Secondary battery

Abstract

Provided is a secondary battery in which it is possible to suppress deterioration in repeated charging and discharging. Provided is a secondary battery including a positive electrode layer, a negative electrode layer, and a bulk electrolyte layer between the positive electrode layer and the negative electrode layer, the secondary battery being characterized in that: the positive electrode layer contains a positive electrode active material and a binder; the bulk electrolyte layer contains a first polymer, and a metal salt including at least one cation selected from the group consisting of Li+, Na+, K+, Mg2+, and Ca2+; the binder contains a second polymer, and a metal salt including at least one cation selected from the group consisting of Li+, Na+, K+, Mg2+, and Ca2+; the second polymer contains a urethane resin to which a cationic functional group is bonded; and the first polymer has a structure different from that of the second polymer.

Description

secondary battery

[0001] The present disclosure relates to secondary batteries.

[0002] In recent years, with the development of IoT devices, fuel cells, and electric vehicles, the demand for secondary batteries as their power sources has increased more than ever before. Secondary batteries are capable of repeated charging and discharging and have high capacities, so they are widely used in devices ranging from small to large. Secondary batteries are primarily composed of a positive electrode, a negative electrode, and an electrolyte. Lithium-ion secondary batteries, which use an electrolytic solution containing lithium ions, are commonly used.

[0003] Currently, many electrolytes are flammable liquids, posing a fire risk if they leak. Therefore, solidification of electrolytes is being considered. Ceramic oxides, sulfides, and polymers are being considered for solid electrolytes. While ceramics offer excellent ionic conductivity, they struggle to conform to the positive and negative electrodes during expansion and contraction during charging and discharging, making it difficult to stabilize the material interface. For this reason, the use of polymer electrolytes, which offer mechanical conformity and a large interfacial area, has been proposed. It is generally known that increasing the interfacial area between the positive electrode and electrolyte improves charge-discharge characteristics. Furthermore, the addition of binders to the positive electrode active material to increase the interfacial area is being considered.

[0004] JP 2016-69388 A JP 2011-529252 A

[0005] In recent years, secondary batteries have been required to have a longer lifespan, and there is a need to suppress deterioration during repeated charge and discharge. Patent Document 1 describes a lithium secondary battery in which the negative electrode is coated with a polymer electrolyte made of a urethane resin. Patent Document 2 describes a lithium secondary battery using a polymer electrolyte. Deterioration during repeated charge and discharge is generally believed to be due to interface deterioration, such as an increase in resistance at the electrode interface, but the cause is not uniquely determined, and battery life may be insufficient depending on the battery configuration and materials. According to the inventors' studies, the lithium secondary batteries described in Patent Documents 1 and 2 did not have sufficient battery life.

[0006] At least one aspect of the present disclosure is directed to providing a secondary battery that can suppress deterioration during repeated charging and discharging.

[0007] At least one aspect of the present disclosure provides a secondary battery having a positive electrode layer, a negative electrode layer, and a bulk electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer includes a positive electrode active material and a binder, and the bulk electrolyte layer includes Li ＋ , Na ＋ , K. ＋ , Mg ２＋ and Ca ２＋ and a first polymer, wherein the binder comprises a second polymer and a metal salt containing at least one cation selected from the group consisting of Li ＋ , Na ＋ , K. ＋ , Mg ２＋ and Ca ２＋ and a metal salt containing at least one cation selected from the group consisting of:

[0008] According to at least one embodiment of the present disclosure, a secondary battery capable of suppressing deterioration during repeated charge and discharge can be obtained.

[0009] FIG. 1 is a schematic cross-sectional view showing an example of a secondary battery according to the present disclosure.

[0010] 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.

[0011] A secondary battery according to one embodiment of the present disclosure is a secondary battery having a positive electrode layer, a negative electrode layer, and a bulk electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer includes a positive electrode active material and a binder, and the bulk electrolyte layer includes Li ＋ , Na ＋ , K. ＋ , Mg ２＋ and Ca ２＋ and a first polymer, wherein the binder comprises a second polymer and a metal salt containing at least one cation selected from the group consisting of Li ＋ , Na ＋ , K. ＋ , Mg ２＋ and Ca ２＋ and a metal salt containing at least one cation selected from the group consisting of: wherein the second polymer comprises a urethane resin having a cationic functional group bonded thereto, and the first polymer has a structure different from that of the second polymer.

[0012] As a result of extensive investigations, the inventors have found that deterioration due to repeated charge and discharge is likely to occur during discharge, i.e., when metal cations in the bulk electrolyte layer are biased toward the positive electrode layer. In the present disclosure, deterioration due to repeated charge and discharge refers to a decrease in ionic conductivity before and after repeated charge and discharge.

[0013] The inventors speculate as follows as to why a secondary battery according to one embodiment of the present disclosure has a configuration capable of suppressing deterioration during repeated charge and discharge. Because metal cations exchange electrons to charge and discharge the secondary battery, a combination of a cation and anion with a high degree of dissociation is selected for the metal salt supporting electrolyte. It is generally known that the degree of dissociation follows the HSAB rule. Because metal cations are hard acids according to the HSAB rule, a soft base is selected as the anion to be combined. Such soft bases generally have a larger molecular size than metal cations. Therefore, in the state of a metal salt supporting electrolyte, the mobility of ions upon dissociation in the electrolyte is lower than that of a metal salt composed of a hard acid and a hard base. Furthermore, because metal salts have a higher polarity than bulk electrolytes, aggregation of metal salts is more likely to occur in the bulk electrolyte. When metal salts are aggregated, the mobility of ions is lower than when they are not aggregated. As a result, it is believed that the ionic conductivity is more likely to decrease.

[0014] The bulk electrolyte layer in the present disclosure contains a metal salt containing a specific metal cation. The metal salt dissociates in the bulk electrolyte, allowing the metal cations to migrate and exchange electrons. However, during repeated charge and discharge, i.e., when the metal cations in the bulk electrolyte layer are biased toward the positive electrode layer, recombination of the metal cations and anions and reaggregation of the metal salts occur, presumably resulting in a decrease in ionic conductivity, particularly at the interface between the bulk electrolyte layer and the positive electrode layer where the mobility of the metal cations decreases. Meanwhile, the binder in the positive electrode layer in the present disclosure contains a second polymer containing a urethane resin to which cationic functional groups are bonded. When anions paired with the cationic functional groups in the binder dissociate from the cationic functional groups, they can recombine with metal cations contained in the bulk electrolyte. Therefore, it was thought that metal cations would recombine at the interface between the positive electrode layer and the bulk electrolyte layer, reducing ionic conductivity. However, the configuration in the present disclosure demonstrated an unexpected effect of suppressing degradation during repeated charge and discharge. This is presumably because cationic functional groups in the positive electrode binder near the interface between the positive electrode layer and the bulk electrolyte layer interact with anions of metal salts in the bulk electrolyte layer, facilitating dissociation of the metal cations paired with the anions. This makes it difficult for recombination and re-aggregation to occur, and promotes re-dissociation, thereby suppressing the decrease in ionic conductivity and suppressing deterioration during repeated charge and discharge.

[0015] The secondary battery according to the present disclosure will be described in detail below.

[0016] <Secondary Battery> The secondary battery has a positive electrode layer, a negative electrode layer, and a bulk electrolyte layer between the positive electrode layer and the negative electrode layer. In the present disclosure, the bulk electrolyte layer contains a first polymer as a polymer electrolyte.

[0017] An example of a secondary battery according to the present disclosure is shown in Fig. 1. The secondary battery 1 shown in Fig. 1 shows an example of the schematic configuration of a secondary battery using a polymer electrolyte as a bulk electrolyte 7. A positive electrode active material 3 provided on a positive electrode current collector 2 is fixed by a positive electrode active material binder 4 to form a positive electrode 6. The positive electrode 6 may contain a conductive additive 5.

[0018] A negative electrode active material 8 provided on a negative electrode current collector 9 forms a negative electrode 10. In Fig. 1, the negative electrode active material represents metallic lithium, indium, etc. A bulk electrolyte layer 11 is provided between the positive electrode 6 and the negative electrode 10.

[0019] <Bulk electrolyte layer> The bulk electrolyte layer is made of Li ＋ , Na ＋ , K. ＋ , Mg ２＋ and Ca ２＋ The bulk electrolyte layer comprises a metal salt containing at least one cation selected from the group consisting of: and a first polymer. The bulk electrolyte layer is preferably a solid or semi-solid electrolyte, such as a dry polymer electrolyte or a gel electrolyte. That is, a non-liquid electrolyte is preferred. A dry polymer electrolyte is more preferred. The polymer electrolyte preferably does not substantially contain a liquid component, such as a liquid electrolyte. This allows the bulk electrolyte layer to have a large contact interface with the positive electrode layer and the negative electrode layer, and further has flexibility to follow the expansion and contraction of the positive electrode layer and the negative electrode layer, thereby improving the characteristics of the secondary battery.

[0020] <Positive Electrode Layer> The positive electrode layer contains a positive electrode active material and a binder. The binder is preferably provided on a positive electrode current collector. The positive electrode layer preferably contains a positive electrode current collector. The positive electrode active material is preferably provided on the positive electrode current collector. The binder is a mixture of a second polymer and Li ＋ , Na ＋ , K. ＋ , Mg ２＋ and Ca ２＋ and a metal salt containing at least one cation selected from the group consisting of: The positive electrode layer may contain a conductive additive.

[0021] The positive electrode current collector may be, for example, a 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.

[0022] 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 O ４ , 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.

[0023] The conductive additive may be any of those commonly used in secondary batteries such as lithium-ion secondary batteries. Examples include 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 additives may be used alone or in combination of two or more.

[0024] <Negative Electrode Layer> The configuration of the negative electrode layer is not particularly limited, but may be, for example, made of a negative electrode current collector and a negative electrode active material provided on the negative electrode current collector. The negative electrode layer may contain a conductive additive.

[0025] (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.

[0026] (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 Sn４ , Mg ２ Examples include Sn.

[0027] 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 the negative electrode layer contains a second polymer, graphite is particularly suitable as the negative electrode active material.

[0028] 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 derivatives.

[0029] <First Polymer> The first polymer has a structure different from that of the second polymer. Examples of the first polymer include vinyl polymers, and more specifically, polyether acrylic resins having a three-dimensional crosslinked structure. The first polymer contained in the bulk electrolyte layer has a structure different from that of the second polymer contained in the positive electrode layer, enabling functional separation. For example, the first polymer has a function of, among other things, improving ionic conductivity, and the second polymer has a function of, among other things, improving adhesion to the current collector, the positive electrode active material, and the bulk electrolyte layer. This allows for further performance improvements while maintaining the energy density of the secondary battery.

[0030] The first polymer preferably has, in its polymer structure, at least one structure selected from the group consisting of a structure represented by the following formula (1) and a structure represented by the following formula (2) and a structure represented by the following formula (3). This gives the first polymer a three-dimensional crosslinked structure and makes it less likely to deform even at high temperatures. Meanwhile, the structure has a terminal free chain, one end of which is not bonded to other polymer chains. This is thought to prevent the polymer from forming a dense network structure, thereby maintaining strength and making it less likely to inhibit the movement of metal ions.

[0031] In formula (1), R １ represents a hydrogen atom or a methyl group. ２ represents a linear or branched alkylene group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 2 to 4). ３ represents an alkyl group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 1). ４ R each independently represents a hydrogen atom or a methyl group. ５ , R ６ each independently represents a linear or branched alkylene group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 2 to 4). ７ R each independently represents a hydrogen atom or a methyl group. ８ , R ９ , R １０ R each independently represents a linear or branched alkylene group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 2 to 4). １１ represents a trivalent organic group having 1 to 6 carbon atoms (preferably 1 to 3, more preferably 1).

[0032] In formulas (1) to (3), A1, B1, D1, D2, and D3 are each independently a linking group having at least an ethylene oxide structure represented by (—CH2CH2—O—).

[0033] The fact that the three-dimensional crosslinked structure of the polymer has many free terminal chains, one end of which is not bonded to a polymer chain, and that the crosslink density is very low is clearly expressed by the volume swelling ratio of the polymer electrolyte measured by the methyl ethyl ketone immersion method. Specifically, the volume swelling ratio of the first polymer measured by the methyl ethyl ketone (MEK) immersion method is preferably 40.0 to 120.0%.

[0034] The volume swelling ratio is a method for evaluating the crosslink density of crosslinked polymers, and water and toluene are used in the JIS method. In the case of polymer electrolytes for secondary batteries, polymers with relatively moderate polarity are often used because they must contain ionic components. Therefore, the solvent used for swelling ratio measurement is preferably one that has affinity for both the ionic components and the polymer. MEK has high affinity with alkali metal salts, organic ionic liquids, and polymers of various compositions, making it particularly suitable for measuring the volume swelling ratio of polymer electrolytes.

[0035] The volume swelling ratio represents the ratio of the volume of a three-dimensional cross-linked polymer before and after it is immersed in a specific solvent and becomes saturated with the solvent. The volume swelling ratio is calculated using the following formula, where the volume of the test specimen is calculated from the weight in air and the weight in water. The specific measurement method will be described later. Volume swelling ratio (%) = (volume when saturated with the solvent due to swelling after immersion) / (volume before immersion in the solvent) x 100

[0036] A volume swelling ratio of the first polymer of less than 40.0% is considered to indicate a low number of terminal free chains (the structure of formula (1)) and a high number of three-dimensional crosslinked structures. This results in low ionic conductivity and a tendency for the rate characteristics of the secondary battery to be poor. On the other hand, a volume swelling ratio of the first polymer of more than 120.0% indicates a lack of three-dimensional crosslinked structures, which is likely to result in a decrease in strength, such as a decrease in impact resistance at high temperatures. The volume swelling ratio of the polymer electrolyte is preferably 60.0 to 110.0%, and more preferably 70.0 to 105.0%.

[0037] The structure represented by formula (1) is preferably a structure represented by the following formula (1-1).

[0038] In formula (1-1), R １ represents a hydrogen atom or a methyl group. ２ represents a linear or branched alkylene group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 2 to 4). ３represents an alkyl group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 1). m1 and n1 represent the average number of moles added, m1 represents an integer of 1 or more (preferably 1 to 110, more preferably 13 to 46), and n1 represents an integer of 0 or more (preferably 5% to 25% of m1, more preferably 11% to 25% of m1).

