Positive electrode for all-solid-state battery and all-solid-state battery comprising same

Abstract

The invention discloses a positive electrode for an all-solid-state battery and the all-solid-state battery comprising the positive electrode. More specifically, a positive electrode active material layer included in the positive electrode of the present invention contains a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material, in which 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, therefore, the contact interface between the positive electrode active material and the sulfide solid electrolyte is increased, and the overall porosity of the positive electrode is reduced, so that the conductivity of the positive electrode is maintained, and the energy density of the battery cell is improved under the condition that the performance of the battery cell is not reduced.

Description

Technical Field

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0121061, filed on September 12, 2023, the disclosure of which is incorporated herein by reference in its entirety.

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

[0003] In order to overcome the current limitations of lithium secondary batteries in terms of capacity, safety, output, upsizing, and miniaturization, various batteries are being studied.

[0004] Representative examples include: metal-air batteries with very high theoretical capacity compared to lithium secondary batteries; all-solid-state batteries that are safe and have no risk of explosion; supercapacitors in terms of output power; NaS batteries or redox flow batteries (RFBs) for large-scale applications, and miniaturized thin-film batteries. Academia and industry are continuously researching these technologies.

[0005] All-solid-state batteries refer to batteries that replace the liquid electrolyte used in conventional lithium secondary batteries with solid electrolytes. Since no flammable solvents are used in the battery, there is no possibility of fire or explosion due to decomposition reactions of conventional electrolytes, which significantly improves safety. In addition, among all-solid-state batteries, the development of sulfide all-solid-state batteries is still ongoing. The ionic conductivity of its solid electrolyte is high, and theoretically, a high energy density of at least 900Wh / L can be achieved. Sulfide all-solid-state batteries refer to all-solid-state batteries containing sulfide solid electrolytes.

[0006] In an all-solid-state battery system, the conduction of lithium ions is not carried out through the liquid electrolyte contained in a conventional lithium-ion battery (LIB). Therefore, when manufacturing the positive electrode of a sulfide-based all-solid-state battery, it is necessary to increase the contact interface between the positive electrode active material and the sulfide solid electrolyte particles by adding small-diameter sulfide solid electrolyte particles inside the positive electrode to improve the conductivity of lithium ions. In addition, in order to improve the energy density, the physical contact between the positive electrode active material, the sulfide solid electrolyte particles, and the other battery components in the positive electrode must be enhanced, and the porosity of the positive electrode must be reduced after rolling, and this state must be maintained during both charging and discharging.

[0007] Therefore, there has been a need to develop a technology that can further reduce the positive electrode porosity of sulfide-based all-solid-state batteries to improve the performance of all-solid-state batteries.

[0008] [Prior art literature]

[0009] [Patent Document]

[0010] (Patent Document 1) Japanese Patent Publication No. 2021-144906 Summary of the invention

[0011] [Technical issues]

[0012] The inventors of the present invention have conducted extensive research to solve the above-mentioned problems, and have found that when manufacturing a positive electrode active material layer of a positive electrode for an all-solid-state battery, in which a positive electrode active material, a sulfide solid electrolyte and a conductive material are used, a conductive material having a particle size between the particle size of the positive electrode active material and the particle size of the sulfide solid electrolyte is used to fill the gaps between the particles of the positive electrode active material and the particles of the sulfide solid electrolyte. If the specific surface area of ​​the conductive material is limited to below a certain level, the porosity of the positive electrode active material is reduced and the energy density of the all-solid-state battery is improved.

[0013] Therefore, an object of the present invention is to provide a positive electrode for an all-solid-state battery with reduced porosity.

[0014] Another object of the present invention is to provide an all-solid-state battery comprising a positive electrode for an all-solid-state battery with reduced porosity.

[0015] [Technical solution]

[0016] In order to achieve the above object, the present invention provides a positive electrode for an all-solid-state battery, which comprises a positive electrode active material, a sulfide 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 solid electrolyte, and the BET specific surface area of ​​the conductive material is 50 m 2 / g or less.

[0017] 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.

[0018] The present invention also provides a positive electrode for an all-solid-state battery, wherein the bulk density of the conductive material is at least 0.05 g / cc.

[0019] The present invention also provides a positive electrode for an all-solid-state battery, wherein the true density of the conductive material is at least 1.5 g / cc.

[0020] The present invention also provides a positive electrode for an all-solid-state battery, wherein the crystal size (Lc(200)) of the conductive material is 30 nm to 80 nm.

[0021] 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.

[0022] The present invention also provides a positive electrode for an all-solid-state battery, wherein the particle size (D50) of the sulfide solid electrolyte is 0.1 μm to 1.5 μm.

[0023] 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 comprising a positive electrode active material, a sulfide-based solid electrolyte and a conductive material.

