A lithium-rich manganese-based cathode material, its preparation method and application

Abstract

This application discloses a lithium-rich manganese-based cathode material, its preparation method, and its applications, relating to the field of lithium battery technology. A gradient lithium distribution is used to design a stable lattice oxygen framework, reducing lattice oxygen escape. This not only reduces gas production but also prevents transition metal ion migration and stabilizes the crystal structure, thereby improving cycle stability. A further coating with a layer of Mn3O4 material containing oxygen vacancies traps the escaped oxygen from the outermost layer and suppresses irreversible phase transitions during charge and discharge, preventing direct contact between the electrolyte and the cathode material and reducing side reactions. Therefore, the lithium-rich manganese-based cathode material provided in this application can isolate lattice oxygen evolution, stabilize the crystal structure, and reduce side reactions, thereby improving electrochemical performance.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular, to a lithium-rich manganese-based cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Among many lithium-ion battery cathode materials, the lithium-rich manganese-based cathode material xLi2MnO3·(1-x)LiMO2 (0 < x < 1, M = Ni, Co, Mn) has attracted much attention from researchers due to its advantages such as high energy density, high working voltage, low toxicity, and low cost. Compared with conventional cathode materials, the anions of this type of material participate in the redox process under high voltage conditions, thereby providing additional capacity. However, it inevitably causes lattice oxygen release and migration of some transition metal ions to the lithium layer to a certain extent, resulting in serious voltage hysteresis, slow kinetics, and irreversible structural phase change. These problems make the lithium-rich manganese-based cathode material have shortcomings such as rapid cycle capacity decay, poor high-rate performance, and high gas production, severely restricting the commercial application of this material.

[0003] To improve the above problems, the surface interface, bulk phase, composition, morphology, etc. of the lithium-rich manganese-based cathode material are often designed and optimized, but there are certain problems: (1) The surface interface modification wraps one or more layers of functional materials on the material surface to block the erosion of the electrolyte on the cathode material. However, the structural differences between the coating layer and the cathode material lead to unstable interface bonding, restricting the improvement of long-term performance; (2) The bulk phase modification is generally doping, replacing transition metal ions with high-valent metal ions to increase the bond energy between transition metal ions and oxygen, inhibit the occupation of lithium sites by transition metal ions, and reduce oxygen release. However, it is difficult to observe the doping sites and regions of such ions, and the controllability is low; (3) The composition design includes adjusting the ratio of Li2MnO3 and LiMO2 and adjusting the gradient distribution of Ni in the material to obtain better comprehensive performance under corresponding test conditions. However, there is a problem that the regulation accuracy is difficult to control; (4) The morphology design is to adjust the preparation conditions to control the particle size and morphology to improve the Li + migration path, element distribution, and overall chemical environment to obtain better kinetic performance, but there is a risk of increased side reactions.

[0004] Therefore, there is an urgent need to provide a new design method to improve the cycle stability of the lithium-rich manganese-based cathode material and reduce the occurrence of side reactions at the same time.

[0005] In view of this, the present application is specifically proposed. Summary of the Invention

[0006] The purpose of the present application is to provide a lithium-rich manganese-based cathode material, a preparation method thereof, and an application thereof, aiming to significantly improve the cycle stability of the lithium-rich manganese-based cathode material.

[0007] This application is implemented as follows:

[0008] In a first aspect, this application provides a lithium-rich manganese-based cathode material, including a lithium-rich manganese-based cathode material matrix and a manganese tetroxide coating layer coated on the lithium-rich manganese-based cathode material matrix;

[0009] Among them, the lithium content on the surface of the lithium-rich manganese-based cathode material matrix is less than the lithium content inside.

[0010] In an optional embodiment, the chemical formula of the lithium-rich manganese-based cathode material matrix is xLi2MnO3·yLiMO2, where 0 < x, 0 < y, 1.15 < 2x + y < 1.2, and M is at least one of Ni, Co, and Mn.

[0011] Preferably, the mass fraction of the manganese tetroxide coating layer in the lithium-rich manganese-based cathode material is 1% - 5%.

[0012] In a second aspect, this application provides a preparation method for a lithium-rich manganese-based cathode material, including: reacting a lithium-rich manganese-based cathode material and a lithium-consuming material as raw materials to obtain a lithium-rich manganese-based cathode material matrix with a gradient lithium content; among them, the lithium-consuming material reacts with the lithium on the surface of the lithium-rich manganese-based cathode material to form a water-soluble salt;

[0013] Using the lithium-rich manganese-based cathode material matrix and an organic manganese source as raw materials to form a coating layer on the lithium-rich manganese-based cathode material matrix.

