Solid-liquid composite electrolyte including sulfide-based solid electrolyte and liquid electrolyte, and Semi-solid-state rechargeable batteries

Abstract

The invention relates to a solid-liquid composite electrolyte comprising a sulfide-based solid electrolyte and a liquid electrolyte, wherein the liquid electrolyte comprises a metal salt and a fluorinated organic solvent that dissolves the metal salt, and to a semi-solid secondary battery.

Description

Technology Field

[0001] This invention relates to a solid-liquid composite electrolyte comprising a sulfide-based solid electrolyte and a liquid electrolyte, and a semi-solid secondary battery. Background Technology

[0002] Conventional rechargeable batteries use flammable electrolytes, posing safety risks where the battery may explode or catch fire in the event of collisions or penetrations. Consequently, all-solid-state or semi-solid rechargeable batteries utilizing solid electrolytes instead of liquid electrolytes are being proposed. Batteries using solid electrolytes are safe as they eliminate the risk of explosions caused by electrolyte leakage. They also offer the advantage of facilitating the fabrication of thin-film batteries, and by enabling a reduction in negative electrode thickness, they improve high-speed charge / discharge performance and allow for high-voltage operation and high energy density. In particular, sulfide-based solid electrolytes 10 -2 to 10 -3 Since it can achieve high ionic conductivity at the S / cm level and excellent electrochemical stability, batteries applying this are being actively researched.

[0003] However, sulfide-based solid electrolytes have problems such as resistance occurring at the interface with solid particles, including the positive electrode active material, and a decrease in ion conductivity performance due to the formation of a depletion layer caused by the junction of solids.

[0004] Accordingly, research is being conducted to resolve the problems of solid electrolytes by manufacturing solid-liquid composite electrolytes through the addition of liquid electrolytes to sulfide-based solid electrolytes. However, existing studies attempting to composite sulfide-based solid electrolytes with liquid electrolytes have the following limitations. First, since liquid electrolytes generally exhibit strong polarity, there is a problem of chemical side reactions occurring at the interface between the sulfide-based solid electrolyte and the liquid electrolyte; second, there is a problem of high resistance to lithium ion movement at the interface between the sulfide-based solid electrolyte and the liquid electrolyte; and third, there is the low lithium ion yield (Li) of the liquid electrolyte. + There is a disadvantage that the single-ion conductivity is reduced due to the transference number, and fourth, there is a problem of loss of flame retardancy due to the introduction of a flammable liquid electrolyte, and fifth, existing composite electrolytes have a limitation that the interface between the electrolyte and the anode is unstable due to low high-voltage oxidation stability. The problem to be solved

[0005] We provide a solid-liquid composite electrolyte that is applicable to practical batteries by minimizing side reactions between sulfide-based solid and liquid electrolytes, maintaining high ionic conductivity, and ensuring oxidation stability, heat resistance, and flame retardancy, and we also provide a semi-solid secondary battery utilizing this electrolyte. means of solving the problem

[0006] In one embodiment, a solid-liquid composite electrolyte is provided, comprising a sulfide-based solid electrolyte and a liquid electrolyte, wherein the liquid electrolyte comprises a metal salt and a fluorinated organic solvent that dissolves the metal salt.

[0007] In another embodiment, a semi-solid secondary battery comprising a positive electrode, a negative electrode, and the solid-liquid composite electrolyte is provided. Effects of the invention

[0008] A solid-liquid composite electrolyte according to one embodiment has minimal side reactions between the sulfide-based solid electrolyte and the liquid electrolyte, can maintain high ionic conductivity, and simultaneously ensures oxidation stability, heat resistance, and flame retardancy, making it applicable to actual batteries and improving the reliability and lifespan characteristics of the battery. Brief explanation of the drawing

[0009] FIG. 1 is a schematic image of a semi-solid secondary battery according to one embodiment. Specific details for implementing the invention

[0010] Specific embodiments are described below in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0011] The terms used herein are for describing exemplary embodiments only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0012] Here, "combinations of these" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0013] The terms "include," "equip," or "have" used herein are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0014] The average particle size can be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by using transmission electron microscope or scanning electron microscope images. Alternatively, the average particle size value can be obtained by measuring using dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Unless otherwise defined, the average particle size is the diameter (D) of the particle at which the cumulative volume in the particle size distribution is 50 volume%. 50 It can mean ).

[0015] Here, “or” is not interpreted in an exclusive sense; for example, “A or B” is interpreted to include A, B, A+B, etc.

[0016] The term “metal” is interpreted as a concept that includes ordinary metals, transition metals, and metalloids (semimetals).

[0017] Solid-liquid composite electrolyte

[0018] A solid-liquid composite electrolyte according to one embodiment comprises a sulfide-based solid electrolyte and a liquid electrolyte, wherein the liquid electrolyte comprises a metal salt and a fluorinated organic solvent that dissolves the metal salt.

[0019] The above-mentioned solid-liquid composite electrolyte is a mixture or composite of a sulfide-based solid electrolyte and a liquid electrolyte, and can be described as a hybrid electrolyte or a mixed electrolyte. The solid electrolyte and the liquid electrolyte may be physically mixed with each other or may form chemical bonds. For example, the liquid electrolyte may be located in the voids between multiple solid electrolyte particles. Alternatively, the liquid electrolyte may be located on the surface of the solid electrolyte particles, and may be attached, adsorbed, connected, or bonded to at least a portion of the surface of the solid electrolyte particles; for example, it may wrap around the surface of the solid electrolyte particles in the form of a film.

[0020] liquid electrolyte

[0021] In a solid-liquid composite electrolyte according to one embodiment, the liquid electrolyte comprises a metal salt and a fluorinated organic solvent that dissolves the metal salt.

[0022] The biggest problem with combining sulfide-based solid electrolytes with liquid electrolytes is that the sulfide-based solid electrolyte and the liquid electrolyte chemically react to form a resistance layer, which in turn lowers ionic conductivity. This is because the solvent of the liquid electrolyte is primarily polar, and polar solvents interact strongly with sulfide-based solid electrolytes, easily causing side reactions. For example, when a liquid electrolyte in which 1M LiPF6 is dissolved in a carbonate-based solvent such as ethylene carbonate or propylene carbonate is combined with a sulfide-based solid electrolyte, it is confirmed that the reactivity between the liquid electrolyte and the solid electrolyte is high, leading to the formation of a resistance layer due to side reactions and a rapid decrease in ionic conductivity over time.

