Positive electrode for all-solid-state battery and all-solid-state battery including the same

Abstract

The present invention relates to a cathode for an all-solid-state battery and an all-solid-state battery including the same. More specifically, the present invention relates to a cathode active material layer included in the cathode, which includes a cathode active material, a sulfide-based solid electrolyte, and a conductive material, and the particle size of the conductive material is between the particle size of the cathode active material and the particle size of the sulfide-based solid electrolyte. This increases the interface between the cathode active material and the sulfide-based solid electrolyte while simultaneously reducing the overall porosity of the cathode, thereby maintaining the conductivity of the cathode and increasing the energy density of the cell without reducing cell performance.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0121061, filed on September 12, 2023, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode for an all-solid-state battery and an all-solid-state battery including the same. [Background technology]

[0003] Currently, various batteries that can overcome the limitations of lithium secondary batteries are being researched from the viewpoints of battery capacity, safety, output, size increase, miniaturization, etc.

[0004] Academia and industry are continuously researching metal-air batteries, which have a much larger theoretical capacity than lithium secondary batteries, all-solid-state batteries, which are safe and do not pose a risk of explosion, supercapacitors, NaS batteries or RFBs (redox flow batteries), which are large-scale batteries, and thin film batteries, which are ultra-miniaturized batteries.

[0005] Among the various next-generation batteries, all-solid-state batteries replace the liquid electrolyte used in conventional lithium secondary batteries with a solid electrolyte. This significantly improves safety by eliminating the use of flammable solvents and eliminating the risk of fires or explosions caused by decomposition reactions of conventional electrolytes. Furthermore, technological development is progressing for sulfide-based all-solid-state batteries, which have high ionic conductivity and can theoretically achieve a high energy density of over 900 Wh / L. Here, sulfide-based all-solid-state batteries refer to all-solid-state batteries that contain a sulfide-based solid electrolyte.

[0006] In all-solid-state battery systems, lithium ion conduction is not possible with the liquid electrolyte found in conventional lithium-ion batteries (LIBs). Therefore, when manufacturing cathodes for sulfide-based all-solid-state batteries, small sulfide-based solid electrolyte particles must be added to the cathode to increase the contact interface between the cathode active material and the sulfide-based solid electrolyte particles, thereby enhancing lithium ion conduction. Furthermore, to improve energy density, physical contact between the cathode active material, sulfide-based solid electrolyte particles, and other battery elements within the cathode must be enhanced, reducing the porosity of the cathode after rolling, and maintaining this reduction during charging and discharging.

[0007] Therefore, there is a continuing need for technological development that can further reduce the porosity in the positive electrode of a sulfide-based all-solid-state battery and improve the performance of the all-solid-state battery. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2021-144906 Summary of the Invention [Problem to be solved by the invention]

[0009] The present inventors have conducted extensive research to solve the above problems, and as a result, have confirmed that when a cathode active material layer for a cathode of an all-solid-state battery is manufactured using a cathode active material, a sulfide-based solid electrolyte, and a conductive material, the conductive material has a particle size between that of the cathode active material and that of the sulfide-based solid electrolyte so as to fill voids between the particles of the cathode active material and the sulfide-based solid electrolyte, and the specific surface area of ​​the conductive material is limited to a certain level or less, the porosity of the cathode active material is reduced, and the energy density of the all-solid-state battery is improved.

[0010] Therefore, an object of the present invention is to provide a positive electrode for an all-solid-state battery having reduced porosity.

[0011] Another object of the present invention is to provide an all-solid-state battery including the anode for the all-solid-state battery having reduced porosity. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention provides a positive electrode for an all-solid-state battery, comprising a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material, wherein the particle size (D50) of the conductive material is between the particle size (D50) of the positive electrode active material and the particle size (D50) of the sulfide-based solid electrolyte, and the BET specific surface area of ​​the conductive material is 50 m 2 / g or less.

[0013] The present invention also provides a positive electrode for an all-solid-state battery, wherein the particle size (D50) of the conductive material is 1.5 μm to 3.8 μm.

[0014] The present invention also provides a positive electrode for an all-solid-state battery, wherein the bulk density of the conductive material is 0.05 g / cc or more.

[0015] The present invention also provides a positive electrode for an all-solid-state battery, wherein the conductive material has a true density of 1.5 g / cc or more.

[0016] The present invention also provides a positive electrode for an all-solid-state battery, wherein the conductive material has a crystal size (Lc(200)) of 30 nm to 80 nm.

[0017] The present invention also provides a positive electrode for an all-solid-state battery, wherein the particle size (D50) of the positive electrode active material is 4.0 μm to 8.0 μm.

[0018] The present invention also provides a positive electrode for an all-solid-state battery, wherein the particle size (D50) of the sulfide-based solid electrolyte is 0.1 μm to 1.5 μm.

