Solid electrolytes and batteries

Abstract

This solid electrolyte contains: a polymer containing a structural unit represented by general formula (1); a metal salt; and at least one solvent selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. (In general formula (1), m is 2 or 3, and each R1 is independently a hydrogen atom or a methyl group.)

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte and a battery. [Background technology]

[0002] Unlike liquid electrolytes, solid electrolytes are lightweight and flexible electrolyte membranes that are free from the risk of leakage. Therefore, solid electrolytes are expected to be applied to secondary batteries using lithium ions and the like. As representative solid electrolytes, polyether-based electrolytes and polycarbonate-based electrolytes have been extensively studied. For example, Patent Document 1 proposes a solid electrolyte containing a copolymer containing both ether structural units and carbonate structural units. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 033805 Summary of the Invention [Problem to be solved by the invention]

[0004] Polycarbonate-based electrolytes such as the solid electrolyte described in Patent Document 1 are usually produced by a casting method. However, polycarbonate-based electrolytes produced by the casting method have an oxidation onset potential of about 4 V in a voltage stability evaluation, and further improvement in terms of oxidation resistance has been desired.

[0005] An object of the present invention is to provide a solid electrolyte and a battery having sufficient oxidation resistance. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a solid electrolyte comprising a polymer including a constitutional unit represented by the following general formula (1), a metal salt, and at least one solvent selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate:

[0007] [ka]

[0008] (In the general formula (1), m is 2 or 3, and R 1 are each independently a hydrogen atom or a methyl group.

[0009] In the solid electrolyte according to one aspect of the present invention, it is preferable that the polymer further contains a structural unit represented by the following general formula (2), and the ratio of the structural unit represented by the general formula (1) is 50 mol % or more relative to all structural units of the polymer:

[0010] [ka]

[0011] (In the general formula (2), n is 2 or 3, and R 2 are each independently a hydrogen atom or a methyl group.

[0012] In the solid electrolyte according to one aspect of the present invention, it is preferable that m in the general formula (1) is 2 and n in the general formula (2) is 2.

[0013] In the solid electrolyte according to one embodiment of the present invention, R 1 is a hydrogen atom, and R in the general formula (2) 2 is preferably a hydrogen atom.

[0014] In the solid electrolyte according to one aspect of the present invention, the metal salt is preferably an alkali metal salt.

[0015] In the solid electrolyte according to one aspect of the present invention, the alkali metal salt is preferably a lithium salt.

[0016] In the solid electrolyte according to one aspect of the present invention, the lithium salt preferably includes at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide.

[0017] In the solid electrolyte according to one aspect of the present invention, it is preferable that the solid electrolyte is obtained by casting an electrolyte preparation solution containing the polymer, the metal salt, and the solvent.

[0018] According to one aspect of the present invention, there is provided a battery including the solid electrolyte according to the above aspect of the present invention.

[0019] According to one aspect of the present invention, a solid electrolyte and a battery having sufficient oxidation resistance can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0020] [Solid electrolyte] The present invention will be described below by taking an embodiment as an example, but the present invention is not limited to the content of the embodiment. The solid electrolyte according to this embodiment includes a polymer described below, a metal salt described below, and at least one solvent selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. In the solid electrolyte according to this embodiment, the use of the above-mentioned solvent can improve oxidation resistance. The inventors speculate that the reason for this is as follows. Polycarbonate-based electrolytes can be prepared by a casting method. Specifically, an electrolyte preparation solution is prepared by dissolving a polycarbonate-based polymer, a metal salt, an additive, etc. in a solvent, and the electrolyte preparation solution is then cast onto a fluororesin mold or the like and dried to produce a polycarbonate-based electrolyte. During this process, a small amount of solvent remains in the polycarbonate-based electrolyte. It has been found that this residual solvent reduces oxidation resistance. For example, acetonitrile, which is used as a solvent for preparing solid electrolytes, reacts with lithium and decomposes at around 4 V, resulting in reduced oxidation resistance. In the solid electrolyte according to this embodiment, dimethyl carbonate or the like is used as a solvent for preparation. Even if dimethyl carbonate or the like remains in the solid electrolyte, it does not lead to a decrease in oxidation resistance. Therefore, the present inventors presume that according to this embodiment, a solid electrolyte having sufficient oxidation resistance can be obtained.

