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

Abstract

This invention provides a lithium-rich manganese-based cathode material and its preparation method, belonging to the technical field of lithium battery cathode materials. This invention utilizes the high-energy ionic bonds formed by the strong electrostatic attraction between yttrium ions in yttrium oxide and oxygen ions in the crystal lattice to effectively anchor lattice oxygen, suppress phase transitions, and improve the capacity retention of the cathode. Phosphate neutralizes residual lithium on the surface to form a lithium phosphate layer, reducing interfacial side reactions and further improving the capacity retention of the cathode. The yttrium ions in the lithium yttrium phosphate transition layer can form strong interactions with oxygen ions in the crystal lattice, while also possessing high ionic conductivity, promoting lithium-ion transport efficiency. The introduction of aluminum into the lithium-rich manganese-based material allows for in-situ bonding with lattice oxygen and residual lithium on the cathode material surface, enriching and forming a dense, continuous interfacial structure on the surface of the lithium-rich manganese-based material, enhancing interfacial adhesion and facilitating the coating of the yttrium oxide layer.

Description

Technical Field

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

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and environmental friendliness, have been widely used in portable electronic devices, electric vehicles, energy storage systems, and other fields. Among them, the cathode material, as the core component of lithium-ion batteries, directly determines the battery's key indicators such as energy density, cycle stability, and voltage performance. Improving its performance is the core driving force propelling lithium-ion batteries towards higher energy, higher safety, and longer lifespan.

[0003] Lithium-rich manganese-based cathode material (LRMC) is a composite cathode material formed by in-situ solid solution of lithium-rich phase Li2MnO3 and layered phase LiMO2 (M is a combination of transition metal elements such as Ni, Co, and Mn). It has extremely high energy density, with a theoretical specific capacity of 250~300mAh / g, which is much higher than that of traditional LiCoO2, LiFePO4 and ternary cathode materials (NCM, NCA). Moreover, it is inexpensive and has low cost, and is widely used in long-range electric vehicles, large-scale energy storage power stations, portable high-performance electronic devices and other fields.

[0004] However, during the initial charge-discharge cycle, the activation of the lithium-rich phase Li2MnO3 in lithium-rich manganese-based cathode materials is accompanied by the irreversible release of lattice oxygen, leading to an irreversible phase transition from the layered structure to the spinel and rock salt phases on the material surface, resulting in capacity decay. Furthermore, during cycling, highly active residual lithium (such as LiOH and Li2CO3) on the surface of the lithium-rich manganese-based cathode material catalyzes the irreversible decomposition of the electrolyte, generating byproducts such as HF and ROCO2Li, which erode the material lattice, causing the dissolution of transition metals (Mn, Ni, Co), further disrupting the integrity of the layered structure and exacerbating capacity decay. Although existing technologies propose coating lithium-rich manganese-based cathodes with alumina or lithium manganese phosphate to improve capacity retention, the improvement effect is limited. For example, the capacity retention of lithium-rich manganese-based cathode materials coated with lithium manganese phosphate is only 86% after 100 cycles at 1C, and further improvement is needed. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium-rich manganese-based cathode material and its preparation method. The cathode sheet prepared from the lithium-rich manganese-based cathode material provided by this invention has a high capacity retention rate.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A lithium-rich manganese-based cathode material includes a lithium-rich manganese-based material body and a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer sequentially coated on the surface of the lithium-rich manganese-based material body. The molecular formula of the lithium-rich manganese-based material is Li. 1.2x [Ni a Mn b Co c Al d O2, where 1.05≤x≤1.15, 0.08≤a≤0.25, 0.4≤b≤0.75, 0.05≤c≤0.18, 0.02≤d≤0.12, and a+b+c+d=1.

[0007] Preferably, the mass of the yttrium oxide layer is 0.5 to 2.5% of the mass of the lithium-rich manganese-based material.

[0008] Preferably, the mass of the lithium phosphate layer is 0.5 to 3.5% of the total mass of the lithium-rich manganese-based material body and the yttrium oxide layer.

[0009] Preferably, the mass of the lithium yttrium phosphate transition layer is 0.25 to 1.5% of the total mass of the lithium-rich manganese-based material body and the yttrium oxide layer.

[0010] This invention also provides a method for preparing the lithium-rich manganese-based cathode material described in the above technical solution, comprising the following steps: The cobalt aluminum hydroxide is mixed with nickel manganese carbonate and lithium salt, and then subjected to a first sintering and a second sintering in sequence to obtain a lithium-rich manganese-based material body. The lithium-rich manganese-based material bulk material is mixed with yttrium oxide powder and then subjected to a third sintering to obtain an intermediate. The intermediate was mixed with phosphate powder and then subjected to a fourth sintering process to obtain a lithium-rich manganese-based cathode material.

[0011] Preferably, the mass ratio of the cobalt aluminum hydroxide to the nickel manganese carbonate is 1:(1~4).

[0012] Preferably, the mass ratio of the lithium-rich manganese-based material to the yttrium oxide powder is 100:(0.5~2.5).

[0013] Preferably, the mass ratio of the intermediate to the phosphate is 100:(0.5~3.5).

[0014] Preferably, the temperature of the first sintering is 480~550℃ and the time of the first sintering is 4~6h; the temperature of the second sintering is 880~950℃ and the time of the second sintering is 10~15h.

[0015] Preferably, the temperature of the third sintering is 600~750℃, and the time of the third sintering is 4~8h; the temperature of the fourth sintering is 350~550℃, and the time of the fourth sintering is 2~5h.

