JP7747646B2 - Solid electrolytes and batteries - Google Patents

Description

The present invention relates to a solid electrolyte and a battery.

Unlike liquid electrolytes, solid electrolytes are lightweight, flexible electrolyte membranes that do not leak. Therefore, solid electrolytes are expected to be used in secondary batteries using lithium ions and other materials. Polyether-based electrolytes and polycarbonate-based electrolytes have been extensively studied as representative solid electrolytes. For example, Patent Document 1 proposes a solid electrolyte containing a copolymer containing both ether structural units and carbonate structural units.

International Publication No. 2017/033805

Polycarbonate-based electrolytes, such as the solid electrolyte described in Patent Document 1, are typically produced by a casting method. However, polycarbonate-based electrolytes produced by the casting method have an oxidation onset potential of approximately 4 V in voltage stability evaluations, and further improvement in terms of oxidation resistance is needed.

The object of the present invention is to provide a solid electrolyte and a battery having sufficient oxidation resistance.

According to one aspect of the present invention, there is provided a solid electrolyte comprising 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:

(In the general formula (1), m is 2 or 3, and each ^R1 is independently a hydrogen atom or a methyl group.)

In a solid electrolyte according to one embodiment of the present invention, the polymer further contains a structural unit represented by the following general formula (2), and it is preferable that 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.

(In the general formula (2), n is 2 or 3, and each ^R2 is independently a hydrogen atom or a methyl group.)

In one embodiment of the solid electrolyte 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.

In the solid electrolyte according to one aspect of the present invention, it is preferable that R ¹ in the general formula (1) is a hydrogen atom, and R ² in the general formula (2) is a hydrogen atom.

In one embodiment of the solid electrolyte of the present invention, it is preferable that the metal salt is an alkali metal salt.

In one embodiment of the solid electrolyte of the present invention, it is preferable that the alkali metal salt is a lithium salt.

In one embodiment of the solid electrolyte of the present invention, it is preferable that the lithium salt contains at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide.

In one embodiment of the solid electrolyte 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.

According to one aspect of the present invention, a battery is provided which includes a solid electrolyte according to the above aspect of the present invention.

According to one aspect of the present invention, a solid electrolyte and a battery having sufficient oxidation resistance can be provided.

[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 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.

(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.

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

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):

In the general formula (2), n is 2 or 3, and each ^R2 is independently a hydrogen atom or a methyl group. The multiple ^R2s may be the same or different.
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, ^R2 is preferably a hydrogen atom. Specifically, a constitutional unit represented by the following general formula (4) is particularly preferred.

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.

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

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 copolymer satisfy the condition represented by the following mathematical formula (F1):
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.

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.

The polymer content 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.

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 structural unit represented by general formula (4), and a portion of the ethylene oxide polymerizes with carbon dioxide while undergoing ring-opening to form a structural unit represented by general formula (3).

The polymerization catalyst used in producing the copolymer is not particularly limited, and examples include metal salen complex catalysts (e.g., cobalt salen complex catalysts, etc.) and organozinc catalysts.

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, relative to 1 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, relative to 1 mol of the epoxide monomer.
Furthermore, when a metal-salen complex catalyst is used, 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 ₅ ), tetra-n-butylammonium chloride (nBu ₄ NCl), and the like are preferable.

The optimum polymerization conditions vary depending on the type of catalyst, but for example, the pressure of carbon dioxide 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.
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 favorable catalytic activity and accelerated reaction rate, and is preferably about 40°C or higher and 100°C or lower, preferably about 60°C or higher and 80°C or lower, in the case of an organozinc catalyst, for example.

In the method of copolymerizing epoxide monomers with carbon dioxide, examples of epoxide monomers used as starting materials include ethylene oxide and propylene oxide.

(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 a lithium salt, a sodium salt, or a potassium salt.

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 contain 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 contained in the solid electrolyte.

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, salt can be sufficiently dissolved, suppressing salt precipitation and thereby suppressing a decrease in ionic conductivity. Furthermore, since the proportion of polymer is not excessively reduced, the solid electrolyte can maintain its solid form.
Here, [z/(x+y)] represents the molar ratio of metal (meaning a metal derived from a metal salt, and including not only metal ions dissociated from the metal salt but also metal not dissociated from the metal salt) to the total of carbonate units and ether units in the solid electrolyte. [z/(x+y)]×100 (unit: mol%) is sometimes also referred to as the salt concentration of the solid electrolyte.

(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 the solvent remains in the solid electrolyte, it does 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.

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 greater than 0% by mass and less than 3% by mass. If the amount of this solvent is within the above range, the solid electrolyte can be produced by a casting method.

The solid electrolyte of this embodiment may contain components other than the polymer, metal salt, and solvent of this embodiment, as long as the objective of the present invention is not impaired.

For example, the solid electrolyte of this embodiment may contain resins known to be used in electrolytes, such as polyethylene oxide resin (PEO-based), polyacrylonitrile resin (acrylonitrile-based), polyvinylidene fluoride resin (fluorine-based), polymethyl methacrylate resin (acrylic-based), and aliphatic polycarbonate resin.

