38%, 35%, or 30% by mass. By setting the content of the ionic liquid relative to the total of the ionic liquid and PVDF within the above range, it is possible to further increase the tensile strength of the non-aqueous electrolyte and to suppress the occurrence of internal short circuits and increases in overvoltage that occur during repeated charge and discharge of the non-aqueous electrolyte storage element.

[0066] (PVDF) PVDF is a polymer consisting essentially of vinylidene fluoride units (-CH2CF2-). "Consisting essentially of vinylidene fluoride units" means that the content of vinylidene fluoride units relative 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 of vinylidene fluoride units relative to all structural units constituting PVDF is preferably 95 mol%, more preferably 99 mol%. The upper limit of the content of vinylidene fluoride units relative to all structural units constituting PVDF is 100%. PVDF may also be a polymer consisting only of vinylidene fluoride units.

[0067] In one embodiment of the present invention, PVDF has a β-type or γ-type crystal structure, preferably a γ-type crystal structure. PVDF having a β-type or γ-type crystal structure can increase the tensile strength of the non-aqueous electrolyte. PVDF in the non-aqueous electrolyte may have multiple crystal structures.

[0068] The crystallinity of PVDF is preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and even more preferably 40% or more. The upper limit of the crystallinity of PVDF may be 100%, 80%, or 60%.

[0069] The crystallinity of PVDF is calculated using Ic and Ia obtained from the X-ray diffraction spectrum of a non-aqueous electrolyte containing PVDF using CuKα radiation, using the formula 100 × Ic / (Ic + Ia). Ic is the integrated intensity of the diffraction peak with the maximum peak intensity among the diffraction peaks corresponding to the crystalline portion, and Ia is the integrated intensity of the halo corresponding to the amorphous portion. The integrated intensities of the diffraction peaks and halos are determined by fitting the diffraction peaks corresponding to the crystalline portion and the halo corresponding to the amorphous portion in the X-ray diffraction spectrum of the non-aqueous electrolyte. X-ray diffraction measurements are performed under the conditions described above.

[0070] Regarding the crystalline structure of PVDF, it is preferable that the X-ray diffraction spectrum of a non-aqueous electrolyte containing PVDF using CuKα radiation does not have a peak with a maximum in the 2θ range of 25° to 28°. Furthermore, in the X-ray diffraction spectrum of the non-aqueous electrolyte using CuKα radiation, the intensity of the peak with a maximum in the 2θ range of 25° to 28° is preferably 1 / 10 or less, more preferably 1 / 20 or less, and even more preferably 1 / 50 or less, of the intensity of the peak with the maximum peak intensity in the 2θ range of 10° to 60°. In the X-ray diffraction spectrum of the non-aqueous electrolyte containing PVDF using CuKα radiation, the peak with a maximum in the 2θ range of 25° to 28° is attributed to the α-type crystalline structure of PVDF, and a crystalline structure in which this peak does not substantially appear tends to have a higher tensile strength.

[0071] The lower limit of the total content of the β-type crystalline structure and the γ-type crystalline structure in the PVDF crystal structure is, for example, preferably 30%, more preferably 50%, and may be 60%, 70%, 80%, 90%, or 95%. The upper limit of the total content may be, for example, 100%, or may be 95%, 90%, 80%, 70%, 60%, or 50%.

[0072] The total content (%) of the β-type crystal structure and the γ-type crystal structure in the crystal structure of PVDF is determined by the following procedure. The solid state of non-aqueous electrolytes containing PVDF was analyzed using a nuclear magnetic resonance (NMR) instrument (Bruker's "Avance400"). 19 F-MAS (Magic Angle Spinning) NMR measurement is performed. The reference material is C6F6, and the observed nucleus is 19 F at -60 to -120 ppm 19 F-NMR spectrum is measured by the single pulse method, and the obtained spectrum is subjected to peak separation. The above PVDF 19The F-NMR spectrum is separated into seven peaks, and each separated peak is known to belong to the following structures: Peak 1 at δ = -81.88 ppm belongs to the α-type crystalline structure; Peak 2 at δ = -88.02 ppm belongs to the γ-type crystalline structure; Peak 3 at δ = -91.11 ppm belongs to the amorphous portion; Peak 4 at δ = -96.38 ppm belongs to the α-type, β-type, and γ-type crystalline structures; Peak 5 at δ = -103.32 ppm belongs to the γ-type crystalline structure; Peak 6 at δ = -112.91 ppm and Peak 7 at -115.02 ppm belong to the heterojunction portion. Here, peaks of three crystal structures, α, β, and γ, overlap at peak 4 at δ = -96.38 ppm. Therefore, the peak area value of the β crystal structure is determined by subtracting the area value of the α crystal structure based on the area value of Peak 1 from the area value of Peak 4, and then subtracting the area value of the γ crystal structure based on the area values ​​of Peaks 2 and 5. Furthermore, for the α crystal structure, the peak area value of the α crystal structure is determined by adding the area value of Peak 4 of the α crystal structure to the area value of Peak 1. Similarly, for the γ crystal structure, the peak area value of the γ crystal structure is determined by adding the area value of Peak 4 of the γ crystal structure to the area values ​​of Peaks 2 and 5. The total of all peak area values ​​of the α-type crystalline structure, β-type crystalline structure, and γ-type crystalline structure is set to 100%, and the area ratio of each crystalline structure is calculated to determine the total content (%) of the β-type crystalline structure and the γ-type crystalline structure in the PVDF crystalline structures (α-type, β-type, and γ-type).

