Composite electrolyte and method for manufacturing the same, and power storage device

Abstract

A composite electrolyte containing: an inorganic solid electrolyte; a polymer; and an alkali metal salt, the polymer having a structure represented by formula (1), the composite electrolyte containing 5 mol% or more and 250 mol% or less of the alkali metal salt relative to the total amount of ester groups in the polymer. In formula (1), R represents a hydrogen atom or an alkyl group. X and Y are 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.

Description

Technical Field

[0001] [Cross-reference to related applications]

[0002] This application claims priority based on Japanese Patent Application No. 2024-27699, filed on February 27, 2024, the entirety of which is incorporated herein by reference.

[0003] This disclosure relates to composite electrolytes and methods for manufacturing them, as well as energy storage devices. Background Technology

[0004] As energy storage devices, various rechargeable batteries, such as nickel-metal hydride batteries and lithium-ion batteries, as well as double-layer capacitors, have been put into practical use. Among them, lithium-ion batteries are widely used due to their high energy density and high battery capacity. In addition, in recent years, sodium-ion batteries, potassium-ion batteries, and magnesium-ion batteries, which use lithium as a substitute for lithium, a rare metal, have attracted attention as alternatives to lithium-ion batteries.

[0005] Lithium-ion secondary batteries, widely used as energy storage devices, have a negative electrode, a positive electrode, and an electrolyte. They are charged and discharged by moving lithium ions between the two electrodes via the electrolyte. Traditionally, non-aqueous electrolytes have been primarily used. However, because non-aqueous electrolytes contain flammable organic solvents, there are concerns about electrolyte leakage and internal short circuits caused by overcharging or over-discharging.

[0006] In response, the use of inorganic materials to replace non-aqueous electrolytes and non-flammable inorganic solid electrolytes has been proposed. However, while inorganic solid electrolytes offer excellent safety, they are manufactured by molding powder, which can easily lead to gaps forming at the interfaces with the positive and negative electrodes or between the particles of the inorganic solid electrolyte material, resulting in higher interfacial resistance.

[0007] Therefore, in recent years, in order to balance improved safety and reduced interfacial resistance, composite electrolytes containing inorganic solid electrolytes and non-aqueous electrolytes have been proposed as electrolytes used in lithium-ion secondary batteries (for example, see Patent Document 1). Patent Document 1 discloses that a composite electrolyte is obtained by sintering an inorganic oxide, which is an inorganic solid electrolyte, to produce a sintered body having a dense portion and a porous portion; the sintered body is then immersed in an electrolyte such as an organic electrolyte or an ionic liquid and a vacuum is drawn, thereby filling the porous portion of the sintered body with the electrolyte.

[0008] Furthermore, Patent Document 2 discloses a lithium-ion conductive composite material containing lithium-ion conductive particles as an inorganic solid electrolyte, polymers such as polyethylene oxide, and alkali metal salts. Patent Document 2 describes a reduction in the interfacial resistance of this composite material regarding lithium-ion conductivity between the polymer and the particles.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2017-111890

[0012] Patent Document 2: Japanese Patent Publication No. 2019-519885 Summary of the Invention

[0013] The technical problem that the invention aims to solve

[0014] In the manufacture of inorganic solid electrolytes, such as oxide-based solid electrolytes, to achieve high ionic conductivity, the powder is typically pressed into shape and then sintered at high temperatures (e.g., exceeding 1000°C) to improve the bonding between particles and between the electrode and the electrolyte, thereby reducing interfacial resistance. However, sintering is an energy-intensive process, necessitating the introduction of large-area sintering equipment for industrial application. Therefore, as mentioned in Patent Document 1, there are concerns that when the inorganic solid electrolyte used to fill the electrolyte is a sintered body, the manufacture of composite electrolytes will require a large amount of energy, making practical application and industrialization difficult. Sulfide-based solid electrolytes also typically require high-pressure (e.g., pressure exceeding 10 MPa) pressing, resulting in significant process constraints. Furthermore, in the manufacture of energy storage devices, good formability of the solid electrolyte layer is also required.

[0015] The inventors studied the lithium-ion conductive composite material of Patent Document 2 and found that the reduction in interfacial resistance was insufficient and there was room for further improvement in ion conductivity.

[0016] This disclosure was made in view of the following circumstances, one object of which is to provide a composite electrolyte that, in the case of a composite electrolyte of an inorganic solid electrolyte and an organic electrolyte, exhibits high ionic conductivity and good formability even without sintering during the manufacture of the composite electrolyte.

[0017] Technical solutions for solving technical problems

[0018] In order to solve the above-mentioned problems, the inventors conducted in-depth research and discovered that, in composite electrolytes of inorganic solid electrolytes and organic electrolytes, by using a specific substance as a polymer, a composite electrolyte exhibiting good ion conductivity can be obtained. Specifically, according to this disclosure, the following composite electrolyte, its manufacturing method, and energy storage device are provided.

[0019] [1] A composite electrolyte comprising: an inorganic solid electrolyte; a polymer; and an alkali metal salt, said polymer having the structure shown in formula (1) below, wherein the composite electrolyte contains 5 mol% or more and 250 mol% or less of said alkali metal salt relative to the total amount of ester groups in said polymer.

[0020] [Chemistry 1]

[0021]

[0022] [In formula (1), R represents a hydrogen atom or an alkyl group. X and Y may be the same or different, representing a hydrogen atom, a hydroxyl group, or an alkyl group. n represents an integer greater than or equal to 1, and m represents an integer from 0 to 10.]

[0023] [2] According to the composite electrolyte of [1], wherein the inorganic solid electrolyte comprises an oxide having a NASICON-type crystal structure.

[0024] [3] The composite electrolyte according to [1] or [2], wherein the inorganic solid electrolyte is granular.

[0025] [4] The composite electrolyte according to [3], wherein the composite electrolyte is a non-sintered body of the mixture of the inorganic solid electrolyte, the polymer and the alkali metal salt.

[0026] [5] The composite electrolyte according to any one of [1] to [4], wherein the inorganic solid electrolyte comprises 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 The solid electrolyte shown (where M1 contains an element that can be a divalent cation, M2 contains an element that can be a trivalent cation, and M3 contains at least one element from Ti and Zr, satisfying a≥0, b>0, c>0 and d≥0).

[0027] [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 95% by mass or less.

[0028] [7] The composite electrolyte according to any one of [1] to [6], wherein the alkali metal salt comprises lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide.

[0029] [8] A method for manufacturing a composite electrolyte, which is the method for manufacturing a composite electrolyte according to any one of [1] to [7], the method for manufacturing a composite electrolyte comprising a step of mixing the granular inorganic solid electrolyte, the polymer and the alkali metal salt.

[0030] [9] An energy storage device comprising any one of [1] to [7] a composite electrolyte.

[0031] Invention Effects

[0032] According to this disclosure, even without a sintering process during the manufacture of the composite electrolyte, a composite electrolyte exhibiting high ionic conductivity and good formability can be obtained. Furthermore, by using the composite electrolyte of this disclosure as the electrolyte in energy storage devices such as secondary batteries and capacitors, energy storage devices that balance the safety guarantees provided by the solidification of the electrolyte with high ionic conductivity can be obtained. Attached Figure Description

[0033] Figure 1 This is a simplified diagram of the mold used in the preparation of the sample particles for Comparative Example 3. Detailed Implementation

[0034] The following provides a detailed description of the composite electrolyte and energy storage device disclosed herein.

