Composite positive electrode sheet, lithium ion battery and preparation method thereof

Abstract

The application discloses a kind of composite positive plate and lithium ion battery and preparation method.The composite positive plate includes positive current collector;Positive current collector surface is coated with positive active material layer;Positive active material layer surface is coated with solid electrolyte layer;Positive active material layer includes positive active material, oxide solid electrolyte, conductive agent, dispersing agent and binder and the mass ratio of these components is (91.9%~97.45%): (0.5%~5%): (1%~1.5%): (0.05%~0.1%): (1%~1.5%);Solid electrolyte layer includes oxide solid electrolyte, conductive agent, dispersing agent and binder and the mass ratio of these components is (13.9%~70.9%): (13.2%~49.2%): (0.6%~3.8%): (13.2%~49.2%);The application is conducive to guaranteeing battery thermal safety while significantly improving battery fast-charging capability.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a composite positive electrode, a lithium-ion battery, and a method for their preparation. Background Technology

[0002] New energy vehicles have been widely used in people's work and life, but the problem of slow charging is becoming increasingly prominent, making it imperative to improve the fast charging capability of vehicle batteries.

[0003] Currently, the traditional solutions for improving battery fast charging capabilities are as follows: First, optimize electrode design: thin-coated electrodes are beneficial for electrolyte wetting and improve lithium-ion conduction speed, thereby enhancing fast charging capability. However, particle scratches are prone to occur during electrode coating, resulting in poor appearance. In addition, the amount of active material per unit area is small, which has a significant impact on the battery's energy density.

[0004] Secondly, optimize the material system: select anode materials with good rate performance and construct an efficient conductive network; and apply high-porosity coating membranes and highly conductive electrolytes. However, selecting anode materials with good rate performance and too many conductive agents reduces the specific capacity and proportion of anode active materials, resulting in low battery energy density; using high-porosity coating membranes and highly conductive electrolytes can lead to a decrease in battery safety performance.

[0005] Therefore, there is an urgent need to develop a technology that can solve the above-mentioned technical problems. Summary of the Invention

[0006] The purpose of this invention is to address the technical deficiencies of existing technologies by providing a composite positive electrode, a lithium-ion battery, and a method for their preparation.

[0007] Therefore, the present invention provides a composite positive electrode sheet, characterized in that it includes a positive current collector; The surface of the positive electrode current collector is coated with a layer of positive electrode active material; A solid electrolyte layer is coated on the surface of the positive electrode active material layer; The positive electrode active material layer includes a positive electrode active material, an oxide solid electrolyte, a conductive agent, a dispersant, and a binder. The solid electrolyte layer includes an oxide solid electrolyte, a conductive agent, a dispersant, and a binder; In the positive electrode active material layer, the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant and binder is: (91.9%~97.45%): (0.5%~5%): (1%~1.5%): (0.05%~0.1%): (1%~1.5%). In the solid electrolyte layer, the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder is: (13.9%~70.9%): (13.2%~49.2%): (0.6%~3.8%): (13.2%~49.2%).

[0008] Furthermore, the present invention also provides a method for preparing the composite positive electrode sheet described above, comprising the following steps: Step S1: Add the adhesive to NMP as a solvent and mix until the adhesive is completely dissolved to obtain an adhesive solution; Step S2: Add the oxide solid electrolyte particles and dispersant to the binder solution, mix evenly, and obtain the first slurry; Step S3: Mix the first slurry, conductive agent, and dispersant evenly to prepare the second slurry; Step S4: Mix the second slurry and the positive electrode active material evenly and stir at high speed to prepare the third slurry; Step S5: The third slurry is coated onto the surface of the positive electrode current collector and dried to obtain the first positive electrode sheet; Step S6: The second slurry is coated onto the surface of the first positive electrode sheet, and then the composite positive electrode sheet is obtained through baking, rolling and slitting processes.

[0009] In addition, the present invention also provides a lithium-ion battery, characterized in that it includes a composite positive electrode as described above.

[0010] As can be seen from the technical solutions provided by the present invention above, compared with the prior art, the present invention provides a composite positive electrode sheet, a lithium-ion battery and a preparation method, which is scientifically designed and conducive to significantly improving the fast charging capability of the battery (including fast charging performance at room temperature and low temperature) while ensuring the thermal safety of the battery, and has significant practical significance.

[0011] Compared with existing technologies, the composite cathode sheet, lithium-ion battery, and preparation method provided by this invention have the following beneficial technical effects: 1. The positive electrode of the present invention contains oxide solid electrolyte between the positive electrode material particles and on the surface of the positive electrode. The oxide solid electrolyte has high ionic conductivity, constructs a three-dimensional conductive network, improves ion conduction capability, and can participate in the formation of SEI (solid electrolyte interphase) film and CEI (positive electrode electrolyte interphase) film, optimizes and stabilizes the inside / interface of the positive electrode, reduces cycle polarization, improves cycle rate, and thus improves fast charging cycle performance.

[0012] 2. Given that the ionic conductivity of liquid electrolytes decreases significantly at low temperatures and the electrochemical reaction rate slows down, by applying this invention, oxide solid electrolyte particles fill the electrode pores and form a solid-phase high-speed ion transport channel inside the positive electrode, effectively improving the interfacial ion transport and charge transfer process, thus enhancing the battery's charging capability at low temperatures.

[0013] 3. This invention stabilizes the positive electrode interface through an oxide solid electrolyte, which can effectively suppress the dissolution of transition metals, reduce side reactions, and improve battery safety performance. At the same time, by adding a solid electrolyte to the positive electrode, the amount of liquid electrolyte used can be reduced, thereby reducing the risk of thermal runaway. Attached Figure Description

[0014] Figure 1 A schematic diagram showing the distribution of the second slurry coating layer, positive electrode active material particles, solid electrolyte particles, and positive electrode current collector in a composite positive electrode sheet provided by the present invention. In the figure, 1: solid electrolyte layer (i.e., the second slurry coating layer), 2: positive electrode active material particles, 3: oxide solid electrolyte particles, 4: positive electrode current collector; Figure 2 The present invention provides a basic flowchart of a method for preparing a composite positive electrode. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0017] In the description of this patent, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this patent according to the specific circumstances.