[0073] The crystal structure of PVDF can be controlled by the crystallization conditions of PVDF (e.g., the type of solvent used to dissolve the components of the non-aqueous electrolyte in the production of the non-aqueous electrolyte, 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.

[0074] (Other ingredients, etc.) The non-aqueous electrolyte may further contain other components in addition to the electrolyte salt, ionic liquid, and PVDF, such as a non-aqueous solvent, a polymer other than PVDF, and other additives.

[0075] Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, ethers, esters, amides, sulfones, lactones, and nitriles. When a non-aqueous electrolyte solution is prepared and then the solvent is dried, the solvent used in preparing the non-aqueous electrolyte solution may remain in the non-aqueous electrolyte. In one embodiment of the present invention, the non-aqueous electrolyte may contain DMSO.

[0076] 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.

[0077] 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. Examples of the amines include benzene, 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, and lithium difluorophosphate.

[0078] 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. When the non-aqueous electrolyte is mainly composed of the electrolyte salt, ionic liquid, and PVDF, the tensile strength of the non-aqueous electrolyte can be further increased, and the occurrence of internal short circuits and increases in overvoltage due to repeated charging and discharging of the non-aqueous electrolyte storage element can be further suppressed.

[0079] The nonaqueous electrolyte in this embodiment preferably has substantially no fluidity. A nonaqueous electrolyte having substantially no fluidity has higher tensile strength and can further suppress the occurrence of internal short circuits and increases in overvoltage that occur during repeated charge and discharge of the nonaqueous electrolyte storage element.

[0080] <Method of manufacturing non-aqueous electrolyte> The non-aqueous electrolyte according to one embodiment of the present invention can be obtained, for example, by mixing an electrolyte salt, an ionic liquid, and polyvinylidene fluoride in a suitable solvent, followed by drying. The solvent used is preferably DMSO.

[0081] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention includes an electrode assembly having a positive electrode, a negative electrode, and a separator layer containing a nonaqueous electrolyte, and a container for accommodating the electrode assembly. The electrode assembly is typically a stacked type in which multiple positive electrodes and multiple negative electrodes are stacked with separator layers interposed therebetween, or a wound type in which multiple positive electrodes and multiple negative electrodes are stacked with separator layers interposed therebetween and wound. A portion of the nonaqueous electrolyte may be present in a state in which it has permeated the voids between the positive electrode and the negative electrode. The separator layer may be a layer consisting solely of the nonaqueous electrolyte, or may be a layer containing components other than the nonaqueous electrolyte. The separator layer may have a porous separator. For example, the separator layer may be a layer in which the nonaqueous electrolyte has permeated a porous separator.

[0082] A nonaqueous electrolyte storage element 1 shown in FIG. 1 , which is one embodiment of the present invention, is a nonaqueous electrolyte secondary battery in which a positive electrode 2 and a negative electrode 3 are disposed with a separator 4 containing a nonaqueous electrolyte interposed therebetween. The positive electrode 2 includes a positive electrode substrate 5 and a positive electrode active material layer 6, with the positive electrode substrate 5 being the outermost layer of the positive electrode 2. The negative electrode 3 includes a negative electrode substrate 7 and a negative electrode active material layer 8, with the negative electrode substrate 7 being 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 4, the positive electrode active material layer 6, and the positive electrode substrate 5 are stacked 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 components, such as a container. Other components, such as a container, are omitted from the nonaqueous electrolyte storage element 1 shown in FIG. 1 .

[0083] 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.

[0084] The nonaqueous electrolyte storage element of the present invention may be a nonaqueous electrolyte secondary battery or a capacitor. Below, the main components constituting the nonaqueous electrolyte storage element according to one embodiment of the present invention will be described in detail, mainly in the case where the nonaqueous electrolyte storage element is a nonaqueous electrolyte secondary battery (particularly a lithium ion secondary battery), but this is not intended to limit the scope of application of the present invention.

[0085] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer laminated on the positive electrode substrate directly or via an intermediate layer. Usually, the positive electrode has a portion where the positive electrode substrate is exposed. This exposed portion of the positive electrode substrate is usually connected to the above-mentioned positive electrode lead. The positive electrode may have a shape such as a sheet, plate, or strip.

[0086] The thickness of the positive electrode is appropriately determined depending on the application of the nonaqueous electrolyte storage element. The average thickness of the positive electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the positive electrode is the average thickness of the portion where the positive electrode active material layer is laminated on the positive electrode substrate directly or via an intermediate layer. When the positive electrode substrate has both a portion where the positive electrode active material layer is laminated on both sides and a portion where the positive electrode active material layer is laminated on only one side, the average thickness of the portion where the positive electrode active material layer is laminated on both sides of the positive electrode substrate is referred to. In addition, in this specification, "average thickness" means the average thickness of thicknesses measured at any five positions.

