Nonaqueous gel electrolyte and nonaqueous electrolyte power storage element

Abstract

To provide a nonaqueous gel electrolyte that contains a fluorinated cyclic carbonate as a nonaqueous solvent and achieves superior ionic conductivity and mechanical strength, and to provide a nonaqueous electrolyte power storage element equipped with the nonaqueous gel electrolyte.SOLUTION: The nonaqueous gel electrolyte includes a crosslinked polymer, a nonaqueous solvent, and an electrolyte salt, wherein a content of the crosslinked polymer is 8 mass% or less, the crosslinked polymer has a crosslinked site including a structure represented by formula (1) below, and the nonaqueous solvent contains a fluorinated cyclic carbonate. In formula (1), * indicates a bonding site with another group or atom.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nonaqueous gel electrolyte and a nonaqueous electrolyte storage element. [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 energy storage elements besides non-aqueous electrolyte secondary batteries include capacitors such as lithium ion capacitors and electric double layer capacitors. Silicon-based active materials, metallic lithium, and the like are known as high-capacity negative electrode active materials used in non-aqueous electrolyte energy storage elements.

[0003] In recent years, non-aqueous electrolyte storage elements that use a gel-type non-aqueous electrolyte instead of a liquid non-aqueous electrolyte solution have also attracted attention (see Patent Document 1; hereinafter, a gel-type non-aqueous electrolyte will also be referred to as a "nonaqueous gel electrolyte"). Non-aqueous electrolyte storage elements that use a non-aqueous gel electrolyte have advantages such as being less susceptible to leakage compared to non-aqueous electrolyte storage elements that use a non-aqueous electrolyte solution. It is also known that when a non-aqueous gel electrolyte with high mechanical strength is applied to a non-aqueous electrolyte storage element that includes a negative electrode containing a silicon-based active material, the charge-discharge cycle life performance is improved compared to non-aqueous electrolyte storage elements that use a non-aqueous electrolyte solution. For example, Non-Patent Document 1 describes that by applying a non-aqueous gel electrolyte having high mechanical strength to a non-aqueous electrolyte energy storage element having a negative electrode containing a silicon-based active material, cracks in the negative electrode active material layer that occur during charge and discharge are suppressed, and the charge and discharge cycle life performance is improved. Another candidate for a non-aqueous gel electrolyte is TetraPEG gel (see Non-Patent Document 2). The TetraPEG gel is formed from two types of four-branched polyethylene glycols with mutually reactive ends. The gelation proceeds through the cross-reaction of the two four-branched polymer ends using a Michael addition reaction using a base catalyst. This reaction has high reaction selectivity and can form a uniform network structure, making it possible to obtain a gel that exhibits excellent mechanical strength with a low polymer content. Therefore, the TetraPEG gel can achieve both high ionic conductivity and high mechanical strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Re-tabled publication No. 2012 / 090855 [Non-Patent Document 1] Qingquan Huang et al., “Supremely elastic gel polymer electrolyte enables a reliable electrode structure for silicon-based anodes”, Nature communications, 10, December 2019, p5586 [Non-patent document 2] Mari Yoshitake et al., “TetraPEG Network Formation via a Michael Addition Reaction in an Ionic Liquid:Application to Polymer Gel Electrolyte for Electric Double-layer Capacitors”, Chemistry Letters, 48, May 2019, p704-707 [Non-patent document 3] Takamasa Sakai et al., “Design and Fabrication of a High-Strength Hydrogel with Ideally Homogeneous Network Structure from Tetrahedron-like Macromonomers”, Macromolecules, 41, 14, June 2008, p5379-5384 Summary of the Invention [Problem to be solved by the invention]

[0005] The nonaqueous gel electrolyte described in Patent Document 1 is not sufficiently strong. Furthermore, due to its high polymer content, the nonaqueous gel electrolyte described in Non-Patent Document 1 has the problem of having an ionic conductivity approximately one order of magnitude lower than that of nonaqueous electrolyte solutions. On the other hand, the capacity retention rate after a charge-discharge cycle life test can be improved by using a fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC), which forms a stable coating on the surface of the negative electrode active material, as the nonaqueous solvent for the nonaqueous gel electrolyte contained in a nonaqueous electrolyte storage element. However, the inventors investigated a method for obtaining a nonaqueous gel electrolyte by using a base catalyst to crosslink a monomer in a nonaqueous solvent containing FEC, forming a crosslinked polymer and gelling it. They found that gelation did not occur when FEC was used in a method using a base catalyst. Furthermore, nonaqueous electrolyte storage elements with a negative electrode containing a silicon-based active material experience large volume changes during charge and discharge of the negative electrode active material, which makes it difficult to keep up with these changes, leading to the formation of cracks in the coating on the surface of the negative electrode active material. Since continuous decomposition of the non-aqueous electrolyte occurs in these cracked areas, non-aqueous electrolyte storage elements equipped with negative electrodes containing silicon-based active materials have the disadvantage that the discharge capacity is prone to decrease with increasing charge-discharge cycles.

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a nonaqueous gel electrolyte that contains a fluorinated cyclic carbonate as a nonaqueous solvent and has excellent ionic conductivity and mechanical strength, and a nonaqueous electrolyte storage element that includes such a nonaqueous gel electrolyte. [Means for solving the problem]

[0007] A nonaqueous gel electrolyte according to one aspect of the present invention comprises a crosslinked polymer, a nonaqueous solvent, and an electrolyte salt, wherein the content of the crosslinked polymer is 8 mass % or less, the crosslinked polymer has a crosslinking moiety including a structure represented by the following formula (1), and the nonaqueous solvent contains a fluorinated cyclic carbonate:

[0008] [ka] In the above formula (1), * indicates a bonding site to another group or atom.

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

[0010] According to any one aspect of the present invention, it is possible to provide a nonaqueous gel electrolyte that contains a fluorinated cyclic carbonate as a nonaqueous solvent and has excellent ionic conductivity and mechanical strength, and a nonaqueous electrolyte storage element that includes such a nonaqueous gel electrolyte. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element. [Figure 2] FIG. 2 is a schematic diagram showing one embodiment of an electricity storage device configured by assembling a plurality of nonaqueous electrolyte electricity storage elements. DETAILED DESCRIPTION OF THE INVENTION

[0012] First, an overview of the nonaqueous gel electrolyte and the nonaqueous electrolyte storage element disclosed in this specification will be described.

[0013] [1] A nonaqueous gel electrolyte according to one aspect of the present invention comprises a crosslinked polymer, a nonaqueous solvent, and an electrolyte salt, wherein the content of the crosslinked polymer is 8 mass % or less, the crosslinked polymer has a crosslinking moiety including a structure represented by the following formula (1), and the nonaqueous solvent contains a fluorinated cyclic carbonate:

[0014] [ka] In the above formula (1), * indicates a bonding site to another group or atom.

[0015] The nonaqueous gel electrolyte described in [1] above contains a fluorinated cyclic carbonate as a nonaqueous solvent and has high ionic conductivity and mechanical strength. The reason for this effect is unclear, but the following reasons are presumed. Conventionally, a method using a Michael addition reaction with a base catalyst has been known to form a nonaqueous gel electrolyte with a low polymer content. However, with this method, if the nonaqueous solvent contains a fluorinated cyclic carbonate, the fluorinated cyclic carbonate reacts with the base catalyst, preventing the gelation reaction from proceeding. As a result, the nonaqueous gel electrolyte is not formed, or even if it is formed, the mechanical strength is low. On the other hand, the nonaqueous gel electrolyte described in [1] above can be obtained by, for example, crosslinking two types of monomers in a 1:1 ratio by a thiol-ene reaction using a radical generator in a nonaqueous solvent containing a fluorinated cyclic carbonate to obtain a crosslinked polymer having a crosslinking moiety containing the structure represented by the following formula (1). This crosslinked polymer, the nonaqueous solvent, and the electrolyte salt form a gel-like nonaqueous electrolyte.