[0014] In an optional embodiment, the preparation process of the lithium-rich manganese-based cathode material matrix with a gradient lithium content includes: dissolving the lithium-consuming material, adjusting the pH value to 8 - 10 and then mixing it with the lithium-rich manganese-based cathode material, then removing the solvent, drying, and then performing calcination; mixing the material obtained after calcination and water, and then separating the solid material to obtain the lithium-rich manganese-based cathode material matrix with a gradient lithium content;

[0015] Preferably, the lithium-consuming material is selected from at least one of ammonium molybdate and ammonium tungstate;

[0016] Preferably, in the total amount of the lithium-consuming material and the lithium-rich manganese-based cathode material, the mass ratio of the lithium-consuming material is 3% - 10%, and the chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·yLiMO2, where 0 < x, 0 < y, 1.2 < 2x + y < 1.25, and M is at least one of Ni, Co, and Mn.

[0017] Preferably, when preparing the lithium-rich manganese-based cathode material matrix, a two-stage calcination process is adopted, first calcining at 250°C - 400°C for 1h - 3h, and then calcining at 600°C - 800°C for 8h - 12h.

[0018] In an optional embodiment, the preparation process of the lithium-rich manganese-based cathode material matrix with gradient lithium content includes: mixing and dissolving lithium-consuming materials with water, adjusting the pH value to 8-10 with ammonia water, ultrasonically dispersing the mixture with the lithium-rich manganese-based cathode material for 0.5-3 hours, stirring at 70-90°C until the water evaporates, drying at 70-90°C for 3-8 hours, calcining the dried material using a two-stage calcination process, ultrasonically treating the calcined material in water for 1-3 hours, and then centrifuging and drying to obtain the lithium-rich manganese-based cathode material matrix with gradient lithium content.

[0019] In an optional embodiment, the process of forming a coating layer on a gradient lithium-rich manganese-based cathode material substrate includes: wet milling and drying the gradient lithium-rich manganese-based cathode material substrate and an organic manganese source, and then calcining them under an inert atmosphere.

[0020] Preferably, the organic manganese source is selected from any one of manganese acetylacetonate, manganese acetate tetrahydrate, and 2-methylcyclopentadiene tricarbonyl manganese; the mass of the organic manganese source accounts for 1%-5% of the total mass of the lithium-rich manganese-based cathode material matrix and the organic manganese source;

[0021] Preferably, the calcination process under an inert atmosphere includes: pre-calcining at 150℃-200℃ for 1h-3h, followed by calcination at 550℃-650℃ for 1h-3h.

[0022] Preferably, the solvent used in the wet milling process is anhydrous ethanol;

[0023] Preferably, after wet milling, the material is dried at 50℃-70℃ for 4-8 hours.

[0024] In an optional embodiment, the preparation process of lithium-rich manganese-based cathode material includes: mixing and dissolving a nickel source, a cobalt source and a manganese source to obtain a mixed salt solution; mixing and reacting the mixed salt solution and a precipitant solution to prepare a precursor material; and mixing and calcining the precursor material with a lithium source.

[0025] Preferably, after mixing and ball milling the precursor material with the lithium source, it is first pre-calcined at 400℃-600℃ for 8h-12h, and then calcined at 800℃-950℃ under oxygen-containing conditions for 12h-18h.

[0026] Preferably, the preparation process of the precursor material includes: reacting a mixed salt solution and a precipitant solution at 150℃-200℃ for 15h-25h, then centrifuging and washing to obtain a solid material, and drying the solid material at 80℃-100℃ for 10h-20h.

[0027] Preferably, the total concentration of nickel, cobalt, and manganese in the mixed salt solution is 0.2 mol / L-0.4 mol / L, the concentration of the precipitant solution is 0.5 mol / L-1.5 mol / L, and the volume ratio of the mixed salt solution to the precipitant solution is 1:(0.8-1.2).

[0028] Preferably, the solvent used to prepare the mixed salt solution and the precipitant solution is selected from at least one of ethylene glycol and water;

[0029] Preferably, the precipitant used in preparing the precipitant solution is ammonium bicarbonate.

[0030] Thirdly, this application provides a positive electrode sheet, including any of the lithium-rich manganese-based positive electrode materials in the foregoing embodiments or the lithium-rich manganese-based positive electrode materials prepared by any of the preparation methods in the foregoing embodiments.