[0018] Furthermore, 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 technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0019] The technical solution of the present invention will be further described below through specific embodiments. Details not specified in the embodiments are all conventional technologies in the industry.

[0020] See Figure 1 The present invention provides a composite positive electrode sheet for use in lithium-ion batteries, which includes a positive current collector 4; The surface of the positive electrode current collector 4 is coated with a positive electrode active material layer 5; A solid electrolyte layer (i.e., the second slurry coating layer) 1 is coated on the surface of the positive electrode active material layer 5; Among them, the positive electrode active material layer 5 includes a positive electrode active material, an oxide solid electrolyte, a conductive agent, a dispersant, and a binder; The solid electrolyte layer (i.e., the second slurry coating layer) 1 includes an oxide solid electrolyte, a conductive agent, a dispersant, and a binder.

[0021] In this invention, specifically, the upper and lower surfaces of the positive current collector 4 are coated with a positive active material layer 5; Each positive electrode active material layer 5 is coated with a solid electrolyte layer 1.

[0022] In this invention, specifically, in the positive electrode active material layer 5, the mass ratio between the positive electrode active material, the oxide solid electrolyte, the conductive agent, the dispersant, and the binder is: (91.9%~97.45%): (0.5%~5%): (1%~1.5%): (0.05%~0.1%): (1%~1.5%).

[0023] Preferably, in the positive electrode active material layer 5, the mass ratio between the positive electrode active material, the oxide solid electrolyte, the conductive agent, the dispersant and the binder is 95%∶2%∶1.5%∶0.1%∶1.4%, or 94%∶3%∶1.5%∶0.1%∶1.4% (that is, the ratio in Examples 3 and 4 below, which are preferred mass ratios).

[0024] In this invention, specifically, in the solid electrolyte layer 1 (i.e. the second slurry coating layer), the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder is: (13.9%~70.9%): (13.2%~49.2%): (0.6%~3.8%): (13.2%~49.2%).

[0025] Preferably, in the solid electrolyte layer 1 (i.e. the second slurry coating layer), the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder is 40%∶30%∶2%∶28%, or 50%∶25%∶1.7%∶23.3% (i.e. the ratio of Examples 3 and 4 below, which are preferred mass ratios).

[0026] In this invention, specifically, the oxide solid electrolyte particles in the positive electrode active material layer 5 are dispersed between the positive electrode active material particles.

[0027] It should be noted that in this invention, see Figure 1 As shown, the surface of the positive electrode current collector 4 is coated with a positive electrode active material layer 5; the surface of the positive electrode active material layer 5 is coated with a solid electrolyte layer (i.e., the second slurry coating layer) 1; the solid electrolyte layer (i.e., the second slurry coating layer) 1 contains oxide solid electrolyte particles 3. The positive electrode active material layer 5 has oxide solid electrolyte particles 3 and positive electrode active material particles 2, and the oxide solid electrolyte particles 3 are distributed on the surface and edge of multiple positive electrode active material particles 2.

[0028] In this invention, the oxide solid electrolyte is a NASICON structure material in both the positive electrode active material layer and the solid electrolyte layer. In practical implementation, NASICON structural materials, including Li 1+x Al x Ti 2-x (PO4)3(LATP) or its isomorphous heteroatomic doped compounds, Li 1+x Al x Ge 2-x (PO4)3 (LAGP) or any one or more of its isomorphous heteroatomic doped compounds, wherein 0.1 ≤ x ≤ 0.7; Preferably, x is 0.3, 0.4, or 0.5.

[0029] In this invention, specifically, in the positive electrode active material layer and the solid electrolyte layer, the particle size of the oxide solid electrolyte is D50 = 0.2-3 μm, preferably 0.4-2 μm.

[0030] In this invention, specifically, the mass of the oxide solid electrolyte in the positive electrode active material layer is equal to 0.5% to 5% of the total mass of all substances in the positive electrode active material layer, preferably 1% to 3%, and more preferably 2% to 3%.

[0031] In this invention, the positive electrode active material in the positive electrode active material layer is a high-nickel positive electrode material; In practice, high-nickel cathode materials include one or more of lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt manganese aluminum oxide (NCMA) (i.e., a mixture of multiple materials). Furthermore, in high-nickel cathode materials, the nickel content is 89-95 mol%; In this invention, specifically, the conductive agent in the positive electrode active material layer and the solid electrolyte layer includes one or more of Ketjen black, acetylene black, conductive carbon black, conductive graphite and carbon nanotubes (i.e., it can be a mixture of multiple materials). In this invention, specifically, the dispersant in the positive electrode active material layer and the solid electrolyte layer is an acrylate copolymer, such as acrylic-2-acrylamide-2-methylpropanesulfonic acid copolymer (AA-AMPS-HPA).

[0032] In this invention, specifically, the binder in the positive electrode active material layer and the solid electrolyte layer is polyvinylidene fluoride (PVDF).

[0033] In this invention, specifically, the positive current collector is an aluminum foil.

[0034] Based on the composite cathode sheet provided by the present invention, the present invention also provides a lithium-ion battery comprising the composite cathode sheet as described above.

[0035] In practice, a lithium-ion battery includes a battery casing, a composite positive electrode, a negative electrode, a separator, and an electrolyte. The battery casing contains battery electrode groups; The battery electrode assembly is prepared by winding composite positive electrode, negative electrode and separator; The separator is located between the composite positive electrode and the negative electrode. In practice, lithium-ion batteries are cylindrical batteries with a full tab structure.

[0036] In practice, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on the surface of the negative electrode current collector; Furthermore, the negative electrode current collector is copper foil.

[0037] Furthermore, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a thickener, and a binder; The negative electrode active material is a mixture of graphite and silicon carbon (the specific mass percentage of graphite and silicon carbon is not required, as long as the sum of the two is 100%). Conductive agents include one or more of conductive carbon black, conductive graphite and carbon nanotubes (i.e., a mixture of multiple materials). The thickener is carboxymethyl cellulose (CMC-Na); The adhesive is styrene-butadiene rubber (SBR).

