Composite solid electrolyte for lithium secondary batteries and method for manufacturing the same

Abstract

The object of the present invention is to provide an all-solid-state battery containing a composite solid electrolyte with improved ionic conductivity. [Solution] The present invention provides a composite solid electrolyte for a lithium secondary battery, comprising a ceramic ion conductor containing a ceramic compound; a second polymer; and a lithium salt, wherein the ceramic ion conductor includes a cross-linked bonding structure containing the ceramic compound. The present invention also provides an all-solid-state battery comprising the composite solid electrolyte for a lithium secondary battery.

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Application No. 10-2022-0067013 dated May 31, 2022, and Korean Patent Application No. 10-2023-0070195 dated May 31, 2023, and incorporates all the contents disclosed in the documents of said Korean Patent Applications as part of this Specification.

[0002] The present invention relates to a composite solid electrolyte for lithium secondary batteries and a method for producing the same. [Background technology]

[0003] Lithium-ion batteries, which use liquid electrolytes, have a structure in which the negative and positive electrodes are separated by a separator membrane. If the separator membrane is damaged due to deformation or external impact, a short circuit can occur, which can lead to dangers such as overheating or explosion. Therefore, the development of solid electrolytes that can ensure safety in the field of lithium-ion secondary batteries is a very important issue.

[0004] Lithium-ion batteries using solid electrolytes offer several advantages: increased battery safety, prevention of electrolyte leakage, improved battery reliability, and the ease of manufacturing thin batteries. Furthermore, the use of lithium metal in the negative electrode allows for increased energy density, making them promising for applications in small secondary batteries as well as high-capacity secondary batteries for electric vehicles, and attracting attention as a next-generation battery.

[0005] Among solid electrolytes, polymer solid electrolytes can utilize polymer materials with ion-conducting properties, or inorganic materials such as oxides or sulfides with ion-conducting characteristics. Composite solid electrolytes, which are mixtures of polymer and inorganic materials, have also been proposed.

[0006] Conventional composite solid electrolytes were manufactured by first creating a solution or slurry by mixing and dispersing polymers and inorganic materials, and then performing a solution casting and high-temperature drying process on a substrate. However, conventional manufacturing techniques for composite solid electrolytes have limitations. Because the uniform dispersion of inorganic materials within the polymer solution is not smooth, a non-uniform distribution of inorganic particles is formed within the composite solid electrolyte, making it difficult to manufacture composite solid electrolytes with improved ionic conductivity.

[0007] To overcome these limitations of conventional composite solid electrolytes, there is a need for the development of technologies that can uniformly disperse polymers and inorganic materials to improve the ionic conductivity of composite solid electrolytes containing them. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Korean Published Patent Publication No. 2017-0045011 [Overview of the project] [Problems that the invention aims to solve]

[0009] The object of the present invention is to provide a composite solid electrolyte with improved ionic conductivity.

[0010] Another object of the present invention is to provide a method for producing a composite solid electrolyte with improved ionic conductivity.

[0011] Another object of the present invention is to provide an all-solid-state battery containing a composite solid electrolyte with improved ionic conductivity. [Means for solving the problem]

[0012] To achieve the above object, the present invention provides a method for manufacturing a composite solid electrolyte for a lithium secondary battery, comprising: (S1) forming a hydrogel of the first polymer from a solution containing the first polymer having a crosslinkable functional group (side chain) and a ceramic compound to produce a first composite; (S2) sintering the first composite to produce a ceramic ion conductor; and (S3) immersing and drying the ceramic ion conductor in a solution containing a second polymer and a lithium salt to produce a second composite.

[0013] The present invention also provides a composite solid electrolyte for a lithium secondary battery, comprising a ceramic ion conductor containing a ceramic compound, a second polymer, and a lithium salt, wherein the ceramic ion conductor has a crosslinked structure containing the ceramic compound.

[0014] The present invention also provides an all-solid-state battery comprising the composite solid electrolyte for a lithium secondary battery.

Advantages of the Invention

[0015] The composite solid electrolyte according to the present invention can effectively improve the ion conduction of lithium ions by forming a ceramic ion conductor containing a ceramic compound.

Brief Description of the Drawings

[0016] [Figure 1] This is an image of a hydrogel of a polymer according to an embodiment of the present invention. [Figure 2] This is an image of a ceramic ion conductor formed after sintering a hydrogel of a polymer according to an embodiment of the present invention. [Figure 3] This is a scanning electron microscope (SEM) photograph of a powder (Pristine LLZO) of a ceramic compound according to an embodiment of the present invention. [Figure 4]This is a scanning electron microscope (SEM) image of a ceramic ion conductor according to one embodiment of the present invention. [Figure 5] This is an image of a polymer hydrogel according to one embodiment of the present invention. [Figure 6] This is an image of a ceramic ion conductor according to one embodiment of the present invention. [Figure 7] This is an image of the ceramic ion conductor according to Comparative Example 1. [Modes for carrying out the invention]

[0017] The present invention will be described in more detail below to aid in understanding the invention.

[0018] The terms and words used in this specification and the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner and concept consistent with the technical idea of ​​the present invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their inventions.

[0019] Method for manufacturing a composite solid electrolyte for lithium secondary batteries A method for producing a composite solid electrolyte according to one embodiment of the present invention may include the following steps: (S1) A step of producing a first composite by forming a hydrogel of the first polymer from a solution containing a first polymer containing a crosslinking functional group (side chain) and a ceramic compound; (S2) The step of sintering the first composite to produce a ceramic ion conductor; (S3) The step of immersing the ceramic ion conductor in a solution containing a second polymer and a lithium salt and drying it to produce a second composite.