[0016] [ka] In the above formula (1), * indicates a bonding site to another group or atom.

[0017] As described above, the nonaqueous gel electrolyte described in [1] above is a nonaqueous gel electrolyte having a uniform network structure obtained without undergoing a Michael addition reaction using a base catalyst, and therefore, it is presumed that the nonaqueous gel electrolyte described in [1] above has high mechanical strength. Furthermore, since the content of the cross-linked polymer in the nonaqueous gel electrolyte described in [1] above is 8% by mass or less, it is presumed that the nonaqueous gel electrolyte described in [1] above has high ionic conductivity, and a nonaqueous electrolyte storage element including the nonaqueous gel electrolyte described in [1] above is presumed to have good high-rate charge-discharge characteristics. Furthermore, since the nonaqueous gel electrolyte described in [1] above contains a fluorinated cyclic carbonate in the nonaqueous solvent, a nonaqueous electrolyte storage element including the nonaqueous gel electrolyte described in [1] above can form a stable coating on the negative electrode surface, suppressing decomposition and consumption of the nonaqueous gel electrolyte on the negative electrode surface, and therefore, is presumed to have excellent capacity retention after charge-discharge cycling.

[0018] [Method for measuring type and content of non-aqueous solvent] The type and content of non-aqueous solvents are measured by liquid chromatography mass spectrometry (LC-MS) and gas chromatography mass spectrometry (GC-MS). Specifically, the procedure is as follows. Note that the LC-MS and GC-MS measurements are carried out consecutively under the same conditions. 1. Collection of non-aqueous solvent First, the nonaqueous electrolyte storage element is disassembled to remove the nonaqueous gel electrolyte. The removed nonaqueous gel electrolyte is immersed in a certain amount of an appropriate extraction solvent (e.g., acetonitrile, etc.), and the nonaqueous solvent diluted with the extraction solvent is removed. If the nonaqueous gel electrolyte cannot be removed, a certain amount of an appropriate extraction solvent (e.g., acetonitrile, etc.) is poured into the nonaqueous electrolyte storage element, and the nonaqueous solvent diluted with the extraction solvent is removed. 2.LC-MS The components of the collected non-aqueous solvent are analyzed by LC-MS. The LC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The LC-MS analysis equipment used is a Waters "ACQUITY UPLC H-Class" and "Xevo G2-SQTof." Water is used as the eluent. (qualitative analysis) The measurement sample (non-aqueous solvent diluted with extraction solvent) is subjected to LC-MS analysis. If the peaks in the obtained liquid chromatogram cannot be separated, GC-MS analysis, described below, is performed instead of LC-MS analysis. If the peaks can be separated, the components contained in the measurement sample are predicted from the MS spectrum of each peak. A known sample of the predicted components (hereinafter referred to as "predicted components") is subjected to LC-MS analysis. The retention times and MS spectra of the peaks corresponding to each predicted component in the measurement sample are compared with the retention times and MS spectra 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 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 0.99 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. 3.GC-MS The GC-MS analysis is performed in the following order: qualitative analysis and quantitative analysis. The GC-MS analysis equipment used is the Agilent Technologies "7890A" and "5975C." Helium is used as the carrier gas. (qualitative analysis) The measurement sample (non-aqueous solvent diluted with extraction solvent) is subjected to GC-MS analysis. The components contained in the sample are predicted from the MS spectrum of each peak in the obtained gas chromatogram. A known sample of the predicted components is subjected to GC-MS analysis. The retention time and MS spectrum of the peak corresponding to each predicted component in the measurement sample are compared with the retention time and MS spectrum of the peak of each predicted component in a known sample. If they match, the prediction is assumed to be correct. (Quantitative analysis) Quantitative analysis is performed using a calibration curve method. Quantitative analysis by GC-MS is performed using the same procedure as the quantitative analysis by LC-MS described above, and the content of each predicted component is determined. 4. Calculation of the content of each component For each component of the non-aqueous solvent, the total content of each predicted component (i.e., each component) measured by LC-MS or GC-MS is used to calculate the content of the non-aqueous solvent. When calculating the content (vol %) of each component in the non-aqueous solvent, the mass-based content of each component measured by LC-MS or GC-MS is converted to a volume at 20°C, and the total volume-converted content of each component is used as the content of the non-aqueous solvent. The extraction solvent is excluded from the calculation.

[0019] [Method for measuring the structure of crosslinked polymers] The structure of the crosslinked polymer is identified using one or more of known analytical methods, such as infrared absorption spectroscopy (IR), Raman spectroscopy, and nuclear magnetic resonance spectroscopy (NMR). Measurements of the crosslinked polymer are performed on samples collected using the following procedure. First, the nonaqueous electrolyte storage element is disassembled to extract the nonaqueous gel electrolyte. The extracted nonaqueous gel electrolyte is washed, dried, etc. to remove the electrolyte salt, nonaqueous solvent, etc., and the crosslinked polymer is isolated. If the nonaqueous gel electrolyte cannot be extracted, the nonaqueous electrolyte storage element is disassembled and the extracted electrode assembly is washed, dried, etc. to remove the electrolyte salt, nonaqueous solvent, etc., and the crosslinked polymer attached to the outermost surface of the electrode assembly is then extracted.

[0020] [2] In the nonaqueous gel electrolyte according to the above [1], the crosslinked polymer may have a polyethylene oxide skeleton.

[0021] The crosslinked polymer having a polyethylene oxide skeleton has a high affinity with the nonaqueous solvent and the electrolyte salt, and therefore, in the nonaqueous gel electrolyte described in [2] above, the nonaqueous solvent is less likely to bleed out over time, and the gel state is highly stable.

[0022] [3] In the nonaqueous gel electrolyte according to the above [1] or [2], the crosslinked site may have an electron-withdrawing group.

[0023] The presence of an electron-withdrawing group in the crosslinking site facilitates the thiol-ene reaction, resulting in the formation of a more uniform network structure in the nonaqueous gel electrolyte described in [3] above, which has higher mechanical strength.

[0024] [4] In the nonaqueous gel electrolyte according to any one of [1] to [3] above, the content of the fluorinated cyclic carbonate in the nonaqueous solvent may be 20% by volume or more.

[0025] In the nonaqueous gel electrolyte described in [4] above, the content of the fluorinated cyclic carbonate in the nonaqueous solvent is 20% by volume or more, and therefore a nonaqueous electrolyte storage element including the nonaqueous gel electrolyte described in [4] above forms a more stable coating on the negative electrode surface, resulting in excellent capacity retention after charge-discharge cycling. Therefore, the nonaqueous gel electrolyte described in [4] above can provide a nonaqueous electrolyte storage element with good charge-discharge cycle life performance.

[0026] [5] A nonaqueous electrolyte storage element according to another aspect of the present invention includes the nonaqueous gel electrolyte according to any one of [1] to [4] above.

[0027] The nonaqueous electrolyte storage element described in [5] above has a nonaqueous gel electrolyte with high ionic conductivity and mechanical strength, and therefore has an excellent capacity retention rate after charge-discharge cycles.

[0028] [6] The nonaqueous electrolyte storage element according to the above item [5] may further include a negative electrode active material layer, and the negative electrode active material layer may contain a silicon-based negative electrode active material or metallic lithium.