[0019] The present invention also provides a positive electrode for an all-solid-state battery, wherein the positive electrode is in the form of a pellet containing a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material.

[0020] The present invention also provides a positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer formed on one surface of the positive electrode current collector, The positive electrode active material layer provides a positive electrode for an all-solid-state battery, including a positive electrode active material, a sulfide-based solid electrolyte, a conductive material, and a binder.

[0021] The present invention also provides a positive electrode for an all-solid-state battery, wherein the binder comprises at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene / propylene copolymer, polybutadiene, polyethylene oxide, chlorosulfonated polyethylene, polyvinylpyrrolidone, polyvinylpyridine, polyvinyl alcohol, polyvinyl acetate, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, cyanoethyl sucrose, polyester, polyamide, polyether, polyimide, polycarboxylate, polycarboxylic acid, polyacrylic acid, polyacrylate, lithium polyacrylate, polymethacrylic acid, polymethacrylate, polyacrylamide, polyurethane, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropene.

[0022] The present invention also provides a positive electrode for an all-solid-state battery, wherein the conductive material may contain graphite, and the graphite is one or more selected from the group consisting of natural graphite and artificial graphite.

[0023] The present invention also provides a positive electrode for an all-solid-state battery, wherein the positive electrode active material layer has a porosity of 5 vol % to 16 vol %.

[0024] The present invention also provides a cathode active material layer, the cathode active material being contained in an amount of 55 to 90 wt % based on the total weight of the cathode active material layer, The sulfide-based solid electrolyte is contained in an amount of 10 to 50 wt % based on the total weight of the positive electrode active material layer, The conductive material is contained in an amount of 0.05 to 10% by weight based on the total weight of the positive electrode active material layer, thereby providing a positive electrode for an all-solid-state battery.

[0025] The present invention also provides an all-solid-state battery comprising the positive electrode, the negative electrode, and the solid electrolyte membrane interposed therebetween. [Effects of the Invention]

[0026] According to the positive electrode for an all-solid-state battery of the present invention, the conductive material fills the voids between the particles of the positive electrode active material and the sulfide-based solid electrolyte, thereby reducing the porosity of the positive electrode, thereby improving the energy density of the all-solid-state battery. Furthermore, by filling the voids in the positive electrode, the conductive material can exhibit the effect of increasing the overall electrical conductivity of the positive electrode. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will now be described in more detail to aid in understanding the invention.

[0028] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best describe his or her invention.

[0029] In this specification, positive electrodes manufactured according to whether or not a binder is included in the positive electrode active material layer may be referred to as a "composite positive electrode" if no binder is included, and as a "positive electrode" if a binder is included.

[0030] Positive electrode for all-solid-state batteries The present invention relates to a positive electrode for an all-solid-state battery.

[0031] The positive electrode for an all-solid-state battery according to the present invention includes a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material.

[0032] In one embodiment of the present invention, the positive electrode may be in the form of a pellet. The pellet-shaped positive electrode may be used without a current collector, or the positive electrode may be formed by placing the pellet on a current collector. The pellet may be formed by compressing a composite powder including a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material. Since the pellet does not include a binder, resistance that may be caused by the binder can be eliminated.

[0033] In another embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on one surface of the positive electrode current collector. The positive electrode active material layer may include the positive electrode active material, a sulfide-based solid electrolyte, a conductive material, and a binder.

[0034] The particle size (D50) of the conductive material is between the particle size (D50) of the positive electrode active material and the particle size (D50) of the sulfide-based solid electrolyte, and the conductive material has a BET specific surface area of ​​50 m 2 / g or less. The conductive material may have a crystalline form with a lattice structure. In this specification, a positive electrode that does not include a binder may be referred to as a composite positive electrode.

[0035] In the positive electrode for an all-solid-state battery according to the present invention, voids are formed due to the difference in particle size between the positive electrode active material and the sulfide-based solid electrolyte particles, and the voids are filled with the conductive material, thereby reducing the porosity of the positive electrode and improving energy density. The particle size (D50) of the conductive material is larger than that of the sulfide-based solid electrolyte and smaller than that of the positive electrode active material, allowing the conductive material to fill the voids.

[0036] In one embodiment of the present invention, the BET specific surface area of ​​the conductive material is 50 m2 Specifically, the BET specific surface area of ​​the conductive material may be 50 m 2 / g or less, 45m 2 / g or less, 40m 2 / g or less, 35m 2 / g or less, 30m 2 / g or less, 25m 2 / g or less, or 20m 2 / g or less. 2 If the BET specific surface area exceeds 5 m / g, the contact interface between the conductive material with a high specific surface area and the sulfide-based all-solid electrolyte increases, which may increase the electrolyte decomposition reaction and reduce the ionic conductivity of the positive electrode itself. 2 / g or more.