[0035] Complex Electrolytes

[0036] The composite electrolyte disclosed herein comprises: an inorganic solid electrolyte; a polymer; and an alkali metal salt. The components contained in the composite electrolyte of this disclosure are described in detail below. It should be noted that, unless otherwise specified, each component may be contained individually or in combination with two or more components.

[0037] Inorganic solid electrolytes

[0038] The inorganic solid electrolyte included in the composite electrolyte of this disclosure is not particularly limited as long as it is an inorganic solid exhibiting ion conductivity. For example, at least one of oxide-based solid electrolytes, sulfide-based solid electrolytes, and chloride-based solid electrolytes can be used. From the perspective of exhibiting high ion conductivity, oxide-based solid electrolytes or sulfide-based solid electrolytes are preferred, and from the perspective of higher safety under atmospheric conditions, oxide-based solid electrolytes are more preferred.

[0039] There are no particular limitations on the crystal structure of inorganic solid electrolytes. Examples of crystal structures that can be considered as inorganic solid electrolytes include the NASICON type, LISICON type, perovskite type, and garnet type.

[0040] As a specific example, Li can be cited as a solid electrolyte with a NASICON-type structure. 1+x Al x Ti 2-x (PO4)3 (x≥0, also known as "LTP" or "LATP"), Li 1+x Al x Ge 2-x (PO4)3 (x≥0, also known as "LGP" or "LAGP"), LiZr2(PO4)3 (also known as "LZP"), and Na3Zr2Si2PO as NASICON 12 (Also known as "NZSP"), oxides obtained by replacing a portion of the elements constituting these compounds with various elements (such as B, Na, Al, Si, Ca, Ga, Ge, Sc, Fe, Sr, In, Ti, Hf, Sn, V, Nb, Ta, Sb, Bi, W and lanthanides, etc.).

[0041] As a solid electrolyte with a LISICON-type structure, examples include Li 14 ZnGe4O 16 Oxides obtained by replacing a portion of the elements constituting the compound with the aforementioned elements.

[0042] As a solid electrolyte with a perovskite-type structure, Li can be cited as an example. 0.35 La 0.55 TiO3, oxides obtained by replacing some of the elements constituting the compound with the aforementioned elements, etc.

[0043] As a solid electrolyte with a garnet-type structure, Li7La3Zr2O can be cited as an example. 12 and Li5La3Nb2O 12 Oxides obtained by replacing some of the elements constituting these compounds with the aforementioned elements.

[0044] One aspect of the composite electrolyte disclosed herein 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 comprises a polymer and an alkali metal salt. The NASICON-type crystal structure differs from layered structures, providing a wide three-dimensional space for the movement of alkali metal ions, and zirconium (Zr) is stable even at high voltages, thus making it useful as a solid electrolyte for high operating voltages. In the composite electrolyte of this disclosure, an oxide having a NASICON-type crystal structure is preferably used as the inorganic solid electrolyte. It should be noted that the crystal structure of the solid electrolyte can be determined by the diffraction pattern obtained by powder X-ray diffraction.

[0045] When using an oxide having a NASICON-type crystal structure as an inorganic solid electrolyte contained in a composite electrolyte, the oxide shown below (x1) is a preferred example of such an oxide.

[0046] Oxide (x1): 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 The solid electrolyte shown (where M1 contains an element that can be a divalent cation, M2 contains an element that can be a trivalent cation, and M3 contains at least one element from Ti and Zr, satisfying a≥0, b>0, c>0 and d≥0)

[0047] Regarding oxides (x1)

[0048] The oxide (x1) is a solid electrolyte formed by replacing at least a portion of Zr or Ti with M2 (containing elements that can become trivalent cations) or M1 (containing elements that can become divalent cations) in an oxide with LiZr2(PO4)3 or LiTi2(PO4)3 as the basic framework, and replacing a portion of P with Si or W in any way.

[0049] In oxides (x1), M1 can be represented by elements from Group 2, Group 12, transition elements (groups 3 to 11) that can become divalent cations, Sn, Pd, etc.

[0050] Examples of M2 include elements from Group 3, Group 13, transition elements (Groups 3-11) that can become trivalent cations, Sb, Bi, and Fe. Among Group 13 elements, Al, B (boron), or In are preferred.

[0051] M3 only needs to contain at least one element from Ti and Zr. That is, M3 can be Ti, Zr, or further contain elements other than Ti and Zr that can be tetravalent cations. Examples of elements other than Ti and Zr that can be tetravalent cations include Group 14 elements, transition elements (Groups 3-11) that can be tetravalent cations, and Te. Among Group 14 elements, Si is preferred.

[0052] In the general formula for oxide (x1), a, b, c, and d are not particularly restricted as long as a≥0, b>0, c>0, and d≥0. For example, in the case of a=0, b>0, c>0, and d=0, oxide (x1) is derived from "Li 1+b+c M2 b M3 2-b Si c P 3-c O 12 "express.

[0053] Regarding a, b, c, and d in the general formula for oxide (x1), more specifically, a is, for example, 0.5 or less, and can be 0.4 or less. From the viewpoint of minimizing the formation of impurity phases and thereby obtaining an inorganic solid electrolyte exhibiting high ionic conductivity, it is preferable that a ≤ 0.3, more preferably that a ≤ 0.15, and even more preferably that a ≤ 0.1. Furthermore, when a > 0, regarding the lower limit of a, it is preferable that a ≥ 0.01, and more preferably that a ≥ 0.03.

[0054] For example, b can be 2.0 or less, or even 1.9 or less. From the perspective of preferentially acting on the formation of the α phase, thereby obtaining an inorganic solid electrolyte with higher ionic conductivity, it is preferable that b ≤ 1.9, and more preferably that b ≤ 1.85. Furthermore, regarding the lower limit of b, it is preferable that b ≥ 0.01, and more preferably that b ≥ 0.02.

[0055] c is, for example, 1.8 or less, or 1.5 or less. From the perspective of obtaining inorganic solid electrolytes exhibiting higher ionic conductivity, it is preferable that c ≤ 1.2, more preferably that c ≤ 1.0, and even more preferably that c ≤ 0.95. Regarding the lower limit of c, it is preferable that c ≥ 0.01, and more preferably that c ≥ 0.03.

[0056] For example, d can be 0.5 or less, or even 0.3 or less. From the viewpoint of not easily forming impurity phases and thus obtaining an inorganic solid electrolyte exhibiting high ionic conductivity, it is preferable that d ≤ 0.2, and more preferably that d ≤ 0.1. In addition, when d > 0, regarding the lower limit of d, it is preferable that d ≥ 0.01, and more preferably that d ≥ 0.02.

[0057] It should be noted that zirconium phosphate oxides with a NASICON-type crystal structure can take on four phases: α, α′, β, and β′. Among them, the α phase has an isotropic crystal structure, thus exhibiting the highest Li-ion conductivity.

[0058] In the above general formula representing oxide (x1), the stoichiometry of O is set to 12. However, as long as the overall electroneutrality of the oxide is maintained, the stoichiometry of O does not have to be strictly 12. That is, the O in oxide (x1) can be a value less than 12 or a value greater than 12, as long as the overall electroneutrality of oxide (x1) is maintained. Regarding oxide (x1), for example, for 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 (where 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 as the general formula of oxide (x1),) and are also included in oxide (x1) as long as the electroneutrality of oxide (x1) as a whole is maintained.