[0023] Accordingly, recent studies have focused on selecting non-polar solvents rather than polar solvents, or solvents that are chemically stable with sulfide-based solid electrolytes; however, analysis showed that even in these cases, the decrease in ionic conductivity over reaction time was not significantly reduced, or there were limitations to commercialization.

[0024] As another alternative, solvent-in-salt solutions have been proposed in which the ratio of the weight of the salt to the weight of the organic solvent is 1 or greater. For example, attempts have been made to prepare a liquid electrolyte by dissolving lithium salts such as LiTFSI and LiBETI in an organic solvent at a very high concentration and to composite it with a sulfide-based solid electrolyte. Although solvent-in-salt liquid electrolytes can be chemically stable due to minimal side reactions with sulfide-based solid electrolytes, their high cost limits their commercialization. Additionally, their high viscosity makes it difficult to impregnate into the voids between sulfide-based solid electrolyte particles and difficult to inject into the battery, resulting in poor processability.

[0025] As another alternative, a method was considered to mix ionic liquids with sulfide-based solid electrolytes by replacing the liquid electrolyte or adding them to the liquid electrolyte. However, while this approach may improve chemical stability, it presents problems such as a significant decrease in ionic conductivity over reaction time and reduced flame retardancy or heat resistance. Similarly, the high cost of ionic liquids limits their application in actual batteries.

[0026] Accordingly, we propose a composite electrolyte applicable to practical batteries by suppressing side reactions between sulfide-based solid and liquid electrolytes to improve ionic conductivity, as well as enhancing high-voltage oxidation stability, heat resistance, and flame retardancy, while ensuring economic feasibility.

[0027] Fluorinated organic solvents that dissolve metal salts

[0028] A liquid electrolyte according to one embodiment is characterized by using a fluorinated organic solvent, that is, an organic solvent substituted with one or more fluorines, as an organic solvent, and specifically using a fluorinated organic solvent capable of dissolving metal salts. The “fluorinated organic solvent dissolving metal salts” according to one embodiment has low reactivity with sulfide-based solid electrolytes, which can increase the chemical stability of the solid-liquid composite electrolyte and improve the ion conductivity retention rate over reaction time. In addition, since the solvent has high flame retardancy and high thermal stability, the problem of loss or degradation of flame retardancy due to the addition of the liquid electrolyte is prevented, thereby maintaining the fire safety advantage of using solid electrolytes. Furthermore, when applying the solvent, the viscosity of the liquid electrolyte is lower compared to salt solvents or high-concentration liquid electrolytes, making it advantageous for impregnation into the interior of solid electrolyte particles or into the anode or cathode, and improving processability. Furthermore, the solvent according to one embodiment has high oxidation stability, so there are few side reactions at the interface between the electrolyte and the anode even in a high voltage region, and accordingly, stable operation of the semi-solid battery is possible across the entire voltage range.

[0029] Dissolving a metal salt can mean, for example, that more than 0.1 moles or more than 0.5 moles of the metal salt are completely dissolved in 1 L of solvent, or that more than 0.1 moles or more than 0.5 moles of the metal salt are completely dissolved in 1 kg of solvent.

[0030] Specifically, when the metal salt is dissolved at a concentration of 1 m or more using only a fluorinated organic solvent capable of dissolving the metal salt as the sole solvent, the ionic conductivity of the solution is approximately 1 × 10⁻⁶ -4It may be greater than S / cm. This implies that the fluorinated organic solvent can dissolve the metal salt, is suitable for application to a solid-liquid composite electrolyte according to one embodiment, and achieves excellent ionic conductivity within the battery. For example, the ionic conductivity of a solution in which the metal salt is dissolved using only the fluorinated organic solvent capable of dissolving the metal salt as the sole solvent is 10 -2 S / cm to 10 -4 It can be S / cm, for example, 10 -2 S / cm to 10 -3 S / cm, or 10 -3 S / cm to 10 -4 It can be S / cm.

[0031] Here, the term "metal salt" refers to a salt containing a metal cation and an anion paired therewith, and may refer to a metal salt according to an embodiment specifically described below, and may be LiFSI (lithium bis(fluorosulfonyl)imide) as an example. Additionally, it may refer to an ionic conductivity value over a total concentration range of approximately 0.5 m to 20 m at a temperature of 25°C, and may be a value measured at a concentration of 1 m as an example. For example, when 1 m of LiFSI is dissolved using only a fluorinated organic solvent that dissolves the metal salt as the sole solvent, 10 -4 It can exhibit an ionic conductivity of S / cm or higher. Here, the ionic conductivity may be measured through electrochemical impedance spectroscopy (EIS), which may be analyzed, for example, under conditions of an amplitude of about 10 mV, a frequency of 1 MHz to 100 mHz, an air atmosphere, and 25°C.

[0032] The concentration of the solution in which the metal salt is dissolved using only a fluorinated organic solvent that dissolves the metal salt as the sole solvent may be 0.1 m or more, for example, 0.5 m or more, or 1 m or more. This means that if the concentration is 0.1 m or more, it can be defined as a solvent that dissolves the metal salt. Here, the concentration of the solution refers to the concentration at 25°C and atmospheric pressure. Specifically, the concentration of the solution in which the metal salt is dissolved using only a fluorinated organic solvent that dissolves the metal salt as the sole solvent may be 0.1 m to 20 m, 0.2 m to 20 m, 0.5 m to 20 m, or 1 m to 20 m. Here, the metal salt may refer to the metal salt according to one embodiment described below, and may be LiFSI as an example. That is, for example, when LiFSI is dissolved at 25°C and atmospheric pressure using a fluorinated organic solvent that dissolves the metal salt as a single solvent, the concentration may be 0.1 m or more or 0.5 m or more.

[0033] Fluorinated organic solvents that cannot dissolve metal salts may refer to solvents in which, for example, when a metal salt is mixed with the solvent, the concentration is measured to be less than about 0.1 m, so that the salt is not practically recognized as being dissolved. For example, studies have proposed adding highly fluorinated ethers that cannot dissolve metal salts, such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), to composite electrolytes. However, since they cannot practically dissolve the salt, they cannot be used as a single solvent and are difficult to regard as serving as a solvent for liquid electrolytes. Furthermore, there are problems in that it is difficult to ensure flame retardancy and oxidation stability and high costs are required because other existing organic solvents must be used as a basis.