[0021] (polymer) The polymer according to this embodiment contains a structural unit (hereinafter sometimes referred to as a carbonate unit) represented by the following general formula (1): Such a polymer can be dissolved in a solvent such as dimethyl carbonate to prepare a preparation solution.

[0022] [ka]

[0023] In the general formula (1), m is 2 or 3, and R 1 are each independently a hydrogen atom or a methyl group. 1 may be the same or different from each other. In this embodiment, m is preferably 2 from the viewpoint of ease of synthesis and improvement of ionic conductivity. 1 is preferably a hydrogen atom. Specifically, a structural unit represented by the following general formula (3) is particularly preferred.

[0024] [ka]

[0025] The polymer according to this embodiment may further contain a structural unit (hereinafter sometimes referred to as an ether unit) represented by the following general formula (2).

[0026] [ka]

[0027] In the general formula (2), n is 2 or 3, and R 2 are each independently a hydrogen atom or a methyl group. 2 may be the same or different from each other. In this embodiment, from the viewpoint of ease of synthesis and improvement of ionic conductivity, n is preferably 2. Furthermore, from the viewpoint of ease of synthesis and improvement of ionic conductivity, R 2 is preferably a hydrogen atom. Specifically, a structural unit represented by the following general formula (4) is particularly preferred.

[0028] [ka]

[0029] The polymer according to the present embodiment may be a homopolymer or a copolymer. The copolymer may be a random copolymer or a block copolymer, but is preferably a random copolymer from the viewpoint of ease of synthesis. The copolymer is preferably a copolymer containing both carbonate units and ether units, but may also be a copolymer containing other structural repeating units.

[0030] When the polymer according to this embodiment is a copolymer, the ratio of the structural units represented by general formula (1) is preferably 50 mol % or more relative to all structural units of the copolymer, from the viewpoint of solubility in solvents such as dimethyl carbonate.

[0031] Furthermore, when the number of moles of the structural unit represented by general formula (1) in this copolymer is x (mol) and the number of moles of the structural unit represented by general formula (2) is y (mol), it is preferable that the condition represented by the following formula (F1) is satisfied. 0.5≦[x / (x+y)]≦0.99 (F1) When the value of [x / (x+y)] is equal to or greater than the lower limit, the ether units in the copolymer can be prevented from forming a strong solvation structure with cations, thereby improving the cation transference number of the solid electrolyte. Furthermore, the decomposition reaction known as backbiting (the formation of cyclic carbonates by depolymerization), which is specific to polymers containing carbonate units, can be suppressed, improving the heat resistance of the copolymer. On the other hand, when the value of [x / (x+y)] is equal to or less than the upper limit, the glass transition temperature of the copolymer can be lowered, improving the ionic conductivity of the solid electrolyte. From the above viewpoint, the value of [x / (x+y)] is more preferably 0.5 or more and 0.97 or less, even more preferably 0.5 or more and 0.95 or less, and particularly preferably 0.5 or more and 0.9 or less. Here, [x / (x+y)] represents the molar ratio of carbonate units in the copolymer.

[0032] The molecular weight of the polymer according to this embodiment, when expressed as a weight average molecular weight (Mw), is preferably 5,000 or more and 5,000,000 or less, and more preferably 10,000 or more and 1,000,000 or less, in terms of standard polystyrene, measured by gel permeation chromatography (GPC). Furthermore, when expressed as a number average molecular weight (Mn), it is preferably 3,000 or more and 3,000,000 or less, and more preferably 5,000 or more and 500,000 or less. The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is preferably 1 or more and 10 or less, and more preferably 1.1 or more and 5 or less.

[0033] The content of the polymer in the solid electrolyte is preferably 5% by mass or more and 99% by mass or less, and more preferably 10% by mass or more and 95% by mass or less, relative to 100% by mass of the solid electrolyte.