[0016] This invention provides a lithium-rich manganese-based cathode material, comprising a lithium-rich manganese-based material body and a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer sequentially coated on the surface of the lithium-rich manganese-based material body; the molecular formula of the lithium-rich manganese-based material body is Li. 1.2x [Ni a Mn b Co c Al d O2, where 1.05≤x≤1.15, 0.08≤a≤0.25, 0.4≤b≤0.75, 0.05≤c≤0.18, 0.02≤d≤0.12, and a+b+c+d=1. This invention sequentially coats the surface of a lithium-rich manganese-based material with a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer. The high-energy ionic bonds formed by the strong electrostatic attraction between yttrium ions in the yttrium oxide and oxygen ions in the crystal lattice effectively anchor lattice oxygen, suppressing phase transitions and thus improving the capacity retention of the cathode. The phosphate efficiently neutralizes residual lithium (lithium hydroxide, lithium carbonate) on the surface to form a lithium phosphate layer, reducing interfacial side reactions, suppressing phase transitions, and further improving the capacity retention of the cathode. The interface between the yttrium oxide layer and the lithium phosphate layer is a lithium yttrium phosphate transition layer. Yttrium ions in the cathode material not only interact strongly with oxygen ions in the crystal lattice, improving the capacity retention of the cathode, but also possess high ionic conductivity, promoting lithium-ion transport efficiency. Furthermore, the introduction of aluminum into the lithium-rich manganese-based material, with its high chemical reactivity, allows it to undergo in-situ bonding with lattice oxygen and residual lithium on the cathode material surface. This results in a dense, continuous interfacial structure enriched on the surface of the lithium-rich manganese-based material, enhancing interfacial adhesion and facilitating the coating of the yttrium oxide layer. This also helps the yttrium oxide layer fully anchor lattice oxygen, suppressing phase transitions and further improving the capacity retention of the cathode. The results of the embodiments show that the cathode material prepared from the lithium-rich manganese-based cathode material provided by this invention achieves an average discharge voltage of 3.58V after 100 cycles, and a capacity retention rate of 97.8%. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the lithium-rich manganese-based cathode material of the present invention. Detailed Implementation

[0018] The present invention provides a lithium-rich manganese-based cathode material, comprising a lithium-rich manganese-based material body and a yttrium oxide layer, a lithium yttrium phosphate transition layer and a lithium phosphate layer sequentially coated on the surface of the lithium-rich manganese-based material body; The molecular formula of the lithium-rich manganese-based material is Li. 1.2x [Nia Mn b Co c Al d O2, where 1.05≤x≤1.15, 0.08≤a≤0.25, 0.4≤b≤0.75, 0.05≤c≤0.18, 0.02≤d≤0.12, and a+b+c+d=1.

[0019] The lithium-rich manganese-based cathode material provided by this invention includes a lithium-rich manganese-based material body, wherein the molecular formula of the lithium-rich manganese-based material body is Li. 1.2x [Ni a Mn b Co c Al d O2. The present invention introduces aluminum into the lithium-rich manganese-based material body. Utilizing its high chemical activity, aluminum can undergo in-situ bonding with lattice oxygen and residual lithium on the surface of the cathode material, enriching and forming a dense, continuous interface structure on the surface of the lithium-rich manganese-based material body. This enhances the interfacial bonding force, facilitates the coating of the yttrium oxide layer, and helps the yttrium oxide layer fully anchor lattice oxygen, suppressing phase transitions and further improving the capacity retention rate of the cathode sheet.

[0020] In this invention, the Li 1.2x [Ni a Mn b Co c Al d In O2, 1.05 ≤ x ≤ 1.15. As one embodiment of the present invention, the value of x can be 1.05 ≤ x ≤ 1.15, 1.07 ≤ x ≤ 1.13, or 1.09 ≤ x ≤ 1.11. In the present invention, the Li... 1.2x [Ni a Mn b Co c Al d In O2, 0.08 ≤ a ≤ 0.25. As one embodiment of the present invention, the value of a can be 0.1 ≤ a ≤ 0.2, 0.12 ≤ a ≤ 0.18, or 0.14 ≤ a ≤ 0.16. In the present invention, the Li... 1.2x [Ni a Mn b Co c Al d In O2, 0.4 ≤ b ≤ 0.75. As one embodiment of the present invention, the value of b can be 0.4 ≤ b ≤ 0.6, or 0.5 ≤ b ≤ 0.6. In the present invention, the Li... 1.2x [Ni a Mn b Co c Al dIn O2, 0.05 ≤ c ≤ 0.18. As one embodiment of the present invention, the value of c can be 0.05 ≤ c ≤ 0.1, or 0.07 ≤ c ≤ 0.09. In the present invention, the Li... 1.2x [Ni a Mn b Co c Al d In O2, 0.02 ≤ d ≤ 0.12. As one embodiment of the present invention, the value of d can be 0.02 ≤ d ≤ 0.08, or 0.03 ≤ d ≤ 0.06. In the present invention, the Li... 1.2x [Ni a Mn b Co c Al d In O2, a+b+c+d=1. This invention addresses key bottlenecks such as low initial efficiency, voltage decay, and oxygen evolution by regulating the redox pathway and stabilizing the crystal structure through limiting the molecular composition of the lithium-rich manganese-based material, thereby achieving a balance between high capacity and long cycling performance.

