Composite solid electrolyte and solid-state battery

Abstract

A composite solid electrolyte and a solid battery comprising a sulfide solid electrolyte and a polymer electrolyte comprising a polymer and a lithium imide salt, wherein the content of the lithium imide salt relative to the polymer electrolyte is 40 mass% or more.

Description

Technology Field

[0001] The present disclosure relates to a composite solid electrolyte and a solid battery. Background Technology

[0002] In recent years, secondary batteries, such as lithium-ion batteries, have been suitablely used as power sources for portable devices like PCs and mobile terminals, as well as for powering vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs).

[0003] Since secondary batteries use electrolytes containing flammable organic solvents, it is necessary to install safety devices to suppress temperature rise during a short circuit or to make structural and material improvements to prevent short circuits. In contrast, solid-state batteries, which replace the electrolyte with a solid electrolyte layer and solidify the material, do not use flammable organic solvents within the battery; therefore, they allow for the simplification of safety devices and are considered to offer superior manufacturing costs and productivity.

[0004] In the field of solid-state batteries, it is known that the lithium ion conductivity of a solid-state battery is improved by using a composite solid electrolyte containing a sulfide solid electrolyte and a polymer electrolyte containing a polymer and a lithium imide salt (e.g., Patent Document 1). Prior art literature

[0005] International Publication No. 2013 / 001623 The problem to be solved

[0006] However, in conventional composite solid electrolytes, when stored, the sulfide solid electrolyte and the polymer included in the polymer electrolyte react at the contact surface between the sulfide solid electrolyte and the polymer to generate reaction products, thereby inhibiting the ion conduction pathway and tending to lower the ion conductivity. This phenomenon becomes more pronounced when stored for a long period at high temperatures (e.g., 60°C for 3 days). Patent Document 1 attempts to suppress the decrease in ion conductivity by using a sulfide solid electrolyte that substantially does not have cross-linked sulfur and a solid electrolyte having a branched polymer. As described above, various studies have been conducted to suppress the decrease in ion conductivity when using the above composite solid electrolyte layer, but further technological development is desired. Therefore, taking into account the above circumstances, the present disclosure aims to provide a composite solid electrolyte and a solid battery in which the decrease in ion conductivity is suppressed. means of solving the problem

[0007] The means for solving the above problem include the following means.

[0008] <1> sulfide solid electrolyte and,

[0009] Polymer electrolyte containing polymer and lithium imide salt

[0010] Contains,

[0011] A composite solid electrolyte in which the content of the lithium imide salt relative to the polymer is 40 mass% or more.

[0012] <2> The above polymer electrolyte comprises an ethylene oxide-based polymer as the polymer, <1> The composite solid electrolyte described in

[0013] <3> In the above polymer electrolyte, the content of the lithium imide salt relative to the polymer is 300 mass% or more, the above <1> or <2> The composite solid electrolyte described in

[0014] <4> In the above polymer electrolyte, the content of the lithium imide salt relative to the polymer is 40 mass% to 900 mass%, <1> The composite solid electrolyte described in

[0015] <5> The volume ratio of the sulfide solid electrolyte to the polymer electrolyte is 80 / 20 or more and 95 / 5 or less, the <1> inside <4> A composite solid electrolyte described in any one of the following.

[0016] <6> The above <1> inside <5> A solid-state battery comprising a composite solid electrolyte as described in any one of the following. Effects of the invention

[0017] According to the present disclosure, a composite solid electrolyte and a solid battery are provided in which the decrease in ion conductivity is suppressed. Specific details for implementing the invention

[0018] Hereinafter, an embodiment that is an example of the present disclosure will be described. The description and embodiments thereof are intended to illustrate embodiments and do not limit the scope of the invention.

[0019] <Complex Solid Electrolyte>

[0020] The composite solid electrolyte according to the present disclosure is a composite solid electrolyte comprising a sulfide solid electrolyte and a polymer electrolyte comprising a polymer and a lithium imide salt, wherein the content of the lithium imide salt relative to the polymer electrolyte is 40 mass% or more.