[0034] When a copolymer containing both carbonate units and ether units is used as the polymer according to this embodiment, the copolymer can be prepared by the following method. For example, as described in the Examples below, it can be produced by copolymerizing an epoxide monomer (e.g., ethylene oxide) with carbon dioxide in the presence of a polymerization catalyst. Specifically, ethylene oxide undergoes ring-opening to form a constitutional unit represented by general formula (4), and a portion of the ethylene oxide undergoes ring-opening polymerization with carbon dioxide to form a constitutional unit represented by general formula (3).

[0035] The polymerization catalyst used in producing the copolymer is not particularly limited, and examples thereof include metal salen complex catalysts (for example, cobalt salen complex catalysts, etc.) and organozinc catalysts.

[0036] The amount of the polymerization catalyst used in the copolymerization reaction of an epoxide monomer with carbon dioxide is, for example, in the case of a metal-salen complex catalyst, preferably 0.05 mol or less, more preferably 0.01 mol or less, and particularly preferably 0.001 mol or less per mol of the epoxide monomer. Also, for example, in the case of an organozinc catalyst, the amount is preferably 0.2 mol or less, more preferably 0.1 mol or less, and particularly preferably 0.05 mol or less per mol of the epoxide monomer. Furthermore, when using a metal-salen complex catalyst, a co-catalyst can be used. As the co-catalyst, for example, an onium salt compound is preferable. Specific examples of the onium salt compound are not particularly limited, but from the viewpoint of high reaction activity, bis(triphenylphosphoranylidene)ammonium chloride (PPNCl), piperidine, bis(triphenylphosphoranylidene)ammonium fluoride (PPNF), ammonium pentafluorobenzoate (PPNOBzF), and tetra-n-butylammonium chloride (nBuNCl) are preferable.

[0037] The optimum polymerization conditions vary depending on the type of catalyst, but for example, the carbon dioxide pressure in the reaction vessel is 0.1 MPa or more and 10 MPa or less, preferably 0.5 MPa or more and 7.0 MPa or less. In addition, the polymerization temperature is preferably about room temperature (25°C) in the case of a cobalt salen complex catalyst, for example, from the viewpoint of good catalytic activity and accelerated reaction rate, and in the case of an organozinc catalyst, for example, the polymerization temperature is about 40°C or higher and 100°C or lower, preferably about 60°C or higher and 80°C or lower.

[0038] In the method of copolymerizing an epoxide monomer with carbon dioxide, examples of the epoxide monomer used as a starting material include ethylene oxide and propylene oxide.

[0039] (metal salts) The metal salt according to the present embodiment is not particularly limited, but may be, for example, at least one alkali metal salt, such as lithium salt, sodium salt, or potassium salt.

[0040] In this embodiment, the metal salt is preferably a lithium salt. In the solid electrolyte, the metal salt may exist as a cation such as an alkali metal and a counter ion of the cation. If the metal salt is a lithium salt, the energy density will be higher. Examples of lithium salts include LiClO4, LiBF4, LiI, LiPF6, LiCF3SO3, LiCF3COO, LiNO3, LiAsF6, LiSbF6, LiAlCl4, LiCl, LiBr, LiB(C2H5)4, LiCH3SO3, LiC4F9SO3, Li(CF3SO2)2N, Li(C2F5SO2)N, and Li(FSO2)2N. Among these, from the viewpoint of ionic conductivity, it is more preferable to include at least one of Li(CF3SO2)2N (lithium bis(trifluoromethanesulfonyl)imide: LiTFSI) and Li(FSO2)2N (lithium bis(fluorosulfonyl)imide: LiFSI). Multiple types of metal salts may be included in the solid electrolyte.