[0034] A fluorinated organic solvent for dissolving a metal salt according to one embodiment may specifically include a fluorinated ether, a fluorinated phosphate, a fluorinated carbonate, or a combination thereof.

[0035] Such solvents may be substituted with one or more fluorine atoms in their chemical formula, but they may not be highly fluorinated compounds. For example, in a fluorinated organic solvent for dissolving a metal salt according to one embodiment, the ratio of the number of F atoms to the total number of H and F atoms in the chemical formula may be 20% to 60%, for example, 25% to 60%, 20% to 50%, or 20% to 45%. A solvent substituted with fluorine in such a ratio is advantageous for dissolving metal salts and is suitable for use as a solvent for a solid-liquid composite electrolyte according to one embodiment.

[0036] A fluorinated organic solvent for dissolving a metal salt according to one embodiment may be, as a specific example, fluorinated 1,2-diethoxyethane, and may be, for example, 1-(2,2,2-trifluoroethoxy)-2-ethoxyethane (F3DEE), 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE), 1-(2,2-difluoroethoxy)-2-(2,2,2-trifluoroethoxy)ethane (F5DEE), 1,2-bis(2,2,2-trifluoroethoxy)ethane (F6DEE), or a combination thereof. Or, specific examples of fluorinated organic solvents that dissolve the metal salt include 2,2,3,3-tetrafluoro-1,4-dimethoxybutane (FDMB), tris(2,2,2-trifluoroethyl)phosphate (TFEP), and 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane ( dioxaphospholane It may be 2-oxide (Cyclic TFEP), tris(3-fluoropropyl)phosphate (TFPP), fluoroethylene carbonate (FEC), or a combination thereof.

[0037] metal salts

[0038] Metal salts can be said to consist of metal cations and their paired anions.

[0039] In metal salts, the cation is Li + , Na + , K + , Mg 2+ , Al 3+ , Zn 2+ , or a combination thereof, for example, Li + , Na + , or a combination thereof, for example, Li + It could be.

[0040] In metal salts, the anion is Cl - , CH3COO - , NO3 - , BF4 - , ClO4 - , SO4 2- , OTf - , FSI - , NFSI - , PF6 - , TFSI - , BOB - DFOB - , or a combination thereof. Here, OTf is trifluoromethanesulfonate, FSI is bis(fluorosulfonyl)imide, NFSI is bis(nonafluorobutanesulfonyl)imide, TFSI is bis(trifluoromethanesulfonyl)imide, BOB is bis(oxalate)borate, and DFOB is difluorobis(oxalate)phosphate.

[0041] For example, the above anion is BF4 - , ClO4 - , OTf - , FSI - , TFSI - , or a combination of these.

[0042] Concentration of liquid electrolyte

[0043] The concentration of the liquid electrolyte according to one embodiment is not particularly limited. For example, the concentration of the liquid electrolyte may be 0.5 m to 20 m, and may be, for example, 0.5 m to 18 m, 0.5 m to 15 m, 0.5 m to 11 m, 0.5 m to 10 m, 0.5 m to 8 m, 0.5 m to 7 m, or 1 m to 5 m.

[0044] The liquid electrolyte according to one embodiment has very low reactivity with sulfide-based solid electrolytes even at low concentrations, such as salt solvents, and therefore, when combined with sulfide-based solid electrolytes, the ion conductivity retention rate over reaction time is very high, thereby enabling the realization of excellent performance of a semi-solid battery. Accordingly, the liquid electrolyte according to one embodiment can realize a composite electrolyte that is chemically stable, has high oxidation stability, and has a very high ion conductivity retention rate even in concentration ranges of 1 m to 5 m, or 1 m to 3 m, or molar concentrations of 0.5 M to 3 M, 0.8 M to 2.5 M, or 1 M to 2.3 M.

[0045] Other organic solvents

[0046] The above liquid electrolyte may additionally include other organic solvents as needed, in addition to the fluorinated organic solvent that dissolves the metal salt.

[0047] The other organic solvents mentioned above may include, for example, carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, aprotic solvents, or combinations thereof. One or more of the organic solvents may be mixed.

[0048] Carbonate-based solvents can be cyclic carbonates, chain carbonates, or combinations thereof. The additional inclusion of carbonate-based solvents can improve the ionic conductivity of solid-liquid composite electrolytes and ensure the strengths of carbonate-based solvents, such as oxidation stability, heat resistance, and flame retardancy, making them advantageous for application in actual batteries.

[0049] Carbonate-based solvents may include, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or a combination thereof.

[0050] In one example, the carbonate-based solvent may include vinylene carbonate or an ethylene carbonate-based compound. Here, the ethylene carbonate-based compound may include, for example, fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or a combination thereof. As an example, the ethylene carbonate-based compound may be a halogenated ethylene carbonate and may include, for example, fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, or a combination thereof.

[0051] Ester-based solvents may include, for example, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, valerolactone, caprolactone, or combinations thereof.

[0052] Ether-based solvents may include, for example, dibutyl ether, monoglame, diglame, triglame, tetraglame, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0053] Ether solvents may include, for example, glyme solvents, halogenated ether solvents, or combinations thereof. Halogenated ether solvents may be, for example, fluorinated ethers containing one or more fluorines.

[0054] Ketone-based solvents may include, for example, cyclohexanone. Alcohol-based solvents may include, for example, ethyl alcohol, isopropyl alcohol, or a combination thereof.

[0055] Aprotic solvents may include, for example, nitriles such as R-CN (where R is a C2 to C20 straight-chain, branched, or cyclic hydrocarbon group and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolenes such as 1,3-dioxolene, 1,4-dioxolene; sulfolenes; or combinations thereof.

[0056] Among aprotic solvents, nitrile-based solvents may include, for example, succinonitrile, adiponitrile, suberonitrile, sebaconitrile, decainedynitrile, dodecanedynitrile, or combinations thereof.