[0059] There is no particular limitation on the method of manufacturing oxide (x1). Oxide (x1) can be manufactured, for example, by weighing and mixing raw materials in a manner that satisfies the stoichiometric ratio of the composition shown in the above general formula (mixing process), and then firing the resulting mixture (firing process).

[0060] As a raw material for oxide (x1), the following supply components can be used: Li supply component, M1 supply component, M2 supply component, M3 supply component, Si supply component, W supply component, and P supply component, which correspond to the elements used to obtain the target oxide (x1). For example, in the case of obtaining an oxide (x1) with a=0, b>0, c>0, and d=0, the following supply components are used as raw materials: Li supply component, M2 supply component, M3 supply component, Si supply component, and P supply component.

[0061] As the Li, M1, M2, M3, Si, W, and P supply components for obtaining the oxide (x1), for example, carbonates, bicarbonates, sulfates, sulfites, nitrates, nitrites, phosphates, acetates, citrates, ammonium salts, oxides, hydroxides, chlorides, sulfides, etc., of these metal elements can be used. It should be noted that these supply components can also be compounds containing two or more elements selected from Li, M1, M2, M3, Si, W, and P. When the oxide (x1) contains Zr, zirconium phosphate compounds are preferably used as the P supply component, with layered zirconium phosphate being the most preferred.

[0062] In the manufacture of oxide (x1), the raw materials can be mixed by dry mixing or by wet mixing using a liquid. By using wet mixing, the density of the calcined inorganic solid electrolyte can be increased compared to dry mixing. Furthermore, the ionic conductivity of the resulting inorganic solid electrolyte can also be relatively improved. Water, various organic solvents, and mixtures thereof can be appropriately used as the liquid in wet mixing.

[0063] In the firing process, firing can be performed without shaping the mixture obtained in the mixing process, or it can be performed after shaping. The firing temperature is not limited; for example, it can be set to 900°C or higher, preferably 1000°C or higher, more preferably 1150°C or higher, and even more preferably 1200°C or higher. Regarding the upper limit of the firing temperature, for example, it can be set to 1500°C or lower, preferably 1400°C or lower, and more preferably 1350°C or lower. During firing, the temperature can also be gradually increased from a temperature lower than the firing temperature, ultimately maintaining the required firing temperature.

[0064] It should be noted that oxide (x1) exhibits high Li-ion conductivity. Therefore, oxide (x1) is suitable as a material for composite electrolytes used in the manufacture of energy storage devices with lithium-ion charge carriers.

[0065] The inorganic solid electrolyte obtained through the calcination process is preferably pulverized into granules using any method before being used in the manufacture of composite electrolytes. Pulverization of the inorganic solid electrolyte can be performed using, for example, ball mills, bead mills, mixers, or other pulverizers. Alternatively, granules formed by granulating powdered inorganic solid electrolytes can be used as granular inorganic solid electrolytes to manufacture composite electrolytes.

[0066] For the average particle size of the inorganic solid electrolyte used in the manufacture of the composite electrolyte, the particle size measured in an aqueous medium, in terms of volume median particle size, is preferably 0.01 μm or more and 20 μm or less. When the average particle size of the inorganic solid electrolyte is within the above range, a composite electrolyte with better processability and high ionic conductivity can be obtained. From the viewpoint of processability, the average particle size of the inorganic solid electrolyte, in terms of volume median particle size, is more preferably 0.05 μm or more, further preferably 0.1 μm or more, and even more preferably 0.2 μm or more. In addition, from the viewpoint of making the ionic conductivity of the composite electrolyte even better, the average particle size of the inorganic solid electrolyte, in terms of volume median particle size, is more preferably 15 μm or less, further preferably 10 μm or less, and even more preferably 5 μm or less. It should be noted that the average particle size of the inorganic solid electrolyte is a value measured based on laser diffraction / scattering particle size distribution.

[0067] From the viewpoint of ensuring the formability of the composite electrolyte and obtaining a composite electrolyte exhibiting high ion conductivity, the content of inorganic solid electrolyte in the composite electrolyte is preferably 20% by mass or more, more preferably 25% by mass or more, further 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. Furthermore, regarding the upper limit of the inorganic solid electrolyte content, from the viewpoint of ensuring the flexibility of the composite electrolyte and thus good processability, 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.

[0068] <Polymer>

[0069] The composite electrolyte disclosed herein contains a polymer (hereinafter also referred to as "polyester polymer") having the structure shown in formula (1). The polyester polymer exhibits ionic conductivity by mixing with an alkali metal salt.

[0070] [Chemistry 2]

[0071]

[0072] [In formula (1), R represents a hydrogen atom or an alkyl group. X and Y may be the same or different, representing a hydrogen atom, a hydroxyl group, or an alkyl group. n represents an integer greater than or equal to 1, and m represents an integer from 0 to 10.]

[0073] In the above formula (1), from the viewpoint of the ease of obtaining raw materials and the ease of synthesizing polyester polymers, R is preferably a hydrogen atom or a methyl group.

[0074] From the viewpoint of ease of obtaining raw materials, m is preferably 0 to 8, more preferably 0 to 6, and most preferably 0 to 4.

[0075] As a repeating unit (-CO-CHR-(CH2)) in the above formula (1), m Monomers introduced into the polymer (-O-) can be categorized as lactones and lactides. Specific examples of lactones include β-propiolactone, γ-butyrolactone, β-butyrolactone, tervalactone, δ-valactone, and ε-caprolactone. Examples of lactides include glycolide formed by the dehydration condensation of 2 molecules of glycolic acid, di-propionide formed by the dehydration condensation of 2 molecules of lactic acid, and tetramethylglycolic acid. It should be noted that when using the above-mentioned lactides as monomers, the two repeating units in formula (1) above are introduced into the polymer through one lactide molecule.

[0076] From the viewpoint of obtaining a composite electrolyte with better ion conductivity, the monomer constituting the polyester polymer is preferably selected from at least one of γ-butyrolactone, δ-valerolactone, ε-caprolactone and dilactide.

[0077] In the above formula (1), n ​​can be appropriately set according to the desired molecular weight of the polyester polymer. For example, n is 10 to 1500, preferably 20 to 1200, more preferably 30 to 1000, and even more preferably 30 to 800.

[0078] It should be noted that the polyester polymer may further have repeating units different from the repeating units in formula (1) above (hereinafter also referred to as "other repeating units") without impairing the effects of the present invention. Examples of other repeating units include dioxepanone, vinyl oxalate, p-dioxanone, γ-nonanolide, γ-decanolide, γ-undecanolide, cyclopentadecanolide, cyclohexadecanolide, etc. In order to suppress the decrease in ionic conductivity of the composite electrolyte, the proportion of other repeating units in the polyester polymer is preferably 5 mol% or less, more preferably 2 mol% or less, more preferably 0.5 mol% or less, and particularly preferably 0.1 mol% or less, relative to all repeating units of the polyester polymer.

[0079] The morphology of the polymer chains in polyester polymers is not particularly limited; they can be linear or branched. When polyester polymers are branched, considering the suppression of crystallization and the ease of molecular movement, star-shaped polymers with a core and three or more branches (arms) extending from the core are preferred.

