Method for manufacturing complex electrolytes

Abstract

To provide a composite electrolyte containing an inorganic solid electrolyte and an organic electrolyte, which exhibits excellent stability with respect to highly active materials. [Solution] A method for producing a composite electrolyte comprising a first step of treating an inorganic solid electrolyte with a surface modifier, and a second step of mixing the inorganic solid electrolyte after treatment with the surface modifier, a polymer, and an alkali metal salt, wherein the amount of surface modifier used in the first step is 30 parts by mass or less per 100 parts by mass of the inorganic solid electrolyte.

Description

[Technical Field]

[0001] This invention relates to a method for producing a composite electrolyte. [Background technology]

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

[0003] Lithium-ion secondary batteries, widely used as energy storage devices, are secondary batteries that have a negative electrode, a positive electrode, and an electrolyte, and charge and discharge by moving lithium ions between the two electrodes via the electrolyte. Conventionally, organic electrolytes have been mainly used as the electrolyte. In contrast, in recent years, as a technology to eliminate concerns about electrolyte leakage and short circuits inside the battery due to overcharging and over-discharging, solid or gel-like electrolytes using inorganic or organic materials have been proposed as an alternative to organic electrolytes. Among these, inorganic solid electrolytes are non-flammable and are suitable as materials that enhance the safety of energy storage devices.

[0004] To obtain inorganic solid electrolytes exhibiting high ionic conductivity, for example, in the case of oxide inorganic solid electrolytes, it is common practice to sinter compacted powder at high temperatures (e.g., 1,000°C or higher). Another method for increasing the ionic conductivity of inorganic solid electrolytes is to composite them by contacting a flexible organic electrolyte with the inorganic solid electrolyte powder (see, for example, Non-Patent Document 1).

[0005] Non-Patent Document 1 discloses a composite electrolyte containing lithium aluminum titanium phosphate (hereinafter also referred to as "LATP") particles which is an inorganic solid electrolyte, polyethylene oxide, and an alkali metal salt. A composite electrolyte obtained by compositing an inorganic solid electrolyte and an organic electrolyte has the advantages that it can exhibit high ionic conductivity without undergoing a sintering step, and an electrolyte material excellent in flexibility can be obtained. [Prior Art Documents] [Non-Patent Documents]

[0006] [Non-Patent Document 1] "The Journal of Physical Chemistry C", 2018, Volume 122, pp. 9852-9858 [Summary of the Invention] [Problem to be Solved by the Invention]

[0007] While inorganic solid electrolytes are excellent in safety and exhibit high ionic conductivity, they may undergo redox reaction and degrade when coming into contact with an active material inside an electricity storage device. In particular, when producing an electricity storage device with high energy density, a highly active active material such as metallic lithium is sometimes used, and there is a concern that the electrolyte inside the electricity storage device is likely to degrade when the inorganic solid electrolyte comes into contact with the active material and undergoes a redox reaction. Therefore, it is necessary to prevent the inorganic solid electrolyte from directly contacting the active material inside the electricity storage device. However, when the present inventors studied the composite electrolyte described in Non-Patent Document 1, they found that the inorganic solid electrolyte may partially directly contact the active material, and there is room for improvement to ensure the stability of the composite electrolyte.

[0008] The present invention has been made in view of such circumstances, and a main object thereof is to provide a composite electrolyte containing an inorganic solid electrolyte and an organic electrolyte, which is excellent in stability against highly active active materials. [Means for Solving the Problem]

[0009] As a result of diligent research to solve the above problems, the present inventors have found that by performing a specific treatment before mixing the inorganic solid electrolyte and the organic electrolyte in a composite electrolyte obtained by compounding an inorganic solid electrolyte and an organic electrolyte, a composite electrolyte with excellent stability against highly active materials can be obtained, and have completed the present invention. Specifically, the present invention provides the following method for producing a composite electrolyte.

[0010] [1] A method for producing a composite electrolyte, comprising: a first step of treating an inorganic solid electrolyte with a surface modifier; and a second step of mixing the inorganic solid electrolyte after treatment with the surface modifier with a polymer and an alkali metal salt, wherein the amount of the surface modifier used in the first step is 30 parts by mass or less per 100 parts by mass of the inorganic solid electrolyte. [2] The method for producing a composite electrolyte according to [1], wherein the first step includes the steps of mixing the inorganic solid electrolyte, the surface modifier, and the dispersion medium to obtain a mixture, and removing the dispersion medium from the mixture. [3] A method for producing a composite electrolyte according to [1] or [2], wherein the inorganic solid electrolyte includes an oxide having a NASICON-type crystal structure. [4] The inorganic solid electrolyte is of the general formula: Li 1+2a+b+c-d M1 a M2 b M3 2-a-b Si c W d P 3-c-d O 12 A method for producing a composite electrolyte according to any one of [1] to [3], comprising a solid electrolyte represented by (wherein M1 contains an element that becomes a divalent cation, M2 contains an element that becomes a trivalent cation, and M3 contains at least one element of Ti and Zr, satisfying a≧0, b>0, c>0 and d≧0). [5] A method for producing a composite electrolyte according to any one of [1] to [4], wherein the surface modifier is a silane coupling agent. [6] A method for producing a composite electrolyte according to any one of [1] to [5], wherein the polymer has a structure represented by the following formula (1). [ka] [In formula (1), R represents a hydrogen atom or an alkyl group. X and Y are the same or different, representing a hydrogen atom, a hydroxyl group, or an alkyl group. n represents an integer of 1 or more, and m represents an integer from 0 to 10.] [7] A method for producing a composite electrolyte according to any one of [1] to [6], wherein the weight-average molecular weight of the polymer is 1,000 to 1,000,000. [8] A method for producing a composite electrolyte according to any one of [1] to [7], wherein the alkali metal salt comprises lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide. [Effects of the Invention]

[0011] According to the present invention, a composite electrolyte with excellent stability against highly active materials can be obtained. Furthermore, by using the composite electrolyte obtained by the manufacturing method of the present invention as an electrolyte in energy storage devices such as secondary batteries and capacitors, it is possible to obtain an energy storage device with excellent electrolyte stability even when using highly active materials, while ensuring safety through the solidification of the electrolyte. [Modes for carrying out the invention]

[0012] The following describes in detail the method for producing the composite electrolyte of the present invention (hereinafter also referred to as "this production method") and the energy storage device equipped with the composite electrolyte obtained by this production method.

[0013] ≪Method for manufacturing complex electrolytes≫ The composite electrolyte obtained by this manufacturing method is an inorganic-organic composite material containing an inorganic solid electrolyte, a polymer, and an alkali metal salt. This composite electrolyte can be manufactured by a method comprising the following first and second steps. Step 1: Process of treating an inorganic solid electrolyte with a surface modifier. Step 2: A process of mixing the inorganic solid electrolyte after treatment with a surface modifier, the polymer, and the alkali metal salt. Hereinafter, each step will be described in detail.

[0014] <First Step> ·Inorganic solid electrolyte In the first step, the inorganic solid electrolyte treated with the surface modifier is not particularly limited as long as it is an inorganic solid exhibiting ion conductivity. As the inorganic solid electrolyte, for example, at least one selected from the group consisting of oxide-based solid electrolytes, sulfide-based solid electrolytes and chloride-based solid electrolytes can be used. Among these, oxide-based solid electrolytes and sulfide-based solid electrolytes are preferred from the viewpoint of exhibiting high ion conductivity, and oxide-based solid electrolytes are more preferred from the viewpoint of higher safety in the atmosphere.