[0021] According to the present disclosure, the ratio of lithium imide salt to the polymer electrolyte is high. Therefore, as the concentration of lithium imide salt increases in the entire composite solid electrolyte, the interaction between the polymer and the lithium imide salt becomes stronger, while the reactivity between the polymer and the sulfide solid electrolyte is reduced, thereby suppressing the decomposition of the sulfide component in the sulfide solid electrolyte. Consequently, even when stored (e.g., at 60°C for 3 days), the reaction between the sulfide solid electrolyte and the polymer at the contact surface between the sulfide solid electrolyte and the polymer to generate reaction products is suppressed. As a result, the conduction pathway is not inhibited by the reaction products, and the decrease in ion conductivity is suppressed.

[0022] [Polymer Electrolyte]

[0023] The polymer electrolyte includes a polymer and a lithium imide salt.

[0024] The polymer is not particularly limited as long as it is a polymer capable of dissociating lithium imide salts. As for the polymer, it is preferable that it be a polymer having polar groups in its main chain, and examples include polyalkylene oxide-based polymers such as polyethylene oxide and polypropylene oxide (more preferably ethylene oxide-based polymers such as polyethylene oxide); nitrile-based polymers such as polyacrylonitrile; ester-based polymers; carbonate-based polymers such as polycarbonate; amide-based polymers; phosphazene-based polymers such as polyphosphazene; siloxane-based polymers such as polydimethylsiloxane; (meth)acrylic-based polymers, etc. The polymer may be used alone or in combination of two or more types.

[0025] Among the above, the polymer preferably includes a polyalkylene oxide-based polymer and more preferably an ethylene oxide-based polymer in order to further suppress the decrease in ion conductivity.

[0026] An ethylene oxide-based polymer refers to a polymer containing a constituent unit derived from ethylene oxide. A polyalkylene oxide-based polymer, such as polypropylene oxide, refers to a polymer containing a constituent unit derived from alkylene oxide. A nitrile-based polymer refers to a polymer containing a constituent unit derived from a nitrile group. An ester-based polymer refers to a polymer containing a constituent unit derived from an ester group. An amide-based polymer refers to a polymer containing a constituent unit derived from an amide group. A phosphazene-based polymer refers to a polymer containing a constituent unit derived from a phosphazene group. A carbonate-based polymer refers to a polymer containing a constituent unit derived from a carbonate group. A siloxane-based polymer refers to a polymer containing a constituent unit derived from a siloxane group. A (meth)acrylic-based polymer refers to a polymer containing at least one of a constituent unit derived from a methacrylic acid derivative and a constituent unit derived from an acrylic acid derivative.

[0027] The ethylene oxide-based polymer may be a copolymer polymer comprising, for example, a constituent unit derived from ethylene oxide, a constituent unit derived from 2-(2-methoxyethoxy)ethylglycidyl ether, and a constituent unit derived from allylglycidyl ether.

[0028] Ethylene oxide-based polymers may have, for example, constituent units derived from ethylene oxide, constituent units derived from alkylene oxide having 3 to 12 carbon atoms, constituent units derived from (2-methoxyethoxy)ethylglycidyl ether, and constituent units derived from oxirane having an ethylenically unsaturated group.

[0029] Examples of constituent units derived from alkylene oxides having 3 to 12 carbon atoms include propylene oxide, butylene oxide, 1,2-epoxydodecane, 1,2-epoxyoctane, 1,2-epoxyheptane, 1,2-epoxyhexane, 1,2-epoxypentane, etc. It is preferable that the constituent unit derived from alkylene oxides having 3 to 12 carbon atoms is a constituent unit derived from propylene oxide.