[0080] The terminal structure of polyester polymers can be hydroxyl or carboxyl groups derived from monomers. Alternatively, the terminals of polyester polymers can be modified using hydroxyl or carboxyl groups present at the polymer terminals. By modifying the terminal hydroxyl or carboxyl groups of polyester polymers, the heat resistance (durability) of the polyester polymers can be improved, or the crystallinity of the polyester polymers can be reduced. When X and Y in the above formula (1) are alkyl groups, from the viewpoint of improving the heat resistance of polyester polymers and promoting the reduction of crystallinity, the alkyl group is preferably a straight-chain or branched alkyl group with 3 to 20 carbon atoms.

[0081] There are no particular limitations on the manufacturing method of polyester polymers, and conventionally known methods can be used appropriately. From the viewpoint of being able to manufacture polyester polymers of the above formula (1) easily and cheaply, it is preferable to manufacture polyester polymers by using ring-opening polymerization of at least one monomer selected from the group consisting of lactones and lactides.

[0082] In the aforementioned ring-opening polymerization, for example, monomers and solvents as needed are added to a reactor, and an initiator is added to carry out polymerization, thereby obtaining the target polyester polymer. The method of adding the raw materials containing the monomers can be an intermittent initial one-time addition of all raw materials, a semi-continuous addition of at least a portion of the raw materials being continuously supplied to the reactor, or a continuous polymerization method in which all raw materials are continuously supplied while the resin is continuously removed from the reactor.

[0083] As an initiator, a monohydric alcohol or polyhydric alcohol is preferred from the perspective of easily obtaining the target polymer. The monohydric alcohol 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, 2,2-dimethyl-1-propanol, etc. Specific examples of polyols include: triols such as glycerol, trimethylolethane, trimethylolpropane, tris(2-hydroxyethyl)isocyanurate, hexanetriol, octanetriol, and decantriol; tetraols such as dimethylolethane, dimethylolpropane, diglycerol, and pentaerythritol; pentaols such as trimethylolethane, trimethylolpropane, and triglycerol; alcohols with six or more members such as polymethylolethane, polymethylolpropane, polyglycerol, dipentaerythritol, tripentaerythritol, sorbitol, and polypentaerythritol; and epoxide adducts of alcohols with three or more members.

[0084] When manufacturing polyester polymers, the amount of initiator used is, for example, 0.01 to 15 parts by mass relative to 100 parts by mass of the total amount of monomers used in the polymerization, preferably 0.02 to 10 parts by mass.

[0085] From the viewpoint of efficiently carrying out the reaction, the above-mentioned ring-opening polymerization is preferably carried out in the presence of a catalyst. As a catalyst, conventionally known acid catalysts, base catalysts, or metal catalysts can be appropriately used. Specific examples of acid catalysts include sulfonic acid, methanesulfonic acid, trifluoroacetic acid, 10-camphorsulfonic acid, phosphoric acid, monophosphate esters (methyl phosphate, ethyl phosphate, octyl phosphate, phenyl phosphate, etc.), diesters (dimethyl phosphate, diethyl phosphate, dibutyl phosphate, diphenyl phosphate, etc.), phosphorous acid, phosphite esters, tin tetrachloride, phosphorus pentafluoride, boron trifluoride complexes, etc.

[0086] Specific examples of alkaline 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-phenylimidazolium, 1-cyanoethyl-2-ethyl-4-methylimidazolium and 2-ethyl-4-methylimidazolium.

[0087] Specific examples of metal catalysts include metal salts of tin, zinc, lead, titanium, aluminum, iron, zirconium, etc. From a reactivity point of view, 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 (IV), and tin(II) trifluoromethanesulfonate.

[0088] When manufacturing polyester polymers, the amount of catalyst used is, for example, 0.01 to 20 parts by mass relative to 100 parts by mass of the total amount of monomers used in the polymerization, preferably 0.05 to 10 parts by mass.

[0089] When a solvent is used in the reaction, an organic solvent is preferred. 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 1500 parts by mass relative to 100 parts by mass of the total amount of monomers used in the polymerization, preferably 20 to 1000 parts by mass.

[0090] The polymerization temperature and time are not particularly limited and can be set appropriately. 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 more preferably in the range of 5°C to 100°C. The polymerization time is preferably from 1 hour to 150 hours, and more preferably from 5 hours to 100 hours. The polymerization pressure is only required to maintain the polymerization temperature. Furthermore, from the viewpoint of suppressing the decrease in the degree of polymerization, the reaction can be carried out under dry air (e.g., under conditions where the dew point is below -40°C at atmospheric pressure). Alternatively, the reaction can be carried out under dry nitrogen or dry argon instead of dry air. The polymerization reaction is preferably carried out in a stirred reactor.

[0091] By using monohydric or polyhydric alcohols as initiators for ring-opening polymerization of lactones or lactides, polyester polymers with hydroxyl groups at the polymer terminals can be obtained. These polyester polymers can then be mixed in their situ (i.e., with terminal hydroxyl groups) with inorganic solid electrolytes and alkali metal salts. Alternatively, the terminal hydroxyl groups of the polyester polymer obtained from the above polymerization reaction can be reacted with a compound (modifier) ​​having reactive functional groups capable of reacting with hydroxyl groups, thereby introducing a structure derived from the modifier into the ends of the polyester polymer. The resulting polymer can then be mixed with inorganic solid electrolytes and alkali metal salts. The reaction of the hydroxyl-terminated polyester polymer with the modifier can, for example, be carried out in a suitable solvent using a catalyst as needed.

[0092] When polyester polymers are manufactured via solution polymerization, the polyester polymer dissolved in the solvent can be separated using known desolvation methods such as reprecipitation, or drying methods such as heat treatment. Alternatively, polyester polymers can be manufactured without the use of solvents, such as via bulk polymerization.

[0093] The glass transition temperature (Tg) of the polyester polymer is, for example, 65°C or below. From the viewpoint of obtaining a composite electrolyte exhibiting higher ionic conductivity, the glass transition temperature of the polyester polymer is preferably 50°C or below, more preferably 20°C or below, more preferably 0°C or below, more preferably -20°C or below, further preferably -30°C or below, even more preferably -40°C or below, and even more preferably -50°C or below. The lower limit of the glass transition temperature of the polyester polymer is not particularly limited, for example, it is -80°C or above. It should be noted that, in this specification, the glass transition temperature of the polyester polymer is a value obtained by differential scanning calorimetry (DSC).

[0094] From the viewpoint of obtaining a composite electrolyte with high strength and high ionic conductivity, and from the viewpoint of ensuring good formability of the composite electrolyte, the number average molecular weight (Mn) of the polyester polymer is preferably 1000 or more, more preferably 3000 or more, further preferably 5000 or more, even more preferably 8000 or more, even more preferably 10000 or more, even more preferably 15000 or more, and particularly preferably 20000 or more. Regarding the upper limit of Mn of the polyester polymer, from the viewpoint of ensuring appropriate flowability of the polyester polymer and the softness of the composite electrolyte obtained from the inorganic solid electrolyte, the polyester polymer, and the alkali metal salt, it is preferably 100000 or less, more preferably 80000 or less, and even more preferably 50000 or less.

[0095] The preferred range of Mn in polyester polymers can be set by appropriately combining the upper and lower limits of the preferred range of Mn. The range of Mn in polyester polymers 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.

[0096] Furthermore, the weight-average molecular weight (Mw) of the polyester polymer is preferably 1500 or more, more preferably 4000 or more, even more preferably 7500 or more, even more preferably 10000 or more, even more preferably 15000 or more, even more preferably 20000 or more, and particularly preferably 26000 or more. Regarding the upper limit of the Mw of the polyester polymer, it is preferably 150000 or less, more preferably 100000 or less, and even more preferably 80000 or less. The range of the Mw of the polyester polymer is preferably 1500 or more and 150000 or less, more preferably 4000 or more and 100000 or less, and even more preferably 7500 or more and 80000 or less.

