Resin, resin solution, solid electrolyte slurry, solid electrolyte layer, positive electrode layer, negative electrode layer, and all-solid-state battery

Abstract

Provided is a resin which is characterized by: having a structure represented by formula (1); and having at least one terminal structure that is selected from the group consisting of formula (2) and formula (3). (In formula (1), m represents an integer of 3 or more, and each R1 independently represents an alkylene group having 3 to 6 carbon atoms. Each R2 independently represents a divalent organic group. n represents an integer of 5 or more.) (In formula (2), R3 represents an alkyl group having 3 or more carbon atoms, or a phenyl group.) (In formula (3), R4 represents an alkyl group having 3 or more carbon atoms, or a phenyl group.)

Description

Resin, resin solution, solid electrolyte slurry, solid electrolyte layer, positive electrode layer, negative electrode layer, and all-solid-state battery

[0001] The present disclosure relates to a resin suitable for a solid electrolyte binder in a solid secondary battery, a resin solution, a solid electrolyte slurry, a solid electrolyte layer, a positive electrode layer, a negative electrode layer, and an all-solid-state battery.

[0002] In recent years, the demand for secondary batteries as a power source has expanded with the development of portable devices such as tablet computers and smartphones, as well as electric vehicles. Secondary batteries generally consist of electrodes (positive and negative electrodes) and an electrolyte, and charge and discharge occur through the movement of ions between the electrodes via the electrolyte. These secondary batteries are used in a wide range of applications, from small devices such as mobile phones to large devices such as electric vehicles. Therefore, high safety and further improvements in performance are required.

[0003] To prevent fires and improve safety, solid-state secondary batteries have been developed, replacing conventional flammable liquid electrolytes with solid electrolytes. Sulfide-based and oxide-based materials are being widely investigated as solid electrolytes.

[0004] To improve the performance of secondary batteries, it is generally important to increase the contact interface between the active material and solid electrolyte in the electrode, as well as the contact interface between solid electrolyte particles. Here, the active material refers to a substance involved in the reaction that generates electricity. While sulfide-based and oxide-based solid electrolytes have excellent ionic conductivity, it is difficult to increase the interface with the active material, and the film strength may be insufficient. Therefore, the use of a binder has been proposed. Patent Document 1 describes a solid electrolyte dispersion paste containing an acrylic resin. Patent Document 2 also describes a solid electrolyte composition that improves affinity with the solid electrolyte by incorporating urethane bonds, urea bonds, etc. into the main chain.

[0005] JP 2019-050174 A International Publication No. 2020 / 138216

[0006] In recent years, solid secondary batteries have been required to have not only high safety but also higher performance and mass productivity. When resins such as those described in Patent Documents 1 and 2 are used as binders for the positive electrode layer and solid electrolyte layer, the strength of each layer is improved. However, depending on the dispersion conditions, the affinity with the solid electrolyte may be insufficient, and the ionic conductivity of the binder may be insufficient, resulting in an increase in the internal resistance of the secondary battery. Furthermore, when stored at high temperatures for long periods, the internal resistance of the secondary battery may increase due to a reaction at the interface between the solid electrolyte and the binder. Therefore, a polymer electrolyte that has high affinity with the solid electrolyte, high ionic conductivity, and reduced risk of reaction with the solid electrolyte even at high temperatures is desired.

[0007] The present disclosure is directed to providing a resin that has excellent affinity with a solid electrolyte and excellent ionic conductivity and is suitable as a binder for the solid electrolyte. Another aspect of the present disclosure is directed to providing a resin solution, a solid electrolyte slurry, a solid electrolyte layer, a positive electrode layer, a negative electrode layer, and an all-solid-state battery that have excellent performance and high-quality characteristics.

[0008] According to at least one embodiment of the present disclosure, there is provided a resin having a structure represented by the following formula (1) and having at least one terminal structure selected from the group consisting of the following formula (2) and formula (3): (In formula (1), m represents an integer of 3 or more, each R1 independently represents an alkylene group having 3 to 6 carbon atoms, each R2 independently represents a divalent organic group, and n represents an integer of 5 or more.) (In formula (2), R3 represents an alkyl group having 3 or more carbon atoms or a phenyl group.) (In formula (3), R4 represents an alkyl group having 3 or more carbon atoms or a phenyl group.)

[0009] According to at least one aspect of the present disclosure, there is provided a resin solution containing the resin and a solvent. According to at least one aspect of the present disclosure, there is provided a solid electrolyte slurry containing the resin, a solid electrolyte, and a solvent. According to at least one aspect of the present disclosure, there is provided a solid electrolyte layer containing the resin and a solid electrolyte. According to at least one aspect of the present disclosure, there is provided a positive electrode layer containing the resin and a solid electrolyte. According to at least one aspect of the present disclosure, there is provided a negative electrode layer containing the resin and a solid electrolyte.

[0010] Furthermore, according to at least one aspect of the present disclosure, there is provided an all-solid-state battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer, wherein at least one layer of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer contains the resin.

[0011] According to one aspect of the present disclosure, a resin, a resin solution, and a solid electrolyte slurry that have excellent affinity with a solid electrolyte and excellent ionic conductivity and are suitable as a binder for the solid electrolyte can be obtained. In addition, another aspect of the present disclosure can provide a solid electrolyte layer, a positive electrode layer, a negative electrode layer, and an all-solid-state battery that have excellent performance and high-quality characteristics.

[0012] Schematic cross-section of an all-solid-state battery

[0013] In the present disclosure, expressions such as "XX or more and YY or less" or "XX to YY" representing a numerical range mean a numerical range including the lower and upper limits, which are the endpoints, unless otherwise specified. Furthermore, when a numerical range is described in stages, the upper and lower limits of each numerical range can be arbitrarily combined. Furthermore, in the present disclosure, expressions such as "at least one selected from the group consisting of XX, YY, and ZZ" mean any of XX, YY, ZZ, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ. Note that when XX is a group, multiple XXs may be selected, and the same applies to YY and ZZ.

[0014] The present inventors have conducted extensive research to achieve affinity with the solid electrolyte and ionic conductivity, and have found that the use of a urethane resin having a polyether structure with a unit structure having three or more carbon atoms in a solid electrolyte binder for an all-solid-state battery makes it possible to suppress a decrease in the ionic conductivity of the solid electrolyte layer.

[0015] That is, the present disclosure relates to a resin having a structure represented by the following formula (1) and having at least one terminal structure selected from the group consisting of the following formula (2) and formula (3): (In formula (1), m represents an integer of 3 or more, each R1 independently represents an alkylene group having 3 to 6 carbon atoms, each R2 independently represents a divalent organic group, and n represents an integer of 5 or more.) (In formula (2), R3 represents an alkyl group having 3 or more carbon atoms or a phenyl group.) (In formula (3), R4 represents an alkyl group having 3 or more carbon atoms or a phenyl group.)

[0016] After further investigation, the inventors discovered that a urethane resin having a specific structure can maintain ionic conductivity after high-temperature storage and can suppress a decrease in secondary battery capacity during charge-discharge cycles when the urethane resin has a molecular end with a specific chemical structure. Specifically, the resin of the present disclosure satisfies the following conditions: A urethane resin having a polyether structure, wherein the polyether structure has a unit structure containing 3 to 6 carbon atoms. The urethane resin has at least one functional group selected from the group consisting of an alkyl group having 3 or more carbon atoms and a phenyl group at the molecular end. The inventors speculate as follows about the reason why the use of a resin according to the present disclosure as a binder for a solid electrolyte provides the unexpected effect of preventing a decrease in the ionic conductivity of the solid electrolyte layer.

[0017] In a solid electrolyte layer, the binder binds the solid electrolyte particles together and increases the strength of the solid electrolyte layer. However, if the surface affinity between the solid electrolyte particles and the binder is insufficient, voids are likely to form on the surface of the solid electrolyte particles. Furthermore, if the ionic conductivity of the binder at the interface between the solid electrolyte particles and the binder is insufficient, carrier ions such as lithium ions have difficulty moving within the binder. As a result of the above, it is thought that the use of a binder reduces the ionic conductivity of the solid electrolyte layer.

[0018] The urethane group in the resin according to the present disclosure is a polar group. Therefore, it has affinity with the surface of the solid electrolyte. Furthermore, the polyether moiety adjacent to the urethane group has ionic conductivity. As a result, when the resin according to the present disclosure is used as a binder, voids are unlikely to occur on the surface of the solid electrolyte particles, and since the ionic conductive resin is present on the surface of the solid electrolyte, it is believed that the ionic conductivity of the solid electrolyte layer is unlikely to decrease.

[0019] Furthermore, the resin according to the present disclosure has a polyether moiety having a unit structure of three or more carbon atoms, and the resin has a non-reactive hydrophobic group at the molecular end. Therefore, it is thought that it is less likely to react with sulfide-based solid electrolytes, which tend to react with other components of solid electrolytes. Therefore, it is thought that it can maintain ionic conductivity even after high-temperature storage.

[0020] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. The components, materials, shapes, relative arrangements, etc. described in these embodiments do not limit the scope of the present disclosure.

[0021] (1) Configuration of All-Solid-State Battery The all-solid-state battery has a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, and at least one layer of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer contains a resin according to the present disclosure. It is preferable that the positive electrode layer, the solid electrolyte layer, and the negative electrode layer contain a resin according to the present disclosure. It is preferable that the all-solid-state battery contains the resin according to the present disclosure as a binder.

[0022] An example of a secondary battery, which is an all-solid-state battery using the resin of the present disclosure, is shown in Fig. 1. The all-solid-state battery 1 shown in Fig. 1 is an example in which a resin is used as a binder for a solid electrolyte layer 3. The solid electrolyte layer 3 is provided between a positive electrode layer 2 provided on a positive electrode current collector 5 and a negative electrode layer 4 provided on a negative electrode current collector 13.

[0023] The positive electrode layer 2 includes at least a positive electrode active material 6, and may also include a solid electrolyte 8, a positive electrode layer binder 7, and a conductive additive 9. It is preferable to use a resin according to the present disclosure as the positive electrode layer binder 7. That is, the positive electrode layer preferably includes a resin according to the present disclosure and a solid electrolyte.

[0024] The solid electrolyte layer 3 includes a solid electrolyte 8 and a solid electrolyte binder 10. A resin according to the present disclosure is preferably used as the solid electrolyte binder 10. That is, the solid electrolyte layer preferably includes a resin according to the present disclosure and a solid electrolyte.

[0025] The negative electrode layer 4 includes at least a negative electrode active material 11, and may also include a solid electrolyte 8, a negative electrode layer binder 12, and a conductive additive 9. It is preferable to use a resin according to the present disclosure as the negative electrode layer binder 12. In addition to the configuration shown in the figure, the negative electrode layer 4 may also be made of, for example, metallic lithium.