[0015] The crystal structure of the inorganic solid electrolyte is not particularly limited. Examples of the crystal structure of the inorganic solid electrolyte include NASICON-type structure, LISICON-type structure, perovskite-type structure, and garnet-type structure.

[0016] As specific examples of these, solid electrolytes having a NASICON-type structure include Li 1+x Al x Ti 2-x (PO4)3 (x≧0, also referred to as "LTP" or "LATP"), Li 1+x Al x Ge 2-x (PO4)3 (x≧0, also referred to as "LGP" or "LAGP"), LiZr2(PO4)3 (also referred to as "LZP"), and Na3Zr2Si2PO, which is a NASICON type, 12 (also referred to as "NZSP"), and oxides obtained by substituting some elements constituting these compounds with various elements (e.g., B, Na, Al, Si, Ca, Ga, Ge, Sc, Fe, Sr, In, Ti, Hf, Sn, V, Nb, Ta, Sb, Bi, W, and lanthanoid elements).

[0017] As solid electrolytes having a LISICON-type structure, Li 14 ZnGe4O 16 and oxides obtained by substituting some elements constituting the compound with the various elements described above. As for solid electrolytes having a perovskite structure, Li 0.35 La 0.55 Examples include TiO3 and oxides in which some of the elements constituting this compound are replaced with the various elements mentioned above. As a solid electrolyte having a garnet-type structure, Li7La3Zr2O 12 and Li5La3Nb2O 12 Examples include oxides in which some of the elements constituting these compounds are substituted with the various elements mentioned above.

[0018] One embodiment of the composite electrolyte obtained by this manufacturing method is an inorganic-organic composite electrolyte comprising an inorganic solid electrolyte having a NASICON-type crystal structure and an organic electrolyte, wherein the organic electrolyte contains a polymer and an alkali metal salt. Unlike layered structures, the NASICON-type crystal structure has a three-dimensionally expanded space for alkali metal ion movement, and zirconium (Zr) is stable even under high voltage, making it useful as a solid electrolyte for high operating voltages. In the composite electrolyte obtained by this manufacturing method, an oxide having a NASICON-type crystal structure can preferably be used as the inorganic solid electrolyte. The crystal structure of the solid electrolyte can be determined from the diffraction profile obtained by powder X-ray diffraction measurement.

[0019] When using an oxide having a NASICON-type crystal structure as the inorganic solid electrolyte contained in a composite electrolyte, a preferred example of the oxide is the oxide (x) shown below. Oxide (x): General formula Li 1+2a+b+c-d M1 a M2 b M3 2-a-b Si c W d P 3-c-d O 12 A solid electrolyte represented by (where M1 contains an element that forms a divalent cation, M2 contains an element that forms a trivalent cation, and M3 contains at least one element of Ti and Zr, satisfying a≧0, b>0, c>0, and d≧0).

[0020] Regarding oxides (x) Oxide (x) is a solid electrolyte in which an oxide based on LiZr2(PO4)3 or LiTi2(PO4)3 is used as the basic framework, in which at least a portion of Zr or Ti is substituted with M2 (containing an element that becomes a trivalent cation) and optionally substituted with M1 (containing an element that becomes a divalent cation), and a portion of P is substituted with Si and optionally substituted with W.

[0021] In oxides (x), M1 can be an element that forms a divalent cation from Group 2 elements, Group 12 elements, or transition elements (Groups 3-11), as well as Sn, Pd, etc.

[0022] Examples of M2 include elements from Group 3, Group 13, and transition elements (Groups 3-11) that form trivalent cations, as well as Sb, Bi, Fe, etc. For Group 13 elements, Al, B (boron), or In are preferred.

[0023] M3 may contain at least one element, such as Ti and Zr. That is, M3 may be Ti, or it may be Zr, and it may further contain elements other than Ti and Zr that form tetravalent cations together with Ti and / or Zr. Examples of elements other than Ti and Zr that form tetravalent cations include Group 14 elements, transition elements (Groups 3 to 11 elements) that form tetravalent cations, and Te. Si is preferred as the Group 14 element.

[0024] In the general formula for oxide(x), a, b, c, and d are not particularly limited as long as a≧0, b>0, c>0, and d≧0. For example, when a=0, b>0, c>0, and d=0, oxide(x) is "Li 1+b+c M2 b M3 2-b Si c P 3-c O 12 This is represented by ".

[0025] More specifically regarding a, b, c, and d in the general formula of oxide (x), a is, for example, 0.5 or less, and may also be 0.4 or less. It is preferable that a ≤ 0.3 is satisfied, more preferably a ≤ 0.15, and even more preferably a ≤ 0.1, in that impurity phases are less likely to form, thereby enabling the acquisition of an inorganic solid electrolyte exhibiting high ionic conductivity. Furthermore, when a > 0, the lower limit of a is preferably a ≥ 0.01, and more preferably a ≥ 0.03.

[0026] b is, for example, 2.0 or less, and may also be 1.9 or less. It is preferable that b ≤ 1.9, and more preferably b ≤ 1.85, as this significantly contributes to α-phase formation and thereby allows for the acquisition of an inorganic solid electrolyte with higher ionic conductivity. Furthermore, for the lower limit of b, it is preferable that b ≥ 0.01, and more preferably b ≥ 0.02.

[0027] c is, for example, 1.8 or less, and may also be 1.5 or less. It is preferable that c ≤ 1.2, more preferably that c ≤ 1.0, and even more preferably that c ≤ 0.95, in that a higher ionic conductivity inorganic solid electrolyte can be obtained. For the lower limit of c, it is preferable that c ≥ 0.01, and more preferably that c ≥ 0.03.

[0028] d is, for example, 0.5 or less, and may also be 0.3 or less. It is preferable that d ≤ 0.2, and more preferably that d ≤ 0.1, because impurity phases are less likely to form, thereby enabling the acquisition of an inorganic solid electrolyte exhibiting high ionic conductivity. Furthermore, when d > 0, it is preferable that the lower limit of d be d ≥ 0.01, and more preferably that d ≥ 0.02.

[0029] Furthermore, zirconium phosphate 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 an isotropic crystal structure and therefore exhibits the highest Li ion conductivity.

[0030] In the above general formula representing oxide(x), the stoichiometric ratio of O is set to 12, but it is sufficient to maintain the charge neutrality of the oxide as a whole, and the stoichiometric ratio of O does not have to be exactly 12. That is, the value of O in oxide(x) may be less than 12 or greater than 12, as long as the charge neutrality of the oxide(x) as a whole is maintained. For example, Li 1+2a+b+c-d M1 a M2 b M3 2-a-b Si c W d P 3-c-d O 12±β (Here, satisfying 0 ≤ β ≤ 1, M1, M2, M3, a, b, c, and d are the same as M1, M2, M3, a, b, c, and d in the above formula shown as the general formula for oxide(x)) are also included in oxide(x) as long as the charge neutrality of the oxide(x) as a whole is maintained.

[0031] The method for producing oxide (x) is not particularly limited. Oxide (x) can be produced, for example, by weighing and mixing raw materials to satisfy the stoichiometric ratio of the composition represented by the general formula above (raw material mixing step), and then calcining the resulting mixture (calcination step).

[0032] As raw materials for oxide(x), the Li-supplying component, M1-supplying component, M2-supplying component, M3-supplying component, Si-supplying component, W-supplying component, and P-supplying component can be used, with the supplying component corresponding to the element required to obtain the desired oxide(x). For example, to obtain oxide(x) where a=0, b>0, c>0, and d=0, the Li-supplying component, M2-supplying component, M3-supplying component, Si-supplying component, and P-supplying component are used as raw materials.