[0087] The positive electrode substrate has electrical conductivity. In this specification, "having electrical conductivity" means that the volume resistivity is 10 -2 The volume resistivity is a value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not having electrical conductivity" or "having (electrical) insulation" means that the volume resistivity is 10 7 This means that the resistance is Ω·cm or more.

[0088] Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and alloys thereof (stainless steel, etc.). Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high electronic conductivity, and cost.

[0089] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of the form of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The positive electrode substrate may be, for example, aluminum foil or aluminum alloy foil.

[0090] The average thickness of the positive electrode substrate may be, for example, 3 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate may be 40 μm, 30 μm, 20 μm, or 15 μm.

[0091] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains, for example, a conductive agent and a binder. When the intermediate layer contains a conductive agent, the contact resistance between the positive electrode substrate and the positive electrode active material layer can be reduced. Examples of the conductive agent and binder used in the intermediate layer include the same conductive agent and binder used in the positive electrode active material layer described below.

[0092] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. The positive electrode active material layer may be formed from a positive electrode mixture containing the positive electrode active material and other optional components. The positive electrode active material layer may be provided on only one side or on both sides of a positive electrode substrate having a shape such as a sheet.

[0093] Known positive electrode active materials can be used for the positive electrode active material. Materials capable of absorbing and releasing lithium ions are typically used for the positive electrode active material of lithium ion secondary batteries. Examples of positive electrode active materials include lithium transition metal composite oxides, polyanion compounds, chalcogen compounds, sulfur-based active materials, and lithium oxide. One or more positive electrode active materials can be used.

[0094] Examples of the transition metal element contained in the lithium transition metal composite oxide include nickel, cobalt, and manganese. The lithium transition metal composite oxide may also contain a typical metal element such as aluminum. Examples of the lithium transition metal composite oxide include lithium transition metal composite oxides having an α-NaFeO2 crystal structure and lithium transition metal composite oxides having a spinel crystal structure.

[0095] As the lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, Li 1+α Ma 1-α O2 (Ma is a metal element other than a lithium element, containing one or more transition metal elements. 0 ≦ α < 1.) can be mentioned. Ma preferably contains one or more of Ni, Co, and Mn. As the total content of Ni, Co, and Mn with respect to Ma ((Ni + Co + Mn) / Ma), 90 mol% or more is preferable, and 98 mol% or more is more preferable.

[0096] As the lithium transition metal composite oxide having a spinel type crystal structure, Li β Mb2O4 (Mb is a metal element other than a lithium element, containing one or more transition metal elements. 0 < β ≦ 1.2.) can be mentioned. Mb preferably contains Mn. As the content of Mn with respect to Mb (Mn / Mb), 50 mol% or more is preferable, and 80 mol% or more is more preferable.

[0097] The polyanion compound is a compound composed of a polyanion (that is, a polyvalent oxoacid ion) and a cation. The polyanion compound preferably contains a lithium cation and a transition metal cation as the cation. Examples of the polyanion compound include LiFePO4, LiMnPO4, LiMn x Fe 1-x PO4 (0 < x < 1), LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. The surface of the particles of the polyanion compound may be coated with another material (for example, a carbon material described later).

[0098] Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc.

[0099] The sulfur-based active material may be elemental sulfur 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. Sulfur-based active materials have advantages such as high theoretical capacity and low cost. In particular, nonaqueous electrolyte storage elements having a positive electrode containing a sulfur-based active material and a negative electrode containing metallic lithium are prone to internal short circuits due to repeated charge and discharge, and tend to be unable to perform good charge and discharge. Therefore, when an embodiment of the present invention is applied to such nonaqueous electrolyte storage elements, the advantage of being able to suppress the occurrence of internal short circuits, increases in overvoltage, and the like due to repeated charge and discharge of the nonaqueous electrolyte storage elements may be significantly obtained.

[0100] The sulfur-based active material may be in the form of a composite with a conductive agent (a material having higher conductivity than the sulfur-based active material), etc. This composite 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 composite of the sulfur-based active material and porous carbon (sulfur-porous carbon composite: SPC), etc.

[0101] The atoms or polyanions in these materials serving as the positive electrode active material may be partially substituted with atoms or anion species of other elements, and the surfaces of these materials may be coated with other materials.

[0102] The positive electrode active material is usually particulate. The average particle size of the positive electrode active material is preferably, for example, 0.1 μm to 20 μm. Setting the average particle size of the positive electrode active material above the lower limit facilitates the production and handling of the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When a composite 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 term "average particle size" refers to the value at which the volume-based cumulative distribution (D50) reaches 50% as calculated in accordance with JIS-Z-8819-2 (2001) based on the particle size distribution measured by laser diffraction / scattering in a diluted solution of particles diluted with a solvent in accordance with JIS-Z-8825 (2013). Methods for obtaining particles of the positive electrode active material and the negative electrode active material described below with a predetermined particle size can be known, for example, using a pulverizer or classifier.

