Method for modifying lithium-rich manganese-based positive electrode material, modified lithium-rich manganese-based positive electrode material and battery

Abstract

The application provides a modification method of a lithium-rich manganese-based positive electrode material, a modified lithium-rich manganese-based positive electrode material and a battery. The modification method of the lithium-rich manganese-based positive electrode material comprises the following steps: dispersing the lithium-rich manganese-based positive electrode material in an aqueous solution of a bicarbonate to prepare a dispersion liquid; introducing carbon dioxide gas into the dispersion liquid to perform a carbonization reaction under a pressure of 0.2 MPa to 1 MPa; after the reaction is completed, performing solid-liquid separation to collect a solid product; and calcining the solid product to obtain the modified lithium-rich manganese-based positive electrode material. The modification method of the lithium-rich manganese-based positive electrode material provided by the application can realize the removal of residual alkali on the surface of the lithium-rich manganese-based positive electrode material and the protection of the surface structure of the material.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a method for modifying lithium-rich manganese-based cathode materials, modified lithium-rich manganese-based cathode materials, and batteries. Background Technology

[0002] Lithium-rich manganese-based cathode materials (xLi2MnO3·(1-x)LiMO2, where M is a transition metal) have high discharge specific capacity and high operating voltage, and are considered to be one of the promising high-energy-density lithium-ion battery cathode materials.

[0003] Lithium-rich manganese-based cathode materials are typically prepared using a co-precipitation method combined with high-temperature calcination. During sintering and subsequent cooling, some lithium source readily migrates to the particle surface and reacts with moisture and carbon dioxide in the air, forming residual lithium compounds such as LiOH and Li₂CO₃ (also known as residual alkali). This residual alkali not only affects the dispersibility and processing performance of the cathode slurry but also readily undergoes side reactions with the electrolyte during battery cycling, causing gas generation, increased interfacial impedance, and decreased cycle performance. This has become a significant factor restricting the industrial application of lithium-rich manganese-based cathode materials.

[0004] To reduce the residual alkali content on the surface of lithium-rich manganese-based cathode materials and improve material performance, the current main approach is acid pickling combined with heat treatment. For example, CN119764374A proposes a solid acid-coated and modified lithium-rich manganese-based cathode material and its preparation method. This method involves the reaction of solid acid with residual alkali on the cathode material surface, followed by a surface modification layer formed during subsequent heat treatment, thus achieving a synergistic effect of residual alkali removal and surface modification. In addition, there are reports of using organic or inorganic acids such as phosphoric acid and citric acid to treat the surface of the material, followed by heat treatment to achieve structural repair and surface stabilization. However, while acid pickling combined with heat treatment can reduce the residual alkali content, the acidic medium easily reacts with the cathode material, adversely affecting its surface structure.

[0005] Besides acid washing, surface coating and elemental doping modification methods are also widely reported. For example, CN119812279A discloses the construction of a disordered spinel layer and a garnet-type solid electrolyte coating layer on the surface of lithium-rich manganese-based materials through a gradient temperature heat treatment process to improve the material's interfacial stability and cycle performance. Other reports describe the introduction of elements such as Mg, Al, Ti, Zr, and F for doping to improve the material's crystal structure stability and ion transport performance. While these modification methods can effectively suppress interfacial side reactions and improve the material's cycle stability, their main function is to improve the material structure and interfacial stability; their direct removal of residual lithium from the material surface is relatively limited.

[0006] Therefore, how to effectively reduce the residual alkali content on the material surface while maintaining the structural stability of the material remains an important technical problem that needs to be solved in this field. Summary of the Invention

[0007] Based on this, this application provides a method for modifying lithium-rich manganese-based cathode materials, the modified lithium-rich manganese-based cathode material, and a battery. The method for modifying lithium-rich manganese-based cathode materials provided in this application involves dispersing the lithium-rich manganese-based cathode material in an aqueous solution of bicarbonate, and then introducing carbon dioxide gas into the dispersion to induce a carbonization reaction under high pressure. Utilizing the synergistic effect between the ammonium bicarbonate buffer system and the high-pressure carbon dioxide, residual lithium on the surface of the lithium-rich manganese-based cathode material is converted and removed under relatively mild reaction conditions, while also maintaining the structural stability of the cathode material.