[0021] In one embodiment of the present invention, the particle size D50 of the lithium-rich manganese-based material body can be 8~18μm, or it can be 10~15μm. The present invention shortens the solid-phase diffusion distance of Li ions, reduces polarization, and improves fast charging / high-rate discharge capability by limiting the particle size of the lithium-rich manganese-based material body.

[0022] The lithium-rich manganese-based cathode material provided by this invention further includes a yttrium oxide layer coated on the surface of the lithium-rich manganese-based material. This invention utilizes the high-energy ionic bond formed by the strong electrostatic attraction between yttrium ions in yttrium oxide and oxygen ions in the crystal lattice to effectively anchor lattice oxygen, suppress phase transitions, and thus improve the capacity retention of the cathode. As one embodiment of this invention, the mass of the yttrium oxide layer can be 0.5-2.5% or 1-1.5% of the mass of the lithium-rich manganese-based material. This invention limits the mass content of the yttrium oxide layer to ensure the formation of a continuous, dense, and appropriately thick coating layer on the surface of the lithium-rich manganese-based material, fully utilizing the high-energy ionic bond formed by the strong electrostatic attraction between yttrium ions in yttrium oxide and oxygen ions in the crystal lattice to effectively anchor lattice oxygen, suppress phase transitions, and thus improve the capacity retention of the cathode. As one embodiment of this invention, such as... Figure 1 As shown, the thickness of the yttrium oxide layer can be 5-15 nm, 4-7 nm, or 5-6 nm. This invention, by limiting the thickness of the yttrium oxide layer, more fully utilizes the high-energy ionic bonds formed by the strong electrostatic attraction between yttrium ions in the yttrium oxide and oxygen ions in the crystal lattice, effectively anchoring lattice oxygen, suppressing phase transitions, and thus improving the capacity retention of the cathode.

[0023] The lithium-rich manganese-based cathode material provided by this invention further includes a lithium yttrium phosphate transition layer coated on the surface of the yttrium oxide layer. This invention utilizes the fact that the yttrium ions of lithium yttrium phosphate not only form a strong interaction with oxygen ions in the crystal lattice, improving the capacity retention of the cathode, but also possess high ionic conductivity, promoting lithium-ion transport efficiency. As one embodiment of this invention, the mass of the lithium yttrium phosphate transition layer can be 0.25~1.5% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer, or it can be 0.5~1%. This invention, by limiting the mass content of the lithium yttrium phosphate transition layer, ensures the formation of a continuous, dense, and appropriately thick coating layer on the surface of the yttrium oxide layer, fully utilizing the fact that the yttrium ions of lithium yttrium phosphate not only form a strong interaction with oxygen ions in the crystal lattice, improving the capacity retention of the cathode, but also possess high ionic conductivity, promoting lithium-ion transport efficiency.

[0024] The lithium-rich manganese-based cathode material provided by this invention further includes a lithium phosphate layer coated on the surface of the lithium yttrium phosphate transition layer. This invention utilizes phosphate to efficiently neutralize residual lithium (lithium hydroxide, lithium carbonate) on the surface to form a lithium phosphate layer, reducing interfacial side reactions, suppressing phase transitions, and improving the capacity retention of the cathode. As one embodiment of this invention, the mass of the lithium phosphate layer can be 0.5-3.5% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer, or it can be 1-1.5%. This invention limits the mass content of the yttrium oxide layer to ensure the formation of a continuous, dense, and appropriately thick coating layer on the surface of the lithium-rich manganese-based material, fully neutralizing residual lithium (lithium hydroxide, lithium carbonate), reducing interfacial side reactions, suppressing phase transitions, and further improving the capacity retention of the cathode. As one embodiment of this invention, such as... Figure 1 As shown, the thickness of the lithium phosphate layer can be 5-30 nm, 7-12 nm, or 9-11 nm. This invention, by limiting the thickness of the lithium phosphate layer, more effectively neutralizes residual lithium (lithium hydroxide, lithium carbonate) on the surface, reduces interfacial side reactions, suppresses phase transitions, and improves the capacity retention of the positive electrode.

[0025] This invention sequentially coats the surface of a lithium-rich manganese-based material with a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer. The high-energy ionic bonds formed by the strong electrostatic attraction between yttrium ions in the yttrium oxide and oxygen ions in the crystal lattice effectively anchor lattice oxygen, suppressing phase transitions and thus improving the capacity retention of the cathode. The lithium phosphate layer is formed after the phosphate efficiently neutralizes residual lithium (lithium hydroxide, lithium carbonate) on the surface, reducing interfacial side reactions and suppressing phase transitions, further improving the capacity retention of the cathode. The interface between the yttrium oxide layer and the lithium phosphate layer is the lithium yttrium phosphate transition layer. Yttrium ions not only form strong interactions with oxygen ions in the crystal lattice, improving the capacity retention of the cathode, but also have high ionic conductivity, promoting lithium-ion transport efficiency. Furthermore, the introduction of aluminum into the lithium-rich manganese-based material, with its high chemical activity, allows it to undergo in-situ bonding with lattice oxygen and residual lithium on the cathode material surface. This enriches the surface of the lithium-rich manganese-based material, forming a dense and continuous interface structure, enhancing interfacial bonding, which is beneficial for the coating of the yttrium oxide layer. This facilitates the anchoring of lattice oxygen by the yttrium oxide layer, suppresses phase transitions, and further improves the capacity retention of the cathode.

