Electrolyte for secondary battery, method for manufacturing same, and lithium secondary battery comprising same

Abstract

An electrolyte for a lithium secondary battery according to an embodiment of the present disclosure may include a lithium salt, a composite film including an organic polymer and an inorganic electrolyte, and a flame retardant compound including a phosphorus-containing functional group. The weight ratio of the flame retardant compound to the composite film may be 0.004 to 0.3. As a result, the flame retardancy and electrical characteristics of the secondary battery can be improved.

Description

Technical Field

[0001] This disclosure relates to an electrolyte for secondary batteries, a method for manufacturing the same, and a lithium secondary battery comprising the same. More specifically, it relates to an electrolyte for secondary batteries comprising a flame-retardant compound, a method for manufacturing the same, and a lithium secondary battery comprising the same. Background Technology

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged. With the development of the information communication and display industries, they are widely used as power sources for portable electronic communication devices such as cameras, mobile phones, and laptops. In addition, in recent years, battery packs containing rechargeable batteries have also been developed and applied as power sources for environmentally friendly vehicles such as hybrid electric vehicles.

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

[0004] Currently, commercially available lithium-ion batteries primarily use liquid electrolytes, which pose safety risks such as leakage, fire, and explosion due to rapid environmental changes including temperature variations and external impacts. To address this issue, efforts are underway to develop solid-state electrolytes, thereby ensuring high stability and increasing energy density.

[0005] All-solid-state batteries can use electrolytes in solid states, such as gel polymers, oxides or sulfides, and composite polymers. This improves their stability against fire and explosion caused by external impacts and changes in the external environment. Summary of the Invention

[0006] Technical issues

[0007] One object of this disclosure is to provide an electrolyte for secondary batteries that has improved electrochemical stability and ionic conductivity.

[0008] One object of this disclosure is to provide a method for manufacturing an electrolyte for secondary batteries that improves electrochemical stability and ionic conductivity.

[0009] One object of this disclosure is to provide a lithium secondary battery with improved stability and electrochemical properties.

[0010] Technical solution

[0011] The electrolyte for a secondary battery according to an exemplary embodiment may include a lithium salt, a composite membrane comprising an organic polymer and an inorganic electrolyte, and a flame-retardant compound comprising a phosphorus-containing functional group. The weight ratio of the flame-retardant compound to the composite membrane may be from 0.004 to 0.3.

[0012] In some embodiments, the inorganic electrolyte may comprise an oxide-based solid electrolyte.

[0013] In some embodiments, the flame-retardant compound described above may contain fluorine atoms.

[0014] In some embodiments, the phosphorus-containing functional group may include at least one of phosphate, phosphite, phosphonate, and phosphazene groups.

[0015] In some embodiments, the flame-retardant compound may be a flame-retardant polymer.

[0016] In some embodiments, the flame retardant compound may include a first flame retardant compound in contact with the interior and surface of the composite film, and a second flame retardant compound distributed on the exterior of the composite film.

[0017] In some embodiments, the composite membrane comprises pores, and at least a portion of the first flame-retardant compound may be distributed within the pores.

[0018] In some embodiments, the content of the organic polymer in the total weight of the composite film can be from 5% to 95% by weight.

[0019] In some embodiments, the composite membrane comprises pores, and the porosity of the composite membrane can be from 50% to 80%.

[0020] A lithium secondary battery according to an exemplary embodiment may include: a housing; an electrode assembly comprising repeatedly stacked positive and negative electrodes; and an electrolyte for the secondary battery, disposed within the housing between the positive and negative electrodes in the electrode assembly, or distributed around the electrode assembly.

[0021] In some embodiments, the composite membrane of the electrolyte for the secondary battery can be disposed as an electrolyte layer between the positive electrode and the negative electrode in the electrode assembly.

[0022] In the method for manufacturing an electrolyte for a secondary battery according to an exemplary embodiment, an organic polymer, an inorganic electrolyte, a first solvent, and a second solvent are mixed to prepare a first mixture. The first mixture is dried to manufacture a composite membrane. A second mixture comprising a flame-retardant monomer and an electrolyte is impregnated in the composite membrane. The second mixture is cured to manufacture the electrolyte for a secondary battery.

[0023] In some embodiments, the solubility of the organic polymer relative to the first solvent may be greater than the solubility of the organic polymer relative to the second solvent.

[0024] In some embodiments, in the first mixture, the organic polymer can be dissolved in the first solvent but not in the second solvent.

[0025] In some embodiments, the step of drying the first mixture to manufacture a composite film may include removing the first solvent at a first temperature and removing the second solvent at a second temperature.

[0026] In some embodiments, the first temperature may be lower than the second temperature.

[0027] In some embodiments, the electrolyte may contain lithium salt.

[0028] In some embodiments, the second mixture may further contain a thermal initiator, and the step of curing the second mixture may include heat treatment of the second mixture.

[0029] In some embodiments, the second mixture may further contain a photoinitiator, and the step of curing the second mixture may include irradiating the second mixture with light.

[0030] Technical effect

[0031] The electrolyte for secondary batteries prepared according to exemplary embodiments of this disclosure can have self-extinguishing properties. Therefore, its stability under repeated charge-discharge cycles or at high temperatures can be improved.

[0032] Furthermore, the electrolyte for secondary batteries prepared according to exemplary embodiments of this disclosure may not be in a liquid state, thus improving the mechanical properties of the electrolyte layer containing the electrolyte.

[0033] The lithium secondary battery according to the exemplary embodiments of this disclosure may include the electrolyte for secondary batteries described above, and its safety at both room temperature and high temperature can be improved, and its lifespan characteristics can be improved even with repeated charging and discharging.

[0034] The electrolyte for lithium secondary batteries disclosed herein, its manufacturing method, and lithium secondary batteries comprising the same are widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. The electrolyte for lithium secondary batteries disclosed herein, its manufacturing method, and lithium secondary batteries comprising the same can be used in eco-friendly electric vehicles and hybrid vehicles, which prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description

[0035] Figure 1 This is a schematic diagram illustrating the structure of an electrolyte for a secondary battery according to an exemplary embodiment;

[0036] Figure 2 This is a schematic process flow diagram illustrating a method for manufacturing an electrolyte for a secondary battery according to an exemplary embodiment.

[0037] Figure 3 This is a schematic diagram illustrating a method for manufacturing an electrolyte for a secondary battery according to an exemplary embodiment;

[0038] Figure 4 This is a schematic diagram illustrating a method for manufacturing an electrolyte for a secondary battery according to an exemplary embodiment;

[0039] Figures 5 to 8 Photographs showing the thermal shrinkage over time of an electrolyte layer for a secondary battery prepared according to an exemplary embodiment, and a separator and electrolyte layer impregnated with electrolyte prepared according to a comparative example.

[0040] Figures 9 to 11 Combustion photographs of an electrolyte layer for a secondary battery prepared according to an exemplary embodiment, and a separator and electrolyte layer impregnated with electrolyte prepared according to a comparative example;

[0041] Figure 12 To illustrate the curve of the open circuit voltage (OCV) of the lithium secondary battery prepared according to the exemplary embodiment and comparative example as a function of time;

[0042] Figure 13 To illustrate the change (capacity retention) of the discharge capacity of the lithium secondary battery prepared according to the exemplary embodiment and the comparative example with the number of charge-discharge cycles;

[0043] Figure 14 This is to show a graph of the current change over time measured by cyclic voltammetry for a coin-shaped battery containing an electrolyte layer for a lithium secondary battery prepared according to an exemplary embodiment and a comparative example. Detailed Implementation

[0044] The present disclosure will now be described in detail with reference to the accompanying drawings. However, the above description is merely exemplary, and the present disclosure is not limited to the specific embodiments described herein.

[0045] Unless otherwise defined, when describing a layer, film, thin film, region, plate, etc., as being "on" other parts, it includes not only the case where it is directly "above" other parts, but also the case where other parts exist in between.