[0038] To prepare the composite positive electrode sheet described above in this invention, see [link to previous document]. Figure 2 The present invention also provides a method for preparing the composite positive electrode sheet described above, characterized by comprising the following steps: Step S1: Add the adhesive to NMP (N-methylpyrrolidone) as a solvent and mix until the adhesive is completely dissolved to obtain an adhesive solution; In step S1, the adhesive is polyvinylidene fluoride (PVDF). In step S1, the solid content of the adhesive solution is 6%.

[0039] Step S2: Add the oxide solid electrolyte particles and dispersant to the binder solution, mix evenly, and obtain the first slurry; In step S2, the oxide solid electrolyte is a NASICON structural material; the NASICON structural material includes Li 1+ x Al x Ti 2-x (PO4)3(LATP) or its isomorphous heteroatomic doped compounds, Li 1+x Al x Ge 2-x (PO4)3 (LAGP) or any one or more of its isomorphous heteroatomic doped compounds, wherein 0.1 ≤ x ≤ 0.7; preferably, x is 0.3, 0.4 and 0.5.

[0040] In step S2, the dispersant is an acrylate copolymer (e.g., AA-AMPS-HPA).

[0041] In step S2, all of the oxide solid electrolyte (i.e., the oxide solid electrolyte required for forming the positive electrode active material layer 5 of the composite positive electrode and the oxide solid electrolyte required for the solid electrolyte layer 1) and half of the dispersant (i.e., 50% of the sum of the dispersant required for forming the positive electrode active material layer 5 of the composite positive electrode and the dispersant required for the solid electrolyte layer 1) are added. At this time, the mass ratio of oxide solid electrolyte, dispersant and binder in the first slurry is (24.4~83%): (0.4~3.2%): (16.5~74.1%).

[0042] Step S3: Mix the first slurry, conductive agent, and dispersant evenly to prepare the second slurry; In step S3, the conductive agent includes one or more of Ketjen black, acetylene black, conductive carbon black, conductive graphite and carbon nanotubes (i.e., it can be a mixture of multiple materials). In step S3, the dispersant is an acrylate copolymer (e.g., AA-AMPS-HPA).

[0043] In step S3, all of the conductive agent (i.e., the conductive agent required for forming the positive electrode active material layer 5 of the composite positive electrode sheet and the conductive agent required for the solid electrolyte layer 1) and the other half of the dispersant (i.e., 50% of the sum of the dispersant required for forming the positive electrode active material layer 5 of the composite positive electrode sheet and the dispersant required for the solid electrolyte layer 1) are added. At this time, in the second slurry, the mass ratio between the oxide solid electrolyte, conductive agent, dispersant and binder is: (13.9%~70.9%): (13.2%~49.2%): (0.6%~3.8%): (13.2%~49.2%).

[0044] Step S4: Mix the second slurry and the positive electrode active material evenly and stir at high speed to prepare the third slurry; In step S4, the positive electrode active material is a high-nickel positive electrode material; the high-nickel positive electrode material includes one or more of lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt manganese aluminum oxide (NCMA) (i.e., it can be a mixture of multiple materials); further, in the high-nickel positive electrode material, the nickel content is 89-95 mol% In step S4, all the positive electrode active material (i.e., the positive electrode active material required to form the positive electrode active material layer 5 of the composite positive electrode sheet) is added. At this time, in the third slurry, the mass ratio between the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant and binder is: (91.9%~97.45%): (0.5%~5%): (1%~1.5%): (0.05%~0.1%): (1%~1.5%).

[0045] In step S4, high-speed stirring is performed, specifically at a stirring speed of 2500 rpm.

[0046] Step S5: The third slurry is coated onto the surface of the positive current collector (e.g., aluminum foil), and then dried to obtain the first positive electrode sheet; Step S6: The second slurry is coated onto the surface of the first positive electrode sheet, and then the composite positive electrode sheet is obtained through baking, rolling and slitting processes (baking, rolling and slitting processes are existing conventional battery electrode sheet production processes).

[0047] In this invention, specifically, the composite positive electrode sheet can also be obtained through double-layer coating.

[0048] In step S6, the thickness of the second slurry coating layer is 3-10µm; In step S6, the compaction density of the composite positive electrode is 3.4-3.6 g / cm³. 3 ; In step S6, the areal density of the composite positive electrode is 40.2~42.2 mg / cm³. 2 .

[0049] To better understand the technical solution of the present invention, the following specific embodiments will be used to illustrate the technical solution of the present invention.

[0050] Example 1 Based on the composite cathode sheet provided by this invention, a lithium-ion battery is prepared, comprising the following operations: The first step is to prepare a composite positive electrode sheet; For the composite positive electrode sheet provided by the present invention, in the positive electrode active material layer, the positive electrode active material LiNi 0.91 Co 0.06 Mn 0.03 (NCM), solid electrolyte Li 1.5 Al 0.5 Ti 1.5 The mass ratio of (PO4)3 (LATP), conductive agent, dispersant and binder polyvinylidene fluoride (PVDF) is 96.5%∶0.5%∶1.5%∶0.1%∶1.4%.

[0051] In Example 1, the mass ratio of oxide solid electrolyte, conductive agent, dispersant, and binder in solid electrolyte layer 1 (i.e., the second slurry coating layer) is 14.3% : 42.9% : 2.8% : 40%. The preparation method of the composite positive electrode provided by the present invention, i.e., the first operation, includes the following steps: Step S1: Add PVDF to NMP and mix until completely dissolved to obtain adhesive solution; In step S1, the solid content of the adhesive solution is 6%.