[0026] The invention also provides a method for preparing the lithium-rich manganese-based cathode material described above, comprising the following steps: After mixing cobalt aluminum hydroxide with nickel manganese carbonate and lithium salt, the first sintering and the second sintering were carried out in sequence to obtain lithium-rich manganese-based material body; The lithium-rich manganese-based material bulk material is mixed with yttrium oxide powder and then subjected to a third sintering to obtain an intermediate. The intermediate was mixed with phosphate powder and then subjected to a fourth sintering process to obtain a lithium-rich manganese-based cathode material.

[0027] The present invention involves mixing the cobalt aluminum hydroxide with nickel manganese carbonate and lithium salt, followed by a first sintering and a second sintering to obtain a lithium-rich manganese-based material body.

[0028] In one embodiment of the present invention, the molecular formula of the cobalt aluminum hydroxide can be Co x Al y (OH)₂, where x can be 0.80 ≤ x ≤ 0.95, y can be 0.05 ≤ y ≤ 0.20, and x + y = 1; the particle size of the cobalt aluminum hydroxide can be 3~7 μm. This invention, by defining the cobalt aluminum hydroxide and utilizing its high activity, ensures a denser and more cohesive interparticle interface after sintering; by utilizing the surface enrichment of aluminum ions and strong Al-O bonds, it achieves lattice oxygen anchoring, fundamentally suppressing interfacial phase transitions and oxygen loss; it also promotes full lithiation, obtaining a cleaner initial surface so that subsequent coating layers can function effectively.

[0029] In one embodiment of the present invention, the molecular formula of the nickel-manganese carbonate can be Nim Mn n CO3, wherein the value of m can be 0.10≤m≤0.20, the value of n can be 0.80≤n≤0.90, m+n=1, and the particle size D50 of the nickel-manganese carbonate can be 10~16μm. This invention, by limiting the nickel-manganese carbonate, achieves atomic-level uniform mixing and precise stoichiometric control of Ni and Mn elements, which is beneficial for high-temperature sintering to form a lithium-rich manganese-based material body with high crystallinity, high phase purity, and a complete layered structure.

[0030] In one embodiment of the present invention, the mass ratio of cobalt aluminum hydroxide to nickel manganese carbonate can be 1:(1~4) or 1:(2~3). The present invention precisely controls the stoichiometric ratio of nickel, manganese, cobalt, and aluminum in lithium-rich manganese-based materials by limiting the mass ratio of cobalt aluminum hydroxide to nickel manganese carbonate. This ensures high discharge specific capacity while introducing aluminum to stabilize the layered crystal structure, suppress cation mixing and the transformation of the layered structure to the spinel / rock salt phase during cycling, thus slowing voltage decay and reducing manganese dissolution.

[0031] In one embodiment of the present invention, the lithium salt can be one or both of lithium hydroxide and lithium carbonate. In another embodiment, the ratio of the total amount of nickel, manganese, cobalt, and aluminum ions in the cobalt aluminum hydroxide and nickel manganese carbonate to the amount of lithium ions in the lithium salt can be 1:(1.25~1.45). The present invention precisely controls the excess lithium ratio by limiting the ratio of the total amount of nickel, manganese, cobalt, and aluminum ions in the cobalt aluminum hydroxide and nickel manganese carbonate to the amount of lithium ions in the lithium salt, ensuring stoichiometry and a layered structure, guaranteeing a pure layered lithium-rich phase without impurities.

[0032] In one embodiment of the present invention, the cobalt aluminum hydroxide is mixed with nickel manganese carbonate and lithium salt under a first stirring and a second stirring. The first stirring rate can be 400-600 rpm and the first stirring time can be 10-20 min. The second stirring rate can be 1000-1500 rpm and the second stirring time can be 30-50 min.

[0033] In one embodiment of the present invention, the first sintering process involves dehydration of cobalt aluminum hydroxide and decarburization of nickel manganese carbonate to form a highly active composite oxide mesophase. In another embodiment, the heating rate of the first sintering can be 3-5°C / min, the temperature of the first sintering can be 480-550°C, or even 500-520°C, and the sintering time can be 4-6 hours. The present invention, by limiting the temperature and time of the first sintering, ensures the complete decomposition of cobalt aluminum hydroxide and nickel manganese carbonate, their initial reaction with lithium salt, and the stabilization of particle morphology, thus providing a guarantee for the subsequent sintering to form a highly crystalline layered structure.

[0034] In one embodiment of the present invention, during the second sintering process, lithium ions and the composite oxide mesophase react fully to form a lithium-rich manganese-based material body with complete crystallization and a uniform layered structure. In another embodiment of the present invention, the heating rate of the second sintering can be 2~4℃ / min, the temperature of the second sintering can be 880~950℃, and the sintering time can be 10~15h. The present invention ensures complete reaction between the lithium salt and the composite oxide mesophase by limiting the temperature and time of the second sintering, ultimately forming a lithium-rich manganese-based layered solid solution with complete crystallization and a uniform single-phase structure.

[0035] After obtaining the lithium-rich manganese-based material body, the present invention mixes the lithium-rich manganese-based material body with yttrium oxide powder and then performs a third sintering to obtain an intermediate.

[0036] In one embodiment of the present invention, the particle size D50 of the yttrium oxide powder can be 20-100 nm or 50-80 nm. In another embodiment, the mass ratio of the lithium-rich manganese-based material to the yttrium oxide powder can be 100:(0.5-2.5) or 100:(1-1.5). The present invention ensures the formation of a uniform, dense, and pinhole-free coating layer on the surface of the lithium-rich manganese-based material by limiting the mass ratio of the lithium-rich manganese-based material to the yttrium oxide powder. In another embodiment, the mixing of the lithium-rich manganese-based material and the yttrium oxide powder can be carried out under stirring, with a stirring rate of 1200-1800 rpm and a stirring time of 15-30 min.

