Positive electrode sheet, method for manufacturing the same, and secondary battery

Abstract

The application relates to the technical field of batteries, in particular to a positive plate, a manufacturing method thereof and a secondary battery; the positive plate comprises a positive current collector, a positive active material layer arranged on at least one side surface of the positive current collector, the positive active material layer comprising a positive active material and a carbon-coated oxide electrolyte, and a composite coating layer arranged on the surface of the positive active material layer away from the positive current collector, the composite coating layer comprising a solid-state electrolyte and SiO2 aerogel. Compared with the prior art, the application realizes overall good interaction by arranging the composite coating layer comprising the SiO2 aerogel and the solid-state electrolyte on the surface of the positive active material layer with a specific composition, and the obtained positive plate has high ion conduction performance, liquid retention capacity and stability, so that the capacity performance, cycle stability and safety performance of the battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a positive electrode sheet and its manufacturing method, and a secondary battery. Background Technology

[0002] With the rapid development of electric vehicles and portable electronic devices, the demand for batteries with high energy density, long lifespan, and high safety is increasing. While traditional liquid lithium-ion batteries offer high energy density, they suffer from safety concerns such as electrolyte leakage and flammability. Semi-solid-state batteries, which use solid electrolytes to replace most of the liquid electrolyte, offer higher safety and longer cycle life, making them a hot research topic. However, traditional cathode materials struggle to achieve good electrical contact in solid electrolytes, resulting in poor electrochemical performance. Furthermore, the large volume change of the anode during charge and discharge can easily lead to material pulverization and interfacial instability, affecting the battery's cycle stability. Therefore, developing a cathode material that can effectively improve the performance of semi-solid-state batteries is of great significance. Summary of the Invention

[0003] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a positive electrode sheet and its manufacturing method, and a secondary battery, which improves the ion conduction performance, liquid retention capacity, and stability of the positive electrode sheet by setting a composite coating comprising SiO2 aerogel and a solid electrolyte, thereby effectively improving the performance of the semi-solid battery.

[0004] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0005] According to one aspect of the present invention, a positive electrode sheet is provided, comprising:

[0006] Positive current collector;

[0007] A positive electrode active material layer is disposed on at least one side surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material and a carbon-coated oxide electrolyte;

[0008] A composite coating is disposed on the surface of the positive electrode active material layer away from the positive electrode current collector, and the composite coating comprises a solid electrolyte and SiO2 aerogel.

[0009] In some embodiments, the positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0010] And / or, the mass percentage of the positive electrode active material in the positive electrode active material layer is 94%~97%;

[0011] And / or, the carbon-coated oxide electrolyte includes one or more of the following: carbon-coated perovskite oxide electrolyte, carbon-coated garnet oxide electrolyte, carbon-coated anti-perovskite oxide electrolyte, and carbon-coated amorphous oxide electrolyte;

[0012] And / or, the particle size of the carbon-coated oxide electrolyte is 5 nm to 20 nm;

[0013] And / or, the thickness of the carbon coating layer in the carbon-coated oxide electrolyte is 1 nm to 2 nm;

[0014] And / or, the mass percentage of the carbon-coated oxide electrolyte in the positive electrode active material layer is 2% to 5%;

[0015] And / or, the positive electrode active material layer further includes a binder and / or a dispersant.

[0016] In some of these embodiments, the solid electrolyte includes sulfide solid electrolytes and oxide solid electrolytes.

[0017] In some of these embodiments, the sulfide solid electrolyte includes one or more of binary sulfide solid electrolytes, ternary sulfide solid electrolytes, and sulfogermanium sulfide solid electrolytes.

[0018] And / or, the oxide solid electrolyte includes one or more of the following: perovskite oxide solid electrolyte, garnet oxide solid electrolyte, anti-perovskite oxide solid electrolyte, and amorphous oxide solid electrolyte;

[0019] And / or, the particle size of the oxide solid electrolyte is 5 nm to 20 nm;

[0020] And / or, the mass ratio of the sulfide solid electrolyte to the oxide solid electrolyte in the solid electrolyte is (3~4):(1~2).

[0021] In some embodiments, the thickness of the positive electrode active material layer is 0.1 mm to 0.2 mm;

[0022] And / or, the thickness of the composite coating is 5μm~15μm;

[0023] And / or, the composite coating may also include an adhesive.

[0024] According to another aspect of the present invention, the present invention provides a method for manufacturing the positive electrode sheet described above, comprising the following steps:

[0025] a) A positive electrode active material slurry is coated on at least one side of the positive electrode current collector and dried in the first stage to form a positive electrode active material layer;

[0026] b) A solid electrolyte composite silica sol is coated on the surface of the positive electrode active material layer obtained in step a), and after a second drying, a composite coating is formed to obtain the positive electrode sheet.

[0027] In some of these implementations, in step a):

[0028] The positive electrode active material slurry comprises a positive electrode active material, a carbon-coated oxide electrolyte, a binder, a dispersant, and a solvent; wherein, the carbon-coated oxide electrolyte comprises one or more of carbon-coated perovskite oxide electrolyte, carbon-coated garnet oxide electrolyte, carbon-coated anti-perovskite oxide electrolyte, and carbon-coated amorphous oxide electrolyte; and / or, the binder comprises one or more of polyvinyl alcohol, polyacrylic acid, polyvinylpyrrolidone, polymethyl methacrylate, polyethylene oxide, and polyacrylonitrile; and / or, the dispersant comprises one or more of polycarboxylate, polyvinylpyrrolidone, and sodium carboxymethyl cellulose.

[0029] And / or, the solid content of the positive electrode active material slurry is 65%~75%;

[0030] And / or, the viscosity of the positive electrode active material slurry is 2000 mPa·s to 5000 mPa·s.

[0031] In some of these implementations, in step b):

[0032] The preparation method of the solid electrolyte composite silica sol includes: dispersing an organosilicon source in ethanol, adding a solid electrolyte and a binder and mixing them evenly to obtain a mixture; then adding an acidic aqueous solution to the above mixture and stirring evenly to obtain the solid electrolyte composite silica sol.

[0033] Wherein: the organosilicon source includes one or more of tetraethyl orthosilicate, methyl orthosilicate, and tetrabutoxytitanium; and / or, the mass ratio of the organosilicon source to the ethanol is (20~25):100; and / or, the solid electrolyte includes sulfide solid electrolytes and oxide solid electrolytes, wherein the sulfide solid electrolyte includes one or more of binary sulfide solid electrolytes, ternary sulfide solid electrolytes, and sulfide-germanium sulfide solid electrolytes; and / or, the oxide solid electrolyte includes perovskite-type oxide solid electrolytes and garnet-type oxide solid electrolytes. The solid electrolyte is selected from one or more of the following: amorphous oxide solid electrolyte, anti-perovskite oxide solid electrolyte, and amorphous oxide solid electrolyte; and / or, the amount of the solid electrolyte added is 20% to 30% of the mass of the organosilicon source; and / or, the amount of the binder added is 1% to 2% of the mass of the organosilicon source; and / or, the acidic aqueous solution includes one or more of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, and nitric acid aqueous solution; and / or, the mass concentration of the acidic aqueous solution is 20% to 30%; and / or, the amount of the acidic aqueous solution added is 3% to 6% of the mass of the organosilicon source.