[0030] As constituent units derived from oxiranes having an ethylenically unsaturated group, constituent units derived from allylglycidyl ether, 4-vinylcyclohexylglycidyl ether, α-terpinylglycidyl ether, cyclohexenylmethylglycidyl ether, p-vinylbenzylglycidyl ether, allylphenylglycidyl ether, vinylglycidyl ether, 3,4-epoxy-1-butene, 3,4-epoxy-1-pentene, 4,5-epoxy-2-pentene, 1,2-epoxy-5,9-cyclododecanediene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5-cyclooctene, glycidyl acrylate, glycidyl methacrylate, glycidyl sorbate, glycidyl cinnamate, glycidyl crotonicate, glycidyl-4-hexanoate, etc. Examples include. It is more preferable that the constituent unit derived from oxirane having an ethylenically unsaturated group be at least one selected from the group consisting of constituent units derived from allylglycidyl ether, glycidyl acrylate, and glycidyl methacrylate.

[0031] In ethylene oxide-based polymers, the molar ratio with each constituent unit 1 It is obtained by the H-NMR spectrum.

[0032] The proportion of constituent units derived from ethylene oxide in the ethylene oxide-based polymer is preferably 30 mol% or more, more preferably 45 mol% or more, and even more preferably 60 mol% or more.

[0033] The proportion of constituent units derived from ethylene oxide in the ethylene oxide-based polymer is preferably 100 mol% or less, more preferably 96 mol% or less, and even more preferably 93.5 mol% or less.

[0034] The proportion of constituent units derived from alkylene oxides having 3 to 12 carbon atoms in the ethylene oxide-based polymer may be 0 mol%, 3 mol% or more, or 5 mol% or more.

[0035] The proportion of constituent units derived from alkylene oxides having 3 to 12 carbon atoms in the ethylene oxide-based polymer may be 30 mol% or less, 20 mol% or less, or 10 mol% or less.

[0036] The proportion of constituent units derived from (2-methoxyethoxy)ethylglycidyl ether in the ethylene oxide-based polymer may be 0 mol%, 3 mol% or more, or 5 mol% or more.

[0037] The proportion of constituent units derived from (2-methoxyethoxy)ethylglycidyl ether in the ethylene oxide-based polymer may be 70 mol% or less, 59 mol% or less, or 39 mol% or less.

[0038] The proportion of constituent units derived from oxirane having ethylenically unsaturated groups in the ethylene oxide-based polymer may be 0 mol%, 1 mol% or more, 1.5 mol% or more, or 2 mol% or more.

[0039] The proportion of constituent units derived from oxirane having ethylenically unsaturated groups in the ethylene oxide-based polymer may be 20 mol% or less, 15 mol% or less, or 12 mol% or less.

[0040] The ethylene oxide-based polymer may be composed only of a constituent unit derived from ethylene oxide, a constituent unit derived from an alkylene oxide having 3 to 12 carbon atoms, a constituent unit derived from (2-methoxyethoxy)ethylglycidyl ether, and a constituent unit derived from an oxirane having an ethylenically unsaturated group, or it may be composed of additional constituent units derived from other monomers.

[0041] In an ethylene oxide-based polymer, the sum of the molar ratios of the constituent unit derived from ethylene oxide, the constituent unit derived from an alkylene oxide having 3 to 12 carbon atoms, the constituent unit derived from (2-methoxyethoxy)ethylglycidyl ether, and the constituent unit derived from an oxirane having an ethylenically unsaturated group is preferably 90 mol% or more with respect to the entire ethylene oxide-based polymer, more preferably 95 mol% or more, even more preferably 98 mol% or more, and particularly preferably 100 mol%.

[0042] The weight average molecular weight (Mw) of polystyrene equivalent obtained by gel permeation chromatography (GPC) of the polymer is not particularly limited, but, for example, it may be 1,000,000 or more, 1,200,000 or more and 5,000,000 or less, or 1,500,000 or more and 3,000,000 or less.