[0008] The first aspect of this application provides a method for modifying lithium-rich manganese-based cathode materials, the technical solution of which is as follows: A method for modifying a lithium-rich manganese-based cathode material includes the following steps: A dispersion was prepared by dispersing lithium-rich manganese-based cathode material in an aqueous solution of bicarbonate. Carbon dioxide gas is introduced into the dispersion, and a carbonization reaction is carried out under a pressure of 0.2 MPa to 1 MPa; after the reaction is completed, the solid and liquid are separated, and the solid product is collected. The solid product is then calcined.

[0009] In some embodiments, the bicarbonate salt is selected from ammonium bicarbonate.

[0010] In some embodiments, the concentration of the bicarbonate in the aqueous bicarbonate solution is 5-15 wt%.

[0011] In some embodiments, the mass ratio of the lithium-rich manganese-based cathode material to the aqueous bicarbonate solution is 1:(3~10).

[0012] In some embodiments, the carbonization reaction satisfies at least one of the following conditions: (1) The carbonization reaction temperature is 15~35℃; (2) The carbonization reaction takes 0.5h to 2h.

[0013] In some embodiments, the calcination satisfies at least one of the following conditions: (1) The calcination temperature is 400~600℃; (2) The calcination time is 2 to 6 hours.

[0014] In some embodiments, the solid product is further subjected to washing and drying steps before calcination.

[0015] In some embodiments, the initial residual alkali content of the lithium-rich manganese-based cathode material is 0.5~1.5wt%.

[0016] In some embodiments, the particle size D50 of the lithium-rich manganese-based cathode material is 3~15 μm.

[0017] In some embodiments, the specific surface area of ​​the lithium-rich manganese-based cathode material is 0.2~1.5 m². 2 / g.

[0018] In some embodiments, the general chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, where 0.1≤x≤0.5 and M represents one or more of Ni, Co and Mn.

[0019] The second aspect of this application provides a modified lithium-rich manganese-based cathode material, which is prepared by the preparation method described above.

[0020] A third aspect of this application provides a battery comprising the modified lithium-rich manganese-based cathode material as described above.

[0021] Compared with traditional solutions, this application has the following advantages: The modification method for lithium-rich manganese-based cathode materials provided in this application involves dispersing the lithium-rich manganese-based cathode material in an aqueous solution of bicarbonate, and then introducing carbon dioxide gas into the dispersion to induce a carbonization reaction under high pressure. The aqueous solution of bicarbonate not only provides a reaction medium for the carbonization reaction but also acts as a buffer system, providing a relatively stable bicarbonate environment under a carbon dioxide atmosphere. This buffers pH fluctuations in the reaction system, thus facilitating the carbonization reaction of residual alkali on the surface of the lithium-rich manganese-based cathode material with carbon dioxide under mild conditions. Through the carbonization reaction, the residual alkali on the surface of the lithium-rich manganese-based cathode material can be converted into soluble lithium salts, and the reaction system does not easily damage the surface structure of the cathode, achieving a balance between removing residual alkali and protecting the surface structure of the cathode material. Detailed Implementation

[0022] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0024] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings: In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0025] In this application, "several" means at least one, such as one, two, etc., unless otherwise expressly and specifically defined.

[0026] In this application, the terms "optionally," "optionally," and "optional" refer to options that are optional, meaning they can be selected from either "with" or "without." If multiple "optional" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" option is independent.

[0027] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0028] In this application, numerical intervals (i.e. numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the above-mentioned numerical intervals are considered continuous, and include the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, as well as every value between the two numerical endpoints.

[0029] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0030] This application provides a method for modifying a lithium-rich manganese-based cathode material. In one embodiment, the method for modifying the lithium-rich manganese-based cathode material includes the following steps: S10. Disperse the lithium-rich manganese-based cathode material in an aqueous solution of bicarbonate to prepare a dispersion.

[0031] The surface of lithium-rich manganese-based cathode materials typically contains a certain amount of residual lithium, which mainly includes LiOH, Li2CO3, and a small amount of other alkaline lithium salts. Optionally, the initial residual alkali content of the lithium-rich manganese-based cathode material is 0.5~1.5wt%. For example, the initial residual lithium content is 0.5wt%, 0.6wt%, 1.2wt%, and 1.5wt%.

[0032] Optionally, the general chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, where 0.1≤x≤0.5, and M represents one or more of Ni, Co and Mn.

[0033] Optionally, the particle size D50 of the lithium-rich manganese-based cathode material is 3~15 μm. The specific surface area of ​​the lithium-rich manganese-based cathode material is 0.2~1.5 m². 2 / g.