[0026] In order to more effectively achieve the effects of the present disclosure, as shown in Fig. 1, it is preferable that the solid electrolyte layer 3 contains a resin according to the present disclosure as a solid electrolyte binder 10. Furthermore, it is preferable that the positive electrode layer binder 7 in the positive electrode layer 2 and the negative electrode layer binder 12 in the negative electrode layer 4 contain a resin according to the present disclosure.

[0027] (Method of Manufacturing All-Solid-State Battery) An all-solid-state battery (solid secondary battery) can be manufactured by known cell manufacturing methods such as laminate cell type, coin cell type, pressurized cell type, etc. The laminate cell type will be described below as an example.

[0028] A laminate is obtained in which a positive electrode layer, a solid electrolyte, and a negative electrode layer are disposed between a positive electrode current collector and a negative electrode current collector. Electrode tabs are welded to the positive electrode current collector and the negative electrode current collector. The laminate, in which the positive electrode current collector, positive electrode layer, solid electrolyte layer, negative electrode layer, and negative electrode current collector are stacked in this order, is wrapped in an aluminum laminate film and sealed under reduced pressure using a vacuum packaging machine. The ends of the electrode tabs are exposed outside the laminate film, and the tabs and the aluminum laminate film are sealed in a state where they are bonded by thermocompression. After sealing, if necessary, pressure may be applied using an isostatic pressure device or the like. The solid electrolyte may include a polymer electrolyte. In addition to the above laminate, other layers such as elastic materials or resin materials may be stacked within the aluminum laminate film for purposes such as strength and formability. A bipolar type in which multiple laminates are stacked may also be used.

[0029] (Positive electrode current collector) Examples of the positive electrode current collector include metal foil. Examples of metals include aluminum, stainless steel, copper, silver, gold, platinum, nickel, and palladium. The metals may be used alone or in combination of two or more.

[0030] (Positive Electrode Active Material) As the positive electrode active material, for example, a material commonly used in secondary batteries such as lithium ion secondary batteries can be used. For example, (CF) ｍ , (C ２ F) ｍ , MnO ２ , TiS ２ , MoS ２ , FeS ２ , Li ｘＡ CoO ２ , Li ｘＡ NiO ２ , Li ｘＡ MnO ２ , Li ｘＡ Co ｙ Ni １－ｙ O ２ , Li ｘＡ Co ｙ M １－ｙ O ｚ , Li ｘＡ Ni １－ｙ M ｙ O ｚ , Li ｘＢ Mn ２ O４ , Li ｘＢ Mn ２－ｙ M ｙ O ４ (In each of the above formulas, M represents at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B; xA = 0 to 1.2, xB = 0 to 2.0, y = 0 to 0.9, z = 2.0 to 2.3), vanadium oxide and its lithium compound, niobium oxide and its lithium compound, conjugated polymers using organic conductive substances, olivine-based compounds, etc. Note that the xA and xB values ​​in each of the above composition formulas are values ​​before the start of charge and discharge, and increase or decrease with charge and discharge. The positive electrode active material can be used alone or in combination of two or more.

[0031] (Conductive auxiliary material) The conductive auxiliary material can be, for example, a material commonly used in secondary batteries such as lithium-ion secondary batteries. For example, graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fiber and metal fiber, metal powders such as aluminum powder, conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers, conductive metal oxides such as titanium oxide, and organic conductive materials such as phenylene derivatives. The conductive auxiliary material can be used alone or in combination of two or more.

[0032] (Active Material Binder) The active material binder is preferably a resin according to the present disclosure. The active material binder may be an active material binder other than the resin according to the present disclosure.

[0033] Other active material binders that can be used include those commonly used in secondary batteries such as lithium-ion secondary batteries, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose.

[0034] The resin of the present disclosure may be used as a solid electrolyte, a positive electrode active material binder, or a negative electrode active material binder, or may be used as a solid electrolyte, a positive electrode active material binder, and a negative electrode active material binder.

[0035] That is, it is preferable that the all-solid-state battery satisfies at least one of the following (i) to (iii): (i) the positive electrode layer 2 has a positive electrode active material 6, a solid electrolyte 8, and a positive electrode layer binder 7 that fixes the positive electrode active material 6 and the solid electrolyte 8 together, and the positive electrode layer binder 7 is a resin according to the present disclosure; (ii) the solid electrolyte layer 3 has a solid electrolyte 8 and a solid electrolyte binder 10 that fixes the solid electrolyte together, and the solid electrolyte binder 10 is a resin according to the present disclosure; and (iii) the negative electrode layer 4 has a negative electrode active material 11, a solid electrolyte 8, and a negative electrode layer binder 12 that fixes the negative electrode active material 11 and the solid electrolyte 8 together, and the negative electrode layer binder 12 is a resin according to the present disclosure.

[0036] Use of a resin according to the present disclosure as the positive electrode layer binder 7 is particularly preferred because lithium ions can easily reach from the surface to the depths of the positive electrode layer 2. The resin used as the positive electrode layer binder 7 may be one type alone or two or more types in combination.

[0037] The positive electrode layer 2 can be produced, for example, by pressing a premixed positive electrode mixture onto the surface of the positive electrode current collector 5, or by applying a positive electrode mixture slurry to the surface, drying the slurry, and then rolling the slurry as needed. The positive electrode layer 2 can also be prepared by kneading a positive electrode active material, a conductive additive, and a positive electrode layer binder. The positive electrode mixture slurry can also be prepared, for example, by dissolving or dispersing the positive electrode active material, solid electrolyte, conductive additive, and positive electrode layer binder in a medium such as dehydrated xylene, butyl butyrate, mesitylene, anisole, or isobutyronitrile.

[0038] (Negative electrode current collector) Examples of the negative electrode current collector include metal foil. Examples of metals include aluminum, stainless steel, copper, silver, gold, platinum, nickel, and palladium. The metals may be used alone or in combination of two or more.

[0039] (Negative Electrode Active Material) Examples of the negative electrode active material include metals, metal fibers, carbon materials, oxides, nitrides, silicon, silicon compounds, tin, tin compounds, and various alloy materials. Among these, from the viewpoint of capacity density, metals, oxides, carbon materials, silicon, silicon compounds, tin, tin compounds, and the like are preferred. Examples of metals include metallic Li and In—Li, and examples of oxides include Li ４ Ti ５ O １２ (LTO: lithium titanate). Examples of carbon materials include various natural graphites, coke, partially graphitized carbon, carbon fiber, spherical carbon, various artificial graphites, and amorphous carbon. Examples of silicon compounds include silicon-containing alloys, silicon-containing inorganic compounds, silicon-containing organic compounds, and solid solutions. Examples of tin compounds include SnO. Ｂ (0<B<2), SnO ２ , SnSiO ３ , Ni ２ Sn ４ , Mg ２ Examples include Sn.

[0040] The negative electrode material may also contain a conductive additive. Examples of the conductive additive include graphite, such as natural graphite and artificial graphite, and carbon black, such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. When a polymer electrolyte is used as the bulk electrolyte, graphite is particularly suitable as the negative electrode active material.

[0041] Examples of the conductive additive include conductive fibers such as carbon fibers, carbon nanotubes, and metal fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide, conductive metal oxides such as titanium oxide, and organic conductive materials such as phenylene dielectrics.

[0042] (Solid Electrolyte) In all-solid-state batteries, a solid electrolyte is disposed between a positive electrode and a negative electrode as a lithium ion migration layer, and may also be used as a bulk electrolyte that functions as a separator. Furthermore, by mixing the solid electrolyte into the active material layers of the positive and negative electrodes, it can also be used as an auxiliary agent that improves the conductivity of lithium ions.

[0043] The resin according to the present disclosure can be suitably used as a binder in any of the solid electrolyte layer, the positive electrode layer, and the negative electrode layer, thereby enabling the contact interface between the solid electrolyte, the positive electrode active material, and the negative electrode active material to be enlarged, and furthermore, having flexibility that allows the resin to follow the expansion and contraction of the positive electrode active material and the negative electrode active material, thereby improving the characteristics of the secondary battery.

[0044] The auxiliary materials for the solid electrolyte layer, the positive electrode layer, and the negative electrode layer can be solid electrolytes, such as oxide-based solid electrolytes, sulfide-based solid electrolytes, and complex hydride-based solid electrolytes.

[0045] The oxide-based solid electrolyte is Li １．５ Al ０．５ Ge １．５ (P.O. ４ ) ３ and Li １．３ Al ０．３ Ti １．７ (P.O. ４ ) ３Nasicon-type compounds such as Li ６．２５ L.A. ３ ZR ２ Al ０．２５ O １２ The oxide-based solid electrolyte may be a garnet-type compound such as Li ０．３３ Li ０．５５ TiO ３ The oxide-based solid electrolyte includes perovskite-type compounds such as Li １４ Zn(GeO ４ ) ４ Lithium-type compounds such as Li ３ P.O. ４ and Li ４ SiO ４ , Li ３ BO ３ Specific examples of sulfide-based solid electrolytes include Li ６ P.S. ５ Cl, Li ２ S-SiS ２ , LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P ２ S ５ , LiI-Li ２ S-P ２ O ５ , LiI-Li ３ P.O. ４ -P ２ S ５ , Li ２ S-P ２ S ５ The solid electrolyte may be crystalline or amorphous, or may be glass ceramics. ２ S-P ２ S ５ The description of Li ２ S and P ２ S ５ The term "sulfide-based solid electrolyte" refers to a sulfide-based solid electrolyte formed using raw materials containing the above.

[0046] The resin according to the present disclosure can be used as a solid electrolyte binder for a solid electrolyte layer, a positive electrode layer binder, and a negative electrode layer binder. The configuration of the resin according to an embodiment of the present disclosure will be described in detail below.

[0047] <Resin> A resin according to one embodiment of the present disclosure has a structure represented by the following formula (1) and has one terminal structure selected from the group consisting of the following formula (2) and formula (3).

[0048] The resin has a structure represented by the following formula (1). In formula (1), m represents an integer of 3 or greater (preferably 3 to 68, more preferably 17 to 68, even more preferably 30 to 68, particularly preferably 40 to 68, and especially preferably 51 to 68), and R1s each independently represent an alkylene group having 3 to 6 (preferably 4 to 5) carbon atoms. That is, multiple R1s represented by m may be the same or different from each other. m represents the average number of moles added. R2s each independently represent a divalent organic group. That is, multiple R2s represented by n may be the same or different from each other. n represents an integer of 5 or greater (preferably 5 to 130, more preferably 15 to 80, and even more preferably 35 to 50). n represents the degree of polymerization.

[0049] When m is within the above range, the content of polyether contributing to ionic conductivity can be ensured. Furthermore, the concentration of urethane groups that interact with the solid electrolyte is within an appropriate range, thereby enhancing affinity with the solid electrolyte. As a result, the initial ionic conductivity can be increased. When n is within the above range, good binding with the solid electrolyte is achieved, thereby increasing the initial ionic conductivity. Furthermore, an increase in the viscosity of the resin can be suppressed, thereby enabling the formation of a slurry that is relevant to moldability. The value of n can be increased by extending the reaction time for reacting the polyol with the isocyanate compound, and can be decreased by shortening the reaction time.