[0020] In the method for producing the composite solid electrolyte, the ceramic compound can be uniformly dispersed in the solution of the first polymer by producing a hydrogel of the first polymer from a solution containing the first polymer and a ceramic compound. Furthermore, by producing a ceramic ion conductor using the hydrogel of the first polymer, the ion conduction of lithium ions can be improved, and a composite solid electrolyte with improved ion conductivity can be produced.

[0021] The method for producing the composite solid electrolyte according to the present invention will be described in more detail below, step by step.

[0022] In the present invention, in step (S1), a first composite can be produced by forming a hydrogel of the first polymer from a solution containing a first polymer containing a crosslinking functional group (side chain) and a ceramic compound.

[0023] The first complex can be produced by hydrogelation of the first polymer.

[0024] Conventional composite solid electrolytes are manufactured by first preparing a solution by mixing and dispersing polymers and inorganic materials, then coating the solution onto a substrate using methods such as solution casting, and finally producing a composite solid electrolyte film through a drying process. However, such composite solid electrolytes have the problem that the inorganic materials are not uniformly dispersed in the polymer solution, resulting in a non-uniform distribution of inorganic particles in the final composite solid electrolyte film, and thus low ionic conductivity.

[0025] Therefore, the inventors have efficiently manufactured a ceramic ion conductor by uniformly dispersing the ceramic compound particles within the first composite through hydrogelation of the first polymer, and then sintering the first composite, thereby completing a composite solid electrolyte with improved ionic conductivity.

[0026] The hydrogelation of the first polymer may include physical or chemical crosslinking of the first polymer, and the physical or chemical crosslinking may include a crosslinking structure between the first polymer containing crosslinkable functional groups and the ceramic compound.

[0027] In the present invention, the crosslinking structure may include (a) crosslinking between crosslinkable functional groups, and (b) crosslinking between crosslinkable functional groups and ceramic compounds.

[0028] The crosslinking between the crosslinking functional groups (a) may include hydrogen bonds between the crosslinking functional groups, for example, the hydrogen bonds may be hydrogen bonds between OH- groups.

[0029] The crosslinking between the (b) crosslinkable functional group and the ceramic compound may include bonding by Lewis acid-base interaction, for example, the bonding may be between the -OH group and Li. The crosslinking between the (b) crosslinkable functional group and the ceramic compound is bonding by Lewis acid-base interaction and may be in the form of a metal-ligand bond.

[0030] Furthermore, the crosslinking between the (b) crosslinking functional group and the ceramic compound prevents aggregation between the particles of the ceramic compound and ensures that the particles of the ceramic compound are uniformly dispersed within the hydrogel. This allows for improvement of the ionic conductivity of the composite solid electrolyte through a ceramic ion conductor produced by sintering the first composite after forming a hydrogel of the first polymer to manufacture the first composite.

[0031] The aforementioned cross-linking structure improves the mobility of lithium ions within the electrolyte, thereby providing a composite solid electrolyte with improved ionic conductivity.

[0032] In the present invention, the crosslinking functional group contained in the first polymer may have the property of being able to form a crosslinked structure by forming bonds as shown in (a) and (b) above.

[0033] For example, the crosslinking functional group may include one or more selected from the group consisting of a hydroxyl group, a carboxyl group, and an amide group.

[0034] Furthermore, the weight-average molecular weight (Mw) of the polymer containing the crosslinking functional group may be between 80,000 g / mol and 130,000 g / mol, specifically, it may be 80,000 g / mol or more, 83,000 g / mol or more, or 85,000 g / mol or more, and may be 90,000 g / mol or less, 110,000 g / mol or less, or 130,000 g / mol or less. If the weight-average molecular weight (Mw) of the polymer containing the crosslinking functional group is less than 80,000 g / mol, the bonds formed by the crosslinking functional group may not be sufficiently formed to obtain a crosslinked structure. If the weight-average molecular weight (Mw) of the polymer containing the crosslinking functional group exceeds 130,000 g / mol, entanglement of the polymer chains increases in the polymer solution used in the manufacturing process, and the solvent penetration rate into the polymer chain decreases. This can accelerate the gelation of the polymer, reduce its solubility, and hinder the smooth bonding by crosslinking functional groups, making it difficult to form a crosslinked structure.

[0035] Furthermore, the first polymer containing the crosslinking functional group may also contain one or more selected from the group consisting of polyvinyl alcohol (PVA), gelatin, methylcellulose, agar, dextrin, poly(vinylpyrrolidone), poly(acrylamide), poly(acrylic acid, PAA), starch-carboxymethylcellulose, hyaluronic acid-methylcellulose, chitosan, poly(N-isopropylacrylamide), and amino-terminated polyethylene glycol (PEG). Preferably, the polymer containing the crosslinking functional group may be PVA, which can efficiently undergo phase separation between the PVA and the solvent during freezing in the manufacturing process of the composite solid electrolyte, and may be advantageous for forming a crosslinked structure by the (a) and (b) bonds derived from the crosslinking functional group of the PVA that has been phase-separated from the solvent.

[0036] In one embodiment of the present invention, the crosslinked bonding structure can be formed by freezing and thawing a solution containing the first polymer and the ceramic compound.