[0024] The present invention also provides a positive electrode for an all-solid-state battery, wherein the positive electrode comprises a positive electrode current collector; and a positive electrode active material layer formed on one side of the positive electrode current collector;

[0025] The positive electrode active material layer includes a positive electrode active material, a sulfide-based solid electrolyte, a conductive material and a binder.

[0026] The present invention also provides a positive electrode for an all-solid-state battery, wherein the binder includes at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene / propylene copolymer, polybutadiene, polyethylene oxide, chlorosulfonated polyethylene, polyvinyl pyrrolidone, polyvinyl pyridine, polyvinyl alcohol, polyvinyl acetate, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenol 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-co-hexafluoropropylene).

[0027] The present invention also provides a positive electrode for an all-solid-state battery, wherein the conductive material may include graphite, and wherein the graphite is at least one selected from the group consisting of natural graphite and artificial graphite.

[0028] The present invention also provides a positive electrode for an all-solid-state battery, wherein the porosity of the positive electrode active material layer is 5 volume % to 16 volume %.

[0029] The present invention also provides a positive electrode for an all-solid-state battery, wherein the content of the positive electrode active material is 55 wt % to 90 wt % based on the total weight of the positive electrode active material layer;

[0030] Wherein, based on the total weight of the positive electrode active material layer, the content of the sulfide-based solid electrolyte is 10 wt % to 50 wt %;

[0031] The conductive material may be contained in an amount of 0.05 wt % to 10 wt % based on the total weight of the positive electrode active material layer.

[0032] The present invention also provides an all-solid-state battery, which comprises the positive electrode, the negative electrode and a solid electrolyte membrane arranged between the positive electrode and the negative electrode.

[0033] [Beneficial Effects]

[0034] According to the positive electrode for an all-solid-state battery of the present invention, the conductive material fills the gaps between the positive electrode active material particles and the sulfide solid electrolyte particles to reduce the porosity of the positive electrode, thereby being able to improve the energy density of the all-solid-state battery. In addition, the conductive material can have the effect of increasing the conductivity of the positive electrode as a whole by filling the gaps in the positive electrode. DETAILED DESCRIPTION

[0035] Hereinafter, the present invention will be described in more detail to provide a better understanding.

[0036] The terms and words used in this specification and claims should not be interpreted by their ordinary meanings or dictionary meanings, but should be interpreted based on the principle that the inventor can appropriately define the concepts of the terms to best describe his / her invention, with the meanings and concepts consistent with the technical ideas of the present invention.

[0037] In this specification, in order to classify positive electrodes manufactured using a binder and not using a binder in a positive electrode active material layer, the one without a binder may be referred to as a "composite positive electrode" and the one with a binder may be referred to as a "positive electrode".

[0038] Positive electrode for all-solid-state battery

[0039] The invention relates to a positive electrode for an all-solid-state battery.

[0040] The positive electrode for an all-solid-state battery of the present invention comprises a positive electrode active material, a sulfide-based solid electrolyte and a conductive material.

[0041] In one example of the present invention, the positive electrode may be in the form of a pressed sheet. The pressed sheet positive electrode may be used in the form of a current collector, or the pressed sheet may be placed on a current collector to form the positive electrode. The pressed sheet may be formed by pressing a composite powder comprising a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material. Since the pressed sheet may not contain a binder, any resistance that may be caused by the binder is eliminated.

[0042] In another example of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on one side of the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, a sulfide-based solid electrolyte, a conductive material, and a binder.

[0043] 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 can be 50 m2 / g or less. The conductive material may have a crystalline form having a lattice structure. As used herein, a positive electrode without a binder may correspond to a composite positive electrode.

[0044] In the positive electrode for the all-solid-state battery of the present invention, a gap is formed due to the difference in particle size between the positive electrode active material particles and the sulfide solid electrolyte particles, and the gap is filled with a conductive material, thereby reducing the positive electrode porosity and improving the energy density. Since the particle size (D50) of the conductive material is larger than the particle size (D50) of the sulfide solid electrolyte and smaller than the particle size (D50) of the positive electrode active material, the gap can be filled with a conductive material.

[0045] In one embodiment of the present invention, the BET specific surface area of ​​the conductive material can be 50 m 2 Specifically, the BET specific surface area of ​​the conductive material can 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. If the BET specific surface area is greater than 50m 2 / g, the contact interface between the high specific surface area conductive material and the sulfide-based all-solid electrolyte can be increased, which can increase the electrolyte degradation reaction and reduce the ionic conductivity of the positive electrode itself. In addition, the lower limit of the BET specific surface area is not particularly limited, but can be 5m 2 / g or above.

