Lithium-rich manganese-based positive electrode material, preparation method thereof, positive electrode sheet and battery

Abstract

The application provides a lithium-rich manganese-based positive electrode material and a preparation method thereof, a positive electrode sheet and a battery. The preparation method of the lithium-rich manganese-based positive electrode material comprises the following steps: mixing a nickel-cobalt-manganese mixed salt solution, a precipitant solution and a complexing agent solution, performing a co-precipitation reaction, and preparing a lithium-rich manganese-based precursor; dispersing the lithium-rich manganese-based precursor in an alkaline aqueous solution, stirring and aging to prepare a modified lithium-rich manganese-based precursor; wherein the alkaline aqueous solution comprises one or more of a soluble molybdate and a soluble tungstate; mixing the modified lithium-rich manganese-based precursor and a lithium source, and sintering to prepare the lithium-rich manganese-based positive electrode material. The preparation method of the lithium-rich manganese-based positive electrode material provided by the application can significantly inhibit voltage decay while maintaining high capacity characteristics, thereby improving the cycle stability of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to lithium-rich manganese-based cathode materials, their preparation methods, cathode sheets, and batteries. Background Technology

[0002] Lithium-rich manganese-based cathode materials (xLi2MnO3·(1-x)LiMO2, M=Ni, Co, Mn) have become a research hotspot for next-generation lithium-ion battery cathode materials due to their high specific capacity (>250mAh / g) and low cost.

[0003] In practical power battery applications, lithium-rich manganese-based cathode materials suffer from severe voltage decay during cycling, affecting the cycle stability of the battery.

[0004] In traditional technologies, oxide layers or other coatings are often applied to the surface of lithium-rich manganese-based substrates to suppress interfacial side reactions. However, during cycling, the interface between the coating layer and the substrate is prone to delamination, leading to increased interfacial impedance and making it difficult to effectively suppress voltage decay over a long period.

[0005] CN112164784A discloses a quaternary concentration gradient core-shell lithium-ion battery cathode material and its preparation method. The method involves designing a gradient of component concentrations and controlling the pH value of the solid-liquid mixture during the reaction to synthesize a high-nickel NCM core and a doped concentration gradient quaternary hybrid precursor material to suppress voltage decay and improve cycle performance. However, this method requires high control over the co-precipitation process, is complex, has a long reaction cycle, demands sophisticated equipment, and suffers from large batch-to-batch variations, making industrial-scale production difficult. Summary of the Invention

[0006] Based on this, the technical problem to be solved by this application is how to provide a new method for preparing lithium-rich manganese-based cathode materials that can significantly suppress voltage decay and improve the cycle stability of the battery while maintaining high capacity characteristics. At the same time, it makes minimal changes to the traditional lithium-rich manganese-based material synthesis process, has low requirements for co-precipitation process control, is simple to prepare, can greatly reduce equipment requirements and batch fluctuations, and is easy to industrialize. To address the aforementioned technical issues, this application involves dispersing a lithium-rich manganese-based precursor in an alkaline aqueous solution containing soluble molybdate and / or soluble tungstate for stirring and aging. This process allows molybdate and / or tungstate ions to be uniformly adsorbed onto the precursor surface beforehand. During calcination, molybdate and / or tungstate ions diffuse from the surface into the bulk phase and enter the crystal lattice, forming a surface-modified layer. Simultaneously, the chemical affinity between Co ions and the diffused Mo / W elements at high temperatures induces Co ions to spontaneously migrate and accumulate in the near-surface region (subsurface layer) with higher Mo / W concentrations, forming a stable composite oxide. Manganese ions, limited by the presence of Co and Mo / W elements in the subsurface layer, tend to remain in the inner layer, thus spontaneously forming a concentration gradient structure of a Mo / W surface-modified layer, a Co-rich and Mo / W-rich subsurface layer, and a Mn-rich inner layer. During electrochemical cycling, the Mo / W surface-modified layer continuously acts as an elemental buffer, reducing direct contact between the electrolyte and highly active surfaces (especially the Li2MnO3 component) and suppressing surface phase transitions. The Co-rich and Mo / W subsurface layers possess extremely high structural stability, mitigating lattice oxygen loss. The Mn-rich inner layer maintains the material's high capacity characteristics. Therefore, the lithium-rich manganese-based cathode material prepared by the above method, when applied to battery systems, can significantly suppress voltage decay and improve battery cycle stability while maintaining high capacity characteristics. Furthermore, the above preparation method involves minimal changes to the traditional synthesis process of lithium-rich manganese-based materials, has low requirements for co-precipitation process control, is simple to prepare, and can significantly reduce equipment requirements and batch variations, facilitating industrial production.