[0037] In the freezing process, the first polymer contained in the aqueous polymer solution containing the crosslinking functional group and water can undergo phase separation. This phase separation can be induced because the hydrogen bonds between the crosslinking functional group and the water molecules are stronger than the hydrogen bonds between the crosslinking functional group and the water molecules. The water molecules aggregated by the hydrogen bonds with the water molecules exist as ice (ice phase) during the freezing process. As a result, the number of crosslinking functional groups that form hydrogen bonds through interaction with the water molecules is significantly reduced.

[0038] As a result of the phase separation, the interior of the hydrogel is divided into (i) a polymer-poor phase and (ii) a polymer-rich phase.

[0039] The aforementioned (i) Polymer-poor phase is a region containing water molecules that have aggregated through hydrogen bonding with other water molecules, and exists in an ice state (ice phase), which can also be called a free water state.

[0040] The (ii) polymer-rich phase is a portion containing polymers that have been phase-separated from water. These phase-separated polymers contain crosslinking functional groups that are free from interaction with water molecules. After phase separation, they become free and do not form crystals through regular folding, but exist in a relatively free, amorphous state, which is called an amorphous polymer chain.

[0041] Furthermore, some of the crosslinking functional groups contained in the phase-separated polymer form localized crystallites. These localized crystallites act as crosslinkable junction points, forming a crosslinked structure that includes the (a) and (b) bonds.

[0042] Furthermore, in the thawing step following the freezing step, the ice contained in the (i) polymer-poor phase melts and evaporates, thereby producing a composite solid electrolyte with increased free volume.

[0043] Furthermore, the freezing can be carried out by appropriately selecting conditions that allow the hydrogel to freeze sufficiently. For example, the freezing temperature can be between -30°C and -10°C. Specifically, the freezing temperature may be above -30°C, above -25°C, or above -23°C, or below -18°C, below -15°C, or below -10°C. If the freezing temperature is below -30°C, cracks may occur in the hydrogel, and if it is above -10°C, phase separation between the polymer and water may not occur sufficiently, making it difficult to form amorphous polymer chain regions. In addition, the freezing can be carried out within the range of 20 to 30 hours, taking into consideration the time required for sufficient freezing.

[0044] Furthermore, the thawing can be carried out by appropriately selecting conditions that allow the frozen hydrogel to thaw to a degree that it can be used as a composite solid electrolyte. For example, the thawing temperature may be 15°C to 35°C, or it may be room temperature (25°C). If the thawing temperature is below 15°C, the water drying efficiency after thawing (ice melting) may decrease, and if it is above 35°C, the hydrogel may shrink, causing wrinkles or warping.

[0045] In one embodiment of the present invention, the crosslinked bonding structure can be formed by adding a chemical cross-linker to a solution containing the first polymer and the ceramic compound.

[0046] In addition to being formed by physical crosslinking through the aforementioned freezing and thawing process, the aforementioned crosslinked bonding structure can also be formed by chemical crosslinking using a chemical crosslinking agent.

[0047] The crosslinking bond comprising the first polymer may include a chemical crosslinking bond, which may be formed by a chemical cross-linker to create a crosslink between the first polymer containing crosslinkable functional groups and the ceramic compound.

[0048] In the crosslinking of the first polymer, chemical crosslinking can be achieved by adding a chemical cross-linker to a mixed solution containing the first polymer and a ceramic compound to form chemical crosslinks of the first polymer.

[0049] The chemical crosslinking agent can form bonds between first polymers containing crosslinking functional groups, or between the first polymer containing the crosslinking functional groups and the ceramic compound.

[0050] The aforementioned chemical crosslinking agent may include one or more selected from the group consisting of boric acid, glutaraldehyde, inorganic salts, and metal salts, but is not limited to these examples; any chemical crosslinking agent that forms the hydrogel of the first polymer is acceptable.

[0051] In the first composite, the ceramic compound may be present in amounts of 1 part by weight or more and less than 10 parts by weight per 1 part by weight of the first polymer. More specifically, the weight ratio of the first polymer to the ceramic compound may be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, or 1:9. If the ceramic compound is present in amounts of less than 1 part by weight per 1 part by weight of the first polymer, after the sintering process in step (S2) below, the bonding between the ceramic compounds does not occur smoothly, making it difficult to form a cross-linked ceramic ion conductor structure. Furthermore, the mechanical properties are also weak, easily crumbling or breaking, and there is a problem in that the composite solid electrolyte cannot be manufactured. Furthermore, if the ceramic compound is present in amounts exceeding 10 parts by weight per 1 part by weight of the first polymer, the ceramic compound will not be uniformly dispersed within the first polymer, and the ceramic compound particles will aggregate and clump together. This will cause phase separation between the first polymer and the aggregated ceramic compound particles, making it difficult to form a ceramic ion conductor, and consequently resulting in the production of a composite solid electrolyte with reduced ionic conductivity.

[0052] In the present invention, in step (S2), the first composite can be sintered to produce a ceramic ion conductor.

[0053] Here, sintering refers to the process of applying sufficient temperature and pressure to create a harder aggregate of particles from the first composite.

[0054] The ceramic ion conductor can be manufactured by sintering the first composite to thermally decompose the hydrogel of the first polymer, and then sintering the remaining ceramic compound particles.

[0055] After the sintering process, the hydrogel of the first polymer acts as a support so that the particles of the ceramic compound can be linked together, and the particles of the ceramic compound can be linked together to form a ceramic ion conductor having a single cross-linked bonding structure.

[0056] The ceramic ion conductor can play a role in forming an ion conduction path for lithium ions.