[0039] In formulas (1) to (3), A1, B1, D1, D2 and D3 each independently represent (—CH ２ CH (CH ３ It is preferable that the copolymer further has a propylene oxide structure represented by the formula -O-R. The arrangement of the ethylene oxide structure and the propylene oxide structure may be a block copolymer or a random copolymer. A random copolymer is preferable. Furthermore, A1, B1, D1, D2, and D3 may each independently further contain a diol structure having 1 to 6 carbon atoms (preferably 4 to 6 carbon atoms) to the extent that the effects of the present disclosure are not impaired. The diol structure is represented by the formula -O-R ｘ -O-, and R ｘ is an alkylene group having 1 to 6 carbon atoms (preferably 4 to 6).

[0040] The structure represented by formula (2) is preferably a structure represented by the following formula (2-1).

[0041] In formula (2-1), R ４ R each independently represents a hydrogen atom or a methyl group. ５ , R ６ each independently represents a linear or branched alkylene group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 2 to 4). m2 and n2 represent the average number of moles added, m2 represents an integer of 1 or more (preferably 1 to 110, more preferably 13 to 46), and n2 represents an integer of 0 or more (preferably 5% to 25% of m2, more preferably 11% to 25% of m2).

[0042] The chain sandwiched between the two -COO- may further contain a diol structure having 1 to 6 carbon atoms (preferably 4 to 6 carbon atoms) to the extent that the effect of the present disclosure is not impaired. For example, a diol structure may be contained between ethylene oxide structures, between propylene oxide structures, or between an ethylene oxide structure and a propylene oxide structure. The diol structure is represented by -O-R ｘ -O-, and R ｘ is an alkylene group having 1 to 6 carbon atoms (preferably 4 to 6).

[0043] The structure represented by formula (3) is preferably a structure represented by the following formula (3-1).

[0044] In formula (3-1), R ７ R each independently represents a hydrogen atom or a methyl group. ８ , R ９ , R １０ R each independently represents a linear or branched alkylene group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 2 to 4). １１ represents a trivalent organic group (preferably a hydrocarbon group) having 1 to 6 carbon atoms (preferably 1 to 3, more preferably 1). m3 and n3 represent the average number of moles added, each m3 independently represents an integer of 1 or more (preferably 1 to 110, more preferably 13 to 46), and each n3 independently represents an integer of 0 or more (preferably 5% to 25% of m3, more preferably 11% to 25% of m3).

[0045] -COO- and R to an extent that does not impair the effects of the present disclosure. １１ The chain sandwiched between these may further contain a diol structure having 1 to 6 carbon atoms (preferably 4 to 6). For example, a diol structure may be contained between ethylene oxide structures, between propylene oxide structures, or between an ethylene oxide structure and a propylene oxide structure. The diol structure is represented by the formula -O-R ｘ -O-, and R ｘ is an alkylene group having 1 to 6 carbon atoms (preferably 4 to 6).

[0046] The average number of moles of ethylene oxide structures added per mole of (meth)acryloyl residue in the polymer contained in the first polymer, Meo, is preferably 2.5 moles or more. Meo is more preferably 13 to 46. When Meo is in the above range, the crosslinking density of the polymer main chain becomes more appropriate, thereby achieving high ionic conductivity while maintaining strength at high temperatures. The (meth)acryloyl residue is a form in which a (meth)acryloyl group is addition-polymerized, and is represented by the following structure in formula (1), for example:

[0047] Furthermore, in the polymer contained in the first polymer, the average number of moles of propylene oxide structures added per mole of (meth)acryloyl residue, Mpo, is preferably 5 to 25%, and more preferably 11 to 25%, of the average number of moles of ethylene oxide structures added per mole of (meth)acryloyl residue, Meo. By being in this range, the crystallinity of the polymer main chain is suppressed even if the molecular weight between crosslinking points is large, and inhibition of metal ion migration, particularly at low temperatures, is more easily suppressed.

[0048] The average numbers of moles added Meo and Mpo can be measured by decomposing the first polymer using pyrolysis GC / MS, and quantifying the fragments derived from (meth)acryloyl residues, the fragments derived from ethylene oxide structures, and the fragments derived from propylene oxide structures by creating respective calibration curves.

[0049] In the first polymer of the present disclosure, the three-dimensional crosslinked structure of the polymer has a very low crosslink density as described above, and the polymer chain has many free chains at one end that are not bonded to other polymer chains, etc. Such a crosslinked structure can be obtained, for example, by reacting the following materials: polyether mono(meth)acrylate; at least one selected from the group consisting of polyether di(meth)acrylate and polyether tri(meth)acrylate; at least one selected from the group consisting of imidazolium-based ionic compounds having an unsaturated reactive functional group, pyridinium-based ionic compounds having an unsaturated reactive functional group, and ammonium-based ionic compounds having an unsaturated reactive functional group, and / or at least one selected from the group consisting of compounds having an unsaturated reactive functional group, an anionic functional group having a fluorinated sulfonylimide group or a perfluoroalkylsulfonylimide group, and a cation.

[0050] (Polyether mono(meth)acrylate) Polyether mono(meth)acrylate can form a structure represented by formula (1) (preferably formula (1-1)). As the polyether mono(meth)acrylate, for example, at least one selected from the group consisting of polyethylene glycol mono(meth)acrylate and mono(meth)acrylate of polyethylene glycol-propylene glycol copolymer can be used. When using mono(meth)acrylate of polyethylene glycol-propylene glycol copolymer, the molar ratio of ethylene glycol structure:propylene glycol structure is preferably 100:0 to 50:50, and more preferably 80:20 to 95:5.

[0051] When the molar ratio of the ethylene glycol structure:propylene glycol structure is within this range, the transportability of metal ions by polyethylene glycol can be maintained at a high level, and the combination with the structure of formula (4) and / or the structure of formula (5) makes it easier to suppress the inhibition of metal ion migration due to crystallization of the polymer.

[0052] The polyether mono(meth)acrylate is represented by, for example, the following formula (1'). In formula (1′), R １ , R ２ , R ３ , m1 and n1 are the same as in formula (1-1).

[0053] (Polyether di(meth)acrylate) Polyether di(meth)acrylate can form a structure represented by formula (2) (preferably formula (2-1)). As the polyether di(meth)acrylate, for example, at least one selected from the group consisting of polyethylene glycol di(meth)acrylate and di(meth)acrylate of polyethylene glycol-propylene glycol copolymer can be used. When di(meth)acrylate of polyethylene glycol-propylene glycol copolymer is used, the molar ratio of ethylene glycol structure:propylene glycol structure is preferably 100:0 to 50:50, and more preferably 95:5 to 80:20.

[0054] When the molar ratio of the ethylene glycol structure:propylene glycol structure is within this range, the transportability of metal ions by polyethylene glycol can be maintained at a high level, and the combination with the structure of formula (4) and / or the structure of formula (5) makes it easier to suppress the inhibition of metal ion migration due to crystallization of the polymer.

[0055] The polyether di(meth)acrylate is represented, for example, by the following formula (2'). In formula (2'), R ４ , R ５ , R ６ , m2, and n2 are the same as in formula (2-1). The chain sandwiched between two -COO- may further contain a diol structure having 1 to 6 carbon atoms (preferably 4 to 6) to the extent that the effect of the present disclosure is not impaired. For example, a diol structure may be contained between ethylene oxide structures, between propylene oxide structures, or between an ethylene oxide structure and a propylene oxide structure. The diol structure is represented by -O-R ｘ -O-, and R ｘ is an alkylene group having 1 to 6 carbon atoms (preferably 4 to 6).

[0056] (Polyether tri(meth)acrylate) Polyether tri(meth)acrylate can form a structure represented by formula (3) (preferably formula (3-1)). As the polyether tri(meth)acrylate, for example, at least one selected from the group consisting of polyethylene glycol tri(meth)acrylate and tri(meth)acrylate of polyethylene glycol-propylene glycol copolymer can be used. When tri(meth)acrylate of polyethylene glycol-propylene glycol copolymer is used, the molar ratio of ethylene glycol structure:propylene glycol structure is preferably 100:0 to 50:50, and more preferably 80:20 to 95:5.

[0057] When the molar ratio of the ethylene glycol structure:propylene glycol structure is within this range, the transportability of metal ions by polyethylene glycol can be maintained at a high level, and the combination with the structure of formula (4) and / or the structure of formula (5) makes it easier to suppress the inhibition of metal ion migration due to crystallization of the polymer.

[0058] The polyether tri(meth)acrylate is represented, for example, by the following formula (3'). In formula (3'), R ７ , R ８ , R ９ , R １０ , R １１ , m3, and n3 are the same as in formula (3-1). １１ The chain sandwiched between these may further contain a diol structure having 1 to 6 carbon atoms (preferably 4 to 6). For example, a diol structure may be contained between ethylene oxide structures, between propylene oxide structures, or between an ethylene oxide structure and a propylene oxide structure. The diol structure is represented by the formula -O-R ｘ -O-, and R ｘ is an alkylene group having 1 to 6 carbon atoms (preferably 4 to 6).

[0059] The structures represented by formula (1), formula (2) and formula (3) (preferably formula (1-1), formula (2-1) and formula (3-1)) can be obtained, for example, by using a polyether polyol obtained by ring-opening polymerization of ethylene oxide and propylene oxide. In formula (1-1), formula (2-1) and formula (3-1) (and formula (1'), formula (2') and formula (3')), (-CH ２ -CH ２ -O-) and an ethylene oxide structure represented by (-CH ２ -CH(CH ３ The arrangement of the propylene oxide structure represented by (III)-(O-) may be a block copolymer or a random copolymer, preferably a random copolymer.

[0060] The mass content of the structure represented by formula (1) in the polymer contained in the first polymer is designated as A. The mass content of the structure represented by formula (2) and the structure represented by formula (3) in the polymer (preferably the content of the structure represented by formula (2)) is designated as B. The mass ratio A:B of A to B is preferably 70:30 to 98:2, more preferably 88:12 to 96:4, and even more preferably 90:10 to 95:5.

[0061] The mass ratio A:B can be adjusted by specifically adjusting the ratio of polyether mono(meth)acrylate to polyether di(meth)acrylate and / or tri(meth)acrylate. When the mass ratio A:B is within the above range, the polymer does not have an excessively dense network structure, and the strength is maintained while the migration of metal ions is less likely to be hindered, which is particularly preferred.

[0062] In the first polymer, it is preferable that m1+n1 in formula (1-1) is 1 to 110 (more preferably 14 to 58), and m2+n2 in formula (2-1) and / or m3+n3 in formula (3-1) (preferably m2+n2 and m3+n3) are 1 to 110 (more preferably 14 to 58). By being in the above ranges, the crosslink density of the polymer main chain becomes appropriate, so that the ionic conductivity of the bulk electrolyte layer is higher and the rate characteristics of the secondary battery are improved while maintaining strength at high temperatures.

[0063] In the first polymer, it is preferable that m1:n1 in formula (1-1) is 80:20 to 95:5 (more preferably 80:20 to 90:10), and m2:n2 in formula (2-1) and / or m3:n3 in formula (3-1) (preferably m2:n2 in formula (2-1) and m3:n3 in formula (3-1)) are 80:20 to 95:5 (more preferably 85:15 to 95:5). By being in the above ranges, the crystallinity of the polymer main chain is suppressed even if the molecular weight between crosslinking points is large, and it becomes easier to suppress the inhibition of metal ion migration, particularly at low temperatures.

[0064] The first polymer preferably has at least one structure selected from the group consisting of the structure represented by formula (4), the structure represented by formula (5), the structure represented by formula (6), and the structure represented by formula (7). The structure represented by formula (4) is an anionic structure, and the structures represented by formula (5), the structure represented by formula (6), and the structure represented by formula (7) are nitrogen-containing cationic structures. Such structures reduce the polarity difference between the metal salt contained in the bulk electrolyte layer and the polymer. As a result, the metal salt does not precipitate and the soluble content can be increased. In particular, cations having nitrogen-containing aromatic structures are highly stable as cations, and are thought to interact with the anions of the metal salt, thereby improving the dissociation rate of the metal salt. Furthermore, the anionic structure and nitrogen-containing cationic structure bonded to the above polymer structure suppress stereoregularity and reduce the crystallinity of the polymer. This is thought to also suppress a decrease in ionic conductivity at low temperatures.

[0065] The first polymer preferably has a structure represented by the following formula (4). In formula (4), R １２ represents a hydrogen atom or a methyl group. １３ represents a linear or branched alkylene group having 1 to 7 carbon atoms (preferably 2 to 4). １４ represents a fluorine atom or a perfluoroalkyl group having 1 to 4 carbon atoms (preferably 1 to 2 carbon atoms). ＋represents at least one selected from the group consisting of a lithium ion, a sodium ion, and a potassium ion.

[0066] The polyether composition of polyether (meth)acrylates, which are the main components of the polymer, is preferably polyethylene glycol in terms of the transportability of ions such as lithium ions. However, polyethylene glycol has high crystallinity, and there is a method of copolymerizing a propylene glycol structure, which has poor ion transportability, at a certain ratio.

[0067] On the other hand, because the structure represented by formula (4) is an anionic structure with a relatively large molecular size, introducing the structure represented by formula (4) into the polymer structure can reduce crystallinity. Therefore, crystallization can be suppressed even by reducing the amount of propylene glycol structures, which have poor lithium ion transport properties, in the polyether composition. As a result, high ionic conductivity can be maintained even after repeated charge and discharge.

[0068] The content of the structure represented by formula (4) in the polymer electrolyte is preferably 1 to 30 parts by mass, more preferably 5 to 25 parts by mass, and even more preferably 10 to 20 parts by mass, relative to a total of 100 parts by mass of the structures represented by formula (1), formula (2), and formula (3). When the content of formula (4) is within this range, it is possible to expect an improvement in ionic conductivity due to a decrease in crystallinity while containing a sufficient amount of ions.

[0069] The state after these reactions can be confirmed by analysis using known means such as pyrolysis GC / MS, FT-IR, and NMR.