[0046] Specifically, 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, 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 particle is too small to fill the gap formed by the particle size difference between the positive electrode active material particles and the sulfide solid electrolyte particles, and the conductive material may only be adsorbed on the surface of the positive electrode active material; if it is greater than 3.8 μm, it is difficult to fill the gap formed by the particle size difference between the positive electrode active material particles and the sulfide solid electrolyte particles, so the effect of reducing the porosity of the positive electrode is not significant.

[0047] The particle size (D50) can be measured by introducing the conductive material into a particle size analyzer (Mastersizer 3000, Malvern).

[0048] Additionally, the conductive material may have a bulk density greater than or equal to 0.05 g / cc.

[0049] Specifically, its bulk density may be greater than or equal to 0.05 g / cc, greater than or equal to 0.06 g / cc, or greater than or equal to 0.07 g / cc. If the bulk density is less than 0.05 g / cc, the density of the conductive material itself may be lower, thereby reducing the overall density of the positive electrode. The upper limit of the bulk density is not particularly limited, but may be less than 0.1 g / cc, less than 0.3 g / cc, or less than 0.5 g / cc.

[0050] Bulk density can be measured according to ASTM D 1895 using a densitometer.

[0051] Additionally, the conductive material may have a true density greater than or equal to 1.5 g / cc.

[0052] Specifically, its true density can 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, thereby reducing the overall density of the positive electrode. The upper limit of the true density is specifically limited, but can be 3.0 g / cc or less, 4.0 g / cc or less, or 5.0 g / cc or less.

[0053] True density can be measured according to ASTM D 1895 using a densitometer.

[0054] In addition, according to XRD measurement, the crystal size (Lc(002)) of the conductive material in the c-axis direction may be 30 nm to 80 nm.

[0055] Specifically, the crystal size may be greater than 30 nm, greater than 35 nm, or greater than 40 nm, and may be less than 65 nm, less than 70 nm, less than 75 nm, or less than 80 nm.

[0056] The crystal size in the c-axis direction is Lc(002), which is the crystal size in the c-axis direction at the time of XRD measurement, and can be calculated by the Scherrer formula in Formula 1 below.

[0057] <Formula 1>

[0058]

[0059] K = Scherrer constant (K = 0.9)

[0060] β = half width

[0061] λ = wavelength (0.154056nm)

[0062] θ = angle of maximum peak

[0063] In addition, the conductive material may include graphite, wherein the graphite may include at least one selected from natural graphite and artificial graphite, but is not limited thereto, provided that the conductive material has the specific surface area, particle size and crystal structure as described above. Preferably, the conductive material may be artificial graphite.

[0064] Natural graphite can be graphite that occurs in nature and is mined, refined, and then produced into a conductive material.

[0065] Since artificial graphite is made by applying high heat of at least 2500°C to form a crystal structure, it can have a more stable crystal structure than natural graphite, and since there are many movement paths for lithium ions, it is beneficial for charging and discharging.

[0066] In addition, based on the total weight of the positive electrode active material layer, the content of the conductive material may be 0.05 wt % to 10 wt %. 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 may be 5 wt % or less, 7 wt % or less, or 10 wt % or less. If the content of the conductive material is less than 0.05 wt %, the conductivity of the positive electrode may deteriorate, and if it is greater than 10 wt %, the content of the positive electrode active material and the sulfide solid electrolyte may be relatively reduced, resulting in degradation of battery performance.

[0067] In one example of the present invention, the particle size (D50) of the positive electrode active material may be 4.0 μm to 8.0 μm.

[0068] 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, and may be 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 solid electrolyte are dispersed in the same weight ratio, the dispersion may be reduced due to the small particle size of the positive electrode active material; if it is greater than 8.0 μm, excessive voids may be formed in the positive electrode active material layer, thereby possibly reducing the performance of the all-solid-state battery.

[0069] The particle size (D50) can be measured by introducing the positive electrode active material into a particle size analyzer (Mastersizer 3000, Malvern).

[0070] In addition, the positive electrode active material may be any material that can reversibly absorb and release lithium ions without particular limitation, and may be, for example, a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), Li[Ni x Co y Mn z M v ]O2 (wherein M is any one or more elements selected from 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' ) 2-c A c (wherein 0≤a≤0.2, 0.6≤b≤1, 0≤b'≤0.2, 0≤c≤0.2; M comprises at least one selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn and Ti; M' comprises at least one selected from Al, Mg, B; A comprises at least one selected from P, F, S and N), or a compound substituted with one or more transition metals; lithium manganese oxide, such as Li 1+y Mn 2-y O4 (wherein y is 0 to 0.33), LiMnO3, LiMn2O3 or LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide, such as LiV3O8, LiFe3O4, V2O5 or Cu2V2O7; compounds of the formula LiNi 1-y M y O2 (wherein M is Co, Mn, Al, Cu, Fe, Mg, B or Ga, y is 0.01 to 0.3) represented by Ni-type lithium nickel oxide; represented by the formula LiMn 2-y M y Lithium manganese composite oxide represented by Li2Mn3MO8 (wherein M is Co, Ni, Fe, Cr, Zn or Ta, and y is 0.01 to 0.1) or Li2Mn3MO8 (wherein M is Fe, Co, Ni, Cu or Zn); LiMn2O4, in which part of the Li in the formula is replaced by alkaline earth metal ions; disulfide; Fe2(MoO4)3; and the like, but not limited to these.