[0046] In the presence of isomers of compounds represented by chemical formulas used in this disclosure, the chemical formula representing the compound refers to a representative chemical formula including its isomers.

[0047] In this disclosure, flame retardancy can be characterized by the fact that the sample burns upon contact with a spark (ignition source), but prevents or inhibits the spontaneous generation of sparks and combustion upon removal of the spark. The aforementioned flame retardancy can be evaluated by measuring the time required for extinguishing the fire after igniting the sample with a spark that supplies a certain amount of heat to the sample for more than one second and then removing the torch. It can be assessed that the shorter the time required for extinguishing the fire, the better the flame retardancy.

[0048] Specifically, the aforementioned flame-retardant polymer can be a polymer that is made into a glass fiber impregnated or self-supporting film with a diameter of 19 mm, and is ignited by a torch that supplies a certain amount of heat to it with a spark for more than 1 second. When the torch is removed, the flame is extinguished within 2 seconds, specifically within 1 second, or more specifically within 0.5 seconds.

[0049] Figure 1 This is a schematic diagram illustrating an electrolyte for a secondary battery according to an exemplary embodiment.

[0050] Reference Figure 1 The electrolyte for secondary batteries (hereinafter referred to as 'electrolyte') may include a lithium salt, a composite membrane 105, and a flame-retardant compound 130. In some embodiments, the electrolyte may include a lithium salt, a composite membrane 105, a flame-retardant compound 130, and an electrolyte solution.

[0051] For ease of illustration, in Figure 1 The flame retardant compound 130 is shown to be formed inside and around the composite membrane 105, but the location of the flame retardant compound 130 is not limited. For example, the flame retardant compound may be disposed inside the housing constituting the secondary battery. For example, the flame retardant compound 130 may be disposed in the internal pores and surface of the composite membrane 105, on the external surface of the composite membrane 105, or around the electrode assembly disposed inside the housing.

[0052] According to an exemplary embodiment, the composite membrane 105 may comprise an organic polymer 110 and an inorganic electrolyte 120. For example, the organic polymer 110 and the inorganic electrolyte 120 may be mixed and dispersed within the composite membrane to physically contact or bond with each other. The composite membrane may be a free-standing membrane.

[0053] The above lithium salt can be represented, for example, Li + X - The anion (X) of the above lithium salt - Examples of ) could be: 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 - wait.

[0054] Organic polymer 110 can be an ion-conducting polymer. The aforementioned organic polymer can be used as a polymer matrix. This polymer matrix exhibits low fluidity within the electrolyte and does not impede the migration of lithium ions within the electrolyte, even when an electrolyte solvent is present.

[0055] For example, organic polymer 110 may contain repeating units such as ethers, styrene, and fluorinated hydrocarbons.

[0056] In some embodiments, the organic polymer 110 may comprise polyvinylidene fluoride (PVDF), polystyrene (PS), polyether sulfone (PES), polyurethane (PU), polyethylene oxide (PEO), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), polyimide (PI), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyethyl methacrylate (PEMA), polycaprolactone (PCL), and polyvinylpyrrolidone (PVA). The organic polymer 110 may include pyrrolidone (PVP), polysulfone (PSF), polyethersulfone (PES), polyamide-imide (PAI), etc. In one embodiment, the organic polymer 110 may include at least one of polyvinylidene fluoride, polystyrene, polyethersulfone, and polyurethane. Therefore, the mobility of lithium ions within the composite membrane can be improved, thereby increasing the ionic conductivity.

[0057] The inorganic electrolyte 120 can be an oxide-based solid electrolyte. For example, an oxide-based solid electrolyte may contain ion-conducting compounds containing metals or oxygen. For example, an oxide-based solid electrolyte may contain LLTO-based compounds, LLZO-based compounds, or Li... 6.4 La3Zr 1.4 Ta 0.6 O 12 LLZTO-based compounds, Li6La2CaTa2O 12 Li6La2ANb2O 12 (A is Ca or Sr), Li2Nd3TeSbO 12 Li3BO 2.5 N 0.5 Li9SiAlO8, LAGP-based compounds, LATP-based compounds, Li 1+x Ti 2-x Al xSi y (PO4)3(0≤x≤1,0≤y≤1), LiAl x Zr 2-x (PO4)3(0≤x≤1,0≤y≤1), LiTi x Zr 2-x (PO4)3 (0≤x≤1, 0≤y≤1), LISICON-based compounds, LIPON-based compounds, perovskite-based compounds, NASICON-based compounds, Al2O3, ZnO2, Ce2O2, TiO2, ZrO2, HfO2, MnO2, MgO, WO2, V2O5 and other metal oxides, etc.

[0058] In some embodiments, the inorganic electrolyte 120 may be a lithium-containing oxide-based solid electrolyte. For example, the lithium-containing oxide-based solid electrolyte may contain LLTO-based compounds, LLZO-based compounds (e.g., garnet-type LLZO-based compounds), NASICON-based compounds, LATP-based compounds, perovskite-based compounds, etc. This improves the ionic conductivity and mechanical strength of the electrolyte 100, thereby suppressing lithium dendrites, and enhancing high-temperature stability and lifetime characteristics.

[0059] In some embodiments, the composite membrane may comprise a sintered body or a micro-sintered body of the inorganic electrolyte 120, specifically a micro-sintered body of the inorganic electrolyte 120. More specifically, it may not comprise a sintered body of the inorganic electrolyte 120.

[0060] According to an exemplary embodiment, the flame retardant compound 130 may contain a phosphorus functional group. In some embodiments, the phosphorus functional group may contain at least one of a phosphate group, a phosphite group, a phosphonate group, and a phosphazene group. For example, the flame retardant compound 130 may be a compound formed by polymerizing or copolymerizing a flame retardant monomer containing at least one of a phosphate group, a phosphite group, a phosphonate group, and a phosphazene group. Thus, the flame retardant compound 130 can suppress side reactions with organic polymers 110, inorganic electrolytes 120, and the aforementioned lithium salts, or electrolytes. Furthermore, the presence of a phosphorus functional group in the flame retardant compound 130 can isolate oxygen during combustion and prevent thermal runaway.

[0061] In some embodiments, the flame-retardant compound 130 may collectively comprise a phosphorus-containing functional group and a fluorine atom. For example, the flame-retardant compound 130 may be a compound obtained by polymerizing or copolymerizing a flame-retardant monomer comprising a phosphorus-containing functional group and a fluorine atom. Specifically, the flame-retardant compound 130 may be a flame-retardant polymer comprising a phosphorus-containing functional group and a fluorine atom, more specifically, it may be a flame-retardant polymer or a flame-retardant copolymer. The aforementioned fluorine atoms form free radicals upon the occurrence of a fire, thereby inhibiting the transfer of the combustion reaction. Thus, the flame-retardancy of the electrolyte 100 can be improved by the flame-retardant compound 130.

[0062] In one embodiment, the flame retardant compound 130 may comprise monomers, oligomers, polymers, or mixtures thereof.

[0063] In some embodiments, the flame retardant compound 130 may be a compound obtained by polymerizing or copolymerizing a flame retardant monomer having thermally reactive functional groups and / or photoreactive functional groups. For example, the flame retardant monomer may be a compound containing thermally reactive functional groups and polymerized by thermal polymerization. For example, the flame retardant monomer may be a compound containing photoreactive functional groups and polymerized by photopolymerization. For example, the thermosetting functional groups and / or photocurable functional groups may use (meth)acrylate groups, acryloyl groups, ether groups, alcohol groups, alkoxy groups, etc. For example, the flame retardant compound 130 may contain groups derived from thermally reactive functional groups and / or photoreactive functional groups. In some embodiments, the flame retardant compound 130 may contain a first flame retardant compound 132 in contact with the interior and surface of the composite film 105 and a second flame retardant compound 134 distributed on the exterior of the composite film 105.

[0064] The first flame retardant compound 132 and the second flame retardant compound 134 can be substantially the same compound. For example, the first flame retardant compound 132 and the second flame retardant compound 134 are the flame retardant compound 130 described above, and can be formed inside the secondary battery as the same compound.