[0037] The particle size (D50) of the conductive material may be 1.5 μm to 3.8 μm. Specifically, the particle size (D50) of the conductive material may be 1.5 μm or more, 1.7 μm or more, 2.0 μm or more, or 2.2 μm or more, or 2.6 μm or less, 2.8 μm or less, 3.0 μm or less, 3.2 μm or less, 3.4 μm or less, 3.6 μm or less, or 3.8 μm or less. If the particle size (D50) of the conductive material is less than 1.5 μm, the particles may be too small and the conductive material may be adsorbed only on the surface of the positive electrode active material rather than filling voids formed by the difference in particle size between the positive electrode active material and the sulfide-based solid electrolyte particles. If the particle size (D50) exceeds 3.8 μm, it may be difficult to fill voids formed by the difference in particle size between the positive electrode active material and the sulfide-based solid electrolyte particles, and the effect of reducing the porosity of the positive electrode may be negligible.

[0038] The particle size (D50) can be measured by putting the conductive material into a particle size analyzer (Mastersizer 3000, Malvern).

[0039] The bulk density of the conductive material may be 0.05 g / cc or more.

[0040] Specifically, the bulk density may be 0.05 g / cc or more, 0.06 g / cc or more, or 0.07 g / cc or more. If the bulk density is less than 0.05 g / cc, the density of the conductive material itself may be low, which may reduce the overall density of the positive electrode. The upper limit of the bulk density is not particularly limited, but may be 0.1 g / cc or less, 0.3 g / cc or less, or 0.5 g / cc or less.

[0041] The bulk density can be measured using a density meter according to ASTM D 1895 method.

[0042] The conductive material may have a true density of 1.5 g / cc or more.

[0043] Specifically, the true density may be 1.5 g / cc or more, 1.7 g / cc or more, 2.0 g / cc or more, or 2.2 g / cc or more. If the true density is less than 1.5 g / cc, the density of the conductive material itself is low, which may reduce the overall density of the positive electrode. The upper limit of the true density is not particularly limited, but may be 3.0 g / cc or less, 4.0 g / cc or less, or 5.0 g / cc or less.

[0044] The true density can be measured using a density meter according to ASTM D 1895 method.

[0045] The conductive material may have a crystal size (Lc(002)) in the c-axis direction of 30 nm to 80 nm when measured by XRD.

[0046] Specifically, the crystal size may be 30 nm or more, 35 nm or more, or 40 nm or more, and may be 65 nm or less, 70 nm or less, 75 nm or less, or 80 nm or less.

[0047] The crystal size in the c-axis direction indicates Lc(002), which is the crystal size in the c-axis direction during XRD measurement, and can be calculated by the Scherrer formula shown in Equation 1 below.

[0048]

number

[0049] K = Scherrer constant (K = 0.9) β = half-width λ=wavelength (0.154056nm) θ = angle at maximum peak

[0050] The conductive material may include graphite, and the graphite may include at least one selected from the group consisting of natural graphite and artificial graphite, but is not limited thereto as long as the conductive material has the specific surface area, particle size, and crystalline structure described above. Preferably, the conductive material may be artificial graphite.

[0051] The natural graphite may be produced as a conductive material by mining graphite that exists in nature and then refining it.

[0052] The artificial graphite has a crystalline structure that is more stable than natural graphite because it is heated to temperatures of 2,500°C or higher, allowing for more paths for lithium ions to move, which is advantageous for charging and discharging.

[0053] The conductive material may be included in an amount of 0.05 to 10 wt % based on the total weight of the positive electrode active material layer. Specifically, the content of the conductive material may be 0.05 wt % or more, 0.1 wt % or more, 0.5 wt % or more, 1 wt % or more, 2 wt % or more, or 3 wt % or more, or 5 wt % or less, 7 wt % or less, or 10 wt % or less. If the conductive material content is less than 0.05 wt %, the electrical conductivity of the positive electrode may be reduced. If the conductive material content exceeds 10 wt %, the content of the positive electrode active material and the sulfide-based solid electrolyte may be relatively reduced, resulting in reduced battery performance.

[0054] In one embodiment of the present invention, the particle size (D50) of the positive electrode active material may be 4.0 μm to 8.0 μm.

[0055] Specifically, the particle size (D50) of the positive electrode active material may be 4.0 μm or more, 4.5 μm or more, or 5.0 μm or more, or 6.0 μm or less, 6.5 μm or less, 7.0 μm or less, 7.5 μm or less, or 8.0 μm or less. If the particle size (D50) of the positive electrode active material is less than 4.0 μm, even if the positive electrode active material and the sulfide-based solid electrolyte are dispersed at the same weight ratio, the particle size of the positive electrode active material may be small and the dispersibility may be reduced. If the particle size (D50) exceeds 8.0 μm, excessively large voids may be formed in the positive electrode active material layer, which may reduce the performance of the all-solid-state battery.

[0056] The particle size (D50) can be measured by putting the positive electrode active material powder into a particle size analyzer (Mastersizer 3000, Malvern).