[0103] 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 may be 80% by mass to 95% by mass. By setting the content of the positive electrode active material within this range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0104] Conductive agents are usually components made of materials that have electrical conductivity. Even if the volume resistivity of a conductive agent cannot be measured directly, it is possible to measure the volume resistivity by measuring the volume resistivity of the conductive agent when the volume resistivity is 10 -2Conductive agents are materials known to have a resistivity of Ω·cm or less. Examples of conductive agents include carbon materials, metals, and conductive ceramics. Carbon materials are materials whose primary constituent element is carbon. The primary constituent element refers to the element with the highest content by mass. For example, the carbon content in a carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. The carbon material is preferably a carbon material other than an uncarbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerene. Conductive agents may be in the form of powder, fiber, or the like. The conductive agent may be one or more kinds. The conductive agent may be a composite of these materials. For example, a composite material of carbon black and CNT may be used.

[0105] The content of the conductive agent in the positive electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 1% by mass to 9% by mass, and even more preferably 3% by mass to 8% by mass. The upper limit of the content of the conductive agent may be 5%, 4%, or 3% by mass. By setting the content of the conductive agent within the above range, it is possible to increase the energy density of the nonaqueous electrolyte storage element. 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.

[0106] Examples of the binder include a water-based binder and an organic solvent-based binder.

[0107] The aqueous binder is a binder that dissolves or disperses in water. The aqueous binder may be a binder that dissolves or disperses at 1 part by mass or more in 100 parts by mass of water at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is water or a mixed solvent mainly composed of water, an aqueous binder (a water-soluble or water-dispersible polymer material) can be used. Examples of aqueous binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0108] The organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). The organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more in 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is an organic solvent or a mixed solvent mainly containing an organic solvent, an organic solvent-based binder (a polymer material that is soluble or dispersible in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, chitosan derivatives, and the like.

[0109] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. One or more types of binders may be used.

[0110] The content of the binder in the positive electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 1% by mass to 9% by mass, and even more preferably 3% by mass to 8% by mass. The upper limit of the binder content may be 5%, 4%, or 3% by mass. By setting the binder content within the above range, it is possible to stably hold the positive electrode active material. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a binder.

[0111] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose 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. The thickener may also function as a binder. One or more types of thickeners may be used. When the positive electrode active material layer contains a thickener, the content of the thickener in the positive electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a thickener.

[0112] The filler is not particularly limited. The filler may be a component other than the positive electrode active material, conductive agent, binder, and thickener, and may be intentionally added. The filler may be added to fill gaps in the positive electrode active material layer, or may be added for other purposes. The filler may be an organic substance such as polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more fillers may be used. When the positive electrode active material layer contains a filler, the content of the filler in the positive electrode active material layer may be 0.1% by mass or more and 8% by mass or less, typically preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0113] The positive electrode active material layer may further contain other components in addition to the positive electrode active material, conductive agent, binder, thickener, and filler. The other components include those unintentionally present in the positive electrode active material layer. The positive electrode active material layer may also contain unintentionally contained impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained impurities in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0114] The thickness of the positive electrode active material layer is appropriately set depending on the type of positive electrode active material, the application of the nonaqueous electrolyte storage element, and the like. The average thickness of one positive electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one positive electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one positive electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one positive electrode active material layer is, for example, 4 mg / cm. 2 More than 100mg / cm 2 The lower limit of the mass per unit area of ​​one positive electrode active material layer may be 6 mg / cm or less. 2 , 8 mg / cm 2 or 10 mg / cm 2 The upper limit of the mass per unit area of ​​one positive electrode active material layer is 50 mg / cm. 2 , 20 mg / cm 2 , 15 mg / cm 2 , 12 mg / cm 2 or 10 mg / cm 2 may be.

[0115] The porosity of the positive electrode active material layer may be, for example, 20% or more and 50% or less. The lower limit of the porosity of the positive electrode active material layer may be 25%, 30%, or 35%. The upper limit of the porosity of the positive electrode active material layer may be 45%, 40%, or 35%. The "porosity (%)" of the positive electrode active material layer and the negative electrode active material layer described below is calculated by the formula (1-V2 / V1) × 100, where V1 is the apparent volume (volume including voids) of the positive (negative) electrode active material layer and V2 is the sum of the actual volumes of the materials constituting the positive (negative) electrode active material layer. The sum V2 of the actual volumes of the materials constituting the positive (negative) electrode active material layer can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0116] (Positive electrode manufacturing method) The positive electrode can be manufactured by a known method. The positive electrode can be manufactured, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) to a positive electrode substrate directly or via an intermediate layer, and then drying the paste to form a positive electrode active material layer. The positive electrode mixture paste usually contains a positive electrode active material, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be pressed, etc.

[0117] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer laminated on the negative electrode substrate directly or via an intermediate layer. Usually, the negative electrode has a portion where the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is usually connected to the above-mentioned negative electrode lead. The negative electrode may have a shape such as a sheet, plate, or strip.

[0118] The thickness of the negative electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element, etc. The average thickness of the negative electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode is the average thickness of a portion where the negative electrode active material layer is laminated on the negative electrode substrate directly or via an intermediate layer. When the negative electrode substrate has both a portion where the negative electrode active material layer is laminated on both sides and a portion where the negative electrode active material layer is laminated on only one side, the average thickness of the portion where the negative electrode active material layer is laminated on both sides of the negative electrode substrate is taken as the average thickness.

