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

Abstract

This invention provides a lithium-rich manganese-based cathode active material, its preparation method, and its application. The material includes a lithium-rich manganese-based core, a first coating layer located at least a portion of the surface of the lithium-rich manganese-based core and between primary grain boundaries on the surface of the core, and a second coating layer coating at least a portion of the surface of the first coating layer. The lithium-rich manganese-based core has the chemical formula xLi₂MnO₃·(1-x)LiTMO₂, where TM is one or more of Ni, Co, Mn, W, Mo, Ta, Zr, and Y, and 0 < x < 1. The first coating layer includes lithium cobalt oxide, and the second coating layer includes a variable-valence metal chalcogenide. This invention yields a lithium-rich manganese-based cathode active material with strong grain boundary stability, low interfacial side reactions, strong electronic conductivity, and strong ion transport capability, thus comprehensively improving the electrochemical performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials technology, specifically to a lithium-rich manganese-based cathode active material, its preparation method, and its application. Background Technology

[0002] Lithium-rich manganese-based cathode materials, as an important branch of lithium-ion battery cathode materials, are considered one of the core materials for next-generation high-energy-density batteries due to their high specific capacity (>250 mAh / g) and low cost. However, their poor rate performance (poor capacity retention at high current) and rapid cycle decay at high voltage severely restrict their practical applications. Lithium-rich manganese-based materials belong to the field of lithium-ion battery cathode materials, and their technological evolution is directly related to the energy density and fast-charging performance requirements of new energy vehicles and energy storage systems.

[0003] Traditional coating processes, such as Al2O3 coating, only improve cycle stability and cannot simultaneously resolve the contradiction between bulk conductivity and interfacial stability. While existing technologies using fast-ion conductor coatings can provide lithium-ion diffusion channels and electrolyte isolation, they lack control over the material's grain boundary structure. Fast-ion conductors cannot solve the problem of microcracks caused by stress accumulation at grain boundaries in lithium-rich manganese-based materials during cycling, and cannot form a more uniform lithium-ion bulk diffusion path. None of the above strategies solve the phase transition problem caused by oxygen loss from the surface of lithium-rich manganese-based materials during charge and discharge, nor do they address the issues of easy fracture at grain boundaries between primary particles, leading to structural collapse and capacity decay.

[0004] In view of the above problems, existing technologies often suffer from poor structural stability, poor high-temperature stability, numerous interfacial side reactions, complex operating conditions during preparation, and poor ion and electron conduction capabilities. There is a need to develop a lithium-rich manganese-based cathode active material that simultaneously possesses strong grain boundary and interface stability, low interfacial side reactions, strong electron conduction capability, and strong ion transport capability, thereby comprehensively improving the electrochemical performance of batteries. Summary of the Invention

[0005] This invention addresses the electrochemical performance problems of existing lithium-rich manganese-based materials used as cathode materials, such as poor structural stability, poor electronic and ion transport capabilities, and large interfacial side reactions leading to poor rate performance and cycle degradation. It develops a lithium-rich manganese-based cathode active material and its preparation method, which is then applied to lithium-ion batteries. This invention utilizes a preliminary pre-sintering process followed by an acidic mixed aqueous solution washing process to initially grow primary lithium-rich manganese-based core particles, forming numerous exposed oxygen vacancies on and near the surface, significantly improving the overall performance of the lithium-rich manganese-based cathode. In the subsequent secondary sintering process, cobalt and lithium sources are mixed to synthesize a lithium cobalt oxide (LiCoO2) surface coating layer and a grain boundary penetration layer in situ between the grain boundaries of the primary particles on and near the surface of the initially grown lithium-rich manganese-based core. Finally, a variable-valence metal chalcogenide compound is added to the obtained product for secondary surface coating to comprehensively improve the rate performance and cycle stability of the lithium-rich manganese-based material.

[0006] This invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a lithium-rich manganese-based cathode active material, comprising a lithium-rich manganese-based core, a first coating layer located at least a portion of the surface of the lithium-rich manganese-based core and between primary grain boundaries on the surface of the lithium-rich manganese-based core, and a second coating layer coating at least a portion of the surface of the first coating layer; wherein the chemical formula of the lithium-rich manganese-based core is xLi2MnO3·(1-x)LiTMO2, wherein TM is one or more of Ni, Co, Mn, W, Mo, Ta, Zr, and Y, and 0 < x < 1; the first coating layer comprises lithium cobalt oxide; and the second coating layer comprises a variable-valence metal chalcogenide compound.

[0008] This invention innovatively employs lithium cobalt oxide as the first coating layer, and coats the surface of the first coating layer with a second coating layer of a variable-valence metal chalcogenide compound. In this case, the nanolayered lithium cobalt oxide, as the first coating layer, not only covers the surface of the lithium-rich manganese-based core material but also penetrates deep into the primary grain boundaries, forming a "grain boundary reinforcement" effect. Since lithium cobalt oxide and the lithium-rich manganese-based core have similar structures, both being R-3m layered structures, they can form a coating layer with good structural adaptability and low lattice strain at the primary grain boundaries and surface, which helps stabilize oxygen vacancies in the core and suppress irreversible phase transitions during cycling, such as the formation of rock salt phases. This design fundamentally addresses the issue. This invention fundamentally solves the problem of fragile grain boundaries in traditional lithium-rich manganese-based materials, significantly improving the structural stability of the material. Simultaneously, this invention employs a variable-valence metal chalcogenide as the second coating layer, where the sulfide vacancies trap reactive oxygen species. These materials exhibit excellent chemical stability and electrochemical inertness, effectively isolating the electrolyte from direct contact with the active material and significantly reducing interfacial side reactions. The variable-valence metal chalcogenide also possesses excellent ion transport and electronic conductivity, overcoming the limitation of single conductivity properties in traditional coating materials. This enhances both ion and electronic conductivity, significantly improving rate performance. Furthermore, the variable-valence metal chalcogenide exhibits higher thermal stability, resisting decomposition at high temperatures, ensuring the material's performance stability under high-temperature conditions and broadening its application temperature range. In summary, this invention employs a nanolayered lithium cobalt oxide as the first coating layer to enhance the structural stability between primary particles of the lithium-rich manganese-based core material. Simultaneously, a variable-valence metal chalcogenide compound is used as the second coating layer to enhance the material's ion transport and electronic conductivity, and improve its thermal stability. This design, through the synergistic effect of the core, the first coating layer, and the second coating layer, forms a multi-layered protection mechanism from the inside out. This mechanism stabilizes oxygen vacancies in the core, blocks oxygen through the first coating layer, and captures oxygen through the second coating layer, collectively ensuring the material's high structural stability and excellent electrochemical performance, thereby improving the battery's cycle performance and rate performance.

[0009] As a further embodiment, the variable valence metal chalcogenide is a variable valence metal chalcogenide from period 4 to 6, selected from one or more of group VIB metal chalcogenides, group VB metal chalcogenides, and group IVB metal chalcogenides.

[0010] The present invention further prefers group VIB metal chalcogenides, group VB metal chalcogenides, and group IVB metal chalcogenides as the outermost coating passivation layer of the material. The chalcogen element vacancies formed by these compounds can capture active oxygen, thereby reducing the contact between active oxygen and metal ions, lowering the dissolution and migration rate of metal ions, thus maintaining the integrity of the material's crystal structure and improving the cycle stability of the battery.

[0011] As a further preferred embodiment, the variable valence metal chalcogenide is selected from one or more of Group VIB metal sulfides, Group VB metal sulfides, and Group IVB metal sulfides.

[0012] This invention further considers the comprehensive advantages of sulfur (S) over selenium (Se) and tellurium (Te) in terms of electrochemical stability and interfacial compatibility. Therefore, this invention further prefers variable-valence metal chalcogenides as the preferred coating. Although selenides and tellurides may have higher intrinsic electronic conductivity, sulfides exhibit more suitable properties as a coating layer for lithium-rich manganese-based cathode materials. Variable-valence metal sulfides have a higher electrochemical stability window, and sulfur ions are less susceptible to oxidation than selenium and tellurium ions. Lithium-rich manganese-based cathodes often operate at extremely high voltages. At these high potentials, the use of sulfides further reduces the risk of electrochemical oxidation at the cathode / electrolyte interface, reducing the risk of corrosion of the first coating layer. The sulfide coating layer is more inert at high voltages, maintaining structural integrity under these harsh conditions and providing durable protection. Furthermore, the chemical reactivity of sulfides with the electrolyte is generally lower than that of the corresponding selenides and tellurides. Choosing sulfides can further effectively reduce interfacial side reactions during charging and discharging, especially under high-temperature conditions, thereby more effectively suppressing impedance growth and gas generation. Sulfides typically have a layered structure, which may offer better morphological and interfacial compatibility with the layered structure of lithium cobalt oxide. They can more uniformly and densely coat the surface of lithium cobalt oxide, forming a low-defect interface and a more stable solid-state electrolyte interface phase during cycling. Variable-valence metal sulfides, while ensuring excellent ion conductivity and effective interfacial isolation, offer advantages in high voltage stability, thermal safety, and manufacturing cost.

[0013] As a further preferred embodiment, the variable valence metal chalcogenide is selected from one of the group VIB metal sulfides.

[0014] This invention further preferably uses a variable-valence metal chalcogenide as a group VIB metal sulfide, particularly molybdenum disulfide. Chromium group metal sulfides have a typical layered hexagonal crystal structure. This layered structure has better topological similarity in crystallography to the core lithium-rich manganese-based material and the first coating layer lithium cobalt oxide (both layered structures), which is beneficial for forming a tight coating with low defects and low stress at the interface. This structure ensures the uniformity and adhesion of the coating layer, avoiding the problem of coating layer peeling due to volume changes during cycling. Furthermore, its moderate electronic conductivity is sufficient to construct an efficient interfacial electron transport path, improving rate performance. Its semiconductor properties achieve a better balance between enhancing electron conduction and suppressing interfacial side reactions.

[0015] As an example, the variable-valence metal chalcogenide is selected from at least one of molybdenum disulfide (MoS2), tungsten disulfide (WS2), vanadium disulfide (VS2), titanium disulfide (TiS2), tin disulfide (SnS2), molybdenum diselenide (MoSe2), tungsten diselenide (WSe2), molybdenum ditelluride (MoTe2), and tungsten ditelluride (WTe2). Among these, group VIB metal sulfides include molybdenum disulfide (MoS2) and tungsten disulfide (WS2).

[0016] As a further embodiment, the D50 particle size of the lithium-rich manganese-based core is 2.5 μm to 7 μm.

[0017] As a further embodiment, the thickness of the first coating layer is 5 nm to 20 nm; and / or, the thickness of the second coating layer is 1 nm to 5 nm.

[0018] The present invention further optimizes the thickness of the first coating layer to 5nm-20nm, achieving a balance between grain boundary penetration reinforcement and electronic conduction optimization. This avoids the situation where the coating layer is too thin, potentially resulting in discontinuity and insufficient coverage of the core surface and effective penetration to the primary grain boundaries, thus reducing its effectiveness in stabilizing oxygen vacancies, suppressing phase transitions, and improving electronic conductivity. Conversely, if the thickness is too thick, it may increase the resistance to lithium-ion cross-interface transport; furthermore, lithium cobalt oxide itself has a low capacity, and an excessively thick inactive coating layer will lower the average specific capacity of the entire positive electrode active material, hindering energy density improvement.