[0057] The sintering can be carried out by appropriately selecting conditions that allow the hydrogel of the first polymer to be thermally decomposed, causing the structures of the ceramic compound particles to link together and form an ion conductor with a cross-linked structure. For example, the sintering temperature can be 800°C to 1300°C, and specifically, the sintering temperature may be 850°C or higher, 900°C or higher, 950°C or higher, or 1300°C or lower, 1250°C or lower, or 1200°C or lower.

[0058] In the present invention, in step (S3), the ceramic ion conductor can be immersed in a solution containing the second polymer and a lithium salt and dried to produce the second composite.

[0059] The second composite can be used to produce a composite solid electrolyte with improved ionic conductivity by including the ceramic ion conductor.

[0060] The second polymer exhibits excellent solubility of lithium salts, and its polymer solution penetrates well into the ceramic ion conductor, making it easy to manufacture the final composite solid electrolyte. Specific examples of the second polymer include polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyacrylate, poly(methyl methacrylate, PMMA), PSTFSI, polyurethane, nylon, poly(dimethylsiloxane), gelatin, methylcellulose, agar, dextrin, poly(vinylpyrrolidone), poly(acrylamide), poly(acrylic acid), starch-carboxymethylcellulose, hyaluronic acid-methylcellulose, chitosan, poly(N-isopropylacrylamide), and amino-terminated polyethylene glycol. It may include one or more selected from the group consisting of PEG.

[0061] In the present invention, the lithium salt is contained in a dissociated state within the structure formed by the ceramic ion conductor, thereby improving the ionic conductivity of the composite solid electrolyte. Furthermore, the lithium salt is mainly dissociated within the second polymer, and in step (S2), it can play a role in compensating for the loss of lithium ions generated from the ceramic compound particles during the high-temperature sintering process.

[0062] The lithium salts mentioned above are (CF3SO2)2NLi (Lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), (FSO2)2NLi (Lithium bis(fluorosulfonyl)imide, LiFSI), LiNO3, LiOH, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 It may also contain one or more selected from the group consisting of LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, and LiC(CF3SO2)3.

[0063] The ceramic ion conductor produced in step (S2) can be immersed in or coated with a solution containing the second polymer and lithium salt, and then dried to produce the second composite. The immersion or coating and drying can be repeated multiple times.

[0064] The molar concentration ([G]) of the second polymer and the molar ratio ([Li] / [G]) of lithium ([Li]) in the lithium salt may be between 0.1 and 0.5, specifically, 0.1 or more, 0.2 or more, or 0.3 or more, and may be 0.4 or less, or 0.5 or less. If the molar ratio ([Li] / [G]) is less than 0.1, the lithium salt content decreases, which may lower the ionic conductivity of the composite solid electrolyte. If the molar ratio ([Li] / [G]) exceeds 0.5, the ionic conductivity may decrease due to lithium ion aggregation. Therefore, the composite solid electrolyte according to the present invention requires the second polymer and an appropriate amount of lithium salt in the composition of the second composite.

[0065] Composite solid electrolyte for lithium secondary batteries The composite solid electrolyte for a lithium secondary battery according to the present invention includes a ceramic ion conductor containing a ceramic compound; a second polymer; and a lithium salt; and the ceramic ion conductor can include a cross-linked structure containing the ceramic compound.

[0066] Conventional composite solid electrolytes were manufactured by coating and drying a solution or slurry in which a polymer and an inorganic substance were mixed and dispersed on a substrate by a method such as solution casting. However, such a method had a problem that the ionic conductivity of the solid electrolyte was not improved due to non-uniform dispersion and precipitation of the inorganic substance in the polymer solution.

[0067] In order to improve this, in the present invention, a composite solid electrolyte including a ceramic ion conductor including a cross-linked structure forming an ionic conduction path (path) of lithium ions, a polymer, and a lithium salt is provided. In the ceramic ion conductor, particles of the ceramic compound are uniformly dispersed therein, and it can play a role of improving the ionic conductivity of the composite solid electrolyte.

[0068] The ceramic compound can be an oxide-based or phosphate-based solid electrolyte. Examples of the oxide-based or phosphate-based solid electrolyte include garnet-type lithium-lanthanum-zirconium oxide-based (LLZO, Li7La3Zr2O 12 ), perovskite-type lithium-lanthanum-titanium oxide-based (LLTO, Li 3x La 2 / 3-x TiO3), phosphate-based NASICON-type lithium-aluminum-titanium phosphate-based (LATP, Li 1+x Al x Ti 2-x (PO4)3), lithium-aluminum-germanium phosphate-based (LAGP, Li 1.5 Al 0.5 Ge 1.5One or more compounds may be selected from the group consisting of (PO4)3), lithium-silicon-titanium phosphate (LSTP, LiSiO2TiO2(PO4)3), and lithium-lanthanum-zirconium-titanium oxide (LLZTO) compounds. The oxide-based or phosphate-based solid electrolytes have very high grain boundary resistance, requiring a sintering process at 1000°C or higher. This results in problems such as lithium volatilization at high temperatures, phase transitions, and impurity phase formation. However, oxide-based or phosphate-based solid electrolytes generally have a maximum temperature of 10°C at room temperature. -4 ~10 -3 It has an ionic conductivity value of S / cm, is stable in the high-voltage range, and has the advantages of being stable in air, easy to synthesize, and easy to handle.

[0069] Therefore, by mixing the first polymer according to the present invention with a different substance to produce a hybrid solid electrolyte, the shortcomings of each material can be compensated for.