[0034] Optionally, the bicarbonate is selected from ammonium bicarbonate. Ammonium bicarbonate can provide NH4 in aqueous solution. + and HCO3 - This constitutes a buffer system. This buffer system can improve the supply capacity of bicarbonate-related substances in the system, alleviate the problem of large fluctuations in the local reaction environment when simply introducing CO2, and make the carbonation reaction more uniform and controllable. Furthermore, ammonium bicarbonate can volatilize after subsequent carbonation and calcination reactions, without introducing metallic impurities. Optionally, the concentration of the bicarbonate in the bicarbonate aqueous solution is 5-15 wt%. Preferably, it is 8-12 wt%. More preferably, it is 10 wt%.

[0035] Optionally, the mass ratio of the lithium-rich manganese-based cathode material to the aqueous bicarbonate solution is 1:(3~10). Preferably, it is 1:(4~10). More preferably, it is 1:5.

[0036] S20. CO2 gas is introduced into the dispersion, and a carbonization reaction is carried out under a pressure of 0.2MPa~1MPa. After the reaction is completed, the solid and liquid are separated and the solid is collected.

[0037] The dispersion can be placed in a pressurized reaction vessel and high-pressure CO2 gas can be introduced. The ambient pressure is preferably 0.2 MPa to 0.6 MPa, and more preferably 0.25 MPa to 0.35 MPa.

[0038] The residual alkali mainly consists of LiOH and Li₂CO₃. LiOH has high water solubility and can be removed during liquid-phase dispersion, solid-liquid separation, and washing. In contrast, Li₂CO₃ has low water solubility and is the main difficult-to-remove component affecting the reduction of residual alkali depth. This application introduces pressurized CO₂ into an ammonium bicarbonate aqueous solution to increase the CO₂ / HCO₃ ratio in the liquid phase. -The concentration of relevant species causes the Li2CO3 on the material surface to undergo hydrocarbonation, and the reaction can be represented as follows: Li₂CO₃ + CO₂ + H₂O ⇌ 2LiHCO₃ The generated lithium bicarbonate enters the liquid phase in dissolved form and is removed during solid-liquid separation and washing. The ammonium bicarbonate system can maintain a relatively mild pH environment and improve the supply capacity of bicarbonate ions, which is conducive to the continuous conversion of Li2CO3 into soluble components. Thus, while avoiding strong acid corrosion of the cathode material surface, it can effectively reduce residual alkali.

[0039] Optionally, the carbonization reaction temperature is 15~35℃, preferably 25℃. Optionally, the carbonization reaction time is 0.5h~2h, preferably 0.8h~1.2h, and more preferably 1h.

[0040] S30. The solid is calcined.

[0041] Optionally, before calcining the solid product, the process further includes washing and drying the solid product. Deionized water can be used to wash the solid product, optionally until the pH of the washing solution is 6.5–7.5 and / or the conductivity of the washing solution is less than 100 μS / cm. The number of washing cycles can be 2–5, preferably 3–4. The drying temperature can be 60–120°C, preferably 80–100°C; the drying time can be 4–12 h, preferably 6–10 h.

[0042] Calcination can be carried out in an air or oxygen atmosphere. Optionally, the calcination temperature is 400~600℃, preferably 450~550℃, more preferably 500℃. Optionally, the calcination time is 2~6h, preferably 4~5h, more preferably 5h. After calcination, the material is naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0043] In this embodiment, a lithium-rich manganese-based cathode material is dispersed in an aqueous solution of bicarbonate, and carbon dioxide gas is introduced into the dispersion to induce a carbonization reaction under high pressure. The aqueous solution of bicarbonate not only provides the reaction medium for the carbonization reaction but also acts as a buffer system, providing a relatively stable bicarbonate environment under a carbon dioxide atmosphere. This buffers pH fluctuations in the reaction system, thus facilitating the carbonization reaction of residual alkali on the surface of the lithium-rich manganese-based cathode material with carbon dioxide under mild conditions. Through the carbonization reaction, the residual alkali can be converted into soluble lithium salts, and the reaction system does not easily damage the surface structure of the cathode, achieving a balance between residual alkali removal and protection of the cathode material's surface structure.

