Ink composition for photosintering, oxide-based solid electrolyte sheet, and all-solid-state lithium secondary battery

Abstract

The ink composition for photosintering according to an embodiment may be prepared by including a binder that has excellent solubility and does not cause unevenness during slurry preparation. The oxide-based thin film sheet according to one embodiment includes an ink composition for photosintering, and thus the interparticle connection form, particle shape, density, etc. are appropriately formed through photosintering, and an oxide-based solid electrolyte sheet having excellent durability and ionic conductivity and free from peeling from the substrate can be produced. The oxide-based solid electrolyte sheet according to one embodiment can be rapidly sintered through photosintering, and can be produced in a short time without losing materials such as lithium or destroying the substrate, and can be made thin and large in area without additional processing steps.

Description

[Technical Field]

[0001] The present disclosure relates to a photosintering ink composition containing a lithium ion conductive oxide, an oxide-based solid electrolyte sheet, and an all-solid-state lithium secondary battery. [Background technology]

[0002] Recently, with growing interest in environmental issues, active research is being conducted on electric vehicles (EVs) that can replace fossil fuel-based vehicles, which are one of the main causes of air pollution, and energy storage systems (ESSs) that utilize new renewable energy sources. Lithium secondary batteries, which have high discharge voltage and stable output, are mainly used as the power source for such electric vehicles (EVs).

[0003] On the other hand, conventional lithium secondary batteries that use liquid electrolytes such as organic solvents have problems such as the risk of fire due to electrolyte leakage and battery expansion due to electrolyte decomposition caused by electrode reactions. Furthermore, to prevent these problems, the separator included in conventional lithium secondary batteries limits the ability to ensure high battery energy density. Therefore, to solve these problems, active research and development is being conducted on all-solid-state lithium secondary batteries that use solid-state electrolytes.

[0004] Solid electrolytes used in all-solid-state lithium secondary batteries are mainly classified into sulfide-based, polymer-based, and oxide-based solid electrolytes, among which oxide-based solid electrolytes are attracting attention as next-generation solid electrolyte materials due to their excellent chemical / thermal stability and mechanical strength.

[0005] The solid electrolyte used in the all-solid-state lithium secondary battery is manufactured by a sintering process, and generally, the solid electrolyte is manufactured using a thermal sintering process, a laser sintering process, or a microwave sintering process.

[0006] However, the thermal sintering process has the drawback of taking a very long time since various processes such as heating, heat treatment, and cooling are performed, and since the process is performed in a high-temperature environment, there are limitations on the selection of substrates.

[0007] Rapid thermal annealing (RTA) is a sintering method that can solve the problem of thermal sintering, which requires a long time for sintering. Rapid thermal annealing (RTA) increases the temperature very quickly, shortening the process time compared to general heat treatment processes. However, it still requires a long cooling time because it relies on natural cooling, and there are problems such as destruction of materials used to form lithium-ion secondary batteries due to residual thermal stress. Summary of the Invention [Problem to be solved by the invention]

[0008] It is an object of one embodiment to provide a photosintering ink composition that includes a binder with good solubility.

[0009] An object of one embodiment is to provide an oxide-based solid electrolyte sheet that can be sintered at high speed by photosintering, can be manufactured in a short period of time, and can be made thin and large in area without any additional processing steps.

[0010] An object of one embodiment is to provide an all-solid-state lithium secondary battery including the oxide-based solid electrolyte sheet and having improved safety, energy density, and the like. [Means for solving the problem]

[0011] According to one embodiment, the ink composition for photosintering includes a binder containing a polymer having a hydroxy group, an acetyl group, and an acetal group, and the polymer has a Hansen Solubility Parameter (HSP) value of 18 MPa. 0.5 ~28MPa 0.5 The weight average molecular weight of the polymer is 1.0×10 4 g / mol ~ 9.0 × 10 4g / mol.

[0012] The polymer can include a polyvinyl acetal copolymer that includes a structural unit having a hydroxy group, a structural unit having an acetyl group, and a structural unit having an acetal group.

[0013] The structural unit having a hydroxy group may be a structural unit represented by the following chemical formula 1. [ka] (In the above chemical formula 1, L1 may be a single bond or alkylene having 1 to 5 carbon atoms.)

[0014] The structural unit having an acetyl group may be a structural unit represented by the following chemical formula 2. [ka] (In the above chemical formula 2, L2 may be a single bond or alkylene having 1 to 5 carbon atoms.)

[0015] The structural unit having an acetal group may be a structural unit represented by the following chemical formula 3. [ka] (In the above chemical formula 3, R may be hydrogen or a substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms.)

[0016] The content of the structural unit having a hydroxy group may be 4% by weight to 25% by weight relative to 100% by weight of the polyvinyl acetal copolymer.

[0017] The content of the structural unit having an acetyl group may be 1% by weight to 12% by weight relative to 100% by weight of the polyvinyl acetal copolymer.

[0018] The content of the structural unit having an acetal group may be 65% by weight to 85% by weight relative to 100% by weight of the polyvinyl acetal copolymer.

[0019] The polymer may be a random copolymer.

[0020] The viscosity of the ink composition for photosintering may be 1,000 cp to 10,000 cp at 25°C.

[0021] The ink composition for photosintering may further include lithium ion conductive oxide particles, a solvent, and a plasticizer.

[0022] The Hansen Solubility Parameter (HSP) value of the above solvent is 18MPa. 0.5 ~28MPa 0.5 It could be.

[0023] The solvent may be one or more selected from the group consisting of 1,3-dioxane, dimethyl carbonate, acetonitrile, methylpyrrolidone, dimethylformamide, acetone, isopropanol, n-propanol, n-hexane, and toluene.

[0024] The plasticizer may be one or more selected from the group consisting of dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), di-isononyl phthalate (DINP), di(2-ethylhexyl) phthalate (DEHP), di(n-octyl) phthalate (DNOP), and di-isodecyl phthalate (DIDP).