[0097] Regarding polyester polymers, from the viewpoint of obtaining composite electrolytes exhibiting good ion conductivity, the molecular weight distribution (Mw / Mn), expressed as the ratio of Mw to Mn, is preferably 4.5 or less, more preferably 4.0 or less, further 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. The lower limit of the Mw / Mn ratio for polyester polymers is not particularly limited, but is 1.0 or more. In this specification, the Mw and Mn of the polymer are standard polystyrene conversion values ​​obtained using gel permeation chromatography (GPC).

[0098] From the viewpoint of reducing interfacial resistance and obtaining a composite electrolyte exhibiting high ionic conductivity, the content of polyester polymer in the composite electrolyte is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, relative to the total amount of the composite electrolyte. Furthermore, regarding the upper limit of the polyester polymer content, from the viewpoint of ensuring the moldability and processability of the composite electrolyte, it is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, and even more preferably 30% by mass or less, relative to the total amount of the composite electrolyte.

[0099] Alkali metal salts

[0100] Alkali metal salts are any salts that produce alkali metal ions; there are no particular limitations. Examples of alkali metal salts include lithium salts, sodium salts, and potassium salts.

[0101] Specific examples of alkali metal salts include 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 - Lithium salts such as lithium(fluorosulfonyl) and lithium(trifluoromethanesulfonyl)imide; and salts of alkali metals other than lithium (e.g., sodium, potassium, etc.). Lithium salts or sodium salts are preferred from the perspective of high ion dissociation and the ability to further improve the ionic conductivity of the composite electrolyte of this disclosure. Furthermore, it is preferable that the inorganic solid electrolyte contains the same type of alkali metal ions as the alkali metal salts.

[0102] From the viewpoint of further improving the ionic conductivity of the composite electrolyte of this disclosure, the alkali metal salt contained in the composite electrolyte of this disclosure preferably comprises an imide-based alkali metal salt. Among them, from the viewpoint of high ion dissociation, an imide-based lithium salt is preferred, and among the imide-based lithium salts, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, or lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide are particularly preferred, lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide are more preferred, and lithium bis(fluorosulfonyl)imide is even more preferred.

[0103] 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. Regarding the lower limit of the molecular weight of the alkali metal salt, it is, for example, 20 or more, preferably 50 or more, more preferably 100 or more, and even more preferably 150 or more.

[0104] The melting point of alkali metal salts 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 alkali metal salts; for example, it can be 300°C or lower, or even 250°C or lower.

[0105] The content of alkali metal salts in the composite electrolyte is between 5 mol% and 250 mol% relative to the total amount of ester groups in the polyester polymer (100 mol%). If the content of alkali metal salts relative to the total amount of ester groups in the polyester polymer is less than 5 mol%, the ion source in the composite electrolyte is insufficient, and a composite electrolyte exhibiting good ionic conductivity cannot be obtained. Furthermore, if the content of alkali metal salts in the composite electrolyte exceeds 250 mol% relative to the total amount of ester groups in the polyester polymer, there is a tendency for the alkali metal salts to not dissolve sufficiently in the polyester polymer, thus failing to adequately improve the ionic conductivity of the resulting composite electrolyte.

[0106] From the viewpoint of obtaining a composite electrolyte with superior ion conductivity, the content of 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, relative to the total amount of ester groups in the polyester polymer. Furthermore, the content of 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, relative to the total amount of ester groups in the polyester polymer.

[0107] Without impairing the effects of the invention, the composite electrolyte disclosed herein may further contain components (hereinafter also referred to as "other components") that are different from inorganic solid electrolytes, polyester polymers, and alkali metal salts. Examples of other components include the following.

[0108] Surface modifiers

[0109] Surface modifiers can be used in the manufacture of composite electrolytes to uniformly disperse the inorganic solid electrolyte within the composite electrolyte, thereby obtaining a composite electrolyte exhibiting high ionic conductivity. Particularly when using granular inorganic solid electrolytes, aggregation of the inorganic solid electrolyte tends to occur when mixing polyester polymers with the granular inorganic solid electrolyte. In view of this, treating the granular inorganic solid electrolyte with a surface modifier and then mixing the surface-modified granular inorganic solid electrolyte with the polyester polymer is effective in suppressing the aggregation of the inorganic solid electrolyte. As such a surface modifier, a substance exhibiting affinity for both the inorganic solid electrolyte and the polyester polymer is preferred; for example, a known silane coupling agent can be used.

[0110] Specific examples of surface modifiers include silane coupling agents having one or more functional groups such as epoxy, (meth)acryloyl, amino, vinyl, thiol, isocyanate, and terminal isocyanate groups. Among these, silane coupling agents having amino groups are preferred from the perspective of higher affinity with polyester polymers and greater effectiveness in improving the uniform dispersion of inorganic solid electrolytes.

[0111] Specific examples of silane coupling agents containing amino groups 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-dimethyl-butylene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, etc.

[0112] When using a surface modifier to treat an inorganic solid electrolyte, the amount of surface modifier used relative to the total amount of the inorganic solid electrolyte is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more. Furthermore, the amount of surface modifier used relative to the total amount of the inorganic solid electrolyte is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0113] Other components, besides those mentioned above, may include antioxidants, colorants, etc. The amounts of these components can be appropriately set without impairing the effects of the present invention.

[0114] <Manufacturing Method of Composite Electrolytes>

[0115] The composite electrolyte disclosed herein can be manufactured by mixing an inorganic solid electrolyte, a polyester polymer, and an alkali metal salt, and then molding it as needed. According to this method, even without a sintering step of the inorganic solid electrolyte or a composition containing an inorganic solid electrolyte, a composite electrolyte exhibiting high ionic conductivity can be obtained during the manufacture of the composite electrolyte. Particularly, when manufacturing the composite electrolyte, a method is preferred that includes using an aggregate of particles (i.e., powder) as the inorganic solid electrolyte, and a step (hereinafter also referred to as the "mixing step") of mixing the granular inorganic solid electrolyte, the polyester polymer, and the alkali metal salt is used.

[0116] In the mixing process of manufacturing composite electrolytes, the method is not particularly limited as long as it can be used to mix the inorganic solid electrolyte, polyester polymer, and alkali metal salt in a manner that ensures uniform mixing. For example, the inorganic solid electrolyte, polyester polymer, and alkali metal salt can be mixed simultaneously in a container, or they can be mixed sequentially. Alternatively, the inorganic solid electrolyte can be added after the polyester polymer and alkali metal salt have been mixed. From the viewpoint of ensuring uniform dispersion of the inorganic solid electrolyte, it is preferable to add the inorganic solid electrolyte and surface modifier to a solvent (hereinafter also referred to as a "dispersion solvent") as needed and mix them to obtain an inorganic solid electrolyte with a surface-modified surface modifier. Then, this surface-modified inorganic solid electrolyte is mixed with the polyester polymer and the alkali metal salt.