[0070] Cation X shown in formula (4) ＋The cation may be at least one selected from the group consisting of lithium ions, sodium ions, and potassium ions. The cation may be selected depending on the carrier in the secondary battery. For example, lithium is selected for a lithium-ion secondary battery that uses lithium cobalt oxide or the like as the positive electrode active material, and sodium is selected for a sodium-sulfur secondary battery. The polymer electrolyte may contain a metal salt such as a lithium salt, a sodium salt, or a potassium salt, as long as the effect of the present disclosure is not impaired.

[0071] A compound having an unsaturated reactive functional group, an anionic functional group having a fluorinated sulfonylimide group or a perfluoroalkylsulfonylimide group, and a cation, which can form a structure represented by formula (4), is represented, for example, by the following formula (4'): In formula (4'), R １２ ~R １４ , X ＋ is the same as that explained in equation (4).

[0072] The first polymer preferably has at least one structure selected from the group consisting of 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).

[0073] The first polymer preferably includes a structure represented by the following formula (5): For example, the structure represented by the following formula (5) may be a reaction product of an imidazolium-based ionic compound having an unsaturated reactive functional group.

[0074] In formula (5), R １５ represents a hydrogen atom or a methyl group. １６ represents a divalent linking group. １７ represents an alkyl group having 1 to 4 carbon atoms (preferably 1 to 3, more preferably 1 or 2, and even more preferably 1). １８ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms (preferably 1 to 3, more preferably 1 or 2, and even more preferably 1).

[0075] In formula (5), R １６ ~R １８is bonded to three elements selected from the group consisting of two nitrogen atoms and three carbon atoms that constitute the imidazolium ring structure. １６ ~R １８ One of X1 is bonded to the cationic nitrogen atom in the imidazolium ring structure. － represents an anion. Preferably, R １６ is bonded to the cationic nitrogen atom constituting the imidazolium ring structure. １７ is bonded to the nitrogen atom that constitutes the imidazolium ring structure.

[0076] R as a linking group １６ Specifically, represents a linear or branched alkylene group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 1 or 2, and even more preferably 1), or a divalent organic group containing an ester bond. The divalent organic group containing an ester bond is preferably an ester bond (—COO—) or a carbonyloxyalkylene having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 1 or 2, and even more preferably 1) in the alkylene. Preferably, the carbonyl group in the divalent organic group containing an ester bond is R １５ is bonded to the carbon to which it is bonded.

[0077] The imidazolium ring structure may have a substituent such as an alkyl group, a substituted alkyl group (substituted with a halogen or the like), or a halogen.

[0078] The first polymer preferably contains a structure represented by the following formula (6): For example, the structure represented by the following formula (6) may be a reaction product of a pyridinium-based ionic compound having an unsaturated reactive functional group.

[0079] In formula (6), R １９ represents a hydrogen atom or a methyl group. ２０ represents a divalent linking group. ２１ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms (preferably 1 to 3, more preferably 1 or 2, and even more preferably 1). ２０ and R ２１One of X2 is bonded to the nitrogen atom constituting the pyridinium ring structure, and the other is bonded to any of the five carbon atoms constituting the pyridinium ring structure. － represents an anion. Preferably, R ２０ is attached to the cationic nitrogen atom that constitutes the pyridinium ring structure.

[0080] R as a linking group ２０ Specifically, represents a linear or branched alkylene group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 1 or 2, and even more preferably 1), or a divalent organic group containing an ester bond. The divalent organic group containing an ester bond is preferably an ester bond (—COO—) or a carbonyloxyalkylene having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 1 or 2, and even more preferably 1) in the alkylene. Preferably, the carbonyl group in the divalent organic group containing an ester bond is R １９ is bonded to the carbon to which it is bonded.

[0081] The pyridinium ring structure may have a substituent such as an alkyl group, a substituted alkyl group (substituted with a halogen or the like), or a halogen.

[0082] The polyether composition of polyether (meth)acrylates, which are the main components of the polymer, is preferably polyethylene glycol in terms of metal ion transportability. However, polyethylene glycol has high crystallinity, and to suppress crystallization, especially at low temperatures, one method is to copolymerize a propylene glycol structure, which has poor metal ion mobility, at a certain ratio.

[0083] On the other hand, the structure represented by formula (5) and the structure represented by formula (6) are cationic structures with a relatively large molecular size and a planar structure, and therefore, by introducing them into a polymer structure, it is possible to reduce crystallinity. Therefore, by using the structure represented by formula (5) or the structure represented by formula (6), it is possible to reduce the amount of propylene glycol structures, which have poor metal ion transport properties, in the polyether composition, and suppress crystallization at low temperatures. As a result, it is possible to maintain high ionic conductivity even at low temperatures.

[0084] Furthermore, by introducing the structure represented by formula (5) or the structure represented by formula (6) into the polymer structure, the polymer itself becomes ionic, and the affinity with metal salts is improved compared to when the polymer does not have the structure represented by formula (5) or the structure represented by formula (6), making it possible to dissolve a larger amount of metal salt without precipitating it.

[0085] Furthermore, the imidazolium group contained in formula (5) and the pyridinium group contained in formula (6) have high stability as cations and a high dissociation rate with anions, and therefore it is believed that the imidazolium group or pyridinium group interacts with the anion of the metal salt contained as the supporting electrolyte, promoting dissociation of the metal salt and thereby improving ionic conductivity.

[0086] The total content of the structure represented by formula (5) and the structure represented by formula (6) in the polymer structure is preferably 1 to 15 parts by mass, and more preferably 2 to 5 parts by mass, per 100 parts by mass of the total of the structures represented by formulas (1), (2), and (3). When the content of formulas (5) and (6) is within this range, it is possible to achieve both improved compatibility with the metal salt contained as the supporting electrolyte and improved ionic conductivity due to reduced crystallinity at a higher level.

[0087] The state after these reactions can be confirmed by analysis using known means such as pyrolysis GC / MS, FT-IR, and NMR.

[0088] An imidazolium-based ionic compound having an unsaturated reactive functional group capable of forming the structure represented by formula (5) is represented, for example, by the following formula (5'): Furthermore, a pyridinium-based ionic compound having an unsaturated reactive functional group capable of forming the structure represented by formula (6) is represented, for example, by the following formula (6'):

[0089] In formula (5') and formula (6'), R １５ ~R ２１ , X1 － , X2 － is the same as that explained in equations (5) and (6).

[0090] The first polymer preferably includes a structure represented by the following formula (7): For example, the structure represented by the following formula (7) may be a reaction product of an ammonium-based ionic compound having an unsaturated reactive functional group.

[0091] In formula (7), R ２２ represents a hydrogen atom or a methyl group. ２３ represents a divalent linking group. ２４ ~R ２６ Each of X3 independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. － represents an anion.

[0092] R as a linking group ２３ Specifically, represents a linear or branched alkylene group having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 1 or 2, and even more preferably 1), or a divalent organic group containing an ester bond. The divalent organic group containing an ester bond is preferably an ester bond (—COO—) or a carbonyloxyalkylene having 1 to 6 carbon atoms (preferably 1 to 4, more preferably 1 or 2, and even more preferably 1) in the alkylene. Preferably, the carbonyl group in the divalent organic group containing an ester bond is R ２２ is bonded to the carbon to which it is bonded.

[0093] The content of the structure represented by formula (7) in the polymer electrolyte is preferably 1 to 30 parts by mass, more preferably 5 to 25 parts by mass, and even more preferably 10 to 20 parts by mass, relative to 100 parts by mass of the total of the structures represented by formula (1), formula (2), and formula (3). When the content of formula (7) is within this range, it is possible to achieve both improved compatibility with the metal salt contained as the supporting electrolyte and improved ionic conductivity due to reduced crystallinity at a higher level.

[0094] <Anion> Anion X1 represented by formula (5) to formula (7) － , X2 － , X3 －Examples of the anion include a fluoroalkylsulfonylimide anion, a fluorosulfonylimide anion, a fluoroalkylsulfonate anion, a fluorosulfonate anion, a fluoroalkylcarboxylate anion, a fluoroalkylmethide anion, a fluoroborate anion, a fluorophosphate anion, a dicyanamide anion, a thiocyanate anion, a bisoxalatoborate anion, a perchlorate anion, and derivatives thereof.

[0095] 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.

[0096] 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 perfluorooctane sulfonate anion.

[0097] Specific examples of the fluoroalkyl carboxylic acid anion include trifluoroacetic acid anion, perfluoropropionic acid anion, perfluorobutyric acid anion, perfluorovaleric acid anion, and perfluorocaproic acid 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.

[0098] Specific examples of fluoroborate anions include tetrafluoroborate anions, and specific examples of fluorophosphate anions include hexafluorophosphate anions.

[0099] 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 ionic conductivity in a low-temperature environment.

[0100] More specifically, bis(trifluoromethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, trifluoromethanesulfonate anion (CF ３ -SO ３ － ), hexafluorophosphate anion (PF ６ － ), tetrafluoroborate anion (BF ４ － ), dicyanamide anion (N(CN) ２ － ), thiocyanate anion (SCN － ) is preferred.

[0101] <Metal Salt> The bulk electrolyte layer is made of Li ＋ , Na ＋ , K. ＋ , Mg ２＋ and Ca ２＋ The metal salt contains at least one cation selected from the group consisting of: The metal salt is contained as a supporting electrolyte in the bulk electrolyte layer. In this case, the cation of the metal salt functions as a carrier in the secondary battery, so that in a lithium secondary battery, for example, the cation of the same kind, Li, ＋ is selected.

[0102] Metal salts have an anion that pairs with the cation, e.g., BF ４ － , P.F. ６ － , N(SO ２ CF ３ ) ２ － , N(SO ２ F) ２ － , N(SO ２ C ２ F ５ ) ２ － , B(OCH(CF ３ ) ２ ) ４ － , B(OCH(CF ３ ) ２ ) ４ － , AlCl ４ － , S.B.F. ６ － , SCN － , C.F. ３ SO ３ － , AsF ６ － , ClO ４ － , N (CN) ２ － , lower aliphatic carboxylic acid anion, CO ３ ２－ , Cl － ,Br － , I －Specifically, the metal salt preferably contains at least one anion selected from the group consisting of a bis(trifluoromethanesulfonyl)imide anion, a bis(fluorosulfonyl)imide anion, a trifluoromethanesulfonate anion, a tetrafluoroborate anion, a hexafluorophosphate anion, a dicyanamide anion, a thiocyanate anion, and a bisoxalatoborate anion.

[0103] Metal salts are preferred because of their chemical stability with the positive electrode active material. ２ CF ３ ) ２ ), lithium bis(fluorosulfonyl)imide (LiN(SO ２ F) ２ ), LiN(C ２ F ５ SO ２ ) ２ It is preferable to use at least one selected from the group consisting of: The lithium salt may be used singly or in combination of two or more. Similarly, it is preferable to select a similar pair anion for sodium or potassium, which are monovalent ions. As for magnesium salts, magnesium bis(trifluoromethanesulfonyl)imide (Mg(N(SO ２ CF ３ ) ２ ) ２ ), magnesium bis(fluorosulfonyl)imide (Mg(N(SO ２ F) ２ ) ２ ) is preferred. The magnesium salts may be used alone or in combination of two or more. Similarly, it is preferred to select a similar counter anion for calcium, which is a divalent ion.

[0104] The content of the metal salt is preferably 5 to 40 parts by mass, more preferably 7 to 20 parts by mass, per 100 parts by mass of the polymer in the first polymer. When the content of the metal salt is within this range, the metal salt is well compatible with the polymer and does not precipitate, and high ionic conductivity is obtained.

[0105] The first polymer is preferably a cured product of an electrolyte solution. The electrolyte solution may be, for example, a mixture of the following materials: polyether mono(meth)acrylate; at least one selected from the group consisting of polyether di(meth)acrylate and polyether tri(meth)acrylate; at least one selected from the group consisting of imidazolium-based ionic compounds having an unsaturated reactive functional group, pyridinium-based ionic compounds having an unsaturated reactive functional group, and ammonium-based ionic compounds having an unsaturated reactive functional group, and / or at least one selected from the group consisting of compounds having an unsaturated reactive functional group, an anionic functional group having a fluorinated sulfonylimide group or a perfluoroalkylsulfonylimide group, and a cation.

[0106] When the first polymer is used as a bulk electrolyte layer, if a metal salt is used as a supporting electrolyte, it is preferable to mix the metal salt into the electrolyte solution. If necessary, the electrolyte solution may contain a known polymerization initiator. Examples of the polymerization initiator include photopolymerization initiators. Also, known organic solvents such as N-methyl-2-pyrrolidone and methyl ethyl ketone may be used.

[0107] <Liquid Electrolyte> The bulk electrolyte layer may contain a liquid electrolyte to the extent that the effects of the present disclosure are not impaired and safety at high temperatures is not impaired. Examples of the liquid electrolyte include an ionic liquid and a non-aqueous electrolytic solution.

[0108] Specific examples of ionic liquids include the following combinations of cations and anions. The cation may be at least one selected from the group consisting of quaternary ammonium, imidazolium, pyridinium, pyrrolidinium, and piperidinium. The anion may be at least one selected from the group consisting of a fluoroalkylsulfonylimide anion, a fluorosulfonylimide anion, a fluoroalkylsulfonate anion, a fluorosulfonate anion, a fluoroalkylcarboxylate anion, a fluoroalkylmethide anion, a fluoroborate anion, a fluorophosphate anion, a dicyanamide anion, a thiocyanate anion, a bisoxalatoborate anion, a perchlorate anion, and derivatives thereof.

[0109] The non-aqueous electrolyte is a liquid in which approximately 1 mol of a metal salt is dissolved in a non-aqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the lithium salt include LiPF ６ , LiBF ４ , LiClO ４ Examples include:

[0110] Although the inclusion of a liquid electrolyte may improve ionic conductivity, in order to avoid a decrease in mechanical strength at high temperatures, the amount of the liquid electrolyte is preferably, for example, 10 parts by mass or less, 5 parts by mass or less, 1 part by mass or less, or 0.5 parts by mass or less relative to 100 parts by mass of the polymer contained in the polymer electrolyte.

[0111] The bulk electrolyte layer may contain, as needed, a non-conductive filler such as silica, quartz powder, titanium oxide, zinc oxide, or calcium carbonate. By adding these non-conductive fillers to the electrolyte layer-forming paint, they function as a film-forming aid when the paint is coated in the electrolyte layer-forming process. The content of such non-conductive fillers is preferably 0.1 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the polymer that forms the electrolyte layer.