[0034] In some of these implementations, in step b):

[0035] The second drying process includes a three-stage drying process: the temperature of the first stage is 60℃~80℃ and the speed is 0.4m / min~0.6m / min; the temperature of the second stage is 80℃~100℃ and the speed is 0.5m / min~1m / min; and the temperature of the third stage is 30℃~50℃ and the speed is 1m / min~2m / min.

[0036] According to another aspect of the present invention, a secondary battery is provided, comprising the positive electrode sheet described in the above technical solution or the positive electrode sheet obtained by the manufacturing method described in the above technical solution.

[0037] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0038] 1. In this embodiment of the invention, the provided positive electrode is a composite positive electrode. By setting a composite coating including SiO2 aerogel and solid electrolyte on the surface of the positive electrode active material layer with a specific composition, a better overall interaction is achieved: SiO2 aerogel, as the framework of the composite coating, can provide a rich porous structure and buffer the volume expansion problem of the negative electrode during cycling. The carbon-coated oxide solid electrolyte distributed in the positive electrode active material layer and the solid electrolyte (especially oxide solid electrolyte) in the SiO2 aerogel framework work together to promote the formation of efficient Li-ion exchange between the positive electrode, coating, and negative electrode. +Transmission network; while sulfide solid electrolytes have excellent ion conduction ability, which can reduce the amount of electrolyte used. Therefore, this composite positive electrode has high ion conduction performance, liquid retention capacity and stability, thereby improving the battery's capacity utilization, cycle stability and safety performance.

[0039] 2. In a preferred embodiment of the present invention, SiO2 aerogel and solid electrolyte are combined into one by means of sol-gel method, and further coated on the surface of the positive electrode active material layer of the positive electrode sheet to form a composite positive electrode sheet with excellent comprehensive performance. Compared with similar composite positive electrode sheets in the prior art, the preparation process of the present invention is simple, low in cost, and easy to realize industrial production.

[0040] 3. In a preferred embodiment of the present invention, the surface of the provided positive electrode sheet has a rich porous structure, which can buffer the volume expansion caused by the negative electrode material. The internal resistance of the battery prepared by using the positive electrode sheet is low, which is beneficial to the capacity utilization, and the cycle performance and safety performance are also significantly improved.

[0041] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0042] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0043] Figure 1 This is a schematic diagram of the structure of the cathode material provided by the present invention.

[0044] Figure 2 This is a SEM image of a partial cross-section of the composite positive electrode sheet prepared in Example 1 of the present invention.

[0045] Explanation of reference numerals in the attached figures:

[0046] 1—Composite coating; 2—Positive electrode active material layer; 3—Positive electrode current collector.

[0047] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0048] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0049] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0050] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0051] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0052] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0053] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0054] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0055] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0056] Currently, semi-solid batteries offer higher safety and longer cycle life due to the use of solid electrolytes to replace most liquid electrolytes. However, traditional cathode materials struggle to achieve good electrical contact in solid electrolytes, resulting in poor electrochemical performance. Furthermore, the large volume change of the anode during charging and discharging can easily lead to material pulverization and interface instability, thus affecting the battery's cycle stability.

[0057] Building upon this, the present invention improves the structure and material composition of the positive electrode by integrating SiO2 aerogel with a solid electrolyte and coating it onto the surface of the positive electrode. This forms a composite coating that isolates the positive and negative electrodes, exhibits high ion conductivity, good stability, and good liquid retention. Combined with the carbon-coated oxide electrolyte in the positive electrode active material layer, this promotes the efficient formation of lithium ions between the positive electrode, coating, and negative electrode. + The transmission network yields a positive electrode sheet with high ion conduction performance, liquid retention capacity, and stability. Using this positive electrode sheet to further prepare a membrane-free semi-solid battery results in a battery with low internal resistance, which is beneficial for capacity utilization. Furthermore, the cycle performance and safety performance are significantly improved, thereby solving the technical problems existing in the prior art.

[0058] Specifically, the present invention adopts the following technical solution:

[0059] According to one aspect of the present invention, a positive electrode sheet is provided, comprising:

[0060] Positive current collector;

[0061] A positive electrode active material layer is disposed on at least one side surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material and a carbon-coated oxide electrolyte;

[0062] A composite coating is disposed on the surface of the positive electrode active material layer away from the positive electrode current collector, and the composite coating comprises a solid electrolyte and SiO2 aerogel.

[0063] Please see Figure 1 As shown, Figure 1 This is a schematic diagram of the structure of the positive electrode material provided by the present invention, wherein 1 is a composite coating, 2 is a positive electrode active material layer, and 3 is a positive electrode current collector.

[0064] In a specific embodiment of the present invention, the positive electrode current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode active material layer is disposed on one or both of the two opposite surfaces of the positive electrode current collector. The positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as a metal foil; the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer; the composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0065] In a specific embodiment of the present invention, the positive electrode active material layer is disposed on at least one side surface of the positive electrode current collector; the positive electrode active material layer includes a positive electrode active material and a carbon-coated oxide electrolyte; wherein, the positive electrode active material preferably includes one or more of lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt aluminum oxide (NCA), more preferably lithium nickel cobalt manganese oxide (NCM); the present invention does not have any special restrictions on the source of the positive electrode active material, and commercially available products well known to those skilled in the art can be used.

[0066] In a specific embodiment of the present invention, the mass percentage of the positive electrode active material in the positive electrode active material layer is preferably 94% to 97%, specifically 94%, 95%, 96%, 97%, etc.

[0067] In specific embodiments of the present invention, the carbon-coated oxide electrolyte preferably includes one or more of carbon-coated perovskite (LLTO) oxide electrolyte, carbon-coated garnet (LLZO) oxide electrolyte, carbon-coated anti-perovskite oxide electrolyte, and carbon-coated amorphous (LiPON) oxide electrolyte; in a preferred embodiment of the present invention, the carbon-coated oxide electrolyte is a carbon-coated lithium titanium aluminum phosphate solid electrolyte; the present invention does not impose any special restrictions on the source of the carbon-coated oxide electrolyte, and commercially available products or self-made products well known to those skilled in the art can be used.

[0068] The inventors of this invention discovered that since traditional oxide electrolytes conduct ions but not electrons, directly applying them to the positive electrode active material layer would reduce the conductivity of the positive electrode. Based on this, the inventors further investigated and found that by carbon coating the oxide electrolyte, the impact of introducing the oxide electrolyte on the conductivity of the electrode can be reduced.

[0069] In a specific embodiment of the present invention, the particle size of the carbon-coated oxide electrolyte is preferably 5nm~20nm, specifically 5nm, 10nm, 15nm, 20nm, etc.; this facilitates its dispersion in the positive electrode active material layer and better achieves its effect of promoting lithium-ion transport.