[0041] In the solid electrolyte according to this embodiment, when the number of moles of the constitutional unit represented by general formula (1) in the polymer is x (mol), the number of moles of the constitutional unit represented by general formula (2) is y (mol), and the number of moles of the metal in the metal salt is z (mol), it is preferable that the condition represented by the following formula (F2) is satisfied. 0.01≦[z / (x+y)]≦2 ···(F2) From the viewpoint of improving ionic conductivity, the value of [z / (x+y)] is more preferably 0.05 or more and 1.8 or less, and even more preferably 0.1 or more and 1.6 or less. When the value of [z / (x+y)] is equal to or greater than the lower limit, ionic conductivity can be sufficiently exhibited. On the other hand, when the value of [z / (x+y)] is equal to or less than the upper limit, the salt can be sufficiently dissolved, thereby suppressing the reduction in ionic conductivity due to the suppression of salt precipitation, and the proportion of polymer is not reduced too much, allowing the solid electrolyte to maintain its solid form. Here, [z / (x+y)] represents the molar ratio of metal (meaning metal derived from metal salt, including metal ions dissociated from metal salt as well as metal not dissociated from metal salt) to the total of carbonate units and ether units in the solid electrolyte. [z / (x+y)] x 100 (unit: mol%) is sometimes referred to as the salt concentration of the solid electrolyte.

[0042] (solvent) The solvent according to the present embodiment is at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. This solvent is capable of dissolving the polymer according to the present embodiment and is necessary for the electrolyte preparation solution for preparing the solid electrolyte. After the solid electrolyte is prepared, a small amount of the solvent remains in the solid electrolyte. However, even if these solvents remain in the solid electrolyte, they do not result in a decrease in oxidation resistance. It is preferable that the electrolyte preparation solution does not contain any solvent other than dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, although solvents other than dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate may be used as long as they do not impair the object of the present invention.

[0043] The amount of at least one solvent selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate in the solid electrolyte is preferably 5% by mass or less, and more preferably more than 0% by mass and 3% by mass or less. If the amount of the solvent is within the above range, the solid electrolyte can be produced by a casting method.

[0044] The solid electrolyte according to this embodiment may contain components other than the polymer, metal salt, and solvent according to this embodiment, as long as the object of the present invention is not impaired.

[0045] For example, the solid electrolyte according to this embodiment may contain a resin known as a resin used in electrolytes, such as a polyethylene oxide resin (PEO-based), a polyacrylonitrile resin (acrylonitrile-based), a polyvinylidene fluoride resin (fluorine-based), a polymethyl methacrylate resin (acrylic-based), or an aliphatic polycarbonate resin.

[0046] Furthermore, for example, the solid electrolyte according to this embodiment may contain a filler or other additives. Examples of fillers include talc, kaolin, clay, calcium silicate, alumina, zirconia, zinc oxide, antimony oxide, indium oxide, tin oxide, titanium oxide, iron oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, silica, calcium carbonate, potassium titanate, barium titanate, mica, montmorillonite, and glass fiber. Among these, it is preferable to include at least one of alumina, zirconia, magnesium oxide, and barium titanate.

[0047] The method for producing the solid electrolyte according to the present embodiment is not particularly limited, but for example, a metal salt may be added after a copolymer is obtained by polymerizing a monomer, or a copolymer may be formed by polymerizing a monomer in the presence of a metal salt. In the former method, for example, a metal salt and a solvent are added to the polymer according to the present embodiment to dissolve the polymer, and the solvent is then removed to obtain a solid electrolyte.

[0048] The form or configuration of the solid electrolyte according to this embodiment is not particularly limited. For example, it may be a membrane-shaped solid electrolyte membrane. The solid electrolyte membrane is preferably self-supporting. A self-supporting solid electrolyte membrane is easy to handle. A self-supporting membrane is a membrane that can be peeled off from a support while maintaining its shape and can be handled. The solid electrolyte membrane can be produced as follows. For example, an electrolyte preparation solution containing the polymer according to this embodiment, a metal salt, and a solvent is prepared, and the electrolyte preparation solution is cast on the surface of a support to form a coating film. The solvent in the coating film is then removed, thereby obtaining a solid electrolyte membrane in a membrane form. In this case, if it is necessary to peel the solid electrolyte membrane from the support, it is preferable that the surface of the support has been subjected to a peeling treatment.