[0057] For example, the organic solvent may include carbonate-based solvents, ether-based solvents, nitrile-based solvents, or combinations thereof. Specifically, the organic solvent may include cyclic carbonate-based solvents, ethylene carbonate-based halogenated solvents, glycine-based solvents, ether-based halogenated solvents, nitrile-based solvents, or combinations thereof. These organic solvents can simultaneously ensure oxidation stability, heat resistance, and flame retardancy while improving the ionic conductivity of the composite electrolyte, and are advantageous for application in actual batteries.

[0058] Sulfide-based solid electrolytes

[0059] Sulfide-based solid electrolytes can be classified into crystalline and non-crystalline types depending on the presence or absence of a crystalline structure. The crystalline type is Li 3.25 Ge 0.25 P 0.75 Thio-LISICON of S4, etc., Li 10 GeP2S 12 Representative examples include agitide structures such as LGPS and Li6PS5Cl. Amorphous systems can be divided into glassy and glass-ceramic types based on differences in heat treatment temperatures; glassy types include, for example, 30Li2S·26B2S3·44LiO, 63Li2S·36SiS2·1Li3PO4, and 57Li2S·38SiS2·5Li4SiO4, while glass-ceramic types include, for example, Li 3.25 P 0.95 S4, Li7P3S 11 There are others.

[0060] Glassy sulfide-based solid electrolytes were actively developed by Professor Hayashi's research group in Japan. They reported that a glassy solid electrolyte was formed by mixing Li2S5 and P2S5 in a ratio of about 7:3 and performing amorphization through high-energy ball milling, and then synthesizing a glass-ceramic electrolyte through heat treatment at a low temperature, thereby achieving a high ionic conductivity of 10³ S / cm.

[0061] LGPS, one of the crystalline sulfide-based electrolytes, has been reported to exhibit a high ionic conductivity of 1.2 × 10² S / cm at room temperature. Since the report of LGPS, research involving the substitution of Ge with Si, Sn, or Al, or the substitution of S with Se, has proceeded explosively; while not all of these yielded higher ionic conductivity than LGPS, they offered advantages in terms of economics. Additionally, the azyrodite-type Li reported in 2016 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 It recorded ionic conductivity at the level of a liquid electrolyte, such as 2.5×10² S / cm.

[0062] Through various studies like these, sulfide-based solid electrolytes have shown progress in terms of improving ionic conductivity. Additionally, sulfide-based solid electrolytes exhibit high thermal safety, resulting in a low risk of fire caused by thermal runaway. Nevertheless, sulfide-based solid electrolytes have high reactivity with moisture, leading to the formation of H2S upon exposure to the atmosphere and resulting in poor stability in air. Furthermore, the unstable interface at the contact between the cathode active material and the sulfide-based solid electrolyte leads to a degradation in lifespan characteristics, and since the electrolyte is solid, interfacial resistance between the electrode and the electrolyte is unavoidable. For these reasons, various studies are being conducted to improve not only ionic conductivity but also reactivity with moisture and interfacial stability of sulfide-based solid electrolytes, with the aim of commercializing them.

[0063] Sulfide-based solid electrolytes may be classified into structures such as azirodite, binary structures such as Li2S-P2S5, and ternary structures such as Li2S-GeS2-P2S5.

[0064] In a composite electrolyte according to one embodiment, the sulfide-based solid electrolyte may be an azirodite-type sulfide-based solid electrolyte. Azirodite is one of the solid electrolytes that exhibits lithium ion conductivity while having the same structure as the ore Ag9GeS6. Li + Representative conductive Li-azirodites include Li7PS6 and Li6PS5X (X=Cl, Br, I). Synthesis methods for azirodite-type sulfide-based solid electrolytes generally include mechanical milling, annealing after milling, solid sintering, and liquid-phase methods. However, azirodite-type sulfide-based solid electrolytes are sensitive to air and humidity, making synthesis conditions difficult. Furthermore, safety issues arise due to the use of organic solvents, and problems regarding the degradation of electrolyte performance are raised due to low solubility of reactants and incomplete reaction mechanisms.

[0065] Li7PS6, an azyrodite type, has been reported to possess a cubic phase at high temperatures and an orthorhombic phase at low temperatures, with the cubic phase at high temperatures potentially exhibiting enhanced ionic conductivity. This compound can be stabilized by replacing sulfur with halogen anions. The substitution of halogen elements forms vacancies in the lithium site portions within the azyrodite unit cell, thereby improving lithium ion conductivity. Furthermore, due to the substitution of halogen ions, the cubic phase is stabilized even at room temperature; for example, Li6PS5Br and Li6PS5Cl are 10 -3 It can exhibit high ionic conductivity of S / cm or higher. Azirodite-type sulfide-based solid electrolytes include, for example, Li7PS5Br, Li5PS4Cl2, Li6PS5Cl, Li6PS5Br, Li6PS5I, Li7P2S8I, Li4PS4I, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li7P 2.9 Mn0.1 S 10.7 I 0.3 , or a combination thereof may be included, but is not limited thereto.

[0066] Sulfide-based solid electrolytes are in the form of particles, and the average particle size (D 50 The ) can be 5.0 μm or less, for example, 0.1 μm to 5.0 μm, 0.5 μm to 5.0 μm, 0.5 μm to 4.0 μm, 0.5 μm to 3.0 μm, 0.5 μm to 2.0 μm, or 0.5 μm to 1.0 μm. Such sulfide-based solid electrolytes can achieve high ionic conductivity and have excellent contact with the cathode active material and connectivity between solid electrolyte particles.

[0067] Other solid electrolytes

[0068] A solid-liquid composite electrolyte according to one embodiment may further include other types of solid electrolytes in addition to sulfide-based solid electrolytes, for example, oxide-based solid electrolytes, halide-based solid electrolytes, hydride composites, or combinations thereof.

[0069] Oxide-based solid electrolytes are, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≤x≤4), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3)O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Lithium Phosphate (Li3PO4), Lithium Titanium Phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), Li 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 (0≤x≤1, 0≤y≤1), lithium lanthanum titanate (Li x La y TiO3, 0 <x<2, 0<y<3), Li2O, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2세라믹스, 가넷형 세라믹스 Li 3+x La3M2O 12 (M=Te, Nb, or Zr, and x is an integer from 1 to 10), or may include a combination thereof.