[0070] In a specific embodiment of the present invention, the thickness of the carbon coating layer in the carbon-coated oxide electrolyte is 1 nm to 2 nm, which further promotes the transport of lithium ions between the positive electrode, the coating, and the negative electrode.

[0071] In a specific embodiment of the present invention, the mass percentage of the carbon-coated oxide electrolyte in the positive electrode active material layer is preferably 2% to 5%, specifically 2%, 3%, 4%, 5%, etc. The present invention selects a suitable ratio, which is beneficial for the carbon-coated oxide electrolyte to achieve better interaction with other components in the positive electrode active material layer, thereby exerting a better effect.

[0072] In a specific embodiment of the present invention, the positive electrode active material layer preferably further includes a binder and / or a dispersant; wherein the binder preferably includes one or more of polyvinyl alcohol, polyacrylic acid, polyvinylpyrrolidone, polymethyl methacrylate, polyethylene oxide, and polyacrylonitrile, more preferably polyvinyl alcohol; the dispersant preferably includes one or more of polycarboxylate, polyvinylpyrrolidone, and sodium carboxymethyl cellulose, more preferably polyvinylpyrrolidone; the present invention does not have any special restrictions on the source of the binder and dispersant, and commercially available products well known to those skilled in the art can be used. The addition of the above-mentioned functional additives to the positive electrode active material layer in the present invention can better promote the bonding and dispersion of the positive electrode active material and the carbon-coated oxide electrolyte, thereby giving the positive electrode active material layer a better application effect.

[0073] In a specific embodiment of the present invention, the thickness of the positive electrode active material layer is preferably 0.1 mm to 0.2 mm.

[0074] In a specific embodiment of the present invention, the composite coating is disposed on the surface of the positive electrode active material layer away from the positive electrode current collector, and on this basis, the positive electrode active material layer is disposed between the positive electrode current collector and the composite coating.

[0075] In a specific embodiment of the present invention, the composite coating includes a solid electrolyte and a SiO2 aerogel; wherein, the solid electrolyte preferably includes a sulfide solid electrolyte and an oxide solid electrolyte, more preferably composed of a sulfide solid electrolyte and an oxide solid electrolyte. The present invention uses the above two solid electrolytes in synergy, which has the following advantages: (1) Improved ionic conductivity: The sulfide solid electrolyte has a high ionic conductivity at room temperature, close to the performance of liquid electrolyte, and can support room temperature fast charging, which is suitable for high energy density demand scenarios such as electric vehicles and drones; while the oxide solid electrolyte has a low ionic conductivity at room temperature, its performance can be improved by high temperature or interface modification; the combination of the two can combine the advantages of both and improve the overall conductivity of the electrolyte. (2) Enhanced battery performance: The sulfide electrolyte has good ductility and can form a tight contact with the electrode, reduce the interface impedance, and improve the charging and discharging efficiency of the battery; at the same time, the oxide electrolyte has the characteristics of high stability, high temperature resistance and strong oxidation resistance, which can improve the safety of the battery; the combination can take into account both the high performance and safety of the battery. (3) Reduce costs and improve industrialization feasibility: Oxide solid electrolytes have mature manufacturing processes, are compatible with traditional lithium-ion battery production equipment, and have relatively low costs, making them suitable for large-scale production; while sulfide electrolytes have high conductivity, their production process is complex and costly; therefore, by using them in combination, overall production costs can be reduced while ensuring high performance, thus improving industrialization feasibility. (4) Improve safety and stability: Oxide solid electrolytes are stable in air, resistant to high temperatures, have strong oxidation resistance, are not prone to side reactions with lithium metal anodes, have low risk of thermal runaway, and have outstanding safety; while sulfide electrolytes have high conductivity, but poor chemical stability and are prone to reaction with high-voltage cathode materials; therefore, using them in combination can combine the advantages of both to improve the overall safety and stability of the battery.

[0076] In this invention, the structure of the SiO2 aerogel is easy to prepare and control. As a framework for the composite coating, it can provide a rich porous structure and buffer the volume expansion of the negative electrode during cycling. The solid electrolyte is uniformly distributed in the SiO2 aerogel framework, wherein the oxide solid electrolyte can promote the efficient formation of lithium ions between the positive electrode, coating, and negative electrode. + The transmission network, wherein the sulfide solid electrolyte has excellent ion conduction ability, which can reduce the amount of electrolyte used. At the same time, the two are combined with SiO2 aerogel to achieve good overall interaction, forming a composite coating that can isolate the positive and negative electrodes, has high ion conduction ability, good stability and good liquid retention. The further prepared composite positive electrode sheet can improve the battery's capacity, cycle stability and safety performance.

[0077] In specific embodiments of the present invention, the sulfide solid electrolyte preferably includes one or more of binary sulfide solid electrolytes, ternary sulfide solid electrolytes, and sulfide-germanium ore type sulfide solid electrolytes; the present invention does not impose any special restrictions on the source of the sulfide solid electrolyte, and commercially available products well known to those skilled in the art can be used. In a preferred embodiment of the present invention, the sulfide solid electrolyte is Li6PS5Cl.

[0078] In specific embodiments of the present invention, the oxide solid electrolyte includes one or more of perovskite (LLTO) oxide solid electrolyte, garnet (LLZO) oxide solid electrolyte, anti-perovskite oxide solid electrolyte, and amorphous (LiPON) oxide solid electrolyte. The present invention does not impose any special restrictions on the source of the oxide solid electrolyte; commercially available products well-known to those skilled in the art can be used. In a preferred embodiment of the present invention, the oxide solid electrolyte is lithium aluminum titanium phosphate solid electrolyte.

[0079] In a specific embodiment of the present invention, the particle size of the oxide solid electrolyte is preferably 5nm~20nm, specifically 5nm, 10nm, 15nm, 20nm, etc.; this facilitates its dispersion in the composite coating, thereby enabling better interaction with other components and improving the overall performance of the composite coating.

[0080] In a specific embodiment of the present invention, the preferred mass ratio of the sulfide solid electrolyte to the oxide solid electrolyte in the solid electrolyte is (3~4):(1~2). The present invention selects a suitable ratio, which facilitates better interaction between the two in the composite coating, thereby achieving better results.

[0081] In a specific embodiment of the present invention, the composite coating preferably further includes an adhesive; the adhesive preferably includes one or more of polyvinyl alcohol, polyacrylic acid, polyvinylpyrrolidone, polymethyl methacrylate, polyethylene oxide, and polyacrylonitrile, more preferably polyvinylpyrrolidone; the present invention does not have any special restrictions on the source of the adhesive, and commercially available products well known to those skilled in the art can be used. The addition of the above-mentioned adhesive to the composite coating in the present invention can better promote the bonding of the solid electrolyte and SiO2 aerogel, thereby giving the composite coating a better application effect.

[0082] In a specific embodiment of the present invention, the thickness of the composite coating is preferably 5μm to 15μm; the present invention uses a composite coating of suitable thickness, which is beneficial to reduce the internal resistance of the battery and improve its electrical performance.