[0031] Fourthly, this application provides a lithium battery including the positive electrode sheet of the aforementioned embodiments.

[0032] Fifthly, this application provides an electrical device including the lithium battery described in the foregoing embodiments.

[0033] This application offers the following advantages: The lithium-rich manganese-based cathode material provided by this application comprises a gradient lithium-rich manganese-based cathode material matrix and a manganese tetroxide coating layer. The lithium content on the surface of the gradient lithium-rich manganese-based cathode material matrix is ​​lower than the lithium content inside, forming a lithium gradient distribution. Designing a stable lattice oxygen framework with a gradient lithium distribution reduces lattice oxygen escape, which not only reduces gas production but also prevents transition metal ion migration and stabilizes the crystal structure, thereby improving cycle stability. Furthermore, coating the outer layer with a layer of Mn3O4 material with oxygen vacancies traps the escaped oxygen from the outermost layer and suppresses irreversible phase transitions during charge and discharge, preventing direct contact between the electrolyte and the cathode material and reducing side reactions. Therefore, the lithium-rich manganese-based cathode material provided by this application can isolate lattice oxygen evolution, stabilize the crystal structure, and reduce side reactions, thereby improving electrochemical performance. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a graph showing the charge-discharge curves for the first cycle.

[0036] Figure 2 This is a graph showing the cyclic performance. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. For those not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0038] Under high-voltage test conditions, lattice oxygen inside the lithium-rich manganese-based cathode material migrates to the surface and precipitates, which can lead to the migration of transition metal ions and irreversible structural phase changes. The precipitated oxygen also reacts with the electrolyte, thus affecting the cycle life. In view of this, from the perspective of controlling the precipitation of lattice oxygen, this application designs a cathode material with gradient lithium and coats a spinel Mn3O4 material with oxygen vacancies on the outer layer to isolate the precipitation of lattice oxygen, stabilize the crystal structure, reduce side reactions, and thus improve the electrochemical performance.

[0039] The embodiments of this application provide a preparation method for a lithium-rich manganese-based cathode material, including the following steps:

[0040] S1. Prepare the lithium-rich manganese-based cathode material

[0041] The preparation process of the lithium-rich manganese-based cathode material includes: mixing and dissolving a nickel source, a cobalt source, and a manganese source to obtain a mixed salt solution, mixing and reacting the mixed salt solution with a precipitant solution to prepare a precursor material, and mixing and calcining the precursor material with a lithium source. By adjusting the amounts of nickel, cobalt, manganese, and lithium, the chemical formula of the prepared lithium-rich manganese-based cathode material meets the requirements. The chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·yLiMO2, where 0 < x, 0 < y, 1.2 < 2x + y < 1.25, and M is at least one of Ni, Co, and Mn. For example, it can be Li 1.2 Ni 0.3 Co 0.1 Mn 0.6 O2, but not limited thereto.

[0042] Specifically, the specific types of the nickel source, cobalt source, and manganese source are not limited and can be chlorides, nitrates, etc. For example, they can be NiCl2·6H2O, CoCl2·6H2O, MnCl2·4H2O. The solvent used to dissolve the nickel source, cobalt source, and manganese source is not limited and can be at least one of ethylene glycol and absolute ethanol, and can be any one or several of the above. Similarly, the precipitant solution is obtained by mixing a precipitant and a solvent, and the solvent for preparing the precipitant solution can be the same as the solvent for preparing the mixed salt solution. The precipitant used for preparing the precipitant solution is ammonium bicarbonate.

[0043] In some embodiments, the total concentration of nickel, cobalt, and manganese in the mixed salt solution is 0.2 mol / L-0.4 mol / L, the concentration of the precipitant solution is 0.5 mol / L-1.5 mol / L, and the volume ratio of the mixed salt solution to the precipitant solution is 1:(0.8-1.2). By adjusting the concentration and amount of the mixed salt solution and the precipitant solution, the reaction is made to proceed fully. Specifically, the total concentration of nickel, cobalt, and manganese in the mixed salt solution can be 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, etc., the concentration of the precipitant solution can be 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, etc., and the volume ratio of the mixed salt solution to the precipitant solution can be 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, etc.

[0044] In some embodiments, the preparation process of the precursor material includes: reacting a mixed salt solution and a precipitant solution at 150°C-200°C for 15-25 hours, then centrifuging and washing to obtain a solid material, and drying the solid material at 80°C-100°C for 10-20 hours. During the reaction, a co-precipitation reaction occurs, surface impurities are removed by centrifugation and washing, and solvents and washing reagents are removed by drying.