[0112] The bulk electrolyte layer may contain a conductive filler, if necessary, within a range that does not impair the effects of the present disclosure. Examples of the conductive filler include conductive fine particles such as carbon black, zinc oxide, tin oxide, and titanium oxide.

[0113] (Method for forming bulk electrolyte layer) The method for forming the bulk electrolyte layer is not particularly limited. For example, the above-mentioned materials are mixed by a known method to obtain an electrolyte solution for forming the bulk electrolyte layer. The electrolyte solution is applied by a known application method such as bar coating, spin coating, or roll coating, and then the polymer material contained in the electrolyte solution is polymerized by a known means such as UV to form the bulk electrolyte layer. The bulk electrolyte layer can be formed at a desired position, such as on a positive electrode or a negative electrode. The thickness of the bulk electrolyte layer is preferably 5.0 μm or more and 100.0 μm or less.

[0114] <Second Polymer> The second polymer contains a urethane resin to which cationic functional groups are bonded. Therefore, the second polymer has a highly polar structure. This reduces the polarity difference between the second polymer and the metal salt contained as a supporting electrolyte in the positive electrode layer, making it less likely for the metal salt to precipitate from the second polymer. As a result, the content of the metal salt as a supporting electrolyte in the polymer electrolyte layer can be increased. Meanwhile, the anions paired with the cationic functional groups in the urethane resin structure also interact with the metal cations contained as the indicator electrolyte, hindering ion migration. This was expected to result in a decrease in ionic conductivity. However, an unexpected improvement in ionic conductivity was observed. This is thought to be due to the presence of cationic functional groups in the urethane resin structure interacting with the anions of the supporting electrolyte, improving the dissociation rate of the metal salt contained as a supporting electrolyte. The improvement in ionic conductivity is thought to be due to the effect of improving the dissociation rate exceeding the effect of the anions present in the urethane resin structure in inhibiting cation migration.

[0115] The urethane resin according to the present disclosure includes a urethane resin having a cationic functional group bonded thereto. Furthermore, the urethane resin according to the present disclosure preferably has a three-dimensional crosslinked structure. The method for obtaining a urethane resin having a three-dimensional crosslinked structure is not particularly limited, but it can be obtained, for example, by reacting an ionic compound having a functional group, such as a hydroxyl group, that can react with an isocyanate group with an isocyanate compound, such as polyisocyanate. Known polyols can also be used. Furthermore, it can also be obtained by reacting a urethane prepolymer, described below, with a polyol and an ionic compound.

[0116] The polyol is not particularly limited, but a polyol having at least two hydroxyl groups is preferred. For example, at least one selected from the group consisting of polyether polyol, polyester polyol, polycaprolactone polyol, polycarbonate polyol, polyolefin polyol, and acrylic polyol can be used. Among these, polyether polyol is preferred from the viewpoint of metal ion mobility. Furthermore, when an isocyanate compound having two isocyanate groups is used as the isocyanate compound described below, the polyol is preferably a polyol having at least three hydroxyl groups.

[0117] The polyether polyol can be at least one selected from the group consisting of diol and triol types of polyethylene glycol, diol and triol types of polypropylene glycol, 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, poly 1,4-butanediol-3-methyl-1,4-butanediol copolymer, and diol and triol types of polyethylene glycol-propylene glycol copolymer.

[0118] When a polyethylene glycol-propylene glycol copolymer is used as the polyol, the molar ratio of polyethylene glycol structure:polypropylene glycol structure is preferably 90:10 to 50:50, and particularly preferably 80:20 to 90:10. When the molar ratio of ethylene glycol structure:propylene glycol structure is within this range, the mobility of metal ions due to polyethylene glycol can be maintained at a high level, and inhibition of metal ion migration caused by crystallization of the polymer can be easily suppressed.

[0119] The number-average molecular weight of the polyol is preferably 1,000 to 10,000, and particularly preferably 3,000 to 5,000. A number-average molecular weight of less than 1,000 provides excellent mechanical strength, but the distance between crosslinking points is shortened, resulting in high crosslink density and a tendency for metal ion mobility to decrease. A number-average molecular weight of 10,000 or more results in a small number of crosslinking points and a low crosslink density, making it difficult for the polymer to exert its stabilizing effect on metal ions and resulting in a tendency for metal ion mobility to decrease. A number-average molecular weight in the range of 1,000 to 10,000 makes it easy to ensure mechanical strength while maintaining ion mobility. A number-average molecular weight in the range of 3,000 to 5,000 is more preferable because crystallization at low temperatures due to interactions between polyols is less likely to occur, improving ion mobility at low temperatures.

[0120] The degree of development of the crosslink density of the urethane resin can be confirmed by the volume swelling ratio of the second polymer, which is a polymer electrolyte, measured by the methyl ethyl ketone immersion method. The volume swelling ratio of the second polymer measured by the methyl ethyl ketone (MEK) immersion method is preferably 30.0 to 100.0%. A volume swelling ratio of the second polymer of 100.0% or less is less likely to cause a decrease in mechanical strength due to low crosslink density. Furthermore, a volume swelling ratio of 30.0% or more is less likely to cause an ion migration inhibition effect due to high crosslink density. As a result, both ion mobility and mechanical strength can be achieved at high levels, which is preferable. The volume swelling ratio of the second polymer is more preferably 30.0 to 80.0%, and even more preferably 40.0 to 80.0%.

[0121] The isocyanate compound is not particularly limited, but is preferably an isocyanate compound having at least two isocyanate groups. For example, aliphatic polyisocyanates such as ethylene diisocyanate and 1,6-hexamethylene diisocyanate (HDI); alicyclic polyisocyanates such as isophorone diisocyanate (IPDI), cyclohexane 1,3-diisocyanate, and cyclohexane 1,4-diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate (TDI), 1,4-phenylene diisocyanate, 4,4-diphenylmethane diisocyanate (MDI), polymeric diphenylmethane diisocyanate (polymeric MDI), xylylene diisocyanate, and naphthalene diisocyanate, as well as copolymers thereof, isocyanurates, TMP adducts, biurets, and block compounds thereof can be used. These isocyanate compounds can be used alone or in combination of two or more. Among these, it is preferable to include at least one selected from the group consisting of 1,4-phenylene diisocyanate, 4,4-diphenylmethane diisocyanate, and polymeric MDI, and it is more preferable to include at least one selected from the group consisting of polymeric MDI and 1,4-phenylene diisocyanate. When a polyol having two hydroxyl groups (i.e., a diol type) is used as the polyol, the isocyanate compound is preferably an isocyanate compound having at least three isocyanate groups, such as polymeric MDI.

[0122] Among the above, polymeric MDI is preferred. Here, polymeric MDI is a mixture of monomeric MDI and high molecular weight polyisocyanate, and is represented by the following formula (A). In formula (A), n is preferably 0 or more and 4 or less. As the polymeric MDI, commercially available products may be used, and examples thereof include Millionate MR series (manufactured by Tosoh Corporation) such as Millionate MR200 (trade name).

[0123] Alternatively, a urethane prepolymer obtained by reacting a polyol such as the polyether polyol described above with the isocyanate compound described above may be used as the isocyanate compound. The urethane prepolymer has at least one isocyanate group and a polyether structure. When the urethane prepolymer is used as the isocyanate compound, the content of the isocyanate compound used in synthesizing the urethane prepolymer is preferably 1.0 to 200.0 parts by mass, more preferably 5.0 to 100.0 parts by mass, even more preferably 10.0 to 50.0 parts by mass, particularly preferably 10.0 to 40.0 parts by mass, and even more preferably 10.0 to 30.0 parts by mass, per 100 parts by mass of the polyol. When the urethane prepolymer is used as the isocyanate compound, the isocyanate content in the urethane prepolymer is preferably 1.0 to 5.0% by mass, more preferably 1.5 to 3.5% by mass. Having the isocyanate content within the above range makes it easier to control the crosslink density.

[0124] The content of the isocyanate compound is not particularly limited, but is preferably 50.0 to 480.0 parts by mass, more preferably 60.0 to 400.0 parts by mass, even more preferably 70.0 to 300.0 parts by mass, particularly preferably 70.0 to 200.0 parts by mass, and even more preferably 70.0 to 150.0 parts by mass, relative to 100 parts by mass of the polyol.

[0125] The urethane resin contained in the second polymer has a cationic functional group bonded thereto. For example, the urethane resin contains a cationic functional group and an anion in the urethane resin structure. The cationic functional group and anion are preferably an ionic compound containing a cation having a substituent reactive with an isocyanate group and an anion, and a residue resulting from the reaction of an isocyanate group. The ionic compound containing a cation having a substituent reactive with an isocyanate group and an anion is composed of a cation having at least one functional group (e.g., a hydroxyl group) reactive with an isocyanate group and an anion. Examples of functional groups reactive with an isocyanate group include hydroxyl groups and amino groups, with a hydroxyl group being preferred. 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, per 100 parts by mass of the polyol and isocyanate combined. When the content of the ionic compound is within this range, it is possible to achieve a high level of both the improvement in compatibility with the metal salt serving as the supporting electrolyte and the improvement in the separation rate. The cationic functional group and anion of the ionic compound are described below. Note that the combination of the cationic functional group and the anion is not particularly limited.

[0126] The cationic functional group preferably contains at least one selected from the group consisting of a cationic nitrogen-containing heterocyclic structure and an ammonium cation having a linear or branched structure. This increases the polarity of the urethane resin. The cationic nitrogen-containing heterocyclic structure is not particularly limited, but 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 imidazolium cation, pyridinium cation, and pyrazinium cation, and more preferably an imidazolium cation. The cationic nitrogen-containing aliphatic heterocyclic structure is preferably at least one selected from the group consisting of a pyrrolidinium cation and a piperazinium cation, and more preferably a pyrrolidinium cation.

[0127] Examples of ammonium cations having a linear or branched structure include primary ammonium cations, secondary ammonium cations, tertiary ammonium cations, and quaternary ammonium cations, among which quaternary ammonium cations are preferred. The hydrocarbon group possessed by the ammonium cation is not particularly limited, but may be, for example, a hydrocarbon group having 1 to 8 carbon atoms (preferably 1 to 4, more preferably 1 to 2, and even more preferably 1).

[0128] The cationic functional group may have any substituent, such as a hydrocarbon group. For example, the cationic functional group preferably includes at least one structure selected from the group consisting of a structure represented by the following formula (10), a structure represented by the formula (11), a structure represented by the formula (12), a structure represented by the formula (13), a structure represented by the formula (14), and a structure represented by the formula (15). Each of the structures represented by the formulas (10) to (15) will be described below.

[0129] The structure represented by formula (10) will be described below. In formula (10), d １ represents an integer of 0 to 3 (preferably 0 or 1). ２７ and R ２８ represents a hydrocarbon group that forms a five-membered nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z １ ~Z ３ each independently represents 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 Z １ , Z ２ , and d １ At least one Z when ３ One selected from the group consisting of is a structure represented by the following formula (X).

[0130] 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 (10) 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 (10) is preferably, for example, an imidazolium cation. The method for incorporating the structure represented by formula (10) into the structure of the urethane resin is not particularly limited. For example, by reacting an ionic compound having a structure corresponding to the cation of the five-membered nitrogen-containing aromatic heterocyclic structure represented by formula (10) with an isocyanate compound, at least one structure represented by formula (10) is incorporated into the structure of the urethane resin.

[0131] As the five-membered nitrogen-containing aromatic heterocyclic structure in formula (10), the cationic nitrogen-containing aromatic heterocyclic structure described in the above-mentioned cationic functional group section can be used, and among them, imidazolium cation is preferred. Examples of ionic compounds having a structure corresponding to the cation of the five-membered nitrogen-containing aromatic heterocyclic structure in formula (10) include Z １ , Z ２ , and d １ At least one Z when ３ and (iii) are ionic compounds in which at least one selected from the group consisting of (a) and (b) is a divalent hydrocarbon having a hydroxyl group and having a straight or branched chain. By reacting such an ionic compound with an isocyanate compound, a structure represented by formula (10) can be obtained. As an example of such an ionic compound, an ionic compound containing an imidazolium cation is given below.

[0132] 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;

[0133] The structure represented by formula (11) will be described below. In formula (11), d ２ represents an integer of 0 to 5 (preferably 0 or 1). ２９ represents a hydrocarbon group which forms a nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z ４ represents 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 Z ５ represents a structure represented by the following formula (X), a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having a hydroxyl group and having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), and Z ４ , and d ２ At least one Z when ５ At least one selected from the group consisting of the above has a structure represented by the following formula (X):

[0134] 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 (11) 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 (11) 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 (11) is preferably, for example, a pyridinium cation. The method for incorporating the structure represented by formula (11) into the structure of the urethane resin is not particularly limited. For example, by reacting an ionic compound having a structure corresponding to the cation of the nitrogen-containing aromatic heterocyclic structure represented by formula (11) with an isocyanate group, at least one structure represented by formula (11) is incorporated into the structure of the urethane resin.

[0135] As the nitrogen-containing aromatic heterocyclic structure in formula (11), the cationic nitrogen-containing aromatic heterocyclic structure described in the above cationic functional group column can be used, and among them, a pyridinium cation is preferred. Examples of ionic compounds having a structure corresponding to the cation of the nitrogen-containing aromatic heterocyclic structure in formula (11) include Z ４ , and d ２ At least one Z when ５ and (iii) are ionic compounds in which at least one selected from the group consisting of (a) and (b) is a divalent hydrocarbon having a hydroxyl group and having a straight or branched chain. By reacting such an ionic compound with an isocyanate compound, a structure represented by formula (11) can be obtained. As an example of such an ionic compound, an ionic compound containing a pyridinium cation is given below.

[0136] 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.

[0137] The structure represented by formula (12) will be described below. In formula (12), d ３ represents an integer of 0 to 4 (preferably 0 to 2). ３０ and R ３１ represents a hydrocarbon group which forms a six-membered nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z ６represents 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 Z ７ represents a structure represented by the following formula (X), a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having a hydroxyl group and having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), and Z ６ , and d ３ At least one Z when ７ At least one selected from the group consisting of the above has a structure represented by the following formula (X):

[0138] 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 (12) 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 (12) is preferably, for example, a pyrazinium cation. The method for incorporating the structure represented by formula (12) into the structure of the urethane resin is not particularly limited. For example, by reacting an ionic compound having a structure corresponding to the cation of the six-membered nitrogen-containing aromatic heterocyclic structure represented by formula (12) with an isocyanate compound, at least one structure represented by formula (12) is incorporated into the structure of the urethane resin.