[0119] The negative electrode substrate is conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and alloys thereof (such as stainless steel), and carbon materials. Among these, copper or copper alloys are preferred.

[0120] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of the form of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The negative electrode substrate may be, for example, copper foil or copper alloy foil.

[0121] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 30 μm, 20 μm, 15 μm, or 10 μm.

[0122] The structure of the intermediate layer of the negative electrode is not particularly limited, and can be selected from the structures exemplified for the intermediate layer of the positive electrode, for example.

[0123] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. 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 above. The negative electrode active material layer may be formed from a negative electrode mixture containing a negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side or on both sides of a negative electrode substrate having a shape such as a sheet.

[0124] The negative electrode active material can be a known negative electrode active material. A material capable of absorbing and releasing lithium ions is typically used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as silicon and tin; metal oxides or semimetal oxides such as silicon oxide, titanium oxide, and tin oxide; and Li4Ti5O. 12 , LiTiO 2、 Examples of the negative electrode active material include titanium-containing oxides such as TiNb2O7, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitic carbon. One or more negative electrode active materials can be used.

[0125] "Graphite" refers to graphite that has an average lattice spacing (d 002 ) is a carbon material with a particle size of 0.33 nm or more and less than 0.34 nm. Graphite includes natural graphite and artificial graphite.

[0126] "Non-graphitic carbon" refers to carbon that has an average lattice spacing (d 002 ) refers to a carbon material in which the particle size is 0.34 nm or more and 0.42 nm or less. Non-graphitizable carbon includes non-graphitizable carbon and graphitizable carbon. "Non-graphitizable carbon" refers to a carbon material in which the particle size is 0.34 nm or more and 0.42 nm or less. 002 The term "easily graphitizable carbon" refers to a carbon material having a particle size of 0.36 nm or more and 0.42 nm or less. 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0127] Here, the "discharged state" of a carbon material refers to a state in which the carbon material, which is a negative electrode active material, is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released from the carbon material. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metallic lithium as a counter electrode is 0.7 V or higher.

[0128] The negative electrode active material may be in a particulate form. The average particle size of the negative electrode active material may 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, a polyphosphate compound, or the like, 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 be equal to or greater than the above lower limit, the production or handling of the negative electrode active material becomes easier. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the electronic conductivity of the negative electrode active material layer is improved.

[0129] 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 negative electrode active material may be metallic lithium. The metallic lithium may be pure metallic lithium consisting essentially of lithium element alone, or may be a lithium alloy containing other metal elements. Examples of lithium alloys include lithium-silver alloys, lithium-zinc alloys, lithium-calcium alloys, lithium-aluminum alloys, lithium-magnesium alloys, and lithium-indium alloys. The lithium alloy may contain multiple metal elements other than lithium.

[0130] 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.

[0131] 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 within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved. Furthermore, 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.

[0132] In the case of a nonaqueous electrolyte storage element configured so that metallic lithium is deposited 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 eluted into the nonaqueous electrolyte during discharging, the negative electrode may not have a negative electrode active material layer in a discharged state.

[0133] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. The content of the conductive agent in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a conductive agent.

[0134] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 8% by mass. The content of the binder in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a binder.

[0135] When the negative electrode active material layer contains a thickener, the content of the thickener in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickener in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a thickener.

[0136] The filler in the negative electrode active material layer may be a component other than the negative electrode active material, conductive agent, binder, and thickener, and may be an intentionally contained component. The filler may be contained as a component to fill gaps in the negative electrode active material layer, or may be contained for other purposes. When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a filler.

[0137] The negative electrode active material layer may further contain other components in addition to the negative electrode active material, conductive agent, binder, thickener, and filler. The other components include those unintentionally present in the negative electrode active material layer. The negative electrode active material layer may also contain unintentionally present impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally present components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally present impurities in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0138] The thickness of the negative electrode active material layer is appropriately set depending on the type of negative electrode active material, the application of the non-aqueous electrolyte storage element, and the like. The average thickness of one negative electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one negative electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one negative electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one negative electrode active material layer is, for example, 2 mg / cm. 2 More than 50mg / cm 2 The lower limit of the mass per unit area of ​​one negative electrode active material layer may be 3 mg / cm or less. 2 , 4 mg / cm 2 , 5 mg / cm 2 or 6 mg / cm 2 The upper limit of the mass per unit area of ​​one negative electrode active material layer is 30 mg / cm. 2 , 20 mg / cm 2 , 15 mg / cm 2 , 12 mg / cm 2 or 10 mg / cm 2 may be.

[0139] The porosity of the negative electrode active material layer may be, for example, 30% or more and 70% or less. The lower limit of the porosity of the negative electrode active material layer may be 35%, 40%, or 45%. The upper limit of the porosity of the negative electrode active material layer may be 60%, 50%, or 40%. When the negative electrode active material layer is in a foil shape, for example, the porosity of the negative electrode active material layer may be 0%.