[0057] The positive electrode active material is not particularly limited as long as it is a material capable of reversibly absorbing and releasing lithium ions. For example, lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), Li[Ni x Co y Mn z M v ]O2 (wherein M is any 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, and x+y+z+v=1), Li (Li a M b-a-b’ M' b’ )O 2-c A c (wherein 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); layered compounds and compounds substituted with one or more transition metals, such as compounds of the formula Li 1+y Mn 2-yLithium manganese oxides such as LiMnO4 (where y is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-y Ni-site lithium nickel oxide represented by MyO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and y is 0.01 to 0.3); chemical formula LiMn 2-y M y Examples of the lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is Co, Ni, Fe, Cr, Zn, or Ta, and y is 0.01 to 0.1) or Li2Mn3MO8 (where M is 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; and Fe2(MoO4)3.

[0058] The positive electrode active material may be included in an amount of 55 to 90 wt % based on the total weight of the positive electrode active material layer. Specifically, the content of the positive electrode active material may be 55 wt % or more, 60 wt % or more, or 65 wt % or more, or 83 wt % or less, 85 wt % or less, or 90 wt % or less. If the content of the positive electrode active material is less than 55 wt %, battery performance may be reduced, and if it exceeds 90 wt %, mass transfer resistance may be increased.

[0059] In one embodiment of the present invention, the particle size (D50) of the sulfide-based solid electrolyte may be 0.1 μm to 1.5 μm.

[0060] Specifically, the particle size (D50) of the sulfide-based solid electrolyte may be 0.1 μm or more, 0.3 μm or more, or 0.5 μm or more, or 0.9 μm or less, 1.0 μm or less, 1.2 μm or less, or 1.5 μm or less. If the particle size (D50) of the sulfide-based solid electrolyte is less than 0.1 μm, the ultrafine particles of the solid electrolyte may not be sufficiently dispersed in the positive electrode layer and may aggregate. If the particle size (D50) exceeds 1.5 μm, dispersion may be somewhat easier, but the contact area with the positive electrode active material particles may decrease, potentially increasing the positive electrode porosity.

[0061] The sulfide-based solid electrolyte may include at least one selected from the group consisting of LiPSX (X = Cl, Br, or I), LiGePS, and LiPS. However, the sulfide-based solid electrolyte is not limited thereto, and a wide range of sulfide-based solid electrolytes commonly used in the art may be used.

[0062] The sulfide-based solid electrolyte may be included in an amount of 10 to 50 wt % based on the total weight of the positive electrode active material layer. Specifically, the content of the sulfide-based solid electrolyte may be 10 wt % or more, 20 wt % or more, or 30 wt % or more, or 40 wt % or less, 45 wt % or less, or 50 wt % or less. If the content of the positive electrode active material is less than 10 wt %, it may be difficult to reduce the porosity of the positive electrode active material because it is insufficient to fill voids formed in the positive electrode active material layer. If the content exceeds 50 wt %, the content of the positive electrode active material and the conductive material may be relatively reduced, which may result in a deterioration in battery performance.

[0063] In one embodiment of the present invention, the positive electrode active material layer may further include a binder. The binder may be included to promote bonding between materials included in the positive electrode active material layer and between the positive electrode active material layer and the positive electrode current collector. The binder may promote bonding between materials included in the positive electrode active material layer and further reduce positive electrode porosity.

[0064] The binder may be a fibrous binder. The binder may be fibrous during mixing during the preparation of the positive electrode, and may be contained in the positive electrode active material layer in a fibrous form. Therefore, it is preferable that the physical properties of the binder be easily changed.

[0065] The binder may include at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene / propylene copolymer, polybutadiene, polyethylene oxide, chlorosulfonated polyethylene, polyvinylpyrrolidone, polyvinylpyridine, polyvinyl alcohol, polyvinyl acetate, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, cyanoethyl sucrose, 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 include polytetrafluoroethylene (PTFE).

[0066] The binder may be included in an amount of 0.1 to 3 wt % based on the total weight of the positive electrode active material layer. Specifically, the binder content may be 0.1 wt % or more, 0.5 wt % or more, or 0.8 wt % or more, or 1.5 wt % or less, 2 wt % or less, or 3 wt % or less. If the binder content is less than 0.1 wt %, the effect of improving the binding strength between materials contained in the positive electrode active material layer is negligible, and an electrode sheet may not be properly formed. If the binder content exceeds 3 wt %, ionic conductivity or electrical conductivity may be reduced.

[0067] In an embodiment of the present invention, the porosity of the positive electrode active material layer may be 5 vol % to 16 vol %.

[0068] Specifically, the porosity may be 5 vol% or more, 8 vol% or more, 10 vol% or more, or 13 vol% or more, or 13.8 vol% or less, 14 vol% or less, 14.5 vol% or less, 15 vol% or less, 15.5 vol% or less, or 16 vol% or less. The porosity is within an optimized range in consideration of performance such as the energy density of the battery, and if the porosity exceeds 16 vol%, the energy density of the battery may decrease.