[0043] GPC measurements are performed at 60°C using RID-6A from Shimadzu Seisakusho Inc., SHODEX KD-807, KD-806, KD-806M and KD-803 columns from Showa Denko Inc., and DMF as the solvent.

[0044] Examples of lithium imide salts include LiN(Rf1SO2)2, LiN(FSO2)2, LiN(Rf1SO2)(Rf2SO2), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Among the above, it is preferable to include LiTFSI as the lithium imide salt from the perspective of battery performance. The lithium imide salt may be used as a single type or in combination of two or more types.

[0045] [Solid Sulfate Electrolytes]

[0046] As a sulfide solid electrolyte, it is preferable to contain sulfur (S) as the main component of the anionic element, and furthermore, it is preferable to contain, for example, Li element, A element, and S element.

[0047] Element A is at least one selected from the group consisting of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In.

[0048] The sulfide solid electrolyte may further contain at least one of O and a halogen element.

[0049] Examples of halogen elements (X) include F, Cl, Br, I, etc. The composition of the sulfide solid electrolyte is not particularly limited, and examples include xLi2S·(100-x)P2S5(70≤x≤80) and yLiI·zLiBr·(100-yz)(xLi2S·(1-x)P2S5)(0.7≤x≤0.8, 0≤y≤30, 0≤z≤30). The sulfide solid electrolyte may have a composition expressed by the following general formula (1).

[0050] Li 4-x Ge 1-x P x S4(0 <x<1) …식 (1)

[0051] In Equation (1), at least a portion of Ge may be substituted with at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. Also, at least a portion of P may be substituted with at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. A portion of Li may be substituted with at least one selected from the group consisting of Na, K, Mg, Ca, and Zn. A portion of S may be substituted with a halogen. As a halogen, it is at least one of F, Cl, Br, and I.

[0052] The sulfide solid electrolyte may be used alone or in combination with two or more types.

[0053] For example, from the perspective of battery performance, it is preferable that the sulfide solid electrolyte be a Li2S-P2S5-based sulfide solid electrolyte. If it is a Li2S-P2S5-based sulfide solid electrolyte, reaction products between the polymer and the sulfide solid electrolyte are likely to form at the contact surface, thereby hindering the conduction pathway. However, with the composition of the composite solid electrolyte of the present disclosure, the decrease in ionic conductivity is suppressed even in this case.

[0054] [Other ingredients]

[0055] The composite solid electrolyte according to the present disclosure may, if necessary and within the scope in which the effects of the present disclosure are exhibited, further include other components other than a polymer electrolyte comprising a sulfide solid electrolyte, a polymer, and a lithium imide salt. Examples of other components include, for instance, an oxide solid electrolyte, a halide solid electrolyte, a binder (e.g., a rubber-based binder, a fluoride-based binder, etc.), and a conductivity aid (e.g., a fibrous carbon material, etc.).

[0056] [Properties of the entire complex solid electrolyte]

[0057] The content of lithium imide salt relative to the polymer (100 parts by mass) in the polymer electrolyte is 40 mass% or more, and from the perspective of further suppressing the decrease in ion conductivity, it is preferable to be 300 mass% or more and 800 mass% or less, and more preferable to be 650 mass% or more and 750 mass% or less.

[0058] The content of lithium imide salt relative to the polymer (100 parts by mass) in the polymer electrolyte is preferably 900 mass% or less, more preferably 800 mass% or less, and even more preferably 750 mass% or less from the perspective of battery performance.

[0059] The volume ratio of the sulfide solid electrolyte to the polymer electrolyte (sulfide solid electrolyte / polymer electrolyte) is preferably 70 / 30 or higher and 98 / 2 or lower, more preferably 75 / 25 or higher and 97 / 3 or lower, and even more preferably 80 / 20 or higher and 95 / 5 or lower, in order to increase ionic conductivity and further suppress the decrease in ionic conductivity.