[0117] When using a dispersing solvent to mix inorganic solid electrolytes and surface modifiers, the dispersing solvent is not particularly limited as long as it does not react with the inorganic solid electrolyte. Specific examples of dispersing solvents include tetrahydrofuran, acetone, tert-butyl methyl ether, diethyl ether, 1,4-dioxane, acetonitrile, ethyl acetate, and N-methyl-2-pyrrolidone. One dispersing solvent can be used alone, or two or more can be combined. The amount of dispersing solvent used can be appropriately set; from the viewpoint of improving the dispersibility of the inorganic solid electrolyte when mixed with organic electrolytes, for example, it can be 50 to 2000 parts by mass relative to 100 parts by mass of the total amount of inorganic solid electrolyte used in the manufacture of the composite electrolyte.

[0118] When mixing two or more of the following: inorganic solid electrolytes, polyester polymers, and alkali metal salts, it is preferable to mix while stirring. The stirring method is not particularly limited; examples include various methods such as using a rotary mixer, magnetic stirrer, stirring rod, three-one motor with stirring blades, and external circulation stirring. Alternatively, stirring can be performed simultaneously using a homogenizer, disperser-type mixer, or homogenizer for mechanical mixing.

[0119] If the mixture obtained through the above mixing process contains solvent, it is preferable to remove the solvent from the mixture (solvent removal process). There are no particular limitations on the method of solvent removal; known solvent removal methods can be appropriately employed. For example, solvent removal can be performed by heating, natural drying, air supply, or reduced pressure treatment. Alternatively, solvent removal can be performed by appropriately combining two or more of these methods. When removing solvent by heating, the heating temperature can be appropriately set according to the type of solvent, for example, from 30°C to 100°C, preferably from 35°C to 65°C. The heating time is, for example, from 30 minutes to 24 hours. Furthermore, the heating treatment can be performed at atmospheric pressure or under reduced pressure. From the viewpoint of removing solvent from the mixture at the lowest possible temperature, the solvent removal process can be carried out under reduced pressure and at a heating temperature of 60°C or below.

[0120] When molding a mixture containing an inorganic solid electrolyte, a polyester polymer, and an alkali metal salt to obtain a molded body, the molding method is not particularly limited, and a known molding method may be appropriately used. Specific examples of molding methods include extrusion molding, injection molding, pressure molding, casting, die casting, and tape casting. The shape of the molded body is not particularly limited and can be appropriately set according to the purpose and shape of the energy storage device. For example, the shape of the molded body may be rectangular or circular.

[0121] Through the above-described mixing process, or through a mixing process combined with a solvent removal process, a composite electrolyte can be obtained. The resulting composite electrolyte exhibits high ionic conductivity. Therefore, by using the composite electrolyte of this disclosure as an electrolyte material in energy storage devices, energy storage devices with high ionic conductivity can be obtained.

[0122] Specifically, for the molded body composed of the composite electrolyte of this disclosure, the ionic conductivity measured by AC impedance spectroscopy at 25°C is preferably 1×10⁻⁶. -6 S / cm or higher. From the viewpoint of obtaining a high-performance energy storage device, an ionic conductivity of 1×10⁻⁶ is more preferable under the same conditions. -5 S / cm or higher, more preferably 1×10 -4 S / cm or higher, and more preferably 1×10⁻⁶ -3 S / cm or higher. Details of the method for determining ionic conductivity are as described in the examples below.

[0123] Inorganic solid electrolytes are non-flammable and highly safe; however, their high grain boundary resistance hinders further improvements in ionic conductivity. To overcome these drawbacks, the manufacturing process typically involves heating the powder to high temperatures (e.g., above 1000°C) after pressing it into shape (sintering) to improve the bonding between particles and between the electrode and electrolyte. However, considering the equipment required for sintering and the energy consumption, the sintering process may not be suitable for industrialization or practical application. Furthermore, if high-temperature sintering is required in the manufacture of all-solid-state batteries, there are concerns about avoiding co-sintering of the positive and negative electrodes with the solid electrolyte to prevent damage. Thus, from the perspectives of energy conservation, industrialization, and practicality, manufacturing methods for solid electrolytes that include a sintering process have high technological barriers.

[0124] The polyester polymer shown in formula (1) exhibits ionic conductivity in the presence of alkali metal salts and takes on a liquid or near-liquid state when containing alkali metal salts. The inventors, focusing on this property of the polyester polymer shown in formula (1), attempted to use it as a binder in a composite electrolyte of inorganic solid electrolyte and organic electrolyte. The results showed that the mixture of inorganic solid electrolyte, the polyester polymer shown in formula (1), and alkali metal salt exhibits high ionic conductivity even without sintering. That is, one preferred embodiment of the composite electrolyte of this disclosure is a non-sintered body of a mixture of inorganic solid electrolyte, polyester polymer, and alkali metal salt.

[0125] It should be noted that the reason for this result is believed to be that the gaps in the inorganic solid electrolyte are filled by the mixture of polyester polymer and alkali metal salt, thereby causing the inorganic solid electrolyte particles to adhere firmly to each other and facilitating the formation of ion conduction pathways in the composite electrolyte. Furthermore, it is speculated that by giving the polyester polymer containing the alkali metal salt a moderate viscosity, the polyester polymer can easily remain in the gaps within the inorganic solid electrolyte, which also contributes to the formation of ion conduction pathways. However, these are merely speculations and do not limit the scope of the present invention in any way.

[0126] Energy Storage Equipment

[0127] The energy storage device disclosed herein (hereinafter also referred to as "the device") possesses the composite electrolyte described above. Examples of the device include secondary batteries and capacitors. When the device is a secondary battery, one approach is an all-solid-state battery; from the perspective of excellent ion conductivity, a lithium-ion secondary battery is preferred.

[0128] A solid-state lithium-ion secondary battery, as 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 disposed between the positive and negative electrode layers in a manner that the solid electrolyte layer is in contact with the electrode layer. The materials constituting the positive and negative electrode layers 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 can be composed of a positive current collector and a positive electrode flux layer. As the positive current collector, metal foils such as aluminum or stainless steel can be used. The positive electrode flux layer is a layer containing a positive electrode active material, disposed on the surface of the positive current collector. Examples of positive electrode active materials include metal oxides having a layered rock salt, spinel, or olivine crystal structure. Furthermore, the negative electrode layer can be composed of a negative current collector and a negative electrode flux layer. As the negative current collector, metal foils such as copper foil or lithium foil can be used. The negative electrode additive layer is a layer containing the negative electrode active material, disposed on the surface of the negative electrode current collector. Examples of negative electrode active materials include lithium metal, graphite, and Li₄Ti₅O₂. 12 Silicon monoxide, silicon, etc.

[0129] In the lithium-ion secondary battery disclosed herein, the solid electrolyte layer is formed of a composite electrolyte comprising an inorganic solid electrolyte, a polyester polymer, and an alkali metal salt. The thickness of the solid electrolyte layer is not particularly limited and can be appropriately set according to the application of the secondary battery. The thickness of the solid electrolyte layer is, for example, 5 μm to 5000 μm. From the viewpoint of miniaturizing, lightening, and increasing the capacity of the all-solid-state secondary battery by making the solid electrolyte layer as thin as possible, the thickness of the solid electrolyte layer is preferably 50 μm or less, more preferably 20 μm or less.

