Composite electrolyte, method for producing same, curable composition for solid electrolyte, and power storage device

Abstract

Disclosed is a composite electrolyte which contains an inorganic solid electrolyte, a polymer, and an alkali metal salt, wherein the inorganic solid electrolyte contains an oxide having a NASICON type crystal structure, and the polymer does not substantially have a repeating unit represented by -(R1-O)- (wherein R1 is an alkylene group) in the main chain.

Description

Composite electrolyte and method for producing the same, curable composition for solid electrolyte, and electricity storage device

[0001] [Cross-Reference to Related Applications] This application claims priority to Japanese Patent Application No. 2024-27700, filed on February 27, 2024, the entire contents of which are incorporated herein by reference. The present disclosure relates to a composite electrolyte and a method for producing the same, a curable composition for a solid electrolyte, and an electricity storage device.

[0002] Various types of energy storage devices have been put to practical use, including various secondary batteries such as nickel-metal hydride secondary batteries and lithium-ion secondary batteries, as well as electric double-layer capacitors. Among these, lithium-ion secondary batteries are used in a wide range of applications due to their high energy density and battery capacity. In recent years, sodium-ion secondary batteries, potassium-ion secondary batteries, and magnesium-ion secondary batteries have been attracting attention as post-lithium-ion secondary batteries that use elements that replace the rare metal lithium.

[0003] Lithium-ion secondary batteries, which are widely used as energy storage devices, have a negative electrode, a positive electrode, and an electrolyte, and are charged and discharged by transferring lithium ions between the electrodes via the electrolyte. Conventionally, nonaqueous electrolytes have been used primarily as the electrolyte. However, nonaqueous electrolytes contain flammable organic solvents, which raise concerns about electrolyte leakage and short-circuiting within the battery due to overcharging and overdischarging.

[0004] In response to this, it has been proposed to use non-flammable inorganic solid electrolytes made from inorganic materials instead of non-aqueous electrolyte solutions as electrolytes for lithium-ion secondary batteries. However, while inorganic solid electrolytes are safe, they are in the form of powder, which makes them less moldable when producing electrolyte layers. Furthermore, because they are produced by molding powder, gaps are likely to form at the interfaces with the positive and negative electrodes or at the interfaces between particles of the inorganic solid electrolyte material. As a result, the high interfacial resistance prevents the inorganic solid electrolyte from fully utilizing its inherent high ionic conductivity. On the other hand, obtaining an electrolyte layer with sufficiently reduced interfacial resistance requires, for example, sintering at high temperatures exceeding 1,000°C with oxide-based solid electrolytes, which has the disadvantage of significant process constraints.

[0005] Therefore, in recent years, in order to achieve both improved safety and reduced interfacial resistance, a composite electrolyte formed of an inorganic solid electrolyte and an organic electrolyte has been studied as an electrolyte for use in lithium ion secondary batteries (see, for example, Patent Document 1). Patent Document 1 discloses a composite electrolyte using lithium lanthanum zirconium oxide as the inorganic solid electrolyte and polyethylene oxide containing a lithium salt as the organic electrolyte.

[0006] Japanese Patent Application Laid-Open No. 2022-160569

[0007] It is believed that an organic electrolyte containing polyethylene oxide and an alkali metal salt such as a lithium salt exhibits ionic conductivity as oxygen in the polymer main chain coordinates with alkali metal ions to form a complex, and the alkali metal ions move within the polymer. Therefore, as in Patent Document 1, a composite electrolyte combining an inorganic solid electrolyte and an organic electrolyte is believed to be able to reduce the high interfacial resistance, which is a disadvantage of inorganic solid electrolytes, while taking advantage of the high safety of inorganic solid electrolytes and the high flexibility of organic electrolytes.

[0008] However, according to the studies of the present inventors, it was found that a composite electrolyte combining an inorganic solid electrolyte with polyethylene oxide containing an alkali metal salt has low ionic conductivity at room temperature (25°C), and the effect of improving ionic conductivity achieved by combining an inorganic solid electrolyte with an organic electrolyte cannot be fully achieved. Furthermore, it was found that the composite electrolyte of Patent Document 1 loses flexibility of the organic electrolyte due to the mixing of the inorganic solid electrolyte and the organic electrolyte, making it prone to cracking. From the viewpoint of further improving the performance and quality of electricity storage devices, it is necessary to develop a new composite electrolyte that has higher ionic conductivity and flexibility than when an inorganic solid electrolyte is used alone.

[0009] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a composite electrolyte of an inorganic solid electrolyte and an organic electrolyte, which exhibits high ionic conductivity and excellent flexibility.

[0010] As a result of intensive research to solve the above problems, the present inventors have found that, in a composite electrolyte comprising an inorganic solid electrolyte and an organic electrolyte containing a polymer and an alkali metal salt, by using specific substances for the inorganic solid electrolyte and the polymer, a composite electrolyte having both good ionic conductivity and flexibility can be obtained. Specifically, the present disclosure provides the following composite electrolyte, a method for producing the same, a curable composition for a solid electrolyte, and an electricity storage device.

[0011] [1] A solid electrolyte battery comprising an inorganic solid electrolyte, a polymer, and an alkali metal salt, wherein the inorganic solid electrolyte contains an oxide having a NASICON-type crystal structure, and the polymer has a structure represented by -(R １ A repeating unit represented by —O)— (where R １ [2] A composite electrolyte in which the oxide is substantially free of a group represented by the general formula: Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ２ P ３－ｙ－ｚ O １２(wherein M1 contains Fe, In, Y or Al, M2 contains Si, M3 contains W, and x > 0, y ≥ 0, and z ≥ 0 are satisfied). [3] The composite electrolyte according to [1] or [2], wherein the polymer is a non-crosslinked polymer. [4] The composite electrolyte according to any one of [1] to [3], wherein the polymer contains a repeating unit having an ester bond. [5] The composite electrolyte according to [4], wherein the repeating unit having an ester bond is a repeating unit represented by the following formula (1) or a repeating unit derived from a (meth)acrylic monomer: [In formula (1), R represents a hydrogen atom or an alkyl group. m represents an integer of 0 to 10.] [6] The composite electrolyte according to any one of [1] to [5], wherein the content of the inorganic solid electrolyte is 20% by mass or more and 80% by mass or less. [7] The composite electrolyte according to any one of [1] to [6], wherein the alkali metal salt includes an imide-based alkali metal salt. [8] A curable composition used in the production of a solid electrolyte, the curable composition for a solid electrolyte comprising an inorganic solid electrolyte containing an oxide having a NASICON-type crystal structure, a (meth)acrylic monomer, and an alkali metal salt. [9] A method for producing the composite electrolyte according to any one of [1] to [7], comprising a step of mixing the inorganic solid electrolyte, the polymer, and the alkali metal salt.

[10] A method for producing the composite electrolyte according to any one of [1] to [7], comprising a step of irradiating the curable composition for a solid electrolyte according to [8] with active energy rays to cure it.

[11] An electricity storage device comprising the composite electrolyte according to any one of [1] to [7].

[0012] According to the present disclosure, a composite electrolyte exhibiting high ionic conductivity and excellent flexibility can be obtained. Furthermore, by using the composite electrolyte of the present disclosure as an electrolyte for an electricity storage device such as a secondary battery or a capacitor, it is possible to obtain an electricity storage device that combines high ionic conductivity with the safety ensured by the solidification of the electrolyte.

[0013] FIG. 1 is a schematic diagram of a press die used to prepare the sample pellets.

[0014] The composite electrolyte and the electricity storage device of the present disclosure will be described in detail below. In this specification, "(meth)acrylic" means acrylic and / or methacrylic. "(meth)acrylo" means acrylo and / or methacrylo. "(meth)acrylate" means acrylate and / or methacrylate.

[0015] <<Composite Electrolyte>> The composite electrolyte of the present disclosure is a composite of an inorganic solid electrolyte and an organic electrolyte, and contains an inorganic solid electrolyte, a polymer, and an alkali metal salt. Hereinafter, each component contained in the composite electrolyte of the present disclosure will be described in detail. Note that, unless otherwise specified, each component may be contained alone or in combination of two or more.

[0016] <Inorganic Solid Electrolyte> The inorganic solid electrolyte included in the composite electrolyte of the present disclosure includes an oxide having a NASICON-type crystal structure (hereinafter also referred to as "NASICON-type oxide"). Unlike layered structures, the NASICON-type crystal structure has a three-dimensionally expanded space for alkali metal ions to move, and zirconium (Zr) is stable even under high voltages, making it useful as a solid electrolyte with a high operating voltage. The crystal structure of the solid electrolyte can be determined from a diffraction profile obtained by powder X-ray diffraction measurement.

[0017] The composition of the NASICON-type oxide is not particularly limited. Specific examples of the NASICON-type oxide include Li １＋ａ Al ｘ Ti ２－ａ (P.O. ４ ) ３ (a≧0, also referred to as “LTP” or “LATP”), Li １＋ａ Al ａ Ge ２－ａ (P.O. ４ ) ３ (a≧0, also referred to as “LGP” or “LAGP”), LiZr ２ (P.O. ４ ) ３ (also called "LZP"), and NASICON, Na ３ Zr ２ Si ２ P.O. １２(also referred to as "NZSP"), and oxides in which some of the elements constituting these compounds are substituted with various elements (for example, B, Na, Al, Si, Ca, Ga, Ge, Sc, Fe, Sr, In, Ti, Hf, Sn, V, Nb, Ta, Sb, Bi, W, La, Mg, Y, lanthanoid elements, etc.).

[0018] A preferred example of the NASICON-type oxide is the oxide (x) shown below. Oxide (x): General formula: Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２ A solid electrolyte represented by the formula (wherein M1 contains Fe, In, Y, or Al, M2 contains Si, M3 contains W, and x > 0, y ≥ 0, and z ≥ 0 are satisfied).

[0019] ・About oxide (x) Oxide (x) is LiZr ２ (P.O. ４ ) ３ In an oxide having a basic skeleton of the above, a portion of Zr is substituted with M1 (including Fe, In, Y, or Al), and a portion of P is substituted with M2 (including Si) and / or M3 (including W).

[0020] In the oxide (x), M1 may contain Fe, In, Y, or Al. That is, M1 may be Fe, In, Y, or Al, or may further contain, together with Fe, In, Y, or Al, an element other than Fe, In, Y, or Al that forms a trivalent cation. Examples of elements that form trivalent cations other than Fe, In, Y, or Al include Group 13 elements, transition elements (Groups 3 to 11 elements) that form trivalent cations, Sb, Bi, etc.

[0021] M2 may contain Si. That is, M2 may be Si, or may further contain an element other than Si that forms a tetravalent cation. Examples of elements other than Si that form a tetravalent cation include Group 14 elements other than Si, transition elements (Groups 3 to 11 elements) that form a tetravalent cation, and Te.

[0022] M3 may contain W. That is, M3 may be W, or may further contain an element other than W that becomes a hexavalent cation. Examples of elements other than W that become a hexavalent cation include transition elements (elements of Groups 3 to 11) other than W that become a hexavalent cation, and Group 16 elements.