[0070] The oxide-based or phosphate-based solid electrolytes do not easily burn or ignite even under high-temperature conditions of 400°C or higher, thus exhibiting high high-temperature stability. Therefore, when the ceramic ion conductor contains the oxide-based or phosphate-based solid electrolyte, it is possible to improve not only the mechanical strength of the composite solid electrolyte for lithium secondary batteries, but also its high-temperature stability and ionic conductivity.

[0071] The second polymer and lithium salt are as described above.

[0072] In one embodiment of the present invention, the ceramic ion conductor may include a crosslinked bonding structure containing a ceramic compound.

[0073] The ceramic ion conductor may include a single cross-linked structure formed by the interconnection of particles of the ceramic compound.

[0074] The ceramic ion conductor can play a role in forming an ion conduction path for lithium ions.

[0075] The specific manufacturing method and specific ceramic compounds for the aforementioned ceramic ion conductors are as described above.

[0076] In the present invention, the composite solid electrolyte may be in the form of a free-standing film. The free-standing film refers to a film that can maintain its film form on its own at room temperature and pressure without the need for a separate support.

[0077] The aforementioned freestanding film exhibits elasticity, minimizes brittleness, and possesses the properties of a support that stably contains lithium ions, making it a suitable form for use as a composite solid electrolyte.

[0078] In the present invention, the ionic conductivity of the composite solid electrolyte is 10 -5 It may be S / cm or higher.

[0079] As mentioned above, despite being a solid electrolyte, the composite solid electrolyte exhibits ionic conductivity at a level equivalent to or higher than that of conventional liquid electrolytes, thereby improving the performance of all-solid-state batteries.

[0080] All solid state battery The present invention also relates to an all-solid-state battery comprising the composite solid electrolyte, wherein the all-solid-state battery comprises a negative electrode, a positive electrode, and a composite solid electrolyte interposed between the negative electrode and the positive electrode, and the composite solid electrolyte has the characteristics described above.

[0081] Specifically, the composite solid electrolyte includes a ceramic ion conductor, which improves the ion conduction of lithium ions, making it suitable as an electrolyte for all-solid-state batteries.

[0082] In the present invention, the positive electrode included in the all-solid-state battery includes a positive electrode active material layer, and the positive electrode active material layer may be formed on one surface of the positive electrode current collector.

[0083] The positive electrode active material layer comprises a positive electrode active material, a binder, and a conductive material.

[0084] Furthermore, the positive electrode active material is not particularly limited as long as it is a material capable of reversibly intercalating and releasing lithium ions, for example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), Li[Ni x Co y Mn z M v ]O2(In the above formula, M is one or more elements selected from the group consisting of Al, Ga, and In; 0.3≦x<1.0, 0≦y, z≦0.5, 0≦v≦0.1, x+y+z+v=1), Li(Li a M b-a-b’ M' b’ )O 2-c A c (In the above formula, 0≦a≦0.2, 0.6≦b≦1, 0≦b'≦0.2, 0≦c≦0.2; M comprises Mn and one or more elements selected from the group consisting of Ni, Co, Fe, Cr, V, Cu, Zn, and Ti; M' is one or more elements selected from the group consisting of Al, Mg, and B; and A is one or more elements selected from the group consisting of P, F, S, and N.) A layered compound such as the above, or a compound substituted with one or more transition metals; chemical formula Li 1+y Mn 2-y Lithium manganese oxides such as O4 (where y is 0-0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-y Ni-site type lithium nickel oxide represented as MyO2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and y = 0.01-0.3); chemical formula LiMn 2-y M yExamples include, but are not limited to, lithium manganese composite oxides represented as O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and y = 0.01-0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion; disulfide compounds; Fe2(MoO4)3, etc.

[0085] Furthermore, the positive electrode active material may be present in an amount of 40 to 80% by weight based on the total weight of the positive electrode active material layer. Specifically, the content of the positive electrode active material may be 40% or more by weight, 50% or more by weight, or 70% or less by weight, or 80% or less by weight. If the content of the positive electrode active material is less than 40% by weight, the connectivity between the wet positive electrode active material layer and the dry positive electrode active material layer may be insufficient, and if it exceeds 80% by weight, the mass transfer resistance may increase.

[0086] Furthermore, the binder contains components that assist in the bonding of the positive electrode active material to conductive materials and to the current collector, such as styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylonitrile copolymer, acrylonitrile-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-styrene-butadiene copolymer, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene / propylene copolymer, polybutadiene, polyethylene oxide, chlorosulfonated polyethylene, polyvinylpyrrolidone, polyvinylpyridine, polyvinyl alcohol, polyvinyl acetate, polyepichlorohydrin, polyphosphazene, and polyacrylic acid. The binder may contain one or more selected from the group consisting of lilonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethylcellulose, hydroxypropylcellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylcellulose, cyanoethyl scrophulari, polyester, polyamide, polyether, polyimide, polycarboxylate, polycarboxylic acid, polyacrylic acid, polyacrylate, lithium polyacrylate, polymethacrylic acid, polymethacrylate, polyacrylamide, polyurethane, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropene. Preferably, the binder may contain one or more selected from the group consisting of styrene-butadiene rubber, polytetrafluoroethylene, carboxymethylcellulose, polyacrylic acid, lithium polyacrylate, and polyvinylidene fluoride.