[0033] For example, the Li-supplying components, M1-supplying components, M2-supplying components, M3-supplying components, Si-supplying components, W-supplying components, and P-supplying components for obtaining oxide (x) can be carbonates, bicarbonates, sulfates, sulfites, nitrates, nitrites, phosphates, acetates, citrates, ammonium salts, oxides, hydroxides, chlorides, sulfides, etc. of these metal elements. Furthermore, one type of supplying component for obtaining oxide (x) may be a compound containing two or more elements from among Li, M1, M2, M3, Si, W, and P.

[0034] In the production of oxide (x), the raw materials may be mixed by dry mixing or by wet mixing using a liquid. By employing wet mixing, the density of the inorganic solid electrolyte after calcination can be increased compared to the case of dry mixing. In addition, the ionic conductivity of the obtained inorganic solid electrolyte can also be relatively improved. As the liquid used in wet mixing, water, various organic solvents, and mixtures thereof can be used as appropriate.

[0035] In the firing process, the mixture obtained in the raw material mixing process may be fired without molding, or it may be fired after molding. The firing temperature is not limited, but for example it can be 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 1,500°C or lower, preferably 1,400°C or lower, and more preferably 1,350°C or lower. During firing, the temperature may be gradually increased from a lower temperature than the firing temperature, and finally maintained at the temperature required for firing.

[0036] Commercially available oxides (x) can also be used. Examples of commercially available oxides (x) include LICGC PW-01, LICGC AG-01, and LICGC SP-01 (all manufactured by Ohara Corporation).

[0037] Furthermore, oxide (x) exhibits high Li ion conductivity. Therefore, oxide (x) is suitable as a material for manufacturing composite electrolytes for energy storage devices in which lithium ions are the ion carriers.

[0038] The inorganic solid electrolyte obtained by the calcination process is preferably pulverized into particles using any method, and then treated with a surface modifier. The pulverization of the inorganic solid electrolyte can be carried out using a pulverizer such as a ball mill, bead mill, or blender. Alternatively, granules obtained by granulating powdered inorganic solid electrolyte may be used as particulate inorganic solid electrolyte and then treated with a surface modifier.

[0039] The average particle size of the inorganic solid electrolyte treated with a surface modifier is preferably 0.01 μm or more and 20 μm or less in volume-based median diameter when 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 maintaining good handling properties. From the viewpoint of handling properties, the average particle size of the inorganic solid electrolyte is more preferably 0.05 μm or more, even more preferably 0.1 μm or more, and even more preferably 0.2 μm or more in volume-based median diameter. 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, even more preferably 10 μm or less, and even more preferably 5 μm or less in volume-based median diameter. In this specification, the average particle size of the inorganic solid electrolyte is a value obtained by laser diffraction-scattering particle size measurement.

[0040] • Surface modifier As a surface modifier, a substance that exhibits affinity for both inorganic solid electrolytes and polymers can be preferably used. Examples of such substances include compounds that possess both functional groups that bind to organic substances and functional groups that bind to inorganic substances, and silane coupling agents can be preferably used.

[0041] Examples of silane coupling agents include silane coupling agents having one or more functional groups such as epoxy groups, (meth)acryloyl groups, amino groups, thiol groups, vinyl groups, isocyanate groups, and blocked isocyanate groups.

[0042] Specific examples of silane coupling agents include oxyranyl group-containing silane coupling agents such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 8-glycidoxyoctyltriethoxysilane; and oxetanyl group-containing silane coupling agents such as 2-(3,4-oxetanylcyclohexyl)ethyltrimethoxysilane, 3-oxetanylpropyltrimethoxysilane, 3-oxetanylpropylmethyldiethoxysilane, 3-oxetanylpropyltriethoxysilane, and 8-oxetanyloctyltriethoxysilane.

[0043] Specific examples of silane coupling agents having a (meth)acryloyl group include 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, 6-(meth)acryloyloxyhexyltrimethoxysilane, and 8-(meth)acryloyloxyoctyltrimethoxysilane.

[0044] Specific examples of silane coupling agents having an amino group include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-(3-cyclohexylamino)propyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane.

[0045] Specific examples of silane coupling agents having a thiol group include 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane.

[0046] Specific examples of silane coupling agents having a vinyl group include vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, vinyl(trimethoxysilyl) ether, vinyl(methyldiethoxysilyl) ether, and vinyl(triethoxysilyl) ether.

[0047] Specific examples of silane coupling agents having an isocyanate group or a blocked isocyanate group include isocyanatomethyltrimethoxysilane compounds such as isocyanatomethyltrimethoxysilane, 3-isocyanatopropyltrimethoxysilane, 6-isocyanatohexyltrimethoxysilane, 8-isocyanatooctyltrimethoxysilane, isocyanatomethyltriethoxysilane, 3-isocyanatopropyltriethoxysilane, 6-isocyanatohexyltriethoxysilane, and 8-isocyanatoctyltriethoxysilane; isocyanatomethylmethyldimethoxysilane, 3-isocyanatopropylmethyldimethoxysilane, 6-isocyanatohexylmethyldimethoxysilane, 8-isocyanatooctylmethyldimethoxysilane, isocyanatomethylmethyldiethoxysilane, 3-isocyanatopropylmethyldiethoxysilane, and 6-isocyanatohexylmethyldiethoxysilane. Examples include isocyanatoalkylmonoalkyldialkoxysilane compounds such as 8-isocyanatooctylmethyldiethoxysilane; isocyanatomethyldimethylmethoxysilane compounds such as 8-isocyanatopropyldimethylmethoxysilane, 6-isocyanatohexyldimethylmethoxysilane, 8-isocyanatooctyldimethylmethoxysilane, isocyanatomethyldimethylethoxysilane, 3-isocyanatopropyldimethylethoxysilane, 6-isocyanatohexyldimethylethoxysilane, and isocyanatooctyldimethylethoxysilane; blocked isocyanatoalkylalkoxysilane compounds in which the isocyanate group of an isocyanatoalkyltrialkoxysilane compound, an isocyanatoalkylmonoalkyldialkoxysilane compound, or an isocyanatoalkyldialkylalkoxysilane compound is protected; and the like. Furthermore, commercially available blocked isocyanatoalkylalkoxysilane compounds include Shin-Etsu Silicone X-12-1195, X-12-1293, and X-12-1308ES (all manufactured by Shin-Etsu Silicone Co., Ltd.) under trade names.

[0048] As a surface modifier, a silane coupling agent having at least one selected from the group consisting of an amino group, a (meth)acryloyl group, and a vinyl group is preferably used because it has high affinity with polymers (especially polyester polymers) and can improve the uniform dispersibility of inorganic solid electrolytes. Among these, a silane coupling agent having an amino group is particularly preferred because it does not require pH adjustment, is easy to use, and has a high effect in improving the uniform dispersibility of inorganic solid electrolytes.

[0049] In the first step, the amount of surface modifier used when treating the inorganic solid electrolyte is 30 parts by mass or less per 100 parts by mass of the inorganic solid electrolyte. If the amount of surface modifier used is greater than 30 parts by mass per 100 parts by mass of the inorganic solid electrolyte, sufficient stability for highly active materials cannot be ensured in the composite electrolyte obtained by mixing it with the polymer and alkali metal salt. From the viewpoint of obtaining a composite electrolyte with excellent stability for highly active materials, the amount of surface modifier used is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the inorganic solid electrolyte. Furthermore, from the viewpoint of uniformly modifying the surface of the inorganic solid electrolyte and thereby obtaining a composite electrolyte with excellent stability for highly active materials, the amount of surface modifier used is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the inorganic solid electrolyte.