[0029] The nonaqueous electrolyte storage element described in [6] above includes a nonaqueous gel electrolyte with high ionic conductivity and mechanical strength, and therefore can suppress the occurrence of cracks in the negative electrode active material layer even when using a silicon-based negative electrode active material that undergoes relatively large expansion and contraction during charge and discharge, and can suppress the dendritic deposition of metallic lithium on the negative electrode surface during charge even when metallic lithium is used (hereinafter, metallic lithium in a dendritic form will be referred to as "dendrite"). Therefore, the nonaqueous electrolyte storage element described in [6] above has an excellent capacity retention rate after charge and discharge cycles.

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

[0031] <Non-aqueous gel electrolyte> A nonaqueous gel electrolyte according to one embodiment of the present invention comprises a crosslinked polymer, a nonaqueous solvent, and an electrolyte salt, wherein the content of the crosslinked polymer is 8 mass % or less, the crosslinked polymer has a crosslinking moiety including a structure represented by the following formula (1), and the nonaqueous solvent contains a fluorinated cyclic carbonate:

[0032] [ka] In the above formula (1), * indicates a bonding site to another group or atom.

[0033] (Crosslinked polymer) The crosslinked polymer is a crosslinked polymer having a crosslinking site containing a structure represented by the following formula (1).

[0034] [ka] In the above formula (1), * indicates a bonding site to another group or atom.

[0035] The crosslinked polymer may be a polymer having a three-dimensional network structure. The crosslinked polymer may be a polymer obtained by a crosslinking reaction of one or more monomers including a monomer having three or more crosslinkable groups. In one embodiment of the present invention, the crosslinked polymer is preferably a polymer obtained by a crosslinking reaction by a thiol-ene reaction using a radical generator.

[0036] The cross-linked polymer has a polyethylene oxide backbone ((-CH2CH2O-) n (n is a natural number). The total of n's of the polyethylene oxide skeletons of the crosslinked polymer is preferably 1×10 2 More than 1×10 50 Less than 1×10 is preferred 10 More than 1×10 40 Less than 1×10 is preferable. 15 More than 1×10 30 The following is even more preferred:

[0037] The crosslinking moiety containing the structure represented by the above formula (1) preferably has an electron-withdrawing group, that is, a structure represented by the following formula (1A).

[0038] [ka] In the above formula (1A), R 1 is an electron-withdrawing group. * indicates a bonding site with another group or atom.

[0039] In the above formula (1A), R 1 Examples of the electron-withdrawing group represented by the formula (I) include a carbonyl group (-C(=O)-) and a sulfonyl group (-S(=O)-), with a carbonyl group being preferred. The carbonyl group may be a part of an ester group, an imide group, or the like.

[0040] In the above formula (1A), R 1The two carbon atoms between R and S may be bonded to at least two hydrogen atoms in total, or may be bonded to at least three hydrogen atoms in total. The carbon atom bonded to S may be bonded to at least one hydrogen atom. Furthermore, the carbon atom bonded to S may be bonded to at least one hydrogen atom, and R 1 The carbon atom bonded to S may be bonded to two hydrogen atoms. That is, the structure represented by the above formula (1) may be a structure represented by the following formula (1B). In this case, the carbon atom bonded to S may further be bonded to a carbonyl group.

[0041] [ka] In the above formula (1B), R 1 is an electron-withdrawing group. * indicates a bonding site with another group or atom.

[0042] The crosslinked polymer may be used alone or in combination of two or more.

[0043] The lower limit of the content of the crosslinked polymer in the nonaqueous gel electrolyte is preferably 1% by mass, more preferably 2%, 3%, 4%, or 5% by mass, based on the total mass of the nonaqueous gel electrolyte. On the other hand, the upper limit of the content of the crosslinked polymer is 8% by mass, more preferably 7%, 6%, or 5% by mass. The content of the crosslinked polymer may be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits. The nonaqueous gel electrolyte has a uniform network structure and therefore high mechanical strength. Furthermore, by setting the content of the crosslinked polymer in the nonaqueous gel electrolyte to a relatively low range, the amounts of nonaqueous solvent and electrolyte salt contained in the nonaqueous gel electrolyte can be increased, thereby improving ionic conductivity. Furthermore, in the nonaqueous gel electrolyte according to one embodiment of the present invention, a crosslinked polymer having a polyethylene oxide skeleton is used, thereby ensuring high stability of the gel state even when the content of the crosslinked polymer is relatively low.

[0044] (non-aqueous solvent) The nonaqueous solvent contains a fluorinated cyclic carbonate. The fluorinated cyclic carbonate can form a good coating on the negative electrode surface. Therefore, by including a fluorinated cyclic carbonate in the nonaqueous solvent, decomposition and consumption of the nonaqueous gel electrolyte on the negative electrode surface can be reduced. Furthermore, the capacity retention rate after charge-discharge cycling can be improved, particularly in a nonaqueous electrolyte storage element having a negative electrode using a silicon-based active material.

[0045] Fluorinated cyclic carbonate is a type of cyclic solvent, and refers to a compound in which some or all of the hydrogen atoms of a cyclic carbonate are substituted with fluorine atoms. Examples of fluorinated cyclic carbonates include fluorinated ethylene carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC), fluorinated propylene carbonates such as 3,3,3-trifluoropropylene carbonate, and fluorinated butylene carbonate. Among these, fluorinated ethylene carbonate is preferred, and FEC is more preferred. FEC has high oxidation resistance and can sufficiently increase the capacity retention rate after charge-discharge cycling in nonaqueous electrolyte storage elements. One or more fluorinated cyclic carbonates can be used.

[0046] The lower limit of the content of the fluorinated cyclic carbonate in the nonaqueous solvent is preferably 20% by volume, more preferably 22% by volume, even more preferably 24% by volume, even more preferably 26% by volume or 28% by volume, and particularly preferably 30% by volume. By setting the content of the fluorinated cyclic carbonate to be equal to or greater than the above lower limit, the capacity retention rate after charge-discharge cycling of the nonaqueous electrolyte storage element can be increased. The upper limit of the content of the fluorinated cyclic carbonate in the nonaqueous solvent is preferably 80% by volume, more preferably 60% by volume, even more preferably 50% by volume, even more preferably 40% by volume, and particularly preferably 35% by volume. By setting the content of the fluorinated cyclic carbonate to be equal to or less than the above upper limit, it is possible to further reduce the amount of gas generated during charge-discharge cycling of the nonaqueous electrolyte storage element and improve the ionic conductivity of the nonaqueous gel electrolyte. The content of the fluorinated cyclic carbonate in the nonaqueous solvent can be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits.

[0047] The non-aqueous solvent may contain a non-aqueous solvent other than the fluorinated cyclic carbonate. Examples of the other non-aqueous solvent include a fluorinated chain carbonate, a non-fluorinated cyclic carbonate, a non-fluorinated chain carbonate, an ester, an ether, etc. The fluorinated chain carbonate is, for example, R a -O-CO-OR b (R a is a fluorinated alkyl group. b is an alkyl group or a fluorinated alkyl group. b is preferably an alkyl group. a and R b Each of the groups preferably has 1 to 3 carbon atoms, and more preferably 1 or 2 carbon atoms.

[0048] Examples of the fluorinated chain carbonate include fluoromethyl methyl carbonate, fluoroethyl methyl carbonate, difluoroethyl methyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl)carbonate, methylfluoropropyl carbonate, methyldifluoropropyl carbonate, methyltrifluoropropyl carbonate, methyltetrafluoropropyl carbonate, methylpentafluoropropyl carbonate, bis(trifluoropropyl)carbonate, bis(tetrafluoropropyl)carbonate, bis(pentafluoropropyl)carbonate, etc. Among these, 2,2,2-trifluoroethyl methyl carbonate (TFEMC), which is trifluoroethyl methyl carbonate, is preferred.