[0083] According to another aspect of the present invention, the present invention provides a method for manufacturing the positive electrode sheet described above, comprising the following steps:

[0084] a) A positive electrode active material slurry is coated on at least one side of the positive electrode current collector and dried in the first stage to form a positive electrode active material layer;

[0085] b) A solid electrolyte composite silica sol is coated on the surface of the positive electrode active material layer obtained in step a), and after a second drying, a composite coating is formed to obtain the positive electrode sheet.

[0086] This invention first coats a positive electrode active material slurry onto at least one surface of the positive electrode current collector, and then dries it to form a positive electrode active material layer. In specific embodiments of this invention, the positive electrode current collector is the same as described in the above technical solutions, and will not be repeated here. Preferably, the positive electrode active material slurry is coated onto one surface of the positive electrode current collector. Specifically, the positive electrode current collector has two surfaces along its thickness direction, and the positive electrode active material slurry can be coated onto either one surface; this invention does not have any particular limitation in this regard.

[0087] In a specific embodiment of the present invention, the coating method is preferably a transfer coating machine well known to those skilled in the art, which can ensure that the slurry is uniformly coated on the surface of the positive electrode current collector. The present invention does not have any special limitations in this regard.

[0088] In a specific embodiment of the present invention, the positive electrode active material slurry preferably includes a positive electrode active material, a carbon-coated oxide electrolyte, a binder, a dispersant, and a solvent; wherein, the positive electrode active material and the carbon-coated oxide electrolyte are the same as those described in the above technical solutions, and will not be repeated here.

[0089] In specific embodiments of the present invention, the adhesive preferably includes one or more of polyvinyl alcohol, polyacrylic acid, polyvinylpyrrolidone, polymethyl methacrylate, polyethylene oxide, and polyacrylonitrile, more preferably polyvinyl alcohol; the present invention does not impose any special restrictions on the source of the adhesive, and commercially available products well known to those skilled in the art can be used.

[0090] In specific embodiments of the present invention, the dispersant preferably includes one or more of polycarboxylate, polyvinylpyrrolidone, and sodium carboxymethyl cellulose, more preferably polyvinylpyrrolidone; the present invention does not impose any special restrictions on the source of the binder, and commercially available products well known to those skilled in the art can be used.

[0091] In a specific embodiment of the present invention, the preferred mass ratio of the positive electrode active material, carbon-coated oxide electrolyte, binder, and dispersant in the positive electrode active material slurry is (94~97):(2~5):(0.1~1):(0.1~1), more preferably (94~95):(4~5):0.5:0.5. By using the above-mentioned suitable ratio, the present invention can ensure that the subsequently obtained positive electrode active material slurry has good performance, thereby further obtaining a positive electrode active material layer that meets the performance requirements of the present invention.

[0092] In a specific embodiment of the present invention, the solvent is used to dissolve and disperse the above-mentioned raw materials to form a slurry with a certain solid content and viscosity, thereby meeting the requirements for subsequent coating; in a preferred embodiment of the present invention, the solvent is N-methyl-2-pyrrolidone (NMP); the solid content of the positive electrode active material slurry is preferably 65%~75%, specifically it can be 65%, 70%, 75%, etc.; the viscosity of the positive electrode active material slurry is preferably 2000mPa·s~5000mPa·s, specifically it can be 2000mPa·s, 3000mPa·s, 4000mPa·s, 5000mPa·s, etc.

[0093] In a specific embodiment of the present invention, the first drying process can employ a drying method well-known to those skilled in the art, the purpose of which is to solidify and shape the coated positive electrode active material slurry to form a positive electrode active material layer. In this invention, the positive electrode active material layer is the same as described in the above technical solutions, and will not be repeated here.

[0094] After obtaining the positive electrode active material layer, the present invention coats the surface of the obtained positive electrode active material layer with a solid electrolyte composite silica sol, and after a second drying, forms a composite coating to obtain a positive electrode sheet.

[0095] In a specific embodiment of the present invention, the preparation method of the solid electrolyte composite silica sol preferably includes: dispersing an organosilicon source in ethanol, adding a solid electrolyte and a binder and mixing them evenly to obtain a mixture; then adding an acidic aqueous solution to the mixture and stirring evenly to obtain the solid electrolyte composite silica sol.

[0096] In a specific embodiment of the present invention, the organosilicon source preferably includes one or more of tetraethyl orthosilicate, methyl orthosilicate, and tetrabutoxytitanium, more preferably tetraethyl orthosilicate; the present invention does not have any special restrictions on the source of the organosilicon source, and commercially available products well known to those skilled in the art can be used.

[0097] In specific embodiments of the present invention, the ethanol used can be commercially available anhydrous ethanol known to those skilled in the art, and the present invention does not have any special restrictions on this.

[0098] In a specific embodiment of the present invention, the preferred mass ratio of the organosilicon source to the ethanol is (20~25):100, specifically it can be 20:100, 21:100, 22:100, 23:100, 24:100, 25:100, etc.

[0099] In a specific embodiment of the present invention, the solid electrolyte and binder are the same as those described in the above technical solution, and will not be repeated here.

[0100] In a specific embodiment of the present invention, the amount of solid electrolyte added is preferably 20% to 30% of the mass of the organosilicon source, specifically 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc. In a preferred embodiment of the present invention, the solid electrolyte is composed of a sulfide solid electrolyte and an oxide solid electrolyte, wherein the amount of sulfide solid electrolyte added is preferably 15% to 20% of the mass of the organosilicon source, and the amount of oxide solid electrolyte added is preferably 5% to 10% of the mass of the organosilicon source. By using the above-mentioned suitable addition amounts, the present invention can ensure that the subsequently obtained solid electrolyte composite silica sol has good performance, thereby further obtaining a composite coating that meets the performance requirements of the present invention.

[0101] In a specific embodiment of the present invention, the amount of adhesive added is preferably 1% to 2% of the mass of the organosilicon source, specifically 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc., thereby achieving a better bonding effect.

[0102] In a specific embodiment of the present invention, it is preferable to slowly add an acidic aqueous solution to the above-mentioned mixture to ensure the formation of silica sol; the acidic aqueous solution preferably includes one or more of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, and nitric acid aqueous solution, more preferably hydrochloric acid aqueous solution; the mass concentration of the acidic aqueous solution is preferably 20% to 30%. The present invention does not impose any special restrictions on the source of the acidic aqueous solution, and commercially available products or laboratory-made products well known to those skilled in the art can be used.

[0103] In a specific embodiment of the present invention, the amount of acidic aqueous solution added is preferably 3% to 6% of the mass of the organosilicon source, specifically 3%, 4%, 5%, 6%, etc. The present invention uses the above-mentioned suitable amount of acidic aqueous solution to ensure that the desired solid electrolyte composite silica sol is successfully obtained.