[0050] The preferred range for the amount of surface modifier used can be determined by appropriately combining the upper and lower limits of the above-mentioned values. Specifically, the amount of surface modifier used is preferably 0.5 parts by mass or more and 30 parts by mass or less, more preferably 1 part by mass or more and 25 parts by mass or less, even more preferably 1 part by mass or more and 20 parts by mass or less, even more preferably 2 parts by mass or more and 15 parts by mass or less, and even more preferably 2 parts by mass or more and 12 parts by mass or less, per 100 parts by mass of inorganic solid electrolyte.

[0051] The method for treating an inorganic solid electrolyte with a surface modifier is not particularly limited. In the first step of the present invention, the surface modification of the inorganic solid electrolyte may be performed by dry mixing of the inorganic solid electrolyte and the surface modifier, or by wet mixing using a dispersion medium. Surface modification of the inorganic solid electrolyte is preferably performed by wet mixing because it allows for uniform modification of the surface of the inorganic solid electrolyte with the surface modifier, thereby further enhancing its stability against highly active materials. Specifically, the first step preferably includes the following dispersion medium mixing step and removal step. Dispersion medium mixing step: A step of mixing an inorganic solid electrolyte, a surface modifier, and a dispersion medium to obtain a mixture. Removal process: A process to remove the dispersion medium from the mixture.

[0052] In the dispersion medium mixing step, the inorganic solid electrolyte and surface modifier are added to the dispersion medium and mixed to perform surface modification of the inorganic solid electrolyte. Examples of dispersion media that can be used include water, various organic solvents, and mixtures thereof. Organic solvents are preferably used as the dispersion medium because they enhance the dispersibility of the surface modifier and the inorganic solid electrolyte, making it easier to obtain a uniformly surface-modified inorganic solid electrolyte, and because the dispersion medium can be removed under relatively mild conditions in the subsequent removal step. Any solvent that does not react with the inorganic solid electrolyte can be used, and specific examples include tetrahydrofuran, acetone, tert-butyl methyl ether, diethyl ether, 1,4-dioxane, acetonitrile, ethyl acetate, and N-methyl-2-pyrrolidone. The amount of dispersion medium used can be set as appropriate, but from the viewpoint of efficiently performing surface modification of the inorganic solid electrolyte with the surface modifier, it is preferable to use 50 to 2,000 parts by mass per 100 parts by mass of the total amount of inorganic solid electrolyte.

[0053] To efficiently modify the surface of the inorganic solid electrolyte, it is preferable to stir the dispersion medium containing the inorganic solid electrolyte and surface modifier after adding the surface modifier and the inorganic solid electrolyte to the dispersion medium. The stirring method is not particularly limited and can be any of the following: for example, a rotary-orbit mixer, a magnetic stirrer, a stirring rod, a stirrer with stirring blades (three-one motor), or external circulation stirring. Stirring may also be performed while mechanically mixing with a homomixer, disper-type mixer, homogenizer, etc. The temperature and time during the stirring process are not particularly limited and can be set as appropriate. The temperature during the stirring process can be set as appropriate depending on the type of dispersion medium, but for example, it is 10 to 85°C. The stirring time is, for example, 1 to 48 hours. The mixture after stirring may be used as is in the next removal process, or it may be used in the next removal process after being subjected to treatment such as filtration.

[0054] In the removal step, the dispersion medium is removed from the mixture obtained in the dispersion medium mixing step. There are no particular restrictions on the method of removing the dispersion medium, and known desolvation methods can be appropriately employed. For example, desolvation may be performed by heating, natural drying, forced air treatment, or reduced pressure treatment. Alternatively, two or more of these treatments may be appropriately combined to perform desolvation. When removing the dispersion medium by heating, the heating temperature can be appropriately set according to the type of dispersion medium, but for example, it can be 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. If it is required to remove the dispersion medium in the mixture at the lowest possible temperature, the desolvation treatment may be performed under reduced pressure and with a heating temperature of 80°C or lower. By removing the solvent in the removal step, a composite of the inorganic solid electrolyte and the surface modifier can be obtained in a solid state as an inorganic solid electrolyte surface-modified with the surface modifier.

[0055] <Second process> In the first step, the inorganic solid electrolyte is surface-modified. In the subsequent second step, the inorganic solid electrolyte treated with the surface modifier is mixed with a polymer and an alkali metal salt. This method allows for the production of a composite electrolyte exhibiting high ionic conductivity without requiring a sintering step to eliminate gaps between inorganic solid electrolyte particles and reduce interfacial resistance. Furthermore, a composite electrolyte with high ionic conductivity can be obtained through a simple method of mixing the inorganic solid electrolyte, polymer, and alkali metal salt, and molding as needed. Therefore, the process is less constrained when producing electrolytes exhibiting high ionic conductivity.

[0056] In particular, in this manufacturing method, in the first step, a surface modifier is applied to the surface of the inorganic solid electrolyte in advance, and then in the subsequent second step, the surface-modified inorganic solid electrolyte, polymer, and alkali metal salt are mixed to composite the inorganic solid electrolyte and the organic electrolyte, thereby ensuring stability against highly active materials such as metallic lithium. The reason for obtaining such results is presumed to be that by applying the surface modifier to the surface of the inorganic solid electrolyte in advance, a sufficient buffer layer is formed on the surface of the inorganic solid electrolyte, and this buffer layer suppresses direct contact between the inorganic solid electrolyte and the active material when an energy storage device is constructed. However, this is merely a hypothesis and does not limit the present invention in any way.

[0057] Furthermore, when obtaining a composite electrolyte by compounding an inorganic solid electrolyte and an organic electrolyte, it is conceivable to use a method in which the inorganic solid electrolyte, polymer, and alkali metal salt are mixed together with a surface modifier, instead of a method in which the inorganic solid electrolyte is surface-modified beforehand. However, according to the inventors' studies, it has become clear that when the method of mixing the inorganic solid electrolyte, polymer, and alkali metal salt together with a surface modifier is used, stability for highly active materials cannot be ensured. This result is thought to be because, in the method of mixing the inorganic solid electrolyte, polymer, and alkali metal salt together with a surface modifier, a sufficient buffer layer is not formed on the surface of the inorganic solid electrolyte, and a redox reaction occurs at the interface due to direct contact between the inorganic solid electrolyte and the active material. For convenience, the inorganic solid electrolyte after treatment with the surface modifier will also be referred to as the "treated inorganic electrolyte" below.

[0058] • Processed inorganic electrolyte As the inorganic electrolyte after processing, the inorganic solid electrolyte obtained by the dispersion medium mixing step and removal step described above can preferably be used. The inorganic solid electrolyte after the dispersion medium mixing step and removal step (i.e., the inorganic electrolyte after processing) may be used as is in the second step, or it may be used in the second step after grinding. The grinding can be carried out as appropriate using known grinders such as ball mills, bead mills, and blenders.

[0059] When mixing the treated inorganic electrolyte, polymer, and alkali metal salt, a particle aggregate (i.e., powder) is preferably used as the treated inorganic electrolyte from the viewpoint of obtaining a composite electrolyte that exhibits high ionic conductivity. The average particle size of the treated inorganic electrolyte is preferably 0.01 μm or more and 20 μm or less in volume-based median diameter when measured in an aqueous medium. From the viewpoint of ease of handling of the treated inorganic electrolyte, the average particle size of the treated inorganic electrolyte is more preferably 0.05 μm or more, even more preferably 0.1 μm or more, and even more preferably 0.2 μm or more in volume-based median diameter. Furthermore, in order to improve the ionic conductivity of the composite electrolyte, the average particle size of the treated inorganic electrolyte is more preferably 15 μm or less, even more preferably 10 μm or less, and even more preferably 5 μm or less in volume-based median diameter.