[0023] In the general formula of the oxide (x), x, y, and z are not particularly limited as long as x > 0, y ≥ 0, and z ≥ 0 are satisfied. For example, when x > 0, y > 0, and z = 0, the oxide (x) is "Li １＋ｘ＋ｙ M1 ｘ Zr ２－ｘ M2 ｙ P ３－ｙ O １２ " When x>0, y=0 and z>0, the oxide (x) is represented by "Li １＋ｘ－ｚ M1 ｘ Zr ２－ｘ M3 ｚ P ３－ｚ O １２ " When x>0, y>0 and z>0, the oxide (x) is represented by "Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２ " is expressed as:

[0024] More specifically, x, y, and z preferably satisfy x≦0.3, and more preferably satisfy x≦0.25, in that an impurity phase is unlikely to be formed, thereby enabling a solid electrolyte exhibiting high ionic conductivity to be obtained. The lower limit of x preferably satisfies x≧0.01, more preferably satisfies x≧0.05, and even more preferably satisfies x≧0.10.

[0025] Regarding y, since it has a dominant effect on the formation of the α phase, thereby enabling a solid electrolyte with higher ion conductivity to be obtained, it is preferable that y≦0.2, more preferably y≦0.15, and even more preferably y≦0.10. Furthermore, when y>0, the lower limit of y is preferably y≧0.01, and more preferably y≧0.03. Note that zirconium phosphate-based oxides having a NASICON-type crystal structure can have four phase structures: α phase, α' phase, β phase, and β' phase. Of these, the α phase has the highest Li ion conductivity because its crystal structure is isotropic.

[0026] Regarding z, in order to suppress the formation of an impurity phase and obtain a solid electrolyte exhibiting higher ionic conductivity, it is preferable that z≦0.2, more preferably z≦0.15, and even more preferably z≦0.10. When z>0, the lower limit of z is preferably z≧0.01, and more preferably z≧0.03.

[0027] In the above general formula representing the oxide (x), the stoichiometric ratio of O is 12, but as long as the charge neutrality of the oxide as a whole can be maintained, the stoichiometric ratio of O does not have to be strictly 12. In other words, the O content in the oxide (x) may be less than 12 or more than 12, as long as the charge neutrality of the oxide (x) as a whole can be maintained. For example, Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ｚ P ３－ｙ－ｚ O １２±β (where 0≦β≦1 is satisfied, and M1, M2, M3, x, y, and z are the same as M1, M2, M3, x, y, and z in the above formula shown as the general formula of oxide (x)) is also included in oxide (x) as long as the charge neutrality of oxide (x) as a whole is maintained.

[0028] The method for producing the oxide (x) is not particularly limited. The oxide (x) can be produced, for example, by weighing and mixing raw materials so as to satisfy the stoichiometric ratio of the composition represented by the general formula above (mixing step), and then firing the resulting mixture (firing step).

[0029] As the raw material of oxide (x), a supply component corresponding to an element for obtaining the target oxide (x) can be used from among the Li supply component, M1 supply component (Fe supply component, In supply component, Y supply component, or Al supply component), M2 supply component (Si supply component), M3 supply component (W supply component), Zr supply component, and P supply component. For example, when obtaining an oxide (x) where y > 0 and z = 0, the Li supply component, M1 supply component, M2 supply component, Zr supply component, and P supply component are used as raw materials.

[0030] Examples of the Li supply component, M1 supply component, M2 supply component, M3 supply component, Zr supply component, and P supply component for obtaining oxide (x) include carbonates, hydrogen carbonates, sulfates, sulfites, nitrates, nitrites, phosphates, acetates, citrates, ammonium salts, oxides, hydroxides, chlorides, sulfides, etc. of these metal elements. Note that these supply components may be compounds in which one type of supply component contains two or more elements selected from Li, M1, M2, M3, Zr, and P.

[0031] As the P supply component, it is preferable to use a compound containing one or more elements selected from Li, M1, M2, M3, and Zr. Among these, it is preferable to use a zirconium phosphate compound as the supply component (Zr and P supply component). As the zirconium phosphate compound, Zr(HPO ４ ) ２ , Zr(HPO ４ ) ２ ・nH ２ Zirconium hydrogen phosphate such as O; Zr ３ (P.O. ４ ) ４ Zirconium phosphate such as Zr(PO ４ ) (H ２ P.O. ４ ), Zr(PO ４ ) (H ２ P.O.４ ) ２ ・nH ２ Zirconium hydrogen phosphate (n is 0≦n≦2) such as HZr ２ (P.O. ４ ) ３ , ZrP ２ O ７ , (ZrO) ２ P ２ O ７ Among these, Zr(HPO), which is called layered zirconium phosphate, is preferred because it has good handling properties as an inorganic solid electrolyte during production. ４ ) ２ ・nH ２ O can be preferably used.

[0032] In producing the oxide (x), the raw materials may be mixed by dry mixing or by wet mixing using a liquid. By adopting wet mixing, the density of the inorganic solid electrolyte after firing can be increased compared to the case of dry mixing. In addition, the ionic conductivity of the resulting inorganic solid electrolyte can be relatively improved. As the liquid used for wet mixing, water, various organic solvents, and mixtures thereof can be appropriately used.

[0033] In the firing step, the mixture obtained in the mixing step may be fired without molding, or may be molded and then fired. The firing temperature is not limited, but can be, for example, 900°C or higher, preferably 1,000°C or higher, more preferably 1,150°C or higher, and even more preferably 1,200°C or higher. The upper limit of the firing temperature can be, for example, 1,500°C or lower, preferably 1,400°C or lower, and more preferably 1,350°C or lower. During firing, preliminary firing may be performed in which the temperature is increased stepwise from a temperature lower than the firing temperature, and then the temperature required for firing may be finally maintained.

[0034] When pre-firing is performed, the obtained pre-firing product may be pulverized before the next firing process. When firing is performed at multiple temperature ranges, firing may be performed in multiple stages, for example, by performing a first pre-firing in a temperature range of 100°C or higher and lower than 800°C, a second pre-firing in a temperature range of 800°C or higher and lower than 1,200°C, and a main firing in a temperature range of 1,200°C or higher, and the pre-firing product may be pulverized each time the firing temperature range is changed. The firing time is not limited, but for example, the pre-firing may be performed for 1 hour to 40 hours and the main firing may be performed for 1 hour to 40 hours.

[0035] The oxide (x) exhibits high Li ion conductivity and is therefore suitable as a material for producing a composite electrolyte for an electricity storage device in which the ion-conducting carrier is lithium ions.

[0036] The inorganic solid electrolyte obtained by the firing step is preferably pulverized by any method to form particles, and then used to produce a composite electrolyte. The pulverization treatment of the inorganic solid electrolyte may be carried out using a pulverizer such as a ball mill, a bead mill, or a blender. Alternatively, a composite electrolyte may be produced by granulating a powdered inorganic solid electrolyte and using the granulated product as a particulate inorganic solid electrolyte.

[0037] The average particle size of the inorganic solid electrolyte used to produce the composite electrolyte is preferably 0.01 μm or more and 20 μm or less in volume-based median diameter measured in an aqueous medium. When the average particle size of the inorganic solid electrolyte is within the above range, a composite electrolyte can be obtained that exhibits high ionic conductivity while providing good handleability of the inorganic solid electrolyte. From the viewpoint of handleability, the average particle size of the inorganic solid electrolyte is more preferably 0.05 μm or more in volume-based median diameter, even more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. Furthermore, from the viewpoint of improving the ionic conductivity of the composite electrolyte, the average particle size of the inorganic solid electrolyte is more preferably 15 μm or less in volume-based median diameter, even more preferably 10 μm or less, and even more preferably 5 μm or less. The average particle size of the inorganic solid electrolyte is a value measured by laser diffraction / scattering particle size measurement. Details of the measurement method follow the method described in the Examples below.

[0038] The content of the inorganic solid electrolyte in the composite electrolyte is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more, and even more preferably 30% by mass or more, based on the total amount of the composite electrolyte, from the viewpoint of obtaining a composite electrolyte with high ion conductivity by utilizing the properties of the inorganic solid electrolyte and ensuring the formability of the composite electrolyte. Furthermore, the upper limit of the content of the inorganic solid electrolyte is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, even more preferably 80% by mass or less, and even more preferably 75% by mass or less, based on the total amount of the composite electrolyte, from the viewpoint of sufficiently reducing the interfacial resistance of the inorganic solid electrolyte in the composite electrolyte, thereby increasing ion conductivity, and obtaining a composite electrolyte with excellent flexibility.

[0039] <Polymer> The composite electrolyte of the present disclosure exhibits ionic conductivity in the presence of an alkali metal salt, and is -(R １ A repeating unit represented by —O)— (where R １ is an alkylene group) in the main chain (hereinafter also referred to as "polymer (P)").

[0040] Here, −(R １The polymer having a repeating unit represented by —(R —O)— in the main chain is typically a polymer obtained by polymerization using alkylene oxides or cyclic ethers as monomers, and １ -O) ｒ - (where r is an integer of 2 or more). １ Generally, the number of carbon atoms is 2 or more, and may be 2 to 10. That is, the polymer (P) is a polymer different from polyether-based polymers such as polyalkylene oxides and polyethers.

[0041] In this specification, "-(R １ The phrase "substantially does not have a repeating unit represented by -(R —O)— in the main chain" means that the polymer (P) does not have a repeating unit represented by -(R —O)— in the main chain. １ This means that the polymer (P) does not exhibit the properties derived from the repeating unit represented by -(R -O)-. However, the polymer (P) may exhibit the properties derived from the repeating unit represented by -(R -O)- to the extent that the effects of the present invention are not impaired. １ It is permissible for the polymer (P) to have a small amount of repeating units represented by —(R —O)— in the main chain. １ The proportion of repeating units represented by -(R -O)- is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, based on the total amount of repeating units constituting the main chain of the polymer (P). １ -O) ｒ It is preferred that the main chain does not have a structure represented by - (where r is an integer of 2 or more).

[0042] Furthermore, a "repeating unit" is a basic unit of the chemical structure of a polymer, and the chemical formula of the polymer is expressed as an integer multiple of the repeating unit. Basically, one molecule of a monomer introduces one repeating unit having a structure corresponding to that monomer into the polymer, or introduces a structure consisting of two or more consecutive repeating units into the polymer. In the latter case, the structure consisting of two or more consecutive repeating units corresponds to one molecule of the monomer.

[0043] The structure of the polymer (P) is not particularly limited and may be linear or branched. A specific example of a branched polymer (P) is a star polymer having a core portion and three or more branched chains (arm portions) extending from the core portion. It is believed that the use of such a star polymer suppresses crystallization of the polymer, facilitating molecular motion of the polymer. Furthermore, the polymer (P) may be a crosslinked polymer or a non-crosslinked polymer. A non-crosslinked polymer is preferably used as the polymer (P) because it can more actively activate the molecular motion of the polymer, thereby facilitating the formation of ion conduction paths in the composite electrolyte.