[0104] In a specific embodiment of the present invention, the coating method is preferably a transfer coating machine well known to those skilled in the art, which can ensure that the above-mentioned solid electrolyte composite silica sol is uniformly coated on the surface of the positive electrode active material layer. The present invention does not have any special limitations in this regard.

[0105] In a specific embodiment of the present invention, the second drying process preferably includes: a three-stage drying process, wherein the temperature of the first stage drying is 60℃~80℃ and the speed is 0.4m / min~0.6m / min; the temperature of the second stage drying is 80℃~100℃ and the speed is 0.5m / min~1m / min; and the temperature of the third stage drying is 30℃~50℃ and the speed is 1m / min~2m / min.

[0106] A more preferred method is to employ a three-stage drying process: the first stage drying temperature is 70℃ and the speed is 0.5m / min; the second stage drying temperature is 90℃ and the speed is 0.8m / min; and the third stage drying temperature is 40℃ and the speed is 1.5m / min.

[0107] The present invention employs the above-mentioned three-stage drying process. The first stage uses the above-mentioned specific temperature range, which enables the silica sol to fully cross-link and form a uniform and stable network structure. The second stage uses the above-mentioned specific temperature range to fully dry the solid electrolyte and silica sol. The third stage uses the above-mentioned specific temperature range to achieve slow cooling and finally form a composite coating, thereby obtaining the positive electrode sheet required by the present invention.

[0108] The present invention does not impose any special restrictions on the implementation of the above three-stage drying process; each stage of drying can be carried out using an oven well known to those skilled in the art.

[0109] This invention combines SiO2 aerogel with a solid electrolyte using a sol-gel method, and then coats the combined aerogel onto the surface of the positive electrode active material layer of the positive electrode sheet to form a composite positive electrode sheet with excellent overall performance. This composite positive electrode sheet has excellent ion conduction and liquid retention capabilities, while its porous surface structure can buffer the volume expansion of the negative electrode sheet. Furthermore, compared with existing technologies, the manufacturing method provided by this invention is simple, low-cost, and easy to implement for industrial production.

[0110] According to another aspect of the present invention, a secondary battery is provided, comprising the positive electrode sheet described in the above-described technical solution or the positive electrode sheet obtained by the manufacturing method described in the above-described technical solution. Thus, the secondary battery possesses all the features and advantages of the positive electrode sheet described in the above-described technical solution, which will not be repeated here.

[0111] Specifically, the secondary battery is a membrane-free semi-solid-state battery, preferably manufactured by stacking positive and negative electrode sheets (without a separator). In a preferred embodiment of the present invention, the preparation process of the membrane-free semi-solid-state battery includes: stacking the positive and negative electrode sheets provided by the present invention (so that the composite coating side of the positive electrode sheet is attached to the negative electrode sheet), welding tabs, and then top-side sealing, followed by drying, electrolyte injection, formation, capacity testing, and venting and sealing to obtain a membrane-free semi-solid-state battery. The specific conditions and parameters of each step in the above preparation process can adopt technical solutions for preparing membrane-free semi-solid-state batteries well known to those skilled in the art, and the present invention does not have any special limitations in this regard; for example, the positive and negative electrode sheets can be stacked in sequence to obtain an electrode assembly, and then the stacked electrode assembly can be welded with tabs and placed in an aluminum-plastic film for top-side sealing, dried, injected with conventional electrolyte, sealed, and subjected to formation treatment, and finally capacity testing, venting and sealing to obtain a membrane-free semi-solid-state battery.

[0112] In a specific embodiment of the present invention, the negative electrode sheet can be any negative electrode sheet known to those skilled in the art for preparing a membrane-free semi-solid-state battery. In a preferred embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; wherein, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector. The negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as a metal foil; the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer; the composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0113] In a preferred embodiment of the present invention, the negative electrode active material layer comprises a negative electrode active material, a binder, and a conductive agent; wherein, the negative electrode active material comprises one or more of natural graphite, artificial graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-carbon composite material (Si / C), and SiOx, more preferably natural graphite and / or artificial graphite; the binder comprises one or more of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS); the conductive agent may comprise one or more of conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The present invention does not impose any special restrictions on the source of the above-mentioned negative electrode active material, binder, and conductive agent; commercially available products well known to those skilled in the art can be used. In this invention, the preferred mass ratio of negative electrode active material, binder and conductive agent in the negative electrode active material layer is (95~98):(1~3):(1~2).

[0114] In a specific embodiment of the present invention, the thickness of the negative electrode active material layer is preferably 0.1 mm to 0.2 mm.

[0115] The present invention does not impose any special restrictions on the manufacturing method of the negative electrode sheet. The negative electrode sheet can be obtained by coating a negative electrode slurry, which includes the above-mentioned negative electrode active material, binder and conductive agent, onto the negative electrode current collector and then performing processes such as drying and cold pressing.

[0116] In a specific embodiment of the present invention, the secondary battery may include an outer packaging for encapsulation. Specifically, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or it may be a soft pack, such as a pouch-type soft pack; the material of the soft pack may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0117] The present invention does not impose any particular limitation on the shape of the secondary battery, which can be cylindrical, square or other arbitrary shapes, and those skilled in the art can choose according to specific practical needs.

[0118] In this invention, the secondary battery provided adopts the positive electrode sheet described in the above-mentioned technical solution of this invention. The surface of the positive electrode sheet has a rich porous structure, which can buffer the volume expansion caused by the negative electrode material. The internal resistance of the battery prepared by using the positive electrode sheet is low, which is conducive to the capacity utilization, and the cycle performance and safety performance are also significantly improved.

[0119] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0120] Example 1

[0121] (1) Preparation of composite cathode:

[0122] 662g of lithium nickel cobalt manganese oxide, 31g of carbon-coated lithium titanium aluminum phosphate solid electrolyte, 3.5g of polyvinyl alcohol, and 3.5g of polyvinylpyrrolidone were added to 300g of N-methyl-2-pyrrolidone (NMP) and stirred until uniformly dispersed. The mixture was then coated onto the surface of an aluminum foil current collector with a thickness of 15μm using a transfer coating machine. After drying, a positive electrode sheet with a positive active material layer thickness of 0.12mm was obtained.

[0123] 40g of tetraethyl orthosilicate was dispersed in 160g of anhydrous ethanol, followed by the addition of 6g of Li6PS5Cl, 3.2g of lithium titanium aluminum phosphate solid electrolyte and 0.8g of polyvinylpyrrolidone. After stirring until uniform, 2g of 25% hydrochloric acid aqueous solution was slowly added to the mixture and stirred until uniform to obtain solid electrolyte composite silica sol.

[0124] The prepared solid electrolyte composite silica sol was coated onto the surface of the prepared positive electrode using a transfer coating machine. After drying (using a three-stage drying process: the first stage temperature was 70℃ and the speed was 0.5m / min; the second stage temperature was 90℃ and the speed was 0.8m / min; the third stage temperature was 40℃ and the speed was 1.5m / min), a composite positive electrode coated with solid electrolyte-SiO2 aerogel was obtained. The thickness of the solid electrolyte-SiO2 aerogel composite coating on the surface of the composite positive electrode was 10±2μm.