[0060] In the production of the composite electrolyte, the amount of the treated inorganic electrolyte added is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, even more preferably 35% by mass or more, and even more preferably 40% by mass or more, relative to the total amount of the composite electrolyte, from the viewpoint of ensuring the moldability of the composite electrolyte and obtaining a composite electrolyte that exhibits high ionic conductivity. Furthermore, regarding the upper limit of the amount of the treated inorganic electrolyte added, from the viewpoint of ensuring the flexibility of the composite electrolyte and improving handling, it is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, relative to the total amount of the composite electrolyte.

[0061] • Polymer The polymer only needs to exhibit ionic conductivity in the presence of an alkali metal salt. Therefore, the polymer can be either a linear polymer or a branched polymer, as long as it exhibits ionic conductivity in the presence of an alkali metal salt. A specific example of a branched polymer is a star-shaped polymer having a core portion and three or more branched chains (arm portions) extending from the core portion. It is thought that using such a star-shaped polymer suppresses the crystallization of the polymer and makes it easier for the polymer to move. The polymer may also be a crosslinked polymer or a non-crosslinked polymer. A non-crosslinked polymer is preferable as the polymer because it can make the molecular motion of the polymer more active and facilitate the formation of ionic conduction paths in the composite electrolyte.

[0062] Examples of the main backbone of the polymer include polyether polymers (such as polyalkylene oxides), polyester polymers, and (meth)acrylic polymers. One preferred embodiment of the polymer is a polymer having ester bonds (hereinafter also referred to as "ester bond-containing polymer"). It is thought that the oxygen in the ester bond (oxygen of the carbonyl group and / or oxygen adjacent to the carbonyl group) does not exert as strong a coordinating force on alkali metal ions as ether oxygen. For this reason, ester bond-containing polymers are thought to have less inhibition of the molecular motion of the polymer due to the coordinating force of alkali metal ions, and ion conduction paths can be easily formed in the complex electrolyte.

[0063] As the ester bond-containing polymer, a polymer having the structure represented by the following formula (1) (hereinafter also referred to as "polyester polymer") can be preferably used because it exhibits good ionic conductivity when mixed with an alkali metal salt. [ka] [In formula (1), R represents a hydrogen atom or an alkyl group. X and Y are the same or different, representing a hydrogen atom, a hydroxyl group, or an alkyl group. n represents an integer of 1 or more, and m represents an integer from 0 to 10.]

[0064] In formula (1) above, R is preferably a hydrogen atom or a methyl group, from the viewpoint of the availability of raw materials and the ease of synthesis of polyester polymers. From the viewpoint of the availability of raw materials, m is preferably 0 to 8, more preferably 0 to 6, and preferably 0 to 4.

[0065] The repeating unit in equation (1) above is (-CO-CHR-(CH2) mMonomers used to introduce -O-) into polymers include lactones and lactides. Specific examples of these include lactones such as β-propiolactone, γ-butyrolactone, β-butyrolactone, pivalolactone, δ-valerolactone, and ε-caprolactone. Examples of lactides include glycolide, obtained by the dehydration condensation of two glycolic acid molecules; dilactide, obtained by the dehydration condensation of two lactic acid molecules; and tetramethylglycolide. When the above lactides are used as monomers, one molecule of lactide introduces two repeating units in formula (1) into the polymer.

[0066] In terms of obtaining a composite electrolyte with superior ionic conductivity, it is preferable that the monomer constituting the polyester polymer is at least one selected from the group consisting of γ-butyrolactone, δ-valerolactone, ε-caprolactone, and dilactide.

[0067] In formula (1) above, n can be appropriately set according to the molecular weight of the desired polyester polymer. n 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.

[0068] Furthermore, the polyester polymer may have additional repeating units different from the repeating units in formula (1) above (hereinafter also referred to as "other repeating units"), as long as the effects of the present invention are not impaired. Examples of other repeating units include dioxepanone, ethylene oxalate, dioxanone, γ-nonalactone, γ-decalactone, γ-undecalactone, cyclopentadecanolide, cyclohexedecanolide, and the like. The proportion of other repeating units in the polyester polymer is preferably 5 mol% or less, more preferably 2 mol% or less, even more preferably 0.5 mol% or less, and particularly preferably 0.1 mol% or less, relative to the total repeating units of the polyester polymer, in order to suppress a decrease in the ionic conductivity of the composite electrolyte.

[0069] The terminal structure of the polyester polymer may be a hydroxyl group or carboxyl group derived from the monomer. Alternatively, the terminals of the polyester polymer may be modified by utilizing the hydroxyl group or carboxyl group present at the polymer terminals. By modifying the terminal hydroxyl group or terminal carboxyl group of the polyester polymer, the heat resistance (durability) of the polyester polymer can be improved or its crystallinity can be reduced. When X and Y in formula (1) above are alkyl groups, the alkyl groups are preferably linear or branched alkyl groups having 3 to 20 carbon atoms, from the viewpoint of promoting improved heat resistance and reduced crystallinity of the polyester polymer.

[0070] Here, the polyester polymer represented by formula (1) exhibits ionic conductivity in the presence of alkali metal salts, and in the presence of alkali metal salts, it is in a liquid or near-liquid state. By using such a polyester polymer as a binder in a composite electrolyte of an inorganic solid electrolyte and an organic electrolyte, the gaps between the particles of the inorganic solid electrolyte are filled with a mixture of the polyester polymer and alkali metal salts, thereby firmly binding the particles of the inorganic solid electrolyte together and facilitating the formation of ion conduction paths within the composite electrolyte.

[0071] The method for producing the polyester polymer is not particularly limited, and it can be produced using conventionally known methods as appropriate. In terms of being able to produce the polyester polymer represented by formula (1) above simply and inexpensively, it is preferable to produce the polyester polymer by ring-opening polymerization using at least one selected from the group consisting of lactones and lactides as a monomer.

[0072] In the ring-opening polymerization described above, for example, monomers and, if necessary, solvents are charged into a reactor, and an initiator is added to carry out polymerization, thereby obtaining the desired polyester polymer. The method of charging each raw material, including the monomers, may be a batch-type initial batch charging in which all raw materials are charged at once, a semi-continuous charging in which at least some of the raw materials are continuously supplied into the reactor, or a continuous polymerization method in which all raw materials are continuously supplied and the resulting resin is continuously withdrawn from the reactor at the same time.

[0073] As initiators, monoalcohols or polyhydric alcohols can be preferably used because they allow for easy acquisition of the desired polymer. Among monoalcohols, alkyl alcohols are preferred, and examples include 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, octantriol, 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.

[0074] In the production of polyester polymers, the amount of 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 monomers used for polymerization.

[0075] The above ring-opening polymerization is preferably carried out in the presence of a catalyst from the viewpoint of efficiently carrying out the reaction. As the catalyst, conventionally known acid catalysts, base catalysts, or metal catalysts can be used as appropriate. Specific examples of acid catalysts include sulfonic acid, methanesulfonic acid, trifluoroacetic acid, 10-camphorsulfonic acid, phosphoric acid, phosphate monoesters (methyl phosphate, ethyl phosphate, octyl phosphate, phenyl phosphate, etc.), phosphate diesters (dimethyl phosphate, diethyl phosphate, dibutyl phosphate, diphenyl phosphate, etc.), phosphorous acid, phosphate esters, tin tetrachloride, phosphorus pentafluoride, boron trifluoride complexes, and the like.