[0070] A halide-based solid electrolyte contains a halogen element as a main component, and the ratio of the halogen element to all elements constituting the solid electrolyte may be 50 mol% or more, 70 mol% or more, 90 mol% or more, or 100 mol%. As an example, the halide-based solid electrolyte may not contain a sulfur element.

[0071] Halide-based solid electrolytes may contain lithium elements, metal elements other than lithium, and halogen elements. Metal elements other than lithium may be, for example, Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or combinations thereof. Halogen elements may be F, Cl, Br, I, or combinations thereof, and for example, Cl, Br, or combinations thereof. Halide-based solid electrolytes may be, for example, Li a It can be represented as M1X6 (M is Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof, X is F, Cl, Br, I, or a combination thereof, and 2≤a≤3). Halide-based solid electrolytes are, for example, Li2ZrCl6, Li 2.7 Y 0.7 Zr 0.3 Cl6, Li 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.5 In 0.5 Zr 0.5 Cl6, Li2In 0.5 Zr 0.5 Cl6, Li3YBr6, Li3YCl6, Li3YBr2Cl4, Li3YbCl6, Li 2.6 Hf 0.4 Yb 0.6 It may include Cl6, or a combination thereof, but is not limited thereto.

[0072] Complex hydrides are, for example, metal cations (M) and M'H n Composed of complex anions of the form (MM'H n) may be. The metal cation (M) may be, for example, Li, Na, K, Mg, Sc, Cu, Zn, Zr, or Hf, and the complex anion may be [BH4] - , [NH2] - , [AlH4] - , [NH] 2- , [AlH6] 3- , or [NiH4] 4- It may be. For hydride complexes, refer to the literature “M. Matsuo, S.-i. Orimo, Adv. Energy Mater. 2011, 1, 161”.

[0073] The ratio of solid to liquid

[0074] In one embodiment, with respect to 100 volume% of the solid-liquid composite electrolyte, the sulfide-based solid electrolyte may be included in an amount of 10 volume% to 99.99 volume% and the liquid electrolyte may be included in an amount of 0.01 volume% to 90 volume%. For example, with respect to 100 volume% of a solid-liquid composite electrolyte, the sulfide-based solid electrolyte may be included in an amount of 30 volume% to 99.99 volume%, 40 volume% to 99.99 volume%, 50 volume% to 99.99 volume%, 60 volume% to 99.99 volume%, 70 volume% to 99.9 volume%, 80 volume% to 99.5 volume%, 90 volume% to 99 volume%, 95 volume% to 98 volume%, or 90 volume% to 95 volume%, and the liquid electrolyte may be included in an amount of 0.01 volume% to 70 volume%, 0.01 volume% to 60 volume%, 0.01 volume% to 50 volume%, 0.01 volume% to 40 volume%, 0.1 volume% to 30 volume%, 0.5 volume% to 20 volume%, or 1 volume% to It may be included in 10 volume%, 2 to 5 volume%, or 5 to 10 volume%.

[0075] The weight ratio of the sulfide-based solid electrolyte to the liquid electrolyte may vary depending on the concentration of the liquid electrolyte. For example, with respect to 100 weight% of a solid-liquid composite electrolyte, the sulfide-based solid electrolyte may be included in an amount of 50 weight% to 99.99 weight% and the liquid electrolyte may be included in an amount of 0.01 weight% to 50 weight%. For example, with respect to 100 wt% of a solid-liquid composite electrolyte, the sulfide-based solid electrolyte may be included in an amount of 30 wt% to 99.99 wt%, 40 wt% to 99.99 wt%, 50 wt% to 99.99 wt%, 60 wt% to 99.99 wt%, 70 wt% to 99.99 wt%, 80 wt% to 99.99 wt%, 90 wt% to 99.99 wt%, 95 wt% to 99.99 wt%, 99 wt% to 99.99 wt%, 90 wt% to 99.9 wt%, or 90 wt% to 99 wt%, and the liquid electrolyte may be included in an amount of 0.01 wt% to 70 wt%, 0.01 wt% to 60 wt%, 0.01 wt% to 50 wt%, or 0.01 wt% to It may be included in 40 wt%, 0.01 wt% to 30 wt%, 0.01 wt% to 20 wt%, 0.01 wt% to 10 wt%, 0.01 wt% to 5 wt%, 0.01 wt% to 1 wt%, 0.1 wt% to 10 wt%, or 1 wt% to 10 wt%, etc.

[0076] In solid-liquid composite electrolytes, if the liquid electrolyte content is excessive, loss of flame retardancy caused by the liquid electrolyte may occur or there may be an inherent risk of battery explosion, potentially failing to ensure battery safety. Conversely, if the liquid electrolyte content is too low, the disadvantages of the solid electrolyte may not be overcome, leading to a decrease in ionic conductivity or a deterioration in lifespan characteristics. When the sulfide-based solid electrolyte and liquid electrolyte satisfy the aforementioned content ranges, the composite formation of the solid and liquid is facilitated, high ionic conductivity can be maintained, and battery safety can be ensured.

[0077] In one embodiment, even if the amount of liquid electrolyte relative to the amount of sulfide-based solid electrolyte is applied in a very small amount, problems such as a decrease in ion conductivity or an increase in resistance due to the solid electrolyte can be effectively resolved, and high-voltage oxidation stability, flame retardancy, and safety can be achieved while maintaining excellent ion conductivity. For example, regarding 100 volume% of the solid-liquid composite electrolyte, the liquid electrolyte may be included in an amount of 15 volume% or less, 10 volume% or less, 5 volume% or less, or 1 volume% or less. In this case, the composite formation of the sulfide-based solid electrolyte and the liquid electrolyte is easy, and safety due to the solid electrolyte can be secured while simultaneously improving ion conductivity, oxidation safety, and lifespan characteristics through the liquid electrolyte according to one embodiment.

[0078] Other ingredients

[0079] The composite electrolyte according to one embodiment may further include other binders, organic dispersants, ionic liquids, conductive polymers, additives, etc.

[0080] The binder may include, for example, nitrile-butadiene rubber, hydrogenated nitrile-butadiene rubber, styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, natural rubber, polydimethylsiloxane, polyethylene oxide, polyvinylpyrrolidone, polyvinylpyridine, chlorosulfonated polyethylene, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, copolymers thereof, or combinations thereof.