[0044] Compared to traditional acid washing processes, the ammonium bicarbonate-carbon dioxide system used in the above method provides a milder reaction environment, reducing the risk of adverse effects of acidic media on the material's surface structure. Subsequent washing and calcination further remove residual components and stabilize the material's surface structure. Furthermore, the lower residual alkali content on the cathode material surface improves slurry viscosity and sedimentation stability, facilitating subsequent coating processes suitable for continuous slurry preparation and coating in industrial production. Moreover, the use of an ammonium bicarbonate buffer system combined with high-pressure CO2 for low-temperature carbonization and subsequent calcination processes shows good compatibility, a simple process flow, and mild treatment conditions, making it suitable for lithium-rich manganese-based cathode materials with varying initial residual alkali contents and demonstrating good industrial adaptability.

[0045] The above-mentioned method for preparing lithium-rich manganese-based cathode materials has the following advantages: (1) Using ammonium bicarbonate buffer system combined with high pressure CO2 for low temperature carbonization reaction can promote the conversion and removal of residual alkali such as LiOH and Li2CO3 on the material surface, so that the residual alkali removal rate can reach about 60~70%. (2) Compared with traditional acid washing, the above method has a milder treatment environment, which can reduce the risk of acidic medium having an adverse effect on the surface of lithium-rich manganese-based cathode material. The modified cathode material treated by the above method shows good capacity retention during long cycle, which is beneficial to improving the cycle stability of lithium-rich manganese-based cathode material. (3) Compared with only introducing CO2 or only using ammonium bicarbonate, the above method improves the controllability of carbonation reaction and the effect of residual alkali removal through the synergistic effect of ammonium bicarbonate buffer system and high pressure CO2.

[0046] (4) Different batches of lithium-rich manganese-based materials have differences in composition, particle size distribution and initial residual alkali content. The above method is applicable to lithium-rich manganese-based cathode materials with different initial residual alkali contents. It has good adaptability and stability and is conducive to consistency control in the large-scale production process.

[0047] In summary, the above preparation method effectively removes residual alkali from the surface of lithium-rich manganese-based cathode materials by synergistically constructing a mild and controllable carbonization reaction environment through an ammonium bicarbonate buffer system and high-pressure carbon dioxide. It also reduces the risk of adverse effects on the surface structure of materials caused by traditional acid washing treatment, thereby improving the cycle stability, slurry processing performance and process consistency of the materials.

[0048] The second aspect of this application provides a modified lithium-rich manganese-based cathode material, which is prepared by the preparation method described above.

[0049] A third aspect of this application provides a battery comprising the modified lithium-rich manganese-based cathode material as described above.

[0050] The following description is further illustrated with specific embodiments and comparative examples. Unless otherwise specified, the raw materials involved in the following specific embodiments and comparative examples are all commercially available; the instruments used are all commercially available unless otherwise specified; and the processes involved are conventionally selected by those skilled in the art unless otherwise specified.

[0051] Example 1 This embodiment provides a method for modifying lithium-rich manganese-based cathode materials, the steps of which are as follows: A lithium-rich manganese-based cathode material is used, wherein the chemical formula of the lithium-rich manganese-based cathode material is 0.5Li₂MnO₃·0.5LiNi. 0.4 Co 0.2 Mn 0.4 O2, with a particle size D50 of 8.0 μm and a specific surface area of ​​1.2 m². 2 / g, with an initial residual alkali content of 0.85wt%.

[0052] Prepare a 10wt% ammonium bicarbonate aqueous solution by adding 100g of the above-mentioned lithium-rich manganese-based cathode material to 500g of the ammonium bicarbonate aqueous solution and stirring to form a uniformly suspended dispersion.

[0053] The dispersion was placed in a high-pressure reactor, and CO2 gas was introduced at 25°C while maintaining the ambient pressure in the reactor at 0.30 MPa. The mixture was stirred, and a carbonization reaction was initiated for 1 hour. After the reaction, solid-liquid separation was performed, and the solid product was collected and washed three times with deionized water until the pH of the washing solution reached 6.5–7.5. The solid product was then dried at 80°C for 8 hours.

[0054] The dried solid product was placed in an air atmosphere and calcined at 500℃ for 5 hours, then naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0055] Example 2 This embodiment provides a method for modifying lithium-rich manganese-based cathode materials, the steps of which are as follows: A lithium-rich manganese-based cathode material is used, wherein the chemical formula of the lithium-rich manganese-based cathode material is 0.5Li₂MnO₃·0.5LiNi. 0.4 Co 0.2 Mn 0.4 O2, with a particle size D50 of 8.0 μm and a specific surface area of ​​1.2 m². 2 / g, with an initial residual alkali content of 0.85wt%.