[0007] A first aspect of this application provides a method for preparing a lithium-rich manganese-based cathode material, the method comprising the following steps: mixing a nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution to perform a co-precipitation reaction to prepare a lithium-rich manganese-based precursor; dispersing the lithium-rich manganese-based precursor in an alkaline aqueous solution for stirring and aging treatment to prepare a modified lithium-rich manganese-based precursor; wherein the alkaline aqueous solution includes one or more of soluble molybdate and soluble tungstate; mixing the modified lithium-rich manganese-based precursor with a lithium source and sintering to prepare a lithium-rich manganese-based cathode material.

[0008] In some embodiments, after the stirring and aging treatment step, the preparation method further includes: sequentially performing solid-liquid separation, water washing, and drying.

[0009] In some embodiments, the preparation method satisfies at least one of the following conditions: (1) the washing endpoint of the water washing is that the washing liquid is neutral; (2) the drying temperature is 100℃~140℃ and the drying time is 8h~12h.

[0010] In some embodiments, the preparation method satisfies at least one of the following conditions: (1) the molar ratio of nickel, cobalt and manganese in the nickel-cobalt-manganese mixed salt solution is x:y:z, where x+y+z=1 and z≥0.6; (2) the mass concentration of the nickel-cobalt-manganese mixed salt solution is 80 g / L~120 g / L; (3) the precipitant in the precipitant solution includes one or more of sodium hydroxide and potassium hydroxide; (4) the mass concentration of the precipitant solution is 50 g / L~200 g / L; (5) the complexing agent in the complexing agent solution includes one or more of ammonia, ammonium bicarbonate, ammonium sulfate and ammonium oxalate; (6) the mass concentration of the complexing agent solution is 2 g / L~20 g / L. g / L; (7) The pH value of the coprecipitation reaction is 9.5~11.5; (8) The alkali in the alkaline aqueous solution includes one or more of sodium hydroxide and potassium hydroxide; (9) The pH value of the alkaline aqueous solution is 9~11; (10) The total mass concentration of soluble molybdate and soluble tungstate in the alkaline aqueous solution is 0.1 g / L~10 g / L; (11) Soluble molybdate includes Na2MoO4 and (NH4)6Mo7O 24 One or more of the following; (12) soluble tungstates include Na2WO4 and (NH4). 10 W 12 O 41 One or more of the following: (13) The mass-volume ratio of lithium-rich manganese-based precursor to alkaline aqueous solution is 1 g: (2~10) mL; (14) The temperature of stirring aging treatment is 25℃~80℃; (15) The time of stirring aging treatment is 0.5h~4h; (16) The stirring speed of stirring aging treatment is 150r / min~350r / min; (17) The lithium source is selected from one or more of lithium hydroxide and lithium carbonate.

[0011] In some embodiments, the alkaline aqueous solution also includes a surfactant.

[0012] In some embodiments, the surfactant satisfies at least one of the following conditions: (1) the surfactant includes one or more of polyethylene glycol and polyvinylpyrrolidone; (2) the concentration of the surfactant in the alkaline aqueous solution is 0.5 g / L to 5 g / L.

[0013] In some embodiments, the sintering step includes: pre-sintering at 400°C to 600°C for 3 to 8 hours in an oxygen-containing atmosphere, followed by high-temperature sintering at 800°C to 1000°C for 8 to 15 hours.

[0014] A second aspect of this application provides a lithium-rich manganese-based cathode material, which is prepared using the method for preparing the lithium-rich manganese-based cathode material provided in the first aspect above.

[0015] A third aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one side surface of the positive current collector, wherein the positive electrode material layer includes the lithium-rich manganese-based positive electrode material provided in the second aspect above.

[0016] A fourth aspect of this application provides a battery having the positive electrode provided in the third aspect above.

[0017] Compared with traditional technologies, the beneficial effects of this application are as follows:

[0018] The method for preparing lithium-rich manganese-based cathode material provided in this application involves dispersing a lithium-rich manganese-based precursor in an alkaline aqueous solution containing soluble molybdate and / or soluble tungstate and then stirring and aging it to allow molybdate and / or tungstate ions to be uniformly adsorbed on the precursor surface beforehand. During calcination, molybdate and / or tungstate ions diffuse from the surface into the bulk phase and enter the crystal lattice through reaction-diffusion coupling, forming a surface-modified layer. At the same time, the chemical affinity between Co ions and Mo / W elements in the diffusion process at high temperature induces Co ions to spontaneously migrate and accumulate in the near-surface region (subsurface layer) with a higher Mo / W concentration, forming a stable composite oxide. Manganese ions, limited by the occupation of Co and Mo / W elements in the subsurface layer, tend to remain in the inner layer, thus spontaneously forming a concentration gradient structure of Mo / W surface-modified layer, Co-rich and Mo / W-rich subsurface layer, and Mn-rich inner layer. During electrochemical cycling, the Mo / W surface-modified layer continuously acts as an elemental buffer, reducing direct contact between the electrolyte and highly active surfaces (especially the Li2MnO3 component) and suppressing surface phase transitions. The Co-rich and Mo / W subsurface layer exhibits extremely high structural stability, mitigating lattice oxygen loss. The Mn-rich inner layer maintains the material's high capacity characteristics. Therefore, the lithium-rich manganese-based cathode material prepared by the above method, when applied to battery systems, can significantly suppress voltage decay and improve battery cycle stability while maintaining high capacity characteristics.