[0044] As the polymer (P), a polymer that exhibits higher ionic conductivity at room temperature (25° C.) in the presence of an alkali metal salt than an organic electrolyte composed of a polyether polymer and an alkali metal salt is preferably used. Examples of such polymers (P) include polymers that have a heteroatom to which an alkali metal ion can be coordinated, and the coordinating power of the heteroatom to the alkali metal ion is weaker than that of ether oxygen.

[0045] One preferred embodiment of the polymer (P) is a polymer having an ester bond (hereinafter also referred to as "polymer (p1)"). The oxygen in the ester bond (the oxygen of the carbonyl group and / or the oxygen adjacent to the carbonyl group) does not have as strong a coordinating force for alkali metal ions as the ether oxygen. Therefore, the molecular motion of the polymer (p1) is less hindered by the coordinating force of the alkali metal ions, and as a result, it is thought that sufficient ion conduction paths are easily formed in the composite electrolyte.

[0046] The polymer (p1) may have an ester bond in the main chain, in the side chain, or in both. In addition, the polymer (p1) preferably contains a repeating unit having an ester bond (hereinafter also referred to as a "repeating unit UE"), in that it exhibits higher ionic conductivity in the presence of an alkali metal salt.

[0047] Preferred specific examples of the repeating unit UE include a repeating unit represented by the following formula (1) and a repeating unit derived from a (meth)acrylic monomer. [In formula (1), R represents a hydrogen atom or an alkyl group, and m represents an integer of 0 to 10.]

[0048] Polymer Having a Repeating Unit Represented by Formula (1) One preferred embodiment of the polymer (p1) is a polymer having a repeating unit represented by the above formula (1) (hereinafter also referred to as "polyester polymer (p1)").

[0049] In the above formula (1), R is preferably a hydrogen atom or a methyl group from the viewpoint of availability of raw materials and ease of synthesis of the polyester polymer (p1). From the viewpoint of availability of raw materials, m is preferably 0 to 8, more preferably 0 to 6, and preferably 0 to 4. Furthermore, m is preferably 1 or more, more preferably 2 to 8, and even more preferably 2 to 6, in order to provide the resulting composite electrolyte with better ionic conductivity and flexibility.

[0050] Monomers used to introduce the repeating unit represented by formula (1) above into a polymer include lactones and lactides. Specific examples of lactones include β-propiolactone, γ-butyrolactone, β-butyrolactone, pivalolactone, δ-valerolactone, and ε-caprolactone. Lactides include glycolide obtained by dehydration condensation of two glycolic acid molecules, dilactide obtained by dehydration condensation of two lactic acid molecules, and tetramethylglycolide. When the above lactides are used as monomers, a structure consisting of two consecutive repeating units represented by formula (1) above is introduced into the polymer per lactide molecule. That is, a structure consisting of two consecutive repeating units represented by formula (1) above corresponds to one lactide molecule.

[0051] From the viewpoint of obtaining a composite electrolyte having superior ionic conductivity, the monomer constituting the polyester polymer (p1) is preferably at least one selected from the group consisting of γ-butyrolactone, δ-valerolactone, ε-caprolactone, and dilactide, among the above.

[0052] The number of repeating units represented by the formula (1) contained in the polyester polymer (p1) can be appropriately set depending on the desired molecular weight of the polyester polymer (p1). The number of repeating units represented by the formula (1) contained in the polyester polymer (p1) is, for example, 10 to 1,500, preferably 20 to 1,200, more preferably 30 to 1,000, and even more preferably 30 to 800.

[0053] The polyester polymer (p1) may further have a repeating unit different from the repeating unit in the above formula (1) (hereinafter also referred to as "other repeating unit"), within the range that does not impair the effects of the present invention. Examples of other repeating units include dioxepanone, ethylene oxalate, dioxanone, γ-nonalactone, γ-decalactone, γ-undecalactone, cyclopentadecanolide, and cyclohexedecanolide.

[0054] In the polyester polymer (p1), the content of the repeating unit represented by the formula (1) is preferably 80 mass % or more, more preferably 85 mass % or more, still more preferably 90 mass % or more, and particularly preferably 95 mass % or more, based on the total repeating units of the polyester polymer (p1). By setting the content of the repeating unit represented by the formula (1) in the polyester polymer (p1) within the above range, a composite electrolyte with superior ionic conductivity can be obtained.

[0055] The terminal structure of the polyester polymer (p1) may be a hydroxyl group or a carboxyl group derived from the monomer. Alternatively, the terminal of the polyester polymer (p1) may be modified by utilizing a hydroxyl group or a carboxyl group present at the polymer terminal. By modifying the terminal hydroxyl group or terminal carboxyl group of the polyester polymer (p1), the heat resistance (durability) of the polyester polymer (p1) can be improved or the crystallinity of the polyester polymer (p1) can be reduced. When the terminal structure of the polyester polymer (p1) is an alkyl group, the alkyl group is preferably a linear or branched alkyl group having 3 to 20 carbon atoms, from the viewpoint of improving the heat resistance of the polyester polymer (p1) and promoting a reduction in crystallinity.

[0056] A preferred example of the polyester polymer (p1) is a polymer represented by the following formula (1-1): [In formula (1-1), R represents a hydrogen atom or an alkyl group. X and Y may be the same or different and represent a hydrogen atom, a hydroxyl group, or an alkyl group. n represents an integer of 1 or more, and m represents an integer of 0 to 10.]

[0057] The method for producing the polyester polymer (p1) is not particularly limited, and the polyester polymer (p1) can be produced by any conventionally known method. In terms of being able to produce the polyester polymer (p1) simply and inexpensively, it is preferred to produce the polyester polymer (p1) by ring-opening polymerization using at least one monomer selected from the group consisting of the lactones and lactides described above.

[0058] In the ring-opening polymerization, for example, the target polyester polymer (p1) can be obtained by charging the monomers and, if necessary, a solvent into a reactor, adding an initiator, and polymerizing. The charging method for the raw materials including the monomers may be a batch-type initial lump-sum charging in which all the raw materials are charged at once, a semi-continuous charging in which at least a portion of the raw materials are continuously fed into the reactor, or a continuous polymerization method in which all the raw materials are continuously fed and, at the same time, the produced resin is continuously withdrawn from the reactor.

[0059] As the initiator, a monoalcohol or a polyhydric alcohol can be preferably used, since the target polymer can be easily obtained. The monoalcohol is preferably an alkyl alcohol, such as methanol, ethanol, propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, and 2,2-dimethyl-1-propanol. Specific examples of polyhydric alcohols include trihydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, tris(2-hydroxyethyl)isocyanurate, hexanetriol, octanetriol, and decanetriol; tetrahydric alcohols such as ditrimethylolethane, ditrimethylolpropane, diglycerin, and pentaerythritol; pentahydric alcohols such as tritrimethylolethane, tritrimethylolpropane, and triglycerin; hexahydric or higher alcohols such as polytrimethylolethane, polytrimethylolpropane, polyglycerin, dipentaerythritol, tripentaerythritol, sorbitol, and polypentaerythritol; and alkylene oxide adducts of trihydric or higher alcohols.

[0060] In producing the polyester polymer (p1), the amount of the initiator used is, for example, 0.01 to 15 parts by mass, preferably 0.02 to 10 parts by mass, per 100 parts by mass of the total amount of the monomers used in the polymerization.

[0061] The ring-opening polymerization is preferably carried out in the presence of a catalyst from the viewpoint of carrying out the reaction efficiently. A conventionally known acid catalyst, base catalyst, or metal catalyst can be appropriately used as the catalyst. Specific examples of the acid catalyst include sulfonic acid, methanesulfonic acid, trifluoroacetic acid, 10-camphorsulfonic acid, phosphoric acid, phosphoric acid monoesters (methyl phosphate, ethyl phosphate, octyl phosphate, phenyl phosphate, etc.), phosphoric acid diesters (dimethyl phosphate, diethyl phosphate, dibutyl phosphate, diphenyl phosphate, etc.), phosphorous acid, phosphorous acid esters, tin tetrachloride, phosphorus pentafluoride, and boron trifluoride complexes.

[0062] Specific examples of the base catalyst include hydroxides such as sodium hydroxide and potassium hydroxide; tertiary amine compounds such as tetrabutylammonium bromide, tetrabutylammonium chloride, tetramethylammonium bromide, tetramethylammonium chloride, 1,8-diazabicyclo[5,4,0]-7-undecene, and 1,4-diazabicyclo[2,2,2]octane; phosphorus compounds such as ethylphosphine, phenylphosphine, dimethylphosphine, diphenylphosphine, triphenylphosphine, and tributylphosphine; imidazole compounds such as 2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 2-ethyl-4-methylimidazole; and the like.

[0063] Specific examples of metal catalysts include metal salts of tin, zinc, lead, titanium, aluminum, iron, zirconium, etc. Among these, tin catalysts are preferred from the viewpoint of reactivity. Examples of tin catalysts include tin(II) 2-ethylhexanoate, tin(II) acetate, tin(IV) acetate, tin(II) chloride, dibutyltin diacetate, dibutyltin dilaurate, dioctyltin(IV) diacetate, and tin(II) trifluoromethanesulfonate.

[0064] In producing the polyester polymer (p1), the amount of catalyst used is, for example, 0.01 to 20 parts by mass, preferably 0.05 to 10 parts by mass, per 100 parts by mass of the total amount of the monomers used in the polymerization.

[0065] When a solvent is used in the reaction, an organic solvent can be preferably used as the solvent. Examples of organic solvents include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane and heptane; esters such as ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; and ethers such as propylene glycol monomethyl ether. One or more solvents can be used. The amount of solvent used is, for example, 10 to 1,500 parts by mass, preferably 20 to 1,000 parts by mass, relative to 100 parts by mass of the total amount of monomers used in the polymerization.

[0066] The polymerization temperature and polymerization time are not particularly limited and may be set appropriately. From the viewpoint of increasing the reaction rate while suppressing side reactions, the polymerization temperature is, for example, within a temperature range of 0°C or higher and 120°C or lower, and preferably within a temperature range of 5°C or higher and 100°C or lower. The polymerization time is, for example, 1 to 150 hours, and preferably 5 to 100 hours. The pressure during polymerization may be any pressure that can maintain the polymerization temperature. From the viewpoint of suppressing a decrease in the degree of polymerization, the reaction may be carried out under dry air (for example, under conditions where the dew point at atmospheric pressure is −40°C or lower). Alternatively, the reaction may be carried out under dry nitrogen or dry argon instead of dry air. The polymerization reaction is preferably carried out while stirring the contents of the reactor.

[0067] By carrying out ring-opening polymerization of lactones or lactides using a monoalcohol or polyalcohol as an initiator, a polyester polymer having hydroxyl groups at the polymer terminals can be obtained. The polyester polymer (p1) thus obtained may be mixed with an inorganic solid electrolyte and an alkali metal salt in its original state (i.e., in a state having terminal hydroxyl groups). Alternatively, the terminal hydroxyl groups of the polyester polymer obtained by the above polymerization reaction may be reacted with a compound (modifier) ​​having a reactive functional group capable of reacting with hydroxyl groups to introduce a structure derived from the modifier into the terminal of the polyester polymer, and the resulting polymer may be mixed with an inorganic solid electrolyte and an alkali metal salt. The reaction of the polyester polymer having hydroxyl groups at its terminals with the modifier may be carried out, for example, in a suitable solvent, optionally using a catalyst.