[0050] In formula (1), R1 represents the number of carbon atoms in the unit structure of the polyether moiety. R1 may be linear or branched. In the resin according to the present disclosure, the polyether moiety in the structure is a hydrophobic polyether having a unit structure with 3 to 6 carbon atoms. From the viewpoints of excellent ionic conductivity and being less susceptible to reaction with the solid electrolyte, it is preferable that the polyether unit structure have 4 to 5 carbon atoms. That is, it is preferable that each R1 is independently an alkylene group having 4 to 5 carbon atoms.

[0051] Examples of the unit structure of the polyether moiety that can be used include 1,2-propylene oxide, 1,3-propylene oxide, 1-ethyl-1,2-ethylene oxide, 1,4-tetramethylene oxide, 1-methyl-1,3-propylene oxide, 2-methyl-1,3-propylene oxide, 2-methyl-1,4-tetramethylene oxide, 1,5-pentamethylene oxide, 1-n-butyl-1,2-ethylene oxide, and 1,6-tetrahexylene oxide.

[0052] The method for obtaining such a polyether moiety is not particularly limited, but can be obtained, for example, by reacting an isocyanate compound described below with a polyol. The polyol is preferably a polyol having at least two hydroxyl groups, and a polyether polyol is preferred. As the polyether polyol, at least one selected from the group consisting of diol-type and triol-type polypropylene glycols, poly 1,4-butanediol, poly 1,5-pentanediol, polyneopentyl glycol, poly 3-methyl-1,4-butanediol, poly 3-methyl-1,5-pentanediol, poly 1,6-hexanediol, poly 1,8-octanediol, poly 1,9-nonanediol, polytetramethylene ether glycol, poly(2-methyl)tetramethylene glycol, and copolymers thereof can be used. Among these, at least one selected from the group consisting of diol-type and triol-type polypropylene glycols, polytetramethylene ether glycols, copolymers of polytetramethylene glycol, and poly(2-methyl)tetramethylene glycol is preferred. The number average molecular weight of the polyol is preferably 300 to 8,000, and particularly preferably 500 to 5,000.

[0053] In formula (1), each R2 independently represents a divalent organic group. The divalent organic group is not particularly limited, but examples thereof include an alkylene group having 1 to 16 carbon atoms (preferably 1 to 10, more preferably 1 to 6), an alkenylene group having 1 to 16 carbon atoms (preferably 1 to 10, more preferably 1 to 6), and an arylene group having 1 to 16 carbon atoms (preferably 1 to 10, more preferably 1 to 6).

[0054] Furthermore, the divalent organic group preferably has a structure derived from an isocyanate compound. The structure derived from an isocyanate compound refers to, for example, the chemical structure of the portion of the isocyanate compound other than the isocyanate group. Examples of the isocyanate compound include isocyanate compounds having two isocyanate groups. Examples include aliphatic polyisocyanates such as ethylene diisocyanate and 1,6-hexamethylene diisocyanate (HMDI); alicyclic polyisocyanates such as isophorone diisocyanate (IPDI), cyclohexane 1,3-diisocyanate, and cyclohexane 1,4-diisocyanate; aromatic isocyanates such as 2,4-toluene diisocyanate (TDI), 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate, and naphthalene diisocyanate, as well as copolymers thereof. These isocyanate compounds can be used alone or in combination of two or more. Among them, the isocyanate compound is preferably at least one selected from the group consisting of MDI (4,4'-diphenylmethane diisocyanate), TDI (2,4-toluene diisocyanate), and HMDI (1,6-hexamethylene diisocyanate).

[0055] A urethane prepolymer can be obtained by reacting a polyol such as the polyether polyol described above with the isocyanate compound described above. The urethane prepolymer refers to a polymer obtained by reacting a polyol with a polyisocyanate. The urethane prepolymer has at least one isocyanate group and a polyether structure. Therefore, the resin according to the present disclosure can be obtained by reacting the urethane prepolymer with a terminal compound described below. In other words, the resin according to the present disclosure is preferably a reaction product of a urethane prepolymer and a terminal compound.

[0056] The content of the isocyanate compound used in synthesizing the urethane prepolymer is preferably 5.0 to 70.0 parts by mass, more preferably 5.0 to 65.0 parts by mass, and even more preferably 8.0 to 50.0 parts by mass, per 100 parts by mass of polyol. The weight-average molecular weight of the urethane prepolymer is not particularly limited, but is preferably 40,000 to 130,000, more preferably 50,000 to 115,000, and even more preferably 60,000 to 90,000. The method for measuring the weight-average molecular weight of the urethane prepolymer will be described later.

[0057] Examples of the terminal compound include at least one compound selected from the group consisting of monohydric alcohols having one hydroxyl group and isocyanate compounds having one isocyanate group. Examples of the monohydric alcohol include alcohols having an alkyl group having 3 or more carbon atoms or a phenyl group, such as propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol, n-pentyl alcohol, neopentyl alcohol, n-hexyl alcohol, cyclohexyl alcohol, n-heptyl alcohol, n-octyl alcohol, 2-methylhexyl alcohol, and phenyl alcohol. In other words, the number of carbon atoms in the monohydric alcohol is preferably 3 to 8. In the case of an alcohol having a phenyl group, the hydrogen atom of the phenyl group may be substituted with an alkyl group having 1 to 3 carbon atoms (more preferably 1 carbon atom), but an unsubstituted phenyl group is preferred.

[0058] Examples of isocyanate compounds having one isocyanate group include isocyanate compounds having an alkyl group having 3 or more carbon atoms or a phenyl group, such as propyl isocyanate, isopropyl isocyanate, n-butyl isocyanate, isobutyl isocyanate, t-butyl isocyanate, n-pentyl isocyanate, neopentyl isocyanate, n-hexyl isocyanate, cyclohexyl isocyanate, n-heptyl isocyanate, octyl isocyanate, 2-methylhexyl isocyanate, and phenyl isocyanate. That is, the number of carbon atoms in an isocyanate compound having one isocyanate group is preferably 4 to 9. In the case of an alcohol having a phenyl group, the hydrogen atom of the phenyl group may be substituted with an alkyl group having 1 to 3 carbon atoms (more preferably 1 carbon atom), but an unsubstituted phenyl group is preferred.

[0059] The content of the structure represented by formula (1) in the resin is preferably 50 to 100% by mass, more preferably 75 to 98% by mass, and even more preferably 85 to 97% by mass.

[0060] The structure represented by formula (1) preferably includes a structure represented by the following formula (1-1) or a structure represented by the following formula (1-2).

[0061] In formula (1-1), m1 and m2 each independently represent an integer of 1 or more (preferably 3 to 30, more preferably 3 to 16), and the sum of m1 and m2 is 3 or more. m1 and m2 represent the average number of moles added. R1a each independently represent an alkylene group having 3 to 6 carbon atoms (preferably 3 to 4, more preferably 4), and R1b each independently represent an alkylene group having 3 to 6 carbon atoms (preferably 5 to 6, more preferably 5). The number of carbon atoms in the alkylene group represented by R1a is different from the number of carbon atoms in the alkylene group represented by R1b. n and R2 are the same as in formula (1).

[0062] In formula (1-2), m3 and m4 each independently represent an integer of 3 or greater (preferably 3 to 68, more preferably 17 to 68, even more preferably 30 to 68, particularly preferably 40 to 68, and especially preferably 51 to 68). m3 and m4 represent the average number of moles added. n1 and n2 each independently represent an integer of 1 or greater (preferably 1 to 130, more preferably 10 to 80). The sum of n1 and n2 is 5 or greater. n1 and n2 represent the degree of polymerization. R1c each independently represent an alkylene group having 3 to 6 carbon atoms (preferably 3 to 4, more preferably 3), and R1d each independently represent an alkylene group having 3 to 6 carbon atoms (preferably 4 to 6, more preferably 4). The number of carbon atoms in the alkylene group represented by R1c is different from the number of carbon atoms in the alkylene group represented by R1d. R2 is the same as in formula (1).

[0063] The resin has at least one terminal structure selected from the group consisting of the following formula (2) and the following formula (3): It is also preferable that the terminal structure of the resin is at least one terminal structure selected from the group consisting of the following formula (2) and the following formula (3): In formula (2), R3 represents an alkyl group having 3 or more carbon atoms or a phenyl group. In formula (3), R4 represents an alkyl group having 3 or more carbon atoms or a phenyl group.

[0064] R3 and R4 are terminal functional groups bonded to the terminal urethane groups, and represent an alkyl group having 3 or more carbon atoms, or a phenyl group. Examples of alkyl groups having 3 or more carbon atoms include a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, a neopentyl group, an n-hexyl group, a cyclohexyl group, an n-heptyl group, an n-octyl group, and a 2-methylhexyl group. That is, the number of carbon atoms in the alkyl group of R3 is preferably 3 to 8, and the number of carbon atoms in the alkyl group of R4 is preferably 3 to 8. When R4 is a phenyl group, a hydrogen atom in the phenyl group may be substituted with an alkyl group having 1 to 3 carbon atoms (more preferably 1 carbon atom), but an unsubstituted phenyl group is preferred.

[0065] <Cationic Structure> The resin has at least one cationic structure selected from the group consisting of a cationic nitrogen-containing heterocyclic structure and an ammonium cation, and the resin may also contain an anion. The cationic structure and the anion contained in the resin are preferably residues resulting from a reaction between an isocyanate group and an ionic compound containing a cationic structure and an anion having a reactive functional group reactive with an isocyanate group. That is, the urethane prepolymer is preferably a reaction product of a polyol, an isocyanate compound, and the ionic compound. The ammonium cation may be linear or branched. The ionic compound containing a cationic structure and an anion having a reactive functional group reactive with an isocyanate group comprises an anion and a cationic structure having at least one functional group (e.g., a hydroxyl group) reactive with an isocyanate group. Examples of functional groups reactive with an isocyanate group include hydroxyl groups and amino groups, with a hydroxyl group being preferred.

[0066] The cationic nitrogen-containing heterocyclic structure is not particularly limited, and may be a four- to eight-membered ring. Examples of the cationic nitrogen-containing heterocyclic structure include cationic nitrogen-containing aromatic heterocyclic structures such as imidazolium cation, pyridinium cation, pyrazinium cation, pyrimidinium cation, azepinium cation, quinolinium cation, isoquinolinium cation, indolinium cation, quinoxalinium cation, triazolium cation, triazinium cation, and thiazolinium cation; and cationic nitrogen-containing aliphatic heterocyclic structures such as pyrrolidinium cation, pyrrolinium cation, imidazolinium cation, imidazolidinium cation, piperazinium cation, azepanium cation, diazepanium cation such as 1,3-diazepanium cation and 1,4-diazepanium cation, azocanium cation, oxazolinium cation, and morpholinium cation. Among these, the cationic nitrogen-containing aromatic heterocyclic structure is preferably at least one selected from the group consisting of an imidazolium cation and a pyridinium cation, and more preferably an imidazolium cation.