[0139] As the six-membered nitrogen-containing aromatic heterocyclic structure in formula (12), the cationic nitrogen-containing aromatic heterocyclic structure described in the above-mentioned cationic functional group section can be used, and among them, pyrimidinium cation and pyrazinium cation are preferred. Examples of ionic compounds having a structure corresponding to the cation of the six-membered nitrogen-containing aromatic heterocyclic structure in formula (12) include Z６ , and d ３ At least one Z when ７ and wherein at least one selected from the group consisting of: is a divalent hydrocarbon having a hydroxyl group and having a straight or branched chain. As an example of this ionic compound, an ionic compound containing a pyrimidium cation is given below.

[0140] 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.

[0141] The structure represented by formula (13) will be described below. In formula (13), R ３２ represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2 carbon atoms); Z ８ ~Z １０ each independently represents 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; Z ８ ~Z １０ At least one selected from the group consisting of the following has a structure represented by the following formula (X):

[0142] 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 (13) represents an ammonium cation having at least one structure represented by the following formula (X). The method for incorporating the structure represented by formula (13) into the structure of a urethane resin is not particularly limited, but for example, by reacting an ionic compound having a structure corresponding to the ammonium cation represented by formula (13) with an isocyanate compound, at least one structure represented by formula (13) can be incorporated into the structure of the urethane resin.

[0143] As the ammonium cation in formula (13), ammonium cations having a linear or branched structure as described in the above-mentioned cationic functional group column can be used, and among them, quaternary ammonium cations are preferred. Examples of ionic compounds having a structure corresponding to the ammonium cation in formula (13) include Z ８ ~Z １０ and wherein at least one selected from the group consisting of: is a divalent hydrocarbon having a hydroxyl group and having a straight or branched chain. Examples of such ionic compounds include ionic compounds containing a quaternary ammonium cation, such as:

[0144] 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.

[0145] The structure represented by formula (14) will be described below. In formula (14), d ４ represents an integer of 0 to 4 (preferably 0 to 2). ３３ and R ３４ represents a hydrocarbon group which forms a nitrogen-containing aliphatic heterocyclic structure together with a nitrogen atom; Z １１ ~Z １３ each independently represents 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 Z １４ each independently represents a structure represented by the following formula (X), a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having a hydroxyl group and having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), and Z １１ ~Z １３ , and d ４ At least one Z when １４ At least one selected from the group consisting of (1) and (2) has a structure represented by the following formula (X).

[0146] 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 (14) represents a cation of a nitrogen-containing aliphatic heterocyclic structure having at least one structure represented by the following formula (X) and two nitrogen atoms. The nitrogen-containing aliphatic heterocyclic structure in formula (14) may be a five- to eight-membered ring, and is preferably a five- or six-membered ring. The nitrogen-containing aliphatic heterocyclic structure in formula (14) is preferably, for example, a piperazinium cation. The method for incorporating the structure represented by formula (14) into the structure of the urethane resin is not particularly limited. For example, by reacting an ionic compound having a structure corresponding to the cation of the nitrogen-containing aliphatic heterocyclic structure represented by formula (14) with an isocyanate compound, at least one structure represented by formula (14) is incorporated into the structure of the urethane resin.

[0147] As the nitrogen-containing aliphatic heterocyclic structure in formula (14), the cationic nitrogen-containing aliphatic heterocyclic structure described in the above cationic functional group column can be used, and among them, piperazinium cation is preferred. Examples of ionic compounds having a structure corresponding to the cation of the nitrogen-containing aliphatic heterocyclic structure in formula (14) include Z １１ ~Z １３ , and d ４ At least one Z when １４ and (iii) are ionic compounds in which at least one selected from the group consisting of (a) and (b) is a divalent hydrocarbon having a hydroxyl group and having a straight or branched chain. By reacting such an ionic compound with an isocyanate compound, a structure represented by formula (14) can be obtained. As an example of such an ionic compound, an ionic compound containing a piperazinium cation is given below.

[0148] 1,1-bis(2-hydroxyethyl)piperazinium cation, 1,1,4-tris(2-hydroxyethyl)piperazinium cation, 1,4-bis(3-hydroxypropyl)-1-ethylpiperazinium cation, 1,4-bis(2-hydroxyethyl)-1,3-diethylpiperazinium cation; and derivatives thereof.

[0149] The structure represented by formula (15) will be described below. In formula (15), d ５ represents an integer of 0 to 4 (preferably 0 or 1). ３５ represents a hydrocarbon group which forms a nitrogen-containing aliphatic heterocyclic structure together with a nitrogen atom; Z １５ ~Z １６ each independently represents 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 Z １７ each independently represents a structure represented by the following formula (X), a hydroxyl group, a hydrocarbon group having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), or a hydrocarbon group having a hydroxyl group and having 1 to 4 carbon atoms (preferably 1 to 2, more preferably 1), and Z １５ , Z １６ , and d ５ At least one Z when １７ At least one selected from the group consisting of (1) and (2) has a structure represented by the following formula (X).

[0150] 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 (15) represents a cation of a nitrogen-containing aliphatic heterocyclic structure having at least one structure represented by the following formula (X). The nitrogen-containing aliphatic heterocyclic structure in formula (15) may be a five- to eight-membered ring, and is preferably a five- or six-membered ring. The nitrogen-containing aliphatic heterocyclic structure in formula (15) is preferably, for example, a pyrrolidinium cation. The method for incorporating the structure represented by formula (15) into the structure of the urethane resin is not particularly limited. For example, by reacting an ionic compound having a structure corresponding to the cation of the nitrogen-containing aliphatic heterocyclic structure represented by formula (15) with an isocyanate group, at least one structure represented by formula (15) is incorporated into the structure of the urethane resin.

[0151] As the nitrogen-containing aliphatic heterocyclic structure in formula (15), the cationic nitrogen-containing aliphatic heterocyclic structure described in the above cation structure column can be used, and among them, a pyrrolidinium cation is preferred. Examples of ionic compounds having a structure corresponding to the cation of the nitrogen-containing aliphatic heterocyclic structure in formula (15) include Z １５ , Z １６ , and d ５ At least one Z when １７ and (iii) are ionic compounds in which at least one selected from the group consisting of (a) and (b) is a divalent hydrocarbon having a hydroxyl group and having a straight or branched chain. By reacting such an ionic compound with an isocyanate compound, a structure represented by formula (15) can be obtained. As an example of such an ionic compound, an ionic compound containing a pyrrolidinium cation is given below.

[0152] 1-methyl-1,2-bis(2-hydroxyethyl)pyrrolidinium cation, 1-ethyl-1,2-bis(2-hydroxyethyl)pyrrolidinium cation, 1-butyl-1,2-bis(2-hydroxyethyl)pyrrolidinium cation, 1-methyl-1,2-bis(4-hydroxybutyl)pyrrolidinium cation; and derivatives thereof.

[0153] The structure represented by formula (X) will be described below. In formula (X), R ３６ represents a linear or branched divalent hydrocarbon group, the symbol "*" represents a bond to a nitrogen atom in formulas (10) to (15) or a bond to a carbon atom in a nitrogen-containing heterocyclic structure in formulas (10) to (12) and formulas (14) to (15), and the symbol "**" represents a bond to a carbon atom in a polymer chain constituting the urethane resin. ３６ is preferably a linear or branched alkylene group having 1 to 8 carbon atoms (preferably 1 to 4, more preferably 1 to 2). ３６ may have an optional substituent such as a hydroxyl group.

[0154] The structure represented by formula (X) may be, for example, a structure formed by reacting an ionic compound having a structure corresponding to the cation of the structure represented by formulas (10) to (15) with an isocyanate compound. The isocyanate compound is preferably the above-mentioned urethane prepolymer.

[0155] Among the structures represented by formulas (10) to (15), when the cationic functional group contains the structure represented by formula (10) or the structure represented by formula (11), 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.

[0156] The urethane resin has a first urethane bond and a second urethane bond. The urethane resin preferably has an ethylene oxide structure represented by the following formula (8) between adjacent first and second urethane bonds. It is more preferable that the urethane resin further has a propylene oxide structure represented by the following formula (9) between the first and second urethane bonds. By including these structures in the urethane resin, the crystallinity of the polymer main chain is suppressed even if the molecular weight between crosslinking points is large, and inhibition of metal ion migration, particularly at low temperatures, is more likely to be suppressed. This makes it easier to improve ionic conductivity and rate characteristics.

[0157] In addition, the average number of moles m of the ethylene oxide structure represented by formula (8) １ and the average number of moles of propylene oxide structures added represented by formula (9) n １ are each independently a natural number of 1 or more, and n １ ≦m １ ≦9n １ Within this range, it is possible to simultaneously suppress the crystallinity of the polymer main chain, the inhibition of metal ion migration, and the reduction in mechanical strength due to a decrease in crosslink density. Therefore, the ionic conductivity and rate characteristics are likely to be improved. １ is preferably 1 to 110, more preferably 34 to 102. １ is preferably 1 to 55, more preferably 5 to 43.

[0158] The method for producing such a urethane resin is not particularly limited, but it can be produced, for example, by using a polyethylene glycol-propylene glycol copolymer as a polyol and reacting it with an isocyanate compound. Alternatively, it can be produced by reacting a urethane prepolymer obtained by reacting a polyethylene glycol-propylene glycol copolymer with an isocyanate compound as the isocyanate compound with a polyol.

[0159] It is more preferable that the urethane resin has a structure represented by the following formula (16). When the urethane resin has the structure represented by the following formula (16), the crystallinity of the polymer main chain is suppressed, and the inhibition of lithium ion migration, particularly at low temperatures, is more easily suppressed. Therefore, the ionic conductivity and rate characteristics are more likely to be improved. In formula (16), m and n are the average number of moles added, each independently a natural number of 1 or more, satisfying n≦m≦9n. m is preferably 1 to 110, more preferably 34 to 102. n is preferably 1 to 55, more preferably 5 to 43.

[0160] The structure represented by formula (16) can be obtained, for example, by using a polyether polyol obtained by ring-opening polymerization of ethylene oxide and propylene oxide. ２ -CH ２ -O-) and an ethylene oxide structure represented by (-CH ２ -CH(CH ３ The arrangement of the propylene oxide structure represented by (III)-(O-) may be a block copolymer or a random copolymer, preferably a random copolymer.

[0161] The structure of the urethane resin can be confirmed by analysis using known means such as pyrolysis GC / MS, TF-IR, and NMR.

[0162] (Anion Structure) The urethane resin contained in the second polymer may contain an anion. Examples of the anion include a fluoroalkylsulfonylimide anion, a fluorosulfonylimide anion, a fluoroalkylsulfonate anion, a fluorosulfonate anion, a fluoroalkylcarboxylate anion, a fluoroalkylmethide anion, a fluoroborate anion, a fluorophosphate anion, a dicyanamide anion, a thiocyanate anion, a bisoxalatoborate anion, a perchlorate anion, and derivatives thereof.

[0163] 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.

[0164] 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.

[0165] Specific examples of fluoroborate anions include tetrafluoroborate anions, and specific examples of fluorophosphate anions include hexafluorophosphate anions.

[0166] 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 low-temperature environments. It is particularly preferred that the second polymer contain at least one anion selected from the group consisting of a bis(trifluoromethanesulfonyl)imide anion, a bis(fluorosulfonyl)imide anion, a trifluoromethanesulfonate anion, a tetrafluoroborate anion, a hexafluorophosphate anion, a dicyanamide anion, a thiocyanate anion, and a bisoxalatoborate anion.

[0167] The binder contained in the positive electrode layer contains a metal salt. The metal salt contained in the binder is selected in the same manner as that contained in the bulk electrolyte layer described above. The content of the metal salt contained in the binder is preferably 5 to 40 parts by mass, more preferably 7 to 20 parts by mass, per 100 parts by mass of the polymer in the second polymer. When the content of the metal salt is within this range, the metal salt is well compatible with the polymer and does not precipitate, and high ionic conductivity is obtained.

[0168] (Method of Manufacturing Solid Secondary Battery) A solid secondary battery can be manufactured by a known cell manufacturing method such as a laminate cell type, a coin cell type, a pressurized cell type, etc. The laminate cell type will be described below as an example.

[0169] A laminate is obtained in which a positive electrode, bulk electrolyte, and negative electrode are disposed between a positive electrode current collector and a negative electrode current collector. Electrode tabs are welded to the positive electrode and negative electrode current collectors. The laminate, in which the positive electrode current collector, positive electrode, bulk electrolyte, negative electrode, and negative electrode current collector are stacked in this order, is wrapped in 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. 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.

[0170] 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.

[0171] An example of a method for synthesizing the material used for the first polymer is described below. <Synthesis of Polyether Monoacrylate> (Polyether Monoacrylate a-1) 33.7 parts by mass of 1-butanol (manufactured by Tokyo Chemical Industry Co., Ltd.) and 2 parts by mass of potassium hydroxide (manufactured by Kojundo Chemical Laboratory Co., Ltd.) were placed in an autoclave and stirred under reduced pressure at 120°C to dissolve and dehydrate. Next, the pressure inside the system was reduced to -0.1 MPa at 100°C, and 984 parts by mass of a gas mixture of ethylene oxide / propylene oxide at a molar fraction of 8:2 was continuously introduced over 240 minutes while maintaining the internal pressure of the vessel at approximately 0.5 MPa. While maintaining the temperature at 100°C, the reaction was carried out for 150 minutes until the internal pressure of the vessel reached 0.2 MPa or less. The temperature was then raised to 130°C over 30 minutes, and stirring was continued until the change in internal pressure of the vessel reached 0.01 MPa / 30 minutes. To the obtained polymer, 20 parts by mass of pure water was added and stirred at 90°C for 30 minutes, and then 50 g of an alkali adsorbent Kyoward 600 (manufactured by Kyowa Chemical Industry Co., Ltd.) was added and stirred for another 30 minutes. Next, the alkali adsorbent was removed by filtration, and the mixture was dried under reduced pressure at 130°C to obtain a polyether monool having an Mn of 2000.