[0081] A solid-liquid composite electrolyte according to one embodiment may be in the form of a pellet or a membrane. The solid-liquid composite electrolyte may be applied to various locations within a battery, for example, it may be mixed with a positive electrode active material to form a positive electrode, may form a solid electrolyte membrane, or may be mixed with a negative electrode active material to form a negative electrode.

[0082] Complex electrolyte membrane

[0083] In one embodiment, a composite electrolyte membrane comprising the aforementioned solid-liquid composite electrolyte may be provided. The thickness of the composite electrolyte membrane may be, for example, 20 μm to 1000 μm, 20 μm to 800 μm, 20 μm to 700 μm, or 200 μm to 600 μm. The composite electrolyte membrane according to one embodiment is positioned between the anode and the cathode to achieve high ionic conductivity while ensuring battery safety and improving the lifespan and rate characteristics of the battery.

[0084] Semi-solid secondary battery

[0085] In one embodiment, a semi-solid secondary battery comprising a positive electrode, a negative electrode, and the aforementioned solid-liquid composite electrolyte is provided. In this case, the solid-liquid composite electrolyte may be located between the positive electrode and the negative electrode. However, the liquid electrolyte in the solid-liquid composite electrolyte may be impregnated not only within the solid-liquid composite electrolyte but also within the positive electrode and / or the negative electrode.

[0086] For the sake of understanding, the shape of a semi-solid secondary battery according to one example is shown in FIG. 1. FIG. 1 shows a single electrode assembly including a negative electrode, a composite electrolyte membrane, and a positive electrode, but a semi-solid secondary battery can also be fabricated by stacking two or more electrode assemblies.

[0087] cathode

[0088] The cathode may be a general cathode containing various cathode active materials such as carbon-based or silicon-based materials, or it may be a cathode made of a metal such as lithium metal, or it may be a precipitation-type cathode in which no cathode active material is present initially but lithium metal, etc., precipitates upon charging to act as the cathode active material.

[0089] For example, the cathode may include a current collector and a cathode active material layer located on the current collector. The cathode active material layer may include a cathode active material, further include a binder and / or a conductive material, and optionally include the aforementioned composite electrolyte.

[0090] The negative electrode active material may include a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0091] A material capable of reversibly intercalating / deintercalating lithium ions is a carbon-based negative electrode active material, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include natural graphite, artificial graphite, or a combination thereof, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc. The carbon-based negative electrode active material may be amorphous, plate-like, flake-like, spherical, or fibrous.

[0092] As the above lithium metal alloy, an alloy of a metal selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0093] As a material capable of doping and undoping the above lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used, and the Si-based negative electrode active material may include silicon, a silicon-carbon composite, or SiO₂. x(0 <x<2), 실리콘 합금 등이 있으며, Sn계 음극 활물질로는 Sn, SnO2, 주석 합금 등을 들 수 있고, 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 일 예로 음극 활물질은 실리콘과 탄소의 복합체를 포함할 수도 있다.

[0094] The binder may include a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0095] Examples of water-insoluble binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0096] Examples of water-soluble binders include rubber-based binders or polymer resin binders. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0097] When a water-soluble binder is used as the cathode binder, a cellulose-based compound may be further included as a type of thickener. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be used in a mixture. Na or Li may be used as the alkali metal.

[0098] The conductive material may be a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjenblack, carbon fiber, carbon nanofiber, carbon nanotube, etc., or a metal-based material in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc., or a conductive polymer such as a polyphenylene derivative, or a mixture thereof.

[0099] anode

[0100] The positive electrode may include a current collector and a positive active material layer located on the current collector, and the positive active material layer may include a positive active material and optionally include a solid electrolyte. The positive active material layer may optionally further include a binder and / or a conductive material.

[0101] positive electrode active material

[0102] The positive electrode active material can be applied without limitation as long as it is commonly used in secondary batteries. For example, the positive electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium, and may include, for instance, a lithium transition metal complex oxide.

[0103] The positive electrode active material may include, for example, lithium nickel-based oxide, lithium cobalt-based oxide, lithium manganese-based oxide, lithium iron phosphate-based compound, cobalt-free nickel-manganese-based oxide, or a combination thereof, and may include, for example, lithium nickel oxide (LNO), lithium cobalt oxide (LCO), lithium nickel cobalt oxide (NC), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium nickel manganese oxide (NM), lithium manganese oxide (LMO), lithium iron phosphate oxide (LFP), or a combination thereof.

[0104] The positive active material may be included in an amount of 55% to 99.5% by weight with respect to 100% by weight of the positive active material layer, for example, 65% to 95% by weight, or 75% to 91% by weight.

[0105] bookbinder

[0106] The binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. Representative examples include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto. The content of the binder in 100 weight% of the positive active material layer may be approximately 0.1 weight% to 5 weight%.

[0107] Challenge

[0108] The conductive material may include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof. The content of the conductive material in 100 weight% of the positive active material layer may be 0 weight% to 3 weight%, 0.01 weight% to 2 weight%, etc.

[0109] The positive active material layer may further include the aforementioned solid-liquid composite electrolyte in addition to the positive active material, binder, and conductive material, in which case the solid-liquid composite electrolyte may be included in an amount of 0.1% to 45% by weight with respect to 100% by weight of the positive active material layer, for example, 1% to 35% by weight, 5% to 30% by weight, 8% to 25% by weight, or 10% to 20% by weight.

[0110] The shape of the semi-solid secondary battery is not particularly limited and may be, for example, coin type, button type, sheet type, stacked type, cylindrical type, etc. The semi-solid secondary battery according to one embodiment can be applied to various electronic devices and can also be applied to electric vehicles or power storage devices.

[0111] Examples and comparative examples of the present invention are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0112] Example 1

[0113] 1. Preparation of Solid-Liquid Composite Electrolytes

[0114] 150 mg of azirodite-type sulfide-based solid electrolyte (Li6PS5Cl) was prepared, pressurized at 370 MPa for 1 minute, and then stabilized at 74 MPa for 12 hours to obtain a thickness of approximately 600 µm or less and an area of ​​1.33 cm² 2 Phosphorus solid electrolyte pellets were fabricated.