[0068] When the polyester polymer (p1) is produced by solution polymerization, the polyester polymer (p1) dissolved in a solvent can be isolated by a known solvent removal method such as reprecipitation, or a drying method such as heat treatment. Alternatively, the polyester polymer (p1) may be produced by bulk polymerization or the like without using a solvent.

[0069] The glass transition temperature (Tg) of the polyester polymer (p1) is, for example, 65°C or lower. From the viewpoint of obtaining a composite electrolyte exhibiting higher ionic conductivity, the glass transition temperature of the polyester polymer (p1) is preferably 50°C or lower, more preferably 20°C or lower, preferably 0°C or lower, more preferably -20°C or lower, even more preferably -30°C or lower, even more preferably -40°C or lower, and even more preferably -50°C or lower. The lower limit of the glass transition temperature of the polyester polymer (p1) is not particularly limited, and is, for example, -80°C or higher. In this specification, the glass transition temperature of the polyester polymer (p1) is a value determined by differential scanning calorimetry (DSC).

[0070] The number average molecular weight (Mn) of the polyester polymer (p1) is preferably 1,000 or more, more preferably 3,000 or more, even more preferably 5,000 or more, even more preferably 8,000 or more, still more preferably 10,000 or more, still more preferably 15,000 or more, and particularly preferably 20,000 or more, from the viewpoint of obtaining a composite electrolyte having high strength and high ionic conductivity and from the viewpoint of improving the formability of the composite electrolyte. The upper limit of Mn of the polyester polymer (p1) is preferably 100,000 or less, more preferably 80,000 or less, and even more preferably 50,000 or less, from the viewpoint of ensuring appropriate fluidity of the polyester polymer (p1) and ensuring flexibility of the composite electrolyte.

[0071] The preferred range of Mn of the polyester polymer (p1) can be set by appropriately combining the upper and lower limits of the preferred ranges of Mn described above. The range of Mn of the polyester polymer (p1) is preferably 1,000 or more and 100,000 or less, more preferably 3,000 or more and 80,000 or less, and even more preferably 5,000 or more and 50,000 or less.

[0072] The weight average molecular weight (Mw) of the polyester polymer (p1) is preferably 1,500 or more, more preferably 4,000 or more, even more preferably 7,500 or more, even more preferably 10,000 or more, even more preferably 15,000 or more, even more preferably 20,000 or more, and particularly preferably 26,000 or more. The upper limit of Mw of the polyester polymer (p1) is preferably 150,000 or less, more preferably 100,000 or less, and even more preferably 80,000 or less. The Mw range of the polyester polymer (p1) is preferably 1,500 or more and 150,000 or less, more preferably 4,000 or more and 100,000 or less, and even more preferably 7,500 or more and 80,000 or less.

[0073] The molecular weight distribution (Mw / Mn) of the polyester polymer (p1), expressed as the ratio of Mw to Mn, is preferably 4.5 or less, more preferably 4.0 or less, even more preferably 3.5 or less, even more preferably 3.0 or less, still more preferably 2.5 or less, and even more preferably 2.0 or less, from the viewpoint of obtaining a composite electrolyte exhibiting good ionic conductivity. The lower limit of Mw / Mn of the polyester polymer (p1) is not particularly limited, and is 1.0 or more. In this specification, the Mw and Mn of the polymer are values ​​calculated in terms of standard polystyrene obtained using gel permeation chromatography (GPC).

[0074] Polymer Having Repeating Units Derived from (Meth)acrylic Monomer Another preferred embodiment of the polymer (p1) is a polymer having repeating units derived from a (meth)acrylic monomer (hereinafter also referred to as "(meth)acrylic polymer (p1)"). The (meth)acrylic polymer (p1) is preferably a polymer mainly composed of repeating units derived from a (meth)acrylic monomer. Specifically, the content of repeating units derived from a (meth)acrylic monomer in the (meth)acrylic polymer (p1) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more, based on the total repeating units of the (meth)acrylic polymer (p1).

[0075] Examples of the (meth)acrylic monomer constituting the (meth)acrylic polymer (p1) include (meth)acrylic acid, (meth)acrylic acid alkyl ester compounds, aliphatic cyclic (meth)acrylic acid ester compounds, aromatic (meth)acrylic acid ester compounds, (meth)acrylic acid alkoxyalkyl compounds, (meth)acrylic acid hydroxyalkyl compounds, polyalkylene glycol mono(meth)acrylate compounds, (meth)acrylate compounds having a heterocyclic structure, and zwitterionic mono(meth)acrylate compounds.

[0076] Specific examples of these include (meth)acrylic acid alkyl ester compounds such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, amyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-decyl and n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, and n-tetradecyl (meth)acrylate. Of these, the (meth)acrylic acid alkyl ester compounds are preferably compounds in which the alkyl group constituting the alkyl ester moiety has 1 to 12 carbon atoms, more preferably compounds in which the alkyl group has 2 to 8 carbon atoms, and even more preferably compounds in which the alkyl group has 2 to 6 carbon atoms.

[0077] Examples of the aliphatic cyclic ester compound of (meth)acrylic acid include cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

[0078] Examples of aromatic ester compounds of (meth)acrylic acid include phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxymethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, and 3-phenoxypropyl (meth)acrylate.

[0079] Examples of the alkoxyalkyl (meth)acrylate compound include methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, n-propoxyethyl (meth)acrylate, n-butoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, ethoxypropyl (meth)acrylate, n-propoxypropyl (meth)acrylate, n-butoxypropyl (meth)acrylate, methoxybutyl (meth)acrylate, ethoxybutyl (meth)acrylate, n-propoxybutyl (meth)acrylate, and n-butoxybutyl (meth)acrylate.

[0080] Examples of the hydroxyalkyl (meth)acrylate compound include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0081] Examples of the polyalkylene glycol mono(meth)acrylate compound include polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and polyethylene glycol-polypropylene glycol mono(meth)acrylate.

[0082] Examples of the (meth)acrylate compound having a heterocyclic structure include (meth)acrylates having a cyclic carbonate structure, a cyclic ether structure, an oxazolidone ring structure, a cyclic amide structure, an oxazoline ring structure, or a morpholine ring structure as the heterocyclic structure. Among these, (meth)acrylates having a cyclic carbonate structure, a cyclic ether structure, an oxazolidone ring structure, or a morpholine ring structure are preferred. Specific examples thereof include glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, 3,4-epoxycyclohexylmethyl (meth)acrylate, (2-oxo-1,3-dioxolan-4-yl)methyl (meth)acrylate, 2-((2-oxo-1,3-dioxolan-4-yl)methoxy)ethyl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, oxazolidone (meth)acrylate, (meth)acryloylmorpholine, etc. Among these, (meth)acrylates having a cyclic carbonate structure are particularly preferred because they can provide a solid electrolyte with excellent ionic conductivity.

[0083] The dipolar ionic mono(meth)acrylate compound may be any monomer having a cationic moiety and an anionic moiety in the same molecule. Examples of the dipolar ionic mono(meth)acrylate include sulfobetaine (meth)acrylates such as 3-[[2-((meth)acryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid, 4-[[2-((meth)acryloyloxy)ethyl]dimethylammonio]butane-1-sulfonic acid, 3-[(3-(meth)acrylamidopropyl)dimethylammonio]propane-1-sulfonic acid, and 4-[(3-(meth)acrylamidopropyl)dimethylammonio]butane-1-sulfonic acid. ) acrylate; carboxybetaine type (meth)acrylates such as 2-[[2-((meth)acryloyloxy)ethyl]dimethylammonio]acetic acid, 3-[[2-((meth)acryloyloxy)ethyl]dimethylammonio]propionate, and 3-[(3-(meth)acrylamidopropyl)dimethylammonio]propanoate; phosphobetaine type (meth)acrylates such as 2-((meth)acryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate; and the like. Of these, sulfobetaine type (meth)acrylates are preferred as the zwitterionic mono(meth)acrylate.

[0084] The (meth)acrylic polymer (p1) may further contain a repeating unit derived from a vinyl monomer other than the (meth)acrylic monomer. Examples of such a vinyl monomer include an aromatic vinyl monomer, maleimide, and a substituted maleimide.

[0085] Among the above, (meth)acrylic acid alkyl ester compounds are preferably used as the monomer constituting the (meth)acrylic polymer (p1), since they can provide the resulting composite electrolyte with better ionic conductivity and flexibility. The content of repeating units derived from (meth)acrylic acid alkyl ester compounds in the (meth)acrylic polymer (p1) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total repeating units of the (meth)acrylic polymer (p1).

[0086] Among the above, polymers (P) having an ester bond in the main chain are preferred, and polyester polymers (p1) are more preferred, since they can provide a composite electrolyte with excellent ionic conductivity and flexibility. Among polyester polymers (p1), polymers represented by the above formula (1-1) are preferred, and polymers in which m in the above formula (1-1) is 1 or more are more preferred.

[0087] When the (meth)acrylic polymer (p1) is used as a raw material in producing a composite electrolyte, i.e., when the composite electrolyte is produced by mixing the (meth)acrylic polymer (p1) with an inorganic solid electrolyte and an alkali metal salt, the method for synthesizing the (meth)acrylic polymer (p1) is not particularly limited. For example, the (meth)acrylic polymer (p1) can be obtained by polymerizing the above-mentioned monomers using a known radical polymerization method such as solution polymerization, suspension polymerization, emulsion polymerization, or bulk polymerization.

[0088] The content of the polymer (P) in the composite electrolyte is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more, based on the total amount of the composite electrolyte, from the viewpoints of reducing the interfacial resistance, exhibiting high ionic conductivity, and obtaining a composite electrolyte that exhibits sufficient flexibility. The upper limit of the content of the polymer (P) is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total amount of the composite electrolyte, from the viewpoints of improving the formability and handleability of the composite electrolyte.

[0089] <Alkali Metal Salt> The alkali metal salt is not particularly limited as long as it generates alkali metal ions. Examples of the alkali metal salt include lithium salt, sodium salt, and potassium salt.

[0090] Specific examples of alkali metal salts include LiCO ３ , LiBr, LiCl, LiI, LiSCN, LiBF ４ , LiAsF ６ , LiClO ４ , C.H. ３ COOLi, CF ３ COOLi, LiCF ３ SO ３ , LiPF ６ , LiC(CF ３ SO ２ ) ３ , lithium bis(fluorosulfonyl)imide (Li ＋ (FSO ２ ) ２ N － ), lithium bis(trifluoromethanesulfonyl)imide (Li ＋ (CF ３ SO ２ ) ２ N － and lithium salts such as lithium (fluorosulfonyl) (trifluoromethanesulfonyl) imide; and salts of the anions of these lithium salts with alkali metals other than lithium (for example, sodium, potassium, etc.). Among these, lithium salts or sodium salts are preferred, and lithium salts are more preferred, in that they have high ionic dissociation properties and can further increase the ionic conductivity of the composite electrolyte of the present disclosure. Furthermore, it is preferable that the type of alkali metal ion contained in the inorganic solid electrolyte is the same as the type of alkali metal ion contained in the alkali metal salt.

