Electrolyte for secondary batteries, method for manufacturing the same, and lithium secondary battery containing the same

Abstract

The electrolyte for a lithium secondary battery according to embodiments of the present disclosure may include a lithium salt, a composite membrane comprising an inorganic electrolyte and an organic binder, and a flame-retardant polymer electrolyte. The lithium secondary battery according to embodiments of the present disclosure may include a positive electrode, a negative electrode facing the positive electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode and containing an electrolyte for a secondary battery.

Description

[Technical Field]

[0001] This disclosure relates to an electrolyte for secondary batteries, a method for manufacturing the same, and a lithium secondary battery containing the same, and more particularly to an electrolyte for secondary batteries containing an inorganic electrolyte, a method for manufacturing the same, and a lithium secondary battery containing the same. [Background technology]

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged, and with the development of the information and communication and display industries, they are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop computers. More recently, battery packs containing rechargeable batteries have also been developed and applied as power sources for environmentally friendly vehicles such as hybrid cars.

[0003] Examples of secondary batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among these, lithium-ion batteries are being actively researched and developed due to their high operating voltage and energy density per unit weight, as well as advantages in charging speed and weight reduction.

[0004] Currently available lithium-ion batteries primarily use liquid electrolytes, which poses safety problems such as leakage, ignition, and explosion due to rapid environmental changes like temperature fluctuations and external shocks. To address these issues, research is underway to solidify the electrolyte to ensure stability and improve energy density.

[0005] All-solid-state batteries can contain solid-state electrolytes such as gel polymers, oxides or sulfides, or composite polymers. This enhances stability against ignition and explosion caused by external shocks, changes in the external environment, etc.

[0006] The electrolyte for a secondary battery, its manufacturing method, and the lithium secondary battery according to the present disclosure can be widely applied to fields of green technologies such as electric vehicles, battery charging stations, and other uses of batteries for solar power generation, wind power generation, etc. Further, the electrolyte for a secondary battery, its manufacturing method, and the lithium secondary battery according to the present disclosure can be used for environmentally friendly (eco-friendly) electric vehicles (electric vehicle), hybrid vehicles, etc. that suppress air pollution and greenhouse gas emissions and aim to prevent climate change.

Summary of the Invention

Problems to be Solved by the Invention

[0007] One problem of the present disclosure is to provide an electrolyte for a secondary battery with improved mechanical properties and high-temperature stability.

[0008] One problem of the present disclosure is to provide a manufacturing method for an electrolyte for a secondary battery with improved mechanical properties and high-temperature stability.

[0009] One problem of the present disclosure is to provide a lithium secondary battery with improved electrochemical stability.

Means for Solving the Problems

[0010] The electrolyte for a secondary battery according to an exemplary embodiment can include a lithium salt, a composite film containing an inorganic electrolyte and an organic binder, and a flame retardant Polyelectrolyte and. The content of the inorganic electrolyte in the total volume of the composite film may be 50% to 95% by volume.

[0011] In some embodiments, the inorganic electrolyte can include an oxide-based solid electrolyte.

[0012] In some embodiments, the content of the organic binder in the total volume of the composite film may be 5% to 50% by volume.

[0013] In some embodiments, the volume ratio of the organic binder content to the inorganic electrolyte content may be 0.05 to 0.5.

[0014] In some embodiments, the flame retardancy with respect to the content of the inorganic electrolyte Polyelectrolyte The volume ratio of the content may be 0.01 to 0.3.

[0015] In some embodiments, the flame retardant Polyelectrolyte It may contain at least one of a phosphorus-containing functional group and a fluorine atom.

[0016] In some embodiments, the phosphorus-containing functional group may include at least one of a phosphate group, a phosphite group, a phosphonate group, and a phosphazene group.

[0017] A lithium secondary battery according to an exemplary embodiment may include a positive electrode, a negative electrode facing the positive electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, which contains the aforementioned electrolyte for secondary batteries.

[0018] In an exemplary embodiment of a method for producing an electrolyte for a secondary battery, a mixed slurry can be produced by mixing an inorganic electrolyte, an organic binder, and a solvent. A composite film can be produced by drying the mixed slurry. A flame-retardant polymer can be added to the composite film. electrolyte Electrolytes for secondary batteries can be manufactured by impregnating with the inorganic electrolyte. The volume ratio of the organic binder to the inorganic electrolyte may be 0.01 to 0.5.

[0019] In some embodiments, the inorganic electrolyte may include an oxide-based solid electrolyte.

[0020] In some embodiments, the inorganic electrolyte content in the total volume of the composite membrane may be 50% to 95% by volume.

[0021] In some embodiments, the flame-retardant polymer electrolyte Impregnation may include impregnating the composite film with a mixture containing a flame-retardant monomer and an electrolyte, and then curing the mixture.

[0022] In some embodiments, the electrolyte may include a lithium salt.

[0023] In some embodiments, the mixture may further contain a thermal initiator, and curing the mixture may include heat treatment of the mixture.

[0024] In some embodiments, the mixture may further contain a photoinitiator, and curing the mixture may include irradiating the mixture with light. [Effects of the Invention]

[0025] Electrolytes for secondary batteries manufactured according to exemplary embodiments of this disclosure can have improved mechanical properties. This can improve the stability of the electrolyte layer and enhance flame retardancy.

[0026] Furthermore, the electrolyte for secondary batteries manufactured according to the exemplary embodiments of this disclosure may have self-extinguishing properties. This improves high-temperature stability and ignition stability even after repeated charging and discharging of the electrolyte layer.

[0027] Lithium secondary batteries according to exemplary embodiments of the present disclosure can include an electrolyte for the secondary battery, thereby improving safety at room temperature and high temperatures and improving electrical properties. [Brief explanation of the drawing]

[0028] [Figure 1] Figure 1 is a schematic diagram showing the structure of an electrolyte for a secondary battery according to an exemplary embodiment. [Figure 2]Figure 2 is a schematic process flow diagram illustrating a method for manufacturing an electrolyte for a secondary battery according to an exemplary embodiment. [Figure 3] Figure 3 is a photograph of the combustion of an electrolyte layer for a secondary battery manufactured according to an exemplary embodiment. [Figure 4] Figure 4 is a photograph of a secondary battery electrolyte layer after combustion, manufactured according to an exemplary embodiment. [Modes for carrying out the invention]

[0029] According to exemplary embodiments, a method for producing an electrolyte for a secondary battery comprising a lithium salt, an inorganic oxide, an organic binder, and a flame-retardant polymer is provided, as well as a secondary battery electrolyte produced thereby. A lithium secondary battery comprising an electrolyte layer containing the secondary battery electrolyte is also provided.