[0019] The present invention further preferably uses a second coating layer with a thickness of 1 nm to 5 nm. This thickness range is preferred while achieving a balance between interface passivation, electronic conduction, and ion transport. When the thickness of the second coating layer is too low, it is difficult for the coating layer to form a complete and dense barrier, which cannot effectively isolate the electrolyte from the erosion of the internal active material, and its effect of capturing reactive oxygen and inhibiting the dissolution of variable valence metals is limited. However, although the electronic conductivity of variable valence metal chalcogenides is beneficial to interfacial electron transport, if the second coating layer is too thick, it will significantly hinder the lateral transport of lithium ions and increase interfacial impedance. The optimized thickness of the second coating layer in this invention achieves excellent chemical isolation while its unique layered channels still ensure the efficient passage of lithium ions, achieving the dual goals of protection and conduction.

[0020] As a further preferred embodiment, the thickness of the first coating layer is 8 nm to 15 nm; and / or, the thickness of the second coating layer is 2 nm to 4 nm.

[0021] Secondly, the present invention also provides a method for preparing a lithium-rich manganese-based positive electrode active material, comprising the following steps:

[0022] S1: The mixture of the precursor and the first lithium source is subjected to low-temperature pre-sintering treatment at 500~700℃ to obtain the lithium-rich manganese-based core;

[0023] S2: After quenching the lithium-rich manganese-based core, it is immersed in a mixed solution containing organic acid and lithium compound, washed with water, and then dried. The mixture of the dried lithium-rich manganese-based core, cobalt source, and second lithium source is sintered once to obtain a lithium-rich manganese-based core with a first coating layer.

[0024] S3: The lithium-rich manganese-based core with the first coating layer is mixed with a variable-valence metal chalcogenide compound and subjected to a secondary sintering process to obtain a lithium-rich manganese-based positive electrode active material.

[0025] This invention addresses the problems existing in the prior art by employing low-temperature pre-sintering in the pre-sintering stage and using a mixed solution containing organic acids and lithium compounds for water washing in the water washing stage to selectively remove alkaline impurities from the surface and maintain the Li... + Concentration and chemical environment stability, inhibiting Li + Loss and O 2- Instability is indirectly protected by oxygen lattice sites. Through a pre-calcination and water washing process, numerous exposed and stable oxygen vacancies are formed on and near the surface of the lithium-rich manganese-based core material. As defects in the crystal lattice, oxygen vacancies significantly improve the overall performance of the lithium-rich manganese-based cathode by regulating the material's electronic structure, surface chemistry, and interfacial reactions. This invention, by using organic acids as complexing agents and lithium-containing compounds as lithium replenishing agents, can regulate the lithium-ion concentration and local chemical environment on the material surface, promoting the controllable generation of oxygen vacancies at the primary grain boundaries and providing suitable conditions for the heterogeneous nucleation of the subsequent first coating layer, lithium cobalt oxide, in the grain boundary region. Compared to simple acid washing, this invention, due to the presence of lithium compounds as lithium replenishing agents, maintains an appropriate lithium content on the material surface, avoiding excessive delithiation leading to irreversible phase transitions or oxygen release. Simultaneously, it regulates the lithium-ion defect concentration in the grain boundary region, thereby affecting the local distribution of oxygen vacancies, promoting heterogeneous nucleation and uniform coating of lithium cobalt oxide (LCO) at the grain boundaries, and improving the bonding force and interfacial stability between the coating layer and the core. In addition, variable valence metal chalcogenides have good chemical stability and SEI compatibility, and can form a stable protective layer on the material surface, inhibiting electrolyte decomposition and improving coulombic efficiency and cycle life.

[0026] As a further embodiment, the specific surface area of ​​the lithium-rich manganese-based core after water washing in S2 is 1~3m². 2 / g, the specific surface area of ​​the lithium-rich manganese-based core with the first coating layer is 0.5~1 m². 2 / g.

[0027] In this invention, the specific surface area of ​​the lithium-rich manganese-based core material is one of the key factors affecting the uniformity and coating effect of the first coating layer. This invention obtains a lithium-rich manganese-based core with a high specific surface area through pre-sintering and water washing processes. A higher specific surface area means that each unit mass of material has a larger surface contact area and more active sites, providing more nucleation centers and adsorption sites for the raw materials (cobalt source and second lithium source) of the first coating layer, thereby promoting the formation of a thinner and more uniform coating layer of lithium cobalt oxide on the surface of the matrix particles. In contrast, if the specific surface area of ​​the lithium-rich manganese-based core material is too low, the first coating layer may tend to agglomerate or deposit unevenly, making it difficult to form an effective protective layer.

[0028] Therefore, this invention controls the specific surface area of ​​the material before the first coating layer is at a high level through pre-sintering and water washing processes, which provides a more favorable surface environment for the subsequent coating of lithium cobalt oxide. This helps to achieve precise control of the coating layer thickness, improve coating uniformity, enhance interface stability, and ultimately significantly improve the cycle life and electrochemical performance of the material under high voltage and high rate conditions.

[0029] As a further embodiment, the precursor includes one or more of nickel manganese hydroxide, nickel manganese oxide, nickel manganese carbonate, and nickel manganese oxalate.

[0030] As a further preferred embodiment, the precursor includes one or more of nickel manganese hydroxides.

[0031] As an example, the first lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate, lithium fluoride, lithium chloride, and lithium oxide.

[0032] As a preferred example, the first lithium source is selected from lithium hydroxide and / or lithium carbonate.

[0033] As a further embodiment, the molar ratio of the first lithium source to the precursor is (1.2 to 1.5):1.

[0034] As a further embodiment, S1 involves mixing the first lithium source with the precursor at a molar ratio of (1.25~1.45):1, heating to 500~700℃, pre-sintering for 4~8 hours, and cooling to room temperature to obtain the lithium-rich manganese-based core.

[0035] This invention further optimizes the molar ratio of the first lithium source to the precursor and employs low-temperature pre-sintering. To induce the initial formation of oxygen vacancies in the bulk phase, controlling the temperature at 550-650°C in an air atmosphere is a key optimization for oxygen vacancy formation. During this stage, after the precursor and the first lithium source are mixed at a more optimized molar ratio and sintered, nickel, manganese, and other metal ions (Mn) are released. 4+ / Ni 2+ (etc.) and lithium (Li +Within this temperature range, it assembles into a layered lithium-rich manganese-based core material. Under a high-temperature air atmosphere, the lattice oxygen (O) on the material surface... 2- Oxygen ions (O₂·₅₀) may partially detach from the crystal lattice through a deoxygenation reaction driven by thermodynamics (e.g., lowering the system energy), forming oxygen vacancies (Vo·, where "·" represents a positively charged defect at the vacancy). During this process, oxygen ions (O₂·₅₀)... 2- The oxygen molecule (O2) loses electrons and escapes, leaving a positively charged oxygen vacancy in the crystal lattice (which needs to be balanced by a change in the valence state of the metal ion or by filling it with electrons); some high-valence metals (such as Mn) lose electrons and become oxygen molecules (O2), leaving a positively charged oxygen vacancy in the crystal lattice (which needs to be balanced by a change in the valence state of the metal ion or by filling it with electrons); 4+ It may be reduced to Mn 3+ To compensate for the positive charge generated by oxygen vacancies (e.g., Mn) 4+ → Mn 3+ + Vo·), further stabilizing the oxygen vacancy structure.

[0036] As a further embodiment, the mixed solution in S2 is an aqueous solution of an organic acid and a lithium compound, wherein the mass concentration of the organic acid in the mixed solution is 30–90 g / L and the mass concentration of the lithium compound is 5–15 g / L.

[0037] As a further preferred embodiment, the organic acid includes at least one of citric acid monohydrate, tartaric acid, and malic acid.

[0038] As a further preferred embodiment, the organic acid is citric acid monohydrate.

[0039] As a further preferred example, the lithium compound and the second lithium source are not limited, and any one or more lithium-containing compounds that are the same as or different from the first lithium source can be selected.

[0040] As a further embodiment, the mass ratio of the quenched lithium-rich manganese-based core to the mixed solution is 0.5 to 1.5; in the mixed solution, the mass concentration of the organic acid is 30 to 90 g / L, and the mass concentration of the lithium compound is 5 to 15 g / L.

[0041] This invention can further optimize the concentration range of organic acids and lithium compounds during the water washing process. This concentration range further regulates the lithium ion concentration and chemical environment on the surface of lithium-rich manganese-based materials during the water washing process.

[0042] As a further preferred embodiment, the lithium compound is lithium hydroxide or lithium carbonate.

[0043] As a further embodiment, the pH value of the mixed solution is 4 to 6.

[0044] As a further embodiment, the mass ratio of the quenched lithium-rich manganese-based core to the mixed solution is 0.75–1.25; in the mixed solution, the mass concentration of citric acid monohydrate is 50–70 g / L, the mass concentration of lithium carbonate is 7–12 g / L, and the pH value of the mixed solution is 4–6.

[0045] As a further embodiment, the cobalt source includes at least one of cobalt tetroxide, cobalt nitrate, cobalt acetate, cobalt oxide, cobalt chloride, cobalt hydroxide, cobalt carbonate, and cobalt oxalate.

[0046] As a further embodiment, step S2 involves heating the lithium-rich manganese-based core to 100–150 °C, holding it at that temperature for 0.2–3 hours, then quenching it. The core is then immersed in a mixed solution containing organic acid and lithium compound. The mass ratio of the quenched lithium-rich manganese-based core to the mixed solution is 0.5–1.5. The organic acid has a mass concentration of 30–90 g / L, and the lithium compound has a mass concentration of 5–15 g / L. After washing with water, the core is filtered and dried. The mixture of the dried lithium-rich manganese-based core, 2–8 wt% of a cobalt source, and 0.5–2 wt% of a second lithium source is sintered at 840–880 °C for 10–18 hours to obtain a lithium-rich manganese-based material with a first coating layer.

[0047] As a further preferred embodiment, step S2 involves heating the lithium-rich manganese-based core to 100–150 °C, holding it at that temperature for 0.2–3 hours, then quenching it. The core is then immersed in a mixed solution containing organic acid and lithium compound. The mass ratio of the quenched lithium-rich manganese-based core to the mixed solution is 0.75–1.25. The organic acid has a mass concentration of 50–70 g / L, and the lithium compound has a mass concentration of 7–12 g / L. After washing with water, the core is filtered and dried. The dried lithium-rich manganese-based core, a cobalt source comprising 3–6 wt% of the dried lithium-rich manganese-based core mass, and a second lithium source comprising 0.75–1.5 wt% of the dried lithium-rich manganese-based core mass are sintered at 840–880 °C for 10–18 hours to obtain a lithium-rich manganese-based material with a first coating layer.