[0067] Examples of ammonium cations include primary ammonium cations, secondary ammonium cations, tertiary ammonium cations, and quaternary ammonium cations, with quaternary ammonium cations being preferred. The hydrocarbon group possessed by the ammonium cation is not particularly limited, and may, for example, have a hydrocarbon group having 1 to 8 carbon atoms (preferably 1 to 4, more preferably 1 to 2, and even more preferably 1). The ammonium cation may have a structure represented by the following formula (7):

[0068] The cationic structure may have any substituent such as a hydrocarbon group. For example, the cationic structure preferably includes at least one structure selected from the group consisting of a structure represented by the following formula (4), a structure represented by the following formula (5), a structure represented by the following formula (6), and a structure represented by the following formula (7). When the resin includes at least one structure selected from the group consisting of a structure represented by the following formula (4), a structure represented by the formula (5), a structure represented by the formula (6), and a structure represented by the formula (7), the ionic conductivity of the resin is further increased, and a decrease in the ionic conductivity of the solid electrolyte layer is further suppressed.

[0069] The content of the ionic compound is preferably 0.5 to 5.0 parts by mass, more preferably 0.7 to 3.0 parts by mass, and even more preferably 1.0 to 2.0 parts by mass, relative to 100 parts by mass of the total of the polyol and the isocyanate. When the content of the ionic compound is within this range, it is possible to achieve high levels of both improved compatibility with the lithium salt serving as the supporting electrolyte and improved separation rate.

[0070] The structure represented by formula (4) will be described below. In formula (4), d1 represents an integer of 0 to 1; R5 and R6 represent a hydrocarbon group which forms a five-membered nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z1 and Z2 each independently represent a structure represented by formula (X) below, a hydrogen atom, a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1) and a hydroxyl group; Z3 represents a structure represented by formula (X) below, a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1) and a hydroxyl group; and the number of structures represented by formula (X) below is 2 or 3 (preferably 2).

[0071] The hydrocarbon group having 1 to 4 carbon atoms is preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 1 to 2 carbon atoms, and even more preferably an alkyl group having 1 carbon atom. The hydrocarbon group having 1 to 4 carbon atoms and having a hydroxyl group is preferably a hydroxyalkyl group having 1 to 4 carbon atoms, more preferably a hydroxyalkyl group having 1 to 2 carbon atoms, and even more preferably a hydroxyalkyl group having 1 carbon atom. The hydrocarbon group may have two or more hydroxyl groups. The structure represented by formula (4) represents a cation of a five-membered nitrogen-containing aromatic heterocyclic structure having at least one structure represented by the following formula (X) and two nitrogen atoms. The nitrogen-containing aromatic heterocyclic structure in formula (4) is preferably, for example, an imidazolium cation. The method for incorporating the structure represented by formula (4) into the resin structure is not particularly limited. For example, at least one structure represented by formula (4) can be incorporated into the resin structure by reacting an ionic compound having a structure corresponding to the cation of the five-membered nitrogen-containing aromatic heterocyclic structure represented by formula (4) with an isocyanate compound.

[0072] Examples of ionic compounds having a structure corresponding to the cation of the five-membered nitrogen-containing aromatic heterocyclic structure in formula (4) include ionic compounds in which at least one selected from the group consisting of Z1 to Z3 in formula (4) is a linear or branched divalent hydrocarbon having a hydroxyl group. Examples of such ionic compounds include ionic compounds containing an imidazolium cation, as shown below.

[0073] 1-methyl-3-hydroxymethylimidazolium cation, 1-methyl-3-(2-hydroxyethyl)imidazolium cation, 1-methyl-3-(3-hydroxypropyl)imidazolium cation, 1-methyl-3-(4-hydroxybutyl)imidazolium cation, 1-ethyl-3-(2-hydroxyethyl)imidazolium cation, 1-n-butyl-3-(2-hydroxyethyl)imidazolium cation, 1,3-dimethyl-2-(2-hydroxyethyl)imidazolium cation, 1,3-dimethyl-2-(4-hydroxybutyl)imidazolium cation, 1,3-dimethyl-4-(2-hydroxyethyl)imidazolium cation; 1,3-bishydroxymethylimidazolium cation, 1,3-bis(2-hydroxyethyl)imidazolium cation, 2-methyl-1,3-bishydroxymethylimidazolium cation, 2-methyl-1,3-bis(2-hydroxyethyl)imidazolium cation, 4-methyl-1,3-bis(2-hydroxyethyl)imidazolium cation, 2-ethyl-1,3-bis(2-hydroxyethyl)imidazolium cation, 4-ethyl-1,3-bis(2-hydroxyethyl)imidazolium cation, 2-n-butyl 1,3-bis(2-hydroxyethyl)imidazolium cation, 4-n-butyl-1,3-bis(2-hydroxyethyl)imidazolium cation, 1,3-bis(3-hydroxypropyl)imidazolium cation, 1,3-bis(4-hydroxybutyl)imidazolium cation, 1-methyl-2,3-bis(2-hydroxyethyl)imidazolium cation, 1-methyl-3,4-bis(2-hydroxyethyl)imidazolium cation, 1-methyl-3,5-bis(2-hydroxyethyl)imidazolium cation;1,2,3-trishydroxymethylimidazolium cation, 1,2,3-tris(2-hydroxyethyl)imidazolium cation, 1,2,3-tris(3-hydroxypropyl)imidazolium cation, 1,2,3-tris(4-hydroxybutyl)imidazolium cation, 1,3,4-trishydroxymethylimidazolium cation, 1,3,4-tris(2-hydroxyethyl)imidazolium cation, 1,3,4-tris(3-hydroxypropyl)imidazolium cation, 1,3,4-tris(4-hydroxybutyl)imidazolium cation; and derivatives thereof;

[0074] The structure represented by formula (5) will be described below. In formula (5), d2 represents an integer of 1 to 3 (preferably 1 or 2), R7 represents a hydrocarbon group which forms a nitrogen-containing aromatic heterocyclic structure together with the nitrogen atom, Z4 represents a structure represented by formula (X) below, a hydrogen atom, a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1) and a hydroxyl group, Z5 represents a structure represented by formula (X) below, a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1) and a hydroxyl group, and the number of structures represented by formula (X) below is 2 or 3 (preferably 2). As the hydrocarbon group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms is preferred, an alkyl group having 1 to 2 carbon atoms is more preferred, and an alkyl group having 1 carbon atom is even more preferred. The hydrocarbon group having 1 to 4 carbon atoms and a hydroxyl group is preferably a hydroxyalkyl group having 1 to 4 carbon atoms, more preferably a hydroxyalkyl group having 1 to 2 carbon atoms, and even more preferably a hydroxyalkyl group having 1 carbon atom. The hydrocarbon group may have two or more hydroxyl groups. The structure represented by formula (5) represents a cation of a nitrogen-containing aromatic heterocyclic structure having at least one structure represented by the following formula (X). The nitrogen-containing aromatic heterocyclic structure in formula (5) may be a five- to eight-membered ring, and is preferably a five- or six-membered ring. The nitrogen-containing aromatic heterocyclic structure in formula (5) is preferably, for example, a pyridinium cation. The method for incorporating the structure represented by formula (5) into the resin structure is not particularly limited. For example, at least one structure represented by formula (5) can be incorporated into the resin structure by reacting an ionic compound having a structure corresponding to the cation of the nitrogen-containing aromatic heterocyclic structure represented by formula (5) with an isocyanate group.

[0075] An example of an ionic compound having a structure corresponding to the cation of the nitrogen-containing aromatic heterocyclic structure in formula (5) is an ionic compound in which at least one selected from the group consisting of Z4 and Z5 in formula (5) is a divalent hydrocarbon having a hydroxyl group and having a linear or branched chain. As an example of this ionic compound, an ionic compound containing a pyridinium cation is given below.

[0076] 1-hydroxymethylpyridinium cation, 1-(2-hydroxyethyl)pyridinium cation, 1-(3-hydroxypropyl)pyridinium cation, 1-(4-hydroxybutyl)pyridinium cation, 2-methyl-1-(2-hydroxyethyl)pyridinium cation, 3-methyl-1-(2-hydroxyethyl)pyridinium cation, 4-methyl-1-(2-hydroxyethyl)pyridinium cation, 3-ethyl-1-(2-hydroxyethyl)pyridinium cation, 3-n-butyl-1-(2-hydroxyethyl)pyridinium cation, 1-methyl-2-hydroxy hydroxymethylpyridinium cation, 1-methyl-3-hydroxymethylpyridinium cation, 1-methyl-4-hydroxymethylpyridinium cation, 1-methyl-2-(2-hydroxyethyl)pyridinium cation, 1-methyl-3-(2-hydroxyethyl)pyridinium cation, 1-methyl-4-(2-hydroxyethyl)pyridinium cation, 1-ethyl-3-(2-hydroxyethyl)pyridinium cation, 1-n-butyl-3-(2-hydroxyethyl)pyridinium cation, 2-methyl-4-n-butyl-1-(2-hydroxyethyl)pyridinium cation;1,2-bishydroxymethylpyridinium cation, 1,3-bishydroxymethylpyridinium cation, 1,4-bishydroxymethylpyridinium cation, 1,2-bis(2-hydroxyethyl)pyridinium cation, 1,3-bis(2-hydroxyethyl)pyridinium cation, 1,4-bis(2-hydroxyethyl)pyridinium cation, 1,2-bis(3-hydroxypropyl)pyridinium cation, 1,2-bis(3-hydroxypropyl)pyridinium cation, 1,3-bis(3-hydroxypropyl)pyridinium cation, 1, 4-bis(3-hydroxypropyl)pyridinium cation, 1,2-bis(4-hydroxybutyl)pyridinium cation, 1,3-bis(4-hydroxybutyl)pyridinium cation, 1,4-bis(4-hydroxybutyl)pyridinium cation, 2-methyl-1,3-bis(2-hydroxyethyl)pyridinium cation, 2-ethyl-1,3-bis(2-hydroxyethyl)pyridinium cation, 5-methyl-1,3-bis(2-hydroxyethyl)pyridinium cation, 5-ethyl-1,3-bis(2-hydroxyethyl)pyridinium cation; 1,2,4-trishydroxymethylpyridinium cation, 1,2,4-tris(2-hydroxyethyl)pyridinium cation, 1,2,4-tris(3-hydroxypropyl)pyridinium cation, 1,2,4-tris(4-hydroxybutyl)pyridinium cation, 1,3,5-trishydroxymethylpyridinium cation, 1,3,5-tris(2-hydroxyethyl)pyridinium cation, 1,3,5-tris(3-hydroxypropyl)pyridinium cation, 1,3,5-tris(4-hydroxybutyl)pyridinium cation; and derivatives thereof.