[0045] Specifically, the reaction temperature of the mixed salt solution and the precipitant solution can be 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, etc., and the reaction time can be 15h, 18h, 20h, 22h, 25h, etc. The reagents used for centrifugal washing can be water or anhydrous ethanol, and the number of washing cycles can be multiple, such as three times. The drying temperature of the solid material can be 80℃, 85℃, 90℃, 95℃, 100℃, etc., and the drying time can be 10h, 15h, 20h, etc.

[0046] In some embodiments, after ball milling the precursor material and lithium source, the mixture is first pre-calcined at 400℃-600℃ for 8h-12h, and then calcined at 800℃-1000℃ under oxygen-containing conditions for 12h-18h. Ball milling makes the precursor material and lithium source more uniformly mixed, and the lithium-rich manganese-based cathode material is obtained through a two-stage calcination process.

[0047] Specifically, the molar ratio of the precursor material to the lithium source can be determined according to the chemical formula of the lithium-rich manganese-based cathode material. For example, the total molar ratio of nickel, cobalt, and manganese to lithium can be 1:1.2, but it is not limited to this. The pre-calcination temperature can be 400℃, 450℃, 500℃, 550℃, 600℃, etc., and the pre-calcination time can be 8h, 10h, 12h, etc.; the high-temperature calcination temperature can be 800℃, 900℃, 1000℃, etc., and the calcination time can be 12h, 15h, 18h, etc.

[0048] S2. Preparation of gradient lithium-rich manganese-based cathode material matrix

[0049] After reacting lithium-rich manganese-based cathode material and lithium-consuming material as raw materials, a lithium-rich manganese-based cathode material matrix with gradient lithium content is obtained; wherein, the lithium-consuming material reacts with lithium on the surface of the lithium-rich manganese-based cathode material to generate water-soluble salt, and after removing the water-soluble salt, the lithium-rich manganese-based cathode material matrix with gradient lithium content can be obtained.

[0050] In some embodiments, the lithium-consuming material is selected from at least one of ammonium molybdate and ammonium tungstate, and the lithium-consuming material can be any one or more of the above. In the total amount of lithium-consuming material and lithium-rich manganese-based cathode material, the mass percentage of lithium-consuming material is 3%-10%, such as 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0051] In some embodiments, the preparation process of the gradient lithium-rich manganese-based cathode material matrix includes: dissolving a lithium-consuming material, adjusting the pH value to 8-10, mixing it with the lithium-rich manganese-based cathode material, removing the solvent, drying, and then calcining; mixing the calcined material with water, and then separating the solid material to obtain a lithium-rich manganese-based cathode material matrix with gradient lithium content. The lithium-consuming material can react with lithium on the surface of the lithium-rich manganese-based cathode material during calcination. Taking ammonium molybdate as an example, it can generate water-soluble Li₂MoO₄. After mixing with water, Li₂MoO₄ enters the liquid phase, and after separation, a lithium-rich manganese-based cathode material matrix with low surface lithium content and high central lithium content can be obtained. The lithium gradient distribution allows the inner and outer regions of the material to share a common oxygen framework. When Li is released, it can prevent structural collapse and block the path of oxygen ions diffusing to the surface, thereby confining oxygen ions inside the particles.

[0052] In practice, water can be used as a solvent and ammonia as a reagent to adjust the pH value. The specific steps are as follows: The lithium-consuming material is mixed and dissolved with water. The pH value is adjusted to 8-10 (e.g., 8, 9, 10, etc.) using ammonia water. Then, it is ultrasonically dispersed with lithium-rich manganese-based cathode material for 0.5h-3h (e.g., 0.5h, 1.0h, 2.0h, 3.0h, etc.). After that, it is stirred at 70℃-90℃ (e.g., 70℃, 80℃, 90℃, etc.) until the water evaporates. Then, it is dried at 70℃-90℃ (e.g., 70℃, 80℃, 90℃, etc.) for 3h-8h (e.g., 3h, 4h, 5h, 6h, 7h, 8h, etc.). The dried material is calcined using a two-stage calcination process. The calcined material is ultrasonically treated in water for 1h-3h (e.g., 1h, 2h, 3h, etc.) to fully dissolve the lithium compounds (e.g., Li2MoO4) generated in the reaction. After that, it is centrifuged and dried to obtain a lithium-rich manganese-based cathode material matrix with gradient lithium content.