[0069] In one embodiment of the present invention, the positive electrode current collector supports the positive electrode active material layer and transfers electrons between an external conductive wire and the positive electrode active material layer.

[0070] 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, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, palladium, baked carbon, stainless steel surface-treated with carbon, nickel, silver, or the like, or an aluminum-cadmium alloy.

[0071] The positive electrode current collector may have a fine uneven structure on its surface or a three-dimensional porous structure to strengthen the bonding strength with the positive electrode active material layer, and may therefore be in various forms such as a film, sheet, foil, mesh, net, porous body, foam, or nonwoven fabric.

[0072] Method for manufacturing positive electrodes for all-solid-state batteries The present invention also relates to a method for manufacturing a positive electrode for an all-solid-state battery. Specific materials, properties, and contents of the positive electrode active material, sulfide-based solid electrolyte, conductive material, and binder used in the method for manufacturing a positive electrode for an all-solid-state battery according to the present invention are as described above.

[0073] In the present invention, the positive electrode can be classified into a "composite positive electrode" when it does not contain a binder and a "positive electrode" when it contains a binder, depending on whether it contains a binder or not.

[0074] In one embodiment of the present invention, a method for preparing a binderless composite positive electrode may include: (A1) mixing a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material; and (A2) forming the mixed powder obtained in step (A1) into a pellet shape. Here, the pellet shape in step (A2) may be formed by pressing the mixed powder in a jig.

[0075] The composite positive electrode prepared as described above can be used in a pressure-sensitive doped cell. Because the composite positive electrode does not contain a binder, the resistance caused by the binder can be eliminated. Therefore, the composite positive electrode can be used to evaluate the performance of a pressure-sensitive doped cell, which eliminates the resistance factor.

[0076] In one embodiment of the present invention, a method for manufacturing a cathode including a binder includes: (B1) mixing a cathode active material, a sulfide-based solid electrolyte, a conductive material, and a binder; (B2) calendering the mixed powder obtained in step (B1) to form a film; and (B3) attaching the film-like cathode active material layer obtained in step (B2) to a cathode current collector.

[0077] The mixing in step (B1) may be physical mixing, which can fiberize the binder. During physical mixing, the binder is rubbed against the particles in the mixed powder due to shear force, causing physical deformation and fiberization. For example, PTFE, which has physical properties that make it susceptible to physical deformation, can be used as the binder. Furthermore, mixing to facilitate physical deformation can be performed using a mortar, ball mill, or roll press.

[0078] In step (B2), the mixed powder obtained in step (B1) can be subjected to a calendering process to be formed into a film.

[0079] The conditions for the calendering step may be appropriately controlled and applied so as to allow the material to be formed into a film. For example, the calendering step may be performed at a temperature of 50°C to 200°C for 5 to 50 loops. However, the calendering step conditions, such as temperature, pressure, and loop count, may be any conditions used in electrode manufacturing processes commonly used in the battery field.

[0080] In step (B3), the film-like positive electrode active material layer obtained in step (B2) is attached to a positive electrode current collector to produce a positive electrode for an all-solid-state battery.

[0081] all solid state battery The present invention also relates to an all-solid-state battery including the sulfide-based solid electrolyte layer.

[0082] The all-solid-state battery according to the present invention includes the positive electrode, the negative electrode, and a sulfide-based solid electrolyte layer interposed therebetween. The positive electrode is as described above.

[0083] In one embodiment of the present invention, the negative electrode may include a negative electrode active material layer, and the negative electrode active material layer may be formed on one surface of a negative electrode current collector.

[0084] The negative electrode active material layer may include a negative electrode active material, a conductive material, and a binder, or may be an anodeless layer.

[0085] In the negative electrode active material layer, the negative electrode active material is lithium (Li + The lithium ion-containing compound may include a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal, or a lithium alloy.

[0086] The lithium ion (Li + The material capable of reversibly inserting or de-inserting lithium ions (Li) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. + The material capable of reacting with lithium (Li) to reversibly form a lithium-containing compound 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 indium (In), 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).

[0087] Preferably, the negative electrode active material may be lithium metal or a lithium-indium alloy (Li-In), specifically, lithium metal, lithium and thin film, lithium-indium alloy thin film, or powder.

[0088] The negative electrode active material may be included in an amount of 40 to 80 wt % based on the total weight of the negative electrode active material layer. Specifically, the content of the negative electrode active material may be 40 wt % or more, or 50 wt % or more, or 70 wt % or less, or 80 wt % or less. If the content of the negative electrode active material is less than 40 wt %, 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 wt %, the mass transfer resistance may be increased.