[0077] The structure represented by formula (6) will be described below. In formula (6), d3 represents an integer of 1 to 3 (preferably 1 or 2); R8 and R9 represent a hydrocarbon group which forms a six-membered nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z6 represents a structure represented by formula (X) below, a hydrogen atom, a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1) and a hydroxyl group; Z7 represents a structure represented by formula (X) below, a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1) and a hydroxyl group; and the number of structures represented by formula (X) below is 2 or 3 (preferably 2).

[0078] The hydrocarbon group having 1 to 4 carbon atoms is preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 1 to 2 carbon atoms, and even more preferably an alkyl group having 1 carbon atom. The hydrocarbon group having 1 to 4 carbon atoms and having a hydroxyl group is preferably a hydroxyalkyl group having 1 to 4 carbon atoms, more preferably a hydroxyalkyl group having 1 to 2 carbon atoms, and even more preferably a hydroxyalkyl group having 1 carbon atom. The hydrocarbon group may have two or more hydroxyl groups. The structure represented by formula (6) represents a cation of a six-membered nitrogen-containing aromatic heterocyclic structure having at least one structure represented by the following formula (X) and two nitrogen atoms. The nitrogen-containing aromatic heterocyclic structure in formula (6) is preferably, for example, a pyrazinium cation. The method for incorporating the structure represented by formula (6) into the resin structure is not particularly limited, but for example, at least one structure represented by formula (6) can be incorporated into the resin structure by reacting an ionic compound having a structure corresponding to the cation of the six-membered nitrogen-containing aromatic heterocyclic structure represented by formula (6) with an isocyanate compound.

[0079] As the six-membered nitrogen-containing aromatic heterocyclic structure in formula (6), the cationic nitrogen-containing aromatic heterocyclic structures described in the above-mentioned section on cationic functional groups can be used, and among these, pyrimidinium cations and pyrazinium cations are preferred. Examples of ionic compounds having a structure corresponding to the cation of the six-membered nitrogen-containing aromatic heterocyclic structure in formula (6) include ionic compounds in which at least one selected from the group consisting of Z6 and Z7 in formula (6) has a hydroxyl group and is a linear or branched divalent hydrocarbon. Examples of such ionic compounds include ionic compounds containing pyrimidinium cations listed below.

[0080] 1,4-bis(2-hydroxyethyl)pyrimidinium cation, 1,5-bis(3-hydroxybutyl)pyrimidinium cation, 1-(4-hydroxybutyl)-4-(2-hydroxyethyl)pyrimidinium cation, 1,4-bis(2-hydroxyethyl)-2-methylpyrimidinium cation; and derivatives thereof.

[0081] The structure represented by formula (7) will be described below. In formula (7), R10 represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 or 2). Z8 to Z10 each independently represent a structure represented by the following formula (X), a hydrogen atom, a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1) and a hydroxyl group, and the number of structures represented by formula (X) is 2 or 3 (preferably 2).

[0082] The hydrocarbon group having 1 to 4 carbon atoms is preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 1 to 2 carbon atoms, and even more preferably an alkyl group having 1 carbon atom. The hydrocarbon group having 1 to 4 carbon atoms and having a hydroxyl group is preferably a hydroxyalkyl group having 1 to 4 carbon atoms, more preferably a hydroxyalkyl group having 1 to 2 carbon atoms, and even more preferably a hydroxyalkyl group having 1 carbon atom. The hydrocarbon group may also have two or more hydroxyl groups. The structure represented by formula (7) represents an ammonium cation having at least one structure represented by the following formula (X). There are no particular limitations on the method for incorporating the structure represented by formula (7) into the resin structure. For example, by reacting an ionic compound having a structure corresponding to the ammonium cation represented by formula (7) with an isocyanate compound, at least one structure represented by formula (7) can be incorporated into the resin structure.

[0083] The ammonium cation in formula (7) can be an ammonium cation having a straight-chain or branched structure as described in the above-mentioned cation structure section, with quaternary ammonium cations being preferred. An example of an ionic compound having a structure corresponding to the ammonium cation in formula (7) is an ionic compound in which at least one selected from the group consisting of Z8 to Z10 in formula (7) is a divalent hydrocarbon having a hydroxyl group and having a straight-chain or branched chain. Examples of such ionic compounds include ionic compounds containing a quaternary ammonium cation listed below.

[0084] 2-hydroxyethyltrimethylammonium cation, 2-hydroxyethyltriethylammonium cation, 4-hydroxybutyltrimethylammonium cation, 4-hydroxybutyl-tri-n-butylammonium cation; bis(hydroxymethyl)dimethylammonium cation, bis(2-hydroxyethyl)dimethylammonium cation, bis(3-hydroxypropyl)dimethylammonium cation, bis(4-hydroxybutyl)dimethylammonium cation; tris(hydroxymethyl)methylammonium cation, tris(2-hydroxyethyl)methylammonium cation, tris(3-hydroxypropyl)methylammonium cation, tris(4-hydroxybutyl)methylammonium cation; and derivatives thereof.

[0085] The structure represented by formula (X) will be described below. In formula (X), R11 represents a divalent hydrocarbon group. The symbol "*" represents a bond to a nitrogen atom in formulas (4) to (7) or a bond to a carbon atom in a nitrogen-containing heterocyclic structure in formulas (4) to (6), and the symbol "**" represents a bond to a carbon atom in a polymer chain constituting the resin. R11 is preferably an alkylene group having 1 to 8 carbon atoms (preferably 1 to 4, more preferably 1 to 2). R11 may have an optional substituent such as a hydroxyl group. Furthermore, R11 may be linear or branched.

[0086] The structure represented by formula (X) may be, for example, a structure formed by reacting an ionic compound having a structure corresponding to a cation having a structure represented by formulas (4) to (7) with an isocyanate compound.

[0087] Among the structures represented by formulas (4) to (7), when the cation structure includes the structure represented by formula (5) or the structure represented by formula (4), the stability as a cation is high and the dissociation rate with the anion serving as the counter ion is high, which is preferable because it easily interacts with the anion of the lithium salt contained as the supporting electrolyte, promotes the dissociation of the lithium salt, and tends to improve the ionic conductivity.

[0088] The content of the cationic structure in the resin is preferably 1 to 5 mass %, more preferably 1 to 3 mass %. The structure of the resin can be confirmed by analysis using known means such as pyrolysis GC / MS, TF-IR, and NMR.

[0089] (Anion Structure) Examples of anions contained in the resin include fluoroalkylsulfonylimide anions, fluorosulfonylimide anions, fluoroalkylsulfonate anions, fluorosulfonate anions, fluoroalkylcarboxylate anions, fluoroalkylmethide anions, fluoroborate anions, fluorophosphate anions, dicyanamide anions, thiocyanate anions, bisoxalatoborate anions, perchlorate anions, and derivatives thereof.

[0090] Specific examples of the fluoroalkylsulfonylimide anion include fluoroalkylsulfonylimide anions having a fluoroalkyl group having from 1 to 6 carbon atoms, such as bis(trifluoromethanesulfonyl)imide anion, bis(pentafluoroethanesulfonyl)imide anion, bis(heptafluoropropanesulfonyl)imide anion, bis(nonafluorobutanesulfonyl)imide anion, bis(dodecafluoropentanesulfonyl)imide anion, and bis(perfluorohexanesulfonyl)imide anion, and cyclic fluoroalkylsulfonylimide anions such as N,N-hexafluoropropane-1,3-disulfonylimide.

[0091] Specific examples of the fluorosulfonylimide anion include bis(fluorosulfonyl)imide anion.Specific examples of the fluoroalkylsulfonate anion include trifluoromethanesulfonate anion, fluoromethanesulfonate anion, perfluoroethanesulfonate anion, perfluoropropanesulfonate anion, perfluorobutanesulfonate anion, perfluoropentanesulfonate anion, perfluorohexanesulfonate anion, and perfluorooctanesulfonate anion.Specific examples of the fluoroalkylcarboxylic acid anion include trifluoroacetic acid anion, perfluoropropionate anion, perfluorobutyrate anion, perfluorovalerate anion, and perfluorocaproate anion. Specific examples of the fluoroalkyl methide anion include fluorinated alkylsulfonyl methide anions such as tris(trifluoromethanesulfonyl)methide anion, tris(perfluoroethanesulfonyl)methide anion, tris(perfluoropropanesulfonyl)methide anion, tris(perfluorobutanesulfonyl)methide anion, tris(perfluoropentanesulfonyl)methide anion, tris(perfluorohexanesulfonyl)methide anion, and tris(perfluorooctanesulfonyl)methide anion.

[0092] Specific examples of fluoroborate anions include tetrafluoroborate anions, and specific examples of fluorophosphate anions include hexafluorophosphate anions.

[0093] Among these anions, at least one selected from the group consisting of a fluoroalkylsulfonylimide anion, a fluorosulfonylimide anion, a fluoroborate anion, a dicyanamide anion, and a thiocyanate anion is particularly preferred because it reduces the decrease in conductivity in a low-temperature environment.

[0094] <Supporting Electrolyte> The resin according to the present disclosure preferably contains at least one supporting electrolyte selected from the group consisting of lithium salts, sodium salts, and potassium salts. For example, the resin may be a resin mixture containing the supporting electrolyte. Examples of anion species contained in the supporting electrolyte include fluoroalkylsulfonylimide anions, fluorosulfonylimide anions, fluoroalkylsulfonate anions, fluorosulfonate anions, fluoroalkylcarboxylate anions, fluoroalkylmethide anions, fluoroborate anions, fluorophosphate anions, dicyanamide anions, thiocyanate anions, bisoxalatoborate anions, perchlorate anions, and derivatives thereof.

[0095] More specifically, the anions contained in the supporting electrolyte are bis(trifluoromethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, trifluoromethanesulfonate anion (CF ３ -SO ３ － ), hexafluorophosphate anion (PF ６ － ), fluoroborate anion (BF ４ － ), dicyanamide anion (N(CN) ２ － ), thiocyanate anion (SCN － ) is preferred.

[0096] The anion is preferably at least one selected from the group consisting of a fluoroalkylsulfonylimide anion and a fluorosulfonylimide anion in terms of chemical stability with respect to the positive electrode active material and the solid electrolyte. Specific examples of the fluoroalkylsulfonylimide anion include fluoroalkylsulfonylimide anions having a fluoroalkyl group having from 1 to 6 carbon atoms, such as the bis(trifluoromethanesulfonyl)imide anion, bis(pentafluoroethanesulfonyl)imide anion, bis(heptafluoropropanesulfonyl)imide anion, bis(nonafluorobutanesulfonyl)imide anion, bis(dodecafluoropentanesulfonyl)imide anion, and bis(perfluorohexanesulfonyl)imide anion, and cyclic fluoroalkylsulfonylimide anions such as N,N-hexafluoropropane-1,3-disulfonylimide. Among these, the bis(trifluoromethanesulfonyl)imide anion is preferred.