[0049] [battery] The battery according to this embodiment includes the solid electrolyte according to this embodiment. In this embodiment, it is preferable that the solid electrolyte according to this embodiment is included as a constituent material of the electrolyte layer of the battery. The battery is composed of an anode, a cathode, and an electrolyte layer disposed between the anode and the cathode. With this configuration, a battery with excellent characteristics can be obtained. Furthermore, the battery is preferably a secondary battery, and more preferably a lithium ion secondary battery. The solid electrolyte membrane may be formed directly on the electrode by casting an electrolyte preparation solution containing the polymer, metal salt, and solvent onto the electrode and removing the solvent. The various components included in the lithium ion secondary battery according to the present embodiment are not particularly limited, and may be, for example, materials generally used in batteries. The solid electrolyte according to this embodiment has ionic conductivity even if it does not substantially contain a solvent, and therefore, if the battery according to this embodiment contains the solid electrolyte according to this embodiment and is substantially free of a solvent, it can be used safely without leakage.

[0050] The present invention is not limited to the above-described embodiment, and includes modifications and improvements within the scope of achieving the object of the present invention. [Example]

[0051] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Measurements and evaluations in the following examples and comparative examples were carried out by the methods shown below.

[0052] [NMR measurement] The polymer samples were analyzed by nuclear magnetic resonance spectroscopy ( 1 The structure was confirmed using H-NMR (JEOL EX-400 manufactured by JEOL Ltd.) The solvent used was d-chloroform (CDCl3, 0.03% by mass TMS). [Voltage stability evaluation] The voltage stability (oxidation onset potential) of the solid electrolyte was evaluated using linear sweep voltammetry (LSV). A BioLogic VMP3 was used for the measurements. A coin cell was fabricated by contacting one side of the sample solid electrolyte film with a lithium metal electrode and the other side with a SUS substrate, and measurements were performed under the following conditions. Voltage range: 3~6V Scanning speed: 1mV / s Temperature: 25℃

[0053] [Preparation Example 1] (Synthesis of polymerization catalyst) (R,R)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminocyclohexanecobalt(II) ((R,R)-salcyCo II ", manufactured by Sigma-Aldrich Co.) and pentafluorobenzoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) were weighed out in a molar ratio of 1:1.1 and placed in a flask, to which was added dehydrated toluene. The flask was shielded from light with aluminum foil, and the reaction was carried out at room temperature for 20 hours. After the reaction was completed, the solvent was removed under reduced pressure, and the mixture was washed several times with an excess amount of hexane. This was then vacuum dried at room temperature to obtain a cobalt salen complex.

[0054] (Polymerization of Copolymer A) Ethylene oxide was used as the epoxide monomer, and the resulting cobalt salen complex (polymerization catalyst) and bis(triphenylphosphoranylidene)ammonium chloride (PPNCl) as the cocatalyst were weighed out in a molar ratio of monomer:catalyst:cocatalyst = 2000:1:1 and stirred in a pressure vessel. All of these operations were carried out under an argon atmosphere inside the pressure vessel. Next, the pressure vessel was purged with CO2, and then CO2 was introduced into the pressure vessel using a liquid pump. The pressure inside the pressure vessel was set to 2.0 MPa, and the polymerization reaction was carried out at 25°C for 20 hours.

[0055] After the reaction was completed, chloroform was added to the contents of the pressure vessel to prepare a chloroform solution, which was then washed several times with 4M hydrochloric acid. The organic layer was then concentrated using a rotary evaporator, and the concentrated solution was added dropwise to stirring methanol to precipitate the product. Thereafter, the product was dried under reduced pressure in a desiccator using a diaphragm pump, and then vacuum dried at 60° C. to obtain copolymer A. The structure of the obtained copolymer A is 1 The results were confirmed by H-NMR. 1 In addition to H-NMR measurements, we also measured the structure of a commercially available polycarbonate (product name "QPAC-25", manufactured by EMPOWER MATERIALS). 1 H-NMR measurement and the analysis of commercially available polyethylene oxide (Sigma-Aldrich) 1 H-NMR measurements were performed. Based on these measurement results, the ratio of carbonate units to ether units was estimated from the integral ratio of the corresponding methylene hydrogens. The molar ratio of carbonate units in copolymer A ([x / (x+y)] × 100) was 70 mol%.

