Solid-state battery positive pole piece with composite structure as well as preparation method and application of solid-state battery positive pole piece

Abstract

The invention relates to a solid-state battery positive pole piece with a composite structure as well as a preparation method and application thereof. The solid-state battery positive pole piece comprises a current collector, a composite positive pole coating attached to the surface of one side of the current collector, and a composite polymer coating attached to the composite positive pole coating, the composite positive electrode coating comprises a positive electrode active material, a first oxyfluoride solid electrolyte, a binder and a conductive agent; the composite polymer coating comprises an in-situ polymerized polymer of a three-dimensional network structure, and a lithium salt and a second oxyfluoride solid electrolyte which are filled in gaps of the three-dimensional network structure; the polymer is formed by initiating in-situ polymerization of a polymer monomer through a thermal initiator; and a composite polymer coating is immersed in a gap of the composite positive electrode coating. The positive pole piece of the solid-state battery has high ionic conductivity, high interface stability and high mechanical reliability, and the cycle performance of the solid-state lithium battery can be improved when the positive pole piece is applied to the solid-state lithium battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid-state battery materials, and particularly relates to a solid-state battery positive electrode sheet with a composite structure and a preparation method and application thereof. BACKGROUND

[0002] With the vigorous development of new energy vehicles, the liquid-state battery using liquid electrolyte has gradually failed to meet people's pursuit of higher energy density and safer lithium ion batteries. The full solid-state battery technology is considered as a key breakthrough because it has higher energy density and higher safety. However, the inherent solid-solid interface contact between the electrolyte and the electrode in the solid-state battery is poor, the interface impedance is high, the interface side reaction is violent, and the lithium dendrite is easy to grow, which seriously restricts the actual application performance. Among them, the internal ion transmission efficiency and interface stability of the positive electrode sheet, as a core component of the battery, are particularly crucial.

[0003] The existing composite positive electrode technology, such as the solid-state electrolyte premixing scheme or the polymer solution impregnation scheme, although aims to improve the interface contact, still has significant defects: firstly, in the premixing technology, the solid-state electrolyte particles and the positive active particles are only simple physical mixing, which is difficult to achieve uniform and dense interface coating, resulting in a large number of positive electrode surfaces still directly exposed to the electrolyte and causing side reactions; secondly, although the polymer impregnation technology can improve the contact, the low conductivity of the polymer phase easily becomes the bottleneck of ion transmission, which restricts the rate performance, and most of the polymers have poor mechanical strength and narrow electrochemical window, which cannot effectively inhibit the volume change and high-voltage oxidative decomposition, but instead introduces new instability. SUMMARY

[0004] The present application aims to solve the defects in the prior art, and provides a solid-state battery positive electrode sheet with a composite structure and a preparation method and application thereof.

[0005] The present application proposes a solid-state battery positive electrode sheet preparation scheme based on particle size gradient design and two-step forming process, and a solid-state battery positive electrode sheet with a composite positive electrode coating and a composite polymer coating is prepared, wherein the composite positive electrode coating uses oxyfluoride solid-state electrolyte to mechanically coat the positive active large particles, and constructs a preliminary ion conduction and interface protection layer; at the same time, by scraping the composite slurry of nanoscale oxyfluoride solid-state electrolyte and in-situ polymer on the outer layer, the composite slurry penetrates and fills the pores of the sheet and forms a flexible composite layer, and finally forms a multi-scale, functional gradient composite structure of "particle coating-pore filling-interface softening". The present application provides an effective and feasible technical path for realizing the solid-state battery positive electrode sheet with high ion conductivity, high interface stability and high mechanical reliability through the synergistic effect of multi-scale structure design and material properties.

[0006] To achieve the above object, in a first aspect, the application provides a solid-state battery positive electrode sheet with a composite structure, comprising: a current collector, a composite positive electrode coating attached to one side surface of the current collector, and a composite polymer coating attached to the composite positive electrode coating;

[0007] The composite positive electrode coating comprises: a positive electrode active material, a first oxyfluoride solid-state electrolyte, a binder, and a conductive agent;

[0008] The composite polymer coating comprises: a polymer with a three-dimensional network structure polymerized in situ, and a lithium salt and a second oxyfluoride solid-state electrolyte filled in the voids of the three-dimensional network structure; the polymer is formed by initiating in-situ polymerization of a polymer monomer by a thermal initiator; the voids of the composite positive electrode coating are impregnated with the composite polymer coating;

[0009] The particle size Dv50 of the first oxyfluoride solid-state electrolyte is between 50 nm and 1 μm, the particle size Dv50 of the second oxyfluoride solid-state electrolyte is between 50 nm and 300 nm, and the particle size of the first oxyfluoride solid-state electrolyte is larger than that of the second oxyfluoride solid-state electrolyte.

[0010] Preferably, the current collector comprises: any one of an aluminum foil, a carbon-coated aluminum foil, and an aluminum-polymer composite foil;

[0011] The thickness of the current collector is between 8 μm and 15 μm;

[0012] The thickness of the composite positive electrode coating is between 50 μm and 200 μm;

[0013] The thickness of the composite polymer coating is between 1 μm and 10 μm.

[0014] Preferably, the chemical formula of the first oxyfluoride solid-state electrolyte and the second oxyfluoride solid-state electrolyte is Li x La y M1 z M2 w M3 u O6F, wherein M1 is a tetravalent cation, M2 is a pentavalent cation, M3 is a hexavalent cation, and 1

[0015] The positive electrode active material comprises: one or more of lithium iron phosphate, lithium cobaltate, lithium manganate, lithium nickelate, and lithium iron manganese phosphate ternary material.

[0016] The binder comprises one or more of polyvinylidene fluoride, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene copolymer;

[0017] The conductive agent comprises one or more of superconducting carbon black, carbon nanotubes or graphene;

[0018] The polymer monomer comprises one or more of pentaerythritol tetraacrylate, polyethylene glycol diacrylate, methyl methacrylate, trimethylolpropane triacrylate, trifluoroethyl acrylate;

[0019] The lithium salt comprises one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bisfluorosulfonylimide, lithium perchlorate, lithium difluoro(oxalato)borate, lithium hexafluorophosphate, lithium tetrafluoroborate;

[0020] The thermal initiator comprises azobis isobutyronitrile and / or benzoyl peroxide.

[0021] Further preferably, M1 can be one or more of Zr, Ti, Hf, Si, Ge, Sn; M2 can be one or more of Nb, Sb, Bi, V, Ta; and M3 can be one or more of W, Cr, Mo, Mn.