[0037] In one embodiment of the present invention, during the third sintering process, yttrium ions in yttrium oxide diffuse slightly into the crystal lattice of the matrix material surface. Simultaneously, lithium ions and transition metal ions on the surface of the lithium-rich manganese-based material also diffuse into the yttrium oxide, forming chemical bonds. The yttrium ions enter the matrix surface lattice (or occupy surface vacancies) and form extremely strong YO bonds with lattice oxygen ions. Simultaneously, yttrium oxide coats the surface of the lithium-rich manganese-based material, resulting in an intermediate. In another embodiment of the present invention, the heating rate of the third sintering can be 3~5℃ / min, the temperature of the third sintering can be 600~750℃, and the time of the third sintering can be 4~8h. The present invention ensures that yttrium oxide uniformly coats the surface of the lithium-rich manganese-based material, forming a yttrium oxide layer, by limiting the temperature and time of the third sintering.

[0038] After obtaining the intermediate, the present invention mixes the intermediate with phosphate powder and performs a fourth sintering to obtain a lithium-rich manganese-based cathode material.

[0039] In one embodiment of the present invention, the phosphate powder can be diammonium hydrogen phosphate or ammonium dihydrogen phosphate; the particle size D50 of the phosphate powder can be 50~200 nm or 100~150 nm. In one embodiment of the present invention, the mass ratio of the intermediate to the phosphate can be 100:(0.5~3.5) or 100:(1~1.5). The present invention uses the mass ratio of the intermediate to the phosphate powder to ensure the formation of a uniform, dense, and pinhole-free coating layer on the surface of the intermediate. In one embodiment of the present invention, the mixing of the intermediate and the phosphate can be carried out under stirring, the stirring rate can be 1000~1500 rpm, and the stirring time can be 10~25 min.

[0040] In one embodiment of the present invention, during the fourth sintering process, phosphate powder reacts with residual lithium to form a lithium phosphate layer, while lithium phosphate and yttrium oxide undergo a solid-state reaction at the interface to generate a NASICON-type fast ion conductor lithium yttrium phosphate transition layer. In another embodiment of the present invention, the heating rate of the fourth sintering can be 2~4℃ / min, the temperature of the fourth sintering can be 350~550℃, and the time of the fourth sintering can be 2~5h. The present invention ensures a sufficiently uniform coating of the lithium phosphate layer and a well-defined lithium yttrium phosphate transition layer surface formed at the interface between the yttrium oxide layer and the lithium phosphate layer by limiting the temperature and time of the fourth sintering.

[0041] After the fourth sintering is completed, the product after the fourth sintering is cooled in the furnace to obtain a lithium-rich manganese-based cathode material.

[0042] This invention employs a mixture of cobalt aluminum hydroxide, nickel manganese carbonate, and lithium salt, followed by a first and second sintering process. By confining the cobalt aluminum hydroxide and utilizing its high activity, a denser and more cohesive interparticle interface is ensured after sintering. The surface enrichment of aluminum ions and strong Al-O bonds anchor lattice oxygen, fundamentally suppressing interfacial phase transitions and oxygen loss in the lithium-rich manganese-based material. A third sintering process is then performed after mixing with yttrium oxide powder, forming a yttrium oxide layer on the surface of the lithium-rich manganese-based material. The high bond energy formed by the strong electrostatic attraction between yttrium ions in the yttrium oxide and oxygen ions in the lattice is utilized. Ionic bonding effectively anchors lattice oxygen, suppressing phase transitions and thus improving the capacity retention of the cathode. After mixing with phosphate powder, a fourth sintering process is performed. The phosphate efficiently neutralizes residual lithium (lithium hydroxide, lithium carbonate) on the surface, forming a lithium phosphate layer on the intermediate surface. This reduces interfacial side reactions, suppresses phase transitions, and further improves the capacity retention of the cathode. The interface between the yttrium oxide layer and the lithium phosphate layer is a lithium yttrium phosphate transition layer. The yttrium ions in this layer not only interact strongly with oxygen ions in the lattice, improving the capacity retention of the cathode, but also exhibit high ionic conductivity, promoting lithium-ion transport efficiency.

[0043] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] Example 1 A lithium-rich manganese-based cathode material is composed of a lithium-rich manganese-based material body and a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer sequentially coated on the surface of the lithium-rich manganese-based material body. The molecular formula of the lithium-rich manganese-based material is Li. 1.23 [Ni 0.11 Mn 0.68 Co 0.14 Al 0.07 O2; The mass of the yttrium oxide layer is 1.2% of the mass of the lithium-rich manganese-based material; the mass of the lithium phosphate layer is 1.2% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer; and the mass of the lithium yttrium phosphate transition layer is 0.9% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer. The thickness of the yttrium oxide layer is 8 nm; the thickness of the lithium yttrium phosphate transition layer is 4 nm; and the thickness of the lithium phosphate layer is 10 nm. The preparation method of the above-mentioned lithium-rich manganese-based cathode material is as follows: 200g of Co with a D50 of 5μm 0.9 Al 0.1 (OH)2, 600g D50 is 13μm Ni 0.15 Mn 0.85 CO3 and lithium carbonate were mixed at 500 rpm for 15 min, then at 1200 rpm for 40 min. The mixture was then heated to 500 °C at 4 °C / min and held for 5 h in an oxygen atmosphere, followed by heating to 920 °C at 3 °C / min and holding for 12 h to obtain the lithium-rich manganese-based material bulk. 0.9 Al 0.1 (OH)2 and Ni 0.15 Mn 0.85 The mass ratio of CO3 to CO3 is 1:3; the Co 0.9 Al 0.1 (OH)2 and Ni 0.15 Mn 0.85 The ratio of the total amount of (Ni+Mn+Co+Al) in CO3 to the amount of lithium ions in lithium carbonate is 1:1.35; 1000g of lithium-rich manganese-based material bulk and 12g of Y2O3 powder with D50 of 50nm were mixed at 1500rpm for 20min, and then heated to 650℃ at 4℃ / min in air atmosphere and kept at the temperature for 6h to obtain an intermediate; the mass ratio of the lithium-rich manganese-based material bulk to the Y2O3 powder was 100:1.2. 1000g of intermediate and 12g of ammonium dihydrogen phosphate with D50 of 100nm were mixed at 1200rpm for 15min, and then heated to 460℃ at 3℃ / min and kept at that temperature for 3.5h in air atmosphere to obtain lithium-rich manganese-based cathode material; the mass ratio of the intermediate to ammonium dihydrogen phosphate was 100:1.2.