[0140] (Method of manufacturing negative electrode) The negative electrode can be manufactured by a known method. The negative electrode can be manufactured, for example, in the same manner as in the above-described method for manufacturing a positive electrode, by applying a paste-like negative electrode mixture (negative electrode mixture paste) to a negative electrode substrate directly or via an intermediate layer, and then drying the applied mixture to form a negative electrode active material layer. After drying, the negative electrode active material layer may be pressed, for example. When the negative electrode active material is a metal such as metallic lithium, the negative electrode can also be manufactured by laminating a metal foil on the negative electrode substrate directly or via an intermediate layer, and then pressing the metal foil.

[0141] (isolation layer) The separator is a layer interposed between the positive electrode and the negative electrode. The separator contains a non-aqueous electrolyte. The non-aqueous electrolyte used in the separator is the non-aqueous electrolyte according to one embodiment of the present invention described above.

[0142] A portion of the non-aqueous electrolyte may be present in a state of permeating the voids between the positive electrode and the negative electrode. In one embodiment of the present invention, the separator may be composed solely of a 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 mass%, 80 mass%, 90 mass%, 95 mass%, 99 mass%, or 99.5 mass%. The separator may further contain other components in addition to the non-aqueous electrolyte. Examples of other components in addition to the non-aqueous electrolyte that may be contained in the separator include a filler and a separator.

[0143] In one embodiment of the present invention, the lower limit of the total content of the electrolyte salt, ionic liquid, and PVDF in the separator layer may be, for example, 50% by mass, or may be 80%, 90%, 95%, 99%, or 99.5% by mass. The upper limit of the total content may be 100%, 99.9%, or 99% by mass. By having the separator layer mainly composed of the electrolyte salt, ionic liquid, and PVDF, the strength of the separator layer can be further optimized.

[0144] The separator may be a separator. The separator may be composed only of a non-aqueous electrolyte and a separator. When a separator is used, the separator may be, for example, a separator composed only of a base layer, or a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both surfaces of a base layer.

[0145] Examples of the form of the substrate layer of the separator include woven fabric, nonwoven fabric, porous resin film, etc. Among these forms, porous resin film is preferred from the viewpoint of strength, etc., and nonwoven fabric is preferred from the viewpoint of non-aqueous electrolyte retention, etc. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefin (polyethylene, polypropylene, etc.), polyimide, aramid, etc. are preferred.

[0146] Examples of inorganic compounds constituting the inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, and magnesium oxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon; mineral-derived substances such as talc, zeolite, kaolin, bentonite, and mica, or artificial products thereof. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, from 0.5 μm to 10 μm. The content of the inorganic particles in the inorganic layer is preferably from 50% to 99% by mass, and more preferably from 80% to 98% by mass.

[0147] Examples of binders used in the inorganic layer include the same binders as those exemplified for the positive electrode active material layer.

[0148] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the porosity of the separator may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the porosity of the separator may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0149] The average thickness of the isolation layer and the separator may be, for example, 10 μm or more and 40 μm or less, or 15 μm or more and 30 μm or less.

[0150] (container) The container accommodates the electrode assembly in its internal space. The container may be made of a metal material such as aluminum or stainless steel, or a resin material. Metal materials are preferred from the viewpoint of strength, etc. A composite material of a metal material and a resin material may also be used.

[0151] The shape of the container is not particularly limited, and may be cylindrical, rectangular (square), disk-like, etc. The container may also be in the shape of a sheet formed from a metal resin composite film.

[0152] (shape, use, etc. of non-aqueous electrolyte storage element) The shape of the nonaqueous electrolyte storage element according to one embodiment of the present invention is not particularly limited, and may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin battery, a button battery, or the like.

[0153] The use of the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention is not particularly limited, and the nonaqueous electrolyte electricity storage element can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, a power source for electronic devices such as personal computers and communication terminals, a power source for power storage, etc.

[0154] The nonaqueous electrolyte electricity storage element of the present invention may be used singly or in plural. When the required output and required voltage are small, the nonaqueous electrolyte electricity storage element may be used singly. On the other hand, when at least one of the required output and required voltage is large, the nonaqueous electrolyte electricity storage element may be used as an electricity storage device in combination with other nonaqueous electrolyte electricity storage elements. In an electricity storage device in which a plurality of nonaqueous electrolyte electricity storage elements are combined, at least one nonaqueous electrolyte electricity storage element included in the electricity storage device may be the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. The electricity storage device will be described in detail later.

[0155] In a nonaqueous electrolyte energy storage element according to one embodiment of the present invention, for example, the container may be constrained so as to maintain a constant thickness, or may not be constrained in this manner. Alternatively, the container may be constrained so as to apply a constant load to it. When the container is constrained, expansion of the container due to charge / discharge cycles, etc., may be suppressed, and deterioration of charge / discharge performance may be suppressed. When the container is constrained, a load may or may not be applied to the electrode assembly within the container. For example, a constraining member that performs such constraining may be provided in the nonaqueous electrolyte energy storage element or the energy storage device.