[0125] The SEM image of a partial cross-section of the composite cathode prepared in Example 1 is shown below. Figure 2 As shown; from Figure 2 The microstructure diagram shows that the solid electrolyte-SiO2 aerogel composite coating has a rich pore structure, which can better buffer the volume expansion caused by the negative electrode material.

[0126] (2) Preparation of membrane-free semi-solid-state batteries:

[0127] The composite positive electrode sheet prepared in step (1) is stacked with the negative electrode sheet (the negative electrode current collector is a copper foil current collector with a thickness of 5 μm; the negative electrode active material is graphite material, the mass ratio of graphite, binder and conductive carbon is 96.5:2:1.5, and the thickness of the negative electrode active material layer is 0.14 mm). After welding the tabs, the top and side are sealed, dried, injected with liquid, formed, capacity tested, and vented and sealed to obtain a membrane-free semi-solid battery.

[0128] Example 2

[0129] (1) Preparation of composite cathode:

[0130] 665g of lithium nickel cobalt manganese oxide, 28g of carbon-coated lithium titanium aluminum phosphate solid electrolyte, 3.5g of polyvinyl alcohol, and 3.5g of polyvinylpyrrolidone were added to 300g of N-methyl-2-pyrrolidone (NMP) and stirred until uniformly dispersed. The mixture was then coated onto the surface of an aluminum foil current collector with a thickness of 15μm using a transfer coating machine. After drying, a positive electrode sheet with a positive active material layer thickness of 0.12mm was obtained.

[0131] 40g of tetraethyl orthosilicate was dispersed in 160g of anhydrous ethanol, followed by the addition of 6g of Li6PS5Cl, 3.2g of lithium titanium aluminum phosphate solid electrolyte and 0.8g of polyvinylpyrrolidone. After stirring until uniform, 2g of 25% hydrochloric acid aqueous solution was slowly added to the mixture and stirred until uniform to obtain solid electrolyte composite silica sol.

[0132] The prepared solid electrolyte composite silica sol was coated onto the surface of the prepared positive electrode using a transfer coating machine. After drying (using a three-stage drying process: the first stage temperature was 70℃ and the speed was 0.5m / min; the second stage temperature was 90℃ and the speed was 0.8m / min; the third stage temperature was 40℃ and the speed was 1.5m / min), a composite positive electrode coated with solid electrolyte-SiO2 aerogel was obtained. The thickness of the solid electrolyte-SiO2 aerogel composite coating on the surface of the composite positive electrode was 10±2μm.

[0133] (2) Preparation of membrane-free semi-solid-state batteries:

[0134] The composite positive electrode sheet prepared in step (1) is stacked with the negative electrode sheet (the negative electrode current collector is a copper foil current collector with a thickness of 5 μm; the negative electrode active material is graphite material, the mass ratio of graphite, binder and conductive carbon is 96.5:2:1.5, and the thickness of the negative electrode active material layer is 0.14 mm). After welding the tabs, the top and side are sealed, dried, injected with liquid, formed, capacity tested, and vented and sealed to obtain a membrane-free semi-solid battery.

[0135] Example 3

[0136] (1) Preparation of composite cathode:

[0137] 662g of lithium nickel cobalt manganese oxide, 31g of carbon-coated lithium titanium aluminum phosphate solid electrolyte, 3.5g of polyvinyl alcohol, and 3.5g of polyvinylpyrrolidone were added to 300g of N-methyl-2-pyrrolidone (NMP) and stirred until uniformly dispersed. The mixture was then coated onto the surface of an aluminum foil current collector with a thickness of 15μm using a transfer coating machine. After drying, a positive electrode sheet with a positive active material layer thickness of 0.12mm was obtained.

[0138] 40g of tetraethyl orthosilicate was dispersed in 160g of anhydrous ethanol, followed by the addition of 8g of Li6PS5Cl, 3.2g of lithium titanium aluminum phosphate solid electrolyte and 0.8g of polyvinylpyrrolidone. After stirring until homogeneous, 2g of 25% hydrochloric acid aqueous solution was slowly added to the mixture and stirred until homogeneous to obtain solid electrolyte composite silica sol.

[0139] The prepared solid electrolyte composite silica sol was coated onto the surface of the prepared positive electrode using a transfer coating machine. After drying (using a three-stage drying process: the first stage temperature was 70℃ and the speed was 0.5m / min; the second stage temperature was 90℃ and the speed was 0.8m / min; the third stage temperature was 40℃ and the speed was 1.5m / min), a composite positive electrode coated with solid electrolyte-SiO2 aerogel was obtained. The thickness of the solid electrolyte-SiO2 aerogel composite coating on the surface of the composite positive electrode was 10±2μm.

[0140] (2) Preparation of membrane-free semi-solid-state batteries:

[0141] The composite positive electrode sheet prepared in step (1) is stacked with the negative electrode sheet (the negative electrode current collector is a copper foil current collector with a thickness of 5 μm; the negative electrode active material is graphite material, the mass ratio of graphite, binder and conductive carbon is 96.5:2:1.5, and the thickness of the negative electrode active material layer is 0.14 mm). After welding the tabs, the top and side are sealed, dried, injected with liquid, formed, capacity tested, and vented and sealed to obtain a membrane-free semi-solid battery.

[0142] Example 4

[0143] (1) Preparation of composite cathode:

[0144] 662g of lithium nickel cobalt manganese oxide, 31g of carbon-coated lithium titanium aluminum phosphate solid electrolyte, 3.5g of polyvinyl alcohol, and 3.5g of polyvinylpyrrolidone were added to 300g of N-methyl-2-pyrrolidone (NMP) and stirred until uniformly dispersed. The mixture was then coated onto the surface of an aluminum foil current collector with a thickness of 15μm using a transfer coating machine. After drying, a positive electrode sheet with a positive active material layer thickness of 0.12mm was obtained.

[0145] 40g of tetraethyl orthosilicate was dispersed in 160g of anhydrous ethanol, followed by the addition of 6g of Li6PS5Cl, 4g of lithium titanium aluminum phosphate solid electrolyte and 0.8g of polyvinylpyrrolidone. After stirring until uniform, 2g of 25% hydrochloric acid aqueous solution was slowly added to the mixture and stirred until uniform to obtain solid electrolyte composite silica sol.

[0146] The prepared solid electrolyte composite silica sol was coated onto the surface of the prepared positive electrode using a transfer coating machine. After drying (using a three-stage drying process: the first stage temperature was 70℃ and the speed was 0.5m / min; the second stage temperature was 90℃ and the speed was 0.8m / min; the third stage temperature was 40℃ and the speed was 1.5m / min), a composite positive electrode coated with solid electrolyte-SiO2 aerogel was obtained. The thickness of the solid electrolyte-SiO2 aerogel composite coating on the surface of the composite positive electrode was 10±2μm.