[0025] The lithium ion conductive oxide particles may be one or more selected from the group consisting of a garnet compound, a NASICON compound, and a perovskite compound.

[0026] An oxide-based solid electrolyte sheet according to an embodiment includes the above-described ink composition for photosintering.

[0027] The oxide-based solid electrolyte sheet is -6 S / cm~10 -2 It can have an ionic conductivity of 100 S / cm.

[0028] The oxide-based solid electrolyte sheet is 0.25 cm 2 It can have an area of ​​the above and a thickness of 10 μm to 300 μm.

[0029] According to one embodiment, a method for manufacturing an oxide-based solid electrolyte sheet includes the steps of applying the ink composition for photosintering onto a substrate, drying the substrate to manufacture an oxide-based sheet, and photosintering the oxide-based sheet to manufacture an oxide-based solid electrolyte sheet.

[0030] The temperature of the oxide sheet during the photosintering can be 25°C to 500°C.

[0031] An all-solid-state lithium secondary battery according to an embodiment includes the oxide-based solid electrolyte sheet. [Effects of the Invention]

[0032] According to one embodiment, it is possible to provide an ink composition for photosintering, which includes a binder that has excellent solubility and does not cause unevenness during slurry preparation.

[0033] According to one embodiment, an oxide-based solid electrolyte sheet can be provided that can be sintered at high speed through photosintering, can be manufactured in a short time without losing materials such as lithium or destroying the substrate, and can be made thin and large in area without any additional processing steps.

[0034] According to one embodiment, it is possible to provide an all-solid-state lithium secondary battery that is highly safe and has a high energy density. [Brief explanation of the drawings]

[0035] [Figure 1a] 1 is a conceptual diagram showing the stages in which the interparticle connection structure and particle shape change as sintering progresses. [Figure 1b] 1 is a conceptual diagram showing the stages in which the interparticle connection structure and particle shape change as sintering progresses. [Figure 1c] 1 is a conceptual diagram showing the stages in which the interparticle connection structure and particle shape change as sintering progresses. [Figure 1d] 1 is a conceptual diagram showing the stages in which the interparticle connection structure and particle shape change as sintering progresses. [Figure 2] 3 is a photograph showing the degree of dissolution of primary slurries in Example 1, Comparative Example 1, and Comparative Example 2. [Figure 3] 3 is a photograph showing the oxide-based solid electrolyte sheet of Production Example 1 before and after sintering. [Figure 4] 1 is a graph showing the results of electrochemical impedance for measuring the ionic conductivity of the oxide-based solid electrolyte sheet of Production Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0036] A specific embodiment of an example will be described below. However, the embodiment of an example can be modified in various different forms, and the scope of an example is not limited to the embodiment described below.

[0037] In this disclosure, singular expressions include plural expressions unless the context clearly indicates otherwise, and the same reference numerals or reference numerals given in a similar manner throughout this disclosure refer to the same components or corresponding components.

[0038] In the present disclosure, the term "sintering" refers to a phenomenon in which powder particles adhere to each other and solidify due to heat, and refers to a process in which the powder particles adhere to each other through a thermal activation process to form a single mass.

[0039] In this disclosure, "light-sintering" refers to sintering a material by inducing a resonance phenomenon between the wavelength range of a material and the wavelength range of light through light, thereby inducing a heat generation phenomenon and generating a thermal reaction within the material.

[0040] In this disclosure, unless otherwise defined, the term "polymer" may include oligomers and polymers, and may also include homopolymers and copolymers. The copolymers may be alternating copolymers, block copolymers, random copolymers, branched copolymers, crosslinked copolymers, or all of these.

[0041] When a typical high-temperature sintering process is used to manufacture an oxide compact, it is necessary to sinter the oxide compact for a long period of time, such as 1 to 24 hours, at temperatures of 1000°C or higher, which can result in loss of materials due to the volatilization or evaporation of components such as lithium, difficulty in controlling density through sintering conditions, and deformation or destruction of the substrate as the entire substrate is heated. Furthermore, it is difficult to thin the oxide sheet manufactured through such a high-temperature sintering process and form a uniform surface, requiring additional processing steps.

[0042] Meanwhile, the RTA (Rapid Thermal Annealing) process can heat up very quickly and can be completed in a shorter time than general high-temperature sintering processes, but the problem of deformation or destruction of the substrate remains difficult to solve. Also, in the case of a laser-based process, the reaction proceeds locally near the laser incident area, which narrows the applicable area during the sintering process and requires a long time for the sintering process, and in the case of a microwave-based process, the sintering depth is shallow, which limits the substrate selection.

[0043] Therefore, one embodiment aims to provide a technology for sintering an oxide-based solid electrolyte sheet by applying a photosintering process.

[0044] The photosintering process is a process of applying a momentary light pulse to densify particles through a photothermal effect, and has the advantage of being able to sinter a slurry printed on a substrate in an extremely short time under room temperature and atmospheric pressure conditions. Furthermore, this photosintering process is not only applicable to large-area substrates, but also allows for high-speed sintering at room temperature in the atmosphere, thereby improving productivity in mass production.

[0045] When producing an oxide-based solid electrolyte sheet by photosintering, photosintering can be performed after applying a slurry containing an oxide-based solid electrolyte, a binder, a solvent, etc. (hereinafter, also referred to as an ink composition for photosintering). In this case, the ink composition for photosintering can be easily controlled so that the slurry has an appropriate viscosity even with a small amount of solvent, and can contain a binder that can effectively bind the oxide-based solid electrolyte.

[0046] Ink composition for photosintering An ink composition for photosintering according to an embodiment is a slurry for producing a thin oxide-based solid electrolyte sheet by a photosintering method, and the ink composition for photosintering may include an oxide-based solid electrolyte.

[0047] The oxide-based solid electrolyte may be particulate lithium ion conductive oxide particles, which are particles in the form of powdered compounds containing oxygen and having conductivity to lithium ions, and may include at least one selected from zirconium (Zr), phosphate (PO4), and titanium (Ti).