[0130] There are no particular limitations on the method for manufacturing the solid electrolyte layer and the lithium-ion secondary battery; known methods can be appropriately adopted depending on the battery structure, etc. For example, a solid electrolyte layer obtained by molding the composite electrolyte of this disclosure can be sandwiched between a positive electrode layer and a negative electrode layer, and preferably subjected to a pressure treatment for bonding, thereby manufacturing a laminate having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. Alternatively, the composite electrolyte before molding can be housed in a container by sandwiching the positive electrode layer and the negative electrode layer, and the housed can preferably be subjected to a pressure treatment for bonding, thereby manufacturing a laminate having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. The laminate having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer is usually housed in a casing and used as a secondary battery.

[0131] This device is not limited to the above-described configuration where the charge carriers for ion conduction are lithium ions. For example, it could also be a secondary battery using other ions such as sodium ions as charge carriers. Alternatively, this device could also be a capacitor. One example of a capacitor configuration is one that includes an anode, a cathode, and a solid electrolyte, with the solid electrolyte disposed between the anode and cathode in connection with the electrodes.

[0132] Energy storage devices incorporating the composite electrolyte disclosed herein can be applied to a variety of uses. Specifically, they can be used as power sources in various mobile devices such as mobile phones, personal computers, smartphones, game consoles, and wearable devices; various mobile vehicles such as electric vehicles, hybrid vehicles, robots, and drones; and various electrical and electronic devices such as digital cameras, camcorders, music players, power tools, and home appliances.

[0133] Example

[0134] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the present invention is not limited to these embodiments. Unless otherwise specified, “parts” and “%” refer to “parts by mass” and “% by mass”, respectively.

[0135] [Molecular weight determination]

[0136] The molecular weight of the polymer was determined using a gel permeation chromatography (GPC) apparatus, following the steps outlined below.

[0137] 4 mg of polymer was dissolved in 4 mL of tetrahydrofuran to obtain a sample solution. The obtained sample solution was filtered through a polytetrafluoroethylene membrane filter, and 100 μL was injected into the GPC device to determine the weight-average molecular weight and number-average molecular weight (hereinafter referred to as "Mw" and "Mn", respectively).

[0138] Column: TSKgel SuperMultiporeHZ-M × 4 columns manufactured by Tosoh Corporation

[0139] Temperature: 40℃

[0140] Eluent: Tetrahydrofuran

[0141] Detector: Differential refractometer

[0142] Flow rate: 600 μL / min

[0143] Standard material: polystyrene

[0144] [Glass transition temperature determination]

[0145] The glass transition temperature of the polymer is determined using a differential scanning calorimeter (hereinafter also referred to as "DSC") following the steps below.

[0146] Five mg of polymer, sealed in an aluminum disk, was cooled to -80°C and then scanned up to 100°C at a rate of 10°C / min to obtain the heat flux curve. The glass transition temperature was determined by the intersection of the baseline of the heat flux curve and the tangent at the inflection point.

[0147] Model: TA Instruments DSC250

[0148] Atmosphere to be measured: nitrogen

[0149] 1. Polymer Synthesis

[0150] [Synthesis Example 1] Synthesis of Polymer A

[0151] 100 parts of ε-caprolactone, 0.33 parts of 1-butanol, 0.17 parts of tin(II) 2-ethylhexanoate, and a stir bar were added to a test tube and stirred at 95°C for 96 hours under dry air (dew point below -60°C). For ε-caprolactone and 1-butanol, a substance dehydrated using molecular sieves was used. The polymerization solution was injected into a large amount of isopropanol, causing the polymer to precipitate. The precipitate was recovered by vacuum filtration and then vacuum dried to obtain polymer A. The molecular weight of polymer A was determined using GPC, yielding Mn 18700 and Mw 26800.

[0152] [Synthetic Examples 2-4] Synthesis of Polymers B-D

[0153] Except for changing the types and amounts of raw materials added to the test tubes as described in Table 1, the same procedures as in Synthesis Example 1 were performed to obtain polymers B through D. For Synthesis Examples 3 and 4, toluene was used as the solvent during addition. The amount (parts by mass) of toluene added is shown in Table 1. Furthermore, for each polymer, Mn and Mw were determined using GPC in the same manner as in Synthesis Example 1.

[0154] [Table 1]

[0155]

[0156] The details of the compounds shown in Table 1 are as follows.

[0157] •CL: ε-caprolactone [Manufactured by Tokyo Chemical Industry Co., Ltd.]

[0158] ·DLLA: DL-lactide (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0159] BuOH: 1-Butanol [Manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.]

[0160] Sn(Oct)2:2-Ethyltin(II)hexanoate [Manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.]

[0161] • Toluene: Toluene (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.)

[0162] 2. Manufacturing and Evaluation of Composite Electrolytes

[0163] [Example 1]

[0164] (1) Manufacturing of composite electrolyte CPE-1

[0165] Add LICGC PW-01 (main crystal phase Li) to the container 1+x+y Al x Ti 2-x Si y P 3-y O 12 81 parts of (Li replaced by NASICON type), D50 0.4μm) [manufactured by OHARA INC.] (hereinafter also referred to as "LICGC"), 8 parts of 3-aminopropyltriethoxysilane, and 800 parts of tetrahydrofuran were stirred at 2000 rpm for 5 minutes at room temperature using a defoaming agent (manufactured by Thinky Corporation, model ARE-310). Next, 100 parts of polymer A and 90 parts of lithium bis(fluorosulfonyl)imide [manufactured by Nippon Shokubai Co., Ltd.] were added, and the mixture was stirred at 2000 rpm for 30 minutes at room temperature using a defoaming agent to obtain composition CA. Composition CA was cast into a silica gel cup and vacuum dried at 40°C for 12 hours to obtain composite electrolyte CPE-1.

[0166] (2) Measurement of ionic conductivity

[0167] The ionic conductivity of the composite electrolyte CPE-1 was determined using the AC impedance method through the following steps.

[0168] The composite electrolyte CPE-1 was clamped between two stainless steel plates and pressurized at 370 MPa before being punched to form particles with a diameter of 10 mm and a thickness of 0.65 mm. Disk-shaped lithium metal foils with a diameter of 8 mm were then placed on both sides of the particles. The particles with the lithium metal foils on both sides were then clamped between two stainless steel plates, and the impedance between the lithium metal foils was measured at 25°C. During the measurement, an alternating current was applied between the electrodes, and the ionic conductivity was calculated from the real impedance intercept of the obtained Cole-Cole plot. All of the above operations were performed in a glove box with a dew point below -80°C.

[0169] The ionic conductivity (σ) is obtained by the following mathematical formula (1).

[0170] σ = L / (R × S) (1)

[0171] (In mathematical formula (1), σ represents ionic conductivity (unit: S / cm), R represents real impedance intercept (unit: Ω), and S represents the cross-sectional area of ​​the lithium foil during measurement (unit: cm²). 2 L represents the distance between stainless steel plates (unit: cm).

[0172] The conditions for measuring impedance are as follows.

[0173] Measurement equipment: Biologic VMP-300

[0174] Applied voltage: 100mV

[0175] Frequency: 10mHz~7MHz

[0176] The measurement results are shown in Table 2.

[0177] (3) The formability of composite electrolytes

[0178] The formability of the composite electrolyte is evaluated based on the ease of forming the sample particles and their self-supporting properties. The evaluation is based on the following criteria.

[0179] ○: It can be easily molded into any shape, and the sample particles have sufficient self-supporting properties.

[0180] △: It can be molded into any shape, but its self-supporting ability is insufficient, such as deformation due to its own weight.

[0181] ×: Difficult to shape into any shape.

[0182] The evaluation results are shown in Table 2.