[0065] In some embodiments, the composite membrane 105 may include pores 150. At least a portion of the first flame-retardant compound 132 may be distributed within the pores 150. For example, at least a portion of the first flame-retardant compound 132 may be disposed on the inner surface of the pores 150 included in the composite membrane 105. For example, at least a portion of the first flame-retardant compound 132 may be disposed in a gel form on the inner surface of the pores 150 included in the composite membrane 105.

[0066] As used in this disclosure, the term "gel form" refers to a wet solid that contains a liquid state while maintaining a low flowability. For example, a "gel form" may include a substance containing a second flame-retardant compound and a liquid such as an electrolyte, while maintaining a solid state.

[0067] In one embodiment, the porosity of the composite membrane 105 can be 50% to 80%, 50% to 75%, 55% to 75%, 55% to 70%, or 60% to 70%. Within the above ranges, pores 150 are sufficiently formed in the composite membrane 105, so that the first flame-retardant compound 132 can be located inside the composite membrane 105 in the aforementioned proportions. As a result, the ionic conductivity and flame retardancy of the electrolyte 100 can be improved, and the resistance can be reduced.

[0068] In one embodiment, the first flame-retardant compound 132 may be distributed on the outer surface of the composite film 105. For example, the first flame-retardant compound 132 may also be distributed in contact with the composite film 105 on its outer surface. For example, the first flame-retardant compound 132 may be disposed in a gel form while in contact with the composite film 105 on its outer surface. Thus, even if heat is applied to the composite film 105, the first flame-retardant compound 132 can protect the composite film 105 from the effects of heat.

[0069] In some embodiments, the second flame retardant compound 134 may exist separately from the composite membrane 105 in a gel form. For example, the second flame retardant compound 134 may be disposed inside the housing constituting the secondary battery. For example, it may be configured to surround the composite membrane 105. For example, the second flame retardant compound may be configured to be distributed around the electrode assembly disposed inside the housing.

[0070] According to an exemplary embodiment, the weight ratio of the flame-retardant compound 130 to the composite film can be 0.004 to 0.3, 0.01 to 0.3, 0.02 to 0.3, or 0.02 to 0.2. For example, the weight ratio of the content of the flame-retardant compound 130 to the content of the composite film can be within the above range. Within the above range, the ionic conductivity of the electrolyte 100 can be improved, and the flame retardancy can be improved. In one embodiment, the weight ratio of the flame-retardant compound 130 to the composite film can be 0.02 to 0.18, 0.024 to 0.18, or 0.03 to 0.18. Within the above range, the flame retardancy of the electrolyte 100 can be improved, and the ionic conductivity can be further improved.

[0071] According to an exemplary embodiment, the content of organic polymer 110 in the total weight of the composite membrane can be from 5% to 95% by weight, from 5% to 70% by weight, or from 5% to 60% by weight. In one embodiment, the content of organic polymer 110 in the total weight of the composite membrane can be from 5% to 50% by weight, from 5% to 40% by weight, or from 5% to 30% by weight. Within the above ranges, organic polymer 110 can enhance the contact between the composite membrane and the electrode, thereby reducing the interfacial resistance between the composite membrane and the electrode. Furthermore, the content of inorganic electrolyte 120 can be increased, thus improving the ionic conductivity.

[0072] In some embodiments, the weight ratio of flame-retardant compound 130 to organic polymer 110 can be 0.004 to 3.6, 0.0042 to 3.6, 0.005 to 3.6, or 0.08 to 3.6. For example, the weight ratio of the content of flame-retardant compound 130 to the content of organic polymer 110 can be within the above range. Within the above range, the resistance between the composite film and the electrode can be reduced, and the flame retardancy of electrolyte 100 can be improved. In one embodiment, the weight ratio of flame-retardant compound 130 to organic polymer 110 can be 0.01 to 3.6, 0.03 to 3.6, 0.04 to 3.6, 0.07 to 3.6, 0.08 to 3.6, or 0.1 to 3.6. Within the above range, the flame-retardant effect provided by flame-retardant compound 130 can be maintained, and the interfacial resistance between electrolyte layer and electrode can be further reduced.

[0073] In some embodiments, the weight ratio of flame-retardant compound 130 to inorganic electrolyte 120 can be 0.004 to 3.6, 0.0042 to 1.8, 0.0042 to 1.0, or 0.0042 to 0.6. For example, the weight ratio of the content of flame-retardant compound 130 to the content of inorganic electrolyte 120 can be within the above ranges. Within the above ranges, the ionic conductivity and flame retardancy of electrolyte 100 can be improved simultaneously. In one embodiment, the weight ratio of flame-retardant compound 130 to inorganic electrolyte 120 can be 0.0042 to 0.5, 0.042 to 0.4, 0.042 to 0.3, or 0.042 to 0.26. Within the above ranges, the flame-retardant effect provided by flame-retardant compound 130 can be maintained, and the ionic conductivity of electrolyte 100 can be further improved.

[0074] Figure 2 This is a process flow diagram illustrating a method for manufacturing an electrolyte for a secondary battery according to an exemplary embodiment. Hereinafter, reference will be made to... Figure 2 The manufacturing method of the electrolyte for secondary batteries described above will be explained.

[0075] Reference Figure 2 The first mixture can be prepared by mixing organic polymers, inorganic electrolytes, a first solvent, and a second solvent (e.g., step S10).

[0076] In some embodiments, the solubility of the organic polymer relative to the first solvent may be greater than the solubility of the organic polymer relative to the second solvent. For example, the solubility of the organic polymer relative to the first solvent may be 1 g / 100 g or more, 33 g / 100 g or more, 10 g / 100 g or more, 100 g / 100 g or more, or from 100 g / 100 g to 1000 g / 100 g. For example, the solubility of the organic polymer relative to the second solvent may be less than 1 g / 100 g, less than 0.1 g / 100 g, or less than 0.01 g / 100 g.

[0077] In one embodiment, in the first mixture, the organic polymer can be dissolved in the first solvent but not in the second solvent.

[0078] For example, the aforementioned organic polymer may be soluble in the aforementioned first solvent. Thus, the aforementioned organic polymer can dissolve in the aforementioned first solvent.

[0079] For example, the aforementioned organic polymer may be insoluble in the aforementioned second solvent. Thus, the aforementioned organic polymer may be substantially insoluble in the aforementioned second solvent.

[0080] The aforementioned 'solubility' refers to the mass (g) of the organic polymer dissolved in 100g of the first solvent or the second solvent. For example, a solubility of 1g / 100g means that 1g of the organic polymer is dissolved in 100g of the first solvent or the second solvent.

[0081] In some embodiments, the first solvent may be miscible with the second solvent. For example, the first solvent and the second solvent may be mixed or blended.

[0082] The aforementioned organic polymer and inorganic electrolyte can be the aforementioned organic polymer and inorganic electrolyte.

[0083] The first solvent mentioned above can be a solvent that dissolves the aforementioned organic polymer and is mixed with the second solvent mentioned above. The first solvent may include, for example: tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-Me-THF), N-methyl-2-pyrrolidone (NMP), 1,3-dioxolane, vinylene carbonate (VC), 1,4-dioxane, dimethylformamide (DMF), dimethylacetamide (DMAc), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), etc. These can be used alone or in combination of two or more. In one embodiment, the first solvent mentioned above may be tetrahydrofuran.

[0084] The second solvent described above can be a solvent that does not dissolve the aforementioned organic polymer and is mixed with the first solvent. The second solvent may include, for example: heptane, octane, nonane, decane, dodecane, 2,2,4-trimethylpentane, ethylene glycol, methylcyclohexane (MCH), 2-methyl-1-butanol, decahydronaphthalene, ethylene carbonate (EC), propylene carbonate (PC), etc. These can be used alone or in combination of two or more. In one embodiment, the second solvent may be octane.