[0048] Specifically, the lithium ion conductive oxide particles may be one or more compounds selected from the group consisting of lithium lanthanum zirconium oxide (LLZO)-based compounds, lithium lanthanum titanate oxide (LLTO)-based compounds, lithium aluminum germanium phosphate (LAGP)-based compounds, and lithium aluminum titanium phosphate (LATP)-based compounds. More specifically, the lithium ion conductive oxide particles may be Li7La3Zr2O 12 The lithium ion conductive oxide particles may be lithium lanthanum zirconium oxide (LLZO)-based compounds having a garnet structure and represented by the chemical formula: When the above-mentioned types of compounds, particularly LLZO-based compounds, are used as the lithium ion conductive oxide particles, an oxide-based solid electrolyte sheet having excellent ion conductivity, stability with lithium metal, a wide potential window range, and the like can be produced.

[0049] The ink composition for photosintering may include a binder containing a polymer containing a hydroxy group, an acetyl group, and an acetal group, which can appropriately bind the oxide-based particles and contribute to improving the adhesive strength of the slurry to the substrate.

[0050] The binder can include a polymer containing a hydroxy group, an acetyl group, and an acetal group, and specifically can include a polyvinyl acetal copolymer containing a structural unit having a hydroxy group, a structural unit having an acetyl group, a structural unit having an acetal group, or a combination thereof.

[0051] The polyvinyl acetal copolymer may contain a structural unit having a hydroxy group. Specifically, the structural unit having a hydroxy group provides the effect of improving strength, bonding power, and solubility in polar solvents, and may be a structural unit represented by the following Chemical Formula 1: [ka]

[0052] In the above chemical formula 1, L1 may be a single bond or alkylene having 1 to 5 carbon atoms, specifically a single bond or alkylene having 1 to 3 carbon atoms, more specifically a single bond or methylene.

[0053] The polyvinyl acetal copolymer may contain structural units having two or more different hydroxy groups.

[0054] The content of the hydroxyl group-containing structural unit relative to 100% by weight of the polyvinyl acetal copolymer may be 4% by weight to 25% by weight, specifically 12% by weight to 20% by weight, and more specifically 15% by weight to 17% by weight. If the content of the hydroxyl group-containing structural unit is less than the above range, problems such as a decrease in the strength of the slurry, a decrease in the intermolecular bonding force, and a decrease in solubility in polar solvents may occur. If the content exceeds the above range, the slurry becomes excessively rigid, making it difficult to form into a sheet (coating, tape casting, etc.).

[0055] The polyvinyl acetal copolymer may contain a structural unit having an acetyl group. Specifically, the structural unit having an acetyl group contributes to reducing the viscosity and glass transition temperature of the solution, and may be a structural unit represented by the following chemical formula 2: [ka]

[0056] In the above chemical formula 2, L2 may be a single bond or alkylene having 1 to 5 carbon atoms, specifically a single bond or alkylene having 1 to 3 carbon atoms, more specifically a single bond or methylene.

[0057] The polyvinyl acetal copolymer may contain structural units having two or more different acetyl groups.

[0058] The content of the acetyl group-containing structural unit, based on 100% by weight of the polyvinyl acetal copolymer, may be 1% by weight to 12% by weight, more specifically, more than 1% by weight to 12% by weight, more specifically, 3% by weight to 9% by weight, and more specifically, 4% by weight to 6% by weight. If the content of the acetyl group-containing structural unit is less than the above range, the solution viscosity may become too high, resulting in a high glass transition temperature. If the content exceeds the above range, the solution viscosity may decrease, resulting in a low glass transition temperature, making the slurry preparation process difficult.

[0059] The polyvinyl acetal copolymer may contain a structural unit having an acetal group. Specifically, the inclusion of the structural unit having an acetal group can improve the ductility and flexibility of the polyvinyl acetal copolymer and enhance compatibility with different resins, and the structural unit may be a structural unit represented by the following chemical formula 3: [ka]

[0060] In the above chemical formula 3, R may be hydrogen or a substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms, specifically a substituted or unsubstituted hydrocarbyl having 1 to 5 carbon atoms, specifically a substituted or unsubstituted hydrocarbyl having 1 to 4 carbon atoms, more specifically methyl or propyl. For example, a polyvinyl acetal copolymer (polyvinyl acetoacetal) in which R is an alkyl group having 1 carbon atom can be obtained by acetalization with acetaldehyde, and a polyvinyl acetal copolymer (polyvinyl butyral) in which R is an alkyl group having 3 carbon atoms can be obtained by acetalization with butyraldehyde.

[0061] The polyvinyl acetal copolymer may contain structural units having two or more different acetal groups, for example, polyvinyl acetal structural units and polyvinyl butyral structural units.

[0062] The content of the acetal group-containing structural unit relative to 100% by weight of the polyvinyl acetal copolymer may be 65% to 85% by weight, more specifically, more than 65% to 85% by weight, more specifically, 70% to 80% by weight, and more specifically, 75% to 79% by weight. If the content of the acetal group-containing structural unit is less than the above range, problems such as low ductility, low flexibility, and low compatibility with other types of resins may occur.

[0063] As an example, the polyvinyl acetal copolymer may include a structural unit having a hydroxy group, a structural unit having an acetyl group, and a structural unit having an acetal group, and the structural unit having a hydroxy group, the structural unit having an acetyl group, and the structural unit having an acetal group may be as described above.

[0064] The polyvinyl acetal copolymer may be a random polyvinyl acetal copolymer in which a hydroxyl group-containing structural unit, an acetyl group-containing structural unit, and an acetal group-containing structural unit are irregularly arranged, and may be represented, for example, by the following chemical formula 4: [ka]

[0065] In the above Chemical Formula 4, l, m, and n are each independently an integer of 1 or greater, and L1, L2, and R can be as defined above.

[0066] For example, the polyvinyl acetal copolymer may contain polyvinyl alcohol structural units, polyvinyl acetate structural units, and polyvinyl acetoacetal structural units and / or polyvinyl butyral structural units.