[0048] As a further embodiment, S3 is: coating the dried lithium-rich manganese-based core with a variable-valence metal chalcogenide compound at 0.2~1.2 wt% of the core mass, followed by a secondary sintering treatment at 320~380 °C for 6~10 h.

[0049] As a further preferred embodiment, S3 is: coating the dried lithium-rich manganese-based core with a variable-valence metal chalcogenide compound at 0.5~0.9wt% of its mass, followed by a secondary sintering treatment at 320~380 °C for 6~10 h.

[0050] As a further preferred embodiment, the heating rate of the pre-sintering, quenching, primary sintering, and secondary sintering is 3–6 °C / min.

[0051] As a further preferred embodiment, the preparation method includes the following steps:

[0052] S1: First, the first lithium source and the precursor are thoroughly mixed in a molar ratio of 1.2 to 1.5. The temperature is increased from room temperature to 550 to 650°C at a heating rate of 3 to 6°C / min. The mixture is pre-sintered for 4 to 6 hours and then naturally cooled to room temperature to form a lithium-rich manganese-based core.

[0053] S2: The material obtained in S1 is heated from room temperature to 100-150℃ at a heating rate of 3-6℃ / min and held for 0.5-2 hours. It is then removed and washed with a mixed solution of deionized water containing 30-90 g / L organic acid and 5-15 g / L lithium compound. The water washing and mixing ratio is 0.5-1.5 (mass of the quenched lithium-rich manganese-based core to the mixed solution). After mixing evenly, the mixture is filtered for 1-8 hours. After drying at 100-150℃ for 8-20 hours, 2-8 wt% Co3O4 and 0.5-2 wt% lithium carbonate are added. The mixture is then ball-milled and mixed evenly. The material is then sintered once at 840-880℃ at a heating rate of 3-6℃ / min for 10-18 hours and then naturally cooled to room temperature.

[0054] S3: Coating with a variable-valence metal chalcogenide compound accounting for 0.2~1.2 wt% of the dried lithium-rich manganese-based core, and then sintering at 320~380℃ for 6~10 hours at a heating rate of 3~6℃ / min.

[0055] As a further preferred embodiment, the preparation method includes the following steps:

[0056] S1: Mix lithium carbonate and the precursor at a molar ratio of 1.25~1.45, and mix in a ball mill at 200~300 rpm for 2~3 hours. Place the mixture in a box-type muffle furnace and introduce an air atmosphere for 1~2 minutes. 3 / h, heating from room temperature to 550~650℃ at a heating rate of 3~6℃ / min, pre-firing for 4~6h, and then naturally cooling to room temperature to form a lithium-rich manganese-based core;

[0057] S2: The material obtained in S1 is heated from room temperature to 100-150℃ at a rate of 3-6℃ / min and held for 0.5-2 hours. It is then treated with citric acid monohydrate containing 50-70 g / L and 7-12 g / L of sodium chloride solution. Wash with a deionized water solution containing g / L lithium hydroxide. The water washing ratio is 0.75~1.25 (mass of the quenched lithium-rich manganese-based core:mass of the mixed solution). Stir in a beaker with a glass stirrer for 1~3 minutes to ensure uniform mixing and no agglomeration at the bottom. Then filter for 1~8 hours until no aqueous solution is filtered out, ensuring the filtered material is non-flowing and sufficiently dry. Disperse the filtered material into fine particles and dry in a vacuum oven at 100~150℃ for 8~20 hours. Then add 3~6wt% Co3O4 and 0.75~1.5wt% lithium carbonate (mass of the dried lithium-rich manganese-based core). Ball mill and mix evenly. Place the mixture in a box-type muffle furnace and purge with air for 1.5m. 3 Sinter at 840-880℃ for 10-18 hours, heating from room temperature to 840-880℃ at a rate of 3-6℃ / min, and then naturally cooling to room temperature.

[0058] S3: Coating with variable valence metal sulfides accounting for 0.5~0.9wt% of the dried lithium-rich manganese-based core, and then sintering at 320~380℃ for 6~10h at a heating rate of 3~6℃ / min.

[0059] Thirdly, the present invention also provides a positive electrode sheet, comprising the lithium-rich manganese-based positive electrode active material or the lithium-rich manganese-based positive electrode active material prepared by the preparation method.

[0060] Fourthly, the present invention also provides a lithium-ion battery, including the positive electrode sheet.

[0061] The features and beneficial effects of this invention are as follows:

[0062] 1. This invention employs a pre-sintering process to regulate the lithium-rich manganese-based core to a metastable structure, creating conditions for the subsequent formation of a lithium cobalt oxide permeation layer between grain boundaries. Water washing is used, and the resulting oxygen vacancies are the result of the synergistic effect of pre-sintering (high-temperature deoxidation) and water washing (selective impurity removal): pre-sintering thermodynamically generates initial oxygen vacancies, while water washing with an aqueous solution containing organic acids and lithium compounds selectively removes surface alkaline impurities, maintaining the Li... + Concentration and chemical environment stability, inhibiting Li + Loss and O 2- Instability indirectly protects oxygen lattice sites. Oxygen vacancies significantly improve the capacity, rate capability, cycle stability, and interface compatibility of lithium-rich manganese-based cathode materials by regulating lattice structure, electronic state, and surface chemistry.

[0063] 2. In-situ synthesis of LiCoO2 at the grain boundaries of primary particles and on the surface of secondary particles in metastable lithium-rich manganese-based cathode materials achieves a dual-functional coating effect: an intergranular penetration layer + a surface coating layer, reducing interfacial impedance and Co... 3+ Penetrating into grain boundaries enhances electronic conductivity and broadens the Li... + Diffusion channels are used to construct a three-dimensional ion / electron conduction network.

[0064] 3. In this invention, sulfur / selenium vacancies formed by coating a passivation layer on the surface of a variable-valence metal chalcogenide compound are used to capture reactive oxygen species. This reduces the contact between reactive oxygen species and variable-valence metal ions, lowers the dissolution and migration rates of variable-valence metal ions, thereby maintaining the integrity of the material's crystal structure and improving the cycle stability of the battery. Attached Figure Description

[0065] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0066] Figure 1 This is a schematic diagram of the structure of the lithium-rich manganese-based positive electrode active material prepared in this invention.

[0067] Figure 2 The images shown are scanning electron microscope (SEM) images and EDS spectra of the lithium-rich manganese-based core after pre-sintering during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0068] Figure 2 Image a is a partial magnified scan electron microscope image (1 μm) taken at 20,000 times magnification) after the pre-sintering of the lithium-rich manganese-based core during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0069] Figure 2 Image b is a scanning electron microscope image magnified 10,000 times (2 μm) after the lithium-rich manganese-based core is pre-sintered during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0070] Figure 2 c is an EDS image magnified 20,000 times (1 μm) after the pre-sintering of the lithium-rich manganese-based core during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0071] Figure 2 In the middle d, it is the EDS Ni elemental diagram magnified 20,000 times (1 μm) after the lithium-rich manganese-based core pre-sintering process during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of the present invention.

[0072] Figure 2 In Figure e, the elemental diagram of Mn obtained by EDS after pre-sintering of the lithium-rich manganese-based core in Example 1 of this invention is magnified 20,000 times (1 μm).

[0073] Figure 2 The image in Figure f is an EDS O elemental diagram magnified 20,000 times (1 μm) after the pre-sintering of the lithium-rich manganese-based core during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0074] Figure 3 The images shown are scanning electron microscope (SEM) images and EDS spectra of the lithium-rich manganese-based core after water washing and drying during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0075] Figure 3 Image a is a partial magnified scanned electron microscope image (1 μm) taken during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention, after the lithium-rich manganese-based core was washed and dried. The image was magnified 20,000 times.

[0076] Figure 3 Image b is a scanning electron microscope image magnified 10,000 times (2 μm) after the lithium-rich manganese-based core is washed and dried during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0077] Figure 3 In Figure c, the image is an EDS image magnified 20,000 times (1 μm) after the lithium-rich manganese-based core is washed and dried during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0078] Figure 3 In the middle d, it is the EDS Ni elemental diagram magnified 20,000 times (1 μm) after the lithium-rich manganese-based core is washed and dried during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of the present invention.

[0079] Figure 3 In Figure e, the elemental diagram of Mn obtained by EDS after washing and drying the lithium-rich manganese-based core in Example 1 of this invention is magnified 20,000 times (1 μm).

[0080] Figure 3 The image in Figure f is an EDS elemental diagram of the lithium-rich manganese-based core after washing and drying in Example 1 of this invention, magnified 20,000 times (1 μm).

[0081] Figure 4 The images shown are scanning electron microscope (SEM) images and EDS spectra of the lithium-rich manganese-based core after the first coating layer is coated during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0082] Figure 4Image a is a partial magnified scanned electron microscope image magnified 20,000 times (1 μm) after the lithium-rich manganese-based core is coated with the first coating layer during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of the present invention.

[0083] Figure 4 Image b is a scanning electron microscope image magnified 10,000 times (2 μm) of the first coating layer of the lithium-rich manganese-based core during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0084] Figure 4 In Figure c, the first coating layer of the lithium-rich manganese-based core is magnified 20,000 times (1 μm) during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0085] Figure 4 In the middle d, it is the EDS Ni elemental diagram magnified 20,000 times (1 μm) during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of the present invention to show the first coating layer of the lithium-rich manganese-based core.

[0086] Figure 4 In Figure e, the elemental diagram of Mn in the first coating layer of the lithium-rich manganese-based core is magnified 20,000 times (1 μm) during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0087] Figure 4 The image in Figure f is an EDS Co elemental diagram magnified 20,000 times (1 μm) during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0088] Figure 5 This is a magnified EDS image of a local spot scan at 40,000 times (500 nm) after the lithium-rich manganese-based core is coated with the first coating layer during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of the present invention.

[0089] Figure 6 The images shown are scanning electron microscope (SEM) images and EDS spectra of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention.

[0090] Figure 6 Image a is a partial magnified view of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention, magnified 20,000 times (1 μm) by scanning electron microscopy.

[0091] Figure 6 Image b is a scanning electron microscope image of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention, magnified 10,000 times (2 μm).

[0092] Figure 6 c is an EDS image of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention, magnified 20,000 times (1 μm);

[0093] Figure 6 In the image, d is an EDS Ni elemental diagram magnified 20,000 times (1 μm) of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention;

[0094] Figure 6 In the image, e is an EDSMn elemental diagram of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention, magnified 20,000 times (1 μm).

[0095] Figure 6 f is an EDSCo elemental diagram of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention, magnified 20,000 times (1 μm).

[0096] Figure 6 The image in g is an EDS elemental diagram of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention, magnified 20,000 times (1 μm).

[0097] Figure 6 The image in h is an EDS elemental diagram of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention, magnified 20,000 times (1 μm).

[0098] Figure 6 In Figure i, the elemental diagram of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention is obtained by magnifying the image by 20,000 times (1 μm) using EDS.

[0099] Figure 7 This is a partial EDS image of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of the present invention, magnified 40,000 times (500 nm).