[0030] Illustrative embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. However, these embodiments are illustrative and do not limit the present disclosure.

[0031] In this specification, unless otherwise defined, the phrase "on top of" a layer, film, thin film, region, plate, or other part may include not only cases where it is "directly on top" of another part, but also cases where another part exists in between.

[0032] If a compound represented by a chemical formula used in this disclosure has isomers, the chemical formula refers to a representative chemical formula that includes those isomers.

[0033] In this disclosure, flame retardancy can refer to the ability to prevent or suppress combustion by preventing the sample from burning while in contact with a flame (ignition source) but from burning on its own once the flame is removed. The flame retardancy can be evaluated from the time it takes for the flame to extinguish after igniting the sample by supplying a certain amount of heat to the sample with a torch for 1 second or more and then removing the torch. The shorter the time it takes for the flame to extinguish, the better the flame retardancy can be evaluated.

[0034] Specifically, the flame-retardant polymer may be produced in the form of a glass fiber-impregnated or self-supporting film with a diameter of 19 mm, and when a flame with a certain calorific value is supplied for 1 second or more using a torch to ignite it and then the torch is removed, it may be a polymer that extinguishes within 2 seconds, specifically within 1 second, more specifically within 0.5 seconds.

[0035] FIG. 1 is a schematic diagram showing an electrolyte for a secondary battery according to an exemplary embodiment.

[0036] Referring to FIG. 1, an electrolyte for a secondary battery (hereinafter, may be abbreviated as "electrolyte") may include a lithium salt, a composite film 105, and a flame-retardant polymer. electrolyte 130. In some embodiments, the The flame-retardant polymer electrolyte 130 may be obtained by curing a mixture containing flame-retardant monomers and an electrolyte. .

[0037] According to an exemplary embodiment, the composite film 105 may include an inorganic electrolyte 110 and an organic binder 120. For example, the inorganic electrolyte 110 and the organic binder 120 may be mixed and dispersed within the composite film 105 and may be physically in contact with or bonded to each other. The composite film may be a free-standing film.

[0038] The inorganic electrolyte 110 and the organic binder 120 of the composite film 105 may be un-sintered, and the composite film 105 may not include a sintered body of the inorganic electrolyte 110 and / or a sintered body of the organic binder 120.

[0039] The lithium salt may be represented by, for example, Li + X - . The anion (X - ) of the lithium salt may include F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 -(CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - , and (CF3CF2SO2)2N - These are some examples.

[0040] In some embodiments, the inorganic electrolyte 110 may be an oxide-based solid electrolyte. For example, an oxide-based solid electrolyte may contain an ion-conducting compound containing a metal or oxygen. For example, an oxide-based solid electrolyte may be an LLTO-based compound, an LLZO-based compound, or Li 6.4 La3Zr 1.4 Ta 0.6 O 12 LLZTO compounds such as Li6La2CaTa2O 12 Li6La2ANb2O 12 (A is Ca or Sr), Li2Nd3TeSbO 12 Li3BO 2.5 N 0.5 , Li9SiAlO8, LAGP compounds, LATP compounds, Li 1+x Ti 2-x Al x Si y (PO4)3(0≦x≦1, 0≦y≦1), LiAl x Zr 2-x (PO4)3(0≦x≦1), LiTi x Zr 2-xThis can include (PO4)3 (0≦x≦1), LISICON compounds, LIPON compounds, perovskite compounds, NASICON compounds, and metal oxides such as Al2O3, ZnO2, Ce2O2, TiO2, ZrO2, HfO2, MnO2, MgO, WO2, and V2O5.

[0041] In one embodiment, the inorganic electrolyte 110 may include an oxide-based solid electrolyte containing lithium. For example, the lithium-based oxide-based solid electrolyte may include LLTO compounds, LLZO compounds (e.g., garnet-type LLZO compounds), LLZTO compounds, NASICON compounds, LATP compounds, perovskite compounds, and the like. This can improve the ionic conductivity and mechanical strength of the electrolyte 100, thereby suppressing lithium dendrites and improving high-temperature stability and lifespan characteristics.

[0042] The organic binder 120 may include at least one selected from the group consisting of polyvinyl compound-based binders, cellulose-based binders, acrylic polymer-based binders, and copolymer resin binders.

[0043] Organic binder 120 includes, for example, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), carboxymethylcellulose (CMC), vinylpyrrolidone / vinylacetate (VP / VA) copolymer resin, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), acrylonitrile-butadiene rubber (NBR), and polybutadiene rubber (polybutadiene It may contain rubber (BR), styrene-butadiene rubber (SBR), polyacrylic acid-based binders, poly(3,4-ethylenedioxythiophene, PEDOT), etc.

[0044] In some embodiments, the organic binder 120 has a glass transition temperature (T g The organic polymer may have a glass transition temperature (T) of 100°C to 600°C, 100°C to 500°C, or 100°C to 300°C. In one embodiment, a PVDF-based binder may be included. g By using a binder having the range of ), in the manufacture of the electrolyte, the organic binder 120 can uniformly distribute and fix the inorganic electrolyte 110, etc., and stabilize the electrolyte 100 without requiring separate heat treatment at high temperatures.

[0045] In some embodiments, flame-retardant polymers electrolyte 130 may include a phosphorus functional group. In one embodiment, the phosphorus functional group may include at least one of a phosphate group, a phosphite group, a phosphonate group, and a phosphazene group.