[0052] Step S2: Add LATP solid electrolyte particles and dispersant AA-AMPS-HPA to the adhesive solution, mix evenly, and obtain the first slurry. In step S2, all of the oxide solid electrolyte (i.e., the oxide solid electrolyte required for forming the positive electrode active material layer 5 of the composite positive electrode and the oxide solid electrolyte required for the solid electrolyte layer 1) and half of the dispersant (i.e., 50% of the sum of the dispersant required for forming the positive electrode active material layer 5 of the composite positive electrode and the dispersant required for the solid electrolyte layer 1) are added. At this point, the mass ratio of oxide solid electrolyte, dispersant, and binder in the first slurry is 25.6% : 2.6% : 71.8%. Step S3: Mix the first slurry, conductive agent (conductive carbon black), and dispersant AA-AMPS-HPA evenly to prepare the second slurry; In step S3, all of the conductive agent (i.e., the conductive agent required for forming the positive electrode active material layer 5 of the composite positive electrode sheet and the conductive agent required for the solid electrolyte layer 1) and the other half of the dispersant (i.e., 50% of the sum of the dispersant required for forming the positive electrode active material layer 5 of the composite positive electrode sheet and the dispersant required for the solid electrolyte layer 1) are added. At this time, in the second slurry, the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder is 14.3%:42.9%:2.8%:40%. It should be noted that the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder in the second slurry is equal to the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder in solid electrolyte layer 1 (i.e. the second slurry coating layer); Step S4: Mix the second slurry and NCM, which is the positive electrode active material, evenly and stir at high speed to prepare the third slurry; In step S4, all the positive electrode active material (i.e., the positive electrode active material required to form the positive electrode active material layer 5 of the composite positive electrode sheet) is added. At this time, in the third slurry, the mass ratio between the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant and binder is 96.5%: 0.5%: 1.5%: 0.1%: 1.4%.

[0053] It should be noted that the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant and binder in the third slurry is equal to the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant and binder in the positive electrode active material layer. In step S4, high-speed stirring is performed, specifically at a stirring speed of 2500 rpm.

[0054] Step S5: The third slurry is coated on both sides of the aluminum foil used as the positive electrode current collector, and then dried to obtain the first positive electrode sheet; In step S5, the third slurry is coated on one side (e.g., the upper surface) of the aluminum foil that serves as the positive electrode current collector, and then coated on the other side (e.g., the lower surface), thus performing double-sided coating to obtain the first positive electrode sheet.

[0055] In step S6, the second slurry is coated on both sides of the first positive electrode sheet, and then the composite positive electrode sheet is obtained through baking, rolling and slitting processes (baking, rolling and slitting processes are existing conventional battery electrode sheet production processes).

[0056] In step S6, the second slurry is coated on one side (e.g., the upper surface) of the first positive electrode sheet, and then coated on the other side (e.g., the lower surface), thus performing double-sided coating to obtain a composite positive electrode sheet. The single-sided coating thickness of the second slurry is 6µm. After rolling and slitting, the composite positive electrode sheet is obtained.

[0057] The second step is to prepare the negative electrode: The negative electrode active material (specifically a mixture of graphite and silicon carbon negative electrode material), conductive agent, thickener and binder are mixed in a mass ratio of 96:1:1:2 to prepare a negative electrode slurry. Then the negative electrode slurry is coated on both sides of the copper foil that serves as the negative electrode current collector (i.e., coating one side first and then the other side, i.e., double-sided coating). After rolling and cutting, the negative electrode sheet is obtained.

[0058] For the negative electrode, the conductive agents include conductive carbon black, conductive graphite, and carbon nanotubes; the thickener is carboxymethyl cellulose (CMC-Na); and the binder is styrene-butadiene rubber (SBR).

[0059] The third step is to select the diaphragm; In this Example 1, a PE-based double-sided ceramic film is used.

[0060] The fourth step is to prepare the electrolyte: The electrolyte consists of lithium salts, organic solvents, and functional additives; The lithium salt is lithium hexafluorophosphate (LiPF6), and the organic solvent includes at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Functional additives include at least one of 1,3-propanesulfonate lactone (PS), fluoroethylene carbonate (FEC), vinylene carbonate (VC), and lithium difluorooxalate borate (LiODFB).

[0061] In practice, for the electrolyte, the mass percentage of lithium salt in the electrolyte is 13%-18%; Organic solvents constitute 67%-77% of the electrolyte by mass. Functional additives account for 10%-15% of the mass percentage in the electrolyte.

[0062] The fifth step is battery manufacturing; Specifically, the positive electrode, separator, and negative electrode are wound, assembled, injected with electrolyte, packaged, and formed to obtain a cylindrical lithium-ion secondary battery with a full tab structure.

[0063] In addition, the batteries of Examples 2-14 and Comparative Examples 1-3 were all manufactured in a similar manner to that of Example 1. The specific differences are listed in Table 1.

[0064] Table 1 lists the solid electrolyte materials, particle size, amount added, and positive electrode surface density parameters for Examples 1-14; The second to fifth operations of Examples 2-14 are the same as those of Example 1. Except for the parameters shown in Table 1, the mass ratio of each component in the positive electrode active material layer 5, the mass ratio of each component in the solid electrolyte layer 1 (i.e. the second slurry coating layer), and the mass ratio of each component in the first slurry, the other processing operations of Examples 2-14 are the same as those of Example 1.

[0065] In Example 2, for the composite positive electrode sheet, in the positive electrode active material layer 5, the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant, and binder is 96%∶1%∶1.5%∶0.1%∶1.4% (this ratio is equal to the mass ratio of the corresponding components in the third slurry). In the solid electrolyte layer 1 (i.e., the second slurry coating layer), the mass ratio of the oxide solid electrolyte, conductive agent, dispersant, and binder is 25%∶37.5%∶2.5%∶35% (this ratio is equal to the mass ratio of the corresponding components in the second slurry); in the first slurry, the mass ratio of the oxide solid electrolyte, dispersant, and binder is 40.8%∶2%∶57.2%.

[0066] In Examples 3 and 6-14, for the composite positive electrode sheet, in the positive electrode active material layer 5, the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant, and binder is 95%∶2%∶1.5%∶0.1%∶1.4% (this ratio is equal to the mass ratio of the corresponding components in the third slurry); in the solid electrolyte layer 1 (i.e., the second slurry coating layer), the mass ratio of the oxide solid electrolyte, conductive agent, dispersant, and binder is 40%∶30%∶2%∶28% (this ratio is equal to the mass ratio of the corresponding components in the second slurry); in the first slurry, the mass ratio of the oxide solid electrolyte, dispersant, and binder is 58%∶1.4%∶40.6%.