[0049] Examples of non-fluorinated cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Examples of non-fluorinated chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, etc.

[0050] A cyclic carbonate and a chain carbonate may be used in combination as a non-aqueous solvent. For example, FEC, which is a cyclic carbonate, may be used in combination with a chain carbonate (DMC, etc.) as another non-aqueous solvent. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably, for example, in the range of 5:95 to 50:50, and more preferably in the range of 20:80 to 40:60.

[0051] The content of the nonaqueous solvent in the nonaqueous gel electrolyte is preferably 60% by mass to 99% by mass, more preferably 70% by mass to 97% by mass, and even more preferably 80% by mass to 95% by mass, based on the total mass of the nonaqueous gel electrolyte. By having the content of the nonaqueous solvent in the nonaqueous gel electrolyte within the above range, it is possible to achieve both high ionic conductivity and high mechanical strength.

[0052] (electrolyte salt) The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0053] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, lithium oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0054] The content of the electrolyte salt in the non-aqueous gel electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 It is more preferable that it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 It is more preferable that it is 0.7 mol / dm or less. 3 More than 1.5mol / dm 3By setting the content of the electrolyte salt within the above range, the ionic conductivity of the nonaqueous gel electrolyte can be increased.

[0055] (Other ingredients) The nonaqueous gel electrolyte may contain additives in addition to the crosslinked polymer, nonaqueous solvent, and electrolyte salt. Examples of additives include oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); 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; methylvinylene carbonate, succinic anhydride, glutaric anhydride, and sucralose anhydride. Examples of the amines include thaconic acid, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, dimethyl sulfoxide, 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. These additives may be used alone or in combination of two or more.

[0056] The content of the additive in the nonaqueous gel electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass, based on the total mass of the nonaqueous gel electrolyte. By setting the content of the additive within the above range, it is possible to improve the capacity retention or cycle performance after high-temperature storage, and to further improve safety.

[0057] The nonaqueous gel electrolyte may contain a gelation initiator, such as radical generators 2,2'-azobis(isobutyronitrile), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), di-tert-butyl peroxide, 2,2'-azobis(2-methylpropionate)dimethyl, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], bis(1-methyl-1-phenylethyl)peroxide, 1,1'-azobis(cyclohexane-1-carbonitrile), benzoyl peroxide, and dicumyl peroxide. Among these, 2,2'-azobis(isobutyronitrile) is preferred.

[0058] The concentration of the gelation initiator contained in the non-aqueous gel electrolyte is 0.0023 mol / dm 3 More than 0.38mol / dm 3 It is preferable that the value is 0.0038 mol / dm or less. 3 More than 0.23mol / dm 3 It is more preferable that it is 0.0053 mol / dm or less. 3 More than 0.15mol / dm 3 It is more preferable that it is 0.0076 mol / dm or less. 3 More than 0.076mol / dm 3By setting the content of the gelation initiator within the above range, a nonaqueous gel electrolyte having high ionic conductivity and mechanical strength can be obtained.

[0059] The non-aqueous gel electrolyte can be suitably used as an electrolyte for non-aqueous electrolyte storage elements such as lithium ion secondary batteries.

[0060] <Method of manufacturing nonaqueous gel electrolyte> The method for producing a nonaqueous gel electrolyte according to one embodiment of the present invention is not particularly limited, and can be carried out, for example, by crosslinking one or more compounds (monomers) that undergo a crosslinking reaction in a nonaqueous solvent in the presence of a gelation initiator. At this time, an electrolyte salt or the like may be further dissolved in the nonaqueous solvent. The method for producing a nonaqueous electrolyte storage element described below also includes a method for producing a nonaqueous gel electrolyte.

[0061] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element (hereinafter also simply referred to as "storage element") according to one embodiment of the present invention comprises an electrode assembly having a positive electrode, a negative electrode, and a separator, a nonaqueous gel electrolyte, and a container that accommodates the electrode assembly and the nonaqueous gel electrolyte. The electrode assembly is typically a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with separators interposed therebetween, or a wound type in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and wound. The nonaqueous gel electrolyte is typically present in a state in which it is impregnated into the positive electrode, the negative electrode, and the separator. As an example of a nonaqueous electrolyte storage element, a nonaqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0062] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0063] The positive electrode substrate is electrically conductive. Whether or not it has "electrical conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 -2The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy of these. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Positive electrode substrates include foils, vapor-deposited films, meshes, and porous materials, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0064] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0065] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0066] The positive electrode active material layer contains a positive electrode active material and, if necessary, optional components such as a conductive agent, a binder, a thickener, and a filler.

[0067] The positive electrode active material can be appropriately selected from known positive electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the positive electrode active material for a lithium ion secondary battery. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having an α-NaFeO2 crystal structure include Li[Lix Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), Li[Li x Ni γ Co β Al (1-x-γ-β) ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β). Lithium transition metal composite oxides with spinel-type crystal structures include Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0068] As the positive electrode active material, lithium transition metal composite oxides having an α-NaFeO2-type crystal structure or a spinel-type crystal structure, and polyanion compounds containing nickel, cobalt, or manganese (LiMnPO4, LiNiPO4, LiCoPO4, Li2MnSiO4, Li2CoPO4F, etc.) are preferred, with lithium transition metal composite oxides having an α-NaFeO2-type crystal structure being more preferred. Among lithium transition metal composite oxides having an α-NaFeO2-type crystal structure, those containing one or more transition metal elements selected from nickel, cobalt, and manganese are more preferred. The lithium transition metal composite oxide may further contain a typical metal element such as aluminum.

[0069] The lower limit of the content of the lithium transition metal composite oxide relative to all the positive electrode active materials in the positive electrode active material layer is preferably 50 mass%, more preferably 80 mass%, and even more preferably 95 mass%, and the content of the lithium transition metal composite oxide relative to all the positive electrode active materials in the positive electrode active material layer may be 100 mass%.

[0070] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to the above lower limit or more, the positive electrode active material becomes easier to manufacture and handle. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. The "average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0071] To obtain powders with a predetermined particle size, grinders, classifiers, etc. are used. Grinding methods include, for example, methods using a mortar, ball mill, sand mill, vibration ball mill, planetary ball mill, jet mill, counter jet mill, swirling airflow jet mill, or sieves. Wet grinding in the presence of water or an organic solvent such as hexane can also be used during grinding. As classification methods, sieves, air classifiers, etc. are used as needed for both dry and wet methods.

[0072] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 95% by mass. By setting the content of the positive electrode active material within this range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0073] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, etc. Examples of carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, etc. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, carbon black, etc. Examples of carbon black include furnace black, acetylene black, ketjen black, etc. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, etc. Examples of CNT include single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT). The conductive agent may be in the form of powder, fiber, etc. As the conductive agent, one of these materials may be used alone, or two or more may be mixed and used. Furthermore, these materials may be used in combination. For example, a composite material of carbon black and CNT may be used.

[0074] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the content of the conductive agent within this range, the energy density of the nonaqueous electrolyte storage element can be increased.

[0075] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0076] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the binder content within this range, the positive electrode active material can be stably maintained.

[0077] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0078] The filler is not particularly limited, and examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof.

[0079] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0080] The positive electrode active material layer may be porous. The porosity of the positive electrode active material layer is preferably 10% or more and 50% or less, and more preferably 20% or more and 40% or less. When the porosity of the positive electrode active material layer is within the above range, charge / discharge performance can be further improved. The voids of the porous positive electrode active material layer may be impregnated with a nonaqueous gel electrolyte according to one embodiment of the present invention.