[0067] The binder, specifically the polymer, more specifically the polyvinyl acetal copolymer, can have an average degree of polymerization of 10,000 or less, and a weight average molecular weight of 1.0×10 4 g / mol ~ 9.0 × 10 4 The weight average molecular weight may be specifically 3.0×10 4 g / mol ~ 8.0 × 10 4 g / mol, more specifically 5.0 × 10 4 g / mol ~ 7.0 × 10 4 If the weight-average molecular weight is less than the above range, the adhesive strength of the ink composition formed from the slurry may be significantly reduced, and if it exceeds the above range, the solubility of the binder may be reduced, and the ductility of the sheet may be significantly reduced.

[0068] The binder may be contained in an amount of 2 wt % to 40 wt % based on the total weight of the ink composition for photosintering. When the binder content is within this range, the flexibility of the electrolyte sheet can be further improved.

[0069] The ink composition for photosintering according to an embodiment may include a solvent. The solvent may be any solvent capable of dissolving the binder, including, but not limited to, one or more selected from the group consisting of alcohols, ketones, amides, esters, ethers, aromatic hydrocarbons, etc. Specifically, the solvent may be one or more selected from the group consisting of 2-propanol, toluene, terpineol, N-methyl-2-pyrrolidone (NMP), etc. More specifically, the solvent may be a mixture of 2-propanol and toluene.

[0070] The solvent may be included in an amount of 15 to 45 wt % based on the total weight of the ink composition for photosintering. If the solvent content is less than 15 wt %, the ink composition for photosintering may not be mixed smoothly, and if it exceeds 45 wt %, the viscosity of the slurry may be reduced, making it difficult to form a sheet.

[0071] The ink composition for photosintering may also contain a plasticizer, which can improve the baking processability of the ink composition for photosintering and impart flexibility to the adhesive layer formed by the ink composition for photosintering.

[0072] The plasticizer is not particularly limited as long as it has good compatibility, low vapor pressure, and high plasticizing efficiency. For example, the plasticizer may be one or more selected from phthalate-based (phthalic acid ester) plasticizers, trimellitic acid ester-based (trimellitic acid ester) plasticizers, phosphoric acid ester-based (phosphoric acid ester) plasticizers, epoxy-based (epoxy) plasticizers, polyester-based (polyester) plasticizers, aliphatic ester-based (aliphatic acid ester) plasticizers, chlorinated paraffin-based (chlorinated paraffin) plasticizers, etc., and specifically may be a phthalate-based (phthalic acid ester) plasticizer.

[0073] More specifically, the plasticizer may be one or more phthalate (phthalic acid ester) plasticizers selected from the group consisting of dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), di-isononyl phthalate (DINP), di(2-ethylhexyl) phthalate (DEHP), di(n-octyl) phthalate (DNOP), di-isodecyl phthalate (DIDP), etc.

[0074] When the plasticizer is added, the content of the plasticizer may be 5 wt % to 20 wt % based on the total weight of the ink composition for photosintering. When the content of the plasticizer is within this range, the flexibility of the resulting electrolyte sheet can be increased and the viscosity of the slurry caused by the binder can be reduced.

[0075] The photosintering ink composition may contain a dispersant. The dispersant can suppress aggregation of the inorganic solid electrolyte even when the concentration is high, thereby forming a uniform solid electrolyte layer. The dispersant is not particularly limited as long as it is a dispersant commonly used for dispersing inorganic materials in inorganic slurries, such as oxide-based solid electrolyte layers. For example, surfactants, polycarboxylic acid ammonium salts, and fatty acid-based dispersants can be used. Specifically, commercially available dispersants such as KD-1, KD-2, KD-4, KD-6, KD-7, KD-9, KD-13, KD-20, KD-24, KD-25, and KD-57 can be used.

[0076] When the dispersant is added, the content of the dispersant may be 0.001 to 10 wt % based on the total weight of the ink composition for photosintering. When the content of the dispersant is within the above range, the homogeneity of the obtained electrolyte sheet can be further improved.

[0077] The Hansen Solubility Parameter (HSP) values ​​of 2-propanol and toluene among the above solvents are shown in Table 1 below.

[0078] [Table 1]

[0079] In the present disclosure, the Hansen Solubility Parameter (HSP, δ t ) refers to the parameter discovered by Charles M. Hansen, and the Hansen solubility parameter value δ t is composed of the following three experimentally and theoretically derived parameters (δ d , δ p , δ h The unit of Hansen Solubility Parameter (HSP) is MPa. 0.5 It could be. δ t : Hansen solubility parameter δ d : Energy parameters due to intermolecular dispersion forces δ p : Energy parameters due to intermolecular dipole interactions δ h : Energy parameters due to intermolecular hydrogen bonds

[0080] Hansen Solubility Parameter (HSP) is (δ d , δ p , δ h) and can be expressed by plotting it in a three-dimensional space (Hansen space) with the three parameters as the coordinate axes. The Hansen Solubility Parameters (HSP) of commonly used substances can be obtained by referencing publicly known information sources such as databases, for example, databases. For substances whose Hansen Solubility Parameters (HSP) are not registered in databases, computer program software such as Hansen Solubility Parameters in Practice (HSPiP) can be used to calculate the Hansen Solubility Parameters (HSP) from the chemical structure of the substance and the Hansen Solubility Sphere method described below.

[0081] The Hansen Solubility Parameter (HSP) of a mixture containing two or more substances can be calculated as the vector sum of the values ​​obtained by multiplying the Hansen Solubility Parameter (HSP) of each substance by the volume ratio of each substance to the total mixture. For example, the Hansen Solubility Parameter (HSP) of a random copolymer containing three structural units can be calculated using the following mathematical formula 1 [Reference: Journal of Applied Polymer Science, vol. 42, 99-106 (1991)].

number

[0082] Hansen Solubility Parameter (HSPδ t) and three parameters (δ d , δ p , δ h ) can be calculated from the following mathematical formula 2. [Mathematical formula 2] δ t 2 =δ d 2 +δ p 2 +δ h 2

[0083] δ is the Hansen solubility parameter (HSP) of the binder according to one embodiment. t The value is 18 MPa. 0.5 ~28MPa 0.5 Specifically, it can be 19 MPa. 0.5 ~22MPa 0.5 The Hansen solubility parameter (HSP) of the polyvinyl acetal copolymer is δ t When the value is within the above range, the polymer can be easily dissolved in a mixed solvent of a polar solvent and a non-polar solvent.