[0115] A liquid electrolyte was prepared by dissolving LiFSI at a molal concentration of 1 m in the organic solvent 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE).

[0116] A solid-liquid composite electrolyte was prepared by dropping 40 µL of liquid electrolyte onto a prepared solid electrolyte pellet and stabilizing it at 74 MPa for 10 minutes. At this time, the volume of the liquid electrolyte relative to 100 vol% of the solid-liquid composite electrolyte is approximately 10 vol%.

[0117] 2. Manufacture of semi-solid secondary batteries

[0118] LiNi 0.7 Co 0.15 Mn 0.15 An anode composition was prepared by mixing 76.8 wt% of O2 anode active material, 19.2 wt% of solid electrolyte Li6PS5Cl, 2 wt% of polyvinylidene fluoride binder, and 2 wt% of conductive material, and an anode was manufactured by coating the composition onto an aluminum anode current collector, followed by drying and rolling.

[0119] A semi-solid secondary battery was manufactured by stacking a solid-liquid composite electrolyte on a lithium metal anode and stacking an anode on top of it to produce a unit cell, placing it in a laminate film, and applying a hydrostatic press.

[0120] Examples 2 to 10 and Comparative Examples 1 to 13

[0121] A solid-liquid composite electrolyte was prepared in substantially the same manner as in Example 1, except that the type and concentration of the organic solvent and metal salt of the liquid electrolyte were changed as shown in Table 1 below.

[0122] Evaluation Example 1: Evaluation of Changes in Ionic Conductivity

[0123] In the solid-liquid composite electrolytes of Examples 1 to 10 and Comparative Examples 1 to 13, the ionic conductivity was measured 72 hours after adding each liquid electrolyte to the sulfide-based solid electrolyte, and the ionic conductivity (σ) of the sulfide-based solid electrolyte SE Ionic conductivity of the complex electrolyte after 72 hours compared to ) (σ HE The ratio of ) was calculated and shown in Table 1 below.

[0124] Liquid electrolyte composition Standardized ionic conductivity (σ) after 72 hours HE / σ SE ) Example 1 1 m LiFSI in F4DEE 1.3851 Example 2 1 m LiTFSI in F4DEE 1.1798 Example 3 1 m LiPF6in F4DEE 1.3405 Example 4 1 m LiFSI in FDMB 1.0372 Example 5 1 m LiFSI in TFEP 1.2044 Example 6 1 m LiTFSI in TFEP 1.0427 Example 7 1 m LiBF4in TFEP 1.1986 Example 8 3m LiFSI in PC / FEC (v / v=93 / 7) 1.0395 Example 9 5.5 m LiFSI in PC / FEC 1.1474 Example 10 2 m LiTFSI in PC / FEC 1.0163 Comparative Example 1 4.3 m LiTFSI in G1 0.8043 Comparative Example 2 4.3 m LiBF4in G1 0.8452 Comparative Example 3 1 M LiTFSI in G3 0.55 Comparative Example 4 TTE (Harry X) 0.79 Comparative Example 5 1 m LiFSI in EC / PC (v / v=1 / 1) 0.9421 Comparative Example 6 1 m LiTFSI in EC / PC 0.7022 Comparative Example 7 2 m LiTFSI in EC / PC 0.9165 Comparative Example 8 4.3 m LiTFSI in EC / PC 0.7468 Comparative Example 9 1 m LiBF4in EC / PC 0.4276 Comparative Example 10 2 m LiBF4in EC / PC 0.7705 Comparative Example 11 4.3 m LiBF4in EC / PC 0.8485 Comparative Example 12 4.3 m LiBF4in SBN 0.8573 Comparative Example 13 6 m LiBF4in SBN 0.9581

[0125] In Table 1, F4DEE is 1,2-bis(2,2-difluoroethoxy)ethane, FDMB is 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, TFEP is tris(2,2,2-trifluoroethyl)phosphate, PC is propylene carbonate, FEC is fluoroethylene carbonate, G1 is dimethoxyethane, G3 is triethylene glycol dimethyl ether, TTE is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, EC is ethylene carbonate, and SBN is suberonitrile.

[0126] Referring to Table 1, it can be seen that the composite electrolytes of Examples 1 to 10 satisfy a ratio of ionic conductivity after 72 hours relative to the ionic conductivity of the sulfide-based solid electrolyte, which is greater than 1. In other words, this means that the composite electrolytes of the examples achieve higher ionic conductivity than the ionic conductivity of the solid electrolyte itself. It is interpreted that the liquid electrolytes used in the examples have low viscosity, allowing them to be effectively impregnated into the pores between the solid electrolyte particles, thereby further improving the ionic conductivity performance. Additionally, it is understood that the liquid electrolytes of the examples have low reactivity with the sulfide-based solid electrolyte, so the tendency for the sulfide-based solid electrolyte to deteriorate due to side reactions or other factors is very low even after 72 hours of composite formation, and consequently, high ionic conductivity can be maintained for a long time.

[0127] In the case of the composite electrolytes of the comparative examples, the reactivity between the added liquid electrolyte and the sulfide-based solid electrolyte was generally high, resulting in lower ionic conductivity compared to the sulfide-based solid electrolyte itself. In the case of Comparative Example 4, the lithium salt did not dissociate in the TTE solvent; therefore, the change in ionic conductivity was evaluated by adding only the TTE solvent to the solid electrolyte. After 72 hours, the ionic conductivity ratio was found to be low at 0.79, which is attributed to the reactivity of the TTE solvent with the sulfide-based solid electrolyte, causing a decrease in ionic conductivity. In the cases of Comparative Examples 1, 2, 8, 11 to 13, the concentration of the liquid electrolyte was high at 4.3 m or higher. Not only was the ionic conductivity of the composite electrolyte lower than that of the solid electrolyte itself after 72 hours, but the high viscosity of the liquid electrolyte also reduced processability, and the use of an excessive amount of lithium salt increased costs, thus limiting commercialization. In addition, for example, when a liquid electrolyte is prepared by dissociating a lithium salt at a high concentration of 15.5 m in a G1 solvent, the reactivity with the sulfide-based solid electrolyte can be reduced, but the concentration of the liquid electrolyte is too high, making it difficult to inject into the battery, which reduces processability and increases costs due to the use of an excessive amount of lithium salt, making it difficult to apply in actual industry.