[0081] The porosity of the positive electrode active material layer refers to a value calculated by the following formula from the true density of the positive electrode active material layer calculated from the true density of each component constituting the positive electrode active material layer and the apparent density of the positive electrode active material layer. Porosity (%) = 100 - (apparent density / true density) x 100

[0082] The apparent density of the positive electrode active material layer is the value obtained by dividing the mass of the positive electrode active material layer by the apparent volume of the positive electrode active material layer. The apparent volume refers to the volume including voids and can be calculated as the product of the average thickness and area of ​​the positive electrode active material layer. The average thickness of the positive electrode active material layer is the average value of thicknesses measured at any five positions. The porosity of the negative electrode active material layer, which will be described later, is also a value calculated by the same method.

[0083] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above, for example.

[0084] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor-deposited films, meshes, and porous materials, with foils being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0085] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while also increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0086] 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.

[0087] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0088] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、Titanium-containing oxides such as TiNb2O7; polyphosphoric acid compounds; silicon carbide; carbon materials such as graphite (graphite), non-graphitic carbon (easily graphitizable carbon or difficult-to-graphitize carbon), etc. Among these materials, silicon-based active materials such as metallic Li or Si and Si oxides are preferred, and silicon-based active materials are more preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used.

[0089] A silicon-based negative electrode active material is an active material containing silicon element. Examples of the silicon-based negative electrode active material include elemental silicon or a compound containing silicon element. Examples of the compound containing silicon element include silicon oxide (SiO x : 0 < x < 2, preferably 0.8 ≤ x ≤ 1.2), silicon nitride, silicon carbide, metal silicon compounds, etc. Examples of the metal silicon compound include compounds containing a metal element such as aluminum element, tin element, zinc element, nickel element, copper element, titanium element, vanadium element, magnesium element, etc. and silicon element. In addition, as the silicon-based negative electrode active material, a composite material such as a SiO / Si / SiO2 composite material, which is a composite material composed of elemental silicon or a compound containing silicon element, may also be used. The silicon-based negative electrode active material can also be one in which the charge transport ions or metal of the non-aqueous electrolyte storage element is pre-doped. That is, for example, the silicon-based negative electrode active material may further contain an alkali metal element such as lithium element or magnesium element, an alkaline earth metal element, etc. The silicon-based negative electrode active material can be used by mixing one kind or two or more kinds. Among the silicon-based negative electrode active materials, elemental silicon and silicon oxide are preferred, silicon oxide is more preferred, and silicon oxide pre-doped with the charge transport ions or metal of the non-aqueous electrolyte storage element is even more preferred.

[0090] The surface of the silicon-based negative electrode active material may be coated with a conductive material such as carbon. The use of such a silicon-based negative electrode active material can enhance the electronic conductivity of the negative electrode active material layer. When the silicon-based negative electrode active material is coated with a conductive material, the mass ratio of the conductive material to the total amount of the silicon-based negative electrode active material and the conductive material coating it is, for example, preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less.

[0091] The shape of the silicon-based negative electrode active material is not particularly limited, but particulate is preferred. The average particle size of the silicon-based negative electrode active material is preferably, for example, 1 nm to 20 μm. By setting the average particle size of the silicon-based negative electrode active material to the above-mentioned lower limit or above, the silicon-based negative electrode active material becomes easier to manufacture and handle. By setting the average particle size of the silicon-based negative electrode active material to the above-mentioned upper limit or below, the silicon-based negative electrode active material can react sufficiently during charging and discharging. Here, "average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50%, based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0092] The negative electrode active material layer containing the silicon-based negative electrode active material may further contain a negative electrode active material other than the silicon-based negative electrode active material. Examples of such other negative electrode active materials include known negative electrode active materials commonly used in lithium ion secondary batteries, such as carbon-based materials, Sn or Sn oxides, titanium-containing oxides, and polyphosphate compounds. Among these materials, it is preferable to contain a carbon-based material. Examples of carbon-based materials include graphite and non-graphitic carbon. As the other negative electrode active material, one of these materials may be used alone, or two or more may be mixed together.

[0093] The negative electrode active material layer may contain metallic lithium. Metallic lithium is a component that functions as a negative electrode active material. Metallic lithium may exist as pure metallic lithium consisting essentially of lithium element alone, or may exist as 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 element.

[0094] When the negative electrode active material layer contains metallic lithium, the negative electrode active material layer may be a layer consisting essentially of metallic lithium. In this case, the content of metallic lithium in the negative electrode active material layer may be 90% by mass or more, 99% by mass or more, or 100% by mass. When the content of metallic lithium in the negative electrode active material layer is equal to or greater than the above lower limit, the energy density of the nonaqueous electrolyte storage element can be further increased. Furthermore, when the negative electrode active material layer contains such a high proportion of metallic lithium, the deposition of dendrites on the surface of the negative electrode active material layer during initial charge / discharge is suppressed, and a rapid decrease in the amount of reversibly usable metallic lithium is suppressed.

[0095] When the negative electrode active material layer contains metallic lithium, the negative electrode active material layer may be metallic lithium foil or lithium alloy foil. In this case, the negative electrode active material layer may be a non-porous layer (solid layer). The average thickness of the negative electrode active material layer is preferably 5 μm or more and 1,000 μm or less, more preferably 10 μm or more and 500 μm or less, and even more preferably 30 μm or more and 300 μm or less.

[0096] "Graphite" refers to graphite that has an average lattice spacing (d 002 ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0097] "Non-graphitic carbon" refers to the carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0098] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic Li as a counter electrode is 0.7 V or higher.

[0099] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0100] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0101] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm to 100 μm. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm to 1 μm. By setting the average particle size of the negative electrode active material to be equal to or greater than the above lower limit, the negative electrode active material can be easily produced or handled. 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. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and classification method can be selected from, for example, the methods exemplified for the positive electrode. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material layer may be in the form of a foil.

[0102] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass to 99% by mass, more preferably 90% by mass to 98% by mass. By setting the content of the negative electrode active material within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0103] The negative electrode active material layer may be porous. The porosity of the negative electrode active material layer is preferably 20% or more and 60% or less, and more preferably 30% or more and 50% or less. When the porosity of the negative electrode active material layer is within the above range, charge / discharge performance can be further improved. The voids of the porous negative electrode active material layer may be impregnated with the nonaqueous gel electrolyte according to one embodiment of the present invention.

[0104] The porosity of the negative electrode active material layer refers to a value calculated by the following formula from the true density of the negative electrode active material layer calculated from the true density of each component constituting the negative electrode active material layer and the apparent density of the negative electrode active material layer. Porosity (%) = 100 - (apparent density / true density) x 100

[0105] (separator) The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of nonaqueous gel electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0106] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere pressure, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; and mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of safety of the nonaqueous electrolyte electricity storage element.

[0107] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0108] The separator may be a nonaqueous gel electrolyte according to one embodiment of the present invention. When the separator is a porous resin film or nonwoven fabric as described above, the pores thereof may be impregnated with the nonaqueous gel electrolyte.

[0109] (non-aqueous gel electrolyte) The nonaqueous gel electrolyte used in the nonaqueous electrolyte storage element is the nonaqueous gel electrolyte according to one embodiment of the present invention. As the nonaqueous gel electrolyte, the nonaqueous gel electrolyte according to one embodiment of the present invention may be used in combination with another nonaqueous gel electrolyte.

[0110] (shape, etc.) The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0111] FIG. 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode assembly 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0112] <Electricity storage device> The nonaqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of nonaqueous electrolyte energy storage elements in automotive power sources such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power sources for electronic devices such as personal computers and communication terminals, or power storage power sources, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte energy storage element included in the energy storage unit.

[0113] 2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte energy storage elements 1, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte energy storage elements.