[0084] According to one embodiment, the Hansen Solubility Parameter (HSP) of the solvent is δ t The value is 18 MPa. 0.5 ~28MPa 0.5 Specifically, it is 18 MPa. 0.5 ~24MPa 0.5 The Hansen solubility parameter (HSP) of the solvent is δ t When the value satisfies the above range, the binder can be easily dissolved.

[0085] According to an embodiment, the viscosity of the ink composition for photosintering may be 1,000 cp to 10,000 cp, specifically 4,000 cp to 8,000 cp, at 25° C. If the viscosity of the ink composition for photosintering exceeds the above range, the fluidity of the slurry may be reduced, resulting in insufficient uniformity during application of the ink composition, such as the occurrence of streaks during molding. If the viscosity is below the above range, it may be difficult to ensure flow properties suitable for coating, making it difficult to apply the ink composition to the substrate surface at a loading of a certain amount or more.

[0086] As described above, the ink composition for photosintering includes an oxide-based electrolyte powder, a binder, and a solvent, and may further include a dispersant and a plasticizer as needed. The method for producing the ink composition for photosintering is not particularly limited, and the ink composition can be produced by mixing and stirring the above components.

[0087] More specifically, a binder solution can be prepared by mixing a binder and a solvent, optionally adding a plasticizer and a dispersant, and then stirring the mixture. The binder solution can then be mixed with an oxide-based electrolyte powder to prepare a slurry. When preparing the ink composition for photosintering, adding the oxide-based electrolyte powder after preparing the binder solution can improve the dispersibility of the oxide in the slurry.

[0088] Oxide-based solid electrolyte sheet The ink composition for photosintering is applied to a substrate and dried to produce an oxide-based sheet, which is then photosintered to produce an oxide-based solid electrolyte sheet.

[0089] The substrate is not particularly limited and may be a current collector in the form of copper (Cu) or aluminum (Al) foil, or may be a negative electrode or positive electrode for an all-solid-state lithium secondary battery. The flexibility, shape, type, and other properties of the substrate can be appropriately selected in consideration of the photosintering process to be performed and the properties of the ink composition for photosintering.

[0090] The substrate may have a thickness of 5 μm to 200 μm, but is not limited thereto, and more specifically may have a thickness of 10 μm to 50 μm.

[0091] The method for applying the ink composition for photosintering to a substrate is not particularly limited, and the ink composition can be applied by bar coating, casting, spraying, or other methods.

[0092] After applying the ink composition for photosintering to the substrate, the composition is dried to remove the solvent, thereby producing an oxide-based sheet. The method for drying the slurry applied to the substrate is not particularly limited, and drying can be performed, for example, using a convection oven. The drying can be performed at a temperature of 50°C to 200°C, specifically 80°C to 120°C, for 0.5 to 5 hours, specifically 1 to 3 hours.

[0093] The oxide-based sheet obtained after the drying can have a thickness of 10 to 300 μm. Specifically, the thickness of the oxide-based sheet can be 50 μm or more, 70 μm or more, 250 μm or less, or 200 μm or less. When the thickness of the oxide-based sheet is within the above range, it is possible to produce an oxide-based solid electrolyte sheet that is thin and has excellent durability.

[0094] The oxide-based thin film sheet thus produced can be photosintered to produce an oxide-based solid electrolyte sheet.

[0095] As mentioned above, photosintering allows for sintering in a short period of time, thereby enabling the degree of sintering to be controlled. This will be explained in detail with reference to Figures 1a to 1d. During the sintering process, the grain boundaries (the boundaries where particles come into contact with each other) gradually expand from point contact in the initial stage of sintering to surface contact (Figures 1a to 1d). As shown in Figure 1a, when the particles maintain their initial shape, they remain in point contact, resulting in significant resistance to ion migration due to simple contact. On the other hand, when the contact area increases through sintering to form surface contact, the resistance to ion migration decreases, enabling faster ion conduction. Furthermore, densification increases durability and allows the sheet shape to be well maintained.

[0096] However, as the contact area between particles increases, the pores between the particles decrease, potentially resulting in volumetric shrinkage. The volumetric shrinkage rate can vary depending on the contact pattern between particles and the degree of coarsening. Specifically, when grain boundaries (GBs) are formed as sintering progresses, the volumetric shrinkage rate is within 3% (Figure 1b). However, when the contact area between particles increases and coarsening progresses due to continuous sintering, the volumetric shrinkage rate can increase to approximately 10% to 20% (Figures 1c-1d). Excessive coarsening of particles within the thin film and an increase in the volumetric shrinkage rate can lead to problems such as peeling from the substrate and / or cracking of the thin film, resulting in reduced functionality.

[0097] This requires that the contact morphology be appropriately adjusted to prevent excessive coarsening and peeling due to volume shrinkage, while maintaining a surface contact state to create a dense structure and a structure that ensures ion migration paths and allows ion conduction (Figure 1b). In this regard, when a photo-sintering process is applied, high-speed sintering is possible, and the particle shape can be controlled by adjusting the sintering degree to form the particle morphology shown in Figure 1b. Furthermore, the particles can be appropriately coarsened as needed, taking into account the flexibility and shape of the substrate.

[0098] The oxide-based solid electrolyte sheet may include photosintered lithium ion conductive oxide-based particles. In the oxide-based solid electrolyte sheet manufactured by photosintering the oxide-based thin film sheet including the lithium ion conductive oxide-based particles, the photosintered lithium ion conductive oxide-based particles may correspond to the lithium ion conductive oxide-based particles. The photosintered lithium ion conductive oxide-based particles may differ from one another in particle shape, color, inter-particle connection structure, etc., due to photosintering of the lithium ion conductive oxide-based particles.