[0056] [Preparation Example 2] (Synthesis of polymerization catalyst) 1.33 g of potassium hexacyanocobaltate(III) (K3[Co(CN)6], Wako Pure Chemical Industries, Ltd.) was dissolved in 20 mL of deionized water and added dropwise over 45 min to a vigorously stirred ZnCl2 solution (11.42 g of ZnCl2 dissolved in a mixture of 60 mL of deionized water and 30 mL of t-butyl alcohol) at 50 °C. The mixture was then vigorously stirred for 60 min. The resulting white suspension was centrifuged at 5,000 rpm to isolate a white solid. The isolated white solid was resuspended in a solution of t-butyl alcohol and deionized water (volume ratio: t-butyl alcohol:deionized water = 5:5) with vigorous stirring for 30 min. The centrifugation and resuspension were then repeated several times by gradually increasing the amount of t-butyl alcohol to water (volume ratio: t-butyl alcohol:deionized water, changed from 6:4 to 7:3, 8:2, and 9:1). Finally, the white solid was resuspended in t-butyl alcohol and isolated by centrifugation, and then dried under vacuum at 50 °C to a constant weight to obtain the DMC catalyst Zn3(Co[CN]6)2.

[0057] (Polymerization of Copolymer B) The obtained DMC catalyst was used as a catalyst, and 5 mg of DMC catalyst was weighed out per 5 mL of monomer. Copolymer B was obtained in the same manner as in Preparation Example 1, except that the pressure in the pressure vessel was 1.0 MPa and the temperature was 40°C. The molar ratio of carbonate units in the obtained copolymer B [x / (x+y)×100] was 58 mol%.

[0058] [Preparation Example 3] (Polymerization of Copolymer C) The DMC catalyst obtained in Preparation Example 2 was used as the catalyst, and 5 mg of DMC catalyst was weighed out per 5 mL of monomer. Copolymer C was obtained in the same manner as in Preparation Example 1, except that the pressure in the pressure vessel was set to 3.9 MPa and the temperature was set to 59°C. The molar ratio of carbonate units in the obtained copolymer C [x / (x+y)×100] was 50 mol%.

[0059] [Example 1] Polycarbonate (PEC, product name "QPAC-25", manufactured by EMPOWER MATERIALS) was used as the polymer. LiFSI was weighed so that the salt concentration ([z / (x+y)] × 100) in the solid electrolyte was 120 mol%. The solution was dissolved in a solvent (dimethyl carbonate (DMC)) and thoroughly stirred to obtain an electrolyte solution. The electrolyte solution was then cast onto a fluororesin mold, dried at 60°C for 6 hours under a dry nitrogen atmosphere, and further dried at 60°C for 24 hours under reduced pressure to remove volatile residues, yielding a solid electrolyte membrane. The amount of dimethyl carbonate in the solid electrolyte membrane was 1.5% by mass.

[0060] [Comparative Example 1] Except for using acetonitrile (AN) as the solvent, a solid electrolyte membrane was obtained in the same manner as in Example 1. The amount of acetonitrile in the solid electrolyte membrane was 0.9 mass %.

[0061] [Example 2] A solid electrolyte membrane was obtained in the same manner as in Example 1, except that the copolymer A obtained in Preparation Example 1 was used as the polymer and the salt concentration in the solid electrolyte was 100 mol %. The amount of dimethyl carbonate in the solid electrolyte membrane was 1.5 mass %.

[0062] Comparative Example 2 Except for using acetonitrile (AN) as the solvent, a solid electrolyte membrane was obtained in the same manner as in Example 2. The amount of acetonitrile in the solid electrolyte membrane was 1.3 mass %.