[0085] In one embodiment, the boiling point of the first solvent may be lower than that of the second solvent. Therefore, the first solvent can vaporize at a lower temperature than the second solvent.

[0086] According to an exemplary embodiment, the first mixture can be dried to manufacture a composite film (e.g., step S20). The first mixture can be cast onto a substrate (e.g., a glass substrate or a plastic substrate) for drying.

[0087] In some embodiments, in step S20, the first solvent can be removed at a first temperature (e.g., first drying), and the second solvent can be removed at a second temperature (e.g., second drying), thereby allowing the first solvent to be removed from the first mixture first and then the second solvent to be removed.

[0088] Figure 3 and Figure 4 These are schematic diagrams illustrating the first drying process and the second drying process, respectively.

[0089] Reference Figure 3 The first mixture is dried to remove the first solvent from the first mixture.

[0090] Reference Figure 4 After removing the first solvent, the remaining first mixture can be dried to remove the second solvent 170. With the second solvent 170 removed, the composite membrane 105 can be obtained.

[0091] In one embodiment, the first drying and the second drying can be performed continuously. In another embodiment, the second drying can be performed after a certain period of time following the first drying.

[0092] The first mixture described above can be a state in which the organic polymer and the second solvent are mixed together using the first solvent. The organic polymer and the second solvent 170 can be separated from each other by preferentially removing the first solvent from the first mixture at a first temperature. For example, when the first solvent is removed, the organic polymer and inorganic electrolyte in the first mixture can be separated from the second solvent in a state of physical contact or binding.

[0093] After removing the first solvent at the first temperature, the second solvent 170 can be removed at the second temperature to form a composite film. Thus, the composite film may contain pores 150 formed due to the removal of the second solvent at the original location of the first solvent.

[0094] In some embodiments, the first temperature may be lower than the second temperature. Therefore, during the period when the first solvent is removed at the first temperature, the second solvent 170 may not be removed or the removal rate may be significantly lower.

[0095] For example, the first temperature can be 25°C to 200°C, 35°C to 200°C, 50°C to 200°C, 50°C to 150°C, 50°C to 100°C, or 50°C to 85°C. Within the above range, the first solvent can be preferentially removed if the second solvent 170 in the first mixture is not removed due to vaporization.

[0096] For example, the second temperature can be 70°C to 300°C, 70°C to 250°C, 70°C to 200°C, 70°C to 175°C, or 70°C to 150°C. Within the above range, during the period when the first solvent is removed at the first temperature, the first solvent can be preferentially removed if the second solvent 170 is not removed due to vaporization.

[0097] In one embodiment, the first solvent can be removed at a first temperature for 10 minutes to 2 hours, 10 minutes to 1.5 hours, or 30 minutes to 1.25 hours. In one embodiment, the second solvent 170 can be removed at a second temperature for 30 minutes to 12 hours, 30 minutes to 6 hours, or 30 minutes to 3 hours. Within the above ranges, the first solvent and the second solvent 170 can be removed by sequentially and sufficiently vaporizing.

[0098] In some embodiments, the organic polymer in the total weight of the composite membrane may be contained in the aforementioned amounts. For example, the organic polymer content in the total weight of the composite membrane may be 5% to 95% by weight, 5% to 70% by weight, or 5% to 60% by weight. In one embodiment, the organic polymer content in the total weight of the composite membrane may be 5% to 50% by weight, 5% to 40% by weight, or 5% to 30% by weight.

[0099] For example, when preparing the first mixture, the organic polymers can be mixed within the aforementioned content range.

[0100] According to an exemplary embodiment, a second mixture comprising a flame-retardant monomer and an electrolyte can be impregnated in the composite membrane (e.g., step S30). For example, the second mixture obtained by impregnating the flame-retardant monomer in the electrolyte can be impregnated in the composite membrane.

[0101] In some embodiments, the second mixture can be injected into the housing while the electrode assembly in which the composite membrane is configured as an electrolyte layer between the positive and negative electrodes is inserted into the housing, thereby immersing the second mixture in the composite membrane.

[0102] In some embodiments, the weight ratio of the flame-retardant monomer to the composite film can be 0.004 to 0.3, 0.01 to 0.3, 0.02 to 0.3, or 0.02 to 0.2. For example, the weight ratio of the content of the flame-retardant monomer to the content of the composite film can be within the aforementioned range. In one embodiment, the weight ratio of the flame-retardant monomer to the composite film can be 0.02 to 0.18, 0.024 to 0.18, or 0.03 to 0.18. For example, the content of the flame-retardant monomer contained in the second mixture relative to the content of the composite film can be within the aforementioned range. Thus, the flame-retardant monomer can be contained in the composite film within the aforementioned range. Furthermore, after the second mixture is cured, the weight ratio of the content of the flame-retardant compound to the content of the composite film can be within the aforementioned range.

[0103] In some embodiments, the composite membrane described above may be a composite membrane formed according to the method described above. Therefore, a porous composite membrane can be used for manufacturing electrolytes for secondary batteries. By using the porous composite membrane, the flame-retardant monomer can be located in the pores of the porous composite membrane. For example, the flame-retardant monomer can be impregnated in the pores of the porous composite membrane.

[0104] In some embodiments, the flame-retardant monomer may be a flame-retardant monomer containing phosphorus-containing functional groups. For example, the phosphorus-containing functional groups may contain at least one selected from phosphate ester groups, phosphite ester groups, phosphonate ester groups, and phosphazene groups. This improves the flame retardancy of the electrolyte for secondary batteries. In one embodiment, the flame-retardant monomer may be a flame-retardant monomer containing both phosphorus-containing functional groups and fluorine atoms. This further improves the flame retardancy of the electrolyte for secondary batteries.

[0105] In some embodiments, the flame-retardant monomer may contain thermally reactive functional groups and / or photoreactive functional groups. For example, the flame-retardant monomer may be a compound containing thermally reactive functional groups and polymerized by thermal polymerization. For example, the flame-retardant monomer may be a compound containing photoreactive functional groups and polymerized by photopolymerization. For example, the thermosetting functional groups and / or photocurable functional groups may use (meth)acrylate groups, acryloyl groups, ether groups, alcohol groups, alkoxy groups, etc.

[0106] In one embodiment, the flame-retardant monomer may simultaneously contain at least one of a phosphorus-containing functional group, a thermally reactive functional group, and a photoreactive functional group. In another embodiment, the flame-retardant monomer may simultaneously contain at least one of a phosphorus-containing functional group, a fluorine atom, and a thermally reactive functional group and a photoreactive functional group.

[0107] In some embodiments, the electrolyte may contain a thermal initiator and / or a photoinitiator for inducing the thermosetting and / or photosetting of the flame-retardant monomer. In one embodiment, the content of the thermal initiator and / or photoinitiator may be from 0.5 parts by weight to 2 parts by weight relative to 100 parts by weight of the flame-retardant monomer contained in each electrolyte composition.

[0108] For example, the aforementioned thermal initiators may include azo compounds such as 2,2-azobis(2-cyanobutane), 2,2-azobis(methylbutyronitrile), 2,2'-azobisisobutyronitrile (AIBN), and azobismethylvalerate (AMVN), or peroxide compounds such as benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, cumene peroxide, and hydrogen peroxide.

[0109] For example, the aforementioned photoinitiators may include acylphosphine such as 2-hydroxy-2-methyl-1-phenylpropane-1-one (HMPP), benzoin ether, dialkyl acetophenone, hydroxylalkylketone, phenyl glyoxylate, benzyl dimethylketal, and 2,4,6-trimethyl-benzoyl-trimethylphosphine oxide, as well as α-aminoketone.

[0110] In some embodiments, the electrolyte may contain a lithium salt. The lithium salt may include the lithium salt described above. Therefore, the ionic conductivity of the electrolyte for secondary batteries can be improved.

[0111] In some embodiments, the electrolyte may contain organic solvents. For example, these organic solvents may include carbonate organic solvents such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), and vinylene carbonate (VC), as well as dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, propylene sulfone, and tetrahydrofuran. These can be used alone or in combination of two or more.