[0022] In a second aspect, the present application provides a preparation method of the solid-state battery positive electrode sheet of the first aspect, which comprises:

[0023] Step S1, weighing the positive electrode active material, the first oxyfluoride solid-state electrolyte, the binder and the conductive agent as raw materials; placing the raw materials and the solvent in a mixing device, and mixing at high speed to obtain a first mixed slurry;

[0024] Step S2, uniformly coating the first mixed slurry on one side of the current collector, and then transferring the coated current collector to a vacuum drying box for first vacuum drying to obtain a current collector with a composite positive electrode coating;

[0025] Step S3, uniformly mixing the polymer monomer, the lithium salt and the thermal initiator in proportion to obtain a polymer precursor solution; then adding the second oxyfluoride solid-state electrolyte into the polymer precursor solution and uniformly dispersing to obtain a second mixed slurry;

[0026] Step S4, uniformly coating the second mixed slurry on the surface of the composite positive electrode coating, and then transferring to a vacuum drying box for second vacuum drying, so that the thermal initiator initiates in-situ polymerization of the polymer monomer to form a three-dimensional network structure of the polymer, to obtain a solid-state battery positive electrode sheet with a composite positive electrode coating and a composite polymer coating.

[0027] Preferably, the first oxyfluoride solid-state electrolyte has a chemical formula of Li x La y M1 z M2 w M3 u O6F, wherein M1 is a tetravalent cation, M2 is a pentavalent cation, M3 is a hexavalent cation, and 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3, 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2, at least one component of M1, M2, and M3 exists, i.e., one of z, w, and u is not 0; the particle size Dv50 of the first oxyfluoride solid-state electrolyte is between 50 nm and 300 nm;

[0028] The positive electrode active material comprises one or more of lithium iron phosphate, lithium cobaltate, lithium manganate, lithium nickelate, and lithium iron manganese phosphate ternary material;

[0029] The binder comprises one or more of polyvinylidene fluoride, polyethylene oxide, and polyvinylidene fluoride-hexafluoropropylene copolymer;

[0030] The conductive agent comprises one or more of superconducting carbon black, carbon nanotube, and graphene;

[0031] The mass ratio of the positive electrode active material, the first oxyfluoride solid-state electrolyte, the binder, and the conductive agent is 50-80:10-40:1-10:1-8;

[0032] The solvent comprises one or more of N-methylpyrrolidone, ethanol, and propanol;

[0033] The solid content of the first mixed slurry is 50wt%-75wt%.

[0034] Preferably, the polymer monomer comprises one or more of pentaerythritol tetraacrylate, polyethylene glycol diacrylate, methyl methacrylate, trimethylolpropane triacrylate, and trifluoroethyl acrylate;

[0035] The lithium salt comprises one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluoro(oxalato)borate, lithium hexafluorophosphate, and lithium tetrafluoroborate;

[0036] The thermal initiator comprises azobisdimethyl isobutyronitrile and / or benzoyl peroxide;

[0037] In the polymer precursor solution, the molar concentration of the polymer monomer is 1 mol / L-4 mol / L, the molar ratio of the lithium salt to the polymer monomer is 1:2-1:8, and the mass ratio of the initiator to the polymer monomer is 0.5:100-3:100.

[0038] The chemical general formula of the second oxyfluoride solid-state electrolyte is Li x La y M1 z M2 w M3 u O6F, wherein M1 is a tetravalent cation, M2 is a pentavalent cation, M3 is a hexavalent cation, and 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3, 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2, M1, M2, M3 at least one component, that is, one of z, w, u is not 0;

[0039] The mass of the second oxyfluoride solid-state electrolyte accounts for 10% to 40% of the total solid mass in the polymer precursor solution; and the particle size Dv50 of the second oxyfluoride solid-state electrolyte is between 50 nm and 300 nm.

[0040] Preferably, the mixing device comprises one or more of a planetary mixer, a high-speed shearing mixer, a vertical stirring tank, and a magnetic stirrer; the rotating speed of the mixing device is 800 rpm to 3000 rpm, and the mixing time is 0.5 hours to 3 hours.

[0041] Preferably, the specific conditions of the first vacuum drying and the second vacuum drying are: vacuum drying at 50℃ to 90℃ for 0.5 hours to 4 hours.

[0042] In a third aspect, the present application provides a lithium battery, which comprises the solid-state battery positive electrode sheet of the first aspect or the solid-state battery positive electrode sheet prepared by the preparation method of the second aspect.

[0043] The solid-state battery positive electrode sheet with a composite structure provided by the present application has the following technical effects.

[0044] (1) The application provides a preparation method of a solid-state battery positive electrode sheet with a composite structure. First, a first mixed slurry is prepared by mixing a positive electrode active material, a first oxyfluoride solid-state electrolyte, a binder and a conductive agent as raw materials with a solvent at a high speed. In this process, the first oxyfluoride solid-state electrolyte mechanically coats the large particles of the positive electrode active material, thereby constructing an initial ion conduction and interface protection layer. Then, the first mixed slurry is coated on a current collector to form a composite positive electrode coating layer. Then, a polymer monomer, a lithium salt and a thermal initiator are mixed to obtain a polymer precursor solution, and then a nano-sized second oxyfluoride solid-state electrolyte is added to obtain a second mixed slurry. The second mixed slurry is coated on the surface of the composite positive electrode coating layer. The polymer precursor solution containing the nano-sized oxyfluoride solid-state electrolyte can penetrate and fill into the gaps of the composite positive electrode coating layer on the surface of the current collector, and form a flexible composite polymer coating layer. Finally, a solid-state battery positive electrode sheet with a multi-scale and functional gradient composite structure of 'particle coating-pore filling-interface softening' is formed.

[0045] (2) The solid-state battery positive electrode sheet prepared by the preparation method has the following advantages. The surface of the positive electrode active material in the composite positive electrode coating layer is coated with an oxyfluoride solid-state electrolyte material. The oxyfluoride solid-state electrolyte material itself has high voltage stability, and can react with the positive electrode interface to form a stable LiF layer during the formation of the battery. Therefore, the positive electrode interface can be passivated from the source, and the side reaction can be inhibited. The gradient-distributed oxyfluoride solid-state electrolyte particles jointly construct an efficient and continuous three-dimensional ion seepage network from the particle surface to the bulk phase of the electrode sheet, which significantly improves the overall ion conductivity. The outer flexible composite layer realizes self-adaptive soft contact with the opposite electrode (such as a solid-state electrolyte separator or a lithium metal negative electrode), effectively relieves stress and inhibits dendrite penetration.