[0056] Prepare a 5wt% ammonium bicarbonate aqueous solution by adding 100g of the above-mentioned lithium-rich manganese-based cathode material to 300g of the ammonium bicarbonate aqueous solution and stirring to form a uniformly suspended dispersion.

[0057] The dispersion was placed in a high-pressure reactor, and CO2 gas was introduced at 15°C while maintaining the ambient pressure in the reactor at 0.5 MPa. The mixture was stirred, and a carbonization reaction was initiated for 2 hours. After the reaction, solid-liquid separation was performed, and the solid product was collected and washed three times with deionized water until the pH of the washing solution reached 6.5–7.5. The solid product was then dried at 80°C for 8 hours.

[0058] The dried solid product was placed in an air atmosphere and calcined at 400℃ for 5 hours, then naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0059] Example 3 This embodiment provides a method for modifying lithium-rich manganese-based cathode materials, the steps of which are as follows: A lithium-rich manganese-based cathode material is used, wherein the chemical formula of the lithium-rich manganese-based cathode material is 0.5Li₂MnO₃·0.5LiNi. 0.4 Co 0.2 Mn 0.4 O2, with a particle size D50 of 8.0 μm and a specific surface area of ​​1.2 m². 2 / g, with an initial residual alkali content of 0.85wt%.

[0060] Prepare a 15wt% ammonium bicarbonate aqueous solution by adding 100g of the above-mentioned lithium-rich manganese-based cathode material to 1000g of the ammonium bicarbonate aqueous solution and stirring to form a uniformly suspended dispersion.

[0061] The dispersion was placed in a high-pressure reactor, and CO2 gas was introduced at 35°C while maintaining the ambient pressure in the reactor at 1.0 MPa. The mixture was stirred, and a carbonization reaction was initiated for 0.5 h. After the reaction, solid-liquid separation was performed, and the solid product was collected and washed three times with deionized water until the pH of the washing solution reached 6.5–7.5. The solid product was then dried at 80°C for 8 h.

[0062] The dried solid product was placed in an air atmosphere and calcined at 600℃ for 5 hours, then naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0063] Example 4 This embodiment provides a method for modifying lithium-rich manganese-based cathode materials, the steps of which are as follows: A lithium-rich manganese-based cathode material is used, wherein the chemical formula of the lithium-rich manganese-based cathode material is 0.5Li₂MnO₃·0.5LiNi. 0.4 Co 0.2 Mn 0.4 O2, with a particle size D50 of 8.0 μm and a specific surface area of ​​1.2 m². 2 / g, with an initial residual alkali content of 0.85wt%.

[0064] Prepare a 10wt% ammonium bicarbonate aqueous solution by adding 100g of the above-mentioned lithium-rich manganese-based cathode material to 700g of the ammonium bicarbonate aqueous solution and stirring to form a uniformly suspended dispersion.

[0065] The dispersion was placed in a high-pressure reactor, and CO2 gas was introduced at 25°C while maintaining the ambient pressure in the reactor at 0.6 MPa. The mixture was stirred, and a carbonization reaction was initiated for 1 hour. After the reaction, solid-liquid separation was performed, and the solid product was collected and washed three times with deionized water until the pH of the washing solution reached 6.5–7.5. The solid product was then dried at 80°C for 8 hours.

[0066] The dried solid product was placed in an air atmosphere and calcined at 500℃ for 5 hours, then naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0067] Example 5 This embodiment provides a method for modifying lithium-rich manganese-based cathode materials, the steps of which are as follows: A lithium-rich manganese-based cathode material is used, wherein the chemical formula of the lithium-rich manganese-based cathode material is 0.5Li₂MnO₃·0.5LiNi. 0.4 Co 0.2 Mn 0.4 O2, with a particle size D50 of 3 μm and a specific surface area of ​​1.5 m². 2 / g, with an initial residual alkali content of 0.5wt%.

[0068] Prepare a 10wt% ammonium bicarbonate aqueous solution by adding 100g of the above-mentioned lithium-rich manganese-based cathode material to 500g of the ammonium bicarbonate aqueous solution and stirring to form a uniformly suspended dispersion.

[0069] The dispersion was placed in a high-pressure reactor, and CO2 gas was introduced at 25°C while maintaining the ambient pressure in the reactor at 0.30 MPa. The mixture was stirred, and a carbonization reaction was initiated for 1 hour. After the reaction, solid-liquid separation was performed, and the solid product was collected and washed three times with deionized water until the pH of the washing solution reached 6.5–7.5. The solid product was then dried at 80°C for 8 hours.