[0060] [Method for Manufacturing a Composite Solid Electrolyte]

[0061] The method for manufacturing the composite solid electrolyte of the present disclosure is not particularly limited, and known methods for manufacturing solid electrolytes may be applied. Examples of methods for manufacturing the composite solid electrolyte of the present disclosure include, for instance, a method of preparing a slurry by mixing a polymer electrolyte and a solid electrolyte material in a solvent, coating the slurry onto a substrate, and then drying the solvent to form a composite solid electrolyte layer; and a method of forming a composite solid electrolyte layer by bonding a polymer electrolyte layer and a sulfide solid electrolyte layer that have been prepared individually.

[0062] Solid-state battery

[0063] The solid-state battery of the present disclosure comprises the composite solid electrolyte of the present disclosure. The solid-state battery of the present disclosure comprises, for example, a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The solid electrolyte layer comprises the composite solid electrolyte of the present disclosure. The solid-state battery includes an all-solid-state battery using an inorganic solid electrolyte (in which the content of the electrolyte solution as the electrolyte is less than 5 mass% of the total amount of electrolyte).

[0064] The composite solid electrolyte of the present disclosure, even in a solid battery having an electrode (e.g., a negative electrode, more specifically, a negative electrode containing silicon) that is prone to swelling and shrinking, suppresses the decrease in ion conductivity caused by the reaction between the polymer in the sulfide solid electrolyte and the polymer in the polymer electrolyte due to friction in the solid electrolyte layer accompanying the swelling and shrinking of the electrode before and after storage.

[0065] The solid-state battery of the present disclosure is a solid-state lithium-ion secondary battery. Solid-state batteries can be used as power sources for vehicles, electronic devices, and electrical storage. Examples of vehicles include electric four-wheeled vehicles, electric two-wheeled vehicles, gasoline cars, diesel cars, etc. Examples of electric four-wheeled vehicles include electric vehicles (BEV), plug-in hybrid vehicles (PHEV), and hybrid vehicles (HEV). Examples of electric two-wheeled vehicles include electric bikes and electric assist bicycles. Examples of electronic devices include portable devices (e.g., smartphones, tablet computers, audio players, etc.), portable devices (e.g., laptop computers, CD (Compact Disc) players, etc.), and movable devices (e.g., power tools, professional video cameras, etc.). Among these, the application of the solid-state battery of the present disclosure is preferably as a power source for driving hybrid vehicles, plug-in hybrid vehicles, or electric vehicles.

[0066] Examples

[0067] <Examples 1 to 6, Comparative Examples 1 to 3>

[0068] (Fabrication of sulfide solid electrolytes)

[0069] Li2S-P2S5-based glass ceramics containing LiI were produced by ball mill mixing and firing.

[0070] (Preparation of polymer electrolyte solution)

[0071] An ethylene oxide-based polymer was synthesized by random copolymerization of ethylene oxide (EO), 2-(2-methoxyethoxy)ethylglycidyl ether (EM), and allylglycidyl ether (AGE). The obtained ethylene oxide-based polymer had a weight-average molecular weight of 2.37 million and a monomer molar ratio of EO / EM / AGE of 81.8 / 16.2 / 2.0. The ethylene oxide-based polymer was dissolved in acetonitrile together with LiTFSI to prepare a polymer electrolyte solution such that the mass ratio of the ethylene oxide-based polymer (PEO) to LiTFSI (PEO / LiTFSI) was the ratio shown in Table 1. The weight-average molecular weight and molar ratio of the polymer were measured by the method described above.

[0072] [Example of polymerization catalyst synthesis]

[0073] 10 parts by mass of tributyltin chloride and 35 parts by mass of tributylphosphate were placed in a 3-necked flask equipped with a stirrer, a thermometer, and a distillation apparatus, and heated at 250°C for 20 minutes while stirring under a nitrogen stream to remove the effluent by distillation, thereby obtaining a solid condensation material as a residue. The obtained condensation material was used as a polymerization catalyst in the following Polymerization Example 1.