[0046] (3) The solid-state battery positive electrode sheet provided by the application has high ion conductivity, high interface stability and high mechanical reliability through the synergistic effect of multi-scale structure design and material properties. When the solid-state battery positive electrode sheet is used in a lithium battery, especially in a solid-state lithium battery, the cycle performance of the solid-state lithium battery can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The preparation method of the solid-state battery positive electrode sheet provided by the embodiment of the application is shown in the flowchart.

[0048] Figure 2 The rate performance test chart of the battery assembled by the solid-state battery positive electrode sheet provided by the embodiment 1 and the positive electrode sheet provided by the comparative example 1 and the comparative example 2. DETAILED DESCRIPTION

[0049] The technical solutions of the present application will be further described in detail below with the aid of the accompanying drawings and examples.

[0050] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with the aid of the accompanying drawings. Obviously, the described examples are only a part of the examples of the present application, but not all the examples. Based on the examples in the present application, all other examples obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0051] The embodiment of the present application provides a solid-state battery positive electrode sheet with a composite structure, which comprises a current collector, a composite positive electrode coating attached to one side surface of the current collector, and a composite polymer coating attached to the composite positive electrode coating.

[0052] The current collector comprises any one of an aluminum foil, a carbon-coated aluminum foil, and an aluminum-polymer composite foil. The thickness of the current collector is between 8 μm and 15 μm, and can be any value within the above range, for example, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc., but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0053] The composite positive electrode coating comprises a positive electrode active material, a first oxyfluoride solid-state electrolyte, a binder, and a conductive agent. The thickness of the composite positive electrode coating is between 50 μm and 200 μm, and can be any value within the above range, for example, 50 μm, 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, etc., but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0054] Specifically, the positive electrode active material comprises one or more of lithium iron phosphate, lithium cobaltate, lithium manganate, lithium nickelate, and lithium iron manganese phosphate ternary material.

[0055] The chemical general formula of the first oxyfluoride solid-state electrolyte is Li x La y M1 z M2 w M3 uO6F, wherein M1 is a tetravalent cation, M2 is a pentavalent cation, M3 is a hexavalent cation, and 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3, 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2, and at least one of M1, M2, and M3 is present, i.e., one of z, w, and u is not 0; preferably, M1 can be one or more of Zr, Ti, Hf, Si, Ge, and Sn; M2 can be one or more of Nb, Sb, Bi, V, and Ta; and M3 can be one or more of W, Cr, Mo, and Mn.

[0056] The binder includes one or more of polyvinylidene fluoride, polyethylene oxide, and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0057] The conductive agent includes one or more of superconducting carbon black, carbon nanotube, and graphene.

[0058] The composite polymer coating includes a polymer of a three-dimensional network structure polymerized in situ, and a lithium salt and a second oxyfluoride solid-state electrolyte filled in a void of the three-dimensional network structure; the polymer is formed by initiating polymerization of a polymer monomer in situ by a thermal initiator; and the composite polymer coating is immersed in the void of the composite positive electrode coating. The thickness of the composite polymer coating is between 1 μm and 10 μm, and can be any value within the range, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc., but is not limited to the listed values, and other values not listed within the range are also applicable.

[0059] The polymer monomer includes one or more of pentaerythritol tetraacrylate, polyethylene glycol diacrylate, methyl methacrylate, trimethylolpropane triacrylate, and trifluoroethyl acrylate.

[0060] The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluoro(oxalato)borate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

[0061] The thermal initiator includes azobis isobutyronitrile and / or benzoyl peroxide.

[0062] The second oxyfluoride solid-state electrolyte has a general chemical formula of Li x La y M1 z M2 w M3 uO6F, wherein M1 is a tetravalent cation, M2 is a pentavalent cation, M3 is a hexavalent cation, and 1 < x + 3y < 5, 0 < x < 2, 1 / 3 < y < 5 / 3, 0 < z < 2, 0 < w < 2, 0 < u < 2, z + w + u = 2, and at least one of M1, M2 and M3 is present, i.e., one of z, w and u is not 0. Preferably, M1 can be one or more of Zr, Ti, Hf, Si, Ge and Sn; M2 can be one or more of Nb, Sb, Bi and V; and M3 can be one or more of W, Cr, Mo and Mn.

[0063] The first oxyfluoride solid-state electrolyte is the same as or different from the second oxyfluoride solid-state electrolyte, and the particle size of the first oxyfluoride solid-state electrolyte is larger than that of the second oxyfluoride solid-state electrolyte.

[0064] The particle size Dv50 of the first oxyfluoride solid-state electrolyte is between 50 nm and 1 μm, and can be any value within the above range, such as 60 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, etc., but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0065] The particle size Dv50 of the second oxyfluoride solid-state electrolyte is between 50 nm and 300 nm, and can be any value within the above range, such as 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, etc., but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0066] In the present application, the particle size Dv50 refers to the volume median particle size of the material, which represents the particle size corresponding to 50% of the volume distribution of the material, which is a well-known meaning in the art. The particle size Dv50 of the raw material used in the embodiments of the present application can be determined by instruments and conventional methods known in the art. Specifically, 1 g of sample is added to 20 ml of deionized water, 50 ul of 1% mass concentration of ethyl phenyl polyethylene glycol dispersant aqueous solution is added, ultrasonic treatment is performed for 5 minutes, then the dispersion liquid is added to a Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Co., Ltd., particle size determination is performed, and then the Dv50 value is read.

[0067] The present application provides a preparation method of the above-mentioned solid-state battery positive electrode sheet, as shown in Figure 1 The preparation method comprises the following steps:

[0068] Step S1: Weigh the positive electrode active material, the first oxyfluoride solid electrolyte, the binder and the conductive agent as raw materials; place the raw materials and solvent in a mixing device and mix them at high speed to obtain the first mixed slurry.

[0069] The chemical formula of the first oxygen fluoride solid electrolyte is Li. x La y M1 z M2 w M3 u O6F, wherein M1 is a tetravalent cation, M2 is a pentavalent cation, M3 is a hexavalent cation, and 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3, 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2, and at least one of M1, M2, and M3 exists, that is, one of z, w, and u is not 0; the particle size Dv50 of the first oxygen fluoride solid electrolyte is between 50 nm and 1 μm.

[0070] The positive electrode active material includes one or more of the following: lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium manganese iron phosphate ternary materials.

[0071] The binder includes one or more of polyvinylidene fluoride, polyethylene oxide, and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0072] Conductive agents include one or more of superconducting carbon black, carbon nanotubes, or graphene.

[0073] The mass ratio of positive electrode active material, first oxygen fluoride solid electrolyte, binder and conductive agent is 50-80:10-40:1-10:1-8.