[0070] The dried solid product was placed in an air atmosphere and calcined at 500℃ for 5 hours, then naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0071] Example 6 This embodiment provides a method for modifying lithium-rich manganese-based cathode materials, the steps of which are as follows: A lithium-rich manganese-based cathode material is used, wherein the chemical formula of the lithium-rich manganese-based cathode material is 0.5Li₂MnO₃·0.5LiNi. 0.4 Co 0.2 Mn 0.4O2, with a particle size D50 of 15 μm and a specific surface area of ​​0.2 m². 2 / g, with an initial residual alkali content of 1.5wt%.

[0072] Prepare a 10wt% ammonium bicarbonate aqueous solution by adding 100g of the above-mentioned lithium-rich manganese-based cathode material to 500g of the ammonium bicarbonate aqueous solution and stirring to form a uniformly suspended dispersion.

[0073] The dispersion was placed in a high-pressure reactor, and CO2 gas was introduced at 25°C while maintaining the ambient pressure in the reactor at 0.30 MPa. The mixture was stirred, and a carbonization reaction was initiated for 1 hour. After the reaction, solid-liquid separation was performed, and the solid product was collected and washed three times with deionized water until the pH of the washing solution reached 6.5–7.5. The solid product was then dried at 80°C for 8 hours.

[0074] The dried solid product was placed in an air atmosphere and calcined at 500℃ for 5 hours, then naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0075] Comparative Example 1 This comparative example provides a method for modifying a lithium-rich manganese-based cathode material, which is basically the same as that in Example 1, except that the lithium-rich manganese-based cathode material is subjected to conventional acid washing, as follows: Prepare a 10wt% citric acid aqueous solution. Add 100g of the same lithium-rich manganese-based cathode material as in Example 1 to 500g of the citric acid aqueous solution for acid washing. After acid washing, collect the solid product and wash it three times with deionized water until the pH of the washing solution reaches 6.5-7.5. Then, dry the solid product at 80°C for 8 hours.

[0076] The dried solid product was placed in an air atmosphere and calcined at 500℃ for 5 hours, then naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0077] Comparative Example 2 This comparative example provides a method for modifying a lithium-rich manganese-based cathode material, which is basically the same as that in Example 1, except that ammonium bicarbonate is not added. The steps are as follows: 100g of the same lithium-rich manganese-based cathode material as in Example 1 was added to 500g of deionized water and stirred to form a uniformly suspended dispersion.

[0078] The dispersion was placed in a high-pressure reactor, and CO2 gas was introduced at 25°C while maintaining the ambient pressure in the reactor at 0.30 MPa. The mixture was stirred, and a carbonization reaction was initiated for 1 hour. After the reaction, solid-liquid separation was performed, and the solid product was collected and washed three times with deionized water until the pH of the washing solution reached 6.5–7.5. The solid product was then dried at 80°C for 8 hours.

[0079] The dried solid product was placed in an air atmosphere and calcined at 500℃ for 5 hours, then naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0080] Comparative Example 3 This comparative example provides a method for modifying a lithium-rich manganese-based cathode material, which is basically the same as that in Example 1, except that CO2 gas is not introduced. The steps are as follows: Prepare a 10wt% ammonium bicarbonate aqueous solution. Add 100g of the same lithium-rich manganese-based cathode material as in Example 1 to 500g of the ammonium bicarbonate aqueous solution, stir to form a uniform suspension, continue stirring for 1 hour, then perform solid-liquid separation, collect the solid product, wash three times with deionized water until the pH of the washing solution is 6.5-7.5. Subsequently, dry the solid product at 80°C for 8 hours.

[0081] The dried solid product was placed in an air atmosphere and calcined at 500℃ for 5 hours, then naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0082] Comparative Example 4 This comparative example provides a method for modifying a lithium-rich manganese-based cathode material, which is basically the same as that in Example 1, the main difference being that direct calcination is performed. The steps are as follows: 100g of the same lithium-rich manganese-based cathode material as in Example 1 was placed in an air atmosphere and calcined at 500°C for 5 hours, then naturally cooled to room temperature to obtain the modified lithium-rich manganese-based cathode material.

[0083] test Project 1: The residual alkali content of the modified lithium-rich manganese-based cathode materials in each example and comparative example was determined by acid-base titration, and the residual alkali removal rate was calculated. The results are shown in Table 1.