[0019] Furthermore, the above preparation method makes minimal changes to the traditional synthesis process of lithium-rich manganese-based materials, has low requirements for co-precipitation process control, is simple to prepare, can significantly reduce equipment requirements and batch fluctuations, and is easy to industrialize. Attached Figure Description

[0020] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the embodiments or examples currently described, or the best mode of these applications as currently understood.

[0021] Figure 1 This is a schematic diagram of the process flow for preparing a lithium-rich manganese-based cathode material in one embodiment. Detailed Implementation

[0022] Reference will now be made to detailed embodiments of this application, one or more of which are described below. Each example is provided for explanation and not for limitation of this application. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to this application without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0023] Therefore, this application is intended to cover such modifications and variations falling within the scope of the appended claims and their equivalents. Other objects, features, and aspects of this application are disclosed in or will be apparent from the following detailed description. It will be understood by those skilled in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of this application.

[0024] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0025] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0026] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0027] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0028] Unless otherwise specified, the terms "comprising" and "including" as used in this application 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.

[0029] The first aspect of this application provides a method for preparing lithium-rich manganese-based cathode materials, such as... Figure 1 As shown, the preparation method includes the following steps:

[0030] S1. Mix the nickel-cobalt-manganese mixed salt solution, precipitant solution and complexing agent solution, and carry out a co-precipitation reaction to prepare a lithium-rich manganese-based precursor.

[0031] S2. A modified lithium-rich manganese-based precursor is prepared by dispersing a lithium-rich manganese-based precursor in an alkaline aqueous solution and then stirring and aging it. The alkaline aqueous solution includes one or more of soluble molybdate and soluble tungstate.

[0032] S3. The modified lithium-rich manganese-based precursor and lithium source are mixed and sintered to prepare lithium-rich manganese-based cathode material.

[0033] The method for preparing lithium-rich manganese-based cathode material provided in this application involves dispersing a lithium-rich manganese-based precursor in an alkaline aqueous solution containing soluble molybdate and / or soluble tungstate and then stirring and aging it to allow molybdate and / or tungstate ions to be uniformly adsorbed on the precursor surface beforehand. During calcination, molybdate and / or tungstate ions diffuse from the surface into the bulk phase and enter the crystal lattice through reaction-diffusion coupling, forming a surface-modified layer. At the same time, the chemical affinity between Co ions and Mo / W elements in the diffusion process at high temperature induces Co ions to spontaneously migrate and accumulate in the near-surface region (subsurface layer) with a higher Mo / W concentration, forming a stable composite oxide. Manganese ions, limited by the occupation of Co and Mo / W elements in the subsurface layer, tend to remain in the inner layer, thus spontaneously forming a concentration gradient structure of Mo / W surface-modified layer, Co-rich and Mo / W-rich subsurface layer, and Mn-rich inner layer. During electrochemical cycling, the Mo / W surface-modified layer continuously acts as an elemental buffer, reducing direct contact between the electrolyte and highly active surfaces (especially the Li2MnO3 component) and suppressing surface phase transitions. The Co-rich and Mo / W subsurface layer exhibits extremely high structural stability, mitigating lattice oxygen loss. The Mn-rich inner layer maintains the material's high capacity characteristics. Therefore, the lithium-rich manganese-based cathode material prepared by the above method, when applied to batteries, can significantly suppress voltage decay and improve battery cycle stability while maintaining high capacity characteristics.

[0034] Furthermore, the above preparation method makes minimal changes to the traditional synthesis process of lithium-rich manganese-based materials, has low requirements for co-precipitation process control, is simple to prepare, can significantly reduce equipment requirements and batch fluctuations, and is easy to industrialize.

[0035] In some embodiments, after the stirring and aging treatment step, the preparation method further includes: sequentially performing solid-liquid separation, water washing, and drying. Thus, by washing the precursor after stirring and aging, residual impurity ions on the surface of the precursor particles can be effectively removed, ensuring that only adsorbed molybdate ions and / or tungstate ions participate in the subsequent sintering diffusion reaction, controlling the amount of modifying elements introduced, and improving the structural stability and purity of the cathode material.

[0036] In some implementations, the washing endpoint is when the washing solution is neutral.

[0037] Furthermore, the number of washes is 2 to 5. For example, the number of washes can be, but is not limited to, 2, 3, 4, or 5.