[0074] Solvents include one or more of N-methylpyrrolidone (NMP), ethanol, and propanol.

[0075] The solid content of the first mixed slurry is 50wt% to 75wt%.

[0076] The mixing equipment includes one or more of the following: planetary mixer, high-speed shear mixer, vertical mixing tank, and magnetic stirrer; the mixing speed of the mixing equipment is 800 rpm to 3000 rpm, and the mixing time is 0.5 hours to 3 hours.

[0077] Step S2: The first mixed slurry is uniformly coated on one side of the current collector, and then the coated current collector is transferred to a vacuum drying oven for first vacuum drying to obtain a current collector with a composite positive electrode coating.

[0078] The coating method is a conventional and known method, such as scraping, spraying, or roller coating.

[0079] The specific conditions for the first vacuum drying are: vacuum drying at 50℃~90℃ for 0.5 hours to 4 hours.

[0080] Step S3: The polymer monomer, lithium salt and thermal initiator are mixed evenly in proportion to obtain a polymer precursor solution; then the second oxyfluoride solid electrolyte is added to the polymer precursor solution and dispersed evenly to obtain a second mixed slurry.

[0081] The polymer monomers include one or more of pentaerythritol tetraacrylate, polyethylene glycol diacrylate, methyl methacrylate, trimethylolpropane triacrylate, and trifluoroethyl acrylate.

[0082] Lithium salts include one or more of the following: lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluorooxalate borate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

[0083] Thermal initiators include: azobisisobutyronitrile and / or benzoyl peroxide.

[0084] In the polymer precursor solution, the molar concentration of the polymer monomer is 1 mol / L to 4 mol / L, and can be any value within the above range, such as 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The molar ratio of lithium salt to polymer monomer is 1:2 to 1:8, and can be any ratio within the above range, such as 1:2. The ratios are 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, etc., but are not limited to the listed ratios; other unlisted ratios within this range are also applicable. The mass ratio of the initiator to the polymer monomer is 0.5:100 to 3:100, and can be any ratio within the above range, such as 0.5:100, 1:100, 1.5:100, 2:100, 3.5:100, 3:100, etc., but are not limited to the listed ratios; other unlisted ratios within this range are also applicable.

[0085] The general chemical formula of the second oxyfluoride solid electrolyte is Li x La y M1 z M2 w M3 u O6F, where M1 is a tetravalent cation, M2 is a pentavalent cation, M3 is a hexavalent cation, and 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3, 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2, and at least one of M1, M2, and M3 exists, that is, one of z, w, and u is not 0.

[0086] The mass of the second oxyfluoride solid electrolyte accounts for 10% to 40% of the total solid mass in the polymer precursor solution; the particle size Dv50 of the second oxyfluoride solid electrolyte is between 50 nm and 300 nm, and the particle size of the first oxyfluoride solid electrolyte is larger than that of the second oxyfluoride solid electrolyte.

[0087] Step S4: The second mixed slurry is uniformly coated on the surface of the composite positive electrode coating, and then transferred to a vacuum drying oven for a second vacuum drying, so that the thermal initiator initiates the in-situ polymerization of polymer monomers to form a three-dimensional network structure of polymer, thereby obtaining a solid battery positive electrode sheet with a composite positive electrode coating and a composite polymer coating.

[0088] The specific conditions for the second vacuum drying are: vacuum drying at 50℃~90℃ for 0.5 hours to 4 hours; at 50℃~90℃, the thermal initiator can initiate the in-situ polymerization of polymer monomers to form a three-dimensional network structure of polymer.

[0089] In this invention, the first oxyfluoride solid electrolyte and the second oxyfluoride solid electrolyte can be the same or different. Both have the characteristics of high mechanical strength, high density, high purity, high volumetric energy density, low internal resistance, and excellent ion conduction performance. Furthermore, the first oxyfluoride solid electrolyte and the second oxyfluoride solid electrolyte have a rigid structure with adjustable elemental composition. By introducing diverse coordination environments through multivalent cation doping, open channels that are conducive to lithium ion transport can be formed. At the same time, fluorine doping can further enhance the polarity and interfacial wettability of the material, improve the interfacial contact with the electrolyte and electrode, and reduce interfacial impedance.

[0090] The solid-state battery positive electrode sheet prepared by the above-described preparation method provided in this invention can be assembled together with the negative electrode sheet, solid electrolyte membrane, and / or separator to form a lithium battery. The lithium battery is a solid-state lithium battery.

[0091] Because the solid-state battery positive electrode of the present invention balances interface stability, ionic conductivity and mechanical stress adaptability through multi-scale structural design and material properties, the solid-state battery positive electrode of the present invention has high ionic conductivity, high interface stability and high mechanical reliability. Applying the solid-state battery positive electrode to lithium batteries, especially solid-state lithium batteries, can improve the cycle performance of solid-state lithium batteries.

[0092] To better understand the technical solution provided by this invention, the following uses several specific examples to illustrate the preparation method and characteristics of the solid-state battery positive electrode sheet of this invention.

[0093] Example 1

[0094] This invention provides a method for preparing a positive electrode sheet for a solid-state battery, which specifically includes the following steps.

[0095] (1) Weigh lithium iron phosphate with a particle size Dv50 of 6.35 μm and Li₂O₃ with a particle size Dv50 of 0.82 μm according to a mass ratio of 65:25:5:5. 1.25 La 0.58 Using Nb2O6F, polyvinylidene fluoride, and carbon nanotubes as raw materials, the raw materials were placed in a planetary mixer containing NMP solvent and mixed at a high speed of 2000 rpm for 2 hours to obtain a first mixed slurry with a solid content of 65 wt%.

[0096] (2) The first mixed slurry is uniformly coated on one side of the current collector aluminum foil with a thickness of 12μm by roller coating, and the coating thickness is 100μm. Then the coated current collector is transferred to a vacuum drying oven and vacuum dried at 80℃ for 2 hours to obtain a current collector with a composite positive electrode coating.

[0097] (3) Using polyethylene glycol diacrylate as the polymer monomer and lithium bis(fluorosulfonyl)imide as the lithium salt, wherein the molar ratio of polymer monomer to lithium salt is 4:1, and adding 1% of the thermal initiator azobisisobutyronitrile (AIBN) by mass of the polymer monomer, a polymer precursor solution is prepared by mixing evenly, wherein the molar concentration of polymer monomer in the polymer precursor solution is 2.5 mol / L; subsequently, 25% of the total solid mass of the polymer precursor solution, with a particle size Dv50 of 100 nm, of the second oxyfluoride solid electrolyte Li 1.25 La 0.58 Nb2O6F was added to the polymer precursor solution and dispersed evenly to obtain the second mixed slurry.