[0067] In Example 4, for the composite positive electrode sheet, in the positive electrode active material layer 5, the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant, and binder is 94%∶3%∶1.5%∶0.1%∶1.4% (this ratio is equal to the mass ratio of the corresponding components in the third slurry). In the solid electrolyte layer 1 (i.e., the second slurry coating layer), the mass ratio of the oxide solid electrolyte, conductive agent, dispersant, and binder is 50%∶25%∶1.7%∶23.3% (this ratio is equal to the mass ratio of the corresponding components in the second slurry); in the first slurry, the mass ratio of the oxide solid electrolyte, dispersant, and binder is 67.4%∶1.1%∶31.5%.

[0068] In Example 5, for the composite positive electrode sheet, in the positive electrode active material layer 5, the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant, and binder is 92%∶5%∶1.5%∶0.1%∶1.4% (this ratio is equal to the mass ratio of the corresponding components in the third slurry). In the solid electrolyte layer 1 (i.e., the second slurry coating layer), the mass ratio of the oxide solid electrolyte, conductive agent, dispersant, and binder is 62.5%∶18.8%∶1.2%∶17.5% (this ratio is equal to the mass ratio of the corresponding components in the second slurry); in the first slurry, the mass ratio of the oxide solid electrolyte, dispersant, and binder is 77.5%∶0.8%∶21.7%.

[0069] Table 1

[0070] In Table 1, the amount of solid electrolyte added is the proportion of the mass of the oxide solid electrolyte to the total mass of all substances in the positive electrode active material layer; in Table 1, the liquid electrolyte content is the proportion of the liquid electrolyte content to the total weight of the battery. Comparative Example 1 Comparative Example 1 prepared a lithium-ion battery. The preparation method of the battery includes the first to the fifth operations, as shown in Table 1. The second to the fifth operations of Comparative Example 1 are the same as those of Example 1.

[0071] In Comparative Example 1, there was no solid electrolyte; In the positive electrode active material layer, the positive electrode active material LiNi 0.91 Co 0.06 Mn 0.03 The mass ratio of NCM, conductive agent, dispersant, and binder polyvinylidene fluoride (PVDF) is 97% : 1.5% : 0.1% : 1.4%. The first operation of Comparative Example 1 is to prepare a positive electrode sheet; The first operation of Comparative Example 1 includes the following steps: Step S1: Add PVDF to NMP and mix until completely dissolved to obtain adhesive solution; In step S1, the solid content of the adhesive solution is 6%; Step S2: Add conductive carbon black and dispersant AA-AMPS-HPA to the adhesive solution and mix evenly to obtain a conductive adhesive solution; Step S3: Add NCM of positive electrode active material to the conductive adhesive solution in step S2 and mix evenly. Stir at a high speed of 2500 rpm to prepare positive electrode slurry. In the positive electrode slurry, the positive electrode active material LiNi 0.91 Co 0.06 Mn 0.03 The mass ratio of NCM, conductive agent, dispersant, and binder polyvinylidene fluoride (PVDF) is 97% : 1.5% : 0.1% : 1.4%. Step S4: The positive electrode slurry is coated on both sides onto the aluminum foil that serves as the positive electrode current collector. After drying, rolling and cutting, the positive electrode sheet is obtained.

[0072] In step S4, the positive electrode slurry is coated on one side (e.g., the upper surface) of the aluminum foil that serves as the positive electrode current collector, and then coated on the other side (e.g., the lower surface), thus performing double-sided coating to obtain the positive electrode sheet.

[0073] Comparative Example 2 Comparative Example 2 prepared a lithium-ion battery. The preparation method of the battery includes the first to the fifth operations, as shown in Table 1. The second to the fifth operations of Comparative Example 2 are the same as those of Example 1.

[0074] In Comparative Example 2, the first operation performed in Comparative Example 2, "preparation of positive electrode sheet", did not involve coating with the second slurry coating.

[0075] The first operation of Comparative Example 2 was to prepare a positive electrode sheet; For the positive electrode of the lithium-ion battery in Comparative Example 2, in the positive electrode active material layer, the positive electrode active material is LiNi. 0.91 Co 0.06 Mn 0.03 (NCM), solid electrolyte Li 1.5 Al 0.5 Ti 1.5 (PO4)3 (LATP), conductive agent, dispersant and binder polyvinylidene fluoride (PVDF) in a mass ratio of 96.5% : 0.5% : 1.5% : 0.1% : 1.4%; The first operation of Comparative Example 2 includes the following steps: Step S1: Add PVDF to NMP and mix until completely dissolved to obtain adhesive solution; In step S1, the solid content of the adhesive solution is 6%; Step S2: Add LATP solid electrolyte particles and dispersant AA-AMPS-HPA to the adhesive solution, mix evenly, and obtain the first slurry. In step S2, all of the oxide solid electrolyte and half of the dispersant are added. At this point, the mass ratio of the oxide solid electrolyte, dispersant, and binder is 25.6% : 2.6% : 71.8%. Step S3: Mix the first slurry, conductive carbon black and dispersant AA-AMPS-HPA evenly to prepare the second slurry; In step S3, all of the conductive agent and the other half of the dispersant are added. At this point, the mass ratio of the oxide solid electrolyte, conductive agent, dispersant, and binder in the second slurry is 14.3% : 42.9% : 2.8% : 40%. Step S4: Mix the second slurry and NCM, which is the positive electrode active material, evenly and stir at high speed to prepare the third slurry; In step S4, all the positive electrode active material is added. At this point, the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant, and binder in the third slurry is 96.5% : 0.5% : 1.5% : 0.1% : 1.4%. In step S4, high-speed stirring is performed, specifically at a stirring speed of 2500 rpm. Step S5: The third slurry is coated on both sides of the aluminum foil used as the positive electrode current collector, and after drying, rolling and cutting, the positive electrode sheet is obtained. In step S5, the third slurry is coated on one side (e.g., the upper surface) of the aluminum foil that serves as the positive electrode current collector, and then coated on the other side (e.g., the lower surface), thus performing double-sided coating to obtain the positive electrode sheet.