[0172] Next, 100 parts by mass of the obtained polyether monool, 3.78 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), 6.05 parts by mass of paratoluenesulfonic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.11 parts by mass of hydroquinone (manufactured by Tokyo Chemical Industry Co., Ltd.), and 250 ml of toluene were charged into a Dean-Stark reactor equipped with a stirrer. The mixture was heated and stirred at 115 ° C., and the reaction was carried out for 6 hours while removing water produced by the reaction from the system. The reaction liquid temperature was then lowered to room temperature, and the mixture was washed twice with 120 g of a 5% aqueous sodium hydroxide solution, and then three times with 120 g of pure water. The organic phase was separated from the reaction liquid after washing, and the solvent was distilled off under reduced pressure to obtain polyether monoacrylate a-1.

[0173] <Synthesis of Polyether Diacrylate> (Polyether Diacrylate b-1) 41.0 parts by mass of 1,4-butanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) and 2 parts by mass of potassium hydroxide (manufactured by Kojundo Chemical Laboratory Co., Ltd.) were charged into an autoclave and stirred under reduced pressure at 120 ° C. to dissolve and dehydrate. Next, the pressure inside the system was reduced to -0.1 MPa at 100 ° C., and 955 parts by mass of a gas mixture of ethylene oxide / propylene oxide at a molar fraction of 9:1 was continuously introduced over 220 minutes while maintaining the vessel internal pressure at approximately 0.5 MPa. While maintaining the temperature at 100 ° C., the reaction was carried out for 150 minutes until the vessel internal pressure reached 0.2 MPa or less. The temperature was then raised to 130 ° C. over 30 minutes, and stirring was continued until the vessel internal pressure change reached 0.01 MPa / 30 minutes. To the resulting polymer, 20 parts by mass of pure water was added and stirred at 90°C for 30 minutes, after which 50 g of an alkali adsorbent Kyoward 600 (manufactured by Kyowa Chemical Industry Co., Ltd.) was added and stirred for another 30 minutes. The alkali adsorbent was then removed by filtration, and the resulting mixture was dried under reduced pressure at 130°C to obtain a polyether diol with Mn of 2000.

[0174] Next, 100 parts by mass of the obtained polyether diol, 7.56 parts by mass of acrylic acid (manufactured by Nippon Shokubai Co., Ltd.), 6.05 parts by mass of paratoluenesulfonic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.11 parts by mass of hydroquinone (manufactured by Tokyo Chemical Industry Co., Ltd.), and 250 ml of toluene were charged into a Dean-Stark reactor equipped with a stirrer. The mixture was heated and stirred at 115 ° C., and the reaction was allowed to proceed for 5 hours while removing water produced by the reaction from the system. The reaction liquid temperature was then lowered to room temperature, and the mixture was washed twice with 120 g of a 5% aqueous sodium hydroxide solution, and then three times with 120 g of pure water. The organic phase was separated from the reaction liquid after washing, and the solvent was distilled off under reduced pressure to obtain polyether diacrylate b-1.

[0175] <Synthesis of Reactive Ionic Compounds Used in First Polymer> (Ionic Compound i-1) 12.9 g of 1-HEPTANESULFONYL CHLORIDE, 7-HYDROXY (manufactured by Hong Kong Chemhere Products Co., Ltd.) and 6.07 g (0.06 mol) of triethylamine (manufactured by Kishida Chemical Co., Ltd.) were added to 80 mL of dichloromethane and stirred at room temperature. The resulting mixture was washed with 100 mL of pure water, and the organic phase was then dried under reduced pressure to obtain an oily liquid. 5.64 g (0.06 mol) of sodium acrylate (manufactured by Merck) was dissolved in 50 mL of ethanol. The entire amount of the oily liquid and 0.022 g (0.20 mmol) of hydroquinone (manufactured by Kanto Chemical Co., Inc.) were added to this and stirred at 70°C for 5 hours. The pale yellow solid (0.06 mol) obtained after drying under reduced pressure was suspended in 100 mL of THF and 0.5 mL of N,N-dimethylformamide, and then 20 mL (0.28 mol) of thionyl chloride was added and stirred for 3 hours. This was concentrated under reduced pressure, and the residue was dissolved in dichloromethane. Thereafter, it was washed with 50 mL of pure water and 50 mL of brine, and then concentrated under reduced pressure again to obtain a pale yellow liquid.

[0176] The resulting pale yellow liquid was added to a solution of 9.20 g (0.06 mol) of trifluoromethanesulfonamide (manufactured by Tokyo Chemical Industry Co., Ltd.) and 27.3 mL (0.20 mol) of triethylamine (manufactured by Kishida Chemical Co., Ltd.) dissolved in 50 mL of tetrahydrofuran, and the mixture was stirred for 2 hours. Thereafter, the reaction solution was concentrated under reduced pressure. The resulting residue was dissolved in dichloromethane, washed with 150 mL of pure water, and the organic layer was dried under reduced pressure to obtain a yellow liquid. The resulting yellow liquid was dissolved in 300 mL of tetrahydrofuran, and 1.43 g (0.18 mol) of lithium hydride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added and the mixture was stirred overnight. Unreacted lithium hydride was filtered off using Celite filtration, and the filtrate was dried under reduced pressure to obtain ionic compound i-1.

[0177] (Ionic Compound i-2) 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.) was used as ionic compound i-2.

[0178] (Synthesis of Ionic Compound i-3) 15.0 g (0.19 mol) of pyridine (manufactured by Tokyo Chemical Industry Co., Ltd.) and 26.9 g (0.20 mol) of allyl bromide (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in 35.0 g of acetonitrile. The reaction mixture was heated and stirred at 30°C for 24 hours, and then cooled to room temperature. Thereafter, the mixture was washed three times with 100 ml of diethyl ether, and then 2 g of activated carbon and 20 ml of ethanol were added. Then, after stirring at room temperature for 1 hour, the activated carbon was filtered, and the solvent was distilled off under reduced pressure.

[0179] The resulting product was dissolved in 160 ml of pure water, and 54.5 g (0.19 mol) of lithium bis(trifluoromethanesulfonyl)imide (product name: EF-N115, manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.) was added as an anion source, followed by stirring at room temperature for 1 hour. 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-3.

[0180] (Synthesis of Ionic Compound i-4) 15.0 g (0.11 mol) of Allyltrimethylammonium chloride (Combi-Blocks Inc.) was dissolved in 160 mL of pure water. 31.7 g (0.11 mol) of lithium bis(trifluoromethanesulfonyl)imide (product name: EF-N115, manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.) was added as an anion source, and the mixture was stirred at room temperature for 1 hour. 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-4.

[0181] The obtained ionic compounds i-1 to i-4 are compounds represented by the following formulas (i-1) to (i-4).

[0182] An example of a method for synthesizing a material used for the second polymer is shown below. <Synthesis of Polyol> (Polyether Polyol A-1) 16.4 parts by mass of 1,4-butanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) and 2 parts by mass of potassium hydroxide (manufactured by Kojundo Chemical Research Institute Co., Ltd.) were placed in an autoclave, and the mixture was stirred under reduced pressure at 120°C to uniformly dissolve and dehydrate. Next, the pressure inside the system was reduced to -0.1 MPa at 100°C, and 983.6 parts by mass of alkylene oxide mixed at a molar fraction of ethylene oxide:propylene oxide = 9:1 was continuously introduced over 300 minutes to maintain a gauge pressure of approximately 0.5 MPa. The reaction was carried out at the same temperature for 170 minutes until the pressure reached 0.2 MPa or less. The temperature was then raised to 130°C over 20 minutes, and the mixture was stirred for 150 minutes until the pressure change inside the autoclave reached 0.01 MPa / 30 minutes, yielding a polyol. To the obtained polyol, 18 parts by mass of water was added and stirred at 90°C for 30 minutes, after which 50 g of an alkali adsorbent (Kyoward 600, manufactured by Kyowa Chemical Industry Co., Ltd.) was added and stirred for another 30 minutes. The obtained liquid was filtered to remove the adsorbent. Subsequently, it was dried under reduced pressure at 130°C to obtain polyether polyol A-1 having a hydroxyl value of 22.5 mgKOH / g and Mn of 5,000.

[0183] (Polyether Polyol A-2) Polyethylene glycol (trade name: Polyethylene Glycol 600, manufactured by Tokyo Chemical Industry Co., Ltd.) was used as polyether polyol A-2.

[0184] <Synthesis of Isocyanate Group-Terminated Prepolymer> (Isocyanate Group-Terminated Prepolymer B-1) In a nitrogen atmosphere, 100.0 parts by mass of polyether polyol A-1 was gradually added dropwise to 16.3 parts by mass of polymeric MDI (trade name: Millionate MR-200, manufactured by Tosoh Corporation) in a reaction vessel while maintaining the temperature inside the reaction vessel at 65°C. After completion of the addition, the mixture was reacted at a temperature of 65°C for 3.5 hours. The resulting reaction mixture was cooled to room temperature, and 49.8 parts by mass of methyl ethyl ketone was added to obtain a solution of isocyanate group-terminated prepolymer B-1 having an isocyanate group content of 2.5% by mass.

[0185] (Isocyanate Group-Terminated Prepolymer B-2) Under a nitrogen atmosphere, 100.0 parts by mass of polyether polyol A-2 was gradually added dropwise to 135.5 parts by mass of polymeric MDI (trade name: Millionate MR-200, manufactured by Tosoh Corporation) in a reaction vessel while maintaining the temperature inside the reaction vessel at 65°C. After completion of the addition, the mixture was allowed to react at a temperature of 65°C for 3.5 hours. The resulting reaction mixture was cooled to room temperature, and 100.9 parts by mass of methyl ethyl ketone was added to obtain a solution of isocyanate group-terminated prepolymer B-2 having an isocyanate group content of 3.3% by mass.

[0186] <Synthesis of Reactive Ionic Compound Used in Second Polymer> (Ionic Compound I-1) 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 therein, 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 resulting product was dissolved in 200 ml of dichloromethane, and an aqueous solution containing 43.6 g (0.15 mol) of bis(trifluoromethanesulfonyl)imide lithium (Tokyo Chemical Industry Co., Ltd.) dissolved therein as an anion source was added, followed by stirring at room temperature for 10 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-1. Ionic compound I-1 is a compound represented by the following formula:

[0187] (Ionic Compound I-2) Ionic Compound I-2 was obtained in the same manner as in the synthesis of Ionic Compound I-1, except that the anion raw material was changed to 33.3 g of potassium bis(fluorosulfonyl)imide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Ionic Compound I-2 is a compound represented by the following formula:

[0188] (Ionic Compound I-3) 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 (Fujifilm Wako Pure Chemical Industries, Ltd.) 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-3, which is a compound represented by the following formula:

[0189] (Ionic Compound I-4) 15.0 g (0.12 mol) of 5-methylpyrazine-2-methanol (Sigma-Aldrich) and 9.2 g of sodium hydride (60% by mass, dispersed in liquid paraffin, Tokyo Chemical Industry Co., Ltd.) were dissolved in 100 ml of THF. 18.9 g (0.13 mol) of iodomethane (Tokyo Chemical Industry Co., Ltd.) dissolved in 90 ml of THF was added dropwise to the solution over 30 minutes at room temperature, and the mixture was then heated to reflux at 85°C for 12 hours. Next, 100 ml of water was added to the reaction solution, and the solvent was distilled off under reduced pressure. 200 ml of ethanol was added to the residue, and the mixture was stirred at room temperature. Insoluble matter was removed by filtration through Celite, and the solvent was again distilled off under reduced pressure. The resulting product was dissolved in 100 ml of pure water, and an aqueous solution containing 37.3 g (0.13 mol) of bis(trifluoromethanesulfonyl)imide lithium (Tokyo Chemical Industry Co., Ltd.), an anion raw material, was added, followed by stirring at room temperature for 1 hour. 200 ml of ethyl acetate was added to the reaction solution, and the organic layer was washed three times with 120 ml of pure water. The solvent was then distilled off under reduced pressure to obtain ionic compound I-4. Ionic compound I-4 is a compound represented by the following formula:

[0190] (Ionic Compound I-5) 50 ml of purified water and 13.7 g (0.05 mol) of 2-hydroxyethyltriethylammonium iodide (manufactured by Tokyo Chemical Industry Co., Ltd.) were placed in a round-bottom flask and stirred for 1 hour. Next, 15.8 g (0.055 mol) of bis(trifluoromethanesulfonyl)imide lithium (manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved in 80 ml of purified water as an anion exchange reagent was added dropwise over 30 minutes, followed by stirring at 30°C for 3 hours. The resulting reaction solution was extracted twice with 100 g of ethyl acetate. Subsequently, the separated ethyl acetate layer was washed three times with 60 g of purified water. Next, ethyl acetate was distilled off under reduced pressure to obtain ionic compound I-5, in which the anion was a bis(trifluoromethanesulfonyl)imide anion. Ionic compound I-5 is a compound represented by the following formula:

[0191] (Ionic Compound I-6) 15.0 g (0.07 mol) of N,N'-bis-(2-hydroxyethyl)-2,5-dimethylpiperazine (Sigma-Aldrich) and 9.2 g of sodium hydride (60% by mass, dispersed in liquid paraffin, Tokyo Chemical Industry Co., Ltd.) were dissolved in 100 ml of THF. 11.6 g (0.08 mol) of iodomethane dissolved in 90 ml of THF was added dropwise to the solution over 30 minutes at room temperature, and the mixture was then heated to reflux at 85°C for 12 hours. Next, 100 ml of water was added to the reaction solution, and the solvent was distilled off under reduced pressure. 200 ml of ethanol was added to the residue, and the mixture was stirred at room temperature. Insoluble matter was removed by filtration through Celite, and the solvent was again distilled off under reduced pressure. The resulting product was dissolved in 100 ml of pure water, and an aqueous solution containing 23.0 g (0.08 mol) of bis(trifluoromethanesulfonyl)imide lithium (Tokyo Chemical Industry Co., Ltd.), an anion raw material, was added, followed by stirring at room temperature for 1 hour. 200 ml of ethyl acetate was added to the reaction solution, and the organic layer was washed three times with 120 ml of pure water. The solvent was then distilled off under reduced pressure to obtain ionic compound I-6. Ionic compound I-6 is a compound represented by the following formula:

[0192] (Ionic Compound I-7) 12.9 g (0.10 mol) of 2-(2-hydroxyethyl)-1-methylpyrrolidine (Tokyo Chemical Industry Co., Ltd.) and 8.1 g of sodium hydride (60% by mass, dispersed in liquid paraffin, Tokyo Chemical Industry Co., Ltd.) were dissolved in 90 ml of THF. Next, the reaction system was placed under a nitrogen atmosphere and ice-cooled. 16.8 g (0.11 mol) of bromoethanol dissolved in 100 ml of THF was added dropwise over 30 minutes, then the temperature was raised to room temperature and stirred for 1 hour. The reaction solution was heated and refluxed at 85°C for 15 hours. Next, 100 ml of water was added to the reaction solution, and the solvent was distilled off under reduced pressure. 80 ml of ethanol was added to the residue, the mixture was stirred at room temperature, insoluble matter was removed by filtration through Celite, and the solvent was again distilled off under reduced pressure. The resulting product was dissolved in 160 ml of pure water, and an aqueous solution containing 31.6 g (0.11 mol) of bis(trifluoromethanesulfonyl)imide lithium (Tokyo Chemical Industry Co., Ltd.) dissolved therein as an anion source was added, followed by stirring at room temperature for 1 hour. 70 ml of chloroform was added to the reaction solution, and the mixture was washed three times with 60 ml of a 5% by mass aqueous solution of sodium carbonate. Next, the chloroform was distilled off under reduced pressure to obtain ionic compound I-7. Ionic compound I-7 is a compound represented by the following formula:

[0193] (Ionic Compound I-8) A stirring bar and 50 ml of acetonitrile were placed in a recovery flask equipped with a Dimroth condenser. 21.5 g (0.15 mol) of 5-(2-hydroxyethyl)-4-methylthiazole (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and dissolved. 22.3 g (0.18 mol) of 2-bromo-1-butanol (manufactured by 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 48 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 a mixture of ethanol and acetone. The resulting product was dissolved in 150 ml of dichloromethane, and an aqueous solution containing 43.6 g (0.15 mol) of lithium bis(trifluoromethanesulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.) as an anion source was added. The mixture was stirred at room temperature for 10 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-8, which is a compound represented by the following formula:

[0194] [Example 1] <Preparation of First Polymer> The obtained materials were mixed to form a first polymer solution, and the solution was prepared so that it could be applied and molded. The first polymer solution was mixed with a metal salt required as a supporting electrolyte in the bulk electrolyte layer, and the cured product of the first polymer solution was used as the bulk electrolyte. Specifically, the following materials were mixed and stirred to form the first polymer solution. Polyether monoacrylate a-1: 95.0 parts by mass Polyether diacrylate b-1: 5.0 parts by mass Ionic compound i-1: 10.0 parts by mass Lithium salt (lithium bis(trifluoromethanesulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.)): 2.0 parts by mass Initiator Omnirad 184 (manufactured by IGM RESINS B.V.): 2.0 parts by mass Next, methyl ethyl ketone (hereinafter referred to as MEK) was added so that the total solids ratio was 60% by mass, and then the mixture was mixed with a motor stirrer to prepare a first polymer solution.

[0195] (Measurement of Volume Swelling Ratio of First Polymer by MEK Immersion Method) A test piece used for measuring the volume swelling ratio of the first polymer by the MEK immersion method was prepared as follows. A predetermined amount of the first polymer solution was added to an aluminum mold with a fluororesin coating on the surface so that the film thickness was 200 μm. Next, the test piece was placed on a sunflower stand and dried until the viscosity increased to such an extent that the film surface did not flow, and then placed on a horizontal stand and dried at 60° C. for 2 hours. Next, a high-pressure mercury UV irradiation device (product name: Handy 1000, manufactured by Mario Network Co., Ltd.) was used to irradiate the test piece with an integrated light dose of 5000 mJ / cm in the air. ２ The membrane surface was irradiated with UV light so that the first polymer was crosslinked and cured. After curing, the membrane was left in an environment of 23°C and 40% RH for 24 hours, and the electrolyte membrane was peeled from the aluminum mold to prepare a sheet with a thickness of 200 μm. The obtained sheet of the first polymer was cut into a 50 mm x 50 mm piece and left in an environment of 23°C and 40% RH for 24 hours to prepare a test piece.

[0196] First, the initial weight in air (W1) and the initial weight in water (W2) were measured in an environment of 23°C and 40% humidity. Next, the test piece after measuring the initial weight was immersed in MEK at 23°C for 48 hours. Immediately after removing the test piece from MEK, the MEK on the surface was wiped off with a nonwoven fabric, and the test piece was placed in a pre-weighed weighing bottle, and the weight after immersion in air (W3) and the weight after immersion in water (W4) were measured. The volume swelling ratio after immersion in MEK was calculated using the following formula: Volume swelling ratio (%) = ((W3 - W4) - (W1 - W2)) / (W1 - W2) x 100 W1: initial weight in air W2: initial weight in water W3: weight after immersion in air W4: weight after immersion in water

[0197] <Preparation of Second Polymer> The obtained materials were mixed to form a second polymer solution, and the solution was prepared so as to enable coating and molding. At this time, the second polymer solution was prepared by mixing a metal salt required as a supporting electrolyte in the binder, and curing the second polymer solution to form a mixed solution in which the cured product functions as a binder. Specifically, the following materials were stirred and mixed to form the second polymer solution. Polyol A-1: ​​81.1 parts by mass Isocyanate-terminated prepolymer B-1: 75.2 parts by mass Ionic compound I-1: 2.7 parts by mass Lithium salt (lithium bis(trifluoromethanesulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.)): 13.6 parts by mass Methyl ethyl ketone (MEK) 127.5 parts by mass

[0198] (Measurement of Volume Swelling Ratio of Second Polymer by MEK Immersion Method) A test piece used to measure the volume swelling ratio of the second polymer by the MEK immersion method was prepared as follows. A predetermined amount of the second polymer solution was added to an aluminum mold whose surface was coated with a fluororesin to give a film thickness of 200 μm. The second polymer solution was then placed on a sunflower stand and dried until the viscosity increased to such an extent that the surface of the film did not flow. It was then placed on a horizontal stand and dried at 30°C for 10 hours. The solution was then heated at 120°C for 1 hour to crosslink and harden the electrolyte solution. After hardening, the solution was left in an environment of 23°C and 40% RH for 24 hours, and the electrolyte membrane was peeled off from the aluminum mold to prepare a sheet with a film thickness of 200 μm. The obtained second polymer sheet was cut into 50 mm x 50 mm and left in an environment of 23°C and 40% RH for 24 hours to prepare a test piece.

[0199] First, the initial weight in air (W1) and the initial weight in water (W2) were measured in an environment of 23°C and 40% humidity. Next, the test piece after measuring the initial weight was immersed in MEK at 23°C for 48 hours. Immediately after removing the test piece from MEK, the MEK on the surface was wiped off with a nonwoven fabric, and the test piece was placed in a pre-weighed weighing bottle, and the weight after immersion in air (W3) and the weight after immersion in water (W4) were measured. The volume swelling ratio after immersion in MEK was calculated using the following formula: Volume swelling ratio (%) = ((W3 - W4) - (W1 - W2)) / (W1 - W2) x 100 W1: initial weight in air W2: initial weight in water W3: weight after immersion in air W4: weight after immersion in water

[0200] <Preparation of Secondary Battery> (Preparation of Negative Electrode) A 20 mm x 20 mm, 60 μm thick lithium foil (manufactured by Honjo Metals Co., Ltd.) was laminated on a 20 mm x 30 mm, 20 μm thick copper foil, leaving a 10 mm non-laminated edge on one side, and then pressed to prepare a negative electrode. The total thickness of the prepared negative electrode was 70 μm. A 5 mm wide copper tab with nickel plating on one non-laminated edge was joined to the negative electrode.

[0201] (Preparation of Positive Electrode) 100 parts by mass of lithium cobalt oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was mixed with 18 parts by mass of a second polymer solution (solid content 50%) and 5 parts by mass of Denka Black Li-100 (manufactured by Denka Co., Ltd.) as a conductive additive, and 40 parts by mass of N-methylpyrrolidone was added and mixed and stirred. Next, the obtained slurry was coated onto a 15 mm x 25 mm, 20 μm thick rolled aluminum foil, leaving a 10 mm uncoated end on one side, and heated at 120 ° C. for one hour to cure. After curing, the mixture was pressed to obtain a positive electrode with a thickness of 80 μm. A 5 mm wide aluminum tab was joined to one uncoated end of the positive electrode.

[0202] (Formation of Bulk Electrolyte Layer) The first polymer solution was applied to the entire active material-coated surface of the obtained positive electrode using a bar coater, and the layer was air-dried at 23° C. for 10 minutes, and then dried at 60° C. for 30 minutes. Next, a high-pressure mercury UV irradiation device (product name: Handy 1000, manufactured by Mario Network Co., Ltd.) was used to apply a bulk electrolyte layer with an accumulated light dose of 5000 mJ / cm. ２ The film surface was irradiated with UV light to cure the film, and the film thickness after curing was 60 μm.

[0203] (Preparation of Secondary Battery) The prepared positive electrode was vacuum dried at 80°C for 48 hours. The positive electrode, bulk electrolyte layer, and negative electrode were then placed in an argon-substituted glove box (temperature 25°C, dew point -70°C). A polyimide sheet punched into a window frame shape to cover the outer periphery of the positive electrode surface was attached to the surface corresponding to the bulk electrolyte layer, forming a short-circuit prevention layer. The bulk electrolyte layer and the lithium layer of the negative electrode were then laminated in this order so that their functional surfaces corresponded to each other. The laminate was sandwiched between aluminum laminate films and vacuum-packed to obtain a secondary battery according to Example 1.

[0204] As described above, the first polymer has at least one structure selected from the group consisting of the structure represented by formula (1), the structure represented by formula (2), and the structure represented by formula (3). This can be confirmed, for example, by pyrolysis GC / MS, FT-IR, or NMR analysis. The first polymer obtained in this example was analyzed using a pyrolysis apparatus (trade name: Pyrofoil Sampler JPS-700, manufactured by Japan Analytical Industry Co., Ltd.) and a GC / MS apparatus (trade name: FocusGC / ISQ, manufactured by Thermo Fisher Scientific). The pyrolysis temperature was 590 ° C., and helium was used as the carrier gas. As a result, from the obtained fragment peaks, it was confirmed that the polymer has at least one structure selected from the group consisting of the structure represented by formula (1), the structure represented by formula (2), and the structure represented by formula (3).

[0205] <Battery characteristic evaluation> (Charge / discharge test) The theoretical capacity was calculated from the total mass of lithium cobalt oxide contained in the positive electrode. A charge / discharge test was performed on the prototype secondary battery at 25°C using a charge / discharge device BCS-805 (manufactured by Biologic). The theoretical capacity was calculated from the total mass of lithium cobalt oxide contained in the positive electrode, and in the first cycle, the battery was charged to 4.3 V at a constant current charge rate of 0.05 C, and then discharged to 3.0 V at a discharge rate of 0.05 C. The discharge capacity obtained at this time was taken as the initial discharge capacity (mAh / g).

[0206] The same cycle was repeated five times in total, and the discharge capacity at the fifth cycle was measured. At this time, the percentage by which the discharge capacity at the fifth cycle had decreased from the initial discharge capacity was calculated. This value is shown in Table 2 as the 5th discharge capacity retention rate. The same cycle was repeated five times in total, and the discharge capacity at the tenth cycle was measured. At this time, the percentage by which the discharge capacity at the tenth cycle had decreased from the initial discharge capacity was calculated. This value is shown in Table 2 as the 10th discharge capacity retention rate. Next, the charge / discharge rate was increased to 0.10 C and the same charge / discharge was performed, and then increased to 0.50 C and the same charge / discharge was performed. These results are shown in Table 2.

[0207] [Examples 2 to 30] Secondary batteries according to Examples 2 to 30 were fabricated in the same manner as in Example 1, except that the types and amounts of the polyether mono(meth)acrylate, polyether di(meth)acrylate, ionic compound, and supporting electrolyte of the first polymer, and the formulation of the second polymer were changed as shown in Table 1. Here, in Examples 2, 3, 10, and 12, polyether tri(meth)acrylate was used instead of polyether di(meth)acrylate. In the table, mono(meth)acrylate refers to polyether mono(meth)acrylate, and di(meth)acrylate refers to polyether di(meth)acrylate.

[0208] The structures of the materials used in Table 1 when polymerized are as follows: AM-130: methoxypolyethylene glycol #600 acrylate, R in formula (1-1) １ : hydrogen atom, R ２ : ethylene group, R ３ : methyl group, m1: 13, n1: 0 (Shin-Nakamura Chemical Co., Ltd.) A-GLY-20E: ethoxylated glycerin triacrylate, R in formula (3-1) ７ : hydrogen atom, R ８ : ethylene group, R ９ : ethylene group, R １０ : ethylene group, R １１ :-CH ２ (CH-)CH ２ -, m3: 20 as the total of formula (3-1), n3: 0 (Shin-Nakamura Chemical Co., Ltd.)

[0209] The materials used in Table 1 were as follows: Li·TFSI: lithium bis(trifluoromethanesulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.) Li·FSI: lithium bis(fluorosulfonyl)imide (Ionel LF-101, Nippon Shokubai Co., Ltd.) Lithium trifluoromethanesulfonate (product name: EF-15, manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.) Lithium tetrafluoroborate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Lithium hexafluorophosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Lithium thiocyanate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Lithium bisoxalatoborate (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0210] Comparative Example 1 The following materials were stirred and mixed to form the first polymer, to obtain an electrolyte solution (first polymer solution) according to Comparative Example 1. Polyol A-1: ​​81.1 parts by mass Isocyanate-terminated prepolymer B-1: 75.2 parts by mass Ionic compound I-1: 2.7 parts by mass Lithium salt Lithium bis(trifluoromethanesulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.): 13.6 parts by mass Methyl ethyl ketone (MEK): 127.5 parts by mass The electrolyte solution of the first polymer was applied to the same positive electrode as that prepared in Example 1, and then heated at 120°C for one hour to perform curing.