[0076] Specific examples of base catalysts 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; and imidazole compounds such as 2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole and 2-ethyl-4-methylimidazole.

[0077] Specific examples of metal catalysts include metal salts of tin, zinc, lead, titanium, aluminum, iron, and zirconium. From the viewpoint of reactivity, tin catalysts are preferred. Examples of tin catalysts include tin(II) 2-ethylhexanoate, tin(II) acetate, tin(IV) acetate, tin(II) chloride, dibutyltin diacetate, dibutyltin dilaurate, dioctyltin diacetate, and tin(II) trifluoromethanesulfonate.

[0078] In the production of polyester polymers, 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 monomers used for polymerization.

[0079] When a solvent is used in the reaction, an organic solvent is preferably used. 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 such that the total amount of monomers used for polymerization is, for example, 10 to 1,500 parts by mass, preferably 20 to 1,000 parts by mass, per 100 parts by mass of the total amount of monomers.

[0080] The polymerization temperature and polymerization time are not particularly limited and can be set as appropriate. From the viewpoint of increasing the reaction rate while suppressing side reactions, the polymerization temperature is preferably in the range of 0°C to 120°C, and preferably in the range of 5°C to 100°C. The polymerization time is preferably 1 to 150 hours, and preferably 5 to 100 hours. The pressure during polymerization can be any pressure that can maintain the polymerization temperature. Furthermore, from the viewpoint of suppressing a decrease in the degree of polymerization, it is preferable to carry out the reaction 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. It is preferable to carry out the polymerization reaction while stirring the reactor.

[0081] By performing ring-opening polymerization of lactones or lactides using a monoalcohol or polyhydric alcohol as an initiator, a polyester polymer having hydroxyl groups at the polymer ends can be obtained. The polyester polymer thus obtained may be mixed with an inorganic solid electrolyte and an alkali metal salt in its original state (i.e., with terminal hydroxyl groups). Alternatively, the terminal hydroxyl groups of the polyester polymer obtained by the above polymerization reaction may be reacted with a compound having a reactive functional group that can react with hydroxyl groups (modifier), thereby introducing a structure derived from the modifier to the ends of the polyester polymer, and the resulting polymer may be mixed with an inorganic solid electrolyte and an alkali metal salt. The reaction between the polyester polymer having terminal hydroxyl groups and the modifier can be carried out, for example, in a suitable solvent and, if necessary, with a catalyst.

[0082] When polyester polymers are produced by solution polymerization, the polyester polymer dissolved in the solvent can be isolated by known desolvation methods such as reprecipitation and drying methods such as heat treatment. Alternatively, polyester polymers may be produced without using a solvent, such as by bulk polymerization.

[0083] The weight-average molecular weight (Mw) of the polymer used in the production of the composite electrolyte 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, even more preferably 10,000 or more, even more preferably 15,000 or more, and particularly preferably 20,000 or more, from the viewpoint of obtaining a composite electrolyte that is high-strength and exhibits high ionic conductivity and good moldability of the composite electrolyte. The upper limit of the Mw of the polymer 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 polymer and flexibility of the composite electrolyte.

[0084] The preferred range for the polymer's Mw can be set by appropriately combining the upper and lower limits of the preferred range for Mw described above. The preferred range for the polymer's Mw is 1,000 to 100,000, more preferably 3,000 to 80,000, and even more preferably 5,000 to 50,000.

[0085] For polymers, the molecular weight distribution (Mw / Mn), expressed as the ratio of Mw to the number-average molecular weight (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, even 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 for polymers is not particularly limited, but is 1.0 or greater. In this specification, Mw and Mn of polymers are standard polystyrene equivalent values ​​obtained using gel permeation chromatography (GPC).

[0086] In the production of the composite electrolyte, the amount of polymer added is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more, per 100 parts by mass of the inorganic solid electrolyte used in the first step of surface modification treatment, from the viewpoint of reducing interfacial resistance and obtaining a composite electrolyte exhibiting high ionic conductivity. Furthermore, regarding the upper limit of the amount of polymer added, from the viewpoint of ensuring the moldability and handling of the composite electrolyte, it is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, and even more preferably 75 parts by mass or less, per 100 parts by mass of the inorganic solid electrolyte used in the first step of surface modification treatment.

[0087] • Alkali metal salts Alkali metal salts are not particularly limited and can be any salt that produces alkali metal ions. Examples of alkali metal salts include lithium salts, sodium salts, potassium salts, and the like.

[0088] Specific examples of alkali metal salts include, for example, Li2CO3, LiBr, LiCl, LiI, LiSCN, LiBF4, LiAsF6, LiClO4, CH3COOLi, CF3COOLi, LiCF3SO3, LiPF6, LiC(CF3SO2)3, and lithium bis(fluorosulfonyl)imide (Li + (FSO2)2N - ), lithium bis(trifluoromethanesulfonyl)imide (Li + (CF3SO2)2N - Examples include lithium salts such as lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide; and salts of the anions of these lithium salts with alkali metals other than lithium (e.g., sodium or potassium). Of these, lithium salts or sodium salts are preferred because they have high ion dissociation properties and can further increase the ionic conductivity of the composite electrolyte of this disclosure. Furthermore, it is preferable that the type of alkali metal ion contained in the inorganic solid electrolyte and the type of alkali metal ion contained in the alkali metal salt are the same.

[0089] In terms of being able to increase the ionic conductivity of the composite electrolyte of this disclosure, it is preferable that the alkali metal salt contained in the composite electrolyte of this disclosure includes an imide-based alkali metal salt. Among these, an imide-based lithium salt is preferred in that it has high ionic dissociation properties, and among the imide-based lithium salts, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide is particularly preferred, lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide is more preferred, and lithium bis(fluorosulfonyl)imide is even more preferred.

[0090] 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.

[0091] 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, and may also be 250°C or lower.

[0092] In the production of a composite electrolyte, the amount of alkali metal salt added is preferably such that the ratio (Mmo / Mal) of the total amount of monomers constituting the polymer to the amount of alkali metal salt (Mal (moles)) is 0.1 to 10, from the viewpoint of obtaining a composite electrolyte that exhibits high ionic conductivity. A ratio (Mmo / Mal) of 0.2 or higher is more preferable, and 0.5 or higher is even more preferable. Furthermore, the upper limit of the ratio (Mmo / Mal) is preferably 9.0 or lower, and even more preferably 8.0 or lower.

[0093] In the second step, the inorganic electrolyte, polymer, and alkali metal salt should be mixed uniformly after processing, and the method of mixing is not particularly limited. When mixing the inorganic electrolyte, polymer, and alkali metal salt after processing, they may be placed in a container and mixed simultaneously. Alternatively, these raw materials may be placed in a container sequentially, and the raw materials may be mixed each time they are placed in the container. The mixing of the inorganic electrolyte, polymer, and alkali metal salt after processing can be carried out using various equipment such as ball mills, planetary ball mills, bead mills, blenders, homogenizers, stamp mills, homomixers, and disper mixers. Furthermore, when manufacturing the composite electrolyte on a small scale, mixing may be done using a mortar and pestle.

[0094] When mixing the inorganic electrolyte, polymer, and alkali metal salt after processing, the mixing may be carried out by dry mixing or wet mixing. Of these, wet mixing is preferred. By employing wet mixing, each component 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.