[0091] In order to further increase the ionic conductivity of the composite electrolyte of the present disclosure, the alkali metal salt contained in the composite electrolyte of the present disclosure preferably includes an imide alkali metal salt. Among these, imide lithium salts are preferred in terms of high ionic dissociation, and among imide lithium salts, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide are particularly preferred, with lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide being more preferred, and lithium bis(fluorosulfonyl)imide being even more preferred.

[0092] The molecular weight of the alkali metal salt is, for example, 500 or less, preferably 400 or less, more preferably 350 or less, and even more preferably 300 or less. The lower limit of the molecular weight of the alkali metal salt is, for example, 20 or more, preferably 50 or more, more preferably 100 or more, and even more preferably 150 or more.

[0093] The melting point of the alkali metal salt is, for example, 60° C. or higher, preferably 70° C. or higher, and more preferably 80° C. or higher. There is no particular upper limit to the melting point of the alkali metal salt, but it may be, for example, 300° C. or lower, or 250° C. or lower.

[0094] From the viewpoint of obtaining a composite electrolyte exhibiting high ionic conductivity, the content of the alkali metal salt in the composite electrolyte is preferably an amount such that the ratio (Mmo / Mal) of the total amount Mmo (number of moles) of monomers constituting the polymer (P) to the content Mal (number of moles) of the alkali metal salt in the composite electrolyte is 0.1 to 10. The ratio (Mmo / Mal) is more preferably 0.2 or more, and even more preferably 0.5 or more. The upper limit of the ratio (Mmo / Mal) is preferably 9.0 or less, and even more preferably 8.0 or less.

[0095] When the polymer (P) has an ester bond, the content of the alkali metal salt in the composite electrolyte is preferably 5 mol % or more and 250 mol % or less, based on the total amount (100 mol %) of ester bonds in the polymer (P). By making the content of the alkali metal salt in the composite electrolyte 5 mol % or more, based on the total amount of ester bonds in the polymer (P), a sufficient ion source can be secured in the composite electrolyte, and a composite electrolyte exhibiting good ionic conductivity can be obtained. Furthermore, by making the content of the alkali metal salt in the composite electrolyte 250 mol % or less, based on the total amount of ester bonds in the polymer (P), the alkali metal salt can be sufficiently dissolved in the polymer (P), and the ionic conductivity of the resulting composite electrolyte can be sufficiently high.

[0096] From the viewpoint of obtaining a composite electrolyte having superior ionic conductivity, the content of the alkali metal salt in the composite electrolyte is preferably 7 mol % or more, more preferably 20 mol % or more, and even more preferably 40 mol % or more, based on the total amount of ester bonds in the polymer (P). The content of the alkali metal salt in the composite electrolyte is preferably 220 mol % or less, more preferably 150 mol % or less, and even more preferably 120 mol % or less, based on the total amount of ester bonds in the polymer (P).

[0097] The composite electrolyte may further contain components (hereinafter also referred to as "other components") other than the inorganic solid electrolyte (NASICON-type oxide), polymer (P), and alkali metal salt, as long as the effects of the present invention are not impaired. Examples of other components include a dispersion aid, a conductive aid, a positive electrode active material, a negative electrode active material, an antioxidant, and a colorant. The content of these components may be appropriately set as long as the effects of the present invention are not impaired. The content of the other components is, for example, 5% by mass or less, or may be 2% by mass or less, based on the total amount of the composite electrolyte.

[0098] <Method for Producing Composite Electrolyte> The method for producing the composite electrolyte of the present disclosure is not particularly limited as long as it can produce a composite electrolyte exhibiting desired properties. Methods for producing the composite electrolyte of the present disclosure include the following methods [1] and [2]. Method [1]: A method including a mixing step of mixing an inorganic solid electrolyte, a polymer (P), and an alkali metal salt. Method [2]: A method including a curing step of irradiating an inorganic solid electrolyte, a (meth)acrylic monomer, and an alkali metal salt with active energy rays to cure the curable composition for a solid electrolyte. Of the above, method [1] is suitable when a polyester polymer (p1) is used as the polymer (P) in the composite electrolyte. Method [2] is suitable when a (meth)acrylic polymer (p1) is used as the polymer (P) in the composite electrolyte. Each method will be described below.

[0099] Regarding Method [1]: According to Method [1], a composite electrolyte can be produced by mixing an inorganic solid electrolyte, a polymer (P), and an alkali metal salt, and molding the mixture as needed. This method is advantageous in that it can produce a composite electrolyte exhibiting high ionic conductivity without requiring a step of sintering the inorganic solid electrolyte or a composition containing the inorganic solid electrolyte during the production of the composite electrolyte, and is less subject to process constraints. Furthermore, a composite electrolyte with high ionic conductivity can be produced by a simple method of mixing an inorganic solid electrolyte, a polymer (P), and an alkali metal salt, and molding the mixture as needed.

[0100] In the mixing step for producing a composite electrolyte, the inorganic solid electrolyte, the polymer (P), and the alkali metal salt may be mixed uniformly, and the method is not particularly limited. For example, when mixing an inorganic solid electrolyte, a polymer (P), and an alkali metal salt, the inorganic solid electrolyte, the polymer (P), and the alkali metal salt may be simultaneously placed in a container and mixed. Alternatively, these raw materials may be sequentially placed in a container, and a process of mixing the raw materials may be performed each time a raw material is placed in the container. The inorganic solid electrolyte, the polymer (P), and the alkali metal salt may be mixed using any method that allows these components to be mixed uniformly. The inorganic solid electrolyte, the polymer (P), and the alkali metal salt may be mixed using various devices, such as a ball mill, a planetary ball mill, a bead mill, a blender, a homogenizer, a stamp mill, a homomixer, or a disperser mixer. Furthermore, when producing a composite electrolyte on a small scale, mixing may also be performed using a mortar and pestle.

[0101] The inorganic solid electrolyte, the polymer (P), and the alkali metal salt may be mixed by dry mixing or by wet mixing using a liquid. Of these, wet mixing is preferred. By using wet mixing, the components can be mixed more uniformly and the density of the composite electrolyte can be increased compared to dry mixing, thereby relatively improving the ionic conductivity of the composite electrolyte.

[0102] As the liquid used in the wet mixing, water, various organic solvents, and mixtures thereof can be appropriately used. When a solvent is used when mixing the inorganic solid electrolyte, the polymer (P), and the alkali metal salt, the amount of the solvent used may be appropriately set. However, from the viewpoint of improving the dispersibility of each component, the amount of the solvent may be, for example, 50 to 2000 parts by mass per 100 parts by mass of the total amount of components other than the solvent used in producing the composite electrolyte. The slurry obtained by wet mixing may be subjected to removal of coarse particles or aggregates using, for example, a sieve. Furthermore, the mixing of the inorganic solid electrolyte, the polymer (P), and the alkali metal salt may be carried out at room temperature, at a low temperature, or under heating.

[0103] When a mixture containing an inorganic solid electrolyte, a polymer (P), and an alkali metal salt is molded to obtain a molded body, the molding method is not particularly limited, and known molding methods can be appropriately adopted. Specific examples of molding methods include extrusion molding, injection molding, pressure molding, slip casting, mold casting, tape casting, etc. The shape of the molded body is not particularly limited, and can be appropriately set depending on the application and shape of the electricity storage device. The shape of the molded body is, for example, rectangular or circular.

[0104] If the mixture obtained by the mixing step contains a solvent, it is preferable to remove the solvent from the mixture after molding (solvent removal step). There are no particular limitations on the method for removing the solvent, and known desolvation methods can be appropriately adopted. For example, the solvent may be removed by heating, or by natural drying, air blowing, or reduced pressure treatment. Furthermore, the solvent may be removed by appropriately combining two or more of these treatments. When removing the solvent by heating, the heating temperature can be appropriately set depending on the type of solvent, but can be, for example, 30 to 120°C, and preferably 35 to 100°C. The heating time is, for example, 30 minutes to 72 hours. The heating treatment may be performed under atmospheric pressure or under reduced pressure. From the viewpoint of removing the solvent from the mixture at as low a temperature as possible, the desolvation treatment is preferably performed under reduced pressure at a heating temperature of 80°C or less.

[0105] Regarding Method [2] (Curable Composition for Solid Electrolyte) The curable composition for solid electrolyte (hereinafter also simply referred to as "curable composition") used in Method [2] contains an inorganic solid electrolyte, a (meth)acrylic monomer, and an alkali metal salt. Here, the inorganic solid electrolyte and alkali metal salt contained in the curable composition correspond to the inorganic solid electrolyte and alkali metal salt contained in the composite electrolyte of the present disclosure, respectively. Furthermore, when the composite electrolyte of the present disclosure contains a (meth)acrylic polymer (p1) as the polymer (P), the (meth)acrylic monomer corresponds to the (meth)acrylic monomer that constitutes the (meth)acrylic polymer (p1). Details of each component are as described above, and description thereof will be omitted here.

[0106] In the curable composition, the content of the inorganic solid electrolyte is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more, and even more preferably 30% by mass or more, relative to the total amount of the curable composition. The content of the inorganic solid electrolyte is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, even more preferably 80% by mass or less, and even more preferably 75% by mass or less, relative to the total amount of the curable composition.

[0107] The content of the (meth)acrylic monomer in the curable composition is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more, relative to the total amount of the curable composition, in order to enhance the ionic conductivity and flexibility of the composite electrolyte. Furthermore, the content of the (meth)acrylic monomer is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, relative to the total amount of the curable composition, in order to obtain a composite electrolyte that exhibits good formability.

[0108] From the viewpoint of obtaining a composite electrolyte exhibiting high ionic conductivity, the content of the alkali metal salt is preferably an amount such that the ratio of the total number of moles of (meth)acrylic monomers to the number of moles of alkali metal salt is 0.1 to 10. This ratio is more preferably 0.2 or more, and even more preferably 0.5 or more. Furthermore, the content of the alkali metal salt is more preferably an amount such that the ratio of the total number of moles of (meth)acrylic monomers to the number of moles of alkali metal salt is 9 or less, and even more preferably 8 or less.

[0109] The curable composition may further contain components other than the inorganic solid electrolyte, the (meth)acrylic monomer, and the alkali metal salt, such as a polymerization initiator and a solvent.

[0110] As the polymerization initiator, known polymerization initiators such as thermal decomposition type and photoinitiator type can be used. Photoinitiator type polymerization initiators (photopolymerization initiators) are preferred. Specific examples of photopolymerization initiators include benzoin and its alkyl ethers, acetophenones, anthraquinones, thioxanthones, ketals, benzophenones, xanthones, acylphosphine oxides, α-diketones, and α-hydroxyketones. Furthermore, when the curable composition is an active energy ray-curable type, a benzoic acid-based or amine-based photosensitizer may be used in combination as needed to improve the sensitivity of the curable composition to the active energy rays irradiated thereto.