[0098] (4) The second mixed slurry is uniformly coated on the surface of the composite positive electrode coating by roller coating. The coating thickness is 5μm. Then it is transferred to a vacuum drying oven and vacuum dried at 70°C for 1 hour. The thermal initiator initiates the in-situ polymerization of polymer monomers to form a three-dimensional network structure of polymer, thus obtaining a solid battery positive electrode sheet with composite positive electrode coating and composite polymer coating.

[0099] The solid-state battery positive electrode sheet prepared in this embodiment was used to assemble a coin cell, and its cycle performance was tested, as follows:

[0100] Assembling the coin cell: The solid-state battery positive electrode sheet prepared in this embodiment is assembled with a solid-state electrolyte sheet and a lithium negative electrode to form an all-solid-state coin cell. The assembly sequence is as follows: negative electrode shell, lithium negative electrode, electrolyte sheet, solid-state battery positive electrode sheet prepared in this embodiment, gasket, spring sheet, and positive electrode shell. Finally, a sealing machine is used to seal the coin cell under a pressure of 0.75 tons. The electrolyte sheet used is a lithium lanthanum zirconium oxide solid-state electrolyte sheet.

[0101] The cycle performance test process is as follows: charge to 4.4V at a 0.5C rate, discharge to 2.75V at a 0.5C rate after charging, and let stand for 5 minutes as one cycle. Test the capacity retention rate after 100 cycles at 0.5C rate and 2.75V to 4.4V. The test data are detailed in Table 1.

[0102] The rate performance testing process is as follows: First, charge the battery at a 0.2C rate to 3.65V, then discharge it at a 0.2C rate to 2.75V, repeating this cycle 5 times. Next, charge at a 0.5C rate to 3.65V, then discharge at a 0.5C rate to 2.75V, repeating this cycle 5 times. Then, charge at a 1C rate to 3.65V, then discharge at a 1C rate to 2.75V, repeating this cycle 5 times. Finally, charge at a 2C rate to 3.65V, then discharge at a 2C rate to 2.75V, repeating this cycle 5 times. The rate performance test curve is shown below. Figure 2 As shown.

[0103] Example 2

[0104] This invention provides a method for preparing a positive electrode sheet for a solid-state battery, which specifically includes the following steps.

[0105] (1) Weigh out lithium cobalt oxide with a particle size Dv50 of 12.04 μm and Li₂O₃ with a particle size Dv50 of 0.82 μm according to a mass ratio of 70:20:6:4. 1.25 La 1.25 Ti2O6F, polyvinylidene fluoride and carbon nanotubes were used as raw materials. The raw materials were placed in a planetary mixer with NMP solvent and mixed at a high speed of 2000 rpm for 2 hours to obtain a first mixed slurry with a solid content of 68 wt%.

[0106] (2) The first mixed slurry is uniformly coated on one side of the current collector aluminum foil with a thickness of 12μm by roller coating, and the coating thickness is 100μm. Then the coated current collector is transferred to a vacuum drying oven and vacuum dried at 80℃ for 2 hours to obtain a current collector with a composite positive electrode coating.

[0107] (3) Using methyl methacrylate as the polymer monomer and lithium difluorosulfonyl imide as the lithium salt, wherein the molar ratio of polymer monomer to lithium salt is 4:1, and 1.5% of the thermal initiator azobisisobutyronitrile (AIBN) by mass of the polymer monomer is added, the mixture is thoroughly mixed to prepare a polymer precursor solution, wherein the molar concentration of polymer monomer in the polymer precursor solution is 2.0 mol / L; subsequently, 20% of the total solid mass of the polymer precursor solution, with a particle size Dv50 of 150 nm, of the second oxyfluoride solid electrolyte Li 1.25 La 0.58Nb2O6F was added to the polymer precursor solution and dispersed evenly to obtain the second mixed slurry.

[0108] (4) The second mixed slurry is uniformly coated on the surface of the composite positive electrode coating by roller coating. The coating thickness is 5μm. Then it is transferred to a vacuum drying oven and vacuum dried at 70°C for 1 hour. The thermal initiator initiates the in-situ polymerization of polymer monomers to form a three-dimensional network structure of polymer, thus obtaining a solid battery positive electrode sheet with composite positive electrode coating and composite polymer coating.

[0109] The solid-state battery positive electrode sheet prepared in this embodiment was used to assemble a coin cell and a cycle performance test was performed. The battery assembly and testing process was the same as in Example 1. The test data are detailed in Table 1.

[0110] Example 3

[0111] This invention provides a method for preparing a positive electrode sheet for a solid-state battery, which specifically includes the following steps.

[0112] (1) Weigh out lithium cobalt oxide with a particle size Dv50 of 12.04 μm and Li₂O₃ with a particle size Dv50 of 0.67 μm according to a mass ratio of 65:25:6:4. 1.2 La 0.6 TiWO6F, polyvinylidene fluoride and carbon nanotubes were used as raw materials. The raw materials were placed in a planetary mixer with NMP solvent and mixed at a high speed of 2000 rpm for 2 hours to obtain a first mixed slurry with a solid content of 65 wt%.

[0113] (2) The first mixed slurry is uniformly coated on one side of the current collector aluminum foil with a thickness of 12μm by roller coating, and the coating thickness is 100μm. Then the coated current collector is transferred to a vacuum drying oven and vacuum dried at 80℃ for 2 hours to obtain a current collector with a composite positive electrode coating.

[0114] (3) Using methyl methacrylate as the polymer monomer and lithium difluorosulfonyl imide as the lithium salt, wherein the molar ratio of polymer monomer to lithium salt is 4:1, and 1.5% of the thermal initiator azobisisobutyronitrile (AIBN) by mass of the polymer monomer is added, the mixture is thoroughly mixed to prepare a polymer precursor solution, wherein the molar concentration of polymer monomer in the polymer precursor solution is 2.0 mol / L; subsequently, 20% of the total solid mass of the polymer precursor solution, with a particle size Dv50 of 70 nm, of the second oxyfluoride solid electrolyte Li 1.2 La 0.6 TiWO6F was added to the polymer precursor solution and dispersed evenly to obtain the second mixed slurry.

[0115] (4) The second mixed slurry is uniformly coated on the surface of the composite positive electrode coating by roller coating. The coating thickness is 5μm. Then it is transferred to a vacuum drying oven and vacuum dried at 70°C for 1 hour. The thermal initiator initiates the in-situ polymerization of polymer monomers to form a three-dimensional network structure of polymer, thus obtaining a solid battery positive electrode sheet with composite positive electrode coating and composite polymer coating.