[0046] For example, the flame-retardant polymer electrolyte 130 may be a polymer obtained by polymerizing or copolymerizing flame-retardant monomers containing at least one of a phosphate group, a phosphite group, a phosphonate group, and a phosphazene group. electrolyte It is possible to suppress side reactions of 130 with the inorganic electrolyte 110, the organic binder 120, compounds such as the lithium salt, or the electrolyte. electrolyte By containing phosphorus-containing functional groups, compound 130 can block oxygen during combustion, thereby preventing thermal runaway.

[0047] In some embodiments, flame-retardant polymers electrolyte 130 can contain fluorine atoms. For example, flame-retardant polymers. electrolyte 130 may be a polymer obtained by polymerizing or copolymerizing flame-retardant monomers containing fluorine atoms. The fluorine atoms can form radicals when a fire occurs, suppressing the transition of the combustion reaction. This results in a flame-retardant polymer. electrolyte The flame retardancy of electrolyte 100 can be improved by using 130.

[0048] In one embodiment, a flame-retardant polymer electrolyte 130 can contain both phosphorus-containing functional groups and fluorine atoms. For example, flame-retardant polymers. electrolyte130 may be a polymer obtained by polymerizing or copolymerizing flame-retardant monomers containing both phosphorus-containing functional groups and fluorine atoms. For example, a flame-retardant polymer. electrolyte 130 may be a polymer obtained by copolymerizing a flame-retardant monomer containing a phosphorus-containing functional group with a flame-retardant monomer containing a fluorine atom. This results in a flame-retardant polymer. electrolyte Adding 130 can further improve the flame retardancy of electrolyte 100.

[0049] In one embodiment, a flame-retardant polymer electrolyte 130 may include monomers, oligomers, polymers, or mixtures thereof.

[0050] In some embodiments, flame-retardant polymers electrolyte 130 may be a compound obtained by polymerizing or copolymerizing a flame-retardant monomer having a heat-reactive functional group and / or a photo-reactive functional group. For example, the flame-retardant monomer may be a compound containing a heat-reactive functional group that polymerizes by heat. For example, the flame-retardant monomer may be a compound containing a photo-reactive functional group that polymerizes upon irradiation with light. For example, the thermosetting functional group and / or photocurable functional group may be a (meth)acrylate group, an acrylic group, an ether group, an alcohol group, an alkoxy group, etc.

[0051] According to exemplary embodiments, the content of the inorganic electrolyte 110 in the total volume of the composite membrane 105 may be 50% to 95% by volume.

[0052] If the inorganic electrolyte 110 content in the total volume of the composite film 105 exceeds 95% by volume, the low content of the organic binder 120 may weaken the cohesive force between particles, resulting in reduced ductility of the composite film. This may lead to a decrease in the mechanical stability of the composite film 105. Furthermore, a high content of the inorganic electrolyte 110 may make it difficult to manufacture the composite film 105 in thin film form.

[0053] If the inorganic electrolyte 110 content in the total volume of the composite membrane 105 is less than 50% by volume, the ionic conductivity of the composite membrane 105 may decrease. Consequently, the output characteristics and initial capacity efficiency of the composite membrane 105 may decrease. Furthermore, if the content of the organic binder 120 increases relatively and combustion occurs, the combustion of the organic binder 120 may make it difficult to maintain the morphology of the composite membrane.

[0054] Within the aforementioned content range, the flame retardancy and mechanical stability of the composite film 105 can be improved, and the output characteristics and initial capacity efficiency can be enhanced.

[0055] In some embodiments, the content of the inorganic electrolyte 110 in the total volume of the composite membrane 105 may be 60% to 95% by volume, 70% to 95% by volume, 70% to 90% by volume, 75% to 90% by volume, or 75% to 85% by volume. For example, the content of the oxide-based solid electrolyte in the total volume of the composite membrane 105 may be within the above ranges by volume. Within these ranges, the high ionic conductivity of the inorganic electrolyte 110 can further improve the ionic conductivity of the electrolyte 100. For example, the mechanical properties of the electrolyte 100 can be further improved by using an oxide-based solid electrolyte, and the membrane structure of the composite membrane 105 can be maintained without disruption.

[0056] In some embodiments, the content of the organic binder 120 in the total volume of the composite membrane 105 may be 5% to 50% by volume, 5% to 40% by volume, or 5% to 30% by volume. In one embodiment, the content of the organic binder 120 in the total volume of the composite membrane 105 may be 10% to 30% by volume, 10% to 25% by volume, or 15% to 25% by volume. Within these ranges, the inorganic electrolyte 110 in the composite membrane 105 can be uniformly dispersed throughout the composite membrane 105, and the structure of the composite membrane 105 can be stably formed.

[0057] In one embodiment, the volume ratio of the organic binder 120 to the inorganic electrolyte 110 may be 0.05-0.5, 0.053-0.5, 0.08-0.5, 0.08-0.4, 0.08-0.3, or 0.1-0.3. Within this range, it is possible to suppress the decrease in ionic conductivity due to a decrease in the inorganic electrolyte 110 content while improving the structural stability of the composite membrane 105 by increasing the organic binder 120 content.

[0058] In some embodiments, the ratio of the content of the flame-retardant polymer 130 to the content of the inorganic electrolyte 110 may be 0.01 to 0.3, 0.05 to 0.3, 0.1 to 0.3, 0.1 to 0.25, or 0.15 to 0.25 by volume. Within this range, the self-extinguishing properties of the flame-retardant polymer 130 can improve the ignition stability and high-temperature stability of the electrolyte 100. Furthermore, even if the organic binder 120 contained in the composite membrane 105 ignites, the flame-retardant polymer 130 can maintain the structure of the composite membrane 105.

[0059] Figure 2 is a process flow diagram illustrating a method for manufacturing an electrolyte for a secondary battery according to an exemplary embodiment. The method for manufacturing an electrolyte for a secondary battery described above will be explained below with reference to Figure 2.

[0060] Referring to Figure 2, a mixed slurry can be prepared by mixing an inorganic electrolyte, an organic binder, and a solvent (for example, step S10).

[0061] In some embodiments, the inorganic electrolyte may be an oxide-based solid electrolyte. The oxide-based solid electrolyte may be the oxide-based solid electrolyte described above. For example, the oxide-based solid electrolyte may be an oxide-based solid electrolyte containing lithium.