[0147] (2) Preparation of membrane-free semi-solid-state batteries:

[0148] The composite positive electrode sheet prepared in step (1) is stacked with the negative electrode sheet (the negative electrode current collector is a copper foil current collector with a thickness of 5 μm; the negative electrode active material is graphite material, the mass ratio of graphite, binder and conductive carbon is 96.5:2:1.5, and the thickness of the negative electrode active material layer is 0.14 mm). After welding the tabs, the top and side are sealed, dried, injected with liquid, formed, capacity tested, and vented and sealed to obtain a membrane-free semi-solid battery.

[0149] Example 5

[0150] (1) Preparation of composite cathode:

[0151] 662g of lithium nickel cobalt manganese oxide, 31g of carbon-coated lithium titanium aluminum phosphate solid electrolyte, 3.5g of polyvinyl alcohol, and 3.5g of polyvinylpyrrolidone were added to 300g of N-methyl-2-pyrrolidone (NMP) and stirred until uniformly dispersed. The mixture was then coated onto the surface of an aluminum foil current collector with a thickness of 15μm using a transfer coating machine. After drying, a positive electrode sheet with a positive active material layer thickness of 0.12mm was obtained.

[0152] 40g of tetraethyl orthosilicate was dispersed in 160g of anhydrous ethanol, followed by the addition of 6g of Li6PS5Cl, 2g of lithium aluminum titanium phosphate solid electrolyte and 0.8g of polyvinylpyrrolidone. After stirring until uniform, 2g of 25% hydrochloric acid aqueous solution was slowly added to the mixture and stirred until uniform to obtain solid electrolyte composite silica sol.

[0153] The prepared solid electrolyte composite silica sol was coated onto the surface of the prepared positive electrode using a transfer coating machine. After drying (using a three-stage drying process: the first stage temperature was 70℃ and the speed was 0.5m / min; the second stage temperature was 90℃ and the speed was 0.8m / min; the third stage temperature was 40℃ and the speed was 1.5m / min), a composite positive electrode coated with solid electrolyte-SiO2 aerogel was obtained. The thickness of the solid electrolyte-SiO2 aerogel composite coating on the surface of the composite positive electrode was 10±2μm.

[0154] (2) Preparation of membrane-free semi-solid-state batteries:

[0155] The composite positive electrode sheet prepared in step (1) is stacked with the negative electrode sheet (the negative electrode current collector is a copper foil current collector with a thickness of 5 μm; the negative electrode active material is graphite material, the mass ratio of graphite, binder and conductive carbon is 96.5:2:1.5, and the thickness of the negative electrode active material layer is 0.14 mm). After welding the tabs, the top and side are sealed, dried, injected with liquid, formed, capacity tested, and vented and sealed to obtain a membrane-free semi-solid battery.

[0156] Comparative Example 1

[0157] The composite positive electrode and the membrane-free semi-solid battery were obtained sequentially using the manufacturing method provided in Example 1. The only difference is that in step (1) the preparation of the composite positive electrode, carbon-coated lithium titanium aluminum phosphate solid electrolyte is not added.

[0158] Comparative Example 2

[0159] The composite positive electrode and the membrane-free semi-solid battery were obtained sequentially using the manufacturing method provided in Example 1. The only difference is that in step (1) the preparation of the composite positive electrode, the sulfide solid electrolyte Li6PS5Cl is not added.

[0160] Comparative Example 3

[0161] The composite positive electrode and the membraneless semi-solid battery were obtained sequentially by the manufacturing method provided in Example 1. The difference is that in step (1) the preparation of the composite positive electrode, SiO2 particles of equal mass were used to replace SiO2 aerogel, and the solid electrolyte, SiO2 and binder were directly coated on the surface of the positive electrode.

[0162] Comparative Example 4

[0163] The composite positive electrode and the membrane-free semi-solid battery were obtained sequentially using the manufacturing method provided in Example 1. The only difference is that in step (1) the preparation of the composite positive electrode, the drying process after the solid electrolyte composite silica sol is coated on the surface of the positive electrode is different: the temperature of the first stage is 120°C and the speed is 0.5m / min; the temperature of the second stage is 90°C and the speed is 0.6m / min; the temperature of the third stage is 40°C and the speed is 1.5m / min.

[0164] Comparative Example 5

[0165] The composite positive electrode and the membrane-free semi-solid battery were obtained sequentially using the manufacturing method provided in Example 1. The only difference is that in step (1) the preparation of the composite positive electrode, the thickness of the solid electrolyte-SiO2 aerogel composite coating is 25±2μm.

[0166] Comparative Example 6

[0167] (1) Preparation of the positive electrode:

[0168] 662g of lithium nickel cobalt manganese oxide, 31g of carbon-coated lithium titanium aluminum phosphate solid electrolyte, 3.5g of polyvinyl alcohol, and 3.5g of polyvinylpyrrolidone were added to 300g of N-methyl-2-pyrrolidone (NMP) and stirred until uniformly dispersed. The mixture was then coated onto the surface of an aluminum foil current collector with a thickness of 15μm using a transfer coating machine. After drying, a positive electrode sheet with a positive active material layer thickness of 0.12mm was obtained.

[0169] (2) Preparation of semi-solid-state batteries:

[0170] The positive electrode, separator, and negative electrode prepared in step (1) are stacked together (the negative electrode current collector is a copper foil current collector with a thickness of 5 μm; the negative electrode active material is graphite material, and the mass ratio of graphite, binder, and conductive carbon is 96.5:2:1.5, and the thickness of the negative electrode active material layer is 0.14 mm). The separator is a conventional polyethylene separator coated with a 3 μm alumina ceramic layer, which is placed between the positive electrode and the negative electrode. After welding the tabs, the top and side are sealed, dried, injected with liquid, formed, tested for capacity, and vented and sealed to obtain a semi-solid battery.

[0171] Performance testing:

[0172] The performance of the lithium batteries prepared according to the above embodiments and comparative examples was tested, as follows:

[0173] Electrical performance testing:

[0174] (1) Use a charge and discharge test cabinet to test the charge and discharge resistance of each lithium battery at 20% SOC to determine the internal resistance of the lithium battery at low SOC.

[0175] (2) At 25°C, each lithium battery was charged to 4.25V at the start and stop voltages of 2.8V and 4.25V respectively, then charged at 4.25V at a constant voltage until the current decreased to 0.05C, and then discharged at 0.1C to 2.8V. The above steps were repeated, and the discharge capacity C1, C200, and C600 of the battery at the 1st, 200th, and 600th cycles were recorded. The capacity retention rate was calculated. The capacity retention rate at the 200th cycle = C200 / C1 × 100%, and the capacity retention rate at the 600th cycle = C600 / C1 × 100%.

[0176] (3) At 25°C, each lithium battery is charged to 4.25V at the start and stop voltages of 2.8V and 4.25V respectively, then charged at 4.25V at a constant voltage until the current decreases to 0.05C, and discharged to 2.8V at 0.1C. The above steps are repeated, and the discharge capacity C1 of the battery in the first charge and discharge cycle is recorded. The number of cycles when the discharge capacity decays to 80% of C1 is recorded.