[0211] The positive electrode with the bulk electrolyte formed thereon and the same negative electrode as prepared in Example 1 were vacuum-dried at 80°C for 48 hours. Then, they were placed in an argon-substituted glove box (temperature 25°C, dew point -70°C), and a polyimide sheet punched into a window frame shape was attached to cover the outer periphery of the positive electrode surface, forming a short-circuit prevention layer. Next, the electrolyte-coated positive electrode electrolyte layer and the negative electrode active material layer were laminated so as to correspond to each other. The laminate was sandwiched between aluminum laminate films and vacuum-packed to prepare a secondary battery according to Comparative Example 1.

[0212] [Comparative Example 2] The following materials were stirred and mixed as materials for the first polymer to obtain an electrolyte solution according to Comparative Example 2. Polyether monoacrylate a-1: 95.0 parts by mass Polyether diacrylate b-1: 5.0 parts by mass Ionic compound i-1: 10.0 parts by mass Lithium salt lithium bis(trifluoromethanesulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.): 2.0 parts by mass Initiator Omnirad 184 (manufactured by IGM RESINS B.V.): 2.0 parts by mass The above electrolyte solution was applied to the same positive electrode as that prepared in Example 1, air-dried at 23 ° C. for 10 minutes, and then dried at 60 ° C. for 30 minutes. Next, using a high-pressure mercury UV irradiation device (trade name: Handy 1000, manufactured by Mario Network Co., Ltd.), an integrated light dose of 5000 mJ / cm ２ The film surface was irradiated with UV light to cure the electrolyte membrane. The positive electrode and the negative electrode were then vacuum dried at 80°C for 48 hours. The electrolyte membrane was then placed in an argon-substituted glove box (temperature 25°C, dew point -70°C), and a polyimide sheet punched into a window frame shape was attached to cover the outer periphery of the positive electrode surface, forming a short-circuit prevention layer. Next, the electrolyte-coated positive electrode electrolyte layer and the negative electrode active material layer were laminated so as to correspond to each other. The laminate was sandwiched between aluminum laminate films and vacuum-packed to produce a secondary battery according to Comparative Example 2.

[0213] [Comparative Example 3] (Preparation of Positive Electrode) 100 parts by mass of lithium cobalt oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was mixed with 7 parts by mass of Kureha KF Polymer L#1120 (manufactured by Kureha Corporation) as an active material binder, and 5 parts by mass of Denka Black Li-100 (manufactured by Denka Corporation) as a conductive additive, and 40 parts by mass of N-methylpyrrolidone was added and mixed and stirred. Next, the obtained slurry was coated onto a 15 mm x 25 mm, 20 μm thick rolled aluminum foil, leaving a 10 mm uncoated end on one side, dried at 100 ° C. for 30 minutes, and pressed to obtain a positive electrode. The thickness of the positive electrode was 80 μm. A 5 mm wide aluminum tab was joined to one uncoated end of the positive electrode. A secondary battery according to Comparative Example 3 was prepared in the same manner as Comparative Example 1, except that the above positive electrode was used.

[0214] Comparative Example 4 A secondary battery according to Comparative Example 4 was fabricated in the same manner as in Comparative Example 1, except that no ionic compound was added and the lithium salt was changed to lithium chloride (manufactured by Kishida Chemical Co., Ltd.).

[0215] For each example and each comparative example, the volume swelling ratio of the first polymer and the volume swelling ratio of the second polymer were measured, and the results are shown in Table 3. In the table, "-" indicates that the cutoff value was reached after a certain number of measurements.

[0216] The secondary batteries according to Examples 1 to 30 included a urethane resin having a cationic functional group bonded thereto as the second polymer, and the first polymer had a structure different from that of the second polymer. As a result, a decrease in ionic conductivity was prevented, and a high discharge capacity retention rate was observed after five measurements of rate characteristics at 0.05 C. Examples 1, 4 to 9, 11, and 13 to 30, in which the first polymer had, in the polymer structure, at least one structure selected from the group consisting of the structure represented by formula (1) above and the structure represented by formula (2) above and the structure represented by formula (3), and in which the polymer did not have a dense network structure, maintained strength while less inhibiting the movement of metal ions, and therefore exhibited a high discharge capacity retention rate of over 90% after ten measurements of rate characteristics at 0.05 C.

[0217] Examples 1, 7 to 9, 11, and 13 to 30, in which the volume swelling ratio of the first polymer was 40.0 to 120.0% by the MEK immersion method, showed a high discharge capacity retention rate of more than 90% after 10 measurements of the rate characteristics at 0.05 C, and also showed a high 0.10 C cycle retention rate without reaching the cutoff value after 10 measurements of the rate characteristics at 0.10 C. Examples 1, 6 to 9, 11, and 14 to 30, in which the first polymer had at least one structure selected from the group consisting of the structure represented by formula (4), the structure represented by formula (5), the structure represented by formula (6), and the structure represented by formula (7), showed a high discharge capacity retention rate of more than 90% after 5 measurements of the rate characteristics at 0.10 C.

[0218] The second polymer has an ethylene oxide structure represented by the above formula (8) and a propylene oxide structure represented by the above formula (9), and the average number of moles added is n １ ≦m １ ≦9n １ For Examples 1 and 10 to 30 containing urethane resins in the range of 0.50 C, a high 0.50 C cycle retention rate was obtained without reaching the cutoff value after five measurements of the rate characteristics at 0.50 C. For Examples 1, 12 to 14, and 19 to 30 in which the volume swelling rate of the second polymer was 30.0 to 100.0% by the MEK immersion method, the discharge capacity was maintained without any significant decrease before and after five measurements of the rate characteristics at 0.50 C.

[0219] In Examples 1 and 15 to 30 in which the cationic functional group in the second polymer contained at least one structure selected from the group consisting of the structure represented by the above formula (10), the structure represented by formula (11), the structure represented by formula (12), the structure represented by formula (13), the structure represented by formula (14), and the structure represented by formula (15), a high 0.50C cycle retention rate was obtained without reaching the cutoff value after measuring the 0.50C rate characteristics 10 times.

[0220] On the other hand, Comparative Examples 1 and 4, in which the first polymer and the second polymer have similar structures, and Comparative Examples 2 and 3, in which the second polymer does not have a second polymer, showed low discharge capacity retention rates after five measurements of the rate characteristics at 0.05C, regardless of the initial IC value.

[0221] 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. 2024-082151, filed May 20, 2024, the entire contents of which are incorporated herein by reference.

[0222] 1: Secondary battery, 2: Positive electrode current collector, 3: Positive electrode active material, 4: Positive electrode active material binder, 5: Conductive additive, 6: Positive electrode, 7: Bulk electrolyte, 8: Negative electrode active material, 9: Negative electrode current collector, 10: Negative electrode, 11: Bulk electrolyte layer

Claims

1. A secondary battery having a positive electrode layer, a negative electrode layer, and a bulk electrolyte layer between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer contains a positive electrode active material and a binder, and the bulk electrolyte layer contains Li ＋ , Na ＋ , K. ＋ , Mg ２＋ and Ca ２＋ and a first polymer, wherein the binder comprises a second polymer and a metal salt containing at least one cation selected from the group consisting of Li ＋ , Na ＋ , K. ＋ , Mg ２＋ and Ca ２＋ and a metal salt containing at least one cation selected from the group consisting of:

2. The secondary battery according to claim 1, wherein the first polymer has, in its polymer structure, a structure represented by the following formula (1), and at least one structure selected from the group consisting of a structure represented by the following formula (2) and a structure represented by the following formula (3): In formula (1), R １ represents a hydrogen atom or a methyl group. ２ represents a linear or branched alkylene group having 1 to 6 carbon atoms. ３ represents an alkyl group having 1 to 6 carbon atoms. ４ R each independently represents a hydrogen atom or a methyl group. ５ , R ６ each independently represents a linear or branched alkylene group having 1 to 6 carbon atoms. ７ R each independently represents a hydrogen atom or a methyl group. ８ , R ９ , R １０ R each independently represents a linear or branched alkylene group having 1 to 6 carbon atoms. １１ represents a trivalent organic group having 1 to 6 carbon atoms. A1, B1, D1, D2 and D3 in formulas (1) to (3) each independently represent at least (—CH ２ CH ２ It is a linking group having an ethylene oxide structure represented by the formula: —O—.

3. The secondary battery according to claim 1 or 2, wherein the volume swelling ratio of the first polymer measured by a methyl ethyl ketone immersion method is 40.0 to 120.0%.

4. The secondary battery according to any one of claims 1 to 3, wherein the first polymer has 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), R １２ represents a hydrogen atom or a methyl group. １３ represents a linear or branched alkylene group having 1 to 7 carbon atoms. １４ represents a fluorine atom or a perfluoroalkyl group having 1 to 4 carbon atoms. ＋ represents at least one selected from the group consisting of a lithium ion, a sodium ion, and a potassium ion. １５ represents a hydrogen atom or a methyl group. １６ represents a divalent linking group. １７ represents an alkyl group having 1 to 4 carbon atoms. １８ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. １６ ~R １８ is bonded to three elements selected from the group consisting of two nitrogen atoms and three carbon atoms that constitute the imidazolium ring structure. １６ ~R １８ One of X1 is bonded to the cationic nitrogen atom in the imidazolium ring structure. － represents an anion. In formula (6), R １９ represents a hydrogen atom or a methyl group. ２０ represents a divalent linking group. ２１ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. ２０ and R ２１ One of X2 is bonded to the nitrogen atom constituting the pyridinium ring structure, and the other is bonded to any of the five carbon atoms constituting the pyridinium ring structure. － represents an anion. In formula (7), R ２２ represents a hydrogen atom or a methyl group. ２３ represents a divalent linking group. ２４ ~R ２６ Each of X3 independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. － represents an anion.

5. The secondary battery according to any one of claims 1 to 4, wherein the metal salt contains at least one anion selected from the group consisting of a bis(trifluoromethanesulfonyl)imide anion, a bis(fluorosulfonyl)imide anion, a trifluoromethanesulfonate anion, a tetrafluoroborate anion, a hexafluorophosphate anion, a dicyanamide anion, a thiocyanate anion, and a bisoxalatoborate anion.

6. The urethane resin has an ethylene oxide structure represented by the following formula (8) between adjacent first and second urethane bonds, and further has a propylene oxide structure represented by the following formula (9) between the first and second urethane bonds: The average number of moles m of the ethylene oxide structure added １ and the average number of moles of the propylene oxide structure added, n １ are each independently a natural number of 1 or more, and n １ ≦m １ ≦9n １ The secondary battery according to any one of claims 1 to 5, 7. The secondary battery according to any one of claims 1 to 6, wherein the volume swelling ratio of the second polymer measured by a methyl ethyl ketone immersion method is 30.0 to 100.0%.

8. The secondary battery according to any one of claims 1 to 7, wherein the cationic functional group includes at least one structure selected from the group consisting of a structure represented by the following formula (10), a structure represented by the formula (11), a structure represented by the formula (12), a structure represented by the formula (13), a structure represented by the formula (14), and a structure represented by the formula (15): In formula (10), d １ represents an integer of 0 to 3, ２７ and R ２８ represents a hydrocarbon group which forms a five-membered nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z １ ~Z ２ each independently represents a structure represented by the following formula (X), 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; Z ３ represents a structure represented by the following formula (X), 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; Z １ , Z ２ , and d １ At least one Z when ３ At least one selected from the group consisting of the following has a structure represented by the following formula (X): In formula (11), d ２ represents an integer of 0 to 5, ２９ represents a hydrocarbon group which forms a nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z ４ represents a structure represented by the following formula (X), 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; Z ５ represents a structure represented by the following formula (X), 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; Z ４ , and d ２ At least one Z when ５ At least one selected from the group consisting of the above has a structure represented by the following formula (X): In formula (12), d ３ represents an integer of 0 to 4, ３０ and R ３１ represents a hydrocarbon group which forms a six-membered nitrogen-containing aromatic heterocyclic structure together with a nitrogen atom; Z ６ represents a structure represented by the following formula (X), 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; Z ７ represents a structure represented by the following formula (X), 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; Z ６ , and d ３ At least one Z when ７ At least one selected from the group consisting of the above has a structure represented by the following formula (X): In formula (13), R ３２ represents a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms; Z ８ ~Z １０ each independently represents a structure represented by the following formula (X), 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; Z ８ ~Z １０ At least one selected from the group consisting of the following has a structure represented by the following formula (X): In formula (14), d ４ represents an integer of 0 to 4, ３３ and R ３４ represents a hydrocarbon group which forms a nitrogen-containing aliphatic heterocyclic structure together with a nitrogen atom; Z １１ ~Z １３ each independently represents a structure represented by the following formula (X), 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; Z １４ each independently represents a structure represented by the following formula (X), 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; Z １１ ~Z １３ , and d ４ At least one Z when １４ At least one selected from the group consisting of (1) and (2) has a structure represented by the following formula (X). In formula (15), d ５ represents an integer of 0 to 4, ３５ represents a hydrocarbon group which forms a nitrogen-containing aliphatic heterocyclic structure together with a nitrogen atom; Z １５ ~Z １６ each independently represents a structure represented by the following formula (X), 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; Z １７ each independently represents a structure represented by the following formula (X), 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; Z １５ , Z １６ , and d ５ At least one Z when １７ At least one selected from the group consisting of (1) and (2) has a structure represented by the following formula (X). In formula (X), R ３６ represents a linear or branched divalent hydrocarbon group, the symbol "*" represents a bond to a nitrogen atom in formulas (10) to (15) or a bond to a carbon atom in the nitrogen-containing heterocyclic structure in formulas (10) to (12) and formulas (14) to (15), and the symbol "**" represents a bond to a carbon atom in the polymer chain constituting the urethane resin.

9. The secondary battery according to any one of claims 1 to 8, wherein the second polymer contains at least one anion selected from the group consisting of bis(trifluoromethanesulfonyl)imide anions, bis(fluorosulfonyl)imide anions, trifluoromethanesulfonate anions, tetrafluoroborate anions, hexafluorophosphate anions, dicyanamide anions, thiocyanate anions, and bisoxalatoborate anions.

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