[0114] <Method of manufacturing nonaqueous electrolyte energy storage element> The method for manufacturing a nonaqueous electrolyte storage element according to one embodiment of the present invention is not particularly limited, and any known method can be used. For example, the method includes the steps of placing a separator or a nonaqueous gel electrolyte between a positive electrode and a negative electrode, and housing the resulting structure in a case, and injecting the nonaqueous gel electrolyte into the case. After injection, the injection port is sealed to obtain a nonaqueous electrolyte storage element.

[0115] <Other embodiments> The nonaqueous gel electrolyte, nonaqueous electrolyte storage element, and method for manufacturing a 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.

[0116] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0117] In the above embodiment, the electrode assembly in which the positive electrode and the negative electrode are stacked with a separator interposed therebetween has been described, but the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state in which a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode.

[0118] In the above embodiment, the crosslinked polymer is mainly described as being obtained by a thiol-ene reaction, but the crosslinked polymer may be obtained by other crosslinking reactions.

[0119] <Example> 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. The main compounds used in the Examples, Comparative Examples and Reference Examples are shown below.

[0120] Monomer A Pentaerythritol tetra(3-mercaptopropionate) (manufactured by Tokyo Chemical Industry Co., Ltd.) represented by the following formula:

[0121] [ka]

[0122] Monomer B A 4-branched polyethylene glycol having a maleimide group at the end, represented by the following formula (number average molecular weight 20,000: manufactured by Aldrich)

[0123] [ka]

[0124] Monomer C A 4-branched polyethylene glycol having an amino group at the end, represented by the following formula (number average molecular weight 20,000: manufactured by Aldrich)

[0125] [ka]

[0126] Base catalyst 1-Ethylimidazole represented by the following formula

[0127] [ka]

[0128] ETPTA (monomer used in Comparative Example 1 and Reference Example 1: molecular weight 428) Trimethylolpropane EO adduct triacrylate represented by the following formula

[0129] [ka]

[0130] AIBN (gelation initiator) 2,2'-azobis(isobutyronitrile) represented by the following formula

[0131] [ka]

[0132] [Example 1] (1) Preparation of non-aqueous gel electrolyte A non-aqueous solvent containing FEC and DMC mixed at a volume ratio of 30:70 was added at a concentration of 1.0 mol / dm 3 A non-aqueous electrolyte solution was obtained by dissolving LiPF6 at a concentration of 0.0076 mol / dm3. Monomer A and AIBN, a gelation initiator, were dissolved in the non-aqueous electrolyte solution to obtain solution A. Separately, monomer B was dissolved in the non-aqueous electrolyte solution to obtain solution B. In the non-aqueous gel electrolyte obtained by mixing and reacting solution A and solution B, the content of the cross-linked polymer, which is the reaction product of monomer A and monomer B, was 5 mass % and the content of AIBN was 0.0076 mol / dm3. 3 Solution A and solution B were prepared so that: The above solutions A and B were mixed to prepare a precursor solution for the nonaqueous gel electrolyte, and this precursor solution was allowed to stand at 60°C for 35 hours. This resulted in the nonaqueous gel electrolyte of Example 1 containing a crosslinked polymer. All of the above operations were carried out in an argon atmosphere.

[0133] (2) Fabrication of non-aqueous electrolyte energy storage element (Preparation of positive electrode) The positive electrode active material has an α-NaFeO2 type crystal structure and LiNi 0.5 Co 0.2 Mn 0.3 A lithium transition metal composite oxide represented by O2 was used. A positive electrode mixture paste was prepared by mixing the positive electrode active material, acetylene black (AB) and single-walled carbon nanotubes (SWCNT) as conductive agents, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone as a dispersion medium. The mass ratio of the positive electrode active material, AB, SWCNT, and PVDF was 98.52:0.4:0.08:1.0 (solid content equivalent). The positive electrode mixture paste was applied to one side of aluminum foil (average thickness 15 μm) as a positive electrode substrate. Thereafter, drying and roll pressing were performed to obtain a positive electrode of Example 1 in which a positive electrode active material layer was formed on the positive electrode substrate. The mass per area of ​​the positive electrode active material layer was 23 mg / cm. 2 The porosity was 30%.

[0134] (Preparation of negative electrode) Silicon oxide (SiO) doped with lithium was used as the negative electrode active material. The negative electrode active material was mixed with flake graphite and single-walled carbon nanotubes (SWCNTs) as conductive agents, styrene butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium to prepare a negative electrode mixture paste. The mass ratio of the negative electrode active material, conductive agent, binder, and thickener was 87.0:2.9:0.1:8.8:1.2 (solid content equivalent). The negative electrode mixture paste was applied to one side of copper foil (average thickness 10 μm) as a negative electrode substrate. The mixture was then dried and roll-pressed to obtain a negative electrode of Example 1 in which a negative electrode active material layer was formed on the negative electrode substrate. The mass per area of ​​the negative electrode active material layer was 4.3 mg / cm. 2 The porosity was 35%.

[0135] (Preparation of solutions for producing non-aqueous gel electrolytes (solution A and solution B)) A non-aqueous solvent containing FEC and DMC mixed at a volume ratio of 30:70 was added at a concentration of 1.0 mol / dm 3A non-aqueous electrolyte solution was obtained by dissolving LiPF6 at a concentration of 0.0076 mol / dm3. Monomer A and AIBN were dissolved in the non-aqueous electrolyte solution to obtain solution A. Separately, monomer B was dissolved in the non-aqueous electrolyte solution to obtain solution B. In the non-aqueous gel electrolyte obtained by mixing and reacting solution A and solution B, the content of the cross-linked polymer, which is the reaction product of monomer A and monomer B, was 5 mass % and the content of AIBN was 0.0076 mol / dm3. 3 Solution A and solution B were prepared so that:

[0136] (Fabrication of non-aqueous electrolyte energy storage element) A polyolefin microporous membrane was used as the separator. The positive electrode and the negative electrode were stacked with this separator between them to produce an electrode assembly. This electrode assembly was housed in a container, and a positive electrode terminal and a negative electrode terminal were attached. Solution A and solution B were mixed to prepare a precursor solution of the nonaqueous gel electrolyte, and this precursor solution was poured into the container, which was then sealed and allowed to stand at a temperature of 60°C for 35 hours. This produced a nonaqueous electrolyte storage element of Example 1, which was equipped with a nonaqueous gel electrolyte containing a crosslinked polymer. All of the above operations were carried out in an argon atmosphere. The capacity density was 3.7 mAh / cm. 2 Here, the "capacity density" is a value determined by dividing the initial discharge capacity obtained in the initial capacity confirmation test described below by the opposing area of ​​the positive electrode active material layer and the negative electrode active material layer.

[0137] [Comparative Examples 1 and 2, Reference Examples 1 to 3] The nonaqueous gel electrolytes of Comparative Examples 1 and 2 and Reference Examples 1 to 3 were obtained in the same manner as in Example 1, except that the type of monomer, the content of polymer, the type of gelation initiator, the content of gelation initiator, the composition of the nonaqueous electrolyte, and the heating temperature in "Preparation of nonaqueous gel electrolyte" were as shown in Table 1.

[0138] [Examples 2 and 3, Comparative Example 5] (1) Preparation of non-aqueous gel electrolyte The nonaqueous gel electrolytes of Examples 2 and 3 and Comparative Example 5 were obtained in the same manner as in Example 1, except that the polymer content, the type of gelation initiator, and the content of gelation initiator were as shown in Table 5.

[0139] (2) Fabrication of non-aqueous electrolyte energy storage element The nonaqueous electrolyte storage elements of Examples 2 and 3 and Comparative Example 5 were obtained in the same manner as in Example 1, except that the nonaqueous gel electrolyte was changed to each of the above nonaqueous gel electrolytes.