[0116] The solid-state battery positive electrode sheet prepared in this embodiment was used to assemble a coin cell and a cycle performance test was performed. The battery assembly and testing process was the same as in Example 1. The test data are detailed in Table 1.

[0117] Example 4

[0118] This invention provides a method for preparing a positive electrode sheet for a solid-state battery, which specifically includes the following steps.

[0119] (1) Weigh lithium iron phosphate with a particle size Dv50 of 6.3 μm and Li₂O₃ with a particle size Dv50 of 0.82 μm according to a mass ratio of 70:20:5:5. 1.25 La 0.58 Ti 0.5 SbW 0.5 O6F, polyvinylidene fluoride and carbon nanotubes were used as raw materials. The raw materials were placed in a planetary mixer with NMP solvent and mixed at a high speed of 1800 rpm for 2 hours to obtain a first mixed slurry with a solid content of 65 wt%.

[0120] (2) The first mixed slurry is uniformly coated on one side of the current collector aluminum foil with a thickness of 12μm by roller coating, and the coating thickness is 100μm. Then the coated current collector is transferred to a vacuum drying oven and vacuum dried at 80℃ for 2 hours to obtain a current collector with a composite positive electrode coating.

[0121] (3) Using polyethylene glycol diacrylate as the polymer monomer and lithium bis(fluorosulfonyl)imide as the lithium salt, with a molar ratio of polymer monomer to lithium salt of 4:1, and adding 1% of the thermal initiator azobisisobutyronitrile (AIBN) by mass of the polymer monomer, a polymer precursor solution was prepared by mixing thoroughly, wherein the molar concentration of the polymer monomer in the polymer precursor solution was 2.5 mol / L; subsequently, 30% of the total solid mass of the polymer precursor solution, with a particle size Dv50 of 100 nm, of the second oxyfluoride solid electrolyte Li 1.25 La 0.58 Nb2O6F was added to the polymer precursor solution and dispersed evenly to obtain the second mixed slurry.

[0122] (4) The second mixed slurry is uniformly coated on the surface of the composite positive electrode coating by roller coating. The coating thickness is 5μm. Then it is transferred to a vacuum drying oven and vacuum dried at 70°C for 1 hour. The thermal initiator initiates the in-situ polymerization of polymer monomers to form a three-dimensional network structure of polymer, thus obtaining a solid battery positive electrode sheet with composite positive electrode coating and composite polymer coating.

[0123] The solid-state battery positive electrode sheet prepared in this embodiment was used to assemble a coin cell and a cycle performance test was performed. The battery assembly and testing process was the same as in Example 1. The test data are detailed in Table 1.

[0124] To better illustrate the effects of the embodiments of the present invention, a comparative example is provided to be made with the embodiments described above.

[0125] Comparative Example 1

[0126] This comparative example provides a positive electrode sheet, which differs from Example 1 in that the current collector has only one layer of conventional positive electrode active material, which does not include a solid electrolyte. The specific preparation process is as follows.

[0127] (1) Weigh lithium iron phosphate, polyvinylidene fluoride and carbon nanotubes with a particle size Dv50 of 6.35μm in a mass ratio of 95:5:5. Place the raw materials in a planetary mixer containing NMP solvent and mix them at a high speed of 2000rpm for 2 hours to obtain a mixed slurry with a solid content of 65wt%.

[0128] (2) The mixed slurry is uniformly coated on one side of a current collector aluminum foil with a thickness of 12μm by roller coating, and the coating thickness is 100μm. Then the coated current collector is transferred to a vacuum drying oven and vacuum dried at 80℃ for 2 hours to obtain the positive electrode sheet.

[0129] The positive electrode sheet prepared in this comparative example was used to assemble a coin cell and perform cycle performance testing. The battery assembly and testing process was the same as in Example 1. The test data are detailed in Table 1.

[0130] The rate performance test curve of the battery assembled in this comparative example is shown in the figure. Figure 2 As shown.

[0131] Comparative Example 2

[0132] This comparative example provides a positive electrode sheet, which differs from Example 1 in that the current collector is only coated with the composite positive electrode coating of Example 1, without the composite polymer coating. The specific preparation process is as follows.

[0133] (1) Weigh lithium iron phosphate with a particle size Dv50 of 6.35 μm and oxyfluorine solid electrolyte Li₂ with a particle size Dv50 of 0.82 μm according to a mass ratio of 65:25:5:5.1.25 La 0.58 Using Nb2O6F, polyvinylidene fluoride, and carbon nanotubes as raw materials, the raw materials were placed in a planetary mixer containing NMP solvent and mixed at a high speed of 2000 rpm for 2 hours to obtain a first mixed slurry with a solid content of 65 wt%.

[0134] (2) The first mixed slurry is uniformly coated on one side of the current collector aluminum foil with a thickness of 12μm by roller coating, and the coating thickness is 100μm. Then the coated current collector is transferred to a vacuum drying oven and vacuum dried at 80℃ for 2 hours to obtain the positive electrode sheet.

[0135] The positive electrode sheet prepared in this comparative example was used to assemble a coin cell and perform cycle performance testing. The battery assembly and testing process was the same as in Example 1. The test data are detailed in Table 1.

[0136] The rate performance test curve of the battery assembled in this comparative example is shown in the figure. Figure 2 As shown. (Through) Figure 2 A comparison of the rate performance test curves of Example 1 with those of Comparative Examples 1 and 2 shows that Example 1 has the best rate performance. This is because Example 1 constructs a highly efficient and continuous three-dimensional ion permeation network from the particle surface to the electrode bulk phase through gradient-distributed oxyfluoride solid electrolyte particles, which significantly improves the overall ionic conductivity and thus enhances the rate performance.

[0137] Comparative Example 3

[0138] This comparative example provides a positive electrode sheet, which differs from Example 1 in that the conventional positive electrode active material layer in Comparative Example 1 is first coated on the current collector, and then the composite polymer coating in Example 1 is coated on the surface of the conventional positive electrode active material layer. The specific preparation process is as follows.

[0139] (1) Weigh lithium iron phosphate, polyvinylidene fluoride and carbon nanotubes with a particle size Dv50 of 6.35μm in a mass ratio of 95:5:5. Place the raw materials in a planetary mixer containing NMP solvent and mix them at a high speed of 2000rpm for 2 hours to obtain a mixed slurry with a solid content of 65wt%.

[0140] (2) The mixed slurry is uniformly coated on one side of a current collector aluminum foil with a thickness of 12μm by roller coating. The coating thickness is 100μm. Then the coated current collector is transferred to a vacuum drying oven and vacuum dried at 80℃ for 2 hours to obtain a positive electrode sheet with a conventional positive electrode active material layer.