[0038] In some embodiments, the drying temperature is 100℃~140℃, and the drying time is 8h~12h. Exemplarily, the drying temperature can be, but is not limited to, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, or 140℃; and the drying time can be, but is not limited to, 8h, 9h, 10h, 11h, or 12h.

[0039] In some embodiments, in step S1, the molar ratio of nickel, cobalt, and manganese in the nickel-cobalt-manganese mixed salt solution is x:y:z, where x+y+z=1 and z≥0.6. Further, 0 <x≤0.4。

[0040] In some embodiments, in step S1, the mass concentration of the nickel-cobalt-manganese mixed salt solution is 80 g / L to 120 g / L. Exemplarily, the mass concentration of the nickel-cobalt-manganese mixed salt solution can be, but is not limited to, 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L, or 120 g / L.

[0041] In some embodiments, in step S1, the precipitant in the precipitant solution includes one or more of sodium hydroxide and potassium hydroxide.

[0042] In some embodiments, in step S1, the mass concentration of the precipitant solution is 50 g / L to 200 g / L. Exemplarily, the mass concentration of the precipitant solution can be, but is not limited to, 50 g / L, 60 g / L, 80 g / L, 100 g / L, 120 g / L, 140 g / L, 160 g / L, 180 g / L, or 200 g / L.

[0043] In some embodiments, in step S1, the complexing agent in the complexing agent solution includes one or more of ammonia, ammonium bicarbonate, ammonium sulfate, and ammonium oxalate.

[0044] In some embodiments, in step S1, the mass concentration of the complexing agent solution is 2 g / L to 20 g / L. Exemplarily, the mass concentration of the complexing agent solution can be, but is not limited to, 2 g / L, 4 g / L, 6 g / L, 8 g / L, 10 g / L, 12 g / L, 14 g / L, 16 g / L, 18 g / L, or 20 g / L.

[0045] In some embodiments, the pH value of the coprecipitation reaction in step S1 is 9.5 to 11.5. Exemplarily, the pH value of the coprecipitation reaction can be, but is not limited to, 9.5, 10, 10.5, 11, or 11.5.

[0046] In some embodiments, step S1 specifically includes: introducing a nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution concurrently into the reaction substrate to perform a co-precipitation reaction and form a lithium-rich manganese-based precursor. The pH of the reaction substrate is 11.0 to 12.5. Exemplarily, the pH of the reaction substrate can be, but is not limited to, 11.0, 11.5, 12.0, or 12.5.

[0047] In some embodiments, in step S2, the alkali in the alkaline aqueous solution includes one or more of sodium hydroxide and potassium hydroxide.

[0048] In some embodiments, the pH value of the alkaline aqueous solution in step S2 is 9-11. Exemplarily, the pH value of the alkaline aqueous solution can be, but is not limited to, 9, 9.5, 10, 10.5, or 11. Thus, by controlling the pH value of the alkaline aqueous solution at 9-11, a highly hydroxylated state on the precursor surface is maintained using a strongly alkaline environment, ensuring that the precursor particle surface has a large number of active sites, thereby inducing molybdate / tungstate ions to be stably anchored to the particle surface through adsorption.

[0049] In some embodiments, in step S2, the total mass concentration of soluble molybdate and soluble tungstate in the alkaline aqueous solution is 0.1 g / L to 10 g / L. Exemplarily, the total mass concentration of soluble molybdate and soluble tungstate in the alkaline aqueous solution can be, but is not limited to, 0.1 g / L, 0.5 g / L, 1 g / L, 2 g / L, 4 g / L, 6 g / L, 8 g / L, or 10 g / L. Thus, an alkaline aqueous solution with a mass concentration of soluble molybdate and soluble tungstate of 0.1 g / L to 10 g / L can achieve uniform adsorption of molybdate / tungstate ions on the particle surface while avoiding localized aggregation caused by excessively high concentrations.

[0050] In some embodiments, in step S2, the soluble molybdate includes Na2MoO4 and (NH4)6Mo7O 24 One or more of them.

[0051] In some embodiments, in step S2, the soluble tungstate includes Na2WO4 and (NH4). 10 W 12 O 41 One or more of them.

[0052] In some embodiments, in step S2, the mass-to-volume ratio of the lithium-rich manganese-based precursor to the alkaline aqueous solution is 1 g: (2~10) mL. Exemplarily, the mass-to-volume ratio of the lithium-rich manganese-based precursor to the alkaline aqueous solution can be, but is not limited to, 1 g: 2 mL, 1 g: 5 mL, or 1 g: 10 mL. Thus, by controlling the mass-to-volume ratio of the precursor to the alkaline aqueous solution, it is ensured that the precursor particles can be completely wetted in the solution, allowing molybdate / tungstate ions to be uniformly adsorbed onto the surface of each particle.

[0053] In some embodiments, the temperature of the stirring aging process in step S2 is 25°C to 80°C. Exemplarily, the temperature of the stirring aging process can be, but is not limited to, 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, or 80°C.