[0084] Table 1

[0085] Project 2: The modified lithium-rich manganese-based cathode materials obtained from each embodiment and comparative example are mixed with conductive agent Super P and binder PVDF at a mass ratio of 8:1:1, and N-methylpyrrolidone is added to prepare cathode slurry. The cathode slurry is coated on the surface of aluminum foil current collector, and cathode sheets are prepared after drying, rolling and cutting.

[0086] Coin cells were assembled using lithium metal sheets as the negative electrode and 1 mol / L LiPF6 with an EC:DMC ratio of 1:1 as the electrolyte. Electrochemical performance was tested at 25°C within a voltage range of 2.0V to 4.6V. The test procedure was as follows: an initial charge-discharge test was performed at 0.1C, recording the initial discharge capacity and initial coulombic efficiency; followed by activation at 0.1C for 3 weeks, and then rate performance testing at 1C. Rate performance was expressed as the retention rate of the 1C discharge capacity relative to the 0.1C discharge capacity. After the rate test, a cycle test was performed at 1C, and the cycle capacity retention rate was expressed as the percentage of the discharge capacity at week 100 relative to the 1C discharge capacity at week 1. The test results are shown in Table 2.

[0087] Table 2

[0088] Project 3: The modified lithium-rich manganese-based cathode materials obtained in each embodiment and comparative example were prepared into cathode slurries, and the viscosity and sedimentation stability of the slurries were tested. The specific testing method was as follows: the modified lithium-rich manganese-based cathode material, conductive agent SuperP, and binder PVDF were mixed at a mass ratio of 8:1:1, with N-methylpyrrolidone as the solvent, and the solid content of the slurry was adjusted to 55wt%. Cathode slurries were prepared under the same stirring conditions. The viscosity of the slurry was tested using a rotational viscometer at 25°C and a rotation speed of 12 rpm.

[0089] The prepared positive electrode slurry was transferred to a covered cylindrical container and allowed to stand at 25°C for 24 hours. After standing, samples were taken from approximately 1 cm below the slurry surface and 1 cm from the bottom of the container to test the solid content of the upper and lower slurries, and the sedimentation stability was calculated using the following formula: Settling stability = Solid content of upper slurry / Solid content of lower slurry The smaller the difference in solid content between the upper and lower layers, the more uniform the distribution of solid components after the slurry has settled, and the better its settling stability. The test results are shown in Table 3.

[0090] Table 3

[0091] Results analysis: 1. As shown in Table 1, after using an ammonium bicarbonate buffer system combined with pressurized CO2 treatment in Examples 1 to 6, the total residual alkali content of the modified lithium-rich manganese-based cathode material decreased from 0.50wt%~1.50wt% to 0.19wt%~0.46wt%, with a residual alkali removal rate of 60.0%~69.4%. In contrast, Comparative Example 2 only introduced CO2 without adding ammonium bicarbonate, and Comparative Example 3 only used ammonium bicarbonate without introducing CO2, with residual alkali removal rates of only 32.9% and 20.0%, respectively. This indicates that CO2 treatment alone or ammonium bicarbonate treatment alone is insufficient to fully remove the insoluble residual alkali, mainly Li2CO3, from the surface of the lithium-rich manganese-based cathode material. However, there is a synergistic effect between the ammonium bicarbonate buffer system and pressurized CO2, which can promote the conversion of Li2CO3 into soluble lithium bicarbonate / dissolved lithium salt, and achieve effective removal through solid-liquid separation and washing.

[0092] 2. As shown in Table 2, in Comparative Example 1, the acid-washed cathode material exhibits certain advantages in terms of initial discharge capacity, initial coulombic efficiency, and rate performance. This is related to the influence of the acid washing process on the surface state and initial activation behavior of the material. However, the acidic medium during the acid washing process has an adverse effect on the surface structure of the cathode material, causing performance degradation during long-term cycling. In contrast, although Examples 1 to 6 are inferior to the acid-washed modified cathode material of Comparative Example 1 in terms of initial discharge capacity, initial coulombic efficiency, or rate performance, they exhibit better retention in terms of cycle stability. The cycle capacity retention rate of Examples 1 to 6 is higher than that of Comparative Example 1. This indicates that the method of using an ammonium bicarbonate buffer system combined with high-pressure CO2 to treat residual alkali can reduce the risk of adverse effects of acidic media on the surface structure of the material while achieving a high residual alkali removal rate, thereby improving the long-term cycle stability of the material. Furthermore, the electrochemical performance of the modified cathode materials after CO2 treatment in Comparative Example 2, ammonium bicarbonate treatment in Comparative Example 3, and direct calcination treatment in Comparative Example 4 was generally inferior to that of Example 1. This indicates that the combination of the ammonium bicarbonate buffer system and high-pressure CO2 is more conducive to the removal of residual alkali and the improvement of electrochemical performance.