[0156] <Method of manufacturing nonaqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention can be manufactured by a known method. For example, a method for manufacturing a nonaqueous electrolyte storage element according to one embodiment of the present invention comprises assembling an uncharged / discharged nonaqueous electrolyte storage element comprising a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, and PVDF, wherein the PVDF has a β-type or γ-type crystal structure. Furthermore, a method for manufacturing a nonaqueous electrolyte storage element according to another embodiment of the present invention comprises assembling an uncharged / discharged nonaqueous electrolyte storage element comprising a nonaqueous electrolyte containing an electrolyte salt, an ionic liquid, PVDF, and DMSO.

[0157] 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 the surface of the positive electrode or negative electrode and drying it to provide a separator 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 separator layer therebetween to prepare an electrode assembly, and housing the electrode assembly in a container.

[0158] The nonaqueous electrolyte solution contains an electrolyte salt, an ionic liquid, PVDF, and a suitable solvent. As described above, DMSO is preferred as the solvent. By using DMSO as the solvent and drying a solution containing the electrolyte salt, the ionic liquid, and PVDF, a nonaqueous electrolyte containing the electrolyte salt, the ionic liquid, and PVDF having a β-type or γ-type crystal structure is obtained. DMSO may remain in the obtained nonaqueous electrolyte.

[0159] An electrode assembly may be fabricated using a positive electrode, a negative electrode, and a separator, and then the electrode assembly may be impregnated with a nonaqueous electrolyte. This forms an isolation layer composed of the separator and the nonaqueous electrolyte. The impregnation with the nonaqueous electrolyte may be performed by impregnating the electrode assembly with a solution of the nonaqueous electrolyte and then drying the electrode assembly.

[0160] Alternatively, a film-like nonaqueous 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 nonaqueous electrolyte. In this case, the porous positive electrode active material layer and the porous negative electrode active material layer may be impregnated with the nonaqueous electrolyte to enhance ionic conductivity.

[0161] The 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 the same as 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.

[0162] The method for producing the nonaqueous electrolyte storage element may further include initially charging and discharging the assembled, uncharged storage element. The initial charging and discharging may be a single charge or a single discharge, or may be a single charge and discharge, or may be two or more charge and discharge cycles.

[0163] <Electricity storage device> 2 includes a plurality of energy storage units 20. Each energy storage unit 20 includes a plurality of electrically connected nonaqueous electrolyte energy storage elements 1. The energy storage device 30 may include a bus bar (not shown) that electrically connects the plurality of nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects the plurality of energy storage units 20, and the like. The energy storage unit 20 or the energy storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more nonaqueous electrolyte energy storage elements 1.

[0164] <Other embodiments> The nonaqueous electrolyte and nonaqueous electrolyte storage element of the present invention are not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0165] In the above embodiment, the nonaqueous electrolyte storage element is described as being used as a chargeable and dischargeable nonaqueous electrolyte 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 and capacitors such as electric double layer capacitors and lithium ion capacitors. A capacitor according to one embodiment of the present invention includes a nonaqueous electrolyte containing an ionic liquid and polyvinylidene fluoride, wherein the polyvinylidene fluoride has a β-type or γ-type crystal structure.

[0166] The positive electrode and the negative electrode may further include layers other than the substrate, the intermediate layer, and the active material layer. The positive electrode and the negative electrode may not necessarily have a layer structure. [Example]

[0167] 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.

[0168] [Manufacturing 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 to a copper foil and dried for 2 hours at 75° C. Thereafter, the foil was dried under reduced pressure at 75° C. for 12 hours to obtain a PVDF film (No. 1) of Production Example 1.

[0169] [Manufacturing 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.

[0170] X-ray diffraction 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, while 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 structure of the obtained PVDF film differed depending on the type of solvent.

[0171] [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(fluorosulfonyl)imide (LiFSI), a lithium salt, was mixed in at a mass molar concentration of 1.3 mol / kg based on the total amount of the ionic liquid and PVDF to obtain a nonaqueous electrolyte solution.

[0172] (Preparation of non-aqueous electrolyte) The nonaqueous electrolyte solution was applied to a copper foil and dried under the same conditions as in Production Example 1, to obtain a nonaqueous electrolyte of Example 1 in the form of a film having a thickness of 100 μm.

[0173] (Preparation of test cell) Two sheets of nickel foil were prepared, each having a metallic lithium layer on its surface. The above non-aqueous electrolyte solution was applied to the metallic lithium layer of each nickel foil, and dried under the same conditions as in Production Example 1, to provide a separation layer made of non-aqueous electrolyte and having a thickness of approximately 25 μm per layer. The two nickel foils were overlapped so that the separation layers were in contact with each other. The reaction area (the area where the metallic lithium layers faced each other) was 441 mm 2 (=21mm x 21mm). This was placed in a container made of a metal-resin composite film, the opening was sealed by heat welding, and the container was subjected to pressure of 1.5kgf / cm from the outside. 2 Thus, a non-charged and non-discharged nonaqueous electrolyte electricity storage element of Example 1 was obtained.

[0174] [Examples 2 to 12] The nonaqueous electrolytes and non-charged / discharged nonaqueous electrolyte storage elements of Examples 2 to 12 were obtained in the same manner as in Example 1, except that the components were adjusted so that the compositions of the nonaqueous electrolytes were as shown in Table 1. Note that, because DMSO was used as a solvent to prepare the solutions of the nonaqueous electrolytes, it was assumed that the PVDF in each nonaqueous electrolyte had a γ-type crystal structure.