[0054] Furthermore, the temperature for the stirring and aging process is 40℃~80℃.

[0055] In some embodiments, the stirring and aging process in step S2 is carried out for 0.5 hours to 4 hours. For example, the stirring and aging process can be, but is not limited to, 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours.

[0056] Thus, by stirring and aging at 25℃~80℃ for 0.5h~4h, it is ensured that molybdate / tungstate ions can be uniformly adsorbed onto the surface of each particle, and the precursor particles can be completely wetted in the solution, so that molybdate / tungstate ions can be uniformly adsorbed onto the surface of each particle.

[0057] In some embodiments, in step S2, the stirring speed of the stirring aging process is 150 r / min to 350 r / min. Exemplarily, the stirring speed of the stirring aging process can be, but is not limited to, 150 r / min, 250 r / min, or 350 r / min.

[0058] In some embodiments, the alkaline aqueous solution in step S2 further includes a surfactant. Thus, by utilizing the wetting and dispersing effects of the surfactant, the interfacial tension between the precursor particles and the aqueous solution is significantly reduced, inhibiting the aggregation of precursor particles and achieving uniform loading of molybdate / tungstate ions on the surface of the precursor particles.

[0059] In some embodiments, in step S2, the surfactant includes one or more of polyethylene glycol and polyvinylpyrrolidone.

[0060] In some embodiments, in step S2, the concentration of the surfactant in the alkaline aqueous solution is 0.5 g / L to 5 g / L. Exemplarily, the concentration of the surfactant in the alkaline aqueous solution can be, but is not limited to, 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L, or 5 g / L.

[0061] In some embodiments, in step S3, the lithium source is selected from one or more of lithium hydroxide and lithium carbonate.

[0062] In some embodiments, step S3, the sintering step, includes: pre-sintering at 400℃~600℃ for 3h~8h in an oxygen-containing atmosphere, followed by high-temperature sintering at 800℃~1000℃ for 8h~15h. Exemplarily, the pre-sintering temperature can be, but is not limited to, 400℃, 450℃, 500℃, 550℃, or 600℃; the pre-sintering time can be, but is not limited to, 3h, 4h, 5h, 6h, 7h, or 8h; the high-temperature sintering temperature can be, but is not limited to, 800℃, 850℃, 900℃, 950℃, or 1000℃; and the high-temperature sintering time can be, but is not limited to, 8h, 9h, 10h, 11h, 12h, 13h, 14h, or 15h.

[0063] Specifically, an oxygen-containing atmosphere includes one or more types of oxygen and air.

[0064] A second aspect of this application provides a lithium-rich manganese-based cathode material, which is prepared using the method for preparing the lithium-rich manganese-based cathode material provided in the first aspect above.

[0065] A third aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one side surface of the positive current collector, wherein the positive electrode material layer includes the lithium-rich manganese-based positive electrode material provided in the second aspect above.

[0066] A fourth aspect of this application provides a battery having the positive electrode provided in the third aspect above.

[0067] The present application will be further described below with reference to specific embodiments and comparative examples.

[0068] Where specific techniques or conditions are not specified in the examples, 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 commercially available conventional products.

[0069] Example 1

[0070] Lithium-rich manganese-based cathode materials:

[0071] S1. Preparation of lithium-rich manganese-based precursor: Nickel sulfate, cobalt sulfate, and manganese sulfate were weighed according to the molar ratio of Ni:Co:Mn=0.30:0.05:0.65 to prepare a nickel-cobalt-manganese mixed salt solution with a mass concentration of 95 g / L. At the same time, a sodium hydroxide solution with a mass concentration of 100 g / L and an ammonia solution with a mass concentration of 10 g / L were prepared. The nickel-cobalt-manganese mixed salt solution, sodium hydroxide solution, and ammonia solution were introduced concurrently into a reaction vessel containing the reaction base liquid (pH 12.5). Co-precipitation reaction was carried out at a temperature of 60℃ and a stirring speed of 500 r / min, and the pH of the reaction system was controlled at 10.0. After the reaction, the precursor was obtained by solid-liquid separation, water washing (washing 3 times until the washing liquid was neutral) and drying (drying temperature 120℃).

[0072] S2. Preparation of modified lithium-rich manganese-based precursor: Prepare an aqueous solution of sodium hydroxide with a pH of 10, add Na2MoO4 and Na2WO4 to it, and simultaneously add polyethylene glycol to obtain an alkaline aqueous solution, wherein the mass concentration of Na2MoO4 is 0.5 g / L, the mass concentration of Na2WO4 is 1 g / L, and the mass concentration of polyethylene glycol is 1 g / L; disperse the lithium-rich manganese-based precursor obtained in step S1 in the alkaline aqueous solution at a mass-volume ratio of 1 g: 5 mL, and stir and age it for 2 h at a temperature of 40℃ and a stirring speed of 200 r / min, then perform solid-liquid separation, water washing, and drying at 120℃ for 10 h to obtain the modified lithium-rich manganese-based precursor.