[0071] In addition, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material may be 55 wt % to 90 wt %. Specifically, the content of the positive electrode active material may be 55 wt % or more, 60 wt % or more, or 65 wt % or more, 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 %, the battery performance may be reduced, and if its content is greater than 90 wt %, the mass transfer resistance may increase.

[0072] In one example of the present invention, the particle size (D50) of the sulfide-based solid electrolyte may be 0.1 μm to 1.5 μm.

[0073] Specifically, the particle size (D50) of the sulfide solid electrolyte may be 0.1 μm or more, 0.3 μm or more, or 0.5 μm or more, and may be 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 solid electrolyte is less than 0.1 μm, the ultrafine solid electrolyte cannot be fully dispersed in the positive electrode layer and may agglomerate, and if it is greater than 1.5 μm, the dispersion may be easier, but the contact surface with the positive electrode active material particles may be reduced, and the positive electrode porosity may increase.

[0074] In addition, the sulfide-based solid electrolyte may include one or more selected from the group consisting of LiPSX (wherein X is Cl, Br or I), LiGePS and LiPS. However, the sulfide-based solid electrolyte is not limited to these, and a wide range of sulfide-based solid electrolytes conventionally used in the art can be used.

[0075] In addition, based on the total weight of the positive electrode active material layer, the content of the sulfide solid electrolyte may be 10% to 50% by weight. Specifically, the content of the sulfide solid electrolyte may be 10% by weight or more, 20% by weight or more, or 30% by weight or more, and may be 40% by weight or less, 45% by weight or less, or 50% by weight or less. If the content of the positive electrode active material is less than 10% by weight, it may not be enough to fill the voids formed in the positive electrode active material layer, thereby making it difficult to reduce the porosity of the positive electrode active material layer. If it is greater than 50% by weight, the content of the positive electrode active material and the conductive material may be relatively reduced, resulting in a decrease in battery performance.

[0076] In one example of the present invention, the positive electrode active material layer may further include a binder. The binder may be included to promote the bonding between the materials contained in the positive electrode active material layer and the bonding between the positive electrode active material layer and the positive electrode current collector. The binder may further reduce the positive electrode porosity by promoting the bonding between the materials contained in the positive electrode active material layer.

[0077] The binder may be a fibrous binder. Due to the fibrillation during the mixing of the positive electrode, the binder may be incorporated into the positive electrode active material layer in the form of fibers. Therefore, it is preferred that the binder has physical properties that are easily deformable.

[0078] 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, polyvinyl pyrrolidone, polyvinyl pyridine, polyvinyl alcohol, polyvinyl acetate, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenol 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-co-hexafluoropropylene). Preferably, the binder may include polytetrafluoroethylene (PTFE).

[0079] In addition, based on the total weight of the positive electrode active material layer, the content of the binder may be 0.1% by weight to 3% by weight. Specifically, the content of the binder may be 0.1% by weight or more, 0.5% by weight or more, 0.8% by weight or more, and may be 1.5% by weight or less, 2% by weight or less, or 3% by weight or less. If the content of the binder is less than 0.1% by weight, the effect of improving the cohesion of each material contained in the positive electrode active material layer may be small, and the electrode sheet may not be properly formed, and if its content is greater than 3% by weight, the ionic conductivity or the electronic conductivity may be reduced.

[0080] In one example of the present invention, the porosity of the positive electrode active material layer may be 5 volume % to 16 volume %.

[0081] Specifically, the porosity may be 5% by volume or more, 8% by volume or more, 10% by volume or more, or 13% by volume or more, 13.8% by volume or less, 14% by volume or less, 14.5% by volume or less, 15% by volume or less, 15.5% by volume or less, or 16% by volume or less. The porosity is within a range optimized in consideration of performance such as battery energy density, and if the porosity is greater than 16% by volume, the energy density of the battery may be reduced.

[0082] In one example of the present invention, the positive electrode current collector supports the positive electrode active material layer and is used to transfer electrons between the external wire and the positive electrode active material layer.

[0083] There is no particular limitation on the positive electrode current collector, as long as it has high electronic conductivity and does not cause chemical changes in the all-solid-state battery. For example, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, stainless steel treated with carbon, nickel or silver, and aluminum-cadmium alloys can be used as the positive electrode current collector.