[0097] Examples of lithium salts include LiBF ４ , LiPF ６ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ F) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiAlCl ４ , LiSBF ６ , LiSCN, LiCF ３ SO ３ , LiAsF ６ , LiClO ４ , lower aliphatic lithium carboxylate, LiCl, LiBR, and LiI. The lithium salts may be used alone or in combination of two or more. Examples of the sodium salts and potassium salts include those in which the lithium in the above lithium salts is replaced by sodium or potassium.

[0098] The content of the supporting electrolyte in the resin mixture is preferably 1 to 40 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 1 to 7 parts by mass, relative to 100 parts by mass of the resin. When the content of the supporting electrolyte is within this range, the supporting electrolyte is well compatible with the resin and does not precipitate, and high ionic conductivity is obtained.

[0099] (Method for forming solid electrolyte layer, positive electrode layer, negative electrode layer) The method for forming the solid electrolyte layer, positive electrode layer, or negative electrode layer is not particularly limited. For example, the above-mentioned resin is mixed with a solid electrolyte, a positive electrode active material, or a negative electrode active material, and a solvent by a known method to obtain a slurry for forming each layer. The slurry is applied by a known application method such as bar coating, doctor blade coating, or roll coating, and then the solvent contained in the applied slurry is dried by heating under reduced pressure to form the solid electrolyte layer, positive electrode layer, or negative electrode layer.

[0100] The present disclosure provides a resin solution. The resin solution includes a resin according to the present disclosure and a solvent. The present disclosure also provides a solid electrolyte slurry. The solid electrolyte slurry includes a resin according to the present disclosure, a solid electrolyte, and a solvent. The solvent is not particularly limited, and any known solvent capable of dissolving the resin may be used. Examples of the solvent include n-butyl n-butyrate, isobutyronitrile, toluene, xylene, mesitylene, dibutyl ether, butyronitrile, dibutyl ketone, and anisole. The concentration of the resin in the resin solution and solid electrolyte slurry is not particularly limited, and may be set appropriately depending on the intended use.

[0101] Specific examples and comparative examples according to the present disclosure are shown below, but the present disclosure is not limited to the following examples and comparative examples.

[0102] <Polyol> (Polyether polyols A-1 to A-8) Polyether polyols A-1 to A-8 used in the examples are shown in Table (1) below.

[0103] (Polyether Polyol A-9) 50 g of 1,6-hexanediol was added to a 100 ml four-neck flask equipped with a distillation tube, a nitrogen inlet tube, a thermometer, and a stirrer, while supplying nitrogen at 100 mL / min. 0.03439 g of pyridine was added to the mixture, and then 0.4489 g of concentrated sulfuric acid (95% by mass) was slowly added with stirring to obtain a mixed solution. The flask was immersed in an oil bath, and the mixed solution was heated to 160°C. The temperature of the mixed solution was adjusted to 160°C ± 2°C and maintained at this temperature for 10 hours to allow the reaction to proceed. The flask was then removed from the oil bath and allowed to cool to room temperature. Water produced during the reaction was distilled off entrained by nitrogen.

[0104] The reaction solution cooled to room temperature was transferred to a 300 ml eggplant-shaped flask using 32 g of tetrahydrofuran, and 32 g of demineralized water was added to the eggplant-shaped flask. The mixture was then gently refluxed for 1 hour to hydrolyze the sulfate ester. After cooling to room temperature, the mixture separated into two layers, and the lower layer (aqueous layer) was removed. 0.32 g of calcium hydroxide was added to the upper layer (oil layer), and the mixture was stirred at room temperature for 1 hour. 32 g of toluene was then added. The mixture was then heated to 60°C and placed under reduced pressure to distill off the tetrahydrofuran, water, and toluene.

[0105] The obtained oil layer was dissolved in 64 g of toluene and filtered through a 0.45 μm filter to remove insoluble matter. The filtrate was heated to 60°C and the toluene was distilled off under reduced pressure. The obtained oil layer was heated to 60°C and vacuum-dried for 6 hours, which was named Polyether Polyol A-9.

[0106] The weight average molecular weight was measured using an HLC-8120GPC (manufactured by Tosoh Corporation) as a measuring instrument, two TSKgel Super HM-M (manufactured by Tosoh Corporation) columns, and THF as a solvent. The measurement was performed at a temperature of 40 ° C., a THF flow rate of 0.6 ml / min, with the measurement sample being a 0.1 mass% THF solution, and an RI (refractive index) detector as a detector. A calibration curve was created using several monodisperse standard polystyrenes (manufactured by Tosoh Corporation) as standard samples for creating a calibration curve, and the weight average molecular weight was calculated from the retention time of the measurement sample obtained based on this. The weight average molecular weight of polyether polyol A-9 was 1800.

[0107] (Polyether Polyols A-10 and A-11) Polyether polyols A-10 and A-11 used in the examples are shown in Table (2) below.

[0108] <Synthesis of Ionic Compounds> (Ionic Compound I-01) A stirring bar and 60 ml of tetrahydrofuran (THF, manufactured by Kanto Chemical Co., Ltd.) were placed in a recovery flask equipped with a Dimroth condenser. 24.0 g (0.60 mol) of sodium hydride (60% by mass, dispersed in liquid paraffin, manufactured by Tokyo Chemical Industry Co., Ltd.) was dispersed in the recovery flask, and the recovery flask was cooled in an ice bath. A solution of 10.2 g (0.15 mol) of imidazole (manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved in 60 ml of THF was slowly added dropwise, after which the ice bath was removed and the mixture was stirred at room temperature for 2 hours. 47.6 g (0.38 mol) of 2-bromoethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) was added at room temperature, and the mixture was heated to reflux at 70°C for 7 hours. After the reaction, the reaction solution was filtered, the insoluble matter was washed away with THF, and the solvent from the resulting filtrate was evaporated under reduced pressure. The obtained product was dissolved in 200 ml of dichloromethane, and an aqueous solution containing 43.6 g (0.15 mol) of bis(trifluoromethanesulfonyl)imide lithium (manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved therein as an anion source was added, followed by stirring at room temperature for 10 hours. The obtained solution was separated to obtain an organic layer. This organic layer was washed three times with pure water. Next, dichloromethane was distilled off under reduced pressure to obtain ionic compound I-01. Ionic compound I-01 is a compound represented by the following formula:

[0109] Ionic Compound I-02 was obtained in the same manner as in the synthesis of Ionic Compound I-01, except that the anion raw materials and their blending amounts were changed as shown in Table 3. Ionic Compound I-02 is a compound represented by the following formula.

[0110] (Ionic Compound I-03) A stirring bar and 50 ml of acetonitrile were placed in a recovery flask equipped with a Dimroth condenser. 22.7 g (0.15 mol) of 4-pyridinebutanol (Sigma-Aldrich) was added and dissolved. 29.1 g (0.19 mol) of 4-bromo-1-butanol (Tokyo Chemical Industry Co., Ltd.) was added dropwise over 30 minutes at room temperature, and the mixture was heated to reflux at 90°C for 12 hours. Next, the reaction solution was cooled to room temperature, and the acetonitrile was removed by distillation under reduced pressure. The mixture was then washed three times with 50 ml of diethyl ether. The resulting product was dissolved in 150 ml of dichloromethane, and an aqueous solution containing 35.1 g (0.16 mol) of potassium bis(fluorosulfonyl)imide as an anion source was added. The mixture was stirred at room temperature for 12 hours. The resulting solution was separated to obtain an organic layer. This organic layer was washed three times with pure water. Next, dichloromethane was distilled off under reduced pressure to obtain ionic compound I-03, which is a compound represented by the following formula.

[0111] (Ionic Compound I-04) 15.0 g of bis(2-hydroxyethyl)dimethylammonium chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 40.0 g of ion-exchanged water. Next, 27.9 g of an anion raw material (lithium N,N-bis(trifluoromethanesulfonyl)imide (trade name, EF-N115; manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.)) dissolved in 60 g of ion-exchanged water was added dropwise over 30 minutes, and the mixture was stirred at 30°C for 2 hours to obtain a reaction solution. Next, the reaction solution was extracted twice with 100.0 g of ethyl acetate. Next, the separated ethyl acetate layer was washed three times with 60 g of ion-exchanged water. Subsequently, the ethyl acetate was distilled off under reduced pressure to obtain ionic compound I-04, in which the anion was a bis(trifluoromethanesulfonyl)imide anion. Ionic compound I-04 is a compound represented by the following formula:

[0112] <Resin Synthesis> [Example 1] A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen gas inlet tube was charged with 100.0 parts by mass of polyether polyol A-1 and 325.0 parts by mass of methyl ethyl ketone (MEK), and the temperature was raised to 70 ° C. under a nitrogen gas stream. Next, 62.5 parts by mass of isocyanate (monomeric MDI, trade name: Millionate MT, manufactured by Tosoh Corporation) was added dropwise over 2 hours, and the mixture was heated to reflux for another 5 hours while maintaining the temperature at 80 ° C. to obtain a urethane prepolymer. The weight average molecular weight of the urethane prepolymer obtained at this point was measured in the same manner as for polyether polyol, and the weight average molecular weight was 50,000.

[0113] Subsequently, the temperature was lowered once to 70°C, and 0.5 parts by mass of terminal isocyanate (n-butyl isocyanate, manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise to 100.0 parts by mass of the urethane prepolymer over 30 minutes, and the mixture was heated under reflux for an additional 3 hours while maintaining the temperature at 80°C. After the temperature was lowered to 30°C, MEK was distilled off under reduced pressure. The mixture was allowed to cool to room temperature, and 502.5 parts by mass of pre-dehydrated isobutyronitrile was added and dissolved by stirring, yielding Resin 1 according to Example 1.

[0114] [Examples 2, 3, 8 to 14] Resins 2, 3, 8 to 14 according to Examples 2, 3, 8 to 14 were obtained in the same manner as in Example 1, except that the raw materials and the amounts of the raw materials were changed as shown in Tables 4-1 and 4-2.

[0115] [Example 4] A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen gas inlet tube was charged with 100.0 parts by mass of polyether polyol A-2 and 230.0 parts by mass of methyl ethyl ketone (MEK), and the temperature was raised to 70 ° C. under a nitrogen gas stream. Next, 15.0 parts by mass of isocyanate (monomeric MDI, trade name: Millionate MT, manufactured by Tosoh Corporation) was added dropwise over 2 hours, and the mixture was heated to reflux for another 7 hours while maintaining the temperature at 80 ° C. to obtain a urethane prepolymer. When the weight average molecular weight of the urethane prepolymer obtained at this point was measured, the weight average molecular weight was 68,000.