[0099] The photosintering can be performed in a pulsed manner. The pulsed manner refers to a method of applying a strong voltage pulse to a light-generating device such as a lamp to instantaneously generate strong light, and the light energy supplied by the irradiation can generate heat to induce photosintering. In this case, the photosintering device that generates light in a pulsed manner is not particularly limited as long as it can operate under pulse conditions set as follows:

[0100] During the above-mentioned light sintering, the light irradiation time per pulse (On-time), operating voltage (V), duty cycle (%), number of cycles, heat pulse frequency (Fire rate, Hz) constituting the total pulse, number of repetitions, etc. can be appropriately varied (adjusted) by controlling the controller, power supply, etc. of the light sintering device.

[0101] The light irradiation time (On-time) per pulse during the photosintering may be 1000 to 4500 μs. Specifically, the light irradiation time (On-time) per pulse may be 1200 μs or more, or 1400 μs or more, or may be 4400 μs or less, 4200 μs or less, or 4000 μs or less.

[0102] The operating voltage V during the photosintering can be 100 to 450 V. Specifically, the operating voltage V may be 120 V or more, or 150 V or more, and may be 440 V or less, 430 V or less, or 420 V or less.

[0103] The duty cycle (%) during the photosintering may be 10 to 100%. Specifically, the duty cycle (%) may be 20 to 90%. The duty cycle can be calculated as a ratio (%) of the light irradiation time (On-time) per pulse to the pulse period.

[0104] The number of cycles during the photosintering can be 1 to 20. Specifically, the number of cycles during the photosintering can be 5 to 15.

[0105] When the light irradiation time (On-time), operating voltage (V), duty cycle (%), and number of cycles during the photosintering are controlled within the above-mentioned ranges, the photosintering process time calculated by the following Chemical Formula 1 can be shortened, and the sintering process can be completed in a short period of time. [Formula 1] T s =C / T r

[0106] In the above formula 1, T s is the photosintering process time (s), and T r is the heat pulse frequency (fire rate, Hz), and C is the number of repetitions.

[0107] The heat pulse frequency (fire rate, Hz) constituting the total pulse during the photosintering may be 1 to 50 Hz. Specifically, the heat pulse frequency (fire rate, Hz) constituting the total pulse during the photosintering may be 10 Hz or more and 40 Hz or less.

[0108] The number of repetitions of the photosintering may be 50 to 1000. Specifically, the number of repetitions of the photosintering may be 100 or more, or 400 or less.

[0109] The substrate temperature during the photosintering may be maintained at 300°C or less. Specifically, the substrate temperature during the photosintering may be maintained at 5°C to 100°C, 10°C to 50°C, or 15°C to 30°C. More specifically, the substrate temperature during the photosintering may be maintained at room temperature (RT), i.e., substantially 20°C to 25°C. When the substrate temperature is maintained within the above range during photosintering, residual thermal stress in the substrate can be prevented, thereby substantially mitigating problems such as substrate breakage and reduced durability, and various types of substrates can be selected without restriction and applied to the photosintering process.

[0110] The light energy irradiated during the above photosintering is 25 to 150 J / s cm 2 Specifically, the light energy irradiated during the photosintering can be 40 to 120 J / s cm 2 It could be.

[0111] The oxide-based solid electrolyte sheet is 0.25 cm 2 Specifically, the oxide-based solid electrolyte sheet can have an area of ​​0.5 to 50 cm. 2 The area of ​​the slit may be 0.05 mm.

[0112] The width and length of the oxide-based solid electrolyte sheet may be 0.5 cm or more, and more specifically, the width and length of the oxide-based solid electrolyte sheet may be 0.5 to 10 cm.

[0113] When the area, width, length, etc. of the oxide-based solid electrolyte sheet are within the above-mentioned ranges, the oxide-based solid electrolyte sheet has a relatively large area and size compared to oxide-based solid electrolytes produced by conventional processes, and the productivity, economy, etc. of the oxide-based solid electrolyte sheet production can be further improved.

[0114] The oxide-based solid electrolyte sheet may have a thickness of 10 to 300 μm. Specifically, the thickness of the oxide-based solid electrolyte sheet may be 30 μm or more, 200 μm or less, or 100 μm or less. When the thickness of the oxide-based solid electrolyte sheet is within the above range, it has excellent ion conductivity as a thin film having a small thickness, and when applied to an all-solid-state lithium secondary battery, a higher energy density can be ensured.

[0115] The oxide-based solid electrolyte sheet may have a porosity of 0.1 to 20%. Specifically, the oxide-based solid electrolyte sheet may have a porosity of 1% or more, 5% or more, 10% or more, or 15% or less. When the porosity of the oxide-based solid electrolyte sheet is within the above range, photosintering proceeds smoothly, and the sheet can have excellent density and durability.

[0116] The ionic conductivity of the oxide-based solid electrolyte sheet is 10 -6 S / cm~10 -2 S / cm, specifically 10 -5 S / cm~10 -2 S / cm, and more specifically, 10 -5 S / cm~10 -3 In this case, the ionic conductivity value may be a value measured at room temperature (25°C).

[0117] When the content of elements and / or binder burning residues contained in the substrate is within the above-mentioned range, the oxide-based solid electrolyte sheet is manufactured through a smooth photosintering process, and element diffusion between the substrate and the sheet is suppressed, thereby substantially suppressing interface formation and resistance increase between the substrate and the sheet.

[0118] The oxide-based solid electrolyte sheet can be manufactured by light sintering to form a thin-film oxide electrolyte layer, and selective sintering is possible because light energy is irradiated locally only on the surface.

[0119] Moreover, by light sintering, it is possible to create a structure that forms the same inter-particle connection points as sintering using heat in a short time within a few seconds, and it can be manufactured without being restricted by the shape of the sheet according to the size of the light source.