[0073] S3. Preparation of lithium-rich manganese-based cathode material: The modified lithium-rich manganese-based precursor obtained in step S2 is mixed with lithium hydroxide at a molar ratio of lithium to total metal elements of 1.5:1. The mixed material is placed in an air atmosphere furnace and pre-sintered at 500℃ for 6 hours, followed by high-temperature sintering at 900℃ for 10 hours. After furnace cooling, pulverization and sieving, lithium-rich manganese-based cathode material is obtained.

[0074] Positive electrode sheet:

[0075] The above-mentioned lithium-rich manganese-based cathode material, SP, and PVDF were mixed and dispersed in N-methylpyrrolidone at a mass ratio of 90:5:5, and stirred to obtain a slurry. The obtained slurry was uniformly coated on aluminum foil, and then rolled and dried sequentially to obtain an areal density of 4.5 mg·cm³. -2 The positive electrode sheet.

[0076] Battery:

[0077] A CR2032 coin cell was assembled using a lithium metal sheet as the negative electrode, a PP microporous membrane (model: Celgard2400) as the separator, and 1 mol / L LiPF6 as the electrolyte (the solvent is a mixed solvent of ethylene carbonate and diethyl carbonate in a 1:1 volume ratio).

[0078] Example 2

[0079] The preparation methods of the lithium-rich manganese-based cathode material, cathode sheet, and battery in this embodiment are basically the same as those in Example 1, except that:

[0080] In step S1, the mass concentration of the mixed salt solution is 80 g / L; the precipitant solution is 50 g / L potassium hydroxide solution; the complexing agent solution is 2 g / L ammonium bicarbonate solution; the pH of the reaction substrate is 11.0; and the pH of the coprecipitation reaction is 9.5.

[0081] In step S2, the pH of the alkaline aqueous solution is adjusted to 9 using potassium hydroxide; the soluble molybdate is (NH4)6Mo7O. 24 (NH4)6Mo7O 24 The mass concentration was 0.1 g / L; the surfactant used was polyvinylpyrrolidone (PVP), with a mass concentration of 0.5 g / L; the mass-volume ratio of the precursor to the alkaline aqueous solution was 1 g: 3 mL; the stirring and aging treatment was carried out at a temperature of 25℃ for 0.5 h; the number of water washes in step S2 was 3, until the washing solution was neutral; the drying temperature was 100℃ and the drying time was 8 h.

[0082] In step S3, lithium carbonate is selected as the lithium source; the pre-sintering temperature is 400℃ and the pre-sintering time is 3h; the high-temperature sintering temperature is 800℃ and the high-temperature sintering time is 8h.

[0083] Example 3

[0084] The preparation methods of the lithium-rich manganese-based cathode material, cathode sheet, and battery in this embodiment are basically the same as those in Example 1, except that:

[0085] In step S1, the mass concentration of the mixed salt solution is 120 g / L; the mass concentration of the precipitant solution is 200 g / L; the complexing agent solution is 20 g / L ammonium oxalate solution; the pH of the reaction substrate is 12.5; and the pH of the coprecipitation reaction is 11.5.

[0086] In step S2, the pH of the alkaline aqueous solution is 11; the soluble tungstate is (NH4)2. 10 W 12 O 41 (NH4) 10 W 12 O 41 The mass concentration of the precursor was 10 g / L; the mass concentration of polyethylene glycol was 5 g / L; the mass-volume ratio of the precursor to the alkaline aqueous solution was 1 g: 6 mL; the stirring and aging treatment was carried out at 80℃ for 4 h; the number of water washes in step S2 was 4, and the washing solution was washed until it was neutral; the drying temperature was 140℃ and the drying time was 8 h.

[0087] In step S3, the lithium source is lithium hydroxide and lithium carbonate with a mass ratio of 1:1; the pre-sintering temperature is 600℃ and the pre-sintering time is 8h; the high-temperature sintering temperature is 1000℃ and the high-temperature sintering time is 15h.

[0088] Example 4

[0089] The preparation methods of the lithium-rich manganese-based cathode material, cathode sheet, and battery in this embodiment are basically the same as those in Example 1, except that:

[0090] In step S2, polyethylene glycol is not added.