[0116] Subsequently, the temperature was lowered once to 70°C, and 0.3 parts by mass of a terminal polyol (1-propanol, manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise to 100.0 parts by mass of the urethane prepolymer over 30 minutes, and the mixture was heated under reflux for an additional 3 hours while maintaining the temperature at 80°C. After the temperature was lowered to 30°C, MEK was distilled off under reduced pressure. The mixture was allowed to cool to room temperature, and 501.5 parts by mass of pre-dehydrated isobutyronitrile was added and dissolved with stirring to obtain Resin 4 according to Example 4.

[0117] Examples 5 to 7 Resins 5 to 7 according to Examples 5 to 7 were obtained in the same manner as in Example 4, except that the raw materials and the blending amounts of the raw materials were changed as shown in Table 5.

[0118] [Example 15] A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen gas inlet tube was charged with 50.0 parts by mass of polyether polyol A-2, 50.0 parts by mass of polyether polyol A-5, and 225.0 parts by mass of methyl ethyl ketone (MEK), and the temperature was raised to 70 ° C. under a nitrogen gas stream. Next, 12.5 parts by mass of isocyanate (monomeric MDI, trade name: Millionate MT, manufactured by Tosoh Corporation) was added dropwise over 2 hours, and the mixture was heated to reflux for another 7 hours while maintaining the temperature at 80 ° C. to obtain a urethane prepolymer. When the weight average molecular weight of the urethane prepolymer obtained at this point was measured, the weight average molecular weight was 68,000.

[0119] Subsequently, the temperature was lowered once to 70°C, and 0.6 parts by mass of terminal isocyanate (octyl isocyanate, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise to 100.0 parts by mass of the urethane prepolymer over 30 minutes, and the mixture was heated under reflux for an additional 3 hours while maintaining the temperature at 80°C. After the temperature was lowered to 30°C, MEK was distilled off under reduced pressure. The mixture was allowed to cool to room temperature, and 503.0 parts by mass of pre-dehydrated isobutyronitrile was added and dissolved by stirring, yielding Resin 15 according to Example 15.

[0120] [Example 16] A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device and a nitrogen gas inlet tube was charged with 100.0 parts by mass of polyether polyol A-5 and 217.4 parts by mass of methyl ethyl ketone (MEK), and the temperature was raised to 70 ° C. under a nitrogen gas stream. Next, 8.7 parts by mass of isocyanate (TDI, manufactured by Mitsui Chemicals, Inc.) was added dropwise over 2 hours, and the mixture was heated to reflux for another 7 hours while maintaining the temperature at 80 ° C. to obtain a urethane prepolymer. When the weight average molecular weight of the urethane prepolymer obtained at this point was measured, the weight average molecular weight was 66,000.

[0121] Subsequently, the temperature was lowered once to 70°C, and 0.5 parts by mass of terminal isocyanate (phenyl isocyanate, manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise to 100.0 parts by mass of the urethane prepolymer over 30 minutes, and the mixture was heated under reflux for an additional 3 hours while maintaining the temperature at 80°C. After the temperature was lowered to 30°C, MEK was distilled off under reduced pressure. The mixture was allowed to cool to room temperature, and 502.5 parts by mass of pre-dehydrated isobutyronitrile was added and dissolved by stirring, yielding Resin 16 according to Example 16.

[0122] [Example 17] A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen gas inlet tube was charged with 100.0 parts by mass of polyether polyol A-5, 0.3 parts by mass of a catalyst (dibutyltin dilaurate, manufactured by Tokyo Chemical Industry Co., Ltd.), 8.4 parts by mass of isocyanate (HDI, manufactured by Tosoh Corporation), and 216.8 parts by mass of methyl ethyl ketone (MEK), and the temperature was raised to 70 ° C. under a nitrogen gas stream. The temperature was maintained at 80 ° C. and refluxed for another 7 hours to obtain a urethane prepolymer. The weight average molecular weight of the urethane prepolymer obtained at this point was measured, and the weight average molecular weight was 66,000.

[0123] Subsequently, the temperature was lowered once to 70°C, and 0.5 parts by mass of terminal isocyanate (phenyl isocyanate, manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise to 100.0 parts by mass of the urethane prepolymer over 30 minutes, and the mixture was heated under reflux for an additional 3 hours while maintaining the temperature at 80°C. After the temperature was lowered to 30°C, MEK was distilled off under reduced pressure. The mixture was allowed to cool to room temperature, and 502.5 parts by mass of pre-dehydrated isobutyronitrile was added and dissolved by stirring, yielding Resin 17 according to Example 17.

[0124] [Example 18] A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen gas inlet tube was charged with 100.0 parts by mass of polyether polyol A-6, 5.0 parts by mass of ionic compound I-01, and 230.0 parts by mass of methyl ethyl ketone (MEK), and the temperature was raised to 70 ° C. under a nitrogen gas stream. Next, 10.0 parts by mass of isocyanate (monomeric MDI, trade name: Millionate MT, manufactured by Tosoh Corporation) was added dropwise over 2 hours, and the mixture was heated to reflux for another 8 hours while maintaining the temperature at 80 ° C. to obtain a urethane prepolymer. When the weight average molecular weight of the urethane prepolymer obtained at this point was measured, the weight average molecular weight was 76,000.

[0125] Subsequently, the temperature was lowered once to 70°C, and 0.4 parts by mass of terminal isocyanate (n-butyl isocyanate, manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise to 100.0 parts by mass of the urethane prepolymer over 30 minutes, and the mixture was heated under reflux for an additional 3 hours while maintaining the temperature at 80°C. After the temperature was lowered to 30°C, MEK was distilled off under reduced pressure. The mixture was allowed to cool to room temperature, and 502.0 parts by mass of pre-dehydrated isobutyronitrile was added and dissolved by stirring, yielding Resin 18 according to Example 18.

[0126] Examples 19 to 21 Resins 19 to 21 according to Examples 19 to 21 were obtained in the same manner as in Example 18, except that the raw materials and the blending amounts of the raw materials were changed as shown in Table (6).

[0127] [Example 22] A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen gas inlet tube was charged with 100.0 parts by mass of polyether polyol A-6, 4.0 parts by mass of ionic compound I-01, and 226.9 parts by mass of methyl ethyl ketone (MEK), and the temperature was raised to 70 ° C. under a nitrogen gas stream. Next, 9.4 parts by mass of isocyanate (monomeric MDI, trade name: Millionate MT, manufactured by Tosoh Corporation) was added dropwise over 2 hours, and the mixture was heated to reflux for another 8 hours while maintaining the temperature at 80 ° C. to obtain a urethane prepolymer. When the weight average molecular weight of the urethane prepolymer obtained at this point was measured, the weight average molecular weight was 76,000.

[0128] Subsequently, the temperature was lowered to 70°C once, and 0.4 parts by mass of terminal isocyanate (n-butyl isocyanate, manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise to 100.0 parts by mass of the urethane prepolymer over 30 minutes, and the mixture was heated under reflux for an additional 3 hours while maintaining the temperature at 80°C. After the temperature was lowered to 30°C, MEK was distilled off under reduced pressure. The mixture was allowed to cool to room temperature, and 5.0 parts by mass of lithium bis(trifluoromethanesulfonyl)imide (manufactured by Kishida Chemical Co., Ltd.) and 502.0 parts by mass of pre-dehydrated isobutyronitrile were added as a supporting electrolyte and dissolved with stirring. In this way, resin 22 according to Example 22 was obtained.

[0129] [Example 23] A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device and a nitrogen gas inlet tube was charged with 100.0 parts by mass of polyether polyol A-6 and 214.3 parts by mass of methyl ethyl ketone (MEK), and the temperature was raised to 70 ° C. under a nitrogen gas stream. Next, 7.1 parts by mass of isocyanate (monomeric MDI, trade name: Millionate MT, manufactured by Tosoh Corporation) was added dropwise over 2 hours, and the mixture was heated to reflux for another 8 hours while maintaining the temperature at 80 ° C. to obtain a urethane prepolymer. When the weight average molecular weight of the urethane prepolymer obtained at this point was measured, the weight average molecular weight was 76,000.

[0130] Subsequently, the temperature was lowered once to 70 ° C., and 0.4 parts by mass of terminal isocyanate (n-butyl isocyanate, manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise to 100.0 parts by mass of the urethane prepolymer over 30 minutes, and the mixture was heated under reflux for an additional 3 hours while maintaining the temperature at 80 ° C. After the temperature was lowered to 30 ° C., MEK was distilled off under reduced pressure. The mixture was allowed to cool to room temperature, and 5.0 parts by mass of lithium bis(trifluoromethanesulfonyl)imide (manufactured by Kishida Chemical Co., Ltd.) and 502.0 parts by mass of pre-dehydrated isobutyronitrile were added as a supporting electrolyte and dissolved with stirring. In this way, Resin 23 according to Example 23 was obtained.

[0131] [Comparative Example 1] A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen gas inlet tube was charged with 100.0 parts by mass of polyether polyol A-10 and 250.0 parts by mass of methyl ethyl ketone (MEK), and the temperature was raised to 70 ° C. under a nitrogen gas stream. Next, 25.0 parts by mass of isocyanate (monomeric MDI, trade name: Millionate MT, manufactured by Tosoh Corporation) was added dropwise over 2 hours, and the mixture was heated to reflux for another 8 hours while maintaining the temperature at 80 ° C. to obtain a urethane prepolymer. When the weight average molecular weight of the urethane prepolymer obtained at this point was measured, the weight average molecular weight was 75,000.

[0132] Subsequently, the temperature was lowered to 30° C., and then MEK was distilled off under reduced pressure. The temperature was allowed to cool to room temperature, and 500.0 parts by mass of isobutyronitrile that had been previously dehydrated was added and dissolved with stirring, thereby obtaining Resin 24 according to Comparative Example 1.

[0133] [Comparative Example 2] A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen gas inlet tube was charged with 100.0 parts by mass of polyether polyol A-11 and 250.0 parts by mass of methyl ethyl ketone (MEK), and the temperature was raised to 70 ° C. under a nitrogen gas stream. Next, 25.0 parts by mass of isocyanate (monomeric MDI, trade name: Millionate MT, manufactured by Tosoh Corporation) was added dropwise over 2 hours, and the temperature was maintained at 80 ° C. for another 5 hours under reflux to obtain a urethane prepolymer. When the weight average molecular weight of the urethane prepolymer obtained at this point was measured, the weight average molecular weight was 50,000.

[0134] Subsequently, the temperature was lowered to 30° C., and then MEK was distilled off under reduced pressure. The mixture was allowed to cool to room temperature, and 500.0 parts by mass of isobutyronitrile that had been previously dehydrated was added and dissolved with stirring, thereby obtaining Resin 25 according to Comparative Example 2.

[0135] Comparative Examples 3 and 4 Resins 26 and 27 according to Comparative Examples 3 and 4 were obtained in the same manner as in Example 1, except that the raw materials and the amounts of the raw materials used were changed as shown in Tables 7-1 and 7-2.