[0053] In some embodiments, the two-stage calcination process used in preparing the gradient lithium-rich manganese-based cathode material matrix is ​​as follows: first, calcination at 250℃-400℃ for 1h-3h, followed by calcination at 600℃-800℃ for 8h-12h. By controlling the calcination temperature and time, the lithium-consuming material can react more fully with the surface lithium.

[0054] Specifically, the temperature of the first stage of calcination can be 250℃, 300℃, 350℃, 400℃, etc., and the calcination time can be 1h, 2h, 3h, etc.; the temperature of the second stage of calcination can be 600℃, 700℃, 800℃, etc., and the calcination time can be 8h, 10h, 12h, etc.

[0055] S3, Formation of a coating layer

[0056] Using a gradient lithium-rich manganese-based cathode material matrix and an organic manganese source as raw materials, a Mn3O4 coating layer is formed on the gradient lithium-rich manganese-based cathode material matrix. As a non-inert material that can participate in electrochemical reactions, the release of lattice oxygen in the high-voltage region triggers an abnormal spinel-to-layer phase transition. Through the rearrangement of Mn and O atoms, Mn3O4 is converted into LiMnO2, reducing the migration of transition metals and maintaining the stability of the bulk structure. In addition, Mn3O4 can also isolate the cathode material from the electrolyte and reduce side reactions.

[0057] In some embodiments, the process of forming a coating layer on a graded lithium-rich manganese-based cathode material substrate includes: wet milling and drying the graded lithium-rich manganese-based cathode material substrate and an organic manganese source, followed by calcination under an inert atmosphere, resulting in a Mn3O4 coating on the surface after calcination. By first performing wet milling and drying, the organic manganese source and the graded lithium-rich manganese-based cathode material substrate can be mixed more uniformly, improving the uniformity of the Mn3O4 coating.

[0058] In some embodiments, the organic manganese source is selected from at least one of manganese acetylacetonate, manganese acetate tetrahydrate, and 2-methylcyclopentadiene tricarbonyl manganese. The organic manganese source can be any one or more of these. The mass of the organic manganese source accounts for 1%-5% of the total mass of the lithium-rich manganese-based cathode material matrix and the organic manganese source, such as 1%, 2%, 3%, 4%, 5%, etc. By controlling the type and amount of the organic manganese source, the Mn3O4 coating is kept within a good range to improve the cycle performance of the material.

[0059] In some embodiments, anhydrous ethanol is used as the solvent in the wet milling process. After wet milling, the mixture is dried at 50°C-70°C for 4-6 hours to thoroughly remove the solvent. Specifically, the drying temperature can be 50°C, 60°C, 70°C, etc., and the drying time can be 4 hours, 5 hours, 6 hours, etc.

[0060] In some embodiments, the process of calcination under an inert atmosphere includes: first pre-calcining at 150°C - 200°C for 1h - 3h, and then calcining at 550°C - 650°C for 1h - 3h. By controlling the calcination temperature and time, a uniform Mn3O4 coating layer can be formed without damaging the matrix.

[0061] Specifically, the type of inert atmosphere is not limited and can be nitrogen, argon, etc.; the pre-calcination temperature can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc., and the pre-calcination time can be 1h, 2h, 3h, etc.; the high-temperature calcination temperature can be 550°C, 580°C, 600°C, 620°C, 650°C, etc., and the high-temperature calcination time can be 1h, 2h, 3h, etc.

[0062] The embodiments of the present application also provide a lithium-rich manganese-based cathode material, which includes a lithium-rich manganese-based cathode material matrix with a gradient lithium content and a manganese tetroxide coating layer coated on the lithium-rich manganese-based cathode material matrix; wherein, the lithium content on the surface of the lithium-rich manganese-based cathode material matrix with a gradient lithium content is less than that inside. By designing a cathode material with gradient lithium and coating a spinel Mn3O4 material with oxygen vacancies on the outer layer to isolate the lattice oxygen evolution, stabilize the crystal structure, and reduce side reactions, thereby improving the electrochemical performance.

[0063] In some embodiments, the chemical formula of the lithium-rich manganese-based cathode material matrix with a gradient lithium content is xLi2MnO3·yLiMO2, where 0 < x, 0 < y, and 1.15 < 2x + y < 1.2, and M is at least one of Ni, Co, and Mn.

[0064] The mass fraction of the manganese tetroxide coating layer in the lithium-rich manganese-based cathode material is 1% - 5%.