[0112] In one embodiment, the electrolyte may further comprise additives. These additives may include, for example, cyclic carbonate compounds, fluorinated cyclic carbonate compounds, sulfonyl lactone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate ester compounds.

[0113] The aforementioned cyclic carbonate compounds may include: vinylene carbonate, ethylene carbonate (VEC), etc.

[0114] The aforementioned fluorinated cyclic carbonate compounds may include fluoroethylene carbonate (FEC), etc.

[0115] The aforementioned sulfonyl compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0116] The aforementioned cyclic sulfate compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0117] The aforementioned cyclic sulfite compounds may include ethylene sulfite, butylene sulfite, etc.

[0118] The aforementioned phosphate compounds may include: lithium difluorobis-oxalato phosphate, lithium difluorophosphate, etc.

[0119] The aforementioned borate ester compounds may include lithium bis(oxalate)borate, etc.

[0120] In one embodiment, the organic solvent may be a carbonate-based organic solvent. This improves the electrical and chemical stability of the electrolyte used in secondary batteries.

[0121] According to an exemplary embodiment, the second mixture can be cured (e.g., step S40). This allows the manufacture of an electrolyte for secondary batteries.

[0122] In some embodiments, the flame-retardant monomer can be polymerized or copolymerized while the second mixture is being cured. Thus, the electrolyte for a secondary battery can contain a flame-retardant compound.

[0123] In one embodiment, the flame retardant monomer disposed on the inner surface of the pores of the composite film or on the outer surface of the composite film and in contact with the composite film can be polymerized or copolymerized to form a first flame retardant compound.

[0124] In one embodiment, flame-retardant monomers not disposed on the inner surface of the pores of the composite film or on the outer surface of the composite film can be polymerized or copolymerized to form a second flame-retardant compound. For example, without contacting the composite film, flame-retardant monomers distributed around the electrode assembly disposed inside the casing of the secondary battery can be polymerized or copolymerized to form a second flame-retardant compound.

[0125] Thus, the second mixture is solidified, thereby enabling the formation of a flame-retardant compound comprising the first and second flame-retardant compounds from the flame-retardant monomer.

[0126] In some embodiments, the weight of the flame-retardant monomer relative to the total weight of the composite film may be substantially the same as the weight of the flame-retardant compound relative to the total weight of the composite film. For example, the weight decrease or increase relative to the total weight of the composite film when the flame-retardant monomer is polymerized or copolymerized into the flame-retardant compound may be less than 0.0001% by weight or less than 0.00001% by weight. Therefore, the ratio of the weight of the flame-retardant monomer to the weight of the composite film may be substantially the same as the ratio of the weight of the flame-retardant compound to the weight of the composite film.

[0127] In some embodiments, curing the second mixture can be achieved by heat treatment. For example, by heat curing the second mixture, the flame-retardant monomers inside the composite film can be polymerized or copolymerized into flame-retardant compounds.

[0128] In some embodiments, the heat treatment described above may be 40°C to 120°C, 50°C to 120°C, 50°C to 100°C, 60°C to 100°C, or 60°C to 90°C.

[0129] In some embodiments, the heat treatment described above may be performed for 20 minutes to 2 hours, 20 minutes to 1.5 hours, 30 minutes to 1.5 hours, 40 minutes to 1.5 hours, or 40 minutes to 70 minutes.

[0130] Within the aforementioned temperature and time range, the flame-retardant monomers within the second mixture can be fully polymerized or copolymerized.

[0131] In some embodiments, curing the second mixture can be achieved by irradiating it with light. For example, by photocuring the second mixture, the flame-retardant monomers inside the composite film can be polymerized or copolymerized into flame-retardant compounds. This allows the polymerization or copolymerization of the flame-retardant monomers to occur at relatively low temperatures. Therefore, damage to the composite film caused by high-temperature heat treatment can be prevented.

[0132] In some embodiments, the UV curing process used for the above-described photopolymerization can utilize wavelengths from 250 nm to 400 nm and a power density of 800 mW / cm². 2 Up to 1100mW / cm 2 The process is performed using light of varying intensity. In one embodiment, the UV curing process can be carried out for 5 to 20 seconds. Within the aforementioned wavelength and intensity range, the flame-retardant monomers within the second mixture can be sufficiently polymerized or copolymerized.

[0133] A lithium secondary battery according to an exemplary embodiment may include: a housing; an electrode assembly comprising repeatedly stacked positive and negative electrodes; and an electrolyte for the secondary battery disposed within the housing between the positive and negative electrodes within the electrode assembly, or distributed around the electrode assembly.

[0134] In some embodiments, the electrode assembly may include: a positive electrode, a negative electrode opposite to the positive electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode.

[0135] The aforementioned positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the aforementioned positive electrode current collector.

[0136] The positive electrode current collector may contain stainless steel, nickel, aluminum, titanium, or alloys thereof. It may also contain aluminum or stainless steel that has been surface-treated with carbon, nickel, titanium, or silver. The positive electrode current collector is not limited to these materials; for example, it may be 10 μm to 50 μm in diameter.

[0137] The aforementioned positive electrode active material may include compounds capable of reversibly inserting and deintercalating lithium ions.

[0138] According to an exemplary embodiment, the aforementioned positive electrode active material may comprise a lithium-nickel metal oxide. The aforementioned lithium-nickel metal oxide may comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0139] In some embodiments, the above-mentioned positive electrode active material or the above-mentioned lithium-nickel metal oxide may contain a layered structure or a crystal structure as shown in Chemical Formula 1.

[0140] [Chemical Formula 1]

[0141] Li x Ni a M b O 2+2

[0142] In chemical formula 1, the values ​​can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.

[0143] The chemical structure represented by Formula 1 indicates the bonding relationships contained within the layered or crystalline structure of the positive electrode active material, without excluding other additional elements. For example, M contains Co and / or Mn, and Co and / or Mn can be provided together with Ni as the main active element of the positive electrode active material. Formula 1 is provided to represent the bonding relationships of the aforementioned main active elements and should be understood as a chemical formula that includes the introduction and substitution of other additional elements.

[0144] In one embodiment, auxiliary elements may also be included for addition to the aforementioned main active elements to enhance the chemical stability of the positive electrode active material or the aforementioned layered structure / crystal structure. These auxiliary elements may be blended within the aforementioned layered structure / crystal to form bonds; this should also be understood as being included within the scope of the chemical structure represented by Formula 1.

[0145] The aforementioned auxiliary elements may include at least one of the following: 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. These auxiliary elements may also function as auxiliary active elements; for example, Al, in conjunction with Co or Mn, contributes to the capacity / power activity of the positive electrode active material.

[0146] For example, the above-mentioned positive electrode active material or the above-mentioned lithium-nickel metal oxide may contain a layered structure or a crystal structure as shown in the following chemical formula 1-1.

[0147] [Chemical Formula 1-1]

[0148] Li x Ni a M1 b1 M2 b2 O 2+z

[0149] In chemical formula 1-1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 1-1, the following values ​​may be present: 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, -0.5≤z≤0.1.

[0150] The aforementioned positive electrode active material may also contain coating elements or doping elements. For example, elements that are substantially the same as or similar to the aforementioned auxiliary elements may be used as coating elements or doping elements. For example, two or more of the aforementioned elements may be used alone or in combination as coating elements or doping elements.

[0151] The coating elements or doping elements mentioned above may exist on the surface of lithium-nickel metal oxide particles, or be contained in the bonding structure shown in the above chemical formula 1 or above chemical formula 1-1 through surface penetration of the above lithium-nickel metal composite oxide particles.

[0152] The aforementioned positive electrode active material may include nickel-cobalt-manganese (NCM)-based lithium oxides. In this case, NCM-based lithium oxides with increased nickel content can be used.