[0089] The binder may be a component that assists in binding the negative electrode active material to the conductive material and the like and in binding the negative electrode current collector, and may be any of styrene-butadiene rubber, acrylated 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, polyacrylic The binder may include one or more selected from the group consisting of lylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, cyanoethyl sucrose, 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 include polytetrafluoroethylene (PTFE).

[0090] The binder may be included in an amount of 0.5 wt % to 4 wt % based on the total weight of the negative electrode active material layer. Specifically, the binder content may be 0.5 wt % or more, 1 wt % or more, or 1.5 wt % or more, and 3 wt % or less, 3.5 wt % or less, or 4 wt % or less. If the binder content is less than 0.5 wt %, the adhesive strength between the positive electrode active material and the negative electrode current collector may be reduced. If the binder content exceeds 4 wt %, the adhesive strength is improved, but the content of the negative electrode active material may be reduced accordingly, which may reduce the battery capacity.

[0091] 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. Representative examples include graphite or conductive carbon. Examples include graphite such as natural graphite and 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 with a graphene or graphite crystalline structure; conductive fibers such as carbon fiber and metal fiber; 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 may be used alone or in combination. Preferably, the conductive material may include vapor-grown carbon fiber (VGCF).

[0092] The conductive material may typically be included in an amount of 1 wt % to 5 wt % based on the total weight of the negative electrode active material layer. Specifically, the content of the conductive material may be 1 wt % or more, 1.5 wt % or more, or 2 wt % or more, and 4 wt % or less, 4.5 wt % or less, or 5 wt % or less. If the conductive material content is too low, such as less than 1 wt %, the electrical conductivity improvement effect may be difficult to expect or the electrochemical characteristics of the battery may be degraded. If the conductive material content is too high, such as more than 5 wt %, the amount of negative electrode active material may be relatively reduced, resulting in reduced capacity and energy density. The method for incorporating the conductive material into the negative electrode is not particularly limited, and conventional methods known in the art, such as mixing with the negative electrode active material or coating, may be used.

[0093] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and may be, for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel whose surface is treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, etc. Similarly to the positive electrode current collector, the negative electrode current collector may be in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric, each having a finely textured surface.

[0094] The method for manufacturing the negative electrode is not particularly limited, and the negative electrode may 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 art. For example, methods such as compression bonding, coating, and vapor deposition may be used. Furthermore, the negative electrode of the present invention also includes a case where a thin lithium film is formed on the metal plate by initial charging after assembling a battery without a thin lithium film on the negative electrode current collector.

[0095] The anode-free layer refers to an anode layer in which, at the time of initial assembly of the battery, lithium metal or a lithium alloy, which can serve as a lithium supply source, among the anode active materials, is not present in the anode, but lithium precipitates in the anode upon charging. A battery including the anode-free layer can be said to be an anode-free battery.

[0096] In the anode-free battery, during charging and discharging of the battery, lithium ions released from the positive electrode migrate to the negative electrode to form a negative electrode active material layer. For example, during charging of the battery, lithium ions are released from the positive electrode active material and then migrate to the negative electrode, becoming lithium metal composed purely of lithium. This can form a layered lithium metal layer on the negative electrode current collector, or a lithium metal structure of any shape other than a layer. The arbitrary shape can be, for example, a structure in which lithium metal aggregates into particles.

[0097] In one embodiment of the present invention, the sulfide-based solid electrolyte included in the sulfide-based solid electrolyte layer may include at least one selected from the group consisting of LiPSX (X = Cl, Br, or I), LiGePS, and LiPS. However, the sulfide-based solid electrolyte is not limited thereto, and a wide range of sulfide-based solid electrolytes commonly used in the art may be used.

[0098] Battery module The present invention also relates to a battery module including the all-solid-state battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source.

[0099] Specific examples of the device include, but are not limited to, power tools powered by electric 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.

[0100] Preferred examples will be described below to aid in understanding the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical idea of ​​the present invention. Naturally, such changes and modifications also fall within the scope of the appended claims.

[0101] In the following examples and comparative examples, a conductive material having the physical properties shown in Table 1 below was used, and a positive electrode and an all-solid-state battery including the same were manufactured in accordance with the composition of the positive electrode active material layer and the physical properties of the raw materials shown in Table 2 below.

[0102] [Table 1]

[0103] [Table 2]

[0104] Example 1: Composite cathode fabrication LiN as the positive electrode active material 0.8 Co 0.1 Mn 0.1 A positive electrode was produced as follows using O2 (NCM 811), Li6PS5Cl as a sulfide-based solid electrolyte, and graphite A as a conductive material. The physical properties of the graphite A are as shown in Table 1 above.

[0105] The positive electrode active material, sulfide-based solid electrolyte, and conductive material were mixed in a weight ratio of 60:35:5 and then powder mixed. Specifically, the positive electrode active material and sulfide-based solid electrolyte were measured in powder form, and then mixed for 15 minutes using an agate mortar in a dry room environment to obtain a mixture. Then, the conductive material was measured and added to the mixture, and mixed for another 15 minutes to obtain a mixed powder.