[0065] The embodiments of the present application also provide a positive electrode plate, which includes the above-mentioned lithium-rich manganese-based cathode material, and may also include a positive electrode current collector, on which a positive electrode active coating is formed, and the lithium-rich manganese-based cathode material exists in this positive electrode active coating. The positive electrode current collector can be a common current collector, and the specific type is not limited.

[0066] The embodiments of the present application also provide a lithium battery, which includes the above-mentioned positive electrode plate, and may also include a negative electrode plate, a separator, an electrolyte, etc., to form a complete battery structure. By optimizing the structure and composition of the lithium-rich manganese-based cathode material, the lithium battery has good cycle stability.

[0067] The embodiments of the present application provide an electrical device, which includes the above-mentioned lithium battery and uses the lithium battery for power supply. The type of the electrical device is not limited and can be a mobile phone, a camera, an electric vehicle, an electric car, etc.

[0068] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0069] Example 1

[0070] This embodiment provides a method for preparing a lithium-rich manganese-based cathode material, including the following steps:

[0071] (1) Preparation of lithium-rich manganese-based cathode materials

[0072] Weigh 3 mmol of NiCl₂·6H₂O, 1 mmol of CoCl₂·6H₂O, and 6 mmol of MnCl₂·4H₂O into 50 mL beakers, add 30 mL of ethylene glycol, and stir for 30 min to obtain solution A. Weigh 30 mmol of NH₄HCO₃ into another beaker containing 30 mL of ethylene glycol, and stir for 30 min to obtain solution B.

[0073] Solutions A and B were placed in a tetrafluoroethylene reactor and reacted at 180°C for 20 hours. The resulting suspensions were washed three times each with deionized water and anhydrous ethanol by centrifugation, and then placed in a drying oven at 90°C for 15 hours to obtain the precursor material. The precursor was ball-milled with LiOH at a molar ratio of 1:1.2 (i.e., the total molar ratio of nickel, cobalt, and manganese to lithium was 1:1.2). The mixture was then pre-calcined at 500°C in air for 10 hours, followed by oxygen calcination at 900°C for 15 hours. After grinding, Li was obtained. 1.2 Ni 0.3 Co 0.1 Mn 0.6 O2 cathode material, denoted as LRO.

[0074] (2) Preparation of graded lithium-rich manganese-based cathode material matrix

[0075] Weigh (NH4)6Mo7O according to a weight ratio of 5:95. 24 ·4H2O and LRO, (NH4)6Mo7O 24 • 4H2O was placed in a beaker containing 50 mL of deionized water and stirred for 30 min. NH3·H2O was slowly added to adjust the pH to 8–10. The LRO sample was then added and ultrasonically dispersed for 1 h. The mixture was then stirred in an 80 °C water bath until the water evaporated, and dried at 80 °C for 5 h. Afterward, it was pre-calcined at 300 °C for 2 h, followed by high-temperature calcination at 700 °C for 10 h to obtain a cathode material with Li2MoO4 on its surface. Finally, the calcined powder sample was ultrasonically treated in deionized water for 2 h, and after centrifugation and drying, a graded lithium cathode material with Li2MoO4 removed was obtained, denoted as GLRO.

[0076] (3) Formation of a coating layer

[0077] Weigh Mn(C5H7O2)2 and GLRO at a weight ratio of 3:97, then add an appropriate amount of anhydrous ethanol (controlling the liquid-to-solid volume ratio to 2:1) and wet grind for 1 hour. Then dry in a 60℃ drying oven for 5 hours. Finally, pre-calcine at 180℃ for 2 hours and calcine at 600℃ for 2 hours under argon atmosphere to obtain the Mn3O4-coated GLRO sample, denoted as GLRO@Mn.

[0078] Example 2

[0079] The only difference from Example 1 is that in step (2), (NH4)6Mo7O is weighed in a weight ratio of 2:98. 24 ·4H2O and LRO.

[0080] Example 3

[0081] The only difference from Example 1 is that in step (2), (NH4)6Mo7O is weighed in a weight ratio of 8:92. 24 ·4H2O and LRO.

[0082] Example 4

[0083] The only difference from Example 1 is that in step (3), Mn(C5H7O2)2 and GLRO are weighed at a weight ratio of 1:99.

[0084] Example 5

[0085] The only difference from Example 1 is that in step (3), Mn(C5H7O2)2 and GLRO are weighed in a weight ratio of 5:95.

[0086] Example 6

[0087] The only difference from Example 1 is that the calcination temperature in step (2) is 800°C.

[0088] Example 7

[0089] The only difference from Example 1 is that the calcination temperature in step (3) is 700°C.