[0062] The organic binder may be any of the organic binders mentioned above. For example, the organic binder may be a PVB-based binder, a PVA-based binder, a PVDF-based binder, or the like.

[0063] In some embodiments, the solvent can be one that can dissolve both the inorganic electrolyte and the organic binder. In one embodiment, the solvent may include an organic solvent. The organic solvent may contain at least one functional group selected from the group consisting of alcohol, ketone, amide, ester, ether, aromatic hydrocarbon, etc. For example, the organic solvent may include 2-propanol, toluene, terpineol, N-methyl-2-pyrrolidone (NMP), etc. The solvent (or organic solvent) may be used alone or in combination of two or more.

[0064] In one embodiment, the solvent can be two types of organic solvents. For example, the solvent can be a mixture of a first solvent and a second solvent that are mutually miscible from the aforementioned solvents. The first solvent and the second solvent can each dissolve at least one of an inorganic electrolyte and an organic binder. This allows either the inorganic electrolyte or the organic binder to dissolve in the second solvent and be mixed, even if one of them does not dissolve in the first solvent.

[0065] In exemplary embodiments, the ratio of the content of the organic binder to the content of the inorganic electrolyte may be 0.05 to 0.5, 0.053 to 0.5, 0.08 to 0.5, 0.08 to 0.45, or 0.08 to 0.4 by volume. For example, the inorganic electrolyte and the organic binder can be mixed with a solvent in the above-mentioned content ratios.

[0066] If the ratio of the organic binder content to the inorganic electrolyte content is less than 0.05 on a volume basis, the brittleness of the composite membrane produced from the mixed slurry may increase, and the mechanical stability of the composite membrane may decrease. If the ratio of the organic binder content to the inorganic electrolyte content exceeds 0.5 on a volume basis, the ionic conductivity of the composite membrane may decrease, and the output characteristics and initial efficiency may decrease.

[0067] In some embodiments, the ratio of the organic binder content to the inorganic electrolyte content may be 0.08 to 0.3, 0.09 to 0.3, or 0.1 to 0.3 by volume. This can further improve the mechanical stability, power characteristics, and initial efficiency of the composite membrane produced from the slurry containing the inorganic electrolyte and the organic binder.

[0068] In some embodiments, the mixed slurry may further include additives such as plasticizers and dispersants. These additives may be organic additives.

[0069] The plasticizer may be, for example, a plasticizer having a phosphate ester, phthalate ester, or citrate ester structure. The phosphate ester may include, for example, triphenyl phosphate (TPP), 4-biphenyl diphenyl phosphate (BDP), and tricresyl phosphate (TCP). The phthalate ester may include, for example, dimethyl phthalate (DMP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP), and diethylhexyl phthalate (DEHP). The citrate ester may include, for example, o-acetyl triethyl citrate (OACTE) and o-acetyl tributyl citrate (OACTB).

[0070] The dispersant may include, for example, hydrogenated nitrile butadiene rubber (HNBR), polyvinyl pyrrolidone (PVP), polylactic acid (PLA), or polyglycolic acid (PGA).

[0071] According to an exemplary embodiment, the mixed slurry can be dried to produce a composite film (e.g., step S20). The mixed slurry may be cast onto a substrate (e.g., a glass substrate and a plastic substrate, etc.) and dried.

[0072] In some embodiments, the mixed slurry can be dried at 60°C to 400°C, 60°C to 300°C, 80°C to 300°C, 100°C to 300°C, or 120°C to 280°C. Within this temperature range, the solvent contained in the mixed slurry vaporizes, allowing the mixed slurry to dry. Furthermore, the inorganic electrolyte and organic binder contained in the mixed slurry can be uniformly distributed within the slurry, and the organic binder can physically bind with the inorganic electrolyte to form and maintain the structure of a composite film.

[0073] In some embodiments, the mixed slurry can be dried for 30 minutes to 2 hours, 30 minutes to 1.5 hours, or 45 minutes to 1.25 hours. Within this range, the solvent in the mixed slurry can be vaporized and removed.

[0074] In some embodiments, the mixed slurry does not need to be sintered after drying. This prevents the removal of the organic binder and improves the elastic modulus of the composite film. This improves the lifespan characteristics of the electrolyte containing the composite film.

[0075] In some embodiments, the content of the inorganic electrolyte in the total volume of the composite membrane may be 50% to 95% by volume, 60% to 95% by volume, or 70% to 95% by volume. Within these ranges, the inorganic electrolyte can improve the mechanical properties of the composite membrane.

[0076] In one embodiment, the content of the inorganic electrolyte in the total volume of the composite membrane may be 70% to 90% by volume, 75% to 90% by volume, or 75% to 85% by volume. Within this range, the inorganic electrolyte can further improve the mechanical properties of the composite membrane.

[0077] According to exemplary embodiments, the composite film can be impregnated with a flame-retardant polymer (for example, in step S30). For example, the composite film may have pores formed between the inorganic electrolyte and the organic binder, and the flame-retardant compound can be impregnated into these pores. The composite film can be impregnated with the flame-retardant polymer to produce an electrolyte for a secondary battery. For example, the composite film formed on the substrate (e.g., a glass substrate and a plastic substrate) can be separated from the substrate, and the flame-retardant polymer can be impregnated into the composite film.

[0078] In some embodiments, the content of the inorganic electrolyte that gives rise to the composite film is Flame-retardant polymer electrolytes The flame-retardant polymer can be impregnated into the composite film such that the ratio of its content is 0.01-0.3, 0.05-0.3, 0.1-0.3, 0.1-0.25, or 0.15-0.25 by volume. This improves the ignition stability of the composite film and improves its electrical conductivity while maintaining its structure even at high temperatures.

[0079] According to an exemplary embodiment, the composite film can be impregnated with a mixture containing a flame-retardant monomer and an electrolyte, and the mixture can be cured to impregnate the composite film with a flame-retardant polymer.