[0111] In the curable composition, the content of the polymerization initiator can be, for example, 0.1 to 50 parts by mass relative to 100 parts by mass of the total of (meth)acrylic monomers blended in the curable composition. From the viewpoint of sufficiently carrying out the polymerization reaction of the (meth)acrylic monomers, the content of the polymerization initiator is preferably 0.3 parts by mass or more, and more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the total of (meth)acrylic monomers. Furthermore, in order to avoid blending an excessive amount of polymerization initiator while sufficiently progressing the polymerization reaction, the content of the polymerization initiator is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, relative to 100 parts by mass of the total of (meth)acrylic monomers.

[0112] The curable composition may contain a solvent such as an organic solvent, or may be a solventless type that does not contain a solvent. A solvent-containing curable composition is preferred in that it can obtain a solid electrolyte in which the inorganic solid electrolyte, the polymer (P), and the alkali metal salt are more uniformly dispersed. In addition, a solventless curable composition is preferred in that it can easily adjust the thickness of the solid electrolyte, does not require a step of removing the solvent, and can simplify the manufacturing process.

[0113] In addition to the above, other components that may be blended into the curable composition include various additives such as antioxidants, ultraviolet absorbers, flame retardants, mildew inhibitors, colorants, etc. The content of these can be appropriately set depending on each component within a range that does not cause a decrease in performance.

[0114] The curable composition can be prepared by mixing the inorganic solid electrolyte, the polymer (P), the alkali metal salt, and other components as needed. The method for mixing the components is not particularly limited as long as the components are mixed uniformly. The components may be mixed at room temperature, or may be mixed while cooling or heating.

[0115] (Production of Composite Electrolyte) In the curing step of method [2], the curable composition is cured by irradiating it with active energy rays. For example, the curable composition is first applied to a substrate or placed in a mold. Next, the curable composition is cured by irradiating it with active energy rays such as ultraviolet rays or electron beams. This allows a composite electrolyte containing an inorganic solid electrolyte and an organic electrolyte to be obtained as a cured product of the curable composition.

[0116] Examples of the active energy ray to be irradiated to the curable composition include ultraviolet light, visible light, and electron beams. Of these, ultraviolet light or electron beams are preferred. The active energy ray may be irradiated to the curable composition from only one direction, or from two or more directions. The irradiation energy can be appropriately set depending on the type of active energy ray, the formulation of the curable composition, and the like.

[0117] For example, when ultraviolet rays are used as the active energy rays, the wavelength is, for example, 250 to 400 nm. Examples of ultraviolet irradiation devices include high-pressure mercury lamps, metal halide lamps, ultraviolet electrodeless lamps, and ultraviolet light-emitting diodes (UV-LEDs). The cumulative light amount is 0.5 J / cm. ２ More than 1.0 J / cm is preferable. ２ More preferably, 1.5 J / cm or more ２ The upper limit of the cumulative light amount is more preferably 250 J / cm in order to minimize the influence on each component in the curable composition and to reduce energy. ２ Preferably, 200 J / cm or less ２ The following is more preferred:

[0118] The illuminance and irradiation time of the ultraviolet light may be appropriately set so that the cumulative light amount is a desired amount. For example, the illuminance is 1.0 mW / cm ２ More than 2.0 mW / cm is preferable. ２ The upper limit of the illuminance is 100 mW / cm. ２ Preferably, 80 mW / cm or less ２ The following is more preferred:

[0119] When electron beams are used as the active energy rays, examples of electron beam irradiation devices include Cockcroft-Walton type, Van de Graaff type, and resonant transformer type devices. The absorbed dose of the electron beam is preferably 1 to 200 kGy, more preferably 10 to 100 kGy. The acceleration voltage of the electron beam may be appropriately set within a range of 80 to 300 kV depending on the thickness of the substrate, etc. The oxygen concentration of the electron beam irradiation atmosphere is preferably 500 ppm or less, more preferably 300 ppm or less.

[0120] By the above-mentioned procedure, a composite electrolyte having high ionic conductivity can be obtained by a relatively simple method. Since the composite electrolyte thus obtained exhibits high ionic conductivity, when used as an electrolyte material for an electricity storage device, an electricity storage device having high ionic conductivity can be obtained.

[0121] Specifically, the ionic conductivity of a molded body of the composite electrolyte of the present disclosure having a thickness of about 0.50 mm (specifically, 0.50±0.05 mm) measured at 25°C using an AC impedance method is 1×10 －７ From the viewpoint of obtaining an electricity storage device with excellent performance, the ionic conductivity under the same conditions is preferably 2×10 S / cm or more. －７ S / cm or more is more preferable, and 1×10 －６ The ionic conductivity is more preferably 25 S / cm or more. Details of the method for measuring the ionic conductivity follow the method described in the examples below.

[0122] <Electricity Storage Device> The electricity storage device of the present disclosure (hereinafter also referred to as "the device") includes the composite electrolyte of the present disclosure described above. Examples of the device include a secondary battery, a capacitor, etc. When the device is a secondary battery, one embodiment is an all-solid-state battery, and a lithium-ion secondary battery is preferred because of its excellent ionic conductivity.

[0123] The following describes an all-solid-state lithium-ion secondary battery, which is one embodiment of the device. The lithium-ion secondary battery is a laminate including an electrode layer made of a positive electrode layer and a negative electrode layer, and a solid electrolyte layer, with the solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer so that the solid electrolyte layer is in contact with the electrode layer.

[0124] The materials constituting the positive electrode layer and the negative electrode layer are not particularly limited, and can be appropriately selected from materials known as electrode materials for lithium ion secondary batteries. For example, the positive electrode layer may be configured to include a positive electrode current collector and a positive electrode mixture layer. The positive electrode current collector can be a metal foil such as aluminum or stainless steel. The positive electrode mixture layer is a layer containing a positive electrode active material and is disposed on the surface of the positive electrode current collector. Examples of the positive electrode active material include metal oxides having a layered rock salt, spinel, or olivine crystal structure. The negative electrode layer may be configured to include a negative electrode current collector and a negative electrode mixture layer. The negative electrode current collector can be a metal foil such as copper foil or lithium foil. The negative electrode mixture layer is a layer containing a negative electrode active material and is disposed on the surface of the negative electrode current collector. Examples of the negative electrode active material include metallic lithium, graphite, Li ４ Ti ５ O １２ , silicon monoxide, silicon, etc.

[0125] The solid electrolyte layer is formed of a composite electrolyte containing an inorganic solid electrolyte, a polymer (P), and an alkali metal salt. The thickness of the solid electrolyte layer is not particularly limited and can be appropriately set depending on the application of the secondary battery, etc. The thickness of the solid electrolyte layer is, for example, 5 to 5,000 μm. From the viewpoint of realizing a smaller, lighter, and higher-capacity all-solid-state secondary battery by making the thickness of the solid electrolyte layer as thin as possible, the thickness of the solid electrolyte layer is preferably 50 μm or less, and more preferably 20 μm or less.

[0126] The method for producing the solid electrolyte layer and the lithium-ion secondary battery is not particularly limited, and known methods can be appropriately adopted depending on the battery structure, etc. For example, a laminate including a positive electrode layer, a solid electrolyte layer, and an anode layer may be produced by sandwiching a molded body of the composite electrolyte of the present disclosure as the solid electrolyte layer between a positive electrode layer and an anode layer, preferably applying a pressure treatment for bonding. Alternatively, a laminate including a positive electrode layer, a solid electrolyte layer, and an anode layer may be produced by placing the pre-molded composite electrolyte between the positive electrode layer and the anode layer in a container and applying a pressure treatment to the container, preferably applying a pressure treatment for bonding. Furthermore, when producing a composite electrolyte in which the polymer (P) contained in the composite electrolyte is a (meth)acrylic polymer, a laminate including a positive electrode layer, a solid electrolyte layer, and an anode layer may be produced by placing the curable composition of the present disclosure between the positive electrode layer and the anode layer in a container, irradiating the curable composition with active energy rays, and then applying a pressure treatment, preferably applying a pressure treatment for bonding. A laminate including a positive electrode layer, a solid electrolyte layer, and an anode layer is usually housed in a case and used as a secondary battery.

[0127] The device is not limited to the above-described configuration in which the carrier for ion conduction is lithium ions, and may be a secondary battery in which other ions, such as sodium ions, are used as the carrier. The device may also be a capacitor. One embodiment of the capacitor includes an anode body, a cathode body, and a solid electrolyte, with the solid electrolyte disposed between the anode body and the cathode body so that the solid electrolyte is in contact with the electrode.

[0128] The power storage device including the composite electrolyte of the present disclosure can be used in a variety of applications, specifically as a power source for various mobile devices such as mobile phones, personal computers, smartphones, game consoles, and wearable devices; various moving objects such as electric vehicles, hybrid vehicles, robots, and drones; and various electric and electronic devices such as digital cameras, video cameras, music players, power tools, and home appliances.

[0129] The present invention will be specifically described below based on examples. However, the present invention is not limited to these examples. In the following, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0130] <<Production and Physical Properties of Inorganic Solid Electrolyte>> [Production Example 1] 1. Production of Inorganic Solid Electrolyte LIZSP Layered zirconium phosphate (Zr(HPO)) was used as a feed component so as to achieve the molar ratio (Li:In:Zr:Si:P=1.25:0.20:1.80:0.05:2.95) shown in Production Example 1 in Table 1. ４ ) ２ ・nH ２ 400 parts of ammonium hydroxide, 43.2 parts of zirconium hydroxide, 41.5 parts of lithium carbonate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 2.7 parts of silicon dioxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 25 parts of indium oxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were weighed and placed in a mortar, and 2,500 parts of pure water were added and wet mixed to obtain a mixture (mixing step). The obtained mixture was dried at 100 ° C. for 2 hours, then transferred to an alumina crucible (capacity 30 mL), heated to 1,250 ° C. over 5.5 hours, and held for 5 hours to perform firing (firing step). Thereafter, it was allowed to cool to room temperature (25 ° C.) to obtain a fired product. The obtained fired product was pulverized in a mortar to obtain an inorganic solid electrolyte LIZSP. Note that Zr(HPO ４ ) ２ ・nH ２ The value of n in O was set to 1.0.

[0131] 2. Confirmation of Crystallinity by Powder X-ray Diffraction Measurement The obtained inorganic solid electrolyte LIZSP was subjected to powder X-ray diffraction measurement using an X-ray diffractometer (D8 ADVANCE, manufactured by Bruker AXS). CuKα was used as the X-ray source, and the applied voltage was 40 kV and the current was 40 mA. The measurement conditions were a measurement range of 2θ = 10-80 deg, a scanning rate of 2.5 deg / min, and a step angle of 0.01 deg. As a result, it was found that the main crystalline phase of the inorganic solid electrolyte LIZSP was monoclinic or rhombohedral LiZr ２ P ３ O １２It was confirmed that the inorganic solid electrolyte LIZSP has a NASICON-type crystal structure.