[0045] Example 2 A lithium-rich manganese-based cathode material is composed of a lithium-rich manganese-based material body and a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer sequentially coated on the surface of the lithium-rich manganese-based material body. The molecular formula of the lithium-rich manganese-based material is Li. 1.25 [Ni 0.08 Mn 0.69 Co 0.16 Al 0.07 O2; The mass of the yttrium oxide layer is 1% of the mass of the lithium-rich manganese-based material; the mass of the lithium phosphate layer is 1.8% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer; and the mass of the lithium yttrium phosphate transition layer is 0.7% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer. The thickness of the yttrium oxide layer is 7 nm; the thickness of the lithium yttrium phosphate transition layer is 5 nm; and the thickness of the lithium phosphate layer is 12 nm. The preparation method of the above-mentioned lithium-rich manganese-based cathode material is as follows: 150g of Co with a D50 of 4μm 0.92 Al 0.08 (OH)2, 450g D50 is 15μm Ni 0.1 Mn 0.9 CO3 and lithium carbonate were mixed at 450 rpm for 18 min, then at 1400 rpm for 35 min. The mixture was then heated to 480 °C at 5 °C / min and held for 5.5 h in an oxygen atmosphere, followed by heating to 950 °C at 2 °C / min and holding for 10 h to obtain a lithium-rich manganese-based material bulk. 0.92 Al 0.08 (OH)2 and Ni 0.1 Mn 0.9 The mass ratio of CO3 to CO3 is 1:3; the Co 0.92 Al 0.08 (OH)2 and Ni 0.1 Mn 0.9The ratio of the total amount of (Ni+Mn+Co+Al) ions in CO3 to the amount of lithium ions in lithium carbonate is 1:1.38. 1000g of lithium-rich manganese-based material bulk and 10g of Y2O3 powder with D80 of 50nm were mixed at 1300rpm for 25min, and then heated to 680℃ at 5℃ / min in air atmosphere and kept at the temperature for 5h to obtain an intermediate; the mass ratio of the lithium-rich manganese-based material bulk to the Y2O3 powder was 100:1. 1000g of intermediate and 18g of diammonium hydrogen phosphate with a D50 of 150nm were mixed at 1400rpm for 13min, and then heated to 420℃ at 4℃ / min and kept at that temperature for 4h in air atmosphere to obtain lithium-rich manganese-based cathode material; the mass ratio of the intermediate to diammonium hydrogen phosphate was 100:1.8.

[0046] Example 3 A lithium-rich manganese-based cathode material is composed of a lithium-rich manganese-based material body and a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer sequentially coated on the surface of the lithium-rich manganese-based material body. The molecular formula of the lithium-rich manganese-based material is Li. 1.20 [Ni 0.12 Mn 0.58 Co 0.18 Al 0.12 O2; The mass of the yttrium oxide layer is 0.8% of the mass of the lithium-rich manganese-based material; the mass of the lithium phosphate layer is 1.0% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer; and the mass of the lithium yttrium phosphate transition layer is 0.5% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer. The thickness of the yttrium oxide layer is 5 nm; the thickness of the lithium yttrium phosphate transition layer is 3 nm; and the thickness of the lithium phosphate layer is 8 nm. The preparation method of the above-mentioned lithium-rich manganese-based cathode material is as follows: 400g of Co with a D50 of 6μm 0.88 Al 0.12 (OH)2, 400g D50 is 15μm Ni 0.18 Mn 0.82 CO3 and lithium carbonate were mixed at 550 rpm for 12 min, then at 1300 rpm for 45 min. The mixture was then heated to 520 °C at 4 °C / min and held for 4.5 h in an oxygen atmosphere, followed by heating to 900 °C at 3 °C / min and holding for 14 h to obtain a lithium-rich manganese-based material bulk. 0.88 Al 0.12 (OH)2 and Ni 0.18 Mn 0.82 The mass ratio of CO3 to CO3 is 1:1; the Co 0.88 Al0.12 (OH)2 and Ni 0.18 Mn 0.82 The ratio of the total amount of (Ni+Mn+Co+Al) ions in CO3 to the amount of lithium ions in lithium carbonate is 1:1.32. 1000g of lithium-rich manganese-based material bulk and 8g of Y2O3 powder with D80 of 30nm were mixed at 1400rpm for 25min, and then heated to 620℃ at 4℃ / min and kept at that temperature for 7h in air atmosphere to obtain an intermediate; the mass ratio of the lithium-rich manganese-based material bulk to the Y2O3 powder was 125:1. 1000g of intermediate and 10g of ammonium dihydrogen phosphate with D50 of 80nm were mixed at 1300rpm for 20min, and then heated to 400℃ at 3℃ / min and kept at that temperature for 5h in air atmosphere to obtain lithium-rich manganese-based cathode material; the mass ratio of the intermediate to ammonium dihydrogen phosphate was 100:1.