[0140] [Comparative Examples 3 and 4] A non-aqueous solvent containing FEC and DMC mixed at a volume ratio of 30:70 was added at a concentration of 1.0 mol / dm 3 LiPF6 was dissolved in the nonaqueous electrolyte solution of Comparative Examples 3 and 4 to obtain the nonaqueous electrolyte solutions of Comparative Examples 3 and 4. Furthermore, a nonaqueous electrolyte storage element of Comparative Example 4 was obtained in the same manner as in Example 1, except that the nonaqueous electrolyte solution of Comparative Example 4 was poured into the container, sealed, and not left to stand at a temperature of 60°C.

[0141] [evaluation] (1) Presence or absence of gelation In "(1) Preparation of non-aqueous gel electrolyte," whether gelation occurred after standing for 35 hours and whether a non-aqueous gel electrolyte was obtained was confirmed visually. If gelation occurred and a non-aqueous gel electrolyte was obtained, it is indicated as "Yes," and if gelation did not occur and a non-aqueous gel electrolyte was not obtained, it is indicated as "No." The results are shown in Tables 1 and 5.

[0142] (2) Ionic conductivity evaluation An ionic conductivity evaluation cell was prepared according to the following procedure. A 10 μm-thick stainless steel foil was used as the working electrode and counter electrode. The working electrode and counter electrode were laminated via a 2 mm-thick PTFE sheet with a 1 cm-diameter circular hole to prepare an electrode body for an ion conductivity evaluation cell. An ion conductivity evaluation cell according to Example 1 was obtained, comprising this electrode body for an ion conductivity evaluation cell and the nonaqueous gel electrolyte of Example 1 (right cylindrical shape: 1 cm diameter, 2 mm thickness). Another ion conductivity evaluation cell according to Comparative Example 3 was obtained, comprising the electrode body for an ion conductivity evaluation cell and the nonaqueous electrolyte of Comparative Example 3. Using these ion conductivity evaluation cells, the ionic conductivities of the nonaqueous gel electrolyte and the nonaqueous electrolyte were determined by AC impedance analysis. The AC impedance was measured at 25°C, with frequencies from 7 MHz to 100 mHz and an amplitude voltage of 10 mV. The ionic conductivity was calculated from the resulting complex impedance using standard methods. The results are shown in Table 2.

[0143] (3) Mechanical properties of non-aqueous gel electrolyte The precursor solution of the nonaqueous gel electrolyte of Example 1 obtained in the "Preparation of Solutions for Producing Nonaqueous Gel Electrolytes (Solution A and Solution B)" section was poured into a resin mold having a right cylindrical cavity with a diameter of 10 mm and a height of 10 mm. The mold was left standing at 60°C for 35 hours to obtain a right cylindrical nonaqueous gel electrolyte test piece (diameter: 10 mm, height: 10 mm) for evaluation of mechanical properties. The obtained nonaqueous gel electrolyte test piece of Example 1 was compressed at a rate of 5 mm / min to evaluate the fracture strength and fracture strain of the nonaqueous gel electrolyte. Specifically, the stress value at the point where the stress, which increases with compression, begins to decrease on the stress-strain curve obtained in the above measurement was taken as the fracture strength, and the strain value at that point was taken as the fracture strain. All operations up to the preparation of the test piece were performed under an argon atmosphere. Measurements were performed at room temperature using an Autograph (registered trademark) AGX-500NV (Shimadzu Corporation). The results are shown in Table 3.

[0144] (4) Performance evaluation of non-aqueous electrolyte energy storage elements (Chemical) Each nonaqueous electrolyte storage element was subjected to formation under the following conditions. At a temperature of 25°C, constant current charging was performed with a charging current of 0.02C and a charging time of 2.5 hours. Subsequently, constant current charging was performed with a charging current of 0.05C and a charging time of 5 hours. A rest period of 12 hours was then allowed. Next, constant current / constant voltage charging was performed with a charging current of 0.05C and a charge cut-off voltage of 4.25V. The charge was terminated until the charging current reached 0.04C. A rest period of 10 minutes was then allowed. Next, constant current discharge was performed with a discharge current of 0.1C and a discharge cut-off voltage of 2.5V. A rest period of 10 minutes was then allowed. Note that 1C=3.7mA / cm 2 is. (Initial capacity confirmation test) Each nonaqueous electrolyte storage element after the above formation was subjected to constant current / constant voltage charging at a temperature of 25°C with a charging current of 0.1 C and a charge cut-off voltage of 4.25 V. The charge was terminated until the charging current reached 0.05 C. A rest period of 10 minutes was then provided. Subsequently, a constant current discharge was performed with a discharge current of 0.1 C and a discharge cut-off voltage of 2.50 V. A rest period of 10 minutes was then provided. The discharge capacity at this time was designated as the "initial discharge capacity."

[0145] (Charge-discharge cycle test) After the initial capacity confirmation test, a charge-discharge cycle test was performed on each of the nonaqueous electrolyte storage elements of Examples 1 to 3 and Comparative Examples 4 and 5 at 25°C as follows. Constant-current, constant-voltage charging was performed with a charging current of 0.5C and a cut-off voltage of 4.25V. The charge was terminated until the charging current reached 0.05C. Subsequently, constant-current discharging was performed with a discharging current of 0.5C and a cut-off voltage of 2.50V. A 10-minute rest period was provided after each charge and discharge. This charge-discharge cycle was repeated 200 times. After the charge-discharge cycle test, a capacity confirmation test after the charge-discharge cycle test was conducted in the same manner as in the "initial capacity confirmation test" described above. The discharge capacity at this time was defined as the "discharge capacity after the charge-discharge cycle test." The discharge capacity after the charge-discharge cycle test was divided by the initial discharge capacity to determine the capacity retention rate (%). The results are shown in Tables 4 and 5.

[0146] (High rate discharge test) After the initial capacity confirmation test, a high-rate discharge test was conducted at 25°C for each of the nonaqueous electrolyte storage elements of Example 1 and Comparative Example 4 in the following manner. Constant-current, constant-voltage charging was performed with a charging current of 0.1 C and a cut-off voltage of 4.25 V. The charging was terminated until the charging current reached 0.05 C. Subsequently, constant-current discharging was performed with a discharging current of 2.0 C and a cut-off voltage of 2.50 V. A 10-minute rest period was provided after each charge and discharge. The discharge capacity at this time was divided by the initial discharge capacity to determine the discharge capacity retention rate (2 C / 0.1 C). The results are shown in Table 4.

[0147] [Table 1]

[0148] As shown in Table 1, gelation occurred in Example 1 and Reference Example 1, which comprised a crosslinked polymer, a nonaqueous solvent, and an electrolyte salt, where the crosslinked polymer had a crosslinking moiety including a structure represented by the following formula (1), and the nonaqueous solvent included a fluorinated cyclic carbonate. However, while gelation occurred in Example 1 when the content of the crosslinked polymer was 8% by mass or less, in Reference Example 1, where the crosslinked polymer did not include the structure represented by the following formula (1), the reaction between monomers proceeded randomly, making it difficult to form a uniform network structure, and a content of the crosslinked polymer of 10% by mass or more was required for gelation to occur.

[0149] [ka] In the above formula (1), * indicates a bonding site to another group or atom.