[0132] 3. Measurement of volume-based median diameter The inorganic solid electrolyte LIZSP was diluted with pure water in a 30 mL sample bottle to a 1% dispersion. The diluted dispersion was irradiated with 1 kHz ultrasound for 10 minutes. Using the dispersion immediately after ultrasound irradiation as a measurement sample, the volume-based median diameter (D50) of the inorganic solid electrolyte LIZSP was measured at room temperature (25 ° C.) using a laser diffraction / scattering particle size measuring device MT-3000 (manufactured by Microtrac). Particle size measurements were performed twice, and the average value was adopted as the volume-based median diameter of the inorganic solid electrolyte LIZSP. The volume-based median diameter of the inorganic solid electrolyte LIZSP was 1.4 μm.

[0133] 4. Measurement of Ionic Conductivity Using a press die consisting of a die set 11, an upper punch 12, and a lower punch 13 (see Figure 1), sample pellets were prepared in a dry room with a dew point of -40°C or less. First, the die set 11 containing 0.150 g of inorganic solid electrolyte LIZSP was placed on the lower punch 13, and the upper punch 12 was placed on the die set 11. The inorganic solid electrolyte LIZSP was compressed using a hydraulic press at a pressure of 10 MPa for 1 minute to obtain a circular sample pellet with a diameter of 1 cm and a thickness of 1,000 μm. Next, the sample pellet was encapsulated in an all-solid-state battery evaluation cell (KP-SolidCell, manufactured by Hosen Co., Ltd.) in a dry room with a dew point of -40°C or less. The resistance value at 25°C was measured by AC impedance measurement using the all-solid-state battery evaluation cell encapsulating the sample pellet. Using the obtained resistance value, the ionic conductivity (σ) was calculated using the following formula (1): σ = L / (R × S) (1) (In formula (1), σ is the ionic conductivity (unit: S / cm), R is the resistance (unit: Ω), and S is the cross-sectional area of ​​the sample pellet (unit: cm ２ ), and L represents the distance between the electrodes (unit: cm). The ionic conductivity (σ ＩＳＥ ) is 2.0 x 10 －7 The viscosity was S / cm.

[0134] [Production Examples 5 to 7] Inorganic solid electrolytes (LAZSP, LAZP, and LYZP) were obtained by the same procedure as in Production Example 1, except that the types and amounts of raw materials were changed as shown in Table 1. In addition, the volume-based median diameter and ionic conductivity (σ ＩＳＥ The results are shown in Table 1. Furthermore, powder X-ray diffraction measurements were carried out on the inorganic solid electrolytes LAZSP, LAZP, and LYZP in the same manner as in Production Example 1. As a result, it was found that the main crystalline phase of the inorganic solid electrolytes LAZSP, LAZP, and LYZP was monoclinic or rhombohedral LiZr ２ P ３ O １２ These results confirmed that the inorganic solid electrolytes LAZSP, LAZP, and LYZP have a NASICON-type crystal structure.

[0135]

[0136] <<Production of Polymer and Physical Properties>> [Production Example 2] 1. Synthesis of Polymer PCL1 100 parts of ε-caprolactone, 0.33 parts of 1-butanol, 0.17 parts of tin(II) 2-ethylhexanoate, and a stirrer were placed in a 100 mL test tube and stirred at 95°C for 96 hours in dry air (dew point -60°C or lower). ε-caprolactone and 1-butanol were used that had been dehydrated using molecular sieves. The polymer solution was poured into a large amount of isopropanol to precipitate the polymer. The precipitate was collected by filtration under reduced pressure and dried in vacuo to obtain Polymer PCL1.

[0137] 2. Molecular Weight Measurement The molecular weight of the polymer was measured using gel permeation chromatography (hereinafter also referred to as "GPC") according to the following procedure. The molecular weight of the polymer PCL1 was Mn 18,700 and Mw 26,800. <Procedure> A sample solution was obtained by dissolving 4 mg of polymer in 4 mL of tetrahydrofuran. This sample solution was filtered through a polytetrafluoroethylene membrane filter, and 100 μL was injected into a GPC apparatus, and the weight average molecular weight and number average molecular weight (hereinafter also referred to as "Mw" and "Mn", respectively) were measured under the following conditions. Column: 4 columns of TSKgel SuperMultiporeHZ-M manufactured by Tosoh Corporation Temperature: 40°C Eluent: Tetrahydrofuran Detector: Differential refractometer Flow rate: 600 μL / min Standard material: Polystyrene

[0138] 3. Glass Transition Temperature Measurement The glass transition temperature of the polymer was determined using a differential scanning calorimeter (hereinafter also referred to as "DSC") according to the following procedure. The glass transition temperature of the polymer PCL1 was -65°C. <Procedure> 5 mg of the polymer sealed in an aluminum pan was cooled to -80°C, and then the temperature was swept up to 100°C at a rate of 10°C / min to obtain a heat flux curve. The glass transition temperature was determined from the intersection of the baseline of the heat flux curve and the tangent at the inflection point. Model: DSC250 manufactured by TA Instruments Measurement atmosphere: Nitrogen

[0139] [Production Examples 3 and 4] Polymers PCL2 and PLA were obtained by the same procedure as in Production Example 2, except that the types and amounts of raw materials charged into the test tube were changed as shown in Table 2 and the reaction time and reaction temperature were appropriately adjusted. Furthermore, the Mn and Mw of the polymers were measured using GPC, and the glass transition temperatures were determined using DSC, in the same manner as in Production Example 2. The results are shown in Table 2.

[0140]

[0141] The details of the compounds used in Table 2 are as follows: CL: ε-caprolactone (manufactured by Tokyo Chemical Industry Co., Ltd.) DLLA: DL-lactide (manufactured by Tokyo Chemical Industry Co., Ltd.) BuOH: 2-butanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Sn(Oct) ２: tin(II) 2-ethylhexanoate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Toluene: toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0142] Physical Properties of Organic Electrolyte Measurement Example 1 In a dry room with a dew point of −40° C. or less, 100 parts of polymer PCL1 as the polymer and 246 parts of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Inc., hereinafter also referred to as “LiFSI”) as the alkali metal salt were dissolved in 346 parts of acetonitrile to obtain an organic electrolyte composition. Subsequently, a 300 μm thick silicone rubber sheet with a 6 mm diameter opening was placed on a 10 mm square stainless steel plate, the opening was filled with the organic electrolyte composition, and the resulting mixture was vacuum dried at 60° C. for 48 hours to obtain an organic electrolyte. The resulting organic electrolyte had a molar ratio of polymer PCL1:LiFSI=1:1, a mass proportion of LiFSI of 71.1%, and a thickness of 0.300 mm. The ionic conductivity (σ) of the resulting organic electrolyte at 25° C. was measured using the same method as in Production Example 1. ОＳＥ ) was measured, and it was 1.0 × 10 －５ S / cm (see Table 3).

[0143] [Measurement Examples 2 and 3] Organic electrolytes were obtained in the same manner as in Measurement Example 1, except that the types and amounts of raw materials were changed as shown in Table 3. In addition, the ionic conductivity (σ) of each of the organic electrolytes obtained in Measurement Examples 2 and 3 at 25°C was measured in the same manner as in Production Example 1. ОＳＥ The results are shown in Table 3.

[0144] Measurement Example 4 An organic electrolyte composition (curable composition) was obtained by dissolving 218 parts of lithium bis(fluorosulfonyl)imide as an alkali metal salt and 5 parts of 2-hydroxy-2-methylpropiophenone (hereinafter also referred to as "HMP") as a photopolymerization initiator in 100 parts of methyl acrylate (hereinafter also referred to as "MA") as a monomer. The MA used was dehydrated using a molecular sieve. Next, a 300 μm silicone rubber sheet with a 15 mm square opening was placed on a 20 mm square heavy-release release PET film, and the organic electrolyte composition was poured into it, followed by laminating it with a light-release release PET film from above. The organic electrolyte composition sandwiched between both sides of the release PET film was irradiated with ultraviolet light at a wavelength of 365 nm (illuminance 56 mW / cm) using an ultraviolet curing device (ultraviolet curing device manufactured by Minaga Electric Mfg. Co., Ltd., mercury xenon lamp, lamp height 10 mm). ２ ) from the light release film side and the heavy release film side, respectively, for 45 seconds each, and this was repeated twice (cumulative light amount: 10,080 mJ / cm ２ ), and an organic electrolyte (thickness 300 μm) containing polymethyl acrylate (hereinafter also referred to as "pMA") and an alkali metal salt was obtained as an active energy ray-cured product. The illuminance was measured using an ultraviolet integrating actinometer (UV Power Puck II manufactured by EIT Corporation (center wavelength of the light-receiving part: 355 nm)). The reaction rate of MA was over 96%. The ionic conductivity (σ) of the obtained organic electrolyte at 25°C was measured in the same manner as in Production Example 1. ОＳＥ The results are shown in Table 3.

[0145] [Measurement Example 5] An organic electrolyte was obtained by the same procedure as in Measurement Example 4, except that the types and amounts of raw materials were changed as shown in Table 3. The ionic conductivity (σ) of the obtained organic electrolyte at 25°C was measured in the same manner as in Measurement Example 4. ОＳＥ The results are shown in Table 3.

[0146] Comparative Measurement Example 1 In a dry room with a dew point of −40° C. or less, 100 parts of polyethylene oxide (polyethylene oxide manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Mw=100,000) as a polymer and 426 parts of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Inc.) as an alkali metal salt were weighed into vials so that the molar ratio of polymer to alkali metal salt was 1:1, and 526 parts of acetonitrile was added and wet-mixed with a stirrer to obtain a mixture. Next, a 300 μm thick silicone rubber sheet having an opening with a diameter of 6 mm was placed on a 10 mm square stainless steel plate, the opening was filled with the mixture, and the mixture was vacuum-dried at 60° C. for 48 hours to obtain an organic electrolyte. The ionic conductivity (σ) of the obtained organic electrolyte at 25° C. was measured in the same manner as in Production Example 1. ОＳＥ The results are shown in Table 3.

[0147]

[0148] Details of the compounds used in Table 3 are shown below. PCL1: Polycaprolactone obtained in Production Example 2 PCL2: Polycaprolactone obtained in Production Example 3 PLA: Polylactic acid obtained in Production Example 4 PEO: Polyethylene oxide (Mw 100,000) [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] MA: Methyl acrylate [manufactured by Tokyo Chemical Industry Co., Ltd.] BA: n-Butyl acrylate [manufactured by Tokyo Chemical Industry Co., Ltd.] HMP: 2-hydroxy-2-methylpropiophenone [manufactured by Tokyo Chemical Industry Co., Ltd.] AcCN: Acetonitrile [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] LiFSI: Lithium bis(fluorosulfonyl)imide [manufactured by Kanto Chemical Co., Ltd.]