[0087] Furthermore, the binder may be present in an amount of 1% to 30% by weight based on the total weight of the positive electrode active material layer. Specifically, the binder content may be 1% or more by weight, 3% or more by weight, 15% or less by weight, or 30% or less by weight. If the binder content is less than 1% by weight, the adhesive strength between the positive electrode active material and the positive electrode current collector may decrease. If it exceeds 30% by weight, the adhesive strength improves, but the content of the positive electrode active material decreases accordingly, which may reduce the battery capacity.

[0088] Furthermore, the conductive material is not particularly limited as long as it prevents side reactions in the internal environment of the all-solid-state battery, does not induce chemical changes in the battery, and has excellent electrical conductivity. Typically, graphite or conductive carbon can be used, for example: graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, lamp black, and summer black; carbon-based materials whose crystalline structure is graphene or graphite; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These can be used individually or in combination of two or more, but are not necessarily limited to these.

[0089] The conductive material may typically be present in an amount of 0.5% to 30% by weight based on the total weight of the positive electrode active material layer. Specifically, the content of the conductive material may be 0.5% or more by weight, 1% or more by weight, 20% or less by weight, or 30% or less by weight. If the content of the conductive material is too low (less than 0.5% by weight), it may be difficult to expect an improvement in electrical conductivity, or the electrochemical properties of the battery may deteriorate. If it is too high (more than 30% by weight), the amount of positive electrode active material will be relatively small, and the capacity and energy density may decrease. The method for incorporating the conductive material into the positive electrode is not significantly limited, and conventional methods known in the art, such as coating the positive electrode active material, can be used.

[0090] Furthermore, the positive electrode current collector supports the positive electrode active material layer and plays a role in transferring electrons between the external conductor and the positive electrode active material layer.

[0091] The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the all-solid-state battery and has high electronic conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., and aluminum-cadmium alloy can be used as the positive electrode current collector.

[0092] The positive electrode current collector may have a fine uneven surface or a three-dimensional porous structure to enhance the bonding force with the positive electrode active material layer. As a result, the positive electrode current collector can take various forms such as film, sheet, foil, mesh, net, porous material, foam, or nonwoven fabric.

[0093] The positive electrode described above can be manufactured according to conventional methods. Specifically, it can be manufactured by mixing a positive electrode active material, a conductive material, and a binder in an organic solvent to produce a composition for forming a positive electrode active material layer, which is then coated onto a positive electrode current collector and dried, and then selectively compressing the current collector to improve electrode density. In this case, it is desirable to use an organic solvent that can uniformly disperse the positive electrode active material, binder, and conductive material and that evaporates easily. Specifically, examples include acetonitrile, methanol, ethanol, tetrahydrofuran, water, and isopropyl alcohol.

[0094] In the present invention, the negative electrode included in the all-solid-state battery includes a negative electrode active material layer, and the negative electrode active material layer may be formed on one surface of the negative electrode current collector.

[0095] The negative electrode active material is lithium (Li + This may include materials that can be reversibly intercalated or deintercalated, materials that can react with lithium ions to reversibly form lithium-containing compounds, lithium metals, or lithium alloys.

[0096] The aforementioned lithium ion (Li +The material that can reversibly insert or remove lithium ions (Li) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. + A substance that can reversibly form a lithium-containing compound by reacting with ) may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy may be, for example, an alloy of lithium (Li) and a metal selected from the group consisting of sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and tin (Sn).

[0097] Preferably, the negative electrode active material may be lithium metal, and more specifically, it may be in the form of a lithium metal thin film or lithium metal powder.

[0098] The negative electrode active material may be present in an amount of 40 to 80% by weight based on the total weight of the negative electrode active material layer. Specifically, the content of the negative electrode active material may be 40% by weight or more, or 50% by weight or more, or 70% by weight or less, or 80% by weight or less. If the content of the negative electrode active material is less than 40% by weight, the connectivity between the wet negative electrode active material layer and the dry negative electrode active material layer may be insufficient, and if it exceeds 80% by weight, the mass transfer resistance may increase.

[0099] Furthermore, the binder is as described above in the positive electrode active material layer.

[0100] Furthermore, the conductive material is as described above in the positive electrode active material layer.

[0101] Furthermore, the negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and is conductive. For example, the negative electrode current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy. Also, similar to the positive electrode current collector, the negative electrode current collector can be made of various forms such as films, sheets, foils, nets, porous materials, foams, or nonwoven fabrics with fine irregularities formed on their surface.

[0102] The method for manufacturing the negative electrode is not particularly limited, and it can be manufactured by forming a negative electrode active material layer on a negative electrode current collector using a layer or film formation method commonly used in the industry. For example, methods such as crimping, coating, and vapor deposition can be used. Furthermore, the negative electrode of the present invention is also included in the case where a metallic lithium thin film is formed on a metal plate by initial charging after the battery has been assembled without a lithium thin film on the negative electrode current collector.

[0103] Furthermore, the present invention provides a battery module including the all-solid-state battery as a unit battery, a battery pack including the battery module, and a device including the battery pack as a power source.

[0104] Specific examples of the aforementioned devices include, but are not limited to, power tools powered by battery-powered motors; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems. Preferred embodiments are shown below to aid in understanding the present invention, but these embodiments are illustrative of the present invention, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and such changes and modifications will naturally fall within the scope of the attached claims.

[0105] The following are preferred embodiments to aid in understanding the present invention, but these embodiments are provided to make the present invention easier to understand and are not limited thereto.

[0106] In the following examples and comparative examples, ceramic ion conductors containing polymers, ceramic compounds, etc., as shown in Table 1 were manufactured, and composite solid electrolytes containing these were produced.