[0095] Various organic solvents and mixtures thereof can be used as solvents for wet mixing. When a solvent is used when mixing the inorganic electrolyte, polymer, and alkali metal salt after processing, the amount of solvent used can be set appropriately, but from the viewpoint of improving the dispersibility of each component, it may be set to 50 to 2,000 parts by mass per 100 parts by mass of the total amount of components other than the solvent used in the production of the composite electrolyte. The slurry obtained by wet mixing may be cleaned of coarse particles or aggregates using, for example, a sieve. The mixing of the inorganic electrolyte, polymer, and alkali metal salt after processing may be carried out at room temperature, or at low or high temperatures.

[0096] In the production of the composite electrolyte, additional components other than the treated inorganic electrolyte, polymer, and alkali metal salt (hereinafter also referred to as "other components") may be added, as long as they do not impair the effects of the present invention. Examples of other components include dispersing aids, conductive aids, positive electrode active materials, negative electrode active materials, antioxidants, and colorants. The amounts of these components can be set appropriately as long as they do not impair the effects of the present invention. The amount of other components may be 5 parts by mass or less, or 2 parts by mass or less, per 100 parts by mass of the total amount of the treated inorganic electrolyte, polymer, and alkali metal salt.

[0097] When a molded body is obtained by molding a mixture containing an inorganic electrolyte, a polymer, and an alkali metal salt after processing, 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, casting, mold casting, and tape molding. The shape of the molded body is not particularly limited and can be appropriately set according to the application and shape of the energy storage device. The shape of the molded body can be, for example, rectangular or circular.

[0098] If the mixture obtained in the second step contains a solvent, it is preferable to remove the solvent from the mixture. There are no particular restrictions on the method of removing the solvent, and known desolvation methods can be appropriately employed. Specific examples of desolvation methods include the various treatments described in the removal step of the first step.

[0099] A composite electrolyte can be obtained by a manufacturing method including the first and second steps described above. The composite electrolyte obtained in this way exhibits excellent stability to highly active materials and high ionic conductivity. Therefore, by using the composite electrolyte obtained by the manufacturing method of the present invention as an electrolyte material for an energy storage device, an energy storage device with excellent stability to highly active materials and high ionic conductivity can be obtained.

[0100] Energy storage devices The energy storage device in the present invention (hereinafter also referred to as "the device") comprises a composite electrolyte obtained by the manufacturing method of the present invention described above. Examples of the device include secondary batteries and capacitors. When the device is a secondary battery, one embodiment is an all-solid-state battery, and a lithium-ion secondary battery is preferred in that it has excellent ion conductivity.

[0101] A fully solid-state lithium-ion secondary battery, which is one embodiment of this device, will be described. The lithium-ion secondary battery is a laminate comprising an electrode layer consisting of a positive electrode layer and a negative electrode layer, and a solid electrolyte layer, wherein the solid electrolyte layer is arranged between the positive electrode layer and the negative electrode layer so as to be in contact with the electrode layer. The materials constituting the positive electrode layer and the negative electrode layer are not particularly limited and can be appropriately selected and used 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.

[0102] As the positive electrode current collector, metal foil such as aluminum or stainless steel can be used. The positive electrode mixture layer is a layer containing the positive electrode active material and is located on the surface of the positive electrode current collector facing the solid electrolyte layer. Examples of positive electrode active material include metal oxides having a layered rock salt type, spinel type, or olivine type crystal structure. The negative electrode layer may consist of a negative electrode current collector and a negative electrode mixture layer. As the negative electrode current collector, metal foil such as copper foil or lithium foil can be used. The negative electrode mixture layer is a layer containing the negative electrode active material and is located on the surface of the negative electrode current collector facing the solid electrolyte layer. Examples of negative electrode active material include metallic lithium, graphite, and Li4Ti5O 12 Examples include silicon monoxide and silicon. When a highly active substance such as metallic lithium is used as the negative electrode active material, it is preferable because it can improve the energy density of the battery and increase the battery capacity. Furthermore, in this device, since the solid electrolyte layer is formed by the composite electrolyte obtained by this manufacturing method, even when a highly active material is used in the manufacture of the energy storage device, degradation due to oxidation-reduction reactions of the inorganic solid electrolyte can be suppressed, resulting in excellent performance stability.

[0103] In the lithium-ion secondary battery of this disclosure, the solid electrolyte layer is formed of a composite electrolyte containing a processed inorganic electrolyte, a polymer, and an alkali metal salt. The thickness of the solid electrolyte layer is not particularly limited and can be set appropriately depending on the application of the secondary battery. For example, the thickness of the solid electrolyte layer is 5 to 5,000 μm. From the viewpoint of miniaturizing, reducing weight, and increasing capacity of the 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.

[0104] The method for manufacturing 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 comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer may be manufactured by sandwiching the solid electrolyte layer, which is formed from the composite electrolyte obtained by this manufacturing method, between a positive electrode layer and a negative electrode layer, and preferably by applying pressure for bonding. Alternatively, a laminate comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer may be manufactured by placing the unformed composite electrolyte between a positive electrode layer and a negative electrode layer in a container, and preferably by applying pressure for bonding to the container. The laminate comprising a positive electrode layer, a solid electrolyte layer, and a negative electrode layer is usually housed in a case and used as a secondary battery.

[0105] This device is not limited to the above configuration in which lithium ions are the ion carriers, but may also be a secondary battery that uses other ions, such as sodium ions, as carriers. Furthermore, this device may be a capacitor. One embodiment of a capacitor includes a positive electrode layer, a negative electrode layer, and a solid electrolyte, with the solid electrolyte positioned between the positive and negative electrode layers such that the solid electrolyte is in contact with the electrode.

[0106] This device can be applied to a variety of uses. Specifically, it can be used as a power source in various mobile devices such as mobile phones, personal computers, smartphones, game consoles, and wearable devices; various mobile devices such as electric vehicles, hybrid vehicles, robots, and drones; and various electrical and electronic devices such as digital cameras, video cameras, music players, power tools, and home appliances. [Examples]

[0107] The present invention will be described in detail below based on the following 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.

[0108] [Molecular weight measurement] The molecular weight of the polymer was determined using gel permeation chromatography (hereinafter also referred to as "GPC") following the procedure below. A sample solution was obtained by dissolving 4 mg of polymer in 4 mL of tetrahydrofuran (hereinafter also referred to as "THF"). The obtained sample solution was filtered through a polytetrafluoroethylene (hereinafter also referred to as "PTFE") membrane filter, and 100 μL was injected into a GPC instrument to measure the weight-average molecular weight and number-average molecular weight (hereinafter also referred to as "Mw" and "Mn", respectively). Columns: 4 x TSKgel SuperMultiporeHZ-M (manufactured by Tosoh Corporation) Temperature: 40℃ Eluent:THF Detector: Differential refractometer Flow rate: 600μL / min Reference material: Polystyrene

[0109] 1. Synthesis of polymers [Synthesis Example 1] 100 parts ε-caprolactone, 0.065 parts 1-butanol, 0.19 parts 2-tin(II) ethylhexanoate, and a stirring bar were placed in a test tube and stirred at 95°C for 96 hours under dry air (dew point below -60°C). The ε-caprolactone and 1-butanol were dehydrated using molecular sieves. The polymerization solution was poured into a large amount of isopropyl alcohol to precipitate the polymer. The precipitate was recovered by vacuum filtration and vacuum drying to obtain polymer P. The molecular weight of polymer P was measured using GPC and found to be Mn 32,800 and Mw 57,700.