[0080] In some embodiments, the composite film can be impregnated with a mixture containing a flame-retardant monomer and an electrolyte. For example, the composite film can be impregnated with a mixture prepared by immersing the flame-retardant monomer in the electrolyte. For example, the composite film may have pores formed between the inorganic electrolyte and the organic binder, and the mixture can be impregnated by penetrating these pores. For example, the composite film formed on a substrate (e.g., a glass substrate and a plastic substrate) can be separated from the substrate, and the mixture can be impregnated into the composite film.

[0081] In some embodiments, the volume ratio of the flame-retardant monomer content to the inorganic electrolyte content in the composite membrane may be substantially the same as the volume ratio of the flame-retardant polymer content to the inorganic electrolyte content in the composite membrane. For example, the volume decrease or increase of the flame-retardant monomer as it polymerizes or copolymerizes with the flame-retardant polymer may be 0.0001% by volume or less, relative to the total volume of the flame-retardant monomer.

[0082] In some embodiments, the flame-retardant monomer may contain a phosphorus-containing functional group. For example, the phosphorus-containing functional group may include at least one of a phosphate group, a phosphite group, a phosphonate group, and a phosphazene group. This can improve the flame retardancy of the electrolyte for secondary batteries.

[0083] In some embodiments, the flame-retardant monomer may contain fluorine atoms. This can improve the flame retardancy of the electrolyte for the secondary battery.

[0084] In one embodiment, the flame-retardant monomer may contain both a phosphorus-containing functional group and a fluorine atom. This can further improve the flame retardancy of the electrolyte for the secondary battery.

[0085] In some embodiments, the flame retardant monomer may contain a heat-reactive functional group and / or a photo-reactive functional group. For example, the flame retardant monomer may be a compound containing a heat-reactive functional group that polymerizes by heat. For example, the flame retardant monomer may be a compound containing a photo-reactive functional group that polymerizes upon irradiation with light. Examples of the thermosetting functional group and / or photocurable functional group include (meth)acrylate groups, acrylic groups, ether groups, alcohol groups, alkoxy groups, and the like.

[0086] In one embodiment, the flame retardant monomer may contain a phosphorus-containing functional group and at least one of a heat-reactive functional group and a photo-reactive functional group. In one embodiment, the flame retardant monomer may contain a phosphorus-containing functional group, a fluorine atom, and at least one of a heat-reactive functional group and a photo-reactive functional group.

[0087] In some embodiments, the electrolyte may include a thermal initiator and / or photoinitiator for inducing the thermosetting and / or photocuring of the flame-retardant monomer. In one embodiment, the content of the thermal initiator and / or photoinitiator may be 0.5 to 2 parts by weight per 100 parts by weight of the flame-retardant monomer contained in each electrolyte composition.

[0088] For example, the thermal initiator may include azo compounds such as 2,2'-azobis(2-cyanobutane), 2,2'-azobis(methylbutyronitrile), 2,2'-azobisisobutyronitrile (AIBN), and azobisdimethylvaleronitrile (AMVN), or peroxide compounds such as benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, cumyl peroxide, and hydrogen peroxide.

[0089] For example, the photoinitiator may include 2-hydroxy-2-methyl-1-phenylpropane-1-one (HMPP), benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal, acyl phosphine such as 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide, and α-aminoketone.

[0090] In some embodiments, the electrolyte may include a lithium salt. The lithium salt may include the lithium salts described above. This can improve the ionic conductivity of the electrolyte for secondary batteries.

[0091] In some embodiments, the electrolyte may contain an organic solvent. For example, the organic solvent may be a carbonate-based organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), and vinylene carbonate (VC), or dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, propylene sulfide, and tetrahydrofuran. These can be used alone or in combination of two or more.

[0092] In one embodiment, the organic solvent may be a carbonate-based organic solvent. This can improve the electrical and chemical stability of the electrolyte for secondary batteries.

[0093] In one embodiment, the electrolyte may further contain additives. These additives may include, for example, cyclic carbonate compounds, fluorine-substituted cyclic carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate compounds.

[0094] The aforementioned cyclic carbonate compound may include vinylene carbonate, vinyl ethylene carbonate (VEC), and the like.

[0095] The fluorine-substituted cyclic carbonate compound may include fluoroethylene carbonate (FEC), among others.

[0096] The sultone compounds mentioned above may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like.

[0097] The cyclic sulfate compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like.

[0098] The cyclic sulfite compound may include ethylene sulfite, butylene sulfite, and the like.

[0099] The phosphate compound may include lithium difluorobis-oxalato phosphate, lithium difluorophosphate, and the like.

[0100] The borate-based compound may include lithium bis(oxalate)borate, among others.

[0101] In some embodiments, the mixture impregnated into the composite film can be cured. This makes it possible to manufacture an electrolyte for a secondary battery.

[0102] In some embodiments, the flame-retardant monomer can be polymerized or copolymerized while the mixture is curing. This allows the electrolyte for secondary batteries to be a flame-retardant polymer. electrolyte It can include...

[0103] In some embodiments, curing the mixture may be done by heat-treating the mixture. For example, the mixture may be heat-cured to make the flame-retardant monomers in the composite film flame-retardant. polymer It can be polymerized or copolymerized.

[0104] In some embodiments, the heat treatment may be performed at temperatures of 40°C to 160°C, 60°C to 160°C, 80°C to 160°C, 80°C to 140°C, or 80°C to 120°C. In one embodiment, the heat treatment may be performed by increasing the temperature from room temperature (e.g., 25°C) at a rate of 1°C / min to 10°C / min, 2°C / min to 10°C / min, or 3°C / min to 10°C / min.

[0105] In some embodiments, the heat treatment can be carried out for 30 minutes to 2 hours, 30 minutes to 1.5 hours, or 45 minutes to 1.25 hours.

[0106] Within the aforementioned temperature and time range, the flame-retardant monomers in the mixture can be sufficiently polymerized or copolymerized.

[0107] In some embodiments, curing the mixture may be done by irradiating the mixture with light. For example, the mixture can be photocured to polymerize or copolymerize the flame-retardant monomers in the composite film into a flame-retardant polymer. This allows the polymerization or copolymerization reaction of the flame-retardant monomers to be carried out at a relatively low temperature. Therefore, damage to the composite film due to high-temperature heat treatment can be prevented.