[0074] [Polymerization Example 1 Polymer 1]

[0075] The interior of a 4-necked glass flask with a net volume of 3L was purged with nitrogen, and 1 part by mass of the condensation material obtained from the synthesis example of the polymerization catalyst above, 114 parts by mass of glycidyl ether compound (a) adjusted to a moisture content of 10 ppm or less, 10 parts by mass of allylglycidyl ether, 0.10 parts by mass of n-butanol, and 1,000 parts by mass of n-hexane as a solvent were added to it. While tracking the polymerization rate of compound (a) by gas chromatography, 136 parts by mass of ethylene oxide were sequentially added. The polymerization temperature was set to 20°C, and the reaction was carried out for 10 hours. The polymerization reaction was stopped by adding 1 mL of methanol. After extracting the polymer by decantation, it was dried at 40°C under atmospheric pressure for 24 hours and then at 45°C under reduced pressure for 10 hours to obtain 210 parts by mass of the polymer. The molar ratio of the obtained polymer was ethylene oxide / diethylene glycol methylglycidyl ether / allyl glycidyl ether (i.e., EO / EM / AGE) = 81.8 / 16.2 / 2.0 mol%, and the weight average molecular weight was 2.37 million.

[0076] (Fabrication of composite solid electrolytes)

[0077] The polymer electrolyte solution was placed in a mortar and dried on a hot plate at 100°C for 30 minutes to volatilize the solution. The sulfide solid electrolyte was then mixed with the polymer electrolyte such that the volume ratio of the sulfide solid electrolyte to the polymer electrolyte was as specified in Table 1, thereby producing the composite solid electrolytes of each example.

[0078] <Evaluation of Conductivity Retention Rate Before and After High-Temperature Storage>

[0079] (Measurement of conductivity before high-temperature storage)

[0080] In a glove box at a dew point of -80℃, weigh 100mg of complex solid electrolyte, place it in a Mako cylinder, and 6 ton / cm² 2It was pressed with [a specific pressure]. Both ends of the obtained pellet were clamped with SUS pins, and a restraining pressure was applied to the pellet by fastening with bolts to obtain an evaluation cell. The ionic conductivity at 25°C was calculated for the evaluation cell using the AC impedance method. For the measurement, a Solartron 1260 was used, with an applied voltage of 10 mV and a measurement frequency range of 0.1 Hz to 1 MHz. The results are shown in Table 1.

[0081] (Measurement of conductivity after high-temperature storage)

[0082] The evaluation cells of each example were placed in a glove box at 60°C for 3 days for a storage test. After the storage test, the ion conductivity of the evaluation cells of each example was measured using the method described above to obtain the ion conductivity before and after storage. The results are shown in Table 1.

[0083]

[0084] As shown in Table 1, it was found that the composite solid electrolyte of the example suppressed the decrease in ion conductivity compared to the composite solid electrolyte of the comparative example.

Claims

Claim 1 A composite solid electrolyte comprising a sulfide solid electrolyte and a polymer electrolyte comprising a polymer and a lithium imide salt, wherein the content of the lithium imide salt relative to the polymer in the polymer electrolyte is 300 mass% or more. Claim 2 In claim 1, the polymer is a composite solid electrolyte comprising an ethylene oxide-based polymer. Claim 3 A composite solid electrolyte according to claim 1, wherein the content of the lithium imide salt relative to the polymer in the polymer is 650 mass% to 900 mass%. Claim 4 A composite solid electrolyte according to claim 1, wherein the content of the lithium imide salt relative to the polymer in the polymer is 300 mass% to 900 mass%. Claim 5 A composite solid electrolyte according to claim 1, wherein the volume ratio of the sulfide solid electrolyte to the polymer electrolyte is 80 / 20 or more and 95 / 5 or less. Claim 6 A solid battery comprising a composite solid electrolyte as described in any one of claims 1 to 5.

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