[0100] Figure 8 The XRD patterns of the materials at each stage of the preparation process of lithium-rich manganese-based positive electrode active materials in Example 1 and Comparative Example 1 of this invention are shown.

[0101] Figure 9 The XRD comparison diagrams of the lithium-rich manganese-based positive electrode active materials prepared in Example 1 and Comparative Example 1 at the (003) peak are shown.

[0102] Figure 10 The XRD comparison diagrams of the lithium-rich manganese-based positive electrode active materials prepared in Example 1 and Comparative Example 1 at the (104) peak are shown.

[0103] Figure 11 The XRD patterns of the materials at the (018) and (110) peaks at each stage of the preparation process of lithium-rich manganese-based positive electrode active materials in Example 1 and Comparative Example 1 are shown.

[0104] Figure 12 The O 1s XPS spectra of the materials at each stage of the preparation process of lithium-rich manganese-based positive electrode active material in Example 1 are shown.

[0105] Figure 13 The image shows the Co 2p XPS spectra of the material before and after the first coating layer was applied during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1.

[0106] Figure 14 The image shows the Mo 3d XPS spectra of the material before and after the second coating layer was applied during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1.

[0107] Figure 15 The image shows the S 2p XPS spectra of the material before and after the second coating layer was applied during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1.

[0108] Figure 16 Impedance diagrams for Examples 1, 4, and Comparative Example 1 after 2 cycles of 1C.

[0109] Figure 17 Impedance diagrams of Examples 1, 4 and Comparative Example 1 under 50 cycles at 1C.

[0110] Figure 18 Impedance diagrams of Examples 1, 4 and Comparative Example 1 under 1C cycling for 100 cycles. Detailed Implementation

[0111] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0112] As a specific example of the implementation of this invention, detailed cases are provided below.

[0113] Example 1: Step 1: Mix Li2CO3 with Ni 0.34 Mn 0.66 (OH)₂ precursors were mixed at a molar ratio of 1.32 and milled in a ball mill at 200-300 rpm for 2-3 hours. The mixture was then placed in a box-type muffle furnace, and an air atmosphere was introduced for 1.5 m³. 3 / h, heating from room temperature to 600℃ at a heating rate of 5℃ / min for 5 h, and then naturally cooling to room temperature to form a lithium-rich manganese-based core with a metastable structure containing local oxygen vacancies;

[0114] Step 2: The pre-calcined material is heated from room temperature to 120℃ at a heating rate of 5℃ / min and held at that temperature for 1 hour. It is then washed with an aqueous solution containing 10 g / L LiOH·H2O and 60 g / L citric acid monohydrate (mixing ratio: mass of the quenched lithium-rich manganese-based core : mass of the aqueous solution containing 10 g / L LiOH·H2O and 60 g / L citric acid monohydrate = 1.25). The mixture is stirred in a beaker with a glass stirrer for 2 minutes to ensure homogeneity and prevent agglomeration at the bottom. Filtering is then performed. Filtering continues for 4 hours until no aqueous solution is filtered out, ensuring the filtered material is non-flowing and sufficiently dry. The filtered material is then dispersed into fine particles and dried in a vacuum oven at 120℃ for 15 hours. The specific surface area of ​​the washed lithium-rich manganese-based core is 1.238 m². 2 / g;

[0115] Step 3: Add 4 wt% Co3O4 and 1 wt% Li2CO3 (based on the mass of the dried lithium-rich manganese-based core), ball mill to mix evenly, place the mixture in a box-type muffle furnace, and purge with air for 1.5m. 3 The temperature was increased from room temperature to 850℃ at a rate of 5℃ / min and sintered for 15 hours, then naturally cooled to room temperature; the specific surface area of ​​the lithium-rich manganese-based core with the first coating layer was 0.742 m². 2 / g; The D50 particle size of the lithium-rich manganese-based core is 4.5 μm, and the thickness of the first coating layer is 11 nm;

[0116] Step 4: Add 0.5 wt% MoS2 (based on the mass of the dried lithium-rich manganese-based core), ball mill to mix evenly, place the mixture in a box-type muffle furnace, and introduce an air atmosphere of 1.5 m. 3 The temperature was increased from room temperature to 350℃ at a heating rate of 5℃ / min and sintered for 8 hours, then naturally cooled to room temperature to obtain a lithium-rich manganese-based positive electrode active material; the thickness of the second coating layer was 2nm.

[0117] The prepared lithium-rich manganese-based cathode active material has the following properties: Figure 1 The diagram shown.

[0118] Example 2: Step 1: Mix Li2CO3 with Ni 0.34 Mn 0.66 (OH)₂ precursors were mixed at a molar ratio of 1.32 and milled in a ball mill at 200-300 rpm for 2-3 hours. The mixture was then placed in a box-type muffle furnace, and an air atmosphere was introduced for 1.5 m³. 3 / h, heating from room temperature to 600℃ at a heating rate of 5℃ / min for 5 h, then naturally cooling to room temperature to form a metastable structure with local oxygen vacancies;

[0119] Step 2: Heat the pre-calcined material from room temperature to 120℃ at a heating rate of 5℃ / min and hold for 1 hour. Wash with a deionized water solution containing 10 g / L LiOH·H2O and 60 g / L citric acid monohydrate (mixing ratio: material mass: deionized water mass = 1.25). Stir in a beaker with a glass stirrer for 2 minutes to ensure uniform mixing and no agglomeration at the bottom. Then filter. Filter for 4 hours until no aqueous solution is filtered out, ensuring the filtered material is non-flowing and sufficiently dry. Disperse the filtered material into fine particles and dry in a vacuum oven at 120℃ for 15 hours.

[0120] Step 3: Add 4 wt% Co3O4 and 1 wt% Li2CO3 (based on the mass of the dried lithium-rich manganese-based core), ball mill and mix evenly. Place the mixture in a box-type muffle furnace and purge with air for 1.5m. 3 The temperature was increased from room temperature to 850℃ at a rate of 5℃ / min and sintered for 15 hours, then naturally cooled to room temperature; the specific surface area of ​​the lithium-rich manganese-based core with the first coating layer was 0.742 m². 2 / g; The D50 particle size of the lithium-rich manganese-based core is 4.5 μm, and the thickness of the first coating layer is 11 nm;

[0121] Step 4: Add 0.2 wt% MoS2 (based on the mass of the dried lithium-rich manganese-based core), ball mill to mix evenly, place the mixture in a box-type muffle furnace, and introduce an air atmosphere of 1.5 m. 3 The temperature was increased from room temperature to 350℃ at a heating rate of 5℃ / min for 8 hours, and then naturally cooled to room temperature to obtain a lithium-rich manganese-based positive electrode active material; the thickness of the second coating layer was 1nm.

[0122] Example 3: Step 1: Mix Li2CO3 with Ni 0.34 Mn 0.66 (OH)₂ precursors were mixed at a molar ratio of 1.32 and milled in a ball mill at 200-300 rpm for 2-3 hours. The mixture was then placed in a box-type muffle furnace, and an air atmosphere was introduced for 1.5 m³. 3 / h, heating from room temperature to 600℃ at a heating rate of 5℃ / min for 5 h, then naturally cooling to room temperature to form a metastable structure with local oxygen vacancies;

[0123] Step 2: Heat the pre-calcined material to 120℃ at a heating rate of 5℃ / min and hold for 1 hour. Wash with a deionized water solution containing 10 g / L LiOH·H2O and 60 g / L citric acid monohydrate (mixing ratio: material mass: deionized water mass = 1.2). Stir in a beaker with a glass stirrer for 2 minutes to ensure uniform mixing and no agglomeration at the bottom. Then filter. Filter for 4 hours until no water solution is filtered out, ensuring the filtered material is non-flowing and sufficiently dry. Disperse the filtered material into fine particles and dry in a vacuum oven at 120℃ for 15 hours.

[0124] Step 3: Add 4 wt% Co3O4 and 1 wt% Li2CO3 (based on the mass of the dried lithium-rich manganese-based core), ball mill and mix evenly. Place the mixture in a box-type muffle furnace and purge with air for 1.5m. 3 The temperature was increased from room temperature to 850℃ at a rate of 5℃ / min and sintered for 15 hours, then naturally cooled to room temperature; the specific surface area of ​​the lithium-rich manganese-based core with the first coating layer was 0.742 m². 2 / g; The D50 particle size of the lithium-rich manganese-based core is 4.5 μm, and the thickness of the first coating layer is 11 nm;

[0125] Step 4: Add 0.8 wt% MoS2 (based on the mass of the dried lithium-rich manganese-based core), ball mill to mix evenly, place the mixture in a box-type muffle furnace, and introduce an air atmosphere of 1.5 m. 3 The temperature was increased from room temperature to 350℃ at a heating rate of 5℃ / min for 8 hours, and then naturally cooled to room temperature; the thickness of the second coating layer was 3.5nm.

[0126] Example 4: Step 1: Mix Li2CO3 with Ni 0.34 Mn 0.66 (OH)₂ precursors were mixed at a molar ratio of 1.32 and milled in a ball mill at 200-300 rpm for 2-3 hours. The mixture was then placed in a box-type muffle furnace, and an air atmosphere was introduced for 1.5 m³. 3 / h, heating from room temperature to 600℃ at a heating rate of 5℃ / min for 5 h, then naturally cooling to room temperature to form a metastable structure with local oxygen vacancies;

[0127] Step 2: Heat the pre-calcined material from room temperature to 120℃ at a heating rate of 5℃ / min and hold for 1 hour. Wash with a deionized water solution containing 10 g / L LiOH·H2O and 60 g / L citric acid monohydrate (mixing ratio: material mass: deionized water mass = 1.2). Stir in a beaker with a glass stir bar for 2 minutes to ensure uniform mixing and no agglomeration at the bottom. Then filter. Filter for 4 hours until no water solution is filtered out, ensuring the filtered material is non-flowing and sufficiently dry. Disperse the filtered material into fine particles and dry in a vacuum oven at 120℃ for 15 hours.

[0128] Step 3: Add 4 wt% Co3O4 and 1 wt% Li2CO3 (based on the mass of the dried lithium-rich manganese-based core), ball mill and mix evenly. Place the mixture in a box-type muffle furnace and purge with air for 1.5m. 3 The temperature was increased from room temperature to 850℃ at a rate of 5℃ / min and sintered for 15 hours, then naturally cooled to room temperature; the specific surface area of ​​the lithium-rich manganese-based core with the first coating layer was 0.742 m². 2 / g; The D50 particle size of the lithium-rich manganese-based core is 4.5 μm, and the thickness of the first coating layer is 11 nm;

[0129] Step 4: Add 1 wt% MoS2 (based on the mass of the dried lithium-rich manganese-based core), ball mill to mix evenly, place the mixture in a box-type muffle furnace, and introduce an air atmosphere of 1.5 m. 3 The temperature was increased from room temperature to 350℃ at a heating rate of 5℃ / min for 8 hours, and then naturally cooled to room temperature; the thickness of the second coating layer was 4.3nm.