[0107] [Table 1]

[0108] Example 1: Production of a composite solid electrolyte (1) Manufacturing of the composite A 10 wt% PVA aqueous solution was prepared by mixing PVA (Mw: 89,000 g / mol; degree of hydrolysis: >99%) with distilled water (DI water). A solution containing LLZO powder, a ceramic compound, was then prepared using the PVA aqueous solution. At this time, the weight ratio of PVA to LLZO was set to 1:2.

[0109] After pouring 3 ml of the above solution into a polycarbonate petri dish, the mixture was frozen at -20°C for 24 hours and then thawed at 25°C to induce physical cross-linking of the PVA, thereby producing a hydrogel-type composite.

[0110] (2) Manufacturing of ceramic ion conductors The hydrogel composite was heated from room temperature to 800°C at a rate of 1°C / min and sintered at 800°C for 2 hours to thermally decompose the PVA hydrogel, and a ceramic ion conductor was produced by sintering the remaining LLZO particles.

[0111] (3) Manufacturing of composite solid electrolytes A solution containing PEO and LiTFSI was prepared (where the molar ratio of "O" in PEO and "Li" in the lithium salt ([Li] / [O]) is 0.4), the ceramic ion conductor was immersed in the prepared solution and dried, and then a composite solid electrolyte was produced.

[0112] Example 2 A composite solid electrolyte was prepared in the same manner as in Example 1, except that LSTP was used instead of the ceramic compound LLZO.

[0113] Example 3 A composite solid electrolyte was prepared in the same manner as in Example 1, except that the weight ratio of the polymer (PVA) and the ceramic compound (LLZO) was 1:10.

[0114] Example 4 A composite solid electrolyte was prepared in the same manner as in Example 1, except that the weight ratio of the polymer (PVA) and the ceramic compound (LLZO) was 10:1.

[0115] Example 5 A composite solid electrolyte was produced in the same manner as in Example 1, except that instead of a freezing and thawing step, 0.1 ml of boric acid (1 wt% aqueous solution) was added as a chemical cross-linker to 20 ml of the solution containing the PVA and ceramic compound, and the mixture was stirred with a magnetic stirrer at 200 rpm / hour to produce a hydrogel-type composite by chemical cross-linking.

[0116] Example 6 A composite solid electrolyte was prepared in the same manner as in Example 5, except that the weight ratio of the polymer (PVA) and the ceramic compound (LLZO) was 1:10.

[0117] Example 7 A composite solid electrolyte was prepared in the same manner as in Example 5, except that the weight ratio of the polymer (PVA) and the ceramic compound (LLZO) was 10:1.

[0118] Comparative Example 1 A composite solid electrolyte was produced in the same manner as in Example 1, except that a solution containing PVA and LLZO was prepared, the solution was applied to a glass slide (which served as a substrate), and then dried at 80°C for 12 hours instead of the freezing and thawing steps.

[0119] Comparative Example 2 A composite solid electrolyte was prepared in the same manner as in Example 1, except that PEO (Mw: 4,000,000 g / mol), a polymer without crosslinking functional groups, was used instead of PVA.

[0120] Comparative Example 3 A composite solid electrolyte was prepared in the same manner as in Example 1, except that a 35% aqueous solution of poly(acrylic acid) (Mw: 100,000 g / mol) was used instead of polymer PVA.

[0121] Experimental example Experimental Example 1 To measure the ionic conductivity of the composite solid electrolytes in film form produced in the examples and comparative examples, 1.7671 cm² was used. 2 The composite solid electrolyte was punched out in a circular shape, and the punched-out composite solid electrolyte was placed between two sheets of stainless steel (SS) to manufacture a coin cell.

[0122] Using an electrochemical impedance spectrometer (EIS, VM3, Bio Logic Science Instrument), the resistance was measured at 25°C with an amplitude of 10mV and a scan range of 500kHz to 20MHz. The ionic conductivity of the composite solid electrolyte was then calculated using Equation 1 below.

[0123] [Formula 1]

number

[0124] In the above formula 1, σ i R is the ionic conductivity (S / cm) of the composite solid electrolyte, R is the resistance (Ω) of the composite solid electrolyte measured by the electrochemical impedance spectrometer, L is the thickness (μm) of the composite solid electrolyte, and A is the area (cm²) of the composite solid electrolyte. 2 ) means.

[0125] The ionic conductivity of the composite solid electrolyte calculated using Equation 1, the feasibility of hydrogel formation, the feasibility of freestanding film formation, and the results of observing the appearance of the composite solid electrolyte are shown in Table 2 below. At this time, the feasibility of hydrogel formation (formed: O, not formed: X), the feasibility of freestanding film formation (formed: O, not formed: X), and the appearance of the composite solid electrolyte were observed with the naked eye.

[0126] [Table 2]

[0127] As shown in Table 2 above, it was confirmed that a hydrogel can be formed by applying a freezing and thawing process to a solution obtained by mixing the polymer containing the crosslinking functional group and a ceramic compound in an appropriate weight ratio, and that a ceramic ion conductor can be formed by sintering the hydrogel to produce a composite solid electrolyte (Examples 1-7 and Figures 1-6).

[0128] Comparative Example 1 was an electrolyte manufactured using a high-temperature drying process at 80°C, resulting in the formation of a brittle film without a cross-linking structure, and no ceramic ion conductor was formed after sintering.