[0076] Comparative Example 3 Comparative Example 3 prepared a lithium-ion battery. The preparation method of this battery includes the first to fifth operations, as shown in Table 1. The second to fifth operations of Comparative Example 3 are the same as those of Example 1. The first operation of Comparative Example 3 is based on Comparative Example 1, except that a second slurry coating is additionally applied.

[0077] For the positive electrode of the lithium-ion battery in Comparative Example 3, in the positive electrode active material layer, the positive electrode active material is LiNi. 0.91 Co 0.06 Mn 0.03 The mass ratio of NCM, conductive agent, dispersant, and binder polyvinylidene fluoride (PVDF) is 97% : 1.5% : 0.1% : 1.4%. The first operation of Comparative Example 3 includes the following sub-operations: The first sub-operation involves preparing the initial positive electrode sheet (the same positive electrode sheet as in Comparative Example 1): Step S1: Add PVDF to NMP and mix until completely dissolved to obtain adhesive solution; In step S1, the solid content of the adhesive solution is 6%; Step S2: Add conductive carbon black and dispersant AA-AMPS-HPA to the adhesive solution and mix evenly to obtain a conductive adhesive solution; Step S3: Add NCM of positive electrode active material to the conductive adhesive solution in step S2 and mix evenly. Stir at high speed of 2500 rpm to prepare positive electrode slurry. Step S4: The positive electrode slurry is coated on both sides onto the aluminum foil that serves as the positive electrode current collector. After drying, rolling and cutting, the initial positive electrode sheet is obtained.

[0078] In step S4, the positive electrode slurry is coated on one side (e.g., the upper surface) of the aluminum foil that serves as the positive electrode current collector, and then coated on the other side (e.g., the lower surface), which is double-sided coating, to obtain the initial positive electrode sheet.

[0079] The second sub-operation involves preparing the second slurry; In the solid electrolyte layer (i.e., the second slurry coating layer), the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder is 14.3% : 42.9% : 2.8% : 40%; The method for preparing the second slurry includes the following steps: Step S1: Add PVDF to NMP and mix until completely dissolved to obtain adhesive solution; In step S1, the solid content of the adhesive solution is 6%; Step S2: Add LATP solid electrolyte particles and dispersant AA-AMPS-HPA to the adhesive solution, mix evenly, and obtain the first slurry. In step S2, all of the oxide solid electrolyte and half of the dispersant are added. At this point, the mass ratio of the oxide solid electrolyte, dispersant, and binder is 25.6% : 2.6% : 71.8%. Step S3: Mix the first slurry, conductive carbon black and dispersant AA-AMPS-HPA evenly to prepare the second slurry; In step S3, all of the conductive agent and the other half of the dispersant are added. At this point, the mass ratio of the oxide solid electrolyte, conductive agent, dispersant, and binder is 14.3% : 42.9% : 2.8% : 40%. The third sub-operation is to prepare the final positive electrode: Step S1: The second slurry is coated on both sides of the initial positive electrode sheet obtained from the first sub-operation, and then the sheet is baked, rolled and slit (baking, rolling and slit are conventional battery electrode sheet production processes) to obtain the final positive electrode sheet.

[0080] In step S1, the second slurry is coated on one side (e.g., the upper surface) of the positive electrode sheet, and then coated on the other side (e.g., the lower surface), thus performing double-sided coating to obtain the positive electrode sheet. The single-sided coating thickness of the second slurry is 6µm. After rolling and slitting, the final desired positive electrode sheet is obtained.

[0081] To ensure a constant battery capacity, in Examples 1-14 of this invention, the areal density and compaction density of the positive electrode sheet are appropriately increased according to different amounts of solid electrolyte added. Since the particle size of the solid electrolyte is much smaller than that of the ternary positive electrode, it can be used as a filler, thereby increasing the compaction density of the positive electrode sheet. This maintains the same thickness of the positive electrode sheet in Examples 1-14, Comparative Examples 2-3, and Comparative Example 1, without affecting the battery's casing ratio.

[0082] In specific implementation, for this invention, when the amount of solid electrolyte added, i.e. in the positive electrode active material layer, the mass of the oxide solid electrolyte accounts for 2% or more (greater than or equal to 2%) of the total mass of all substances in the positive electrode active material layer, the content of liquid electrolyte accounts for less than 10% of the total weight of the battery (i.e., less than 10%), which meets the semi-solid battery standard.

[0083] To understand the performance of the batteries in Examples 1-14 and Comparative Examples 1-3, performance tests were conducted on these batteries as follows: I. Battery Fast Charging Cycle Life Test: For the batteries of Examples 1-14 and Comparative Examples 1-3, at room temperature, with a maximum current of 6C and a step-down current to a minimum of 1.5C, the batteries were charged from 10% SOC to 80% SOC, with the charging time controlled at 12 minutes. Then, the batteries were discharged at 1C to 3.0V. This is one charge-discharge cycle, defined as F charge-discharge cycle. Then, it is charged at 0.5C and discharged at 1C in sequence, cycling in the 0%-100% SOC range. This is one charge-discharge cycle process, defined as the N charge-discharge cycle process.

[0084] Repeat the charge-discharge cycle process 3 times F and 3 times N (3N3F cycle) until the battery reaches 600 cycles or the battery capacity retention drops to 80%.

[0085] II. Low-temperature battery cycling test: For the batteries of Examples 1-14 and Comparative Examples 1-3, in an environment of -20°C, in the range of 0%-100% SOC, one cycle is formed by charging at 1C and discharging at 1C, until the battery cycle count reaches 50 or the battery capacity retention rate drops to 90%.

[0086] III. Battery Thermal Safety Test: For the batteries of Examples 1-14 and Comparative Examples 1-3, the batteries were tested using an adiabatic accelerated calorimeter (ARC) at 100% SOC, and T1, T2, T3 and Δt were recorded to compare thermal runaway (TR) performance.