[0047] Example 4 A lithium-rich manganese-based cathode material is composed of a lithium-rich manganese-based material body and a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer sequentially coated on the surface of the lithium-rich manganese-based material body. The molecular formula of the lithium-rich manganese-based material is Li. 1.32 [Ni 0.10 Mn 0.71 Co 0.12 Al 0.07 O2; The mass of the yttrium oxide layer is 0.8% of the mass of the lithium-rich manganese-based material; the mass of the lithium phosphate layer is 1% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer; and the mass of the lithium yttrium phosphate transition layer is 0.6% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer. The thickness of the yttrium oxide layer is 12 nm; the thickness of the lithium yttrium phosphate transition layer is 7 nm; and the thickness of the lithium phosphate layer is 22 nm. The preparation method of the above-mentioned lithium-rich manganese-based cathode material is as follows: 250g of Co with a D50 of 3μm 0.95 Al 0.05 (OH)2, 750g D50 is 16μm Ni 0.12 Mn 0.88 CO3 and lithium hydroxide were mixed at 480 rpm for 20 min, then at 1100 rpm for 50 min. The mixture was then heated to 540 °C at 3 °C / min and held for 5 h in an oxygen atmosphere, followed by heating to 930 °C at 4 °C / min and holding for 13 h to obtain the lithium-rich manganese-based material bulk. 0.95 Al 0.05 (OH)2 and Ni 0.12 Mn0.88 The mass ratio of CO3 to CO3 is 1:3; the Co 0.95 Al 0.05 (OH)2 and Ni 0.12 Mn 0.88 The ratio of the total amount of (Ni+Mn+Co+Al) ions in CO3 to the amount of lithium ions in lithium carbonate is 1:1.45. 1000g of lithium-rich manganese-based material bulk and 20g of Y2O3 powder with D50 of 40nm were mixed at 1600rpm for 18min, and then heated to 700℃ at 3℃ / min and kept at that temperature for 4h in air atmosphere to obtain an intermediate; the mass ratio of the lithium-rich manganese-based material bulk to the Y2O3 powder was 50:1. 1000g of intermediate and 30g of diammonium hydrogen phosphate powder with D50 of 120nm were mixed at 1100rpm for 25min, and then heated to 400℃ at 2℃ / min and kept at that temperature for 5h in air atmosphere to obtain lithium-rich manganese-based cathode material; the mass ratio of the intermediate to diammonium hydrogen phosphate powder was 3.

[0048] Example 5 A lithium-rich manganese-based cathode material is composed of a lithium-rich manganese-based material body and a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer sequentially coated on the surface of the lithium-rich manganese-based material body. The molecular formula of the lithium-rich manganese-based material is Li. 1.28 [Ni 0.14 Mn 0.63 Co 0.16 Al 0.07 O2; The mass of the yttrium oxide layer is 1.5% of the mass of the lithium-rich manganese-based material; the mass of the lithium phosphate layer is 2.5% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer; and the mass of the lithium yttrium phosphate transition layer is 1.1% of the total mass of the lithium-rich manganese-based material and the yttrium oxide layer. The thickness of the yttrium oxide layer is 10 nm; the thickness of the lithium yttrium phosphate transition layer is 6 nm; and the thickness of the lithium phosphate layer is 18 nm. The preparation method of the above-mentioned lithium-rich manganese-based cathode material is as follows: 300g of Co with a D50 of 5μm 0.9 Al 0.1 (OH)2, 700g D50 is 12μm Ni 0.16 Mn 0.84 CO3 and lithium hydroxide were mixed at 520 rpm for 16 min, then at 1450 rpm for 32 min. The mixture was then heated to 490 °C at 5 °C / min and held for 5.5 h in an oxygen atmosphere, followed by heating to 880 °C at 3 °C / min and holding for 16 h to obtain the lithium-rich manganese-based material bulk.0.9 Al 01 (OH)2 and Ni 0.16 Mn 0.84 The mass ratio of CO3 to CO3 is 3:7; the Co 0.9 Al 01 (OH)2 and Ni 0.16 Mn 0.84 The ratio of the total amount of (Ni+Mn+Co+Al) ions in CO3 to the total amount of lithium ions in lithium hydroxide is 1:1.40. 1000g of lithium-rich manganese-based material bulk and 15g of Y2O3 powder with D50 of 60nm were mixed at 1700rpm for 22min, and then heated to 660℃ at 5℃ / min and kept at that temperature for 4h in air atmosphere to obtain an intermediate; the mass ratio of the lithium-rich manganese-based material bulk to the Y2O3 powder was 100:1.5. 1000g of intermediate and 25g of ammonium dihydrogen phosphate with D50 of 200nm were mixed at 1500rpm for 18min, and then heated to 480℃ at 4℃ / min and kept at that temperature for 3h in air atmosphere to obtain lithium-rich manganese-based cathode material; the mass ratio of the intermediate to ammonium dihydrogen phosphate was 100:2.5.