[0129] Comparative Examples 2 and 3 were prepared using polymers that did not contain crosslinking functional groups, and no polymer hydrogel was formed.

[0130] In summary, even though the present invention has been described by limited embodiments and drawings, the present invention is not limited thereto, and various modifications and variations are possible by persons with ordinary skill in the art to which the present invention pertains, within the equivalent scope of the technical concept of the present invention and the claims described below.

Claims

1. (S1) A step of producing a first composite by forming a hydrogel of the first polymer from a solution containing a first polymer containing a crosslinking functional group (side chain) and a ceramic compound; (S2) The step of sintering the first composite to produce a ceramic ion conductor; (S3) The step of immersing the ceramic ion conductor in a solution containing a second polymer and a lithium salt and drying it to produce a second composite; A method for manufacturing a composite solid electrolyte for lithium secondary batteries.

2. The method for producing a composite solid electrolyte for a lithium secondary battery according to claim 1, wherein the hydrogel of the first polymer includes a crosslinking bonding structure between the first polymer and the ceramic compound.

3. The method for producing a composite solid electrolyte for a lithium secondary battery according to claim 2, wherein the crosslinking structure includes (a) crosslinking between crosslinking functional groups and (b) crosslinking between a crosslinking functional group and a ceramic compound.

4. The crosslinking between the crosslinkable functional groups (a) includes hydrogen bonding, The method for producing a composite solid electrolyte for a lithium secondary battery according to claim 3, wherein the crosslinking bond between the crosslinkable functional group and the ceramic compound includes a bond formed by Lewis acid-base interaction.

5. The method for producing a composite solid electrolyte for a lithium secondary battery according to claim 2, wherein the crosslinked bonding structure is formed by freezing and thawing a solution containing the first polymer and the ceramic compound.

6. The method for producing a composite solid electrolyte for a lithium secondary battery according to claim 2, wherein the crosslinked bonding structure is formed by adding a chemical crosslinker to a solution containing the first polymer and the ceramic compound.

7. The method for producing a composite solid electrolyte for a lithium secondary battery according to claim 5, wherein the freezing is performed at -30°C to -10°C.

8. The method for producing a composite solid electrolyte for a lithium secondary battery according to claim 5, wherein the thawing is performed at 15°C to 35°C.

9. The method for producing a composite solid electrolyte for a lithium secondary battery according to claim 1, wherein the crosslinking functional group comprises one or more selected from the group consisting of a hydroxyl group, a carboxyl group, and an amide group.

10. The first polymer containing the aforementioned crosslinking functional group is polyvinyl alcohol (PVA), gelatin, methylcellulose, agar, dextrin, poly(vinylpyrrolidone), poly(acrylamide), starch-carboxymethylcellulose, hyaluronic acid-methylcellulose. A method for producing a composite solid electrolyte for a lithium secondary battery according to claim 1, comprising one or more selected from the group consisting of acid-methylcellulose, chitosan, poly(N-isopropylacrylamide), and amino-terminated polyethylene glycol.

11. A composite solid electrolyte for lithium secondary batteries comprising a ceramic ion conductor containing a ceramic compound; a second polymer; and a lithium salt.

12. The composite solid electrolyte for lithium secondary batteries according to claim 11, wherein the ceramic compound comprises one or more selected from the group consisting of lithium-lanthanum-zirconium oxide (LLZO), lithium-silicon-titanium phosphate (LSTP), lithium-lanthanum-titanium oxide (LLTO), lithium-aluminum-titanium phosphate (LATP), lithium-aluminum-germanium phosphate (LAGP), and lithium-lanthanum-zirconium-titanium oxide (LLZTO) compounds.

13. The second polymer is polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyacrylate, poly(methyl methacrylate) (PMMA), PSTFSI, polyurethane, nylon, poly(dimethylsiloxane), gelatin, methylcellulose, agar, dextrin, poly(vinylpyrrolidone), poly(acrylamide), poly(acrylic acid) A composite solid electrolyte for a lithium secondary battery according to claim 11, comprising one or more selected from the group consisting of (acid), starch-carboxymethylcellulose, hyaluronic acid-methylcellulose, chitosan, poly(N-isopropylacrylamide), and amino-terminated polyethylene glycol.

14. The lithium salt is (CF ３ SO ２ ), ２ NLi (lithium bis(trifluoromethanesulfonyl)imide (LiTFSl), (FSO ２ ), ２ NLi (lithium bis(fluorosulfonyl)imide (LiFSI), LiNO ３ , LiOH, LiCl, LiBr, LiI, LiClO ４ , LiBF ４ , LiB １０ Cl １０ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiAlCl ４ , CH ３ SO ３ Li, CF ３ SO ３ Li, LiSCN and LiC(CF ３ SO ２ ), ３ The composite solid electrolyte for a lithium secondary battery according to claim 11, comprising one or more selected from the group consisting of.

15. The composite solid electrolyte for a lithium secondary battery according to claim 11, wherein the molar ratio of lithium ([Li]) of the lithium salt to the molar concentration ([G]) of the second polymer is 0.1 to 0.

5.

16. The composite solid electrolyte for lithium secondary batteries according to claim 11, wherein the composite solid electrolyte is in the form of a freestanding film.

17. The ionic conductivity of the composite solid electrolyte is 1.0 x 10⁻¹⁰ －５ A composite solid electrolyte for a lithium secondary battery according to claim 11, wherein the S / cm is 1 or higher.

18. A solid-state battery comprising a composite solid electrolyte for a lithium secondary battery according to any one of claims 11 to 17.

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