[0120] All-solid-state lithium secondary battery The all-solid-state lithium secondary battery according to one embodiment can include an oxide-based solid electrolyte sheet according to any one of the above-described embodiments.

[0121] The all-solid-state lithium secondary battery according to another embodiment can include an oxide-based solid electrolyte sheet according to any one of the above-described embodiments. At this time, the substrate may be a positive electrode or a negative electrode for the all-solid-state lithium secondary battery. Specifically, the all-solid-state lithium secondary battery can include the oxide-based solid electrolyte sheet between the positive electrode and the negative electrode for the all-solid-state lithium secondary battery.

[0122] The positive electrode is not particularly limited, and can include a lithium-transition metal oxide such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), or lithium nickel oxide (LiNiO2) as a positive electrode active material, or a lithium-transition metal composite oxide in which some of these transition metals are substituted with other transition metals. Specifically, the lithium-transition metal composite oxide can be an NCM-based positive electrode active material represented by the chemical formula Li x Ni a Co b Mn c Al d [[ID=​​​​​The above-mentioned negative electrode is not particularly limited, and it can contain carbon-based active materials such as artificial graphite and natural graphite, silicon-based active materials such as silicon oxide (SiOx; 0 < x < 2) and Si-C composites, and metals such as lithium metal as the negative electrode active material.

[0124] The method for manufacturing the above-mentioned all-solid-state lithium secondary battery is not particularly limited. After forming a slurry containing a negative electrode or a positive electrode active material on a current collector, the negative electrode or the positive electrode is respectively manufactured through processes such as drying and rolling. After forming a slurry containing colored oxide particles or the like on the above-mentioned negative electrode or positive electrode, a light sintering process is performed on the oxide-based thin film sheet formed by drying to form an oxide-based solid electrolyte sheet, and the above-mentioned all-solid-state lithium secondary battery can be manufactured through this method.

[0125] When the above-mentioned all-solid-state lithium secondary battery includes the oxide-based solid electrolyte sheet described above, there is no risk of ignition due to electrolyte leakage, and it can have excellent performance such as a high energy density.

Examples

[0126] Hereinafter, the examples of the present invention will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present invention and do not limit the scope of the appended claims. It is obvious to those skilled in the art that various changes and modifications to the examples are possible within the scope of the present disclosure and the scope of the technical idea, and it is natural that such deformations and modifications belong to the scope of the appended claims.

[0127] 1. Production of Ink Composition for Light Sintering (1) Example 1 A primary slurry was prepared by primary stirring 3.16g of a solvent mixture of 0.42g of PVA1 binder, 1.58g of 2-propanol, and 1.58g of toluene (Table 2 below), 0.2g of Croda's Hypermer KD-6 dispersant, and 0.65g of DBP plasticizer in a Thinky paste mixer at 3,000 rpm for 5 minutes. The polyvinyl acetal structural unit had a structure in which a small amount of polyvinyl acetoacetal structural unit was mixed into polyvinyl butyral structural unit.

[0128] Lithium lanthanum zirconium oxide (LLZO; Li7La3Zr2O 12 The lithium ion conductive oxide particles and the primary slurry were weighed in a weight ratio of 1:1 and mixed together, and then the mixture was stirred at 3,000 rpm for 5 minutes using a Thinky paste mixer to prepare an ink composition for photosintering.

[0129] In addition, the Hansen solubility parameter (HSP) value of the PVA1 binder was calculated using the above mathematical formula 1. The molecular weight, density, and Hansen solubility parameter (HSP) of the polymer consisting of only each of the three components of the random copolymer, which are values ​​required for using the above mathematical formula 1, are shown in Table 3. The Hansen solubility parameter (HSP) value of the PVA1 binder is shown in Table 4 below.

[0130] (2) Comparative Example 1 A photosintering ink composition was produced by polymerization in the same manner as in Example 1, except that the binder was changed to the PVA2 binder shown in Table 2 below.

[0131] In addition, the Hansen solubility parameter (HSP) value of the PVA2 binder was measured and is shown in Table 4. The Hansen solubility parameter value was determined using Equation 1 above.

[0132] (3) Comparative Example 2 A photosintering ink composition was produced by polymerization in the same manner as in Example 1, except that the binder was changed to PVA3 in Table 2 below.

[0133] In addition, the Hansen solubility parameter (HSP) value of the PVA3 binder was measured and is shown in Table 4. The Hansen solubility parameter value was determined using Equation 1.

[0134] [Table 2]

[0135] [Table 3]

[0136] [Table 4]

[0137] 2. Evaluation of solubility of primary slurry Figure 2 is a photograph showing the degree of dissolution of the primary slurries of Example 1, Comparative Example 1, and Comparative Example 2. Referring to Figure 2, it can be seen that the binder is completely dissolved and present in liquid form in the primary slurry of Example 1, while it can be seen with the naked eye that the binder is not completely dissolved and solids remain in the primary slurries of Comparative Examples 1 and 2.

[0138] 3. Fabrication of oxide-based solid electrolyte sheets by photosintering Manufacturing Example 1 The photosintering ink composition of Example 1 was applied to a substrate (Cu-foil current collector) having a thickness of 20 μm at a concentration of 2000 mg / cm 2 After casting at a loading weight (LW) of 1000 μm, the mixture was dried at room temperature for 1 hour to prepare an oxide-based thin film sheet having a thickness of about 60 to 200 μm.

[0139] The oxide-based thin film sheet thus prepared was cut into pieces measuring 1cm x 1cm to 3cm x 3cm and loaded into a photosintering device (PulseForge Invent). Then, photosintering was performed on the oxide-based thin film sheet according to the photosintering conditions shown in Table 5 below to prepare an oxide-based solid electrolyte sheet of Preparation Example 1 having a thickness of approximately 50 to 150µm, as shown in Figure 3. The substrate temperature was maintained at room temperature, between 20°C and 25°C.