[0090] Comparative Example 1

[0091] The only difference from Example 1 is that steps (2) and (3) are not performed, denoted as LRO.

[0092] Comparative Example 2

[0093] The only difference from Example 1 is that step (2) is omitted, and step (3) directly replaces GLRO with an equal amount of LRO.

[0094] Comparative Example 3

[0095] The only difference from Example 1 is that step (3) is not performed.

[0096] Test case

[0097] The performance of the cathode materials prepared in the test examples and comparative examples is shown in Table 1. Figure 1 and Figure 2 As shown.

[0098] Test method: The cathode material was assembled into a CR2025 coin cell and its electrochemical performance was tested.

[0099] Table 1. Performance test results of the cathode materials prepared in the examples and comparative examples.

[0100] Group Initial discharge capacity (mAh / g) Initial efficiency (%) 300 cycle capacity retention (%) Example 1 258.90 91.41 90.25 Example 2 254.71 90.11 88.62 Example 3 253.19 91.03 86.36 Example 4 254.33 90.96 87.51 Example 5 251.28 91.38 89.78 Example 6 252.46 90.25 87.47 Example 7 253.29 90.14 87.53 Comparative Example 1 249.92 89.92 85.69 Comparative Example 2 256.83 90.57 89.26 Comparative Example 3 253.61 90.24 88.57

[0101] Figure 1 The first charge-discharge curves of Example 1 and Comparative Example 1 show that the capacity of the cathode material prepared in Example 1 is significantly higher than that in Comparative Example 1. Figure 2 The graphs show the cycle performance of Example 1 and Comparative Example 1. It can be seen that the cathode material prepared in Example 1 has better cycle stability.

[0102] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a lithium-rich manganese-based positive electrode material, characterized in that, The preparation process of the lithium-rich manganese-based positive electrode material substrate with gradient lithium content comprises: dissolving the lithium-consuming material and water, and then mixing the lithium-rich manganese-based positive electrode material with the lithium-consuming material after adjusting the pH value to 8-10 by using ammonia water and ultrasonic dispersion for 0.5-3 hours; then, stirring is performed at 70-90 DEG C until the water evaporates, and then drying is performed at 70-90 DEG C for 3-8 hours; the dried material is calcined by using a two-stage calcination process; the obtained material is subjected to ultrasonic treatment in water for 1-3 hours, and then centrifugal separation and drying are performed to obtain the lithium-rich manganese-based positive electrode material substrate with gradient lithium content. The preparation process of the lithium-rich manganese-based positive electrode material substrate with gradient lithium content comprises: dissolving the lithium-consuming material and water, and then mixing the lithium-rich manganese-based positive electrode material with the lithium-consuming material after adjusting the pH value to 8-10 by using ammonia water and ultrasonic dispersion for 0.5-3 hours; then, stirring is performed at 70-90 DEG C until the water evaporates, and then drying is performed at 70-90 DEG C for 3-8 hours; the dried material is calcined by using a two-stage calcination process; the obtained material is subjected to ultrasonic treatment in water for 1-3 hours, and then centrifugal separation and drying are performed to obtain the lithium-rich manganese-based positive electrode material substrate with gradient lithium content. The lithium-consuming material is selected from at least one of ammonium molybdate and ammonium tungstate. In the preparation of the lithium-rich manganese-based positive electrode material substrate, a two-stage calcination process is adopted, and first, calcination is performed at 250-400 DEG C for 1-3 hours, and then calcination is performed at 600-800 DEG C for 8-12 hours. In the total amount of the lithium-consuming material and the lithium-rich manganese-based positive electrode material, the mass ratio of the lithium-consuming material is 3%-10%, and the chemical formula of the lithium-rich manganese-based positive electrode material is x Li2MnO3· y LiMO2, wherein, 0 x , 0 y , 1.2 <2 x + y <1.25, M is at least one of Ni, Co and Mn; the lithium-rich manganese-based positive electrode material comprises a lithium-rich manganese-based positive electrode material matrix and a trimanganese tetroxide coating layer coated on the lithium-rich manganese-based positive electrode material matrix; the mass fraction of the trimanganese tetroxide coating layer in the lithium-rich manganese-based positive electrode material is 1%-5%. The preparation process of the lithium-rich manganese-based positive electrode material substrate with gradient lithium content comprises: dissolving the lithium-consuming material and water, and then mixing the lithium-rich manganese-based positive electrode material with the lithium-consuming material after adjusting the pH value to 8-10 by using ammonia water and ultrasonic dispersion for 0.5-3 hours; then, stirring is performed at 70-90 DEG C until the water evaporates, and then drying is performed at 70-90 DEG C for 3-8 hours; the dried material is calcined by using a two-stage calcination process; the obtained material is subjected to ultrasonic treatment in water for 1-3 hours, and then centrifugal separation and drying are performed to obtain the lithium-rich manganese-based positive electrode material substrate with gradient lithium content.