[0130] Example 5: Step 1: Mix Li2CO3 with Ni 0.34 Mn 0.66 (OH)2 precursors are mixed at a molar ratio of 1.32 and mixed in a ball mill at 200-300 rpm for 2-3 hours. The mixture is then placed in a box-type muffle furnace, and an air atmosphere of 1.5 m³ / h is introduced. The temperature is increased from room temperature to 600℃ at a heating rate of 5℃ / min for 5 hours for pre-calcination. The mixture is then naturally cooled to room temperature to form a metastable structure with local oxygen vacancies.

[0131] Step 2: Heat the pre-calcined material from room temperature to 120℃ at a heating rate of 5℃ / min and hold for 1 hour. Wash with a deionized water solution containing 10 g / L LiOH·H2O and 60 g / L citric acid monohydrate (mixing ratio: material mass: deionized water mass = 1.2). Stir in a beaker with a glass stir bar for 2 minutes to ensure uniform mixing and no agglomeration at the bottom. Then filter. Filter for 4 hours until no water solution is filtered out, ensuring the filtered material is non-flowing and sufficiently dry. Disperse the filtered material into fine particles and dry in a vacuum oven at 120℃ for 15 hours.

[0132] Step 3: Add 3wt% Co3O4 and 0.75wt% Li2CO3 (based on the mass of the dried lithium-rich manganese-based core), ball mill to mix evenly, place the mixture in a box-type muffle furnace, and purge with air for 1.5m. 3 The temperature was increased from room temperature to 850℃ at a rate of 5℃ / min and sintered for 15 hours, then naturally cooled to room temperature; the specific surface area of ​​the lithium-rich manganese-based core with the first coating layer was 0.713 m². 2 / g; The D50 particle size of the lithium-rich manganese-based core is 4.5 μm, and the thickness of the first coating layer is 8 nm;

[0133] Step 4: Add 0.5 wt% MoS2 (based on the mass of the dried lithium-rich manganese-based core), ball mill to mix evenly, place the mixture in a box-type muffle furnace, and introduce an air atmosphere of 1.5 m. 3 The temperature was increased from room temperature to 350℃ at a rate of 5℃ / min and sintered for 8 hours, then naturally cooled to room temperature; the thickness of the second coating layer was 2nm.

[0134] Example 6: Step 1: Mix Li2CO3 with Ni 0.34 Mn 0.66 (OH)₂ precursors were mixed at a molar ratio of 1.32 and milled in a ball mill at 200-300 rpm for 2-3 hours. The mixture was then placed in a box-type muffle furnace, and an air atmosphere was introduced for 1.5 m³. 3 / h, heating from room temperature to 600℃ at a heating rate of 5℃ / min for 5 h, then naturally cooling to room temperature to form a metastable structure with local oxygen vacancies;

[0135] Step 2: Heat the pre-calcined material from room temperature to 120℃ at a heating rate of 5℃ / min and hold for 1 hour. Wash with a deionized water solution containing 10 g / L LiOH·H2O and 60 g / L citric acid monohydrate (mixing ratio: material mass: deionized water mass = 1.2). Stir in a beaker with a glass stir bar for 2 minutes to ensure uniform mixing and no agglomeration at the bottom. Then filter. Filter for 4 hours until no water solution is filtered out, ensuring the filtered material is non-flowing and sufficiently dry. Disperse the filtered material into fine particles and dry in a vacuum oven at 120℃ for 15 hours.

[0136] Step 3: Add 2 wt% Co3O4 and 0.5 wt% Li2CO3 (based on the mass of the dried lithium-rich manganese-based core), ball mill to mix evenly, place the mixture in a box-type muffle furnace, and introduce an air atmosphere of 1.5 m. 3 The temperature was increased from room temperature to 850℃ at a rate of 5℃ / min and sintered for 15 hours, then naturally cooled to room temperature; the specific surface area of ​​the lithium-rich manganese-based core with the first coating layer was 0.693 m². 2 / g; The D50 particle size of the lithium-rich manganese-based core is 4.5 μm, and the thickness of the first coating layer is 6 nm;

[0137] Step 4: Add 0.5 wt% MoS2 (based on the mass of the dried lithium-rich manganese-based core), ball mill to mix evenly, place the mixture in a box-type muffle furnace, and introduce an air atmosphere of 1.5 m. 3 The temperature was increased from room temperature to 350℃ at a rate of 5℃ / min and sintered for 8 hours, then naturally cooled to room temperature; the thickness of the second coating layer was 2nm.

[0138] Example 7: Unlike Example 1, step 4 involves adding 0.5 wt% MoSe2, ball milling to mix evenly, placing the mixture in a box-type muffle furnace, and introducing an air atmosphere for 1.5 m... 3 The temperature is increased from room temperature to 350℃ at a rate of 5℃ / min for 8 hours, and then naturally cooled to room temperature.

[0139] Example 8: Unlike Example 1, step 4 involves adding 0.5 wt% TiS2, ball milling to mix evenly, placing the mixture in a box-type muffle furnace, and introducing an air atmosphere for 1.5 m... 3 The temperature is increased from room temperature to 350℃ at a rate of 5℃ / min for 8 hours, and then naturally cooled to room temperature.

[0140] Example 9: Unlike Example 1, step 1 involves Ni... 0.34 Mn 0.66 (OH)2 precursor and lithium hydroxide are mixed at a molar ratio of 1.32 and pre-calcined at 700°C for 5 h.

[0141] Example 10: Unlike Example 1, in step 2, the pre-fired material is heated to 120°C and kept at that temperature for 1 hour. After washing with a deionized water solution containing 10 g / L LiOH·H2O and 60 g / L citric acid monohydrate (mixing ratio of material mass: deionized water solution mass = 1.5), it is dried in a vacuum oven at 120°C for 15 hours.

[0142] Example 11: Unlike Example 1, in step 2, the pre-fired material is heated to 120°C and kept at that temperature for 1 hour. After washing with a deionized water solution containing 5 g / L LiOH·H2O and 30 g / L citric acid monohydrate (mixing ratio is 1.5:material mass:deionized water solution mass), it is dried in a vacuum oven at 120°C for 15 hours.

[0143] Comparative Example 1: Unlike Example 1, this is a lithium-rich manganese-based material without any coating, prepared by reacting Li2CO3 with Ni. 0.34 Mn 0.66 The (OH)2 precursors were mixed at a molar ratio of 1.32, heated from room temperature to 350℃ at a heating rate of 5℃ / min and held for 5 hours, then heated to 600℃ at a heating rate of 5℃ / min and held for 5 hours, and finally heated to 850℃ at a heating rate of 5℃ / min and sintered for 15 hours.

[0144] Comparative Example 2: Unlike Example 1, this is a lithium-rich manganese-based material without any coating. It was prepared in the same steps 1-2 as in Example 1 and then sintered at 850°C for 15 hours.

[0145] Comparative Example 3: Unlike Example 1, the raw materials were directly mixed and heated from room temperature to 350°C at a heating rate of 5°C / min and held for 5 hours. Then, the temperature was increased to 600°C at a heating rate of 5°C / min and held for 5 hours. Finally, the temperature was increased to 850°C at a heating rate of 5°C / min and sintered for 15 hours in a single gradient high-temperature sintering process. Other washing and coating processes were the same as steps 2, 3, and 4 of Example 1.

[0146] Comparative Example 4: Unlike Example 1, only LiCoO2 coating was performed (same as steps 1-3 of Example 1, but without MoS2 coating).

[0147] Comparative Example 5: Unlike Example 1, it was not washed with water after pre-calcination, but instead coated with LiCoO2 (same as steps 1, 3, and 4 of Example 1, except for step 2).

[0148] Comparative Example 6: Unlike Example 1, the complexing agent in step 2 was replaced with a hydrochloric acid solution with a mass fraction of 6% to 10% (other steps are the same as in Example 1, steps 1 to 4).

[0149] Comparative Example 7: Unlike Example 1, step 4 is changed to adding 0.5wt% nano Al2O3 and sintering at 350°C in an air atmosphere for 8 hours (other steps are the same as in Example 1, steps 1-3).

[0150] Comparative Example 8: Unlike Example 1, step 2 is changed to not adding lithium supplementation compound (other steps are the same as steps 1 to 4 of Example 1).

[0151] Comparative Example 9: Unlike Example 1, step 4 is performed first, followed by step 3.

[0152] Comparative Example 10: Unlike Example 1, step 2 was changed to not adding organic acid (other steps are the same as steps 1-4 of Example 1), and the pH of the mixed solution was 6.7.

[0153] Coin cells were prepared using the lithium-rich manganese-based positive electrode active materials obtained in Examples 1-11 and Comparative Examples 1-10.

[0154] The preparation steps for the positive electrode sheet are as follows:

[0155] The prepared lithium-rich manganese-based positive electrode active material, conductive agent (Super P), and binder (PVDF:NMP = 5%) were thoroughly mixed in a degassing machine for 10 min at a mass ratio of 90:5:5; simultaneously, the coating speed of the flatbed coating machine was set to 20 mm / s. -1 The coating thickness of the scraper was adjusted to 70 μm. The homogenized slurry was then evenly coated onto aluminum foil using a flatbed coating machine. After coating, the electrode was placed in an 80 ℃ forced-air drying oven for 1 h, and then transferred to a 120 ℃ vacuum oven for 6 h. After cooling to room temperature, it was cut into circular positive electrode sheets with a diameter of 12 mm and weighed on an electronic analytical balance for subsequent use.

[0156] The assembly steps for the CR2032 button battery are as follows:

[0157] First, place the weighed positive electrode sheet into a glove box. Then, assemble the battery in the following order: negative electrode shell, lithium sheet (1 mm), electrolyte (35 μL), separator (Celgard 2325), electrolyte (35 μL), positive electrode sheet, gasket, spring sheet, and positive electrode shell. Seal the battery using a sealing machine. After standing for about 3 hours, perform charge-discharge tests on an electrochemical workstation. 1C = 250 mAh g -1 .

[0158] The batteries prepared in Examples 1-11 and Comparative Examples 1-10 were tested for first-cycle coulombic efficiency, cycle capacity retention, rate performance, and high-temperature cycle capacity retention. The specific test methods are as follows:

[0159] (1) First-cycle coulombic efficiency and 50-cycle capacity retention: After preparing the battery and allowing it to stand for 3 hours, charge / discharge tests were performed on the LAND battery testing system. The voltage range was 2.0–4.8V, and the ambient temperature was 25℃. The charge and discharge specific capacities of the battery in the first two cycles at a current of 0.1C were recorded, and the coulombic efficiency of the battery in the first cycle at a current of 0.1C was calculated as: first-cycle discharge specific capacity / first-cycle charge specific capacity. The capacity retention rate of the battery after 50 cycles at a current of 1C after two cycles at 0.1C was calculated and recorded as: 50th cycle discharge specific capacity / 1C first-cycle discharge specific capacity.

[0160] (2) Rate performance (capacity retention at different rates): After the battery was prepared and allowed to stand for 3 hours, it was charged / discharged on the LAND battery testing system with a voltage range of 2.0 to 4.6V. The capacity retention was recorded at currents of 0.1C, 0.33C, 1C, 3C, and 5C. The capacity retention at different rates was calculated as: discharge specific capacity at different rates / average discharge specific capacity at 0.1C for 5 cycles.