[0150] Furthermore, in Comparative Example 1, in which the crosslinked polymer did not contain a structure represented by the following formula (1) and the content of the crosslinked polymer was 5% by mass, no gelation occurred. On the other hand, in Comparative Example 2, in which FEC was included as the nonaqueous solvent, gelation using a base catalyst did not occur sufficiently, and a nonaqueous gel electrolyte was not obtained. This is thought to be due to the reaction of FEC with the base catalyst. Note that, as shown in Reference Example 2, when the nonaqueous solvent does not contain a fluorinated cyclic carbonate, the problem of no gelation occurring even when a base catalyst is used does not exist. Furthermore, in Reference Example 3, in which the terminal group of the monomer was changed and a crosslinked polymer was formed by an acid-base reaction, no gelation occurred.

[0151] [Table 2]

[0152] As shown in Table 2, the ionic conductivity of the nonaqueous gel electrolyte of Example 1 was equivalent to that of the nonaqueous electrolytic solution of Comparative Example 3.

[0153] [Table 3]

[0154] Generally, in radical polymerization reactions, when the polymer content is 5% by mass, gelation does not occur, or even if it does occur, the mechanical strength of the resulting gel is low. Therefore, to obtain a gel with a certain mechanical strength, a polymer content of at least 10% to 30% by mass is required. A typical example of a gel produced by a radical polymerization reaction is acrylamide gel obtained by radical polymerization of acrylamide. Regarding the mechanical strength of acrylamide gel, it has been reported that when the polymer content is 6% by mass, the breaking strength is 0.6 MPa and the breaking strain is approximately 85% (see Non-Patent Document 3). On the other hand, as shown in Table 3, the nonaqueous gel electrolyte of Example 1 exhibits significantly higher mechanical strength than the above-mentioned acrylamide gel, despite having a cross-linked polymer content of 5% by mass. This is thought to be due to the uniform network structure of the cross-linked polymer in the nonaqueous gel electrolyte of Example 1.

[0155] [Table 4]

[0156] As shown in Table 4, the nonaqueous electrolyte storage element of Example 1 had high-rate discharge characteristics equivalent to those of Comparative Example 4, which is a nonaqueous electrolyte storage element having a polymer content of 0 mass%, i.e., using a nonaqueous electrolyte solution, and also had a high capacity retention rate after charge-discharge cycling.

[0157] [Table 5]

[0158] As shown in Table 5, the nonaqueous electrolyte storage elements of Examples 1, 2, and 3 had higher capacity retention rates after charge-discharge cycles than the nonaqueous electrolyte storage element of Comparative Example 5, which used a nonaqueous electrolyte solution.

[0159] [Example 4, Comparative Example 6] (1) Fabrication of non-aqueous electrolyte energy storage element (Preparation of positive electrode) The positive electrode active material has an α-NaFeO2 type crystal structure and LiNi 0.5 Co 0.2 Mn 0.3 A lithium transition metal composite oxide represented by O2 was used. The positive electrode active material was mixed with acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone as a dispersion medium to prepare a positive electrode mixture paste. The mass ratio of the positive electrode active material, AB, and PVDF was 92:4:4 (solid content equivalent). The positive electrode mixture paste was applied to one side of aluminum foil (average thickness 15 μm) as a positive electrode substrate. After that, drying and roll pressing were performed to obtain positive electrodes of Example 4 and Comparative Example 6 in which a positive electrode active material layer was formed on the positive electrode substrate. The mass per area of ​​the positive electrode active material layer was 27.3 mg / cm. 2 The porosity was 30%.

[0160] (Preparation of negative electrode) Copper foil (average thickness 10 μm) was prepared as the metal foil constituting the negative electrode substrate. A pure lithium metal plate having a thickness of 100 μm was laminated on the copper foil as the negative electrode active material layer to obtain negative electrodes of Example 4 and Comparative Example 6.

[0161] (Fabrication of non-aqueous electrolyte energy storage element) A nonaqueous electrolyte storage element of Example 4 was fabricated in the same manner as in Example 1, except that the positive electrode and negative electrode of Example 4 were used. Also, a nonaqueous electrolyte storage element of Comparative Example 6 was fabricated in the same manner as in Comparative Example 4, except that the positive electrode and negative electrode of Comparative Example 6 were used. The capacity density was 4.5 mAh / cm 2 Here, the "capacity density" is a value determined by dividing the initial discharge capacity obtained in the initial capacity confirmation test described below by the opposing area of ​​the positive electrode active material layer and the negative electrode active material layer.

[0162] (2) Performance evaluation of non-aqueous electrolyte energy storage elements (Initial capacity confirmation test) Each of the above nonaqueous electrolyte storage elements was subjected to constant current / constant voltage charging at a temperature of 25°C with a charging current of 0.1C and a charge cut-off voltage of 4.4V. The charge was terminated until the charging current reached 0.05C. A rest period of 10 minutes was then provided. Subsequently, a constant current discharge was performed with a discharge current of 0.1C and a discharge cut-off voltage of 2.70V. A rest period of 10 minutes was then provided. This charge / discharge cycle was repeated for two cycles, and the discharge capacity in the second cycle was designated as the "initial discharge capacity." Note that 1C=4.5mA / cm 2 is.

[0163] (Charge-discharge cycle test) After the initial capacity confirmation test, each nonaqueous electrolyte storage element was subjected to a charge-discharge cycle test at 25°C as follows. Constant-current, constant-voltage charging was performed with a charge current of 0.5C and a charge cut-off voltage of 4.4V. Charging was terminated until the charge current reached 0.05C. Subsequently, constant-current discharging was performed with a discharge current of 0.22C and a discharge cut-off voltage of 2.70V. A 10-minute rest period was provided after each charge and discharge. This charge-discharge cycle was repeated 200 times. After the charge-discharge cycle test, a capacity confirmation test after the charge-discharge cycle test was conducted in the same manner as in the "initial capacity confirmation test" described above. The discharge capacity at this time was defined as the "discharge capacity after the charge-discharge cycle test." The discharge capacity after the charge-discharge cycle test was divided by the initial discharge capacity to determine the capacity retention rate (%). The results are shown in Table 6.

[0164] [Table 6]

[0165] As shown in Table 6, the capacity retention rate after charge-discharge cycling of the nonaqueous electrolyte storage element of Example 4 was higher than that of Comparative Example 6, which was a nonaqueous electrolyte storage element with a polymer content of 0 mass %, i.e., using a nonaqueous electrolyte solution. This is thought to be because the mechanical strength of the nonaqueous gel electrolyte of Example 4 was high, suppressing the precipitation of lithium metal dendrites. [Industrial Applicability]

[0166] The nonaqueous gel electrolyte according to the present invention is suitably used as the nonaqueous electrolyte of a nonaqueous electrolyte storage element. [Explanation of symbols]

[0167] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage unit 30 Energy storage device

Claims

1. A cross-linked polymer, a non-aqueous solvent, and an electrolyte salt, The content of the crosslinked polymer is 8% by mass or less, The crosslinked polymer has a crosslinking moiety including a structure represented by the following formula (1): The non-aqueous gel electrolyte, wherein the non-aqueous solvent contains a fluorinated cyclic carbonate. 【Chemistry 1】 In the above formula (1), * indicates a bonding site with another group or atom.

2. 2. The nonaqueous gel electrolyte according to claim 1, wherein the crosslinked polymer has a polyethylene oxide skeleton.

3. The nonaqueous gel electrolyte according to claim 1 , wherein the crosslinked site has an electron-withdrawing group.

4. 2. The nonaqueous gel electrolyte according to claim 1, wherein the content of the fluorinated cyclic carbonate in the nonaqueous solvent is 20% by volume or more.

5. A nonaqueous electrolyte storage element comprising the nonaqueous gel electrolyte according to claim 1 .

6. 6. The nonaqueous electrolyte storage element according to claim 5, further comprising a negative electrode active material layer, the negative electrode active material layer containing a silicon-based negative electrode active material or metallic lithium.

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