[0141] (3) Using polyethylene glycol diacrylate as the polymer monomer and lithium bis(fluorosulfonyl)imide as the lithium salt, with a molar ratio of polymer monomer to lithium salt of 4:1, and adding 1% (by mass) of thermal initiator azobisisobutyronitrile (AIBN) as the polymer monomer, a polymer precursor solution was prepared by mixing thoroughly. The molar concentration of the polymer monomer in the polymer precursor solution was 2.5 mol / L. Subsequently, 25% (by mass) of the total solid mass of the polymer precursor solution, with a particle size Dv50 of 100 nm, of oxyfluoride solid electrolyte Li 1.25 La 0.58 Nb2O6F was added to the polymer precursor solution and dispersed evenly to obtain the second mixed slurry.

[0142] (4) The second mixed slurry is uniformly coated on the surface of the conventional positive electrode active material layer by roller coating. The coating thickness is 5μm. Then it is transferred to a vacuum drying oven and vacuum dried at 70°C for 1 hour. The thermal initiator initiates the in-situ polymerization of polymer monomers to form a three-dimensional network structure of polymer, forming a composite polymer coating on the surface of the conventional positive electrode active material layer, and finally the positive electrode sheet is prepared.

[0143] Comparative Example 4

[0144] This comparative example provides a positive electrode sheet, which differs from Example 1 in that the conventional positive electrode active material layer in Comparative Example 1 is first coated on the current collector, and then a conventional polymer coating is coated on the surface of the conventional positive electrode active material layer. No oxygen fluoride solid electrolyte is added to either layer. The specific preparation process is as follows.

[0145] (1) Weigh lithium iron phosphate, polyvinylidene fluoride and carbon nanotubes with a particle size Dv50 of 6.35μm in a mass ratio of 95:5:5. Place the raw materials in a planetary mixer containing NMP solvent and mix them at a high speed of 2000rpm for 2 hours to obtain a mixed slurry with a solid content of 65wt%.

[0146] (2) The mixed slurry is uniformly coated on one side of a current collector aluminum foil with a thickness of 12μm by roller coating. The coating thickness is 100μm. Then the coated current collector is transferred to a vacuum drying oven and vacuum dried at 80℃ for 2 hours to obtain a positive electrode sheet with a conventional positive electrode active material layer.

[0147] (3) Polyethylene glycol diacrylate is used as the polymer monomer and lithium bis(fluorosulfonyl)imide is used as the lithium salt. The molar ratio of polymer monomer to lithium salt is 4:1. Azobisisobutyronitrile, a thermal initiator accounting for 1% of the polymer monomer mass, is added and mixed evenly to prepare a polymer precursor solution. The molar concentration of polymer monomer in the polymer precursor solution is 2.5 mol / L.

[0148] (4) The polymer precursor solution is uniformly coated onto the surface of the conventional positive electrode active material layer by roller coating. The coating thickness is 5μm. Then it is transferred to a vacuum drying oven and vacuum dried at 70℃ for 1 hour to obtain the positive electrode sheet.

[0149] Comparative Example 5

[0150] This comparative example provides a positive electrode sheet, which differs from Example 1 in that the composite positive electrode coating of Example 1 is first coated on the current collector, and then the conventional polymer coating of Comparative Example 4 is coated on the surface of the composite positive electrode coating. The specific preparation process is as follows.

[0151] (1) Weigh lithium iron phosphate with a particle size Dv50 of 6.35 μm and Li₂O₃ with a particle size Dv50 of 0.82 μm according to a mass ratio of 65:25:5:5. 1.25 La 0.58 Using Nb2O6F, polyvinylidene fluoride, and carbon nanotubes as raw materials, the raw materials were placed in a planetary mixer containing NMP solvent and mixed at a high speed of 2000 rpm for 2 hours to obtain a first mixed slurry with a solid content of 65 wt%.

[0152] (2) The first mixed slurry is uniformly coated on one side of the current collector aluminum foil with a thickness of 12μm by roller coating, and the coating thickness is 100μm. Then the coated current collector is transferred to a vacuum drying oven and vacuum dried at 80℃ for 2 hours to obtain a current collector with a composite positive electrode coating.

[0153] (3) Polyethylene glycol diacrylate is used as the polymer monomer and lithium bis(fluorosulfonyl)imide is used as the lithium salt. The molar ratio of polymer monomer to lithium salt is 4:1. Azobisisobutyronitrile, a thermal initiator accounting for 1% of the polymer monomer mass, is added and mixed evenly to prepare a polymer precursor solution. The molar concentration of polymer monomer in the polymer precursor solution is 2.5 mol / L.

[0154] (4) The polymer precursor solution is uniformly coated onto the surface of the composite positive electrode coating by roller coating. The coating thickness is 5μm. Then it is transferred to a vacuum drying oven and vacuum dried at 70℃ for 1 hour to obtain the positive electrode sheet.

[0155] Table 1 summarizes the test data for Examples 1-4 and Comparative Examples 1-5.

[0156] Number Capacity retention rate (%) after 100 cycles Example 1 92.15 Example 2 91.51 Example 3 90.23 Example 4 90.92 Comparative Example 1 80.59 Comparative Example 2 85.36 Comparative Example 3 83.52 Comparative Example 4 81.13 Comparative Example 5 84.92

[0157] Table 1

[0158] As can be seen from the comparison of the test data in Table 1, the solid-state battery positive electrode sheets prepared in Examples 1-4 have a better capacity retention rate after 100 cycles than those in Comparative Examples 1-5. This is because the solid-state battery positive electrode sheets in Examples 1-4 of this invention solve the contradiction between interface stability and mechanical stress adaptability through multi-scale structural design and synergistic effect of material properties, thereby improving the cycle performance of the battery.

[0159] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A solid-state battery positive electrode with a composite structure, characterized in that, The solid-state battery positive electrode includes: a current collector, a composite positive electrode coating attached to one side surface of the current collector, and a composite polymer coating attached to the composite positive electrode coating; The composite positive electrode coating comprises: a positive electrode active material, a first oxyfluoride solid electrolyte, a binder, and a conductive agent; The composite polymer coating comprises: a polymer with an in-situ polymerized three-dimensional network structure, and a lithium salt and a second oxyfluoride solid electrolyte filling the voids of the three-dimensional network structure; the polymer is formed by in-situ polymerization of polymer monomers initiated by a thermal initiator; the composite polymer coating is immersed in the voids of the composite cathode coating. The particle size Dv50 of the first oxyfluoride solid electrolyte is between 50 nm and 1 μm, and the particle size Dv50 of the second oxyfluoride solid electrolyte is between 50 nm and 300 nm, and the particle size of the first oxyfluoride solid electrolyte is larger than that of the second oxyfluoride solid electrolyte.