[0161] (3) High-temperature 50-cycle capacity retention: After the battery was prepared and allowed to stand for 3 hours, it was charged / discharged on the LAND battery testing system with a voltage range of 2.0 to 4.8V and an ambient temperature of 45℃. The battery was charged and discharged at a current of 0.1C for the first two cycles. The capacity retention rate of the battery after 50 cycles at a current of 1C was calculated and recorded after the second cycle at 0.1C. The capacity retention rate was calculated as: discharge capacity at the 50th cycle / discharge capacity at the first cycle at 1C.

[0162] The test results of Examples 1-11 and Comparative Examples 1-10 are shown in Table 1 below:

[0163] Table 1

[0164]

[0165] As can be seen from Comparative Example 1, when the present invention does not employ a two-coating strategy, the outer surface of the lithium-rich manganese-based material does not have the first coating layer containing lithium cobalt oxide as defined in the present invention, nor does it have the second coating layer containing a variable-valence metal chalcogenide compound. At this time, due to the unstable intergranular structure between the primary particles of the lithium-rich manganese-based material, and the absence of the nano-layered lithium cobalt oxide as defined in the present invention, it is impossible to form stable oxygen vacancies in the primary particles. Therefore, the structure lacks a certain degree of stability. At the same time, the comparative example does not have the variable-valence metal chalcogenide compound located on the outermost layer as defined in the present invention. Therefore, the battery cannot form good ion-electron conduction capability, and it also lacks the high thermal stability enhancement effect of the variable-valence metal chalcogenide compound. Therefore, its cycle performance, rate performance, and high-temperature performance are all far lower than those of the example.

[0166] As can be seen from Comparative Example 2, although it underwent low-temperature pre-calcination and was washed with a mixed solution containing organic acids and lithium compounds, the washing and lithium replenishing agents created many exposed oxygen vacancies on and near the material surface. Due to the lack of lithium cobalt oxide, the LCO grain boundary penetration layer and surface coating layer were missing, failing to effectively reduce interfacial impedance, improve electronic conductivity, and broaden the Li... + Diffusion channels cannot form a three-dimensional ion / electron conduction network.

[0167] As can be seen from Comparative Example 3, high-temperature pre-sintering was used. At this time, due to the excessively high pre-sintering temperature, a large number of oxygen vacancies were generated in the lithium-rich manganese-based core. The large number of oxygen vacancies greatly reduced the structural stability of the material. At this time, the lithium cobalt oxide coating layer could not stabilize or was insufficient to stabilize the oxygen vacancies in the core, resulting in a significant decrease in structural stability.

[0168] As can be seen from Comparative Example 4, no variable valence metal chalcogenide was used for coating. At this time, the lithium cobalt oxide layer was exposed on the outer surface of the material. Due to the lack of a second coating layer formed by the variable valence metal chalcogenide, the material lacked good chemical stability and SEI compatibility. It could not form a stable protective layer on the material surface, and could not suppress electrolyte decomposition. The coulombic efficiency and cycle life were significantly reduced.

[0169] As can be seen from Comparative Example 5, no water washing was used after pre-sintering. Due to the lack of a water washing step, a large amount of alkaline impurities remained on the material surface, making it impossible to maintain the Li... + Due to the lack of concentration and chemical environment stability, coupled with the absence of suitable oxygen vacancies generated during the water washing process, it is impossible to synthesize a grain boundary penetration layer of lithium cobalt oxide in situ between grain boundaries. This prevents an effective improvement in the structural stability of the material.

[0170] As can be seen from Comparative Example 6, hydrochloric acid with a low pH was used as the mixed solution in the water washing process. On the one hand, hydrochloric acid is an inorganic acid, and inorganic acids may not be able to form or form enough soluble complexes with the variable valence metal ions in the lithium-rich manganese-based material of this invention. At this time, it is impossible to effectively remove LiOH, Li2CO3 and unreacted lithium carbonate, and it is impossible to form enough surface and near-surface oxygen vacancies in the pre-calcination stage, and it is impossible to form active sites for the subsequent Co3O4 decomposition reaction, thereby reducing the stability of the material.

[0171] As can be seen from Comparative Example 7, which uses nano-Al2O3 as the second coating layer, Al2O3 is a typical ion insulator. Its extremely low lithium-ion conductivity severely hinders the transport of lithium ions at the cathode particle interface, resulting in a significant increase in interface impedance. Although Al2O3 can provide a certain degree of physical isolation and improve the cycle stability of the battery to some extent, its single passivation function cannot achieve the dual effect of interface protection and ion / electron synergistic conduction of the variable valence metal sulfide in this invention. Therefore, the rate performance is much lower than that of the example.

[0172] As can be seen from Comparative Example 8, the mixed solution in the water washing process of Comparative Example 8 does not contain lithium compounds, and the mixed solution cannot stabilize O at this time. 2- With Li + The bonding of Li leads to + Excessive dissolution makes it impossible to achieve the formation and stabilization of oxygen vacancies using only acid. Simultaneously, it's impossible to control the stability of the Mn valence state and the appropriate dissolution of residual alkali on the surface. This leads to violent chemical reactions on the material surface, resulting in excessive oxygen vacancies and an inability to provide structurally stable precursors for subsequent coating processes. This further highlights the role of lithium compounds as lithium replenishers in maintaining appropriate lithium content on the material surface, avoiding excessive delithiation that could lead to irreversible phase transitions or oxygen release. They regulate the lithium-ion defect concentration in grain boundary regions, thereby affecting the local distribution of oxygen vacancies; promote heterogeneous nucleation and uniform coating of LCO at grain boundaries; and improve the bonding force and interfacial stability between the coating layer and the core.

[0173] As can be seen from Comparative Example 9, which first applied a variable-valence metal chalcogenide coating before applying lithium cobalt oxide coating, the dense and chemically inert variable-valence metal chalcogenide layer physically blocks the direct contact between the subsequent cobalt and lithium sources and the lithium-rich manganese-based core surface. This prevents the lithium cobalt oxide from undergoing the expected in-situ reaction and lattice epitaxial growth with the core surface and grain boundaries during high-temperature sintering, ultimately forming only a poorly adhered and unevenly distributed physical mixed layer, rather than the structurally integrated "grain boundary penetration layer" and "surface coating layer" achieved in this invention. As a result, the structural fragility between primary particles is not fundamentally resolved, the oxygen vacancies in the core cannot be effectively stabilized, and the outer lithium cobalt oxide layer is easily peeled off during cycling due to weak bonding. Consequently, the dual design goals of enhanced electron conduction and interface protection are not achieved, resulting in a significant decrease in overall electrochemical performance.

[0174] As can be seen from Comparative Example 10, during the water washing process, if only deionized water or a solution with a high pH is used, it can easily lead to the selective dissolution of lithium ions on the material surface, damaging the original Li... + -O 2- Bonding network. At this point, with Li... + Coordination O 2-Without stabilizing effects, local oxygen lattice sites become unstable, making them prone to oxygen extraction. This leads to the formation of numerous oxygen vacancies in the crystal structure. These surface oxygen vacancies are typically "uncontrolled, highly concentrated, and surface-enriched," resulting in more negative effects than positive ones. The loss of lattice oxygen further induces the release of variable-valence metal ions (such as Mn). 3+ The valence fluctuations of Mn can even trigger Jahn-Teller distortion, exacerbating local structural distortions and defect aggregation; water molecules may react with residual alkali or adsorbed oxygen species on the surface, releasing reactive oxygen species, increasing the chemical activity of the material surface, and promoting side reactions with the subsequent electrolyte; if the washing environment is weakly acidic or has large pH fluctuations, it may also accelerate the reaction of Mn. 3+ → Mn 4+ The cycle is accompanied by oxygen migration and vacancy formation. The above processes lead to an increase in oxygen vacancy concentration on the material surface, an increase in lattice defects, and a decrease in surface lithium content. This disrupts the lithium-ion insertion / extraction balance during the first charge and discharge, reduces interface stability, and ultimately affects the material's first coulombic efficiency, cycle life, and rate performance.

[0175] A comparison of Examples 1 and 3 with Examples 2 and 4 shows that the present invention further optimizes the amount of variable valence metal chalcogenide. In this case, the thickness of the second coating layer is 1 nm to 5 nm, a range preferred for achieving a balance between interface passivation, electron conduction, and ion transport. This avoids the situation where, when the amount of variable valence metal chalcogenide is too low, the second coating layer thickness is too low, making it difficult to form a complete and dense barrier, thus failing to effectively isolate the electrolyte from the erosion of the internal active material, and limiting its effectiveness in capturing reactive oxygen species and inhibiting the dissolution of variable valence metals. While the electronic conductivity of the variable valence metal chalcogenide itself is beneficial for interfacial electron transport, it also avoids the situation where, when the amount of variable valence metal chalcogenide is too high, the second coating layer is too thick, which would significantly hinder the lateral transport of lithium ions and increase interfacial impedance. The optimized thickness of the second coating layer in this invention achieves excellent chemical isolation while its unique layered channels still ensure efficient lithium ion passage, achieving the dual goals of protection and conduction.

[0176] A comparison of Examples 1 and 5-6 shows that the present invention further optimizes the amount of Co3O4 and Li2CO3 raw materials in the first coating layer. At this point, the thickness of the first coating layer is 8nm-15nm, achieving a balance between grain boundary penetration reinforcement and optimized electronic conduction. This avoids the situation where, when the amount of Co3O4 and Li2CO3 is too low, the first coating layer thickness is too low, which may result in a discontinuous coating layer that cannot cover the core surface extensively or effectively penetrate to the primary grain boundaries, thus reducing its effects on stabilizing oxygen vacancies, suppressing phase transitions, and improving electronic conductivity. Conversely, if the amount of Co3O4 and Li2CO3 is too high, leading to an excessively thick first coating layer, on the one hand, it may increase the resistance to lithium-ion cross-interface transport; on the other hand, lithium cobalt oxide itself has a low capacity, and an excessively thick inactive coating layer will lower the average specific capacity of the entire positive electrode active material, which is detrimental to improving energy density.

[0177] A comparison of Examples 1 and 7-8 shows that the present invention can further optimize the selection of a variable-valence metal chalcogenide compound from chromium group metal sulfides. Since chromium group metal sulfides have a typical layered hexagonal crystal structure, this layered structure has better topological similarity in crystallography to the core lithium-rich manganese-based material and the first coating layer lithium cobalt oxide (both layered structures), which is beneficial for forming a tight coating with low defects and low stress at the interface. This structure ensures the uniformity and adhesion of the coating layer, avoiding the problem of coating layer peeling due to volume changes during cycling. Furthermore, its moderate electronic conductivity is sufficient to construct an efficient interfacial electron transport path, improving rate performance. Its semiconductor properties achieve a better balance between improving electron conduction and suppressing interfacial side reactions.