2. The production method according to claim 1, characterized by, The preparation process of the lithium-rich manganese-based positive electrode material substrate with gradient lithium content comprises: dissolving the lithium-consuming material and water, and then mixing the lithium-rich manganese-based positive electrode material with the lithium-consuming material after adjusting the pH value to 8-10 by using ammonia water and ultrasonic dispersion for 0.5-3 hours; then, stirring is performed at 70-90 DEG C until the water evaporates, and then drying is performed at 70-90 DEG C for 3-8 hours; the dried material is calcined by using a two-stage calcination process; the obtained material is subjected to ultrasonic treatment in water for 1-3 hours, and then centrifugal separation and drying are performed to obtain the lithium-rich manganese-based positive electrode material substrate with gradient lithium content.

3. The production method according to claim 1, characterized by, The preparation process of the lithium-rich manganese-based positive electrode material substrate with gradient lithium content comprises: dissolving the lithium-consuming material and water, and then mixing the lithium-rich manganese-based positive electrode material with the lithium-consuming material after adjusting the pH value to 8-10 by using ammonia water and ultrasonic dispersion for 0.5-3 hours; then, stirring is performed at 70-90 DEG C until the water evaporates, and then drying is performed at 70-90 DEG C for 3-8 hours; the dried material is calcined by using a two-stage calcination process; the obtained material is subjected to ultrasonic treatment in water for 1-3 hours, and then centrifugal separation and drying are performed to obtain the lithium-rich manganese-based positive electrode material substrate with gradient lithium content. The preparation process of the lithium-rich manganese-based positive electrode material substrate with gradient lithium content comprises: dissolving the lithium-consuming material and water, and then mixing the lithium-rich manganese-based positive electrode material with the lithium-consuming material after adjusting the pH value to 8-10 by using ammonia water and ultrasonic dispersion for 0.5-3 hours; then, stirring is performed at 70-90 DEG C until the water evaporates, and then drying is performed at 70-90 DEG C for 3-8 hours; the dried material is calcined by using a two-stage calcination process; the obtained material is subjected to ultrasonic treatment in water for 1-3 hours, and then centrifugal separation and drying are performed to obtain the lithium-rich manganese-based positive electrode material substrate with gradient lithium content. The preparation process of the lithium-rich manganese-based positive electrode material substrate with gradient lithium content comprises: dissolving the lithium-consuming material and water, and then mixing the lithium-rich manganese-based positive electrode material with the lithium-consuming material after adjusting the pH value to 8-10 by using ammonia water and ultrasonic dispersion for 0.5-3 hours; then, stirring is performed at 70-90 DEG C until the water evaporates, and then drying is performed at 70-90 DEG C for 3-8 hours; the dried material is calcined by using a two-stage calcination process; the obtained material is subjected to ultrasonic treatment in water for 1-3 hours, and then centrifugal separation and drying are performed to obtain the lithium-rich manganese-based positive electrode material substrate with gradient lithium content. ​ ​ 4. The production method according to any one of claims 1 to 3, characterized by, ​ ​ The preparation process of the precursor material comprises: reacting the mixed salt solution and the precipitant solution at 150-200℃ for 15-25h, and then centrifuging and washing to obtain a solid material, and drying the solid material at 80-100℃ for 10-20h; The total concentration of nickel, cobalt and manganese in the mixed salt solution is 0.2-0.4mol / L, the concentration of the precipitant solution is 0.5-1.5mol / L, and the volume ratio of the mixed salt solution to the precipitant solution is 1:(0.8-1.2); The solvent used for preparing the mixed salt solution and the precipitant solution is at least one selected from ethylene glycol and water; The precipitant used for preparing the precipitant solution is ammonium bicarbonate.

5. A lithium-rich manganese-based positive electrode material, characterized in that, The lithium-rich manganese-based positive electrode material is prepared by the preparation method of any one of claims 1-4.

6. A positive electrode sheet characterized by comprising: The lithium-rich manganese-based positive electrode material of claim 5 is included.

7. A lithium battery, characterized by The positive electrode sheet of claim 6 is included.

8. An electrical device, characterized by The lithium battery of claim 7 is included.

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