[0106] The mixed powder was compressed using a pressure jig to obtain a pressure of 3 mAh / cm 2 The composite positive electrode was fabricated into a pellet-shaped loading pellet.

[0107] Example 2: Positive electrode fabrication LiN as the positive electrode active material 0.8 Co 0.1 Mn 0.1 A positive electrode was fabricated using O2 (NCM 811), Li6PS5Cl as a sulfide-based solid electrolyte, graphite A as a conductive material, and polytetrafluoroethylene (PTFE) as a binder as follows. The physical properties of graphite A are listed in Table 1.

[0108] The positive electrode active material, sulfide-based solid electrolyte, conductive material, and binder were mixed in a weight ratio of 78:19.5:1:1.5 and then powder mixed. Specifically, the positive electrode active material and sulfide-based solid electrolyte were measured in powder form and then mixed for 15 minutes using a blade mixer in a dry room environment to obtain a mixture. Next, the conductive material was measured and added to the mixture and mixed. PTFE (Polytetrafluoroethylene) powder, which serves as the binder, was measured and further mixed to obtain a mixed powder.

[0109] The mixed powder was put into a mortar, and then fiberized in the mortar and calendered with a roller to obtain a fiber strength of 6 mAh / cm 2 A loading positive electrode was fabricated.

[0110] Example 3: Composite cathode fabrication The same procedure as in Example 1 was carried out, except that graphite B was used as the conductive material instead of graphite A. The physical properties of graphite B are as shown in Table 1 above.

[0111] Example 4: Positive electrode fabrication The same procedure as in Example 2 was carried out, except that graphite B was used as the conductive material instead of graphite A. The physical properties of graphite B are as shown in Table 1 above.

[0112] Comparative Example 1 The same procedure as in Example 1 was carried out, except that carbon black was used as the conductive material instead of graphite A. The physical properties of the carbon black are as shown in Table 1 above.

[0113] Comparative Example 2 The same procedure as in Example 2 was carried out, except that carbon black was used as the conductive material instead of graphite A. The physical properties of the carbon black are as shown in Table 1 above.

[0114] Experimental example 1: Performance evaluation of all-solid-state batteries The performance of all-solid-state batteries was evaluated depending on the type of conductive material in the positive electrode active material layer. The composite positive electrodes produced in Example 1, Example 3, and Comparative Example 1 were evaluated.

[0115] To evaluate the performance of the all-solid-state battery, a pressure jig cell was fabricated as follows.

[0116] The pellet-shaped composite cathode was transferred to a pressure-sealed cell, and then sulfide-based solid electrolyte powder (200 mg) was placed on the pellet and pressed at 400 MPa for 60 seconds to form a film-shaped sulfide-based solid electrolyte layer. A lithium metal anode was then placed facing one side of the sulfide-based solid electrolyte layer and pressed again at 100 MPa to increase contact between the sulfide-based solid electrolyte layer and the anode. The cell was then clamped at an appropriate pressure to fabricate a pressure-sealed cell.

[0117] The pressure-sensitive cell was activated in a charger / discharger for two cycles at 0.05 C, and then discharged up to 1 C to observe the rate characteristics (capacity capability), and the results are shown in Tables 3 and 4. Specifically, the charger / discharger was used to perform two cycles of 0.05 C CC / CV (Constant Current / Constant Voltage) charging and 0.05 C CC (Constant Current) discharging, followed by CC discharging at 0.1 C / 0.2 C / 0.33 C / 0.5 C / 1 C while maintaining the 0.1 C CC / CV charging process.

[0118] [Table 3]

[0119] Referring to Table 3, Examples 1 and 3 show the particle size (D 50) was between the particle size of the positive electrode active material and the particle size of the sulfide-based solid electrolyte, and when graphite A and graphite B with a low specific surface area of ​​<30 m2 / g were used, it was confirmed that they exhibited superior performance in terms of discharge capacity compared to Comparative Example 1, in which carbon black with a high specific surface area of ​​~1300 m2 / g was used as the conductive material. Furthermore, it was confirmed that Comparative Example 1 exhibited a rapid increase in initial charge capacity, resulting in a decrease in efficiency, and also exhibited lower efficiency during the second charge / discharge compared to Examples 1 and 3.

[0120] [Table 4]

[0121] Referring to Table 4, it was confirmed that Examples 1 and 3 had a better discharge capacity retention rate than Comparative Example 1. Specifically, Examples 1 and 3 maintained a discharge capacity of 150 mAh / g even at 1C discharge, while Comparative Example 1 measured a discharge capacity of 28 mAh / g. This is because when the specific surface area of ​​the carbon material in the composite positive electrode is large (Comparative Example 1), the decomposition reaction of the sulfide-based solid electrolyte in contact with the carbon material is accelerated as the c-rate increases.