[0093] 3. As shown in Table 3, the slurry viscosities of the modified lithium-rich manganese-based cathode materials obtained in Examples 1 to 6 ranged from 2720 mPa·s to 3360 mPa·s, and the solid content difference between the upper and lower layers after standing for 24 hours was 0.4 wt% to 1.8 wt%, indicating that the slurry has good fluidity and sedimentation stability. In contrast, the slurry viscosities of Comparative Examples 2, 3, and 4 were 4180 mPa·s, 4860 mPa·s, and 6350 mPa·s, respectively, and the solid content differences between the upper and lower layers were 3.5 wt%, 4.8 wt%, and 7.4 wt%, respectively, which were significantly higher than those of Example 1. This indicates that CO2 treatment alone, ammonium bicarbonate treatment alone, or direct calcination are insufficient to sufficiently reduce the residual alkali content on the material surface. Residual alkali affects the dispersibility of the cathode slurry, leading to increased slurry viscosity and uneven solid content distribution after standing.

[0094] After conventional acid washing, the viscosity of the slurry in Comparative Example 1 was 3560 mPa·s, and the solid content difference between the upper and lower layers was 2.4 wt%. Although this was an improvement over Comparative Examples 2 to 4, it was still inferior to Examples 1 to 4. This indicates that the ammonium bicarbonate buffer system combined with pressurized CO2 treatment in this application can reduce the insoluble residual alkali, mainly Li2CO3, on the material surface under mild conditions, while avoiding the adverse effects of strong acid media on the material surface, thereby improving the processing stability of the cathode slurry.

[0095] 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.

[0096] The embodiments described above are merely examples 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 invention patent. 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.

Claims

1. A method for modifying a lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: A dispersion was prepared by dispersing lithium-rich manganese-based cathode material in an aqueous solution of bicarbonate. Carbon dioxide gas is introduced into the dispersion, and a carbonization reaction is carried out under a pressure of 0.2 MPa to 1 MPa; after the reaction is completed, the solid and liquid are separated, and the solid product is collected. The solid product is then calcined.

2. The method for modifying the lithium-rich manganese-based cathode material according to claim 1, characterized in that, The bicarbonate is selected from ammonium bicarbonate.

3. The method for modifying the lithium-rich manganese-based cathode material according to claim 1, characterized in that, The concentration of the bicarbonate in the aqueous bicarbonate solution is 5-15 wt%.

4. The method for modifying the lithium-rich manganese-based cathode material according to claim 3, characterized in that, The mass ratio of the lithium-rich manganese-based cathode material to the aqueous bicarbonate solution is 1:(3~10).

5. The method for modifying the lithium-rich manganese-based cathode material according to claim 1, characterized in that, The carbonization reaction satisfies at least one of the following conditions: (1) The carbonization reaction temperature is 15~35℃; (2) The carbonization reaction takes 0.5h to 2h.

6. The method for modifying the lithium-rich manganese-based cathode material according to any one of claims 1 to 5, characterized in that, The calcination satisfies at least one of the following conditions: (1) The calcination temperature is 400~600℃; (2) The calcination time is 2 to 6 hours.

7. The method for modifying the lithium-rich manganese-based cathode material according to any one of claims 1 to 5, characterized in that, Before calcining the solid product, the process further includes washing and drying the solid product.

8. The method for modifying the lithium-rich manganese-based cathode material according to any one of claims 1 to 5, characterized in that, Includes at least one of the following features: (1) The initial residual alkali content of the lithium-rich manganese-based cathode material is 0.5~1.5 wt%; (2) The particle size D50 of the lithium-rich manganese-based cathode material is 3~15μm; (3) The specific surface area of ​​the lithium-rich manganese-based cathode material is 0.2~1.5m². 2 / g; (4) The general chemical formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2, where 0.1≤x≤0.5 and M represents one or more of Ni, Co and Mn.

9. A modified lithium-rich manganese-based cathode material, characterized in that, It is prepared by any one of the preparation methods according to claims 1 to 8.

10. A battery, characterized in that, Including the modified lithium-rich manganese-based cathode material as described in claim 9.

Images