[0108] In some embodiments, the UV photocuring step for photopolymerization uses a wavelength of 250 nm to 400 nm and 800 mW / cm². 2 ~1100mW / cm 2This can be carried out using light of a certain intensity. In one embodiment, the UV light curing process can be performed for 5 to 20 seconds. Within the range of wavelength and intensity, the flame-retardant monomers in the mixture can be sufficiently polymerized or copolymerized.

[0109] A secondary battery according to an exemplary embodiment may include a positive electrode, a negative electrode facing the positive electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode.

[0110] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0111] The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive electrode current collector may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector is not limited to, but may be, for example, 10 μm to 50 μm.

[0112] The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0113] According to exemplary embodiments, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0114] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystalline structure represented by the following chemical formula 1.

[0115] [Chemical formula 1] Li x Ni a M b O 2+z

[0116] In chemical formula 1, 0.9 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.4, and -0.5 ≤ z ≤ 0.1 may also be true. As previously stated, M may include Co, Mn, and / or Al.

[0117] The chemical structure represented by chemical formula 1 indicates the bonding relationships contained within the layered or crystalline structure of the positive electrode active material and does not exclude additional elements. For example, M may include Co and / or Mn, and Co and / or Mn, together with Ni, may be provided as the main active elements of the positive electrode active material. Chemical formula 1 is provided to represent the bonding relationships of the aforementioned main active elements and should be understood as a formula that includes the introduction and substitution of additional elements.

[0118] In one embodiment, in addition to the main active element, auxiliary elements may be further included to improve the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements can be incorporated together within the layered / crystal structure to form bonds. In this case as well, it should be understood that the chemical structure falls within the range represented by chemical formula 1.

[0119] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may also act as an auxiliary active element, such as Al, together with Co or Mn, contributing to the capacity / power activity of the positive electrode active material.

[0120] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystalline structure represented by the following chemical formula 1-1.

[0121] [Chemical formula 1-1] Li x Ni a M1 b1 M2 b2 O2+z

[0122] In chemical formula 1-1, M1 may include Co, Mn, and / or Al, and M2 may include the aforementioned auxiliary elements. In chemical formula 1-1, 0.9 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 0.99, 0.01 ≤ b1 + b2 ≤ 0.4, and -0.5 ≤ z ≤ 0.1 may also be true.

[0123] The positive electrode active material may further contain coating elements or doping elements. For example, elements substantially identical or similar to the aforementioned auxiliary elements may be used as coating elements or doping elements. For example, the aforementioned elements may be used individually or in combination of two or more as coating elements or doping elements.

[0124] The coating element or doping element may be present on the surface of the lithium-nickel metal oxide particles, or it may penetrate from the surface of the lithium-nickel metal oxide particles and be included in the bonding structure represented by chemical formula 1 or chemical formula 1-1.

[0125] The positive electrode active material may include nickel-cobalt-manganese (NCM) lithium oxide. In this case, an NCM lithium oxide with an increased nickel content can be used.

[0126] Ni can be provided as a transition metal related to the output and capacity of lithium secondary batteries. As a result, by employing a composition with a high content (High-Ni) in the positive electrode active material as described above, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0127] However, as the Ni content increases, the long-term storage stability and lifespan stability of the positive electrode or secondary battery may decrease relatively, and side reactions with the electrolyte may increase. In contrast, according to an exemplary embodiment, electrical conductivity can be maintained by including Co, while lifespan stability and capacity maintenance characteristics can be improved by Mn.

[0128] The content of Ni in the NCM-based lithium oxide (for example, the molar fraction of Ni in the total number of moles of nickel, cobalt, and manganese) may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0129] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (for example, LiFePO4).

[0130] In some embodiments, the positive electrode active material may include, for example, an Mn-rich-based active material having a chemical structure or crystal structure represented by the following Chemical Formula 2, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide)-based active material, or a Co-less-based active material.

[0131] [Chemical Formula 2] p[Li2MnO3]·(1-p)[Li q JO2]

[0132] In Chemical Formula 2, 0 < p < 1 and 0.9 ≤ q ≤ 1.2, and J may include at least one element of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0133] In some embodiments, the positive electrode active material may be a sodium-based active material or a potassium-based active material. The sodium-based active material or potassium-based active material may include a layered structure or crystal structure in which Li in the aforementioned Chemical Formula 1, Chemical Formula 1-1, and / or Chemical Formula 2 is substituted with Na and / or K.

[0134] In some embodiments, the positive electrode active material may be a calcium-based active material. The calcium-based active material may include, for example, a calcium-cobalt active material and a calcium-phosphate active material.

[0135] For example, a positive electrode slurry can be produced by mixing the positive electrode active material in a solvent. After coating a positive electrode current collector with the positive electrode slurry, a positive electrode active material layer can be produced by drying and rolling. The coating process can be carried out by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting, but is not limited to these. The positive electrode active material layer may further contain a binder and optionally further contain an electrolyte, conductive material, thickener, etc.

[0136] Examples of solvents used in the production of the positive electrode active material layer include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), N,N-dimethylaminopropylamine (DMAPA), ethylene oxide (EO), and tetrahydrofuran (THF).

[0137] In one embodiment, the electrolyte contained in the positive electrode active material layer may be the aforementioned electrolyte for secondary batteries. In another embodiment, the electrolyte contained in the positive electrode active material layer may be the aforementioned inorganic electrolyte, but the electrolyte contained in the positive electrode active material layer may be the same as or different from the inorganic electrolyte contained in the composite film. For example, the secondary battery may be provided as an all-solid-state battery containing the aforementioned electrolyte or inorganic electrolyte.

[0138] The binder may include at least one selected from the group consisting of polyvinyl compound-based binders, cellulose-based binders, acrylic polymer-based binders, and copolymer resin binders.

[0139] The binder may include, for example, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), carboxymethylcellulose (CMC), vinylpyrrolidone / vinylacetate (VP / VA) copolymer resin, polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethyl methacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), and the like. In one embodiment, a PVDF-based binder can be used as the positive electrode binder.