[0149] <<Production and Evaluation of Composite Electrolyte>> [Example 1] 1. Production of Composite Electrolyte HSE1 In a dry room with a dew point of −40° C. or less, Li, １．２５ In ０．２ Zr １．８ Si ０．０５ P ２．９５ O １２100 parts of the inorganic solid electrolyte LIZSP obtained in Production Example 1, 15.55 parts of polycaprolactone (polymer PCL1 obtained in Production Example 2), and 38.25 parts of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Inc.) were each weighed out, and 100 parts of acetonitrile was added. The mixture was mechanically mixed at room temperature (25°C) using a mortar to obtain a mixture. Using the press mold 10 shown in FIG. 1 , a sample pellet consisting of a mixture of an inorganic solid electrolyte and an organic electrolyte was prepared in a dry room with a dew point of -40°C or less by the following procedure. First, a die set 11 containing 0.075 g of the mixture was placed on the lower punch 13, and an upper punch 12 was placed on the die set 11. The mixture was compressed for 1 minute at a pressure of 10 MPa using a hydraulic press to obtain a circular sample pellet having a diameter of 1 cm and a thickness of 500 μm. Next, the sample pellet was vacuum dried at 60°C for 48 hours to obtain a composite electrolyte HSE1.

[0150] 2. Evaluation (1) Measurement of Ionic Conductivity The ionic conductivity (σ) of the composite electrolyte HSE1 at 25°C was measured in the same manner as in Production Example 1. ＳＥ As a result, the σ of the composite electrolyte HSE1 ＳＥ is 9.5 x 10 －６ S / cm (see Table 4).

[0151] (2) Comparison of Measured and Calculated Ion Conductivities (Calculation of Δσ) The measured ionic conductivities (σ) of the inorganic solid electrolyte (LIZSP obtained in Production Example 1) and the organic electrolyte (organic electrolyte obtained in Measurement Example 1) used in the production of the composite electrolyte HES1 were compared. ＩＳＥ and σ ОＳＥ ) to calculate the average ionic conductivity σ of the composite electrolyte HSE1 using the following formula (2): ａｖｅ was calculated. σ ａｖｅ = P × σ ＩＳＥ + (1-P) × σ ОＳＥ ...(2) (In formula (2), σ ａｖｅ is the average ionic conductivity of the composite electrolyte (unit: S / cm), σ ＩＳＥ is the measured ionic conductivity of the inorganic solid electrolyte at 25°C (unit: S / cm), σ ОＳＥrepresents the measured value of the ionic conductivity of the organic electrolyte at 25°C (unit: S / cm), and P represents the mass % of the inorganic solid electrolyte in the composite electrolyte.) As a result, σ of the composite electrolyte HSE1 ａｖｅ is 3.6 x 10 －６ S / cm (see Table 4).

[0152] Ionic conductivity σ of composite electrolyte HSE1 ＳＥ and the average ionic conductivity σ ａｖｅ Using the above, the difference between the measured value and the calculated value of the ionic conductivity of the composite electrolyte HSE1 was calculated as the change Δσ relative to the average ionic conductivity using the following formula (3): Δσ = σ ＳＥ -σ ａｖｅ (3) (In formula (3), Δσ is the change in average ionic conductivity (unit: S / cm), σ ＳＥ is the measured value of the ionic conductivity of the composite electrolyte (unit: S / cm), σ ａｖｅ and represent the calculated average ionic conductivity of the composite electrolyte (unit: S / cm). As a result, the Δσ of the composite electrolyte HSE1 was 5.9 × 10 －６ S / cm (see Table 4).

[0153] (3) Flexibility Test The end of the sample pellet was pinched with tweezers and bent, and the flexibility was evaluated based on the angle at which the sample pellet broke when bent. The evaluation was based on the following criteria: ○: No break even when bent by 90° or more △: Bendable, but breaks when bent by 90° ×: Cannot be bent, breaks when force is applied The composite electrolyte HSE1 did not break even when pinched with tweezers and bent by 90° or more, and its flexibility was evaluated as ○.

[0154] [Examples 2 to 5 and Examples 8 to 10] Composite electrolytes HSE2 to HSE5 and HSE8 to 10 were obtained by the same procedure as in Example 1, except that the types and amounts of raw materials were changed as shown in Table 4. The ionic conductivities (σ ＳＥ The change in ionic conductivity (Δσ) relative to the average ionic conductivity was calculated. The results are shown in Table 4.

[0155] [Example 6] In a dry room with a dew point of -40°C or less, Li was mixed with an inorganic solid electrolyte and an organic electrolyte in a mass ratio of 50:50. １．２５ In ０．２ Zr １．８ Si ０．０５ P ２．９５ O １２ 333 parts of the inorganic solid electrolyte LIZSP (obtained in Production Example 1), 100 parts of methyl acrylate (hereinafter also referred to as "MA"), and 218 parts of lithium bis(fluorosulfonyl)imide (manufactured by Kanto Chemical Co., Inc.) were weighed out, and 5 parts of HMP was added and dissolved to obtain a curable composition for a solid electrolyte. Using the press mold 10 shown in FIG. 1 , in a dry room with a dew point of −40°C or less, sample pellets were prepared from the curable composition for a solid electrolyte by the following procedure. First, a die set 11 containing 0.075 g of the curable composition for a solid electrolyte was placed on the lower punch 13, and an upper punch 12 was placed on the die set 11. The mixture was compressed for 1 minute at a pressure of 10 MPa using a hydraulic press to obtain a circular sample pellet having a diameter of 1 cm and a thickness of 500 μm. Next, in a dry room with a dew point of -40°C or less, the sample pellets were irradiated with ultraviolet light of 365 nm wavelength (illuminance 60 mW / cm) using an ultraviolet curing device (UV curing device manufactured by Eye Graphics, high-pressure mercury lamp, lamp height 30 cm). ２ ) from the light release film side and the heavy release film side for 90 seconds each, and this was repeated twice (cumulative light dose of 10,800 mJ / cm ２ ), a composite electrolyte HSE6 (thickness: 500 μm) was obtained. The illuminance was measured using an ultraviolet integrating actinometer (UV Power Puck II manufactured by EIT (center wavelength of the light receiving part: 355 nm)). The ionic conductivity (σ ＳＥ The change in ionic conductivity (Δσ) relative to the average ionic conductivity was calculated. The results are shown in Table 4.

[0156] [Example 7] Composite electrolyte HSE7 was obtained by the same procedure as in Example 6, except that the types and amounts of raw materials were changed as shown in Table 4. In addition, the ionic conductivity (σ ＳＥThe change in ionic conductivity (Δσ) relative to the average ionic conductivity was calculated. The results are shown in Table 4.

[0157] Comparative Example 1 Composite electrolyte HSE11 was obtained by the same procedure as in Example 1, except that the types and amounts of raw materials were changed as shown in Table 4. In addition, the ionic conductivity (σ ＳＥ The change in ionic conductivity (Δσ) relative to the average ionic conductivity was calculated. The results are shown in Table 4.

[0158]

[0159] Details of the compounds used in Table 4 are as follows: LIZSP: oxide (inorganic solid electrolyte) obtained in Production Example 1 PCL1: polycaprolactone obtained in Production Example 2 PCL2: polycaprolactone obtained in Production Example 3 PLA: polylactic acid obtained in Production Example 4 pMA: polymethyl acrylate pBA: polyn-butyl acrylate PEO: polyethylene oxide (Mw 100,000) [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] LiFSI: lithium bis(fluorosulfonyl)imide [manufactured by Kanto Chemical Co., Ltd.]

[0160] <Evaluation Results> As is clear from the results in Table 4, all of the composite electrolytes of Examples 1 to 10 had flexibility and exhibited positive values ​​for the change in ionic conductivity Δσ relative to the average ionic conductivity, resulting in favorable results. Among them, the composite electrolytes produced using polycaprolactone as the polymer exhibited excellent flexibility and exhibited large values ​​for the change in ionic conductivity Δσ relative to the average ionic conductivity (Examples 1 to 4 and 8 to 10).

[0161] In contrast, the composite electrolyte HSE11 of Comparative Example 1, which was produced using PEO as the polymer, exhibited a negative value for the change in ionic conductivity Δσ relative to the average ionic conductivity. This is thought to be because the grain boundary resistance of the inorganic solid electrolyte in the composite electrolyte HSE11 was large, and ionic conduction paths were not sufficiently formed.

[0162] From the above results, it is clear that in the composite electrolyte containing an inorganic solid electrolyte, a polymer, and an alkali metal salt, the inorganic solid electrolyte contains an oxide having a NASICON-type crystal structure, and -(R １ It has become clear that by using a polymer that does not substantially have a repeating unit represented by —O)— in the main chain, a composite electrolyte that exhibits high ionic conductivity and excellent flexibility can be obtained.

[0163] The present invention is not limited to the above-described embodiments, and encompasses various modifications and equivalent modifications within the scope of the spirit of the present invention. Therefore, in light of the above teachings, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are to be understood as falling within the scope and spirit of the present invention.

[0164] 10... Press mold

Claims

1. A solid electrolyte battery comprising: an inorganic solid electrolyte; a polymer; and an alkali metal salt; wherein the inorganic solid electrolyte contains an oxide having a NASICON-type crystal structure; and the polymer contains -(R １ A repeating unit represented by —O)— (where R １ is an alkylene group) in the main chain.

2. The oxide has the general formula: Li １＋ｘ＋ｙ－ｚ M1 ｘ Zr ２－ｘ M2 ｙ M3 ２ P ３－ｙ－ｚ O １２ wherein M1 comprises Fe, In, Y, or Al; M2 comprises Si; M3 comprises W; and x > 0, y ≥ 0, and z ≥ 0 are satisfied.

3. The composite electrolyte of claim 1, wherein the polymer is a non-crosslinked polymer.

4. The composite electrolyte of claim 1, wherein the polymer comprises repeating units having ester bonds.

5. The composite electrolyte according to claim 4, wherein the repeating unit having an ester bond is a repeating unit represented by the following formula (1) or a repeating unit derived from a (meth)acrylic monomer: [In formula (1), R represents a hydrogen atom or an alkyl group, and m represents an integer of 0 to 10.] 6. The composite electrolyte according to claim 1, wherein the content of the inorganic solid electrolyte is 20% by mass or more and 80% by mass or less.

7. The composite electrolyte of claim 1, wherein said alkali metal salt comprises an imide-based alkali metal salt.

8. A curable composition for use in producing a solid electrolyte, the curable composition for a solid electrolyte comprising: an inorganic solid electrolyte containing an oxide having a NASICON-type crystal structure; a (meth)acrylic monomer; and an alkali metal salt.

9. A method for producing a composite electrolyte according to any one of claims 1 to 7, comprising the step of mixing the inorganic solid electrolyte, the polymer, and the alkali metal salt.

10. A method for producing a composite electrolyte according to any one of claims 1 to 7, comprising the step of irradiating the curable composition for a solid electrolyte according to claim 8 with active energy rays to cure it.

11. An electricity storage device comprising the composite electrolyte according to any one of claims 1 to 7.

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