[0178] A comparison of Examples 1 and 9 shows that the present invention further optimizes the molar ratio of the first lithium source to the nickel-manganese hydroxide precursor and employs low-temperature pre-sintering. Controlling the temperature at 550-650°C in an air atmosphere is a key optimization for inducing the initial formation of oxygen vacancies in the bulk phase. In this stage, after the nickel-manganese hydroxide precursor is mixed with the first lithium source, it undergoes high-temperature sintering, resulting in the formation of variable-valence metals (Mn, nickel, manganese, etc.) 4+ / Ni 2+ (etc.) and lithium (Li + ( ) are assembled into layered lithium-rich materials at high temperatures. Under high-temperature air atmosphere, the lattice oxygen (O) on the material surface... 2- Oxygen ions (O₂·₅₀) may partially detach from the crystal lattice through a deoxygenation reaction driven by thermodynamics (e.g., lowering the system energy), forming oxygen vacancies (Vo·, where "·" represents a positively charged defect at the vacancy). During this process, oxygen ions (O₂·₅₀)... 2- The oxygen molecule (O2) loses electrons and escapes, leaving a positively charged oxygen vacancy in the crystal lattice (which needs to be balanced by a change in the valence state of the metal ion or by filling it with electrons); some high-valence metals (such as Mn) lose electrons and become oxygen molecules (O2), leaving a positively charged oxygen vacancy in the crystal lattice (which needs to be balanced by a change in the valence state of the metal ion or by filling it with electrons);4+ It may be reduced to Mn 3 + To compensate for the positive charge generated by oxygen vacancies (e.g., Mn) 4+ → Mn 3+ + Vo·), further stabilizing the oxygen vacancy structure.

[0179] As can be seen from the comparison between Example 1 and Examples 10-11, the present invention can further optimize the concentration range of organic acids and lithium compounds during the water washing process. This concentration range further regulates the lithium ion concentration and chemical environment on the surface of lithium-rich manganese-based materials during the water washing process.

[0180] In summary, the embodiments represented by Examples 1-11, through the pre-firing and water washing process, formed numerous exposed and stable oxygen vacancies on and near the surface of the material. As defects in the crystal lattice, oxygen vacancies significantly improve the overall performance of the lithium-rich manganese-based cathode by modulating the electronic structure, surface chemical properties, and interfacial reactions of the material. The lattice oxygen (O2) near the oxygen vacancies... 2- It has higher reactivity and is more likely to participate in redox reactions (such as O) during charge and discharge. 2- O 0 Or O 2- ↔ O - (Contributing additional capacity). For example, oxygen vacancies can promote "anion redox" (such as O2) in lithium-rich materials. 2- / O - The reversibility of the lithium oxide layer improves the initial coulombic efficiency and specific capacity (especially in the high voltage range above 4.5V). Oxygen vacancies disrupt the regular arrangement of oxygen lattice, forming "defect channels" between the variable valence metal layer and the lithium layer, which is conducive to lithium ion (Li₂O₃) formation. + The rapid migration of oxygen vacancies (lowering the diffusion barrier) improves rate performance (e.g., capacity retention at high current densities). Lithium-rich materials undergo irreversible phase transitions during cycling (e.g., layered → spinel → rock salt phase), leading to structural collapse. Oxygen vacancies can suppress the adverse effects of phase transitions and maintain the integrity of the layered structure by modulating local lattice stresses (e.g., the migration paths of variable-valence metal ions), thereby extending cycle life. Oxygen vacancies interact with variable-valence metal ions (e.g., Mn...) 3+ Ni 3+ There are electronic interactions that can prevent high-valence metals (such as Mn) from being affected. 4+ Excessive reduction or low-valence metals (such as Mn) 3+Excessive oxidation helps maintain a stable chemical environment for active sites. Oxygen vacancies reduce the presence of strongly alkaline sites on the material surface (such as residual LiOH), lowering side reactions with the electrolyte (such as LiPF6 / EC-DMC) (such as HF formation and excessive SEI film growth), thereby reducing capacity decay. Oxygen vacancies also provide more anchoring sites (such as Co) for the subsequent LiCoO2 grain boundary layer (or MoS2 coating layer) formed by Co3O4 decomposition. 2+ Oxygen vacancies can form coordination bonds with variable-valence metal ions around oxygen vacancies, improving the uniformity and bonding strength of the coating layer and further protecting the electrode material from electrolyte corrosion. Oxygen vacancies can also act as electron traps or defect levels, increasing the concentration of free electrons in the material (or regulating the density of electronic states), thereby improving electronic conductivity (especially beneficial for interlayer electron migration of variable-valence metals) and improving rate performance.

[0181] This invention further utilizes a two-stage coating process to form an LCO grain boundary penetration layer and a surface coating layer on the surface and between grain boundaries, as well as a nano-variable valence metal chalcogenide surface coating passivation layer: the LCO grain boundary penetration layer and the surface coating layer significantly reduce interfacial impedance, Co 3+ Penetrating into grain boundaries enhances electronic conductivity and broadens the Li... + Diffusion channels are established to construct a three-dimensional ion / electron conduction network. During the charge and discharge process of lithium-rich manganese-based cathode materials, especially in the high-voltage range, the lattice oxygen (O2) on the material surface... 2- Oxidation reactions occur, causing lithium ions to escape from the crystal lattice and form a series of reactive oxygen species. The presence of reactive oxygen species affects the diffusion and migration of lithium ions in the electrode material, reducing the rate performance of the battery. When sulfur vacancies formed during the heat treatment of variable valence metal chalcogenide coating capture reactive oxygen species, the chemical environment on the surface of the electrode material is improved, and the diffusion channels for lithium ions are more unobstructed, thereby improving the battery performance under high-rate charge and discharge conditions. The surface of the lithium-rich manganese-based core is prone to side reactions with the electrolyte (such as the dissolution of variable valence metals and gas generation). LiCoO2 and the variable valence metal chalcogenide coating layer can act as a physical barrier, reducing direct contact with the electrolyte and suppressing interfacial side reactions. Mn in the core 3+Jahn-Teller distortion and dissolution are prone to occur (especially under high-voltage conditions), leading to capacity decay. The coating layer can reduce the direct contact between Mn and the electrolyte, inhibit Mn dissolution, and extend cycle life. Furthermore, LCO exhibits better thermal stability than lithium-rich manganese-based materials. The coating layer can reduce the exothermic reaction between the core and the electrolyte at high temperatures, reducing the risk of thermal runaway and improving safety. The core is prone to lattice oxygen loss and phase transitions (such as layered → spinel → rock salt phase transition) during cycling. The stable layered structure of LCO can slow down this process, inhibiting capacity decay and structurally improving cycle stability. The sulfur / selenium vacancies formed during the heat treatment of the variable-valence metal chalcogenide coating capture active oxygen, reducing the contact between active oxygen and variable-valence metal ions, lowering the dissolution and migration rates of variable-valence metal ions, thereby maintaining the integrity of the material's crystal structure and improving the battery's cycle stability.

[0182] Table 2 below shows the mass and atomic percentages of each element in EDS after pre-sintering the lithium-rich manganese-based core in Example 1 of this invention, magnified 20,000 times (1 μm).

[0183] Table 2

[0184]

[0185] Table 3 below shows the mass and atomic percentages of each element in EDS after the lithium-rich manganese-based core is washed and dried by water during the preparation of lithium-rich manganese-based positive electrode active material in Example 1 of this invention, magnified 20,000 times (1 μm).

[0186] Table 3

[0187]

[0188] Table 4 below shows the mass and atomic percentages of each element in EDS magnified 20,000 times (1 μm) during the preparation of lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0189] Table 4

[0190]

[0191] Table 5 below shows the atomic percentage of each element in a local EDS scan magnified 40,000 times (500 nm) during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1 of this invention.

[0192] Table 5

[0193]

[0194] Table 6 below shows the mass and atomic percentages of each element in the EDS of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention, magnified 20,000 times (1 μm).

[0195] Table 6

[0196]

[0197] Table 7 below shows the atomic percentage of each element in a local spot scan of the lithium-rich manganese-based positive electrode active material prepared in Example 1 of this invention, magnified 40,000 times (500 nm).

[0198] Table 7

[0199]

[0200] The total of atomic percentages or mass percentages calculated in Tables 2 to 7 is not 100% due to automatic rounding by the instrument. The difference between 99.99% and 100.01% is due to system error and can be ignored.

[0201] Depend on Figures 2-7 As can be seen from Tables 2 to 7, Figure 2 The lithium-rich manganese-based core is pre-sintered and exhibits high oxygen and Mn / Ni elemental composition. It does not contain elements such as Co, Mo, and S. The material is in the transition metal oxide (such as Mn-Ni-O) stage after the first calcination, and the crystal structure has not yet fully formed a layered lithium-rich phase. Figure 3 After washing and drying, the lithium-rich manganese-based core showed a decrease in oxygen content and an increase in the proportion of Mn and Ni atoms, especially a significant increase in Ni. Figures 4-5 It can be seen that the presence of Co is due to the addition of cobalt and lithium sources during high-temperature calcination, which react to form the first coating layer on the surface or grain boundaries of the particles. This coating layer is rich in Co and O, hence the high levels of Co and O detected by EDS during surface scanning. The decrease in the Mn and Ni ratio is because the coating layer is mainly on the surface, while the substrate remains a layered oxide enriched in Mn / Ni. Figures 6-7 It can be seen that O (61.27%), Mn (23.79%), Ni (12.54%), and Co (1.95%) are still the main components, indicating that the bulk phase is still a lithium-rich manganese-based cathode material; the Co (~2 at.%) has increased, which comes from the first coating layer at the surface / grain boundary.

[0202] Figure 8 The XRD patterns of the materials at each stage of the preparation process of lithium-rich manganese-based positive electrode active materials in Example 1 and Comparative Example 1 of this invention are shown. Figure 8 In Figure A, the XRD pattern of Comparative Example 1 is shown. Figure 8In Example 1, B is the XRD pattern of the lithium-rich manganese-based core after pre-sintering during the preparation of the lithium-rich manganese-based positive electrode active material. Figure 8 In Example 1, C represents the XRD pattern of the lithium-rich manganese-based core after water washing and drying during the preparation of the lithium-rich manganese-based positive electrode active material. Figure 8 In Example 1, D is the XRD pattern of the lithium-rich manganese-based core after the first coating layer is coated during the preparation of the lithium-rich manganese-based positive electrode active material. Figure 8 E in the image is the XRD pattern of the lithium-rich manganese-based cathode active material prepared in Example 1.

[0203] Depend on Figure 9 It can be seen that by comparing the positions of the (003) peaks in the XRD of Example 1 and Comparative Example 1, the (003) peak has shifted to the left, directly proving that the spacing d(003) of the (003) crystal planes of the coated material has increased, i.e., lattice expansion has occurred. This is mainly due to S 2- Its enormous radius (~1.84 Å) allows it to physically "stuff" itself into or strongly interact with the lithium layer, mechanically prying open the upper and lower TM layers like a wedge. This effect is huge and directional, acting directly along the c-axis, and is therefore the primary and most direct cause of c-axis expansion.