[0084] The positive electrode current collector may have a microscopic uneven structure or a three-dimensional porous structure on the surface of the positive electrode current collector to strengthen the bonding force with the positive electrode active material layer. Therefore, the positive electrode current collector may include various forms, such as films, sheets, foils, screens, nets, porous materials, foams, non-woven fabrics, etc.

[0085] Method for preparing positive electrode for all-solid-state battery

[0086] The present invention relates to a method for manufacturing a positive electrode for an all-solid-state battery. The specific materials, properties and contents of the positive electrode active material, sulfide solid electrolyte, conductive material, conductive material and binder used in the method for manufacturing a positive electrode for an all-solid-state battery of the present invention are as described above.

[0087] In the present invention, the positive electrode can be classified as a "composite positive electrode" without a binder or a "positive electrode" with a binder.

[0088] In one example of the present invention, a method for preparing a composite positive electrode without a binder 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 tablet form. The tablet form in step (A2) may be formed by pressing with a jig.

[0089] The composite cathode prepared as described above can be applied to a pressure fixture battery cell. Since the composite cathode does not contain a binder, the factor of the binder acting as a resistor can be eliminated. Therefore, the composite cathode can be used to perform performance evaluation using a pressure fixture battery cell that eliminates the resistor factor.

[0090] In addition, in one example of the present invention, a method for manufacturing a positive electrode containing a binder includes: (B1) mixing a positive electrode active material, a sulfide solid electrolyte, a conductive material and a binder; (B2) the mixed powder obtained in step (B1) should be subjected to a calendering process to form a film; and (B3) attaching the film layer of the positive electrode active material obtained in step (B2) to the positive electrode current collector.

[0091] The mixing in step (B1) can be a physical mixing, wherein the adhesive can be fibrillated by the physical mixing. During the physical mixing, the adhesive can be physically deformed by the friction of the particles in the mixed powder under shear force, thereby causing fibrillation. For example, PTFE with a physical property that is easy to deform can be used as an adhesive. In addition, physical deformation can be achieved by introducing induction, ball milling or roller pressing during mixing.

[0092] Furthermore, in step (B2), the mixed powder obtained in step (B1) may be subjected to a calendering process to be formed into a film.

[0093] The conditions of the calendering process may be appropriately controlled process conditions to form a film. For example, the calendering process may be performed at a temperature of 50° C. to 200° C. for 5 to 50 cycles. However, the calendering process conditions (such as temperature pressure or number of cycles) may be any conditions used in the electrode manufacturing process used in the conventional battery field.

[0094] Furthermore, in step (B3), the film-formed cathode active material layer obtained in step (B2) is attached to a cathode current collector to prepare a cathode for an all-solid-state battery.

[0095] All-solid-state battery

[0096] The present invention also relates to an all-solid-state battery comprising a sulfide-based solid electrolyte layer.

[0097] The all-solid-state battery of the present invention comprises a positive electrode, a negative electrode and a sulfide-based solid electrolyte layer disposed therebetween. The positive electrode is as described above.

[0098] In one example of the present invention, the negative electrode includes a negative electrode active material layer, wherein the negative electrode active material layer may be formed on one side of a negative electrode current collector.

[0099] The negative electrode active material layer may include a negative electrode active material, a conductive material, and a binder. Alternatively, the negative electrode active material layer may be an anode-free layer.

[0100] In the negative electrode active material layer, the negative electrode active material may include a material capable of reversibly inserting or deinserting lithium (Li + ), a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal or a lithium alloy.

[0101] Able to reversibly insert or remove lithium ions (Li + ) can be, for example, crystalline carbon, amorphous carbon or a mixture thereof. +) 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).

[0102] Preferably, the negative electrode active material may be lithium metal or lithium indium alloy (Li-In), and more specifically, it may be in the form of lithium metal or lithium thin film, or lithium indium alloy thin film or powder.

[0103] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material may be 40% to 80% by weight. Specifically, the content of the negative electrode active material may be 40% by weight or more, 50% by weight or more, 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 layer and the dry negative electrode active layer may be insufficient, and if the content is greater than 80% by weight, the mass transfer resistance may increase.

[0104] The binder is a component that helps the bonding of the negative electrode active material and the conductive material or helps the bonding with the negative electrode current collector, and may include at least one selected from the group consisting of styrene butadiene rubber, acrylated styrene butadiene rubber, acrylonitrile copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene / propylene copolymer, polybutadiene, polyethylene oxide, chlorosulfonated polyethylene, polyvinyl pyrrolidone, polyvinyl pyridine, polyethylene The binder may include polytetrafluoroethylene (PTFE), 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-co-hexafluoropropylene). Preferably, the binder may include polytetrafluoroethylene (PTFE).