[0091] Comparative Example 1

[0092] Lithium-rich manganese-based cathode materials:

[0093] S1. Preparation of lithium-rich manganese-based precursor: Nickel sulfate, cobalt sulfate, and manganese sulfate were weighed according to the molar ratio of Ni:Co:Mn=0.30:0.05:0.65 to prepare a nickel-cobalt-manganese mixed salt solution with a mass concentration of 95 g / L. At the same time, a sodium hydroxide solution with a mass concentration of 100 g / L and an ammonia solution with a mass concentration of 10 g / L were prepared. The nickel-cobalt-manganese mixed salt solution, sodium hydroxide solution, and ammonia solution were introduced concurrently into a reaction vessel containing the reaction base liquid (pH 12.5). Co-precipitation reaction was carried out at a temperature of 60℃ and a stirring speed of 500 r / min, and the pH of the reaction system was controlled at 10. After the reaction, the precursor was obtained by solid-liquid separation, water washing (washing 3 times until the washing liquid was neutral) and drying (drying temperature 120℃).

[0094] S2. Preparation of lithium-rich manganese-based cathode material: The lithium-rich manganese-based precursor obtained in step S1 is mixed with lithium hydroxide at a molar ratio of lithium to total metal elements of 1.5:1. The mixed material is placed in an air atmosphere furnace and pre-sintered at 500℃ for 6 hours, followed by high-temperature sintering at 900℃ for 10 hours. After cooling in the furnace, crushing and sieving, the lithium-rich manganese-based cathode material is obtained.

[0095] Positive electrode sheet:

[0096] The above-mentioned lithium-rich manganese-based cathode material, SP, and PVDF were mixed and dispersed in N-methylpyrrolidone at a mass ratio of 90:5:5, and stirred to obtain a slurry. The obtained slurry was uniformly coated on aluminum foil, and then rolled and dried sequentially to obtain an areal density of 4.5 mg·cm³. -2 The positive electrode sheet.

[0097] Battery:

[0098] A CR2032 coin cell was assembled using a lithium metal sheet as the negative electrode, a PP microporous membrane (model: Celgard2400) as the separator, and 1 mol / L LiPF6 as the electrolyte (the solvent is a mixed solvent of ethylene carbonate and diethyl carbonate in a 1:1 volume ratio).

[0099] Performance testing

[0100] (1) XPS test

[0101] XPS (X-ray photoelectron spectroscopy) tests were performed on the lithium-rich manganese-based cathode material particles of Example 1. The lithium-rich manganese-based cathode material particles were etched from the surface to the inside using argon ion etching technology, and the changes in the intensity of the Mo 3d, W 4f, Co 2p and Mn 2p energy spectrum peaks were recorded.

[0102] The test results of XPS deep profiling data are shown in Table 1.

[0103] Table 1

[0104]

[0105] Test results show that as the etching depth increases, the signal intensities of Mo and W gradually weaken, the signal intensity of Co shows a trend of first increasing and then decreasing, while the signal intensity of Mn gradually increases and tends to stabilize. This demonstrates that the lithium-rich manganese-based cathode material obtained in Example 1 of this application successfully forms a concentration gradient structure from the outside in: a Mo / W surface modification layer, a Co / Mo / W subsurface layer, and a Mn-rich inner layer.

[0106] (2) Electrochemical performance testing

[0107] Coin cells prepared from the lithium-rich manganese-based cathode materials of Examples 1-4 and Comparative Example 1 were subjected to charge-discharge tests at 25°C. The voltage range for the charge-discharge tests was 2.0V to 4.8V.

[0108] Continuous charge-discharge cycles were performed at a constant current density of 0.1C. The discharge capacity of the first cycle and the discharge capacity after the 100th cycle were recorded, and the capacity retention rate was calculated using the following formula: Capacity retention rate (%) = (Discharge capacity of the 100th cycle / Discharge capacity of the first cycle) × 100%.

[0109] Meanwhile, the average median voltage of the discharge platform in the 1st and 100th cycles is recorded, and the voltage decay rate of 100 cycles is calculated by the following formula: [(average median voltage of the 1st cycle - average median voltage of the 100th cycle) / average median voltage of the 1st cycle] × 100%.

[0110] The test results are shown in Table 2.

[0111] Table 2

[0112]

[0113] As shown in Table 2, comparing Examples 1-3 and Comparative Example 1, it can be seen that the coin cells made from the lithium-rich manganese-based cathode materials prepared in Examples 1-3 can maintain a high first-cycle discharge specific capacity (>250 mAh·g). -1 At the same time, the voltage decay rate was significantly lower than that of Comparative Example 1 (all were lower than 3.2%), and the cycle capacity retention rate was above 95%. This indicates that the gradient structure of "Mo / W surface modified layer - Co / Mo / W rich subsurface layer - Mn rich inner layer" formed by the preparation method of lithium-rich manganese-based cathode material provided in this application can be applied to the battery system to improve the structural stability of the material while maintaining high capacity characteristics, thereby effectively suppressing voltage decay and improving the cycle stability of the battery.