[0153] Ni can serve as a transition metal relevant to the power and capacity of lithium secondary batteries. Therefore, as described above, by employing a high-content (High-Ni) composition in the aforementioned positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0154] However, as the content of Ni increases, the long-term storage stability and life stability of the positive electrode or secondary battery may be relatively reduced, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, by including Co, conductivity can be maintained, and at the same time, life stability and capacity retention characteristics can be improved by Mn.

[0155] The content of Ni in the above NCM-based lithium oxide (for example, the molar fraction of Ni in the total moles of nickel, cobalt, and manganese) can be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni can 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.

[0156] In some embodiments, the above positive electrode active material may further 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).

[0157] In some embodiments, the above positive electrode active material may include, for example, a Mn-rich-based active material, a Li rich layered oxide (LLO) / Over Lithiated Oxode (OLO)-based active material, or a Co-less-based active material having a chemical structure or crystal structure shown in Chemical Formula 2 below.

[0158] [Chemical Formula 2]

[0159] p[Li2MnO3]·(1-p)[Li q JO2]

[0160] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0161] In some embodiments, the above positive electrode active material may be a sodium-based active material or a potassium-based active material. The above sodium-based active material may include a layered structure or crystal structure in which Li in Chemical Formula 1, Chemical Formula 1-1, and / or Chemical Formula 2 is replaced by Na and / or K.

[0162] In some embodiments, the above positive electrode active material may also be a calcium-based active material. The above calcium-based active material may include, for example, a calcium-cobalt active material and a calcium-phosphate active material.

[0163] For example, the aforementioned positive electrode active material can be mixed into a solvent to manufacture a positive electrode slurry. The positive electrode slurry can be coated onto a positive electrode current collector, then dried and calendered to manufacture a positive electrode active material layer. The coating process can be performed using gravure coating, slot die coating, multilayer simultaneous extrusion coating, embossing, doctor blade coating, dip coating, bar coating, casting, etc., but is not limited to these methods. The aforementioned positive electrode active material layer may also contain a binder, and optionally, may also contain an electrolyte, a conductive agent, a thickener, etc.

[0164] Solvents used in the manufacture of the above-mentioned positive electrode active material layer include, for example, N-methyl-2-pyrrolidone (nmP), dimethylformamide (DMF), dimethylacetamide (DMA), dimethylaminopropylamine (DMAPA), ethylene oxide (EO), tetrahydrofuran (THF), etc.

[0165] In one embodiment, the electrolyte contained in the positive electrode active material layer can be the electrolyte for a secondary battery as described above. In another embodiment, the electrolyte contained in the positive electrode active material layer can be the inorganic electrolyte as described above, but the inorganic electrolyte contained in the composite film and the inorganic electrolyte contained in the positive electrode active material layer can be the same or different. For example, the secondary battery can be provided as an all-solid-state battery containing the electrolyte or inorganic electrolyte described above.

[0166] The aforementioned binders may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethyl methacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, the positive electrode binder may be a PVDF series binder.

[0167] The aforementioned conductive agents can be added to enhance the conductivity of the positive electrode active material layer and / or the mobility of lithium ions or electrons. For example, the aforementioned conductive agents may include carbon-based conductive agents such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fibers, and / or metal-based conductive agents containing perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, but are not limited to these.

[0168] The aforementioned positive electrode active material layer may also contain thickeners and / or dispersants. As an example, the aforementioned positive electrode active material layer may contain thickeners, such as carboxymethyl cellulose (CMC).

[0169] The aforementioned negative electrode may include a layer of negative electrode active material disposed on at least one side of the negative electrode current collector and the aforementioned negative electrode current collector.

[0170] The positive electrode current collector may include, for example, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and polymer substrates coated with conductive metals. The negative electrode current collector is not limited to these materials and may, for example, be 10 μm to 50 μm in diameter.

[0171] The negative electrode active material layer may contain a negative electrode active material. This negative electrode active material can be any substance capable of adsorbing and desorbing lithium ions. 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.

[0172] Examples of amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0173] Examples of crystalline carbon mentioned above include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and other graphitic carbons.

[0174] Examples of lithium metals mentioned above include pure lithium metal or lithium metal with a protective layer formed to inhibit dendrite growth, etc. In one embodiment, the lithium-containing metal layer deposited or coated on the negative electrode current collector can be used as the negative electrode active material layer. In one embodiment, the lithium thin film layer can be used as the negative electrode active material layer.

[0175] The elements contained in the aforementioned lithium alloys may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0176] The above silicon-containing material can provide further increased capacity characteristics. The above silicon-containing material may include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), silicon-carbon composite, etc. The above metal may include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) may include metal silicate.

[0177] For example, the above negative electrode active material can be mixed into a solvent to prepare a negative electrode paste. After the above negative electrode paste is coated / deposited on the negative electrode current collector, it can be dried and rolled to manufacture the negative electrode active material layer. The above coating process can be carried out using a process substantially the same as the manufacturing method of the positive electrode active material layer. The above negative electrode active material layer may further include a binder, and optionally, may further include an electrolyte, a conductive agent, a thickening agent, etc.

[0178] In some embodiments, the negative electrode may include a negative electrode active material layer in the form of lithium metal formed by a deposition / coating process.

[0179] Examples of the solvent for the above negative electrode active material layer include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, tert-butanol, etc.

[0180] In one embodiment, the electrolyte included in the above negative electrode active material layer may be the above electrolyte for the secondary battery. In one embodiment, the electrolyte included in the above negative electrode active material layer may be the above inorganic electrolyte, but the inorganic electrolyte included in the above composite film and the inorganic electrolyte included in the above negative electrode active material layer may be the same or different. For example, the secondary battery can be provided as an all-solid (All-Solid) battery including the above electrolyte or inorganic electrolyte.

[0181] The above binder, conductive agent, and thickening agent can use the above materials that can be used when manufacturing the positive electrode.

[0182] In some embodiments, the negative electrode binder can use a styrene-butadiene rubber-based binder, carboxymethyl cellulose, a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene) (PEDOT)-based binder, etc.

[0183] In some embodiments, an electrolyte layer may be disposed between the positive electrode and the negative electrode within the electrode assembly. For example, the positive electrode, the negative electrode, and the electrolyte layer constitute an electrode unit, and multiple electrode units stacked together can form an electrode assembly. For example, the electrode assembly can be formed by winding, lamination, folding, etc.

[0184] In some embodiments, the weight ratio of the flame-retardant compound to the composite film can be fixed regardless of the number of electrode units included in the electrode assembly. For example, when the electrode assembly includes one electrode unit, the weight ratio of the flame-retardant compound to the composite film can be within the aforementioned range. Furthermore, when the electrode assembly includes two or more electrode units, the weight ratio of the flame-retardant compound to the composite film can also be within the aforementioned range.

[0185] In some embodiments, the composite membrane of the electrolyte for a secondary battery described above can be configured as an electrolyte layer between the positive electrode and the negative electrode. For example, the electrolyte layer may include a composite membrane impregnated with the flame-retardant compound described above. For example, in the composite membrane impregnated with the flame-retardant compound, the flame-retardant compound may be disposed in a gel form on the inner surface of the pores of the composite membrane.

[0186] In some embodiments, a portion of the electrolyte for a secondary battery may be distributed in a gel form around the electrode assembly. For example, a portion of the flame-retardant compound contained in the electrolyte for a secondary battery may be distributed in a gel form around the electrode assembly.

[0187] For example, electrode tabs (positive electrode tab and negative electrode tab) may protrude from the positive electrode current collector and the negative electrode current collector, respectively, and extend to one side of the housing. The aforementioned electrode tabs are fused together with the aforementioned one side of the housing and connected to electrode leads (positive electrode lead and negative electrode lead) that extend to or are exposed outside the housing.

[0188] For example, pouch-shaped shells, prismatic shells, cylindrical shells, coin-shaped shells, etc. can be used.