[0087] Here, T1 refers to the temperature at which the battery exhibits detectable self-generated heat, i.e., a heating rate of 0.02℃ / min. T2 represents the temperature at which the battery's heating rate exceeds 1℃ / s; and T3 refers to the highest temperature of the battery during thermal runaway (TR). Furthermore, Δt refers to the time interval between T1 and T2, which assesses the time required for the battery to enter thermal runaway (TR) under adiabatic conditions.

[0088] The test results for the batteries are shown in Table 2.

[0089] Table 2

[0090] Referring to Table 2, by comparing Examples 1-5 and Comparative Example 1 in Table 2, it can be seen that when solid electrolyte LATP is added to the positive electrode and coated, the fast charging cycle life and -20℃ cycle performance of the battery are improved. Examples 2-4 can meet the requirements of more than 80% for 600 cycles and more than 90% for 50 cycles, and Examples 3 and 4 are better.

[0091] Referring to Table 2, the fast-charge cycle and -20°C cycle performance of the battery in Example 5 were lower than those in Examples 3 and 4. This may be related to the high amount of LATP, which increases the ohmic resistance of the battery and reduces its conductivity. In addition, the addition of too much LATP led to a decrease in the amount of main material of the positive electrode and an excessively high areal density. The results of the adiabatic accelerated calorimeter (ARC) test showed that when solid electrolyte LATP was added to the positive electrode and coated, T1 and T2 did not improve significantly, while T3 gradually decreased with the increase of LATP content, and Δt gradually increased.

[0092] Referring to Table 2, comparing Examples 3, 7-9, and Comparative Example 1, it can be seen that when solid electrolyte LATP with different particle sizes (D50) is added to the positive electrode and a coating is applied to the positive electrode surface, the battery's fast-charging cycle life and -20°C cycle performance decrease as the LATP particle size increases. This may be related to the larger LATP particle size, resulting in gaps between particles and a decrease in ionic conductivity. The differences in T1 and T2 in the ARC test are not significant, while T3 generally shows a decreasing trend. Δt generally increases, but the difference is not significant, and the pattern is not obvious. In Example 6, the LATP particle size is too small, leading to a decrease in the battery's fast-charging cycle life and -20°C cycle performance, which should be related to poor dispersion of small-particle LATP.

[0093] Referring to Table 2, and comparing Examples 3, 10-11 and Comparative Example 1 in Table 2, it can be seen that when the Al content in the solid electrolyte LATP is different, the battery's fast charging capability, -20℃ cycling capability and ARC thermal stability change to some extent. This may be related to the fact that a high Al content can block ion channels, causing a decrease in fast charging and low-temperature discharge capability, while the thermal stability is better.

[0094] Referring to Table 2, a comparison of Examples 3, 12 and Comparative Example 1 in Table 2 shows that when the type of solid electrolyte is different, all of them have a positive effect on the battery's fast charging capability, -20℃ charging capability and ARC test results, while there is no significant difference between LAGP and LATP.

[0095] Referring to Table 2, and comparing Examples 3, 13-14 and Comparative Example 1 in Table 2, it can be seen that when the thickness of the solid electrolyte coating is reduced or increased, it has a certain impact on the battery's fast charging capability, -20℃ charging capability, and ARC test results. Increasing the thickness improves the electrothermal safety performance. In the ARC test, T3 decreases and Δt increases, but excessive coating thickness will lead to an overall decrease in battery capacity and energy density.

[0096] Referring to Table 2, a comparison of Example 3 and Comparative Examples 1-3 in Table 2 shows that when only the solid electrolyte LATP is added to the positive electrode or only a solid electrolyte coating is applied to the surface of the positive electrode, both have a positive impact on the battery's fast charging capability and thermal stability. When both work together, the improvement in battery performance is more significant.

[0097] The battery performance test results above basically achieve the objectives of this invention. The above embodiments demonstrate that, for this invention, by mixing different solid electrolytes and coating the surface to obtain the positive electrode, the battery can improve fast charging capability and low-temperature charging cycle performance while also possessing good thermal stability. This invention does not change the current mainstream manufacturing processes for positive electrodes and lithium-ion batteries, making it suitable for large-scale applications.

[0098] The present invention has been described through the above embodiments; however, the present invention is not limited to the embodiments described above. Similar effects can be obtained by using different solid electrolytes, different slurry ratios, different coating methods, and by updating the electrode design and changing the auxiliary materials.

[0099] This invention uses a cylindrical battery as an example, but it can also be applied to other types of batteries such as square and pouch batteries.

[0100] Compared with existing technologies, the composite cathode sheet, lithium-ion battery, and preparation method provided by this invention have the following technical advantages: 1. This invention provides a method for preparing a composite positive electrode sheet. First, an adhesive solution is prepared, then a first slurry, a second slurry, and finally a third slurry are obtained sequentially. After coating the third slurry into a first positive electrode sheet, a second slurry is then coated onto the surface of the first positive electrode sheet to obtain a composite positive electrode sheet. This method enables the solid electrolyte to be uniformly dispersed on the edge and surface of the positive electrode active material and to completely cover the surface of the electrode sheet. This improves the ion conduction capability and allows the electrolyte to participate in the formation of SEI / CEI, optimizing and stabilizing the internal / interface of the positive electrode, thereby improving the performance of the battery.

[0101] 2. The solid electrolyte of the present invention has a good match between its composition, particle size and addition amount, and the positive electrode surface density and compaction density design, so as to improve the battery performance without sacrificing battery capacity.

[0102] 3. This invention deeply explores the performance advantages of solid electrolytes for ternary all-tab cylindrical lithium-ion batteries. It not only shows great advantages in battery fast charging performance and 1C charging cycle performance at -20℃, but also has certain advantages in battery thermal safety.