[0105] In addition, based on the total weight of the negative electrode active material layer, the content of the binder may be 0.5% by weight to 4% by weight, more specifically, the content of the binder may be 0.5% by weight or more, 1% by weight or more, 1.5% by weight or more, 3% by weight or less, 3.5% by weight or less, or 4% by weight or less. If the binder content is less than 0.5% by weight, the adhesion of the positive electrode active material to the negative electrode current collector may be reduced, and if the binder content is greater than 4% by weight, the adhesion may be improved, but the content of the negative electrode active material may be reduced, resulting in a reduction in the capacity of the battery cell.

[0106] In addition, the conductive material is not particularly limited as long as it prevents side reactions in the internal environment of the all-solid-state battery and has excellent conductivity and does not cause chemical changes in the battery. As a representative, it can be graphite or conductive carbon, such as graphite, such as natural graphite, artificial graphite, etc.; carbon black, such as carbon black, acetylene black, Ketjen black, denka black, hot carbon black, channel black, furnace black, lamp black, summer black, etc.; carbon-based materials with a crystal structure of graphene or graphite; conductive fibers, such as carbon fibers, metal fibers, etc.; fluorocarbons; metal powders, such as aluminum powder, nickel powder, etc.; conductive whiskers, such as zinc oxide, potassium titanate, etc.; conductive oxides, such as titanium oxide; conductive polymers, such as polyphenylene derivatives, which can be used alone or in a mixture of two or more, but are not necessarily limited thereto. Preferably, the conductive material may include vapor-grown carbon fibers (VGCF).

[0107] In addition, based on the total weight of the negative electrode active material layer, the content of the conductive material may be 1 wt % to 5 wt %, more specifically, the content of the conductive material may be 1 wt % or more, 1.5 wt % or more, 2 wt % or more, 4 wt % or less, 4.5 wt % or less, or 5 wt % or less. If the content of the conductive material is too low, for example, less than 1 wt %, it is difficult to expect the conductivity improvement effect, or the electrochemical performance of the battery may deteriorate, and if the content is too high, for example, more than 5 wt %, the content of the negative electrode active material may be relatively low, resulting in reduced capacity and energy density. There is no substantial limitation on the method of incorporating the conductive material into the negative electrode, and any conventional method known in the art may be used, such as mixing with the negative electrode active material or coating the negative electrode active material.

[0108] In addition, the negative electrode current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel whose surface is treated with carbon, nickel or silver, aluminum-cadmium alloy, etc. can be used. In addition, similar to the positive electrode current collector, the negative electrode current collector can take various forms, for example, a film, sheet, foil, net, porous material, foam, non-woven fabric, etc., with fine concavoconvexity formed on the surface.

[0109] The manufacturing method of the negative electrode is not particularly limited, and can be manufactured by forming a negative electrode active material layer on the negative electrode current collector using a conventional layering or film forming method. For example, methods such as pressing, coating or deposition can be used. The negative electrode of the present invention also includes the following case: the battery is assembled without a lithium film on the negative electrode current collector, and then a metallic lithium film is formed on the metal plate by initial charging.

[0110] In addition, the anode-free layer refers to a negative electrode layer in which, when the battery is initially assembled, no lithium metal or lithium alloy that can serve as a lithium source in the negative electrode active material exists in the negative electrode, but lithium is precipitated in the negative electrode by charging. A battery including the anode-free layer may be referred to as an anode-free battery.

[0111] In an anode-free battery, during the battery charge and discharge process, lithium ions released from the positive electrode migrate to the negative electrode to form a negative electrode active material layer. For example, during battery charging, lithium ions are released from the positive electrode active material and migrate to the negative electrode side to form lithium metal composed only of lithium, thereby forming a lithium metal layer on the negative electrode current collector, or forming any other form of lithium metal structure other than a layer form. Any other form may refer to a structure in which lithium metal is aggregated in the form of particles, for example.

[0112] In one example of the present invention, the sulfide solid electrolyte contained in the sulfide solid electrolyte layer may include one or more selected from the group consisting of LiPSX (wherein X is Cl, Br or I), LiGePS and LiPS. However, the sulfide solid electrolyte is not limited to these, and a wide range of sulfide solid electrolytes conventionally used in the art can be used.

[0113] Battery Module

[0114] The present invention also relates to a battery module comprising the all-solid-state battery as a unit cell, a battery pack comprising the battery module, and a device comprising the battery pack as a power source.

[0115] Specific examples of such devices include, but are not limited to: power tools powered by electric motors; electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and power storage systems; etc.

[0116] Example

[0117] Hereinafter, for the purpose of illustrating the present invention, preferred embodiments of the present invention are described, but it will be apparent to those skilled in the art that various changes and modifications may be made within the scope and technical concept of the present invention, and such changes and modifications fall within the scope of the appended patent claims.