[0128] Evaluation Example 2: Oxidation Stability Evaluation

[0129] Meanwhile, for each of the liquid electrolytes used in Examples 1, 4, 8, 9 and Comparative Example 1, the current density characteristics according to voltage were analyzed using Linear Sweep Voltammetry (LSV). The voltage range at which the current density rapidly increases was approximately 4.3 V for Comparative Example 1, whereas it was analyzed to be 5.2 V for Example 1, 5.2 V for Example 4, 5.1 V for Example 8, and 5.4 V for Example 9. Through this, it can be confirmed that the high-voltage oxidation stability of the liquid electrolyte applied to the composite electrolytes of the examples is superior, and that stable operation of the semi-solid battery is possible even in the high-voltage region.

[0130] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts defined in the following claims are also included within the scope of the present invention.

Claims

Claim 1 A solid-liquid composite electrolyte comprising a sulfide-based solid electrolyte and a liquid electrolyte, wherein the liquid electrolyte comprises a metal salt and a fluorinated organic solvent that dissolves the metal salt, and the fluorinated organic solvent that dissolves the metal salt is a solvent capable of dissolving the metal salt alone, and wherein 0.1 mole or more of the metal salt is dissolved in 1 L of the fluorinated organic solvent at 25°C and atmospheric pressure. Claim 2 In claim 1, the ionic conductivity of the solution in which the metal salt is dissolved using only the fluorinated organic solvent that dissolves the metal salt as the sole solvent is 1×10 -4 Solid-liquid composite electrolyte with a S / cm or greater. Claim 3 A solid-liquid composite electrolyte according to claim 1, wherein the concentration of the solution in which the metal salt is dissolved using only a fluorinated organic solvent that dissolves the metal salt is 0.1 m or more. Claim 4 In claim 1, the fluorinated organic solvent dissolving the metal salt is a solid-liquid composite electrolyte comprising a fluorinated ether, a fluorinated phosphate, a fluorinated carbonate, or a combination thereof. Claim 5 In claim 1, the fluorinated organic solvent dissolving the metal salt is a solid-liquid composite electrolyte in which the ratio of the number of F to the total number of H and F in the chemical formula is 20% to 60%. Claim 6 In claim 1, the fluorinated organic solvent dissolving the metal salt is 1-(2,2,2-trifluoroethoxy)-2-ethoxyethane (F3DEE), 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE), 1-(2,2-difluoroethoxy)-2-(2,2,2-trifluoroethoxy)ethane (F5DEE), 1,2-bis(2,2,2-trifluoroethoxy)ethane (F6DEE), 2,2,3,3-tetrafluoro-1,4-dimethoxybutane (FDMB), tris(2,2,2-trifluoroethyl)phosphate (TFEP), 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane 2-oxide (Cyclic TFEP), Solid-liquid composite electrolyte that is tris(3-fluoropropyl)phosphate (TFPP), fluoroethylene carbonate (FEC), or a combination thereof. Claim 7 In claim 1, the cation in the metal salt is Li + , Na + , K + , Mg 2+ , Al 3+ , Zn 2+ , or a combination thereof, and the anion is Cl - , CH3COO - , NO3 - , BF4 - , ClO4 - , SO4 2- , OTf - , FSI - , NFSI - , PF6 - , TFSI - , BOB - DFOB - , or a combination thereof, a solid-liquid composite electrolyte. Claim 8 A solid-liquid composite electrolyte according to claim 1, wherein the molal concentration of the liquid electrolyte is 0.5 m to 20 m. Claim 9 In claim 1, the liquid electrolyte further comprises another organic solvent in addition to the fluorinated organic solvent that dissolves the metal salt, and the other organic solvent comprises a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, an aprotic solvent, or a combination thereof, forming a solid-liquid composite electrolyte. Claim 10 In claim 1, the sulfide-based solid electrolyte is in the form of particles, and the average particle size (D 50 ) is a solid-liquid composite electrolyte with a particle size of 0.1 μm to 5 μm. Claim 11 In claim 1, the sulfide-based solid electrolyte is a solid-liquid composite electrolyte that is an azirodite-type sulfide-based solid electrolyte. Claim 12 In claim 1, the solid-liquid composite electrolyte further comprises an oxide-based solid electrolyte, a halide-based solid electrolyte, a hydride composite, or a combination thereof. Claim 13 A solid-liquid composite electrolyte according to claim 1, wherein, with respect to 100 volume% of the solid-liquid composite electrolyte, the sulfide-based solid electrolyte is included in an amount of 10 volume% to 99.99 volume% and the liquid electrolyte is included in an amount of 0.01 volume% to 90 volume%. Claim 14 A solid-liquid composite electrolyte according to claim 1, wherein, with respect to 100 volume% of the solid-liquid composite electrolyte, the sulfide-based solid electrolyte is included in an amount of 70 volume% to 99.99 volume% and the liquid electrolyte is included in an amount of 0.01 volume% to 30 volume%. Claim 15 A solid-liquid composite electrolyte according to claim 1, wherein, with respect to 100 volume% of the solid-liquid composite electrolyte, the sulfide-based solid electrolyte is included in an amount of 85 volume% to 99 volume% and the liquid electrolyte is included in an amount of 1 volume% to 15 volume%. Claim 16 In claim 1, the solid-liquid composite electrolyte comprises a plurality of sulfide-based solid electrolyte particles and a liquid electrolyte located in the voids between the particles. Claim 17 A semi-solid secondary battery comprising a positive electrode, a negative electrode, and a solid-liquid composite electrolyte according to any one of claims 1 to 16. Claim 18 A semi-solid secondary battery according to claim 17, wherein the solid-liquid composite electrolyte is located between the anode and the cathode, and the liquid electrolyte is impregnated not only within the solid-liquid composite electrolyte but also within the anode and / or cathode. Claim 19 A semi-solid secondary battery according to claim 17, wherein the positive electrode comprises a positive active material containing a lithium transition metal composite oxide, and the negative electrode comprises a carbon-based negative active material or lithium metal. Claim 20 A solid-liquid composite electrolyte according to claim 1, wherein the ratio of the ionic conductivity of the solid-liquid composite electrolyte to the ionic conductivity of the sulfide-based solid electrolyte alone is greater than 1.

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