[0175] [Comparative Example 1] A nonaqueous electrolyte and a non-charged / discharged nonaqueous electrolyte storage element of Comparative Example 1 were obtained in the same manner as in Example 1, except that the components were adjusted so that the composition of the nonaqueous electrolyte was as shown in Table 1 and that NMP was used as the solvent for the nonaqueous electrolyte solution. Note that, because NMP was used as the solvent for preparing the nonaqueous electrolyte solution, it was assumed that the PVDF in the nonaqueous electrolyte had an α-type crystal structure.

[0176] The components listed in Table 1 are as follows: LiFSI: Lithium bis(fluorosulfonyl)imide LiTFSI: Lithium bis(trifluoromethanesulfonyl)imide EMI-FSI: 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide Py13-FSI: 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide EMI-TFSI: 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

[0177] (tensile strength measurement) The tensile strength of each of the nonaqueous electrolytes of Examples 1 to 4, 7, 9, and 11 and Comparative Example 1 was measured under the following conditions. A 100 μm-thick film was cut into a No. 7 dumbbell shape to serve as a sample. The samples were subjected to a tensile test using a tensile tester (Shimadzu Corporation, Autograph AGX-500N) with a 10 N load cell at a tension speed of 200 mm / min. The results are shown in Table 1.

[0178] (Lithium dissolution and precipitation test) For each of the non-charged and discharged non-aqueous electrolyte storage elements of Examples 2 to 12, a lithium dissolution and deposition test was carried out under the following conditions: 50°C, current density 0.3 mA / cm 2 and a capacity density of 3.0mAh / cm 2 After the current was applied, a charge-discharge test was performed in which the direction of the current was alternately reversed, with a 5-minute rest period between each current application. The above charge / discharge cycle was repeated 50 times, and the number of cycles was determined when the closed circuit voltage, which increased with internal short-circuiting or repeated charge / discharge, reached the cutoff voltage of 3.0 V. The results are shown in Table 1.

[0179] [Table 1]

[0180] As shown in Table 1, the nonaqueous electrolyte of Comparative Example 1, in which PVDF had an α-type crystal structure, had a tensile strength of 1268 kPa, whereas the nonaqueous electrolyte of Example 2, which differed from the nonaqueous electrolyte of Comparative Example 1 only in that PVDF had a γ-type crystal structure, had a tensile strength of 7788 kPa. Furthermore, the nonaqueous electrolytes of the other Examples whose tensile strengths were measured also had high tensile strengths of 3023 kPa or more. The tensile strength of each of the nonaqueous electrolytes of the Examples could be further increased by adjusting the content of the ionic liquid, the molar concentration of the electrolyte salt, etc. Furthermore, in each of the nonaqueous electrolyte storage elements of the Examples, by adjusting the content of the ionic liquid in the nonaqueous electrolyte, the molar concentration of the electrolyte salt, etc., an internal short circuit or the number of cycles until the closed circuit voltage reached the cutoff voltage was increased, and good repeated charging and discharging was possible. [Industrial Applicability]

[0181] 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]

[0182] 1. Non-aqueous electrolyte energy 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. Contains an electrolyte salt, an ionic liquid, and polyvinylidene fluoride, The non-aqueous electrolyte, wherein the polyvinylidene fluoride has a β-type or γ-type crystal structure.

2. 2. The nonaqueous electrolyte according to claim 1, wherein a content of the ionic liquid relative to a total of the ionic liquid and the polyvinylidene fluoride is 20% by mass or more and less than 40% by mass.

3. 3. The nonaqueous electrolyte according to claim 1, wherein the mass molar concentration of the electrolyte salt is 1.0 mol / kg or more and less than 2.5 mol / kg.

4. 3. The non-aqueous electrolyte according to claim 1, wherein the electrolyte salt is a lithium salt.

5. 3. The non-aqueous electrolyte according to claim 1, wherein the electrolyte salt is an imide salt.

6. 6. The non-aqueous electrolyte according to claim 5, wherein the imide salt is at least one selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide.

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

8. 3. The non-aqueous electrolyte according to claim 1, wherein the ionic liquid has at least one cation selected from the group consisting of a 1-ethyl-3-methylimidazolium cation and a 1-methyl-1-propylpyrrolidinium cation.

9. The non-aqueous electrolyte according to claim 1 or 2, wherein the ionic liquid has an imide anion.

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

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

12. The non-aqueous electrolyte according to claim 1 or 2, which has substantially no fluidity.

13. A non-aqueous electrolyte comprising an electrolyte salt, an ionic liquid, polyvinylidene fluoride, and dimethyl sulfoxide.

14. A nonaqueous electrolyte storage element comprising the nonaqueous electrolyte according to claim 1 or 13.

15. The nonaqueous electrolyte electricity storage element according to claim 14 , further comprising a negative electrode containing metallic lithium.

16. Contains an ionic liquid and polyvinylidene fluoride, A capacitor comprising the non-aqueous electrolyte in which the polyvinylidene fluoride has a β-type or γ-type crystal structure.

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