[0122] Experimental Example 2: Confirmation of the internal structure of the positive electrode An experiment was conducted to measure the internal structure of a positive electrode depending on the type of conductive material in a binder-containing positive electrode active material layer. Example 2, Example 4, and Comparative Example 2 were evaluated. All of these positive electrode active material layers contained a binder. Example 2, Example 4, and Comparative Example 2 all involved the use of a binder during the manufacture of the positive electrode. Example 2 contained graphite A as the conductive material, Example 4 contained graphite B as the conductive material, and Comparative Example 2 contained carbon black as the conductive material. As shown in Table 1 above, carbon black has a significantly larger specific surface area than graphite A and graphite B.

[0123] The positive electrodes prepared according to Examples 2, 4, and Comparative Example 2 were further pressed using a warm isostatic press (WIP) to form a completely adhered positive electrode element, and then the thickness and porosity were measured, and the results are shown in Table 5. The porosity was measured using the following equation 2, where 1) the thickness of the positive electrode after WIP pressing, 2) the weight of the positive electrode, 3) the area of ​​the positive electrode, and 4) the positive electrode density calculated from the true density of the positive electrode element used.

[0124] [Formula 2] Positive electrode porosity (%) = (1 - ([positive electrode weight] / [positive electrode area × positive electrode thickness] / [positive electrode density] × 100)

[0125] [Table 5]

[0126] Referring to Table 5, it can be seen that the thickness and porosity of the positive electrodes of Examples 2 and 4 were smaller both before and after rolling than those of Comparative Example 2. This indicates that graphite A and graphite B, which have a smaller specific surface area than carbon black, effectively fill voids in the positive electrode, thereby reducing the thickness and porosity of the positive electrode.

[0127] Therefore, in Example 2, when the particle size of the conductive material is between the particle size of the positive electrode active material and the particle size of the sulfide-based solid electrolyte and has a low specific surface area, it is predicted that the porosity of the positive electrode active material layer will be reduced, thereby improving the performance of the positive electrode.

Claims

1. A positive electrode for an all-solid-state battery, comprising a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material, the particle size (D50) of the conductive material is between the particle size (D50) of the positive electrode active material and the particle size (D50) of the sulfide-based solid electrolyte, The BET specific surface area of ​​the conductive material is 50 m ２ / g or less.

2. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the particle diameter (D50) of the conductive material is 1.5 μm or more and 3.8 μm or less.

3. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the conductive material has a bulk density of 0.05 g / cc or more.

4. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the conductive material has a true density of 1.5 g / cc or more.

5. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the conductive material has a crystal size (Lc(200)) of 30 nm or more and 80 nm or less.

6. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the particle size (D50) of the positive electrode active material is 4.0 μm or more and 8.0 μm or less.

7. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the particle diameter (D50) of the sulfide-based solid electrolyte is 0.1 μm or more and 1.5 μm or less.

8. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the positive electrode is in the form of a pellet containing a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material.

9. The positive electrode includes a positive electrode current collector; and a positive electrode active material layer formed on one surface of the positive electrode current collector, 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the positive electrode active material layer comprises a positive electrode active material, a sulfide-based solid electrolyte, a conductive material, and a binder.

10. The binder is polytetrafluoroethylene (polytetrafluoroethylene, PTFE), polyethylene, polypropylene, ethylene / propylene copolymer, polybutadiene, polyethylene oxide, chlorosulfonated polyethylene, polyvinylpyrrolidone, polyvinylpyridine, polyvinyl alcohol, polyvinyl acetate, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, cyanoethyl sucrose, polyester, polyamide, polyether, polyimide, polycarboxylate, polycarboxylic acid, polyacrylic acid, polyacrylate, lithium polyacrylate, polymethacrylic acid, polymethacrylate, polyacrylamide, polyurethane, polyvinylidene fluoride, and poly (vinylidene fluoride) - hexafluoropropene. The positive electrode for an all-solid-state battery according to claim 9, comprising one or more selected from the group consisting of hexafluoropropene.

11. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the conductive material contains graphite, and the graphite is at least one selected from the group consisting of natural graphite and artificial graphite.

12. 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the positive electrode active material layer has a porosity of 5 vol% or more and 16 vol% or less.

13. The positive electrode active material is contained in an amount of 55 wt % or more and 90 wt % or less based on the total weight of the positive electrode active material layer, the sulfide-based solid electrolyte is included in an amount of 10 wt % or more and 50 wt % or less based on the total weight of the positive electrode active material layer, 2. The positive electrode for an all-solid-state battery according to claim 1, wherein the conductive material is contained in an amount of 0.05 wt % or more and 10 wt % or less based on the total weight of the positive electrode active material layer.

14. An all-solid-state battery comprising the positive electrode according to any one of claims 1 to 13, a negative electrode, and a sulfide-based solid electrolyte layer interposed therebetween.

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