[0204] Depend on Figure 10 It can be seen that by comparing the positions of the (104) peaks in XRD of Example 1 and Comparative Example 1, the (104) peak shifts to the right, directly proving that the spacing d(104) of the (104) crystal planes of the coated material has decreased, i.e., lattice shrinkage has occurred. During the high-temperature annealing process after coating, the Co in the LCO coating layer... 3+ It may partially diffuse into the surface lattice of the bulk phase of the lithium-rich manganese-based cathode material, or into the Ni in the bulk phase of the lithium-rich manganese-based cathode material. 2+ / Mn 4+ It may also diffuse in the reverse direction. When an ion with a larger radius (such as Ni) diffuses in the reverse direction... 2+ ) by an ion with a smaller radius (such as Co) 3+ When partial substitution occurs, slight displacement of surrounding oxygen ions may occur to maintain charge balance, leading to shrinkage of cell parameters (including the a-axis). Furthermore, after coating MoS2, the strength of Mo-S bonds and potential transition metal-S bonds is much higher than that of transition metal-O bonds. Stronger bonds mean tighter interatomic bonding, with atoms pulled closer together, resulting in local lattice shrinkage. Under the combined effect of lattice shrinkage induced by heterovalent ion substitution and strong bonds, this manifests as a systematic rightward shift of all relevant diffraction peaks in XRD, including the (104) peak.

[0205] Figure 11 In Figure A, the XRD pattern of Comparative Example 1 is shown at the peaks at (018) and (110); Figure 11 In Example 1, B is the XRD pattern of the lithium-rich manganese-based core at the (018) and (110) peaks after pre-sintering during the preparation of the lithium-rich manganese-based positive electrode active material. Figure 11 C is the XRD pattern of the lithium-rich manganese-based core at the (018) and (110) peaks after water washing and drying during the preparation of the lithium-rich manganese-based positive electrode active material in Example 1; Figure 11 In Example 1, D is the XRD pattern of the lithium-rich manganese-based positive electrode active material prepared by coating the lithium-rich manganese core with the first coating layer at the (018) and (110) peaks. Figure 11 E represents the XRD pattern of the lithium-rich manganese-based cathode active material prepared in Example 1 at the (018) and (110) peaks. Figure 11 It can be seen that in the pre-sintering and water washing stages, the 018 / 110 diffraction peaks in the XRD of the lithium-rich manganese-based cathode material overlap or merge into a relatively broad peak. However, after two subsequent high-temperature sintering processes involving coating, the 018 / 110 peak splits from a single peak into a double peak, which directly reflects the key transformation of its crystal structure from disorder to high order.

[0206] Depend on Figure 12 As can be seen from the XPS spectra of O1s corresponding to the four stages of preparation in Example 1, the oxygen vacancy rate in the pre-calcination stage accounts for 40.24% of the total peak area of ​​(oxygen vacancy + lattice oxygen), which increases to 50.9% after water washing. This demonstrates that by using organic acid as a complexing agent and lithium-containing compounds as lithium replenishing agents in the water washing scheme, the lithium ion concentration and local chemical environment on the material surface can be controlled, exposing the deeply buried oxygen vacancy formed during pre-calcination and promoting the controllable generation of oxygen vacancy on the primary particle surface. After the first coating, the oxygen vacancy rate decreases from 50.9% to 50.52%, possibly due to Co... 3+ Through oxygen vacancies and lithium-rich core transition metal ions (such as Mn) 3+ The formation of coordination bonds (Co-O-Mn) partially repairs surface oxygen vacancies. Meanwhile, LiCoO2 grows in situ at grain boundaries, pushing high-concentration oxygen vacancies from the surface to the near-surface region, forming a "gradient oxygen vacancy structure" (reduced surface oxygen vacancies, enriched near-surface oxygen vacancies). Additionally, the air introduced during sintering also promotes the repair of surface oxygen vacancies. After secondary coating with MoS2, the oxygen vacancy ratio further decreases to 41.75%, because the MoS2 coating layer captures active oxygen species (such as ·O) through sulfur vacancies (VS··). 2- This blocks the reaction pathway between the reactive oxygen species and transition metal ions, while simultaneously stabilizing the remaining reactive oxygen vacancies.

[0207] Depend on Figure 13As can be seen from the XPS spectra of Co 2p before and after the first coating layer in Example 1 of the present invention, it is clear that the intensity of the spectral lines after the first coating layer is generally higher than that before the first coating layer, and the binding energy peak is very obvious. This means that the content of cobalt on the sample surface increases significantly after the coating treatment.

[0208] Depend on Figure 14 As can be seen from the XPS spectra of Mo 3d before and after coating with molybdenum disulfide as the second coating layer in Example 1, the XPS curve before coating shows almost no obvious Mo 3d characteristic peaks, or the peaks are very weak and close to the baseline; while the curve after coating shows a typical Mo 3d bimodal structure, with two sharp and high-intensity peaks, indicating that the content of molybdenum in the sample surface or bulk phase increases significantly after coating. The binding energy of Mo after coating falls within the Mo3D region of MoS2. 4+ The characteristic range indicates that molybdenum mainly exists as the MoS2 phase after coating, without other obvious oxidation states (such as Mo). 6+ Mo 5+ (If these high valence states exist, the binding energy will be significantly higher).

[0209] Depend on Figure 15 As can be seen from the XPS spectra of S 2p before and after coating with molybdenum disulfide in Example 1, the S content on the sample surface before coating is extremely low, and the S signal is almost undetectable by XPS; after coating, obvious characteristic peaks of S element appear on the sample surface, indicating that S element was successfully introduced during the coating process.

[0210] Depend on Figures 16-18 It can be seen that the impedance of Example 1 at 1C cycles, 2 cycles, 50 cycles, and 100 cycles is significantly lower than that of Example 4 and Comparative Example 1.

[0211] In summary, this invention, through a specific material design and preparation process involving low-temperature pre-calcination, washing with lithium-containing organic acid, grain boundary penetration and surface coating, and surface coating with variable-valence metal sulfides, successfully addresses multiple challenges related to the structural stability, interfacial side reactions, and ion / electron conductivity of lithium-rich manganese-based materials, thereby significantly improving their rate performance and cycle stability.

[0212] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions, and variations to the above embodiments within the scope of the present invention. Furthermore, without contradiction, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A lithium-rich manganese-based cathode active material, characterized in that, The system comprises a lithium-rich manganese-based core, a first coating layer located at least a portion of the surface of the lithium-rich manganese-based core and between primary grain boundaries on the surface of the lithium-rich manganese-based core, and a second coating layer covering at least a portion of the surface of the first coating layer; wherein the chemical formula of the lithium-rich manganese-based core is xLi2MnO3·(1-x)LiTMO2, where TM is one or more of Ni, Co, Mn, W, Mo, Ta, Zr, and Y, and 0 < x < 1; the first coating layer comprises lithium cobalt oxide; and the second coating layer comprises a variable-valence metal chalcogenide compound.

2. The lithium-rich manganese-based positive electrode active material according to claim 1, characterized in that, The variable valence metal chalcogenides are variable valence metal chalcogenides from periods 4 to 6, and are selected from one or more of group VIB, group VB, and group IVB metal chalcogenides.

3. The lithium-rich manganese-based positive electrode active material according to claim 1, characterized in that, The lithium-rich manganese-based core has a D50 particle size of 2.5 μm to 7 μm, and / or the thickness of the first coating layer is 5 nm to 20 nm, and / or the thickness of the second coating layer is 1 nm to 5 nm.

4. A method for preparing a lithium-rich manganese-based positive electrode active material according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: The mixture of the precursor and the first lithium source is subjected to low-temperature pre-sintering treatment at 500~700℃ to obtain the lithium-rich manganese-based core; S2: After quenching the lithium-rich manganese-based core, it is immersed in a mixed solution containing organic acid and lithium compound, washed with water, and then dried. The mixture of the dried lithium-rich manganese-based core, cobalt source, and second lithium source is sintered once to obtain a lithium-rich manganese-based core with a first coating layer. S3: The lithium-rich manganese-based core with the first coating layer is mixed with a variable-valence metal chalcogenide compound and subjected to a secondary sintering process to obtain a lithium-rich manganese-based positive electrode active material.

5. The method for preparing the lithium-rich manganese-based positive electrode active material according to claim 4, characterized in that, The specific surface area of ​​the lithium-rich manganese-based core in S2 after water washing is 1~3m². 2 / g, the specific surface area of ​​the lithium-rich manganese-based material with the first coating layer is 0.5~1 m². 2 / g; And / or, the precursor includes one or more of nickel manganese hydroxide, nickel manganese oxide, nickel manganese carbonate, and nickel manganese oxalate; And / or, the first lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate, lithium fluoride, lithium chloride, and lithium oxide; And / or, the molar ratio of the first lithium source to the precursor is (1.2 to 1.5):

1.

6. The method for preparing the lithium-rich manganese-based positive electrode active material according to claim 4, characterized in that, The mixed solution in S2 is an aqueous solution of an organic acid and a lithium compound, wherein the mass concentration of the organic acid in the mixed solution is 30–90 g / L and the mass concentration of the lithium compound is 5–15 g / L. And / or, the organic acid includes at least one of citric acid monohydrate, tartaric acid, and malic acid.

7. The method for preparing the lithium-rich manganese-based positive electrode active material according to claim 4, characterized in that, The S3 is: coating with a variable valence metal chalcogenide compound accounting for 0.2~1.2 wt% of the mass of the dried lithium-rich manganese-based core, followed by a secondary sintering treatment at 320~380℃ for 6~10 hours; And / or, the heating rate of the pre-sintering, quenching, primary sintering, and secondary sintering is 3 to 6 °C / min.

8. The method for preparing the lithium-rich manganese-based positive electrode active material according to claim 4, characterized in that, The preparation method includes the following steps: S1: The first lithium source and the precursor are thoroughly mixed at a molar ratio of 1.2 to 1.5, and the temperature is increased from room temperature to 500 to 650°C at a heating rate of 3 to 6°C / min. The mixture is pre-sintered for 4 to 6 hours and then naturally cooled to room temperature to form a lithium-rich manganese-based core. S2: The material obtained in S1 is heated from room temperature to 100-150℃ at a heating rate of 3-6℃ / min and held for 0.5-2 hours. It is then removed and washed with a mixed solution of deionized water containing 30-90 g / L organic acid and 5-15 g / L lithium compound. The water washing and mixing ratio is 0.5-1.5 (mass of the quenched lithium-rich manganese-based core to the mixed solution). After mixing evenly, the mixture is filtered for 1-8 hours. After drying at 100-150℃ for 8-20 hours, 2-8 wt% Co3O4 and 0.5-2 wt% lithium carbonate are added. The mixture is then ball-milled and mixed evenly. The material is then sintered once at 840-880℃ at a heating rate of 3-6℃ / min for 10-18 hours and then naturally cooled to room temperature. S3: Coating with a variable-valence metal chalcogenide compound accounting for 0.2~1.2 wt% of the dried lithium-rich manganese-based core, and then sintering at 320~380℃ for 6~10 hours at a heating rate of 3~6℃ / min.

9. A positive electrode plate, characterized in that, Includes the lithium-rich manganese-based positive electrode active material according to any one of claims 1 to 3.

10. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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