[0063] [Example 3] A solid electrolyte membrane was obtained in the same manner as in Example 1, except that the copolymer B obtained in Preparation Example 2 was used as the polymer. The amount of dimethyl carbonate in the solid electrolyte membrane was 1.5 mass %.

[0064] Comparative Example 3 Except for using acetonitrile (AN) as the solvent, a solid electrolyte membrane was obtained in the same manner as in Example 3. The amount of acetonitrile in the solid electrolyte membrane was 1.1 mass %.

[0065] [Example 4] A solid electrolyte membrane was obtained in the same manner as in Example 1, except that the copolymer C obtained in Preparation Example 3 was used as the polymer and the salt concentration in the solid electrolyte was 100 mol %. The amount of dimethyl carbonate in the solid electrolyte membrane was 1.3 mass %.

[0066] Comparative Example 4 Except for using acetonitrile (AN) as the solvent, a solid electrolyte membrane was obtained in the same manner as in Example 4. The amount of acetonitrile in the solid electrolyte membrane was 1.0 mass %.

[0067] Comparative Example 5 Polyethylene oxide (PEO, manufactured by Sigma-Aldrich) was used as a polymer, and LiFSI was weighed so that the salt concentration ([z / (x+y)]×100) in the solid electrolyte was 120 mol%. The mixture was mixed with a solvent (dimethyl carbonate (DMC)) and stirred thoroughly to obtain an electrolyte solution. However, polyethylene oxide was insoluble, and a solid electrolyte membrane could not be fabricated.

[0068] [Evaluation of solid electrolytes] The voltage stability of the solid electrolyte membranes obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was evaluated. The results are shown in Table 1. Note that in Comparative Example 5, a solid electrolyte membrane could not be produced, so voltage stability was not evaluated. Table 1 also shows the type of polymer, the molar ratio of carbonate units, the salt concentration, and the type of solvent in Examples 1 to 4 and Comparative Examples 1 to 5.

[0069] [Table 1]

[0070] As is clear from the results shown in Table 1, the solid electrolyte membranes obtained in Examples 1 to 4, which used dimethyl carbonate as the solvent, had a higher oxidation onset potential and improved oxidation resistance compared to the solid electrolyte membranes obtained in Comparative Examples 1 to 4, which used acetonitrile as the solvent. This confirmed that the solid electrolyte of the present invention has sufficient oxidation resistance.

Claims

1. A polymer containing a structural unit represented by the following general formula (1), A metal salt, and at least one solvent selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, The amount of the solvent in the solid electrolyte is more than 0% by mass and 5% by mass or less. solid electrolyte. 【Chemical 1】 (In the general formula (1), m is 2 or 3, and R １ are each independently a hydrogen atom or a methyl group.

2. The solid electrolyte according to claim 1, The polymer further contains a structural unit represented by the following general formula (2): the ratio of the structural unit represented by the general formula (1) is 50 mol % or more relative to all structural units of the polymer; solid electrolyte. 【Chemistry 2】 (In the general formula (2), n is 2 or 3, and R ２ are each independently a hydrogen atom or a methyl group.

3. The solid electrolyte according to claim 2, In the general formula (1), m is 2, and in the general formula (2), n is 2. solid electrolyte.

4. The solid electrolyte according to claim 2 or 3, R in the general formula (1) １ is a hydrogen atom, and R in the general formula (2) ２ is a hydrogen atom, solid electrolyte.

5. The solid electrolyte according to any one of claims 1 to 4, The metal salt is an alkali metal salt. solid electrolyte.

6. The solid electrolyte according to claim 5, The alkali metal salt is a lithium salt. solid electrolyte.

7. The solid electrolyte according to claim 6, The lithium salt contains at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide. A solid electrolyte characterized by:

8. The solid electrolyte according to any one of claims 1 to 7, an electrolyte preparation solution containing the polymer, the metal salt, and the solvent is cast; solid electrolyte.

9. The solid electrolyte according to any one of claims 1 to 8 is included. battery.

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