[0189] The embodiments of this disclosure are further illustrated below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating this disclosure and are not intended to limit the scope of the appended claims. It will be obvious to those skilled in the art that various changes and modifications can be made to the embodiments within the scope and technical concept of this disclosure, and such variations and modifications should fall within the scope of the appended patent claims.

[0190] Examples and Comparative Examples

[0191] Example 1

[0192] (1) Manufacturing of electrolytes for secondary batteries

[0193] Polyvinylidene fluoride (PVDF) as an organic polymer and LLZTO (Li₂O₃) as an inorganic electrolyte were used. 6.4 La3Zr 1.4 Ta 0.6 O 12 The first mixture is prepared by mixing a mixed solvent, which is a mixture of tetrahydrofuran (THF) and octane in a volume ratio of 1:1, at a weight ratio of 50:50.

[0194] The first mixture was dried at 80°C for 1 hour, and then dried again at 125°C for 45 minutes to form a composite membrane.

[0195] (2) Preparation of the second mixture

[0196] The second mixture was prepared by mixing the compound shown in Formula 3 as a flame retardant monomer with a 1.0 M LiPF6 solution (a mixed solvent of EC / EMC with a volume ratio of 1:3).

[0197] [Chemical Formula 3]

[0198]

[0199] (3) Manufacturing of lithium secondary batteries

[0200] LiNi will be used as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, polyvinylidene fluoride (PVDF) as a binder, and carbon black as a conductive agent are mixed in a weight ratio of 94:3:3 to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto aluminum foil, dried, and calendered to obtain the positive electrode.

[0201] A negative electrode slurry is prepared by mixing natural graphite (as the negative electrode active material), SBR / CMC (as a binder), and carbon black (as a conductive agent) in a weight ratio of 96:3:1. The negative electrode slurry is then uniformly coated onto copper foil, dried, and rolled to obtain the negative electrode.

[0202] Prepare the composite membrane using the method described above. After placing the positive and negative electrodes in the middle of the composite membrane and arranging them opposite each other, weld the tabs of the positive electrode and the tabs of the negative electrode respectively.

[0203] The welded positive / composite film / negative electrode assembly is placed inside a soft pack, with the tab portion contained within the sealed area. The other three sides, except for the side containing the second mixture prepared using the method described above, are sealed. The remaining portion is injected with the second mixture, and the remaining side is sealed, then immersed for 12 hours. Afterward, it is heat-cured in an oven at 70°C for 1 hour to obtain a lithium secondary battery.

[0204] The weight ratio of the flame-retardant monomer to the composite film is 0.03.

[0205] Examples 2 to 8

[0206] In manufacturing the electrolyte for secondary batteries, the lithium secondary battery was prepared using the same method as in Example 1, except that the types of organic polymers, the weight ratio of organic polymers to inorganic electrolytes, and the weight ratio of flame-retardant monomers to composite membranes were changed according to Table 1.

[0207] Comparative Example 1

[0208] LiNi will be used as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, polyvinylidene fluoride (PVDF) as a binder, and carbon black as a conductive agent are mixed in a weight ratio of 94:3:3 to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto aluminum foil, dried, and calendered to obtain the positive electrode.

[0209] A negative electrode slurry is prepared by mixing natural graphite (the negative electrode active material), SBR / CMC (as a binder), and carbon black (as a conductive agent) in a weight ratio of 96:3:1. The negative electrode slurry is then uniformly coated onto copper foil, dried, and rolled to obtain the negative electrode.

[0210] Prepare polyethylene (PE) as a separator. After placing the separator between the positive and negative electrodes and positioning them opposite each other, weld the tabs of the positive electrode and the tabs of the negative electrode respectively.

[0211] The welded positive / separator / negative electrode assembly is placed inside a soft package, ensuring the tab area is contained within the sealed region, and the three sides except for the electrolyte injection side are sealed. The remaining portion is used to inject the electrolyte and the compound shown in Formula 3 (as a flame-retardant monomer) at a weight ratio of 95:5, and the remaining side is sealed, then impregnated for 12 hours. Afterwards, it is heat-cured in an oven at 70°C for 1 hour to obtain a lithium secondary battery.

[0212] The electrolyte was prepared by dissolving 1.0 M LiPF6 in a mixed solvent of EC / EMC (3 / 7; volume ratio) and then adding 5 wt% of fluorinated ethylene carbonate (FEC).

[0213] Comparative Example 2

[0214] The secondary battery was prepared using the same method as Comparative Example 1, except that a polyethylene coated with 3 μm of boehmite was used as the separator.

[0215] Comparative Example 3

[0216] In manufacturing the electrolyte for secondary batteries, the lithium secondary battery was prepared using the same method as in Example 1, except that the weight ratio of the flame-retardant monomer to the composite membrane was 0.002.

[0217] Comparative Example 4

[0218] In manufacturing the electrolyte for secondary batteries, the lithium secondary battery was prepared using the same method as in Example 1, except that the weight ratio of the flame-retardant monomer to the composite membrane was 0.4.

[0219] Table 1

[0220]

[0221] The specific components listed in Table 1 are as follows:

[0222] PVDF: Polyvinylidene fluoride

[0223] PS: Polystyrene

[0224] PI: Polyimide

[0225] Experimental Example 1: Electrolyte Evaluation

[0226] (1) Porosity measurement

[0227] The porosity of the electrolyte layer for secondary batteries according to the above-described embodiments and Comparative Example 3 was measured. The porosity was calculated using the density calculation method shown in Formula 1 below.

[0228] [Formula 1]

[0229]

[0230] In Formula 1, BW is the basis weight (g / m³) of the composite membrane (or separator). 2 ), T c ρ represents the thickness of the composite membrane (or diaphragm). c The density (g / cm³) of the composite membrane (or diaphragm) 2 ).

[0231] The calculated porosity is shown in Table 2 below.

[0232] (2) Evaluation of Thermal Shrinkage

[0233] The electrolyte layer for secondary batteries prepared according to the above embodiments and the separator and electrolyte layer impregnated with electrolyte prepared according to the comparative example were cut into 2cm×2cm cross sections, placed at a temperature of 150°C, and the cross-sectional area was measured as a function of time.

[0234] Based on the measured cross-sectional area, calculate the rate of change of cross-sectional area using the following formula 2.

[0235] [Equation 2]

[0236]

[0237] In Equation 2, S i Minimum cross-sectional area (4cm) 2 ), S k This is the cross-sectional area measured after m minutes.

[0238] The calculated rate of change of cross-sectional area is shown in Table 2 below.

[0239] (3) Combustion evaluation

[0240] The electrolyte layer for secondary batteries prepared according to the above embodiments and the separator and electrolyte layer impregnated with electrolyte prepared according to the comparative example were burned for 50 minutes to evaluate whether they burned.

[0241] The evaluation of whether it is combustible is as follows:

[0242] ○: Burning area less than 10%

[0243] △: The burning area is 10% to 20%.

[0244] ×: Burning area exceeds 20%

[0245] The evaluation results are shown in Table 2 below.

[0246] Table 2

[0247]

[0248] Figure 5 and Figure 6 The images show the thermal shrinkage of the electrolyte layer for secondary batteries prepared according to Examples 5 and 6 over time.

[0249] Figure 9 This is a photograph of the combustion of the electrolyte layer for a secondary battery prepared according to Example 5.

[0250] Reference Figure 5 , 6 In the examples using a composite membrane comprising organic polymers and inorganic electrolytes, and where the weight ratio of the flame retardant compound to the composite membrane is 0.004 to 0.3, the cross-sectional area change rate is less than 15.7%.

[0251] Figure 7 and Figure 8 The images show the thermal shrinkage of the diaphragms impregnated with electrolyte prepared according to Comparative Example 1 and Comparative Example 2 over time.

[0252] Figure 10 and 11 The images show combustion photographs of the diaphragm and electrolyte layer impregnated with electrolyte prepared according to Comparative Example 1 and Comparative Example 2, respectively.

[0253] Reference Figure 7 , 8 According to Tables 11 and 1, in the comparative examples without composite membranes, the cross-sectional area change rate exceeded 50%.