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.

The method for producing the solid electrolyte according to this embodiment is not particularly limited. For example, a monomer may be polymerized to obtain a copolymer and then a metal salt may be added, or a monomer may be polymerized in the presence of a metal salt to form a copolymer. In the former method, for example, a metal salt and a solvent may be added to the polymer according to this embodiment to dissolve it, and the solvent may then be removed to obtain a solid electrolyte.

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.

[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.

The present invention is not limited to the above-described embodiments, and modifications, improvements, etc. that achieve the objectives of the present invention are included in the present invention.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples. Measurements and evaluations in the following examples and comparative examples were performed using the methods described below.

[NMR measurement]
The structure of the sample polymer was confirmed using nuclear magnetic resonance spectroscopy ( ¹ H-NMR, JEOL EX-400 manufactured by JEOL Ltd.) The solvent used was d-chloroform (CDCl ₃ , 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 measurement. A coin cell was fabricated by contacting one side of the solid electrolyte film of the sample with a lithium metal electrode and the other side with a SUS substrate, and measurements were performed under the following conditions.
Voltage range: 3 to 6 V
Scanning speed: 1 mV/s
Temperature: 25℃

[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) and pentafluorobenzoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) were weighed out to 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 completion of the reaction, 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.

(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.

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 4 M 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 was confirmed by ¹ H-NMR. Specifically, in addition to ¹ H-NMR measurement of the obtained copolymer A, 1 H-NMR measurement of a commercially available polycarbonate (trade name "QPAC-25", manufactured by EMPOWER MATERIALS) and ¹ H-NMR measurement of a commercially available polyethylene oxide (manufactured by ^Sigma -Aldrich) were also performed. Based on the results of these measurements, 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%.

[Preparation Example 2]
(Synthesis of Polymerization Catalyst)
1.33 g of potassium hexacyanocobaltate(III) ( _K3 [Co(CN) ₆ ], manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 20 mL of deionized water and added dropwise over 45 minutes to a vigorously stirred _ZnCl2 solution (11.42 _g of ZnCl2 dissolved in a mixed solution of 60 mL of deionized water and 30 mL of t-butyl alcohol) at 50°C. The mixture was then vigorously stirred for 60 minutes. 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 of t-butyl alcohol:deionized water = 5:5) with vigorous stirring for 30 minutes. The white solid was then isolated by centrifugation and resuspended several times by gradually increasing the amount of t-butyl alcohol relative to water (varying the volume ratio of t-butyl alcohol to deionized water from 6:4 to 7:3, 8:2, and 9:1). Finally, the white solid was resuspended in t-butyl alcohol and then isolated by centrifugation. The solid was then dried under vacuum at 50°C until a constant weight was obtained, yielding the DMC catalyst _Zn3 (Co[CN] ₆ ) ₂ .

(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. In addition, the pressure in the pressure vessel was set to 1.0 MPa, and the temperature was set to 40 ° C., except that the copolymer B was obtained in the same manner as in Preparation Example 1. The molar ratio of carbonate units in the obtained copolymer B [x / (x + y) × 100] was 58 mol%.

[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%.

[Example 1]
Polycarbonate (PEC, trade name "QPAC-25", manufactured by EMPOWERMATERIALS) as a polymer and LiFSI weighed out so that the salt concentration ([z/(x+y)] × 100) in the solid electrolyte was 120 mol % were dissolved in a solvent (dimethyl carbonate (DMC)) and thoroughly stirred to obtain an electrolyte preparation solution. The electrolyte preparation 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.

[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 %.

[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 %.

[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 %.

[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 %.

[Comparative Example 3]
Aside from 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 %.

[Example 4]
A solid electrolyte membrane was obtained in the same manner as in Example 1, except that 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 %.

[Comparative Example 4]
A solid electrolyte membrane was obtained in the same manner as in Example 4, except that acetonitrile (AN) was used as the solvent. The amount of acetonitrile in the solid electrolyte membrane was 1.0 mass %.

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

[Evaluation of solid electrolyte]
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.

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 confirms that the solid electrolyte of the present invention has sufficient oxidation resistance.

Claims (9)

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.
(In the general formula (1), m is 2 or 3, and each ^R1 is independently a hydrogen atom or a methyl group.) 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.
(In the general formula (2), n is 2 or 3, and each ^R2 is independently a hydrogen atom or a methyl group.) 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. The solid electrolyte according to claim 2 or 3,
R ¹ in the general formula (1) is a hydrogen atom, and R ² in the general formula (2) is a hydrogen atom.
solid electrolyte. The solid electrolyte according to any one of claims 1 to 4,
The metal salt is an alkali metal salt.
solid electrolyte. The solid electrolyte according to claim 5,
The alkali metal salt is a lithium salt.
solid electrolyte. 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: 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. The solid electrolyte according to any one of claims 1 to 8 is included.
battery.