[0118] In the following Examples and Comparative Examples, a conductive material having the properties described in Table 1 below was used to prepare a positive electrode and an all-solid-state battery including the same according to the composition of the positive electrode active material layer and the properties of the raw materials described in Table 2 below.

[0119] [Table 1]

[0120]

[0121] [Table 2]

[0122]

[0123] Example 1: Preparation of composite positive electrode

[0124] The positive electrode was prepared as follows: LiN 0.8 Co 0.1 Mn 0.1 O2 (NCM811) is used as the positive electrode active material, Li6PS5Cl is used as the sulfide solid electrolyte, and graphite A is used as the conductive material. The properties of graphite A are shown in Table 1 above.

[0125] The positive electrode active material, the sulfide solid electrolyte and the conductive material were powder mixed at a weight ratio of 60:35:5. Specifically, the positive electrode active material and the sulfide solid electrolyte were quantitatively measured in a powder state and mixed for 15 minutes using an agate mortar in a dry room environment to obtain a mixture. Then, the conductive material was weighed and added to the above mixture, and mixed for another 15 minutes to obtain a mixed powder.

[0126] The mixed powder was pressurized using a pressurizing fixture and prepared to have a load of 3 mAh / cm 2 A pressed sheet composite positive electrode.

[0127] Example 2: Preparation of positive electrode

[0128] The positive electrode was prepared as follows: LiN 0.8 Co 0.1 Mn 0.1 O2 (NCM811) is used as the positive electrode active material, Li6PS5Cl is used as the sulfide solid electrolyte, graphite A is used as the conductive material, and polytetrafluoroethylene (PTFE) is used as the binder. The properties of graphite A are shown in Table 1 above.

[0129] The positive electrode active material, sulfide solid electrolyte, conductive material and binder are powder mixed in a weight ratio of 78:19.5:1:1.5. Specifically, the positive electrode active material and the sulfide solid electrolyte are quantitatively mixed in a powder state and mixed for 15 minutes using a blade mixer in a dry chamber environment to obtain a mixture. The conductive material is then quantitatively added to the above mixture, and the binder polytetrafluoroethylene (PTFE) powder is quantitatively mixed and then further mixed to obtain a mixed powder.

[0130] After the mixed powder was introduced into a mortar, it was fiberized in the mortar and calendered in a roller press to prepare a 6 mAh / cm 2 The positive electrode.

[0131] Example 3: Preparation of composite positive electrode

[0132] The same procedure as in Example 1 was performed except that graphite B was used as the conductive material instead of graphite A. The properties of graphite B are shown in Table 1 above.

[0133] Example 4: Preparation of positive electrode

[0134] The same procedure as in Example 2 was performed except that graphite B was used as the conductive material instead of graphite A. The properties of graphite B are shown in Table 1 above.

[0135] Comparative Example 1

[0136] The same procedure as in Example 1 was performed, except that carbon black was used as the conductive material instead of Graphite A. The properties of the carbon black are shown in Table 1 above.

[0137] Comparative Example 2

[0138] The same procedure as in Example 2 was performed, except that carbon black was used as the conductive material instead of Graphite A. The properties of the carbon black are shown in Table 1 above.

[0139] Experimental Example 1: Performance evaluation of all-solid-state batteries

[0140] The performance of the all-solid-state battery was evaluated according to the type of conductive material in the positive electrode active material layer. The composite positive electrodes prepared in Example 1, Example 3 and Comparative Example 1 were evaluated.

[0141] In order to evaluate the performance of all-solid-state batteries, a press fixture cell was prepared by the following method.

[0142] After the pressed sheet composite cathode was transferred to the pressure fixture unit, the sulfide solid electrolyte powder (200 mg) was placed on the pressed sheet and pressurized with a force of 400 MPa for 60 seconds to form a film-like sulfide solid electrolyte layer. Then, the lithium metal negative electrode was placed on one side of the sulfide solid electrolyte layer and pressurized again with a force of 100 MPa to increase the contact between the sulfide solid electrolyte layer and the negative electrode. Then, the pressure fixture cell was prepared by tightening under appropriate pressure.

[0143] The capacity capability of the pressure fixture cell was observed using a scheme in which the cell was activated at 0.05C for 2 cycles and then discharged to 1C in a charger / discharger, and the results are shown in the following Tables 3 and 4. Specifically, the capacity capability was observed in a charger / discharger by performing CC / CV (constant current / constant voltage) charging at 0.05C, performing CC (constant current) discharge at 0.05C for 2 cycles, and then performing CC / CV charging at 0.1C, but performing CC discharge at 0.1C / 0.2C / 0.33C / 0.5C / 1C.