[0183] [Examples 2-14 and Comparative Example 1]

[0184] By changing the types and amounts of raw materials as described in Tables 2 and 3, and otherwise performing the same operations as in Example 1, composite electrolytes CPE-2 to CPE-15 were obtained. Furthermore, the ionic conductivity of composite electrolytes CPE-2 to CPE-15 was measured in the same manner as in Example 1, and the moldability of each composite electrolyte was evaluated. The results are shown in Tables 2 and 3.

[0185] [Comparative Examples 2-4]

[0186] The types and amounts of raw materials were changed as described in Table 3, and the same procedures as in Example 1 were performed to obtain organic electrolytes PE-1 to PE-3. Furthermore, organic electrolytes PE-1 to PE-3 were used instead of composite electrolyte CPE-1, and the ionic conductivity of organic electrolytes PE-1 to PE-3 was measured in the same manner as in Example 1, and the moldability of each organic electrolyte was evaluated. The results are shown in Table 3.

[0187] [Comparative Example 5]

[0188] A die 10 consisting of a module 11, an upper punch 12, and a lower punch 13 is used (see reference). Figure 1 Sample particles were prepared. A module 11 containing 0.1 g of LICGC was placed on a lower punch 13, and an upper punch 12 was placed on the module 11. The particles were compressed using a hydraulic press at a pressure of 340 MPa to obtain spherical inorganic solid electrolyte particles IE-1 with a diameter of 10 mm and a thickness of 0.65 mm. The ionic conductivity was then measured in the same manner as in Example 1, and the formability of the inorganic solid electrolyte particles IE-1 was evaluated. The results are shown in Table 3.

[0189] [Table 2]

[0190]

[0191] [Table 3]

[0192]

[0193] The details of the compounds shown in Tables 2 and 3 are as follows.

[0194] •LICGC:LICGC PW-01 (Main crystal phase Li) 1+x+y Al x Ti 2-x Si y P 3-y O 12 (Li replaces NASICON type), D500.4μm) [Manufactured by OHARA INC.]

[0195] • AES: 3-Aminopropyltriethoxysilane [Manufactured by Tokyo Chemical Industry Co., Ltd.]

[0196] • Polymers A to D: Polymers produced in Synthesis Examples 1 to 4

[0197] • PEO: Polyethylene oxide (Mw100000) [Manufactured by Sigma-Aldrich]

[0198] • LiFSI: Lithium Bis(Fluorosulfonyl)imide [Nippon Shokubai Co., Ltd.]

[0199] • THF: Tetrahydrofuran (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.)

[0200] •AcCN: Acetonitrile (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.)

[0201] 3. Evaluation Results

[0202] The composite electrolytes of Examples 1-14 exhibited high ionic conductivity at 25°C. This result is attributed to the polyester polymer contributing to the reduction of grain boundary resistance by filling the interparticle spaces of the inorganic solid electrolyte. Specifically, the composite electrolytes manufactured using polymer B (Examples 3-12) showed higher ionic conductivity at 25°C compared to those manufactured using polymer A (Examples 1 and 2), which used polymer B with a smaller molecular weight. Similarly, the composite electrolyte of Example 14 (Example 14) showed higher ionic conductivity at 25°C compared to those manufactured using polymer C (Example 13), which used polymer D with a smaller molecular weight. Furthermore, when observing the results of examples with the same polymer type and alkali metal salt concentration, a trend was observed: the higher the mass proportion of the inorganic solid electrolyte, the easier it was to obtain a composite electrolyte with good moldability and sufficient self-supporting properties (Example 2 compared to Example 1, Examples 9-12 compared to Example 8). These results suggest that the larger the molecular weight of the polymer and the higher the mass proportion of inorganic solid electrolyte, the easier it is to obtain a composite electrolyte with excellent ion conductivity, good formability, and sufficient self-sustaining properties. This is presumably because the polymer chains of high molecular weight polymers are strongly entangled, enabling them to immobilize the inorganic solid electrolyte powder in a small amount.

[0203] In contrast, the composite electrolyte of Comparative Example 1, manufactured using PEO as the polymer, exhibited low ionic conductivity at 25°C. This result is attributed to insufficient reduction of grain boundary resistance by PEO. Furthermore, for organic electrolytes (Comparative Examples 2-4) manufactured using polymers and alkali metal salts instead of inorganic solid electrolytes, the ionic conductivity at 25°C was lower compared to composite electrolytes using the same polymer (compared to Examples 1-2 of Comparative Examples 2, Examples 3-12 of Comparative Examples 3, and Example 13 of Comparative Example 4). These results indicate that organic electrolytes composed of polyester-based polymers and alkali metal salts have low ionic conductivity, while those combined with inorganic solid electrolytes exhibit high ionic conductivity at room temperature (25°C). Additionally, the inorganic solid electrolyte of Comparative Example 5, manufactured by compressing inorganic solid electrolyte powder, had high grain boundary resistance, making it impossible to measure its ionic conductivity. Furthermore, the inorganic solid electrolyte of Comparative Example 5 also exhibited poor formability.

[0204] As can be seen from the above results, by preparing a composite electrolyte containing an inorganic solid electrolyte, a polyester polymer as shown in the above formula (1), and an alkali metal salt, even without sintering during the manufacturing of the composite electrolyte, the interfacial resistance can be sufficiently reduced, and a composite electrolyte exhibiting high ionic conductivity can be obtained.

[0205] This invention is not limited to the embodiments described above, and includes various modifications and variations within the same scope without departing from the spirit of the invention. Therefore, it should be understood that, in accordance with the above teachings, various combinations, forms, and other combinations and forms including only one element, its superordinate concept, or its subordinate concept also fall within the scope and spirit of this invention.

[0206] Explanation of reference numerals in the attached figures

[0207] 10… Press mold.

Claims

1. A composite electrolyte, characterized in that, contain: Inorganic solid electrolytes; polymers; and Alkali metal salts, The polymer has the structure shown in formula (1) below. The composite electrolyte contains, relative to the total amount of ester groups in the polymer, more than 5 mol% and less than 250 mol% of the alkali metal salt. 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 greater than or equal to 1, and m represents an integer from 0 to 10.

2. The composite electrolyte according to claim 1, wherein, The inorganic solid electrolyte contains an oxide having a NASICON-type crystal structure.

3. The composite electrolyte according to claim 1, wherein, The inorganic solid electrolyte is in granular form.

4. The composite electrolyte according to claim 3, wherein, The composite electrolyte is a non-sintered mixture of the inorganic solid electrolyte, the polymer, and the alkali metal salt.

5. The composite electrolyte according to claim 1, wherein, The inorganic solid electrolyte comprises 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 The solid electrolyte shown has M1 containing an element that can be a divalent cation, M2 containing an element that can be a trivalent cation, and M3 containing at least one element from Ti and Zr, satisfying a≥0, b>0, c>0, and d≥0.

6. The composite electrolyte according to claim 1, wherein, The content of the inorganic solid electrolyte is above 20% by mass and below 95% by mass.

7. The composite electrolyte according to claim 1, wherein, The alkali metal salt comprises lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide.

8. A method for manufacturing a composite electrolyte, characterized in that, The method for manufacturing the composite electrolyte according to any one of claims 1 to 7 The method for manufacturing the composite electrolyte includes a step of mixing the granular inorganic solid electrolyte, the polymer, and the alkali metal salt.

9. An energy storage device, characterized in that, The composite electrolyte comprises any one of claims 1 to 7.

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