[0140] The conductive material may be added to improve the conductivity and / or the mobility of lithium ions or electrons in the positive electrode active material layer. For example, the conductive material may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjenblack, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fibers, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0141] The positive electrode active material layer may further contain a thickener and / or a dispersant. In one embodiment, the positive electrode active material layer may contain a thickener such as carboxymethyl cellulose (CMC).

[0142] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0143] The negative electrode current collector may include, for example, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal. The thickness of the negative electrode current collector is not limited to this, but may be, for example, 10 μm to 50 μm.

[0144] The negative electrode active material layer may contain a negative electrode active material. As the negative electrode active material, a material capable of adsorbing and desorbing lithium ions can be used. For example, the negative electrode active material can be carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon (Si)-containing materials or tin (Sn)-containing materials.

[0145] Examples of the amorphous carbon include hard carbon, soft carbon, coke, mesocarbon, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), and the like.

[0146] Examples of the crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0147] Examples of the lithium metal include pure lithium metal or lithium metal with a protective layer formed for dendrite growth suppression or the like. In one embodiment, a lithium metal-containing layer deposited or coated on a negative electrode current collector can be used as the negative electrode active material layer. In one embodiment, a thin lithium film layer can also be used as the negative electrode active material layer.

[0148] Examples of the elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, and the like.

[0149] The silicon-containing substance can provide more enhanced capacity characteristics. The silicon-containing substance can include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), a silicon-carbon composite, and the like. The metal can include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) can include metal silicate.

[0150] For example, a negative electrode slurry can be produced by mixing the negative electrode active material in a solvent. After coating / depositing the negative electrode slurry onto a negative electrode current collector, a negative electrode active material layer can be produced by drying and rolling. The coating step can be carried out using substantially the same method as the method for producing the positive electrode active material layer. The negative electrode active material layer may further contain a binder, and may selectively further contain an electrolyte, a conductive material, a thickener, etc.

[0151] In some embodiments, the negative electrode may also include a negative electrode active material layer in the form of lithium metal formed by a vapor deposition / coating process.

[0152] Examples of solvents for the negative electrode active material layer include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, and t-butanol.

[0153] In one embodiment, the electrolyte contained in the negative electrode active material layer may be the aforementioned electrolyte for secondary batteries. In another embodiment, the electrolyte contained in the negative electrode active material layer may be the aforementioned inorganic electrolyte, but the electrolyte contained in the negative electrode active material layer may be the same as or different from the inorganic electrolyte contained in the composite membrane. For example, the secondary battery may be provided as an all-solid-state battery containing the aforementioned electrolyte or inorganic electrolyte.

[0154] As the binder, conductive material, and thickener, the aforementioned substances that can be used during the manufacture of the positive electrode can be used.

[0155] In some embodiments, styrene-butadiene rubber binders, carboxymethylcellulose binders, polyacrylic acid binders, polyethylenedioxythiophene (poly(3,4-ethylenedioxythiophene), PEDOT) binders, etc., can be used as the negative electrode binder.

[0156] According to an exemplary embodiment, an electrolyte layer may be interposed between the positive electrode and the negative electrode. The electrolyte layer may be a solid electrolyte layer. For example, the solid electrolyte layer may be an electrolyte layer containing the aforementioned electrolyte.

[0157] According to exemplary embodiments, an electrode cell is defined by a positive electrode, a negative electrode, and a solid electrolyte layer, and multiple such electrode cells can be stacked to form an electrode assembly. For example, the electrode assembly can be formed by winding, lamination, folding, etc.

[0158] For example, electrode tabs (positive and negative tabs) can protrude from the positive and negative current collectors, respectively, and extend to one side of the case. These electrode tabs can be fused together with the aforementioned side of the case and connected to electrode leads (positive and negative leads) that extend or are exposed outside the case.

[0159] For example, pouch-type cases, rectangular cases, cylindrical cases, and coin-type cases can be used.

[0160] The embodiments of this disclosure will be further described below with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of this disclosure and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications can be made to these embodiments within the scope of this disclosure and the technical concept, and that these variations and modifications will naturally fall within the scope of the appended claims.

[0161] Examples and Comparative Examples Example 1 Manufacturing of electrolytes for secondary batteries LLZTO(Li) as an inorganic electrolyte 6.4 La3Zr 1.4 Ta 0.6 O 12A mixed slurry was prepared by mixing polyvinyl butyral (PVB) as an organic binder in a 4:1 volume ratio with a mixed solvent containing propylene carbonate (PC) and diethyl sulfoxide (DMSO) in a 1:1 volume ratio.

[0162] The mixed slurry was cast onto a polyethylene terephthalate (PET) film and then dried at 250°C for 1 hour to form a composite film.

[0163] The inorganic electrolyte content in the total volume of the composite membrane was 80% by volume.

[0164] A mixture was prepared by mixing a compound represented by the following chemical formula 3 as a flame retardant monomer with a 1.0 M LiTFSi solution (EC / EMC mixed solvent in a volume ratio of 25:75).

[0165] The composite membrane was separated from the PET film, and the composite membrane was impregnated with the mixture in a volume ratio of 10:1. The ratio of the flame-retardant monomer content to the inorganic electrolyte content was 0.2 by volume.

[0166] [ka]

[0167] Subsequently, the mixture was heated at 5°C / min and then thermally cured at 80°C for 1 hour to produce an electrolyte for secondary batteries.

[0168] Examples 2-9 In the production of an electrolyte for secondary batteries, an electrolyte for secondary batteries was produced in the same manner as in Example 1, except that the content of the inorganic material in the total volume of the composite membrane and the volume ratio of the flame-retardant monomer content to the inorganic electrolyte content were changed as shown in Table 1 below.

[0169] Comparative Example 1 In the production of an electrolyte for secondary batteries, an electrolyte for secondary batteries was produced in the same manner as in Example 1, except that a flame-retardant monomer was not included in the mixture.

[0170] Comparative Examples 2-7 In the production of an electrolyte for secondary batteries, an electrolyte for secondary batteries was produced in the same manner as in Example 1, except that the content of the inorganic material in the total volume of the composite membrane and the volume ratio of the flame-retardant monomer content to the inorganic electrolyte content were changed as shown in Table 1 below.