[0254] Experimental Example 2: Evaluation of Lithium Secondary Batteries

[0255] (1) Evaluation of OCV based on temperature

[0256] After setting the voltage of the lithium secondary battery according to the above embodiments and comparative examples to 4.0V, the change of open circuit voltage (OCV) over time was measured at 150°C and 100% SOC.

[0257] After 45 minutes of measurement, the temperature was raised to 160℃ and the voltage was measured before and after the temperature rise (30 minutes and 60 minutes after the start of measurement) and at 120 minutes after the start of measurement.

[0258] The rate of change of OCV and the total rate of change of OCV are calculated using the following formula 3.

[0259]

Formula 3

[0260]

[0261] In Equation 3, A m B is the voltage measured after m minutes from the start of the measurement. nThis is the voltage measured after n minutes from the start of the measurement.

[0262] Specifically, the rate of change of OCV in A 30 and B 60 The calculated rate of change of OCV, the total rate of change of OCV in A0 and B 120 The calculated rate of change of OCV.

[0263] The voltage and OCV change rate measured before and after heating to 160℃ are shown in Table 3 below.

[0264] (2) Capacity retention rate

[0265] The lithium secondary batteries prepared according to the above embodiments and comparative examples were repeatedly charged (CC-CV 2.0C 4.2V 0.05C cut-off) and discharged (CC 1.0C 2.7V cut-off) 250 times in a chamber at 25°C. The capacity retention rate was calculated by taking the ratio of the discharge capacity of the 250th discharge to the discharge capacity of the 1st discharge as a percentage.

[0266] The measurements are shown in Table 4 below.

[0267] Table 3

[0268]

[0269] Figure 12 To show the curves of OCV change over time for the lithium secondary batteries prepared according to Examples 6 and 7 and Comparative Examples 1 and 2.

[0270] Figure 13 To show the curves of the discharge capacity of the lithium secondary batteries prepared according to Examples 4, 5 and Comparative Example 2 as a function of the number of charge-discharge cycles (capacity retention rate).

[0271] Reference Figures 12 to 13 According to Table 3, in the examples using a composite membrane containing organic polymers and inorganic electrolytes, and where the weight ratio of the flame retardant compound to the composite membrane is 0.04 to 0.3, the total change rate of OCV is less than 50.50%, and the capacity retention rate is more than 80.3%.

[0272] In comparative examples where no composite membrane was used, or where, even if a composite membrane was used, the weight ratio of the flame retardant compound to the composite membrane was less than 0.04 or greater than 0.3, the capacity retention rate decreased.

[0273] Compared to Example 3, where the weight ratio of flame retardant compound to composite film was reduced to 0.002 using a composite film, the total change rate of OCV increased and the capacity retention decreased in Example 3, where the weight ratio of flame retardant compound to composite film was 0.004.

[0274] Comparative Example 4, which used a composite membrane but increased the weight ratio of the flame retardant compound to the composite membrane to 0.4, showed a decrease in capacity retention compared to Example 2, where the weight ratio of the flame retardant compound to the composite membrane was 0.18.

[0275] Experimental Example 3: Evaluation of Electrochemical Stability

[0276] For coin-shaped batteries using the electrolyte layer for lithium secondary batteries prepared according to the above-described embodiments and comparative examples, the voltage was swept at a constant speed, and the change in current was measured. Specifically, measurements were performed at a scan rate of 1.0 mV / s within a voltage range of 3V to 6V.

[0277] The aforementioned coin-shaped battery uses stainless steel as the working electrode and Li foil as the counter electrode (reference electrode), employing a Li foil-electrolyte layer-stainless steel structure.

[0278] Figure 14 This is a graph showing the change of current over time measured by cyclic voltammetry for a coin-shaped battery containing an electrolyte layer for a lithium secondary battery prepared according to an exemplary embodiment and a comparative example.

[0279] Specifically, the graphs show the current versus time changes of two independent evaluations based on the cyclic voltammetry method for coin-shaped batteries containing the electrolyte layers for lithium secondary batteries prepared according to Examples 4, 5 and Comparative Example 2.

[0280] Reference Figure 14 In Examples 4 and 5, which use electrolytes for secondary batteries according to exemplary embodiments, the current amount changing over time is reduced compared to Comparative Example 2, which uses liquid electrolytes, due to the reduced surface oxidation rate.

[0281] Furthermore, as the content of inorganic electrolytes increases, the degree of oxidation decreases, thus reducing the amount of current that changes over time.

[0282] Therefore, when using the electrolyte for a secondary battery according to the exemplary embodiment, its high voltage stability is improved compared to the case of using a liquid electrolyte.

Claims

1. An electrolyte for a secondary battery, comprising: Lithium salts; Composite membrane, which contains organic polymers and inorganic electrolytes; as well as Flame-retardant compounds containing phosphorus-containing functional groups. The weight ratio of the flame retardant compound to the composite film is from 0.004 to 0.

3.

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 flame-retardant compound contains fluorine atoms.

4. The electrolyte for a secondary battery according to claim 1, wherein, The phosphorus-containing functional group includes at least one of phosphate, phosphite, phosphonate, and phosphazene.

5. The electrolyte for a secondary battery according to claim 1, wherein, The flame-retardant compound is a flame-retardant polymer.

6. The electrolyte for a secondary battery according to claim 1, wherein, The flame retardant compound comprises a first flame retardant compound in contact with the interior and surface of the composite membrane, and a second flame retardant compound distributed on the exterior of the composite membrane.

7. The electrolyte for a secondary battery according to claim 6, wherein, The composite membrane contains pores, and at least a portion of the first flame-retardant compound is distributed within the pores.

8. The electrolyte for a secondary battery according to claim 1, wherein, The content of the organic polymer in the total weight of the composite membrane is from 5% to 95% by weight.

9. The electrolyte for a secondary battery according to claim 1, wherein, The composite membrane contains pores, and the porosity of the composite membrane is 50% to 80%.

10. A lithium secondary battery, comprising: case; An electrode assembly comprising repeatedly stacked positive and negative electrodes; as well as The electrolyte for a secondary battery according to claim 1 is disposed within the housing between the positive electrode and the negative electrode in the electrode assembly, or distributed around the electrode assembly.

11. The lithium secondary battery according to claim 10, wherein, The composite membrane of the electrolyte for the secondary battery is disposed as an electrolyte layer between the positive electrode and the negative electrode in the electrode assembly.

12. A method for manufacturing an electrolyte for a secondary battery, comprising: The first mixture is prepared by mixing organic polymer, inorganic electrolyte, first solvent and second solvent; The first mixture is dried to produce a composite membrane; The composite membrane is impregnated with a second mixture containing flame-retardant monomers and electrolyte; as well as The second mixture is then cured.

13. The method for manufacturing an electrolyte for a secondary battery according to claim 12, wherein, The solubility of the organic polymer relative to the first solvent is greater than the solubility of the organic polymer relative to the second solvent.

14. The method for manufacturing an electrolyte for a secondary battery according to claim 12, wherein, In the first mixture, the organic polymer is dissolved in the first solvent but not in the second solvent.

15. The method for manufacturing an electrolyte for a secondary battery according to claim 12, wherein, The step of drying the first mixture to manufacture the composite membrane includes: Remove the first solvent at a first temperature; and The second solvent is removed at a second temperature.

16. The method for manufacturing an electrolyte for a secondary battery according to claim 15, wherein, The first temperature is lower than the second temperature.

17. The method for manufacturing an electrolyte for a secondary battery according to claim 12, wherein, The electrolyte contains lithium salt.

18. The method for manufacturing an electrolyte for a secondary battery according to claim 12, wherein, The second mixture contains a thermal initiator. The step of curing the second mixture includes heat treatment of the second mixture.

19. The method for manufacturing an electrolyte for a secondary battery according to claim 12, wherein, The second mixture also contains a photoinitiator. The step of curing the second mixture includes irradiating the second mixture with light.

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