[0103] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite positive electrode, characterized in that, Including the positive current collector (4); A positive electrode active material layer (5) is coated on the surface of the positive electrode current collector (4); A solid electrolyte layer (1) is coated on the surface of the positive electrode active material layer (5); Among them, the positive electrode active material layer (5) includes a positive electrode active material, an oxide solid electrolyte, a conductive agent, a dispersant and a binder; The solid electrolyte layer (1) includes an oxide solid electrolyte, a conductive agent, a dispersant, and a binder; In the positive electrode active material layer (5), the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant and binder is: (91.9%~97.45%): (0.5%~5%): (1%~1.5%): (0.05%~0.1%): (1%~1.5%). In the solid electrolyte layer (1), the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder is: (13.9%~70.9%): (13.2%~49.2%): (0.6%~3.8%): (13.2%~49.2%).

2. The composite positive electrode sheet as described in claim 1, characterized in that, The upper and lower surfaces of the positive current collector (4) are coated with a layer of positive active material (5); Each positive electrode active material layer (5) is coated with a solid electrolyte layer (1); The positive electrode active material layer (5) has oxide solid electrolyte particles (3) and positive electrode active material particles (2), and the oxide solid electrolyte particles (3) are distributed on the surface and edge of multiple positive electrode active material particles (2).

3. The composite positive electrode sheet as described in claim 1, characterized in that, In the positive electrode active material layer (5), the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant and binder is: 95%∶2%∶1.5%∶0.1%∶1.4%; Alternatively, in the positive electrode active material layer (5), the mass ratio between the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant and binder is 94%∶3%∶1.5%∶0.1%∶1.4%.

4. The composite positive electrode sheet as described in claim 1, characterized in that, In the solid electrolyte layer (1), the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder is 40%∶30%∶2%∶28%; Alternatively, in the solid electrolyte layer (1), the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder is 50%: 25%: 1.7%: 23.3%.

5. The composite positive electrode sheet as described in claim 1, characterized in that, In the positive electrode active material layer and the solid electrolyte layer, the oxide solid electrolyte is a NASICON structural material; NASICON structural materials, including Li 1+x Al x Ti 2-x (PO4)3(LATP) or its isomorphous heteroatomic doped compounds, Li 1+ x Al x Ge 2-x (PO4)3 (LAGP) or any one or more of its isomorphous heteroatomic doped compounds, wherein 0.1 ≤ x ≤ 0.7; In the positive electrode active material layer and the solid electrolyte layer, the particle size of the oxide solid electrolyte is D50 = 0.2~3μm; In the positive electrode active material layer, the mass of the oxide solid electrolyte is equal to 0.5% to 5% of the total mass of all substances in the positive electrode active material layer.

6. The composite positive electrode sheet as described in claim 5, characterized in that, For NASICON structural materials, x is 0.3, 0.4, or 0.5; The particle size of the oxide solid electrolyte is D50 = 0.4–2 μm; In the positive electrode active material layer, the mass of the oxide solid electrolyte is equal to 2% to 3% of the total mass of all substances in the positive electrode active material layer.

7. The composite positive electrode sheet as described in claim 1, characterized in that, In the positive electrode active material layer, the positive electrode active material is a high-nickel positive electrode material; High-nickel cathode materials include one or more of lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt manganese aluminum oxide (NCMA); In high-nickel cathode materials, the nickel content is 89-95 mol%; In the positive electrode active material layer and the solid electrolyte layer, the conductive agent includes one or more of Ketjen black, acetylene black, conductive carbon black, conductive graphite and carbon nanotubes; In both the positive electrode active material layer and the solid electrolyte layer, the dispersant is an acrylate copolymer; In both the positive electrode active material layer and the solid electrolyte layer, the binder is polyvinylidene fluoride (PVDF).

8. A method for preparing a composite positive electrode sheet as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step S1: Add the adhesive to NMP as a solvent and mix until the adhesive is completely dissolved to obtain an adhesive solution; Step S2: Add the oxide solid electrolyte particles and dispersant to the binder solution, mix evenly, and obtain the first slurry; Step S3: Mix the first slurry, conductive agent, and dispersant evenly to prepare the second slurry; Step S4: Mix the second slurry and the positive electrode active material evenly and stir at high speed to prepare the third slurry; Step S5: The third slurry is coated onto the surface of the positive electrode current collector and dried to obtain the first positive electrode sheet; Step S6: The second slurry is coated onto the surface of the first positive electrode sheet, and then the composite positive electrode sheet is obtained through baking, rolling and slitting processes. In step S2, the mass ratio of oxide solid electrolyte, dispersant and binder in the first slurry is (24.4~83%): (0.4~3.2%): (16.5~74.1%). In step S3, the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder in the second slurry is: (13.9%~70.9%): (13.2%~49.2%): (0.6%~3.8%): (13.2%~49.2%). In step S4, the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant and binder in the third slurry is: (91.9%~97.45%): (0.5%~5%): (1%~1.5%): (0.05%~0.1%): (1%~1.5%).

9. The preparation method according to claim 8, characterized in that, In step S2, the mass ratio of oxide solid electrolyte, dispersant, and binder in the first slurry is 58% : 1.4% : 40.6%; Alternatively, in step S2, the mass ratio of the oxide solid electrolyte, dispersant, and binder in the first slurry is 67.4% : 1.1% : 31.5%; In step S3, the mass ratio of oxide solid electrolyte, conductive agent, dispersant and binder in the second slurry is 40%∶30%∶2%∶28%; Alternatively, in step S3, the mass ratio of the oxide solid electrolyte, conductive agent, dispersant, and binder in the second slurry is 50% : 25% : 1.7% : 23.3%; In step S4, the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant, and binder in the third slurry is 95%∶2%∶1.5%∶0.1%∶1.4%; Alternatively, in step S4, the mass ratio of the positive electrode active material, oxide solid electrolyte, conductive agent, dispersant, and binder in the third slurry is 94%∶3%∶1.5%∶0.1%∶1.4%; In step S6, the thickness of the second slurry coating layer is 3-10µm; In step S6, the compaction density of the composite positive electrode is 3.4-3.6 g / cm³. 3 ; In step S6, the areal density of the composite positive electrode is 40.2~42.2 mg / cm³. 2 .

10. A lithium-ion battery, characterized in that, Includes the composite positive electrode sheet as described in any one of claims 1 to 7.

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