[0136] Comparative Example 5: 100.0 parts by mass of 1,4-butanediol (manufactured by Mitsubishi Chemical Corporation) and 472.4 parts by mass of methyl ethyl ketone (MEK) were charged into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen gas inlet tube, and the temperature was raised to 70°C under a nitrogen gas stream. Next, 277.9 parts by mass of isocyanate (monomeric MDI, trade name: Millionate MT, manufactured by Tosoh Corporation) was added dropwise over 2 hours, and the mixture was heated to reflux for an additional 5 hours while maintaining the temperature at 80°C, yielding a urethane prepolymer. The weight average molecular weight of the urethane prepolymer obtained at this point was measured and found to be 5,000.

[0137] Subsequently, the temperature was lowered once to 70°C, and 4.8 parts by mass of terminal isocyanate (n-butyl isocyanate, manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise to 100.0 parts by mass of the urethane prepolymer over 30 minutes, and the mixture was heated under reflux for an additional 3 hours while maintaining the temperature at 80°C. After the temperature was lowered to 30°C, MEK was distilled off under reduced pressure. The mixture was allowed to cool to room temperature, and 524.0 parts by mass of pre-dehydrated isobutyronitrile was added and dissolved by stirring, yielding Resin 28 according to Comparative Example 5.

[0138] The structure of formula (1) and the terminal structure in each example and each comparative example are shown in Tables 8 and 9 below.

[0139] The ionic conductivity of the solid electrolyte layer using the resins according to the examples and comparative examples will be described below. All operations were carried out in an argon-substituted glove box (temperature 25°C, dew point -70°C).

[0140] <Preparation of Slurry for Forming Solid Electrolyte Layer> 35.0 parts by mass of isobutyronitrile as a dispersion medium was added to 50.0 parts by mass of argyrodite-type sulfide LPSCl (manufactured by Sigma-Aldrich Japan) as a solid electrolyte and 2.5 parts by mass of Resin 1 according to Example 1. The mixture was then mixed and stirred for 30 minutes using a planetary mixer to obtain a slurry for forming a solid electrolyte layer according to Example 1.

[0141] <Formation of Solid Electrolyte Layer> The obtained solid electrolyte-forming slurry was applied onto a polypropylene sheet using a doctor blade, dried under reduced pressure at 140° C. for 3 hours, and allowed to cool to 25° C. The thickness of the obtained solid electrolyte layer was 85 μm.

[0142] <Evaluation of Ionic Conductivity> (Measurement of Ionic Conductivity of Solid Electrolyte Layer) The solid electrolyte layer formed on the polypropylene sheet was peeled off and sandwiched between SUS sheets to prepare a cell. Using an impedance analyzer E4990A (manufactured by KEYSIGHT), the AC impedance between the electrodes was measured at an applied voltage of 10 mV and a frequency range of 100 MHz to 1 Hz, and the bulk resistance value R was calculated from the real impedance intercept of the obtained cole-cole plot. Ｂ (Ω) was measured, and the ionic conductivity was calculated using the following formula: σ=L / R Ｂ × S (σ: ionic conductivity (S cm -１ ), L: sample thickness (cm), S: sample area (cm ２ ))

[0143] (Ionic Conductivity of Sulfide Electrolyte Compacted Pellet) For comparison, a sulfide electrolyte was compacted without using a binder, and the ionic conductivity was measured. Specifically, 200 mg of an argyrodite-type sulfide electrolyte LPSCl (manufactured by Sigma-Aldrich Japan) was weighed as a solid electrolyte, placed in a ceramic cylinder, and compressed to 4 ton / cm. ２The pellet was pressed at a pressure of 1000 kJ / cm2. The thickness of the obtained circular pellet was measured. Next, both sides of the pellet were sandwiched between SUS sheets, and the pellet was pressed by bolts to prepare a pressed powder cell. Hereinafter, the ionic conductivity was determined in the same manner as in the evaluation of the solid electrolyte layer. The obtained (ionic conductivity of the solid electrolyte layer including the binder / ionic conductivity of the sulfide electrolyte pressed powder pellet) was defined as the initial maintenance rate of ionic conductivity.

[0144] The same procedure was carried out for the resins of Examples 2 to 23 and Comparative Examples 1 to 5, and the ionic conductivity of the solid electrolyte layer and the initial maintenance rate of the ionic conductivity were determined. The results are shown in Table 10.

[0145] (Measurement of ionic conductivity of solid electrolyte layer after high-temperature storage) The cell in which the ionic conductivity of the solid electrolyte layer had been measured was kept at 60°C for 7 days. Thereafter, the cell was left at 25°C for 3 hours, and the ionic conductivity was measured again in the same manner as in the initial state to determine the ionic conductivity after high-temperature storage. The obtained (ionic conductivity after high-temperature storage / initial ionic conductivity) was defined as the ionic conductivity retention rate after high-temperature storage. The results are shown in Table 10.

[0146] The resins according to Examples 1 to 23 have a structure represented by formula (1) and one terminal structure selected from the group consisting of formula (2) and formula (3). Therefore, solid electrolyte layers using these resins as binders maintain high ionic conductivity compared to those obtained by compacting only the solid electrolyte, and the decrease in ionic conductivity is suppressed even after high-temperature storage. In particular, Examples 18 to 22, which have a cation structure in addition to the structure represented by formula (1), and Example 23, which includes a supporting electrolyte, exhibit higher initial ionic conductivity retention rates. Furthermore, Examples 10 to 23, in which the polyether moiety contained in the structure represented by formula (1) has an ether unit structure with four or more carbon atoms, also exhibit high values ​​for ionic conductivity retention rates after high-temperature storage.

[0147] On the other hand, in Comparative Examples 1 to 5, which are resins that do not have the structure represented by formula (1) or resins that do not have at least one terminal structure selected from the group consisting of formula (2) and formula (3), the ionic conductivity of the solid electrolyte layer using these as binders was significantly reduced, and a significant reduction in ionic conductivity during high-temperature storage was also observed.

[0148] The present disclosure is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to clarify the scope of the present disclosure. This application claims priority based on Japanese Patent Application No. 2024-041959, filed March 18, 2024, the entire contents of which are incorporated herein by reference.

[0149] 1: Secondary battery, 2: Positive electrode layer, 3: Solid electrolyte layer, 4: Negative electrode layer, 5: Positive electrode current collector, 6: Positive electrode active material, 7: Positive electrode layer binder, 8: Solid electrolyte, 9: Conductive additive, 10: Solid electrolyte binder, 11: Negative electrode active material, 12: Negative electrode layer binder, 13: Negative electrode current collector

Claims

1. A resin having a structure represented by the following formula (1) and having at least one terminal structure selected from the group consisting of the following formulas (2) and (3): (In formula (1), m represents an integer of 3 or more, each R1 independently represents an alkylene group having 3 to 6 carbon atoms, each R2 independently represents a divalent organic group, and n represents an integer of 5 or more.) (In formula (2), R3 represents an alkyl group having 3 or more carbon atoms or a phenyl group.) (In formula (3), R4 represents an alkyl group having 3 or more carbon atoms or a phenyl group.) 2. The resin according to claim 1, wherein in formula (1), R1 is an alkylene group having 4 to 5 carbon atoms.

3. The resin according to claim 1 or 2, wherein the resin has at least one cationic structure selected from the group consisting of a cationic nitrogen-containing heterocyclic structure and an ammonium cation, and the resin contains an anion.

4. The resin according to claim 3, wherein the cation structure includes at least one structure selected from the group consisting of a structure represented by the following formula (4), a structure represented by the following formula (5), a structure represented by the following formula (6), and a structure represented by the following formula (7). (In formula (4), d1 represents an integer of 0 to 1; R5 and R6 represent a hydrocarbon group which forms a five-membered nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z1 and Z2 each independently represent a structure represented by formula (X) below, a hydrogen atom, a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms, or a hydrocarbon group having 1 to 4 carbon atoms and a hydroxyl group; Z3 represents a structure represented by formula (X) below, a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms, or a hydrocarbon group having 1 to 4 carbon atoms and a hydroxyl group, and the number of structures represented by formula (X) below is 2 or 3.) (In formula (5), d2 represents an integer of 1 to 3; R7 represents a hydrocarbon group which forms a nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z4 represents a structure represented by formula (X) below, a hydrogen atom, a hydroxyl group, a hydrocarbon group of 1 to 4 carbon atoms, or a hydrocarbon group of 1 to 4 carbon atoms having a hydroxyl group; Z5 represents a structure represented by formula (X) below, a hydroxyl group, a hydrocarbon group of 1 to 4 carbon atoms, or a hydrocarbon group of 1 to 4 carbon atoms having a hydroxyl group, and the number of structures represented by formula (X) below is 2 or 3.) (In formula (6), d3 represents an integer of 1 to 3; R8 and R9 represent a hydrocarbon group which forms a six-membered nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z6 represents a structure represented by formula (X) below, a hydrogen atom, a hydroxyl group, a hydrocarbon group of 1 to 4 carbon atoms, or a hydrocarbon group of 1 to 4 carbon atoms having a hydroxyl group; Z7 represents a structure represented by formula (X) below, a hydroxyl group, a hydrocarbon group of 1 to 4 carbon atoms, or a hydrocarbon group of 1 to 4 carbon atoms having a hydroxyl group, and the number of structures represented by formula (X) below is 2 or 3.) (In formula (7), R10 represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms. Z8 to Z10 each independently represent a structure represented by formula (X) below, a hydrogen atom, a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms, or a hydrocarbon group having 1 to 4 carbon atoms and a hydroxyl group, and the number of structures represented by formula (X) below is 2 or 3.) (In formula (X), R11 represents a divalent hydrocarbon group. The symbol "*" represents a bond to a nitrogen atom in formulas (4) to (7) or a bond to a carbon atom in a nitrogen-containing heterocyclic structure in formulas (4) to (6). The symbol "**" represents a bond to a carbon atom in a polymer chain constituting the resin.) 5. The resin according to any one of claims 1 to 4, further comprising at least one supporting electrolyte selected from the group consisting of lithium salts, sodium salts, and potassium salts.

6. The resin according to claim 3 or 4, wherein the content of the cationic structure in the resin is 1 to 5% by mass.

7. The resin according to any one of claims 1 to 6, wherein the resin is a binder for a solid electrolyte.

8. A resin solution comprising the resin according to any one of claims 1 to 7 and a solvent.

9. A solid electrolyte slurry comprising the resin according to any one of claims 1 to 7, a solid electrolyte, and a solvent.

10. A solid electrolyte layer comprising the resin according to any one of claims 1 to 7 and a solid electrolyte.

11. A positive electrode layer comprising the resin according to any one of claims 1 to 7 and a solid electrolyte.

12. An anode layer comprising the resin according to any one of claims 1 to 7 and a solid electrolyte.

13. An all-solid-state battery having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, wherein at least one layer of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer contains the resin described in any one of claims 1 to 7.

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