[0140] [Table 5]

[0141] 3, it can be seen that the oxide-based solid electrolyte sheet of Preparation Example 1 was effectively sintered using light energy within a few seconds. In addition, it can be seen that the metal sheet used as the current collector was not deformed by the thermal energy because light energy was irradiated only to the surface, and only the oxide-based thin film sheet was selectively sintered.

[0142] Comparative Examples 1 and 2 The oxide-based thin film sheets of Comparative Production Examples 1 and 2 were produced in the same manner as Production Example 1, except that the photosintering ink composition of Example 1 was changed to the photosintering ink compositions of Comparative Examples 1 and 2. However, no thin films were formed.

[0143] 4. Ionic Conductivity Characterization The oxide-based solid electrolyte sheet of Production Example 1 was subjected to electrochemical impedance analysis using a potentiostat (VMP-300) in an air atmosphere at room temperature (25°C) to measure the resistance component, and the ionic conductivity was calculated using the following equation 2. The results are shown in FIG. 4. [Formula 2] σ=D / (R×S)

[0144] In the above formula 2, σ is the ionic conductivity value (S / cm), D is the thickness of the oxide-based solid electrolyte sheet (cm), R is the measured impedance resistance value (1 / S), and S is the area of ​​the oxide-based solid electrolyte sheet (cm 2)

[0145] Referring to Figure 4, the electrolyte sample after photosintering had a melting point of 1.32 × 10 -5 S / cm, demonstrating excellent performance.

[0146] As a result, the oxide-based solid electrolyte sheet of Production Example 1 can provide an all-solid-state lithium secondary battery that is free from the risk of fire due to electrolyte leakage and has high energy density and excellent ion conductivity.

[0147] What has been described above is merely illustrative of the application of the principles of the present disclosure, and other arrangements may be included without departing from the scope of the present invention.

Claims

1. a binder comprising a polymer containing hydroxy groups, acetyl groups, and acetal groups; The Hansen Solubility Parameter (HSP) value of the polymer is 18 MPa. ０．５ ~28 MPa ０．５ and The weight average molecular weight of the polymer is 1.0×10 ４ g / mol~9.0×10 ４ g / mol of the photosintering ink composition.

2. The ink composition for photosintering according to claim 1 , wherein the polymer comprises a polyvinyl acetal copolymer including a structural unit having a hydroxy group, a structural unit having an acetyl group, and a structural unit having an acetal group.

3. The ink composition for photosintering according to claim 2 , wherein the structural unit having a hydroxy group is a structural unit represented by the following chemical formula 1: 【Chemistry 1】 (In the above Chemical Formula 1, L １ is a single bond or alkylene having 1 to 5 carbon atoms.

4. The ink composition for photosintering according to claim 2 , wherein the structural unit having an acetyl group is a structural unit represented by the following chemical formula 2: 【Chemistry 2】 (In the above Chemical Formula 2, L ２ is a single bond or alkylene having 1 to 5 carbon atoms.

5. The ink composition for photosintering according to claim 2 , wherein the structural unit having an acetal group is a structural unit represented by the following chemical formula 3: 【Transformation 3】 (In the above Chemical Formula 3, R is hydrogen or a substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms.)

6. 3. The ink composition for photosintering according to claim 2, wherein the content of the structural unit having a hydroxy group is 4% by weight to 25% by weight relative to 100% by weight of the polyvinyl acetal copolymer.

7. 3. The ink composition for photosintering according to claim 2, wherein the content of the structural unit having an acetyl group is 1% by weight to 12% by weight relative to 100% by weight of the polyvinyl acetal copolymer.

8. 3. The ink composition for photosintering according to claim 2, wherein the content of the structural unit having an acetal group is 65% by weight to 85% by weight relative to 100% by weight of the polyvinyl acetal copolymer.

9. The photosintering ink composition according to claim 1 , wherein the polymer is a random copolymer.

10. 2. The ink composition for photosintering according to claim 1, wherein the viscosity of the ink composition for photosintering is 1,000 cp to 10,000 cp at 25°C.

11. The ink composition for photosintering according to claim 1 , further comprising lithium ion conductive oxide particles, a solvent, and a plasticizer.

12. The Hansen Solubility Parameter (HSP) value of the solvent is 18 MPa. ０．５ ~28 MPa ０．５ The photosintering ink composition according to claim 11,

13. The solvent is at least one selected from the group consisting of 1,3-dioxane, dimethyl carbonate, acetonitrile, methylpyrrolidone, dimethylformamide, acetone, isopropanol, n-propanol, n-hexane, and toluene. The ink composition for photosintering according to claim 11.

14. The photosintering ink composition according to claim 11, wherein the plasticizer is one or more selected from the group consisting of dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), diisononyl phthalate (DINP), diethylhexyl phthalate (Di(2-ethylhexyl) phthalate (DEHP), di-n-octyl phthalate (DNOP), and di-isodecyl phthalate (DIDP).

15. The ink composition for photosintering according to claim 11, wherein the lithium ion conductive oxide particles are at least one selected from the group consisting of a garnet compound, a NASICON compound, and a perovskite compound.

16. An oxide-based solid electrolyte sheet produced using the ink composition for photosintering according to claim 1 .

17. The oxide-based solid electrolyte sheet is 10 －６ S / cm to 10 －２ S / cm ionic conductivity, The oxide-based solid electrolyte sheet is 0.25 cm ２ 17. The oxide-based solid electrolyte sheet according to claim 16, having the above area and a thickness of 10 μm to 300 μm.

18. Applying the photosintering ink composition according to any one of claims 1 to 15 onto a substrate; drying the substrate to produce an oxide-based sheet; The method for producing an oxide-based solid electrolyte sheet includes a step of photosintering the oxide-based sheet to produce an oxide-based solid electrolyte sheet.

19. The method for producing an oxide-based solid electrolyte sheet according to claim 18, wherein the temperature of the oxide-based sheet during photosintering is 25°C to 500°C.

20. An all-solid-state lithium secondary battery comprising the oxide-based solid electrolyte sheet according to claim 16.

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