[0171] [Table 1]

[0172] Experimental Example 1: Evaluation of Electrolytes (1) Evaluation of cohesive force The cohesive forces between inorganic electrolyte particles contained in the electrolytes for secondary batteries manufactured according to the above-described examples and comparative examples were measured. Specifically, using a SAICAS apparatus, the force required to release contact between inorganic electrolyte particles at a depth of 10 μm from the surface of the electrolyte for the secondary battery was measured as the cohesive force.

[0173] (2) Evaluation of flame retardancy - Evaluation of combustion The electrolytes for secondary batteries produced according to the above-described examples and comparative examples were burned for 5 minutes, and the presence or absence of combustion was evaluated. The presence or absence of combustion was evaluated as follows. ○: Combustion area less than 5% △: Combustion area is 5% to 20% ×: Combustion area exceeds 20%, or the composite film cannot maintain its shape during combustion. The evaluation results are shown in Table 2 below.

[0174] [Table 2]

[0175] Referring to Table 2, the examples in which the inorganic electrolyte content in the total volume of the composite membrane is 50% to 95% by volume can maintain the shape of the composite membrane with an organic binder while ensuring sufficient contact between the inorganic electrolytes. This allows for excellent flame retardancy, with an interparticle cohesive force of 0.01 N or more and a combustion area of ​​20% or less during combustion.

[0176] Figure 3 is a photograph of combustion during the combustion evaluation of an exemplary embodiment. Specifically, Figure 3 is a photograph of combustion of the electrolyte for a secondary battery during the combustion evaluation of Example 1.

[0177] Figure 4 shows a photograph of the electrolyte for the secondary battery after combustion evaluation in an exemplary embodiment. Specifically, Figure 4 shows a photograph of the electrolyte for the secondary battery after combustion evaluation in Example 1.

[0178] Referring to Figures 3 and 4, in Example 1, where the volume ratio of inorganic electrolyte to organic binder was adjusted to 4:1 and the volume ratio of flame-retardant monomer content to inorganic electrolyte content was adjusted to 0.2, the shape of the composite film was maintained even after combustion evaluation.

[0179] In comparative examples that did not contain flame-retardant monomers or flame-retardant polymers that can be formed by polymerization of flame-retardant monomers, or in which the volume of inorganic electrolytes in the total volume of the composite film was adjusted to less than 50% by volume or more than 95% by volume, the combustion area after combustion exceeded 20%.

[0180] In Comparative Example 1, which did not contain flame-retardant monomers or flame-retardant polymers that can be formed by polymerization of flame-retardant monomers, the combustion area after combustion evaluation exceeded 20%.

[0181] In Comparative Examples 2, 4, and 5, where the volume of the inorganic electrolyte in the total volume of the composite membrane was reduced to less than 50% by volume, no contact occurred between the inorganic electrolyte particles, making it impossible to evaluate the cohesive force. Furthermore, after the combustion evaluation, the combustion of the organic binder created empty spaces between the inorganic electrolytes, eliminating the interparticle contact force, and the combustion area exceeded 20%.

[0182] In Comparative Examples 3, 6, and 7, where the inorganic oxide content was increased to over 95% by volume, a thin-film composite film was not formed due to the high inorganic oxide content. Furthermore, it was difficult for the composite film to maintain its thin-film form, and the combustion area after combustion exceeded 20%.

Claims

1. Lithium salts and A composite membrane containing an inorganic electrolyte and an organic binder, It contains a flame-retardant polymer electrolyte, The inorganic electrolyte content in the total volume of the composite membrane is 50% to 95% by volume, an electrolyte for secondary batteries.

2. The electrolyte for a secondary battery according to claim 1, wherein the inorganic electrolyte includes an oxide-based solid electrolyte.

3. The electrolyte for a secondary battery according to claim 1, wherein the content of the organic binder in the total volume of the composite membrane is 5% to 50% by volume.

4. The electrolyte for a secondary battery according to claim 1, wherein the volume ratio of the content of the organic binder to the content of the inorganic electrolyte is 0.05 to 0.

5.

5. The electrolyte for a secondary battery according to claim 1, wherein the volume ratio of the content of the flame retardant compound to the content of the inorganic electrolyte is 0.01 to 0.

3.

6. The electrolyte for a secondary battery according to claim 1, wherein the flame retardant compound comprises at least one of a phosphorus-containing functional group and a fluorine atom.

7. The electrolyte for a secondary battery according to claim 6, wherein the phosphorus-containing functional group comprises at least one of a phosphate group, a phosphite group, a phosphonate group, and a phosphazene.

8. Positive electrode and, A negative electrode opposite the positive electrode, A lithium secondary battery comprising: an electrolyte layer disposed between the positive electrode and the negative electrode, and containing the electrolyte for a secondary battery as described in claim 1.

9. A step of mixing an inorganic electrolyte, an organic binder, and a solvent to produce a mixed slurry, The steps include drying the mixed slurry to produce a composite film, The step of impregnating the composite film with a flame-retardant polymer electrolyte is included. A method for producing an electrolyte for a secondary battery, wherein the volume ratio of the content of the organic binder to the content of the inorganic electrolyte is 0.01 to 0.

5.

10. The method for producing an electrolyte for a secondary battery according to claim 9, wherein the inorganic electrolyte includes an oxide-based solid electrolyte.

11. The method for producing an electrolyte for a secondary battery according to claim 9, wherein the content of the inorganic electrolyte in the total volume of the composite membrane is 50% by volume to 95% by volume.

12. The method for producing an electrolyte for a secondary battery according to claim 9, wherein the step of impregnating the composite film with the flame-retardant polymer electrolyte includes impregnating the composite film with a mixture containing a flame-retardant monomer and an electrolyte, and curing the mixture.

13. The method for producing an electrolyte for a secondary battery according to claim 12, wherein the electrolyte contains a lithium salt.

14. The aforementioned mixture further contains a thermal initiator, The method for producing an electrolyte for a secondary battery according to claim 12, wherein curing the mixture includes heat treatment of the mixture.

15. The aforementioned mixture further contains a photoinitiator, The method for producing an electrolyte for a secondary battery according to claim 12, wherein curing the mixture includes irradiating the mixture with light.

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