[0144] [Table 3]

[0145]

[0146] Referring to Table 3 above, it can be seen that in Examples 1 and 3, the particle size (D 50 ) is between the particle size of the positive electrode active material and the particle size of the sulfide solid electrolyte and has a specific surface area of ​​less than 30 m 2 / g of graphite A and graphite B, with a specific surface area of ​​up to about 1300m 2 / g carbon black as a conductive material, showed more excellent performance in terms of discharge capacity. In addition, it was observed that compared with Examples 1 and 3, Comparative Example 1 had a rapid increase in initial charge capacity and a lower efficiency, and also showed lower efficiency during the second charge and discharge.

[0147] [Table 4]

[0148]

[0149] Referring to Table 4 above, it is observed that Examples 1 and 3 have better discharge capacity retention than Comparative Example 1. Specifically, Examples 1 and 3 maintain a discharge capacity of 150 mAh / g at 1C discharge, while the discharge capacity measured in Comparative Example 1 is 28 mAh / g. This is because when the specific surface area of ​​the carbon material in the composite positive electrode is high (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.

[0150] Experimental Example 2: Confirmation of the internal structure of the positive electrode

[0151] According to the type of conductive material in the positive electrode active material layer containing a binder, experiments were conducted to measure the internal structure of the positive electrode. Example 2, Example 4 and Comparative Example 2 were evaluated. They all contain a binder in the positive electrode active material layer. Example 2, Example 4 and Comparative Example 2 all used a binder when manufacturing the positive electrode, wherein Example 2 contains graphite A as a conductive material, Example 4 contains graphite B as a conductive material, and Comparative Example 2 contains carbon black as a conductive material. As shown in Table 1 above, carbon black has a significantly larger specific surface area than graphite A and graphite B.

[0152] The positive electrodes prepared in Example 2, Example 4 and Comparative Example 2 were further pressed using a hot isostatic press (WIP) to ensure that the positive electrode components were fully contacted, and the thickness and porosity were measured, and the results are shown in Table 5 below. According to the following formula 2, the porosity is calculated using the positive electrode density calculated from the following parameters: 1) the thickness of the positive electrode after WIP rolling, 2) the positive electrode weight, 3) the positive electrode area, and 4) the true density of the positive electrode component used.

[0153] <Formula 2>

[0154] Porosity of positive electrode (%) = (1-([positive electrode weight] / [positive electrode area × positive electrode thickness]) / [positive electrode component true density]) × 100

[0155] [Table 5]

[0156]

[0157] Referring to Table 5 above, it can be seen that the positive electrode thickness and porosity of Example 2 and Example 4 before and after rolling are smaller than those of Comparative Example 2. It can be seen that graphite A and graphite B, which have a smaller specific surface area than carbon black, effectively fill the voids in the positive electrode, thereby reducing the thickness and porosity of the positive electrode.

[0158] Therefore, it can be expected that if 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 solid electrolyte and has a low specific surface area as in Example 2, the porosity of the positive electrode active material layer will decrease and the performance of the positive electrode will be improved accordingly.

Claims

1. A positive electrode for an all-solid-state battery, comprising a positive electrode active material, a sulfide solid electrolyte and a conductive material, in, 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. Wherein, the BET specific surface area of ​​the conductive material is 50m 2 / g or less.

2. The positive electrode for an all-solid-state battery according to claim 1, wherein The particle size D50 of the conductive material is 1.5 μm to 3.8 μm.

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

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

5. The positive electrode for an all-solid-state battery according to claim 1, wherein The crystal size Lc(200) of the conductive material is 30 nm to 80 nm.

6. 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 to 8.0 μm.

7. The positive electrode for an all-solid-state battery according to claim 1, wherein: The particle size D50 of the sulfide-based solid electrolyte is 0.1 μm to 1.5 μm.

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

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

10. The positive electrode for an all-solid-state battery according to claim 9, in, The binder includes at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene / propylene copolymer, polybutadiene, polyethylene oxide, chlorosulfonated polyethylene, polyvinyl pyrrolidone, polyvinyl pyridine, polyvinyl alcohol, polyvinyl acetate, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenol 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-co-hexafluoropropylene).

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

12. 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 volume % to 16 volume %.

13. The positive electrode for an all-solid-state battery according to claim 1, in, The content of the positive electrode active material is 55 wt % to 90 wt % based on the total weight of the positive electrode active material layer. Wherein, based on the total weight of the positive electrode active material layer, the content of the sulfide-based solid electrolyte is 10 wt % to 50 wt %, Wherein, based on the total weight of the positive electrode active material layer, the content of the conductive material is 0.05 wt % to 10 wt %.

14. An all-solid-state battery comprising the positive electrode according to claim 1, a negative electrode and a sulfide-based solid electrolyte layer disposed therebetween.

Images