[0177] The test results are shown in Tables 1 and 2 below.

[0178] Table 1. Discharge and charge resistance of each group of lithium-ion solid-state batteries at 20% SOC

[0179]

[0180] Table 2 Capacity retention of each group of lithium-ion solid-state batteries

[0181]

[0182] Experimental results show that the membrane-free semi-solid batteries prepared using the composite positive electrode sheets prepared in Examples 1-5 of this invention have lower internal resistance, which is beneficial to capacity utilization, and the cycle performance and safety performance are also significantly improved. This is because the composite positive electrode sheets prepared in Examples 1-5 of this invention have abundant pore structures, which can buffer the volume expansion caused by the negative electrode material. In Comparative Example 1, the absence of carbon-coated lithium titanium aluminum phosphate solid electrolyte in the positive electrode resulted in decreased conductivity of the composite positive electrode compared to Example 1, leading to higher internal resistance and reduced initial efficiency and capacity performance. In Comparative Example 2, the absence of sulfide solid electrolyte in the positive electrode surface coating resulted in increased internal resistance and poorer electrical performance at the electrode interface compared to Example 1. In Comparative Example 3, the use of SiO2 particles instead of SiO2 aerogel resulted in greater volume expansion of the negative electrode compared to Example 1, leading to poorer cycle performance. In Comparative Example 4, the lack of a suitable drying process during the formation of the solid electrolyte-SiO2 aerogel composite coating resulted in an unstable composite positive electrode structure compared to Example 1, leading to reduced capacity performance and cycle stability. In Comparative Example 5, the thickness of the solid electrolyte-SiO2 aerogel composite coating was 25±2μm, which, compared to Example 1, resulted in an excessively thick coating, increasing internal resistance and causing poor electrical performance. In addition, Comparative Example 6 did not apply a composite coating to the surface of the positive electrode and prepared a semi-solid battery using a conventional separator. Compared with Example 1, the internal resistance of the prepared battery was not significantly different, but the cycle performance of the battery deteriorated due to the large volume expansion of the negative electrode. At the same time, the battery preparation cost was higher and the preparation process was more complex after using a separator.

[0183] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0184] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0185] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0186] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode plate, characterized in that, include: Positive current collector; A positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and a carbon-coated oxide electrolyte. The carbon-coated oxide electrolyte includes one or more of the following: carbon-coated perovskite oxide electrolyte, carbon-coated garnet oxide electrolyte, carbon-coated anti-perovskite oxide electrolyte, and carbon-coated amorphous oxide electrolyte. The mass percentage of the carbon-coated oxide electrolyte in the positive electrode active material layer is 2% to 5%. A composite coating is disposed on the surface of the positive electrode active material layer away from the positive electrode current collector, the composite coating comprising a solid electrolyte and SiO2 aerogel; The composite coating is formed by drying a solid electrolyte composite silica sol. The preparation method of the solid electrolyte composite silica sol includes: dispersing an organosilicon source in ethanol, adding a solid electrolyte and a binder and mixing them evenly to obtain a mixture. Then, an acidic aqueous solution was added to the above mixture, and after stirring evenly, a solid electrolyte composite silica sol was obtained.

2. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. And / or, the mass percentage of the positive electrode active material in the positive electrode active material layer is 94%~97%; And / or, the particle size of the carbon-coated oxide electrolyte is 5 nm to 20 nm; And / or, the thickness of the carbon coating layer in the carbon-coated oxide electrolyte is 1 nm to 2 nm; And / or, the positive electrode active material layer further includes a binder and / or a dispersant.

3. The positive electrode sheet according to claim 1, characterized in that, The solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes.

4. The positive electrode sheet according to claim 3, characterized in that, The sulfide solid electrolyte includes one or more of binary sulfide solid electrolytes, ternary sulfide solid electrolytes, and sulfosilver germanium ore type sulfide solid electrolytes. And / or, the oxide solid electrolyte includes one or more of the following: perovskite oxide solid electrolyte, garnet oxide solid electrolyte, anti-perovskite oxide solid electrolyte, and amorphous oxide solid electrolyte; And / or, the particle size of the oxide solid electrolyte is 5 nm to 20 nm; And / or, the mass ratio of the sulfide solid electrolyte to the oxide solid electrolyte in the solid electrolyte is (3~4):(1~2).

5. The positive electrode sheet according to claim 1, characterized in that, The thickness of the positive electrode active material layer is 0.1 mm to 0.2 mm; And / or, the thickness of the composite coating is 5μm~15μm; And / or, the composite coating may also include an adhesive.

6. The positive electrode sheet according to claim 1, characterized in that, The organosilicon source includes one or more of tetraethyl orthosilicate, methyl orthosilicate, and tetrabutoxytitanium; and / or, the mass ratio of the organosilicon source to the ethanol is (20~25):100; and / or, the amount of the solid electrolyte added is 20%~30% of the mass of the organosilicon source; and / or, the amount of the binder added is 1%~2% of the mass of the organosilicon source; and / or, the acidic aqueous solution includes one or more of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, and nitric acid aqueous solution; and / or, the mass concentration of the acidic aqueous solution is 20%~30%; and / or, the amount of the acidic aqueous solution added is 3%~6% of the mass of the organosilicon source.

7. A method for manufacturing a positive electrode sheet according to any one of claims 1 to 6, characterized in that, Includes the following steps: a) A positive electrode active material slurry is coated on at least one side of the positive electrode current collector and dried in the first stage to form a positive electrode active material layer; b) A solid electrolyte composite silica sol is coated on the surface of the positive electrode active material layer obtained in step a), and after a second drying, a composite coating is formed to obtain the positive electrode sheet.

8. The manufacturing method according to claim 7, characterized in that, In step a): The positive electrode active material slurry includes a positive electrode active material, a carbon-coated oxide electrolyte, a binder, a dispersant, and a solvent; wherein the binder includes one or more of polyvinyl alcohol, polyacrylic acid, polyvinylpyrrolidone, polymethyl methacrylate, polyethylene oxide, and polyacrylonitrile; and / or the dispersant includes one or more of polycarboxylate, polyvinylpyrrolidone, and sodium carboxymethyl cellulose. And / or, the solid content of the positive electrode active material slurry is 65%~75%; And / or, the viscosity of the positive electrode active material slurry is 2000 mPa·s to 5000 mPa·s.

9. The manufacturing method according to claim 7, characterized in that, In step b): The second drying process includes a three-stage drying process: the temperature of the first stage is 60℃~80℃ and the speed is 0.4m / min~0.6m / min; the temperature of the second stage is 80℃~100℃ and the speed is 0.5m / min~1m / min; and the temperature of the third stage is 30℃~50℃ and the speed is 1m / min~2m / min.

10. A secondary battery, characterized in that, This includes the positive electrode sheet as described in any one of claims 1 to 6 or the positive electrode sheet produced by the manufacturing method described in any one of claims 7 to 9.

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