[0110] 2. Manufacturing and evaluation of composite electrolytes [Example 1] (1) Manufacturing of the composite electrolyte CPE-1 (composite formation method A) LICGC PW-01 (main crystal phase Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 100 parts of (Li-substituted NASICON type), D50 0.4 μm) [Ohara Corporation] (hereinafter also referred to as "LICGC") and 10 parts of 3-aminopropyltriethoxysilane (APTS) [Tokyo Chemical Industries Co., Ltd.] were added to 1,000 parts of tetrahydrofuran (THF) and stirred at 70°C for 24 hours. This mixture was cast into a polytetrafluoroethylene (PTFE) container and the THF was removed by distillation at 80°C and atmospheric pressure for 24 hours (Step 1). The residue was ground using 5 mm diameter tungsten carbide balls in a planetary ball mill (Fritsch Japan Premium Line P-7) at room temperature and 400 rpm for 10 hours, and then passed through a 500-mesh sieve to obtain precursor composition A1. Next, 800 parts of THF were added to precursor composition A1 and stirred for 10 minutes at room temperature and 2,000 rpm using an Awatori Neritaro (Sinky Co., Ltd., ARE-310). Subsequently, 61 parts of polymer P and 49 parts of lithium bis(fluorosulfonyl)imide [Nippon Shokubai Co., Ltd.] (hereinafter also referred to as "LiFSI") were added and stirred for 30 minutes at room temperature and 2,000 rpm using an Awatori Neritaro (second step). The stirred mixture was cast into a PTFE container and dried at 40°C for 24 hours to obtain the composite electrolyte CPE-1.

[0111] (2) Stability evaluation for metallic lithium The stability of the composite electrolyte CPE-1 and metallic lithium was evaluated by constant current cycling tests on a metallic lithium symmetric cell. All of the following procedures were performed in a glove box with a dew point of -80°C or lower. The composite electrolyte CPE-1 was cold-pressed under 340 MPa for 2 minutes, then punched out to form 10 mm diameter pellets. Metal lithium foil, shaped into 8 mm diameter discs, was placed on both sides of the pellets, and this was sandwiched between two stainless steel plates to create a measurement cell. The measurement cell was connected to a potentiometer / galvanostat (Biologic VMP-300) and measured at 0.312 mA / cm². 2 After applying a current for one hour, the direction of the current was reversed and this process was repeated. The absolute value of the overvoltage generated by the initial applied current and the absolute value of the overvoltage 15 hours after the start of measurement were read and used as indicators for evaluating stability. The smaller the absolute value of the overvoltage and the smaller the change in overvoltage over time, the higher the stability of the composite electrolyte relative to metallic lithium.

[0112] [Examples 2-4, Comparative Examples 2, 3] Except for changing the types and quantities of raw materials as shown in Table 1, the same procedure as in Example 1 was performed to obtain composite electrolytes CPE-2 to CPE-4, CPE-6, and CPE-7. Furthermore, the stability of composite electrolytes CPE-2 to CPE-4, CPE-6, and CPE-7 against metallic lithium was evaluated in the same manner as in Example 1.

[0113] [Comparative example 1] (Combining method B) 100 parts of LICGC and 20 parts of APTS were added to 800 parts of THF and stirred for 10 minutes at room temperature and 2,000 rpm using a foam stirring machine. Subsequently, 67 parts of polymer P and 53 parts of LiFSI were added and stirred for 30 minutes at room temperature and 2,000 rpm using a foam stirring machine. The resulting mixture was cast into a PTFE container and dried at 40°C for 12 hours to obtain the composite electrolyte CPE-5. The stability of the composite electrolyte CPE-5 against metallic lithium was evaluated in the same manner as in Example 1.

[0114] [Table 1]

[0115] The details of the compounds used in Table 1 are shown below. • Polymer P: Polymer produced in Synthesis Example 1 APTS: 3-aminopropyltriethoxysilane [manufactured by Tokyo Chemical Industry Co., Ltd.] • TMSPA: 3-(trimethoxysilyl)propyl acrylate [manufactured by Tokyo Chemical Industry Co., Ltd.] • VTMS: Vinyltrimethoxysilane [Manufactured by Tokyo Chemical Industry Co., Ltd.] ·LICGC:LICGC PW-01 (main crystal phase Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (Li-substituted NASICON type, D50 0.4μm) [Manufactured by Ohara Corporation] • LiFSI: Lithium bis(fluorosulfonyl)imide [manufactured by Nippon Shokubai Co., Ltd.]

[0116] 3. Evaluation Results Compared to the case where an inorganic solid electrolyte, surface modifier, polymer, and alkali metal salt were mixed and compounded at once (Comparative Example 1: Compounding Method B), the compound electrolyte obtained by the method in which the inorganic solid electrolyte was pre-treated with a surface modifier and then mixed with the polymer and alkali metal salt after treatment with the surface modifier (Composite Method A) showed improved stability against metallic lithium (Examples 1-4). This is thought to be due to the effective formation of a buffer layer by the surface modifier. Among these, the compound electrolyte of Example 1, in which the amount of surface modifier used was 10 parts by mass per 100 parts by mass of inorganic solid electrolyte, showed superior stability against metallic lithium and yielded particularly favorable results.

[0117] In contrast, when the amount of surface modifier used was 40 parts by mass per 100 parts by mass of inorganic solid electrolyte (Comparative Example 2), the overvoltage was so large that it reached the upper limit of the device's measurement limit, making measurement impossible. Furthermore, when alumina was used instead of the inorganic solid electrolyte (Comparative Example 3), ion conduction within the composite electrolyte was inhibited, making it difficult to evaluate stability.

[0118] From the above results, it has become clear that the manufacturing method of the present invention, which includes the first and second steps described above, and in which the amount of surface modifier used in the first step is 30 parts by mass or less per 100 parts by mass of inorganic solid electrolyte, can be obtained as a composite electrolyte with excellent stability for highly active materials.

Claims

1. The first step involves treating an inorganic solid electrolyte with a surface modifier, A second step involves mixing the inorganic solid electrolyte after treatment with the surface modifier, a polymer, and an alkali metal salt. Includes, A method for producing a composite electrolyte, wherein the amount of the surface modifier used in the first step is 30 parts by mass or less per 100 parts by mass of the inorganic solid electrolyte.

2. The first step is, A step of mixing the inorganic solid electrolyte, the surface modifier, and the dispersion medium to obtain a mixture, A step of removing the dispersion medium from the mixture, A method for producing a composite electrolyte according to claim 1, including the method described in claim 1.

3. A method for producing a composite electrolyte according to claim 1 or 2, wherein the inorganic solid electrolyte includes an oxide having a NASICON-type crystal structure.

4. The inorganic solid electrolyte is, General formula: Li １＋２ａ＋ｂ+ｃ－ｄ M1 ａ M2 ｂ M3 ２－ａ－ｂ Si ｃ W ｄ P ３－ｃ－ｄ O １２ A method for producing a composite electrolyte according to claim 1 or 2, comprising a solid electrolyte represented by (wherein M1 contains an element that forms a divalent cation, M2 contains an element that forms a trivalent cation, and M3 contains at least one element of Ti and Zr, satisfying a≧0, b>0, c>0, and d≧0).

5. The method for producing a composite electrolyte according to claim 1 or 2, wherein the surface modifier is a silane coupling agent.

6. A method for producing a composite electrolyte according to claim 1 or 2, wherein the polymer has a structure represented by the following formula (1). 【Chemistry 1】 [In formula (1), R represents a hydrogen atom or an alkyl group. X and Y are the same or different, representing a hydrogen atom, a hydroxyl group, or an alkyl group. n represents an integer of 1 or more, and m represents an integer from 0 to 10.]

7. A method for producing a composite electrolyte according to claim 1 or 2, wherein the weight-average molecular weight of the polymer is 1,000 to 1,000,000.

8. A method for producing a composite electrolyte according to claim 1 or 2, wherein the alkali metal salt comprises lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide.

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