[0114] Comparing Examples 1 and 4, it can be seen that the voltage decay rate (1.5%) of the coin cell prepared with the lithium-rich manganese-based cathode material of Example 1 after 100 cycles is lower than that of Comparative Example 1 (3.2%). At the same time, the capacity retention rate (96.8%) of the coin cell prepared with the lithium-rich manganese-based cathode material of Example 1 after 100 cycles is higher than that of Comparative Example 1 (95.1%). This proves that the surfactant can improve the dispersibility of the precursor in alkaline aqueous solution, inhibit the agglomeration of precursor particles, and enable molybdate and tungstate ions to be more uniformly adsorbed on the surface of precursor particles, thereby significantly improving the uniformity of the distribution of modified elements. After calcination, a gradient concentration structure with more complete coverage and a denser structure can be formed, which can more effectively suppress voltage decay and improve the cycle stability of the battery.

[0115] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0116] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing lithium-rich manganese-based cathode materials, characterized in that, Includes the following steps: A lithium-rich manganese-based precursor was prepared by mixing a nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution and carrying out a co-precipitation reaction. The lithium-rich manganese-based precursor is dispersed in an alkaline aqueous solution and subjected to stirring and aging treatment to prepare a modified lithium-rich manganese-based precursor; wherein, the alkaline aqueous solution includes one or more of soluble molybdate and soluble tungstate; The modified lithium-rich manganese-based precursor and lithium source are mixed and sintered to prepare lithium-rich manganese-based cathode material.

2. The method for preparing lithium-rich manganese-based cathode material according to claim 1, characterized in that, Following the stirring and aging process, the method further includes: The solid-liquid separation, water washing, and drying processes are carried out sequentially.

3. The method for preparing lithium-rich manganese-based cathode material according to claim 2, characterized in that, At least one of the following conditions must be met: (1) The washing endpoint of the water washing is when the washing liquid becomes neutral; (2) The drying temperature is 100℃~140℃ and the drying time is 8h~12h.

4. The method for preparing the lithium-rich manganese-based cathode material according to any one of claims 1 to 3, characterized in that, At least one of the following conditions must be met: (1) The molar ratio of nickel, cobalt and manganese in the nickel-cobalt-manganese mixed salt solution is x:y:z, where x+y+z=1 and z≥0.6; (2) The mass concentration of the nickel-cobalt-manganese mixed salt solution is 80 g / L to 120 g / L; (3) The precipitant in the precipitant solution includes one or more of sodium hydroxide and potassium hydroxide; (4) The mass concentration of the precipitant solution is 50 g / L to 200 g / L; (5) The complexing agent in the complexing agent solution includes one or more of ammonia, ammonium bicarbonate, ammonium sulfate and ammonium oxalate; (6) The mass concentration of the complexing agent solution is 2 g / L to 20 g / L; (7) The pH value of the coprecipitation reaction is 9.5~11.5; (8) The alkali in the alkaline aqueous solution includes one or more of sodium hydroxide and potassium hydroxide; (9) The pH value of the alkaline aqueous solution is 9~11; (10) The total mass concentration of the soluble molybdate and the soluble tungstate in the alkaline aqueous solution is 0.1 g / L to 10 g / L; (11) The soluble molybdate includes Na2MoO4 and (NH4)6Mo7O 24 One or more of the following; (12) The soluble tungstate includes Na2WO4 and (NH4) 10 W 12 O 41 One or more of the following; (13) The mass-to-volume ratio of the lithium-rich manganese-based precursor to the alkaline aqueous solution is 1 g: (2~10) mL; (14) The temperature of the stirring and aging treatment is 25℃~80℃; (15) The stirring and aging treatment time is 0.5h~4h; (16) The stirring speed of the stirring aging treatment is 150 r / min to 350 r / min; (17) The lithium source is selected from one or more of lithium hydroxide and lithium carbonate.

5. The method for preparing the lithium-rich manganese-based cathode material according to any one of claims 1 to 3, characterized in that, The alkaline aqueous solution also includes a surfactant.

6. The method for preparing lithium-rich manganese-based cathode material according to claim 5, characterized in that, The surfactant satisfies at least one of the following conditions: (1) The surfactant includes one or more of polyethylene glycol and polyvinylpyrrolidone; (2) The concentration of the surfactant in the alkaline aqueous solution is 0.5 g / L to 5 g / L.

7. The method for preparing the lithium-rich manganese-based cathode material according to any one of claims 1 to 3, characterized in that, The sintering step includes: Under an oxygen-containing atmosphere, the material is first pre-sintered at 400℃~600℃ for 3h~8h, and then sintered at 800℃~1000℃ for 8h~15h.

8. A lithium-rich manganese-based cathode material, characterized in that, It is prepared by the method for preparing lithium-rich manganese-based cathode material as described in any one of claims 1 to 7.

9. A positive electrode sheet, characterized in that, It includes a positive current collector and a positive electrode material layer disposed on at least one side surface of the positive current collector, wherein the positive electrode material layer includes the lithium-rich manganese-based positive electrode material as described in claim 8.

10. A battery, characterized in that, Including the positive electrode sheet as described in claim 9.

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