2. The solid-state battery positive electrode according to claim 1, characterized in that, The current collector includes any one of aluminum foil, carbon-coated aluminum foil, and aluminum-polymer composite foil; The thickness of the current collector is between 8 μm and 15 μm; The thickness of the composite positive electrode coating is between 50 μm and 200 μm; The thickness of the composite polymer coating is between 1 μm and 10 μm.

3. The solid-state battery positive electrode according to claim 1, characterized in that, The chemical formula of both the first oxyfluoride solid electrolyte and the second oxyfluoride solid electrolyte is Li. x La y M1 z M2 w M3 u O6F, wherein M1 is a tetravalent cation, M2 is a pentavalent cation, M3 is a hexavalent cation, and 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3, 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2, and at least one of M1, M2, and M3 exists, that is, one of z, w, and u is not 0; the first oxyfluoride solid electrolyte is the same as or different from the second oxyfluoride solid electrolyte; The positive electrode active material includes one or more of the following: lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium manganese iron phosphate ternary materials. The adhesive includes one or more of polyvinylidene fluoride, polyethylene oxide, and polyvinylidene fluoride-hexafluoropropylene copolymer; The conductive agent includes one or more of superconducting carbon black, carbon nanotubes, or graphene. The polymer monomers include one or more of the following: pentaerythritol tetraacrylate, polyethylene glycol diacrylate, methyl methacrylate, trimethylolpropane triacrylate, and trifluoroethyl acrylate; The lithium salt includes one or more of the following: lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluorooxalate borate, lithium hexafluorophosphate, and lithium tetrafluoroborate. The thermal initiator includes: azobisisobutyronitrile and / or benzoyl peroxide.

4. The solid-state battery positive electrode according to claim 3, characterized in that, M1 can be one or more of Zr, Ti, Hf, Si, Ge, and Sn; M2 can be one or more of Nb, Sb, Bi, V, and Ta; and M3 can be one or more of W, Cr, Mo, and Mn.

5. A method for preparing a solid-state battery positive electrode sheet according to any one of claims 1-4, characterized in that, The preparation method includes: Step S1: Weigh the positive electrode active material, the first oxyfluoride solid electrolyte, the binder and the conductive agent as raw materials; place the raw materials and solvent in a mixing device and mix them at high speed to obtain the first mixed slurry; Step S2: The first mixed slurry is uniformly coated on one side of the current collector, and then the coated current collector is transferred to a vacuum drying oven for first vacuum drying to obtain a current collector with a composite positive electrode coating. Step S3: The polymer monomer, lithium salt and thermal initiator are mixed evenly in proportion to obtain a polymer precursor solution; then the second oxyfluoride solid electrolyte is added to the polymer precursor solution and dispersed evenly to obtain a second mixed slurry. Step S4: The second mixed slurry is uniformly coated on the surface of the composite positive electrode coating, and then transferred to a vacuum drying oven for a second vacuum drying, so that the thermal initiator initiates the in-situ polymerization of the polymer monomers to form a polymer with a three-dimensional network structure, thereby obtaining a solid battery positive electrode sheet with a composite positive electrode coating and a composite polymer coating. The particle size Dv50 of the first oxyfluoride solid electrolyte is between 50 nm and 1 μm, and the particle size Dv50 of the second oxyfluoride solid electrolyte is between 50 nm and 300 nm, and the particle size of the first oxyfluoride solid electrolyte is larger than that of the second oxyfluoride solid electrolyte.

6. The preparation method according to claim 5, characterized in that, The chemical formula of the first oxygen fluoride solid electrolyte is Li. x La y M1 z M2 w M3 u O6F, where M1 is a tetravalent cation, M2 is a pentavalent cation, M3 is a hexavalent cation, and 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3, 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2, and at least one of M1, M2, and M3 exists, that is, one of z, w, and u is not 0; The positive electrode active material includes one or more of the following: lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium manganese iron phosphate ternary materials. The adhesive includes one or more of polyvinylidene fluoride, polyethylene oxide, and polyvinylidene fluoride-hexafluoropropylene copolymer; The conductive agent includes one or more of superconducting carbon black, carbon nanotubes, or graphene. The mass ratio of the positive electrode active material, the first oxyfluoride solid electrolyte, the binder, and the conductive agent is 50-80:10-40:1-10:1-8; The solvent includes one or more of N-methylpyrrolidone, ethanol, and propanol; The solid content of the first mixed slurry is 50wt% to 75wt%.

7. The preparation method according to claim 5, characterized in that, The polymer monomers include one or more of the following: pentaerythritol tetraacrylate, polyethylene glycol diacrylate, methyl methacrylate, trimethylolpropane triacrylate, and trifluoroethyl acrylate; The lithium salt includes one or more of the following: lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluorooxalate borate, lithium hexafluorophosphate, and lithium tetrafluoroborate. The thermal initiator includes: azobisisobutyronitrile and / or benzoyl peroxide; In the polymer precursor solution, the molar concentration of the polymer monomer is 1 mol / L to 4 mol / L, the molar ratio of the lithium salt to the polymer monomer is 1:2 to 1:8, and the mass ratio of the initiator to the polymer monomer is 0.5:100 to 3:

100. The general chemical formula of the second oxyfluoride solid electrolyte is Li x La y M1 z M2 w M3 u O6F, where M1 is a tetravalent cation, M2 is a pentavalent cation, M3 is a hexavalent cation, and 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3, 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2, and at least one of M1, M2, and M3 exists, that is, one of z, w, and u is not 0; The mass of the second oxyfluoride solid electrolyte accounts for 10% to 40% of the total solid mass in the polymer precursor solution.

8. The preparation method according to claim 5, characterized in that, The mixing equipment includes one or more of the following: a planetary mixer, a high-speed shear mixer, a vertical mixing tank, and a magnetic stirrer; the mixing equipment has a rotation speed of 800 rpm to 3000 rpm and a mixing time of 0.5 hours to 3 hours.

9. The preparation method according to claim 5, characterized in that, The specific conditions for the first vacuum drying and the second vacuum drying are: vacuum drying at 50℃~90℃ for 0.5 hours to 4 hours.

10. A lithium battery, characterized in that, The lithium battery includes the solid-state battery positive electrode sheet according to any one of claims 1-4, or the solid-state battery positive electrode sheet prepared by any one of claims 5-9.

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