[0049] Example 6 A lithium-rich manganese-based cathode material is composed of a lithium-rich manganese-based material body and a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer sequentially coated on the surface of the lithium-rich manganese-based material body. The molecular formula of the lithium-rich manganese-based material is Li. 1.30 [Ni 0.12 Mn 0.66 Co 0.16 Al 0.06 O2; The mass of the yttrium oxide layer is 0.6% of the mass of the lithium-rich manganese-based material body; the mass of the lithium phosphate layer is 0.6% of the total mass of the lithium-rich manganese-based material body and the yttrium oxide layer; and the mass of the lithium yttrium phosphate transition layer is 0.4% of the total mass of the lithium-rich manganese-based material body and the yttrium oxide layer.

[0050] The thickness of the yttrium oxide layer is 6 nm; the thickness of the lithium yttrium phosphate transition layer is 3.5 nm; and the thickness of the lithium phosphate layer is 6 nm. The preparation method of the above-mentioned lithium-rich manganese-based cathode material is as follows: 160g of Co with a D50 of 7μm 0.9 Al 0.1 (OH)2, 640g D50 is 14μm Ni 0.14 Mn 0.86CO3 and lithium carbonate were mixed at 600 rpm for 10 min, then at 1000 rpm for 60 min. The mixture was then heated to 550 °C at 3 °C / min and held for 4 h in an oxygen atmosphere, followed by heating to 950 °C at 2 °C / min and holding for 11 h to obtain the lithium-rich manganese-based material bulk. 0.9 Al 01 (OH)2 and Ni 0.16 Mn 0.84 The mass ratio of CO3 to CO3 is 1:4; the Co 0.9 Al 01 (OH)2 and Ni 0.16 Mn 0.84 The ratio of the total amount of (Ni+Mn+Co+Al) ions in CO3 to the total amount of lithium ions in lithium carbonate is 1:1.42. 1000g of lithium-rich manganese-based material bulk and 6g of Y2O3 powder with D50 of 40nm were mixed at 1200rpm for 30min, and then heated to 600℃ at 3℃ / min and kept at that temperature for 8h in air atmosphere to obtain an intermediate; the mass ratio of the lithium-rich manganese-based material bulk to the Y2O3 powder was 100:0.6. 1000g of intermediate and 6g of diammonium hydrogen phosphate with a D50 of 50nm were mixed at 1000rpm for 28min, and then heated to 350℃ at 2℃ / min and kept at that temperature for 5h in air atmosphere to obtain lithium-rich manganese-based cathode material; the mass ratio of the intermediate to diammonium hydrogen phosphate was 100:0.6.

[0051] Comparative Example 1 The difference between this comparative example and Example 1 is that the coating step is omitted, so that the resulting lithium-rich manganese-based material body is the lithium-rich manganese-based cathode material.

[0052] Comparative Example 2 The difference between this comparative example and Example 1 is that the following is omitted: "1000g of intermediate and 10g of ammonium dihydrogen phosphate powder with D50 of 100nm were mixed at 1200rpm for 15min, and then heated to 450℃ at 3℃ / min and kept at that temperature for 3h in air atmosphere to obtain lithium-rich manganese-based cathode material; the mass ratio of the intermediate to ammonium dihydrogen phosphate powder was 100:1". The intermediate obtained is the lithium-rich manganese-based cathode material; the thickness of the yttrium oxide layer is 5nm.

[0053] Comparative Example 3 The difference between this comparative example and Example 1 is that the following is omitted: "1000g of lithium-rich manganese-based material bulk and 10g of Y2O3 powder with a D50 of 50nm were mixed at 1500rpm for 20min, then heated to 650℃ at 4℃ / min in air and held for 6h to obtain an intermediate; the mass ratio of the lithium-rich manganese-based material bulk to the Y2O3 powder was 100:1;" Instead, 1000g of lithium-rich manganese-based material bulk and 10g of Li3PO4 powder with a D50 of 100nm were directly mixed at 1200rpm for 15min, then heated to 550℃ at 3℃ / min in air and held for 5h to obtain a lithium-rich manganese-based cathode material; the mass ratio of the lithium-rich manganese-based material bulk to ammonium dihydrogen phosphate was 100:1; and the thickness of the lithium phosphate layer was 7nm.

[0054] Comparative Example 4: This comparative example refers to the preparation method described in Example 1 of Chinese Patent CN 119994022 A, and synthesizes a lithium-rich manganese-based cathode material with the same total thickness of the coating layer (yttrium oxide layer, lithium yttrium phosphate transition layer and lithium phosphate layer) as in Example 1 of this invention.

[0055] The lithium-rich manganese-based cathode materials prepared in Examples 1-6 and Comparative Examples 1-4 were mixed with conductive carbon black, polyvinylidene fluoride (PVDF) in a mass ratio of 90:5:5 and N-methylpyrrolidone to prepare a slurry with a solid content of 55%. The slurry was coated on aluminum foil and dried to obtain a cathode sheet. Using lithium metal as the counter electrode, CR2032 button cells were assembled in an argon glove box. The electrochemical performance was tested on the Xinwei Battery Testing System, and the results are shown in Table 1.

[0056] Table 1. Electrochemical performance data of CR2032 coin cells assembled with lithium-rich manganese-based cathode materials prepared in Examples 1-6 and Comparative Examples 1-4.

[0057] As shown in Table 1, the lithium-rich manganese-based cathode materials prepared in Examples 1-6 of this invention exhibit a capacity retention rate of 95.8-97.8% after 100 cycles at 1C, an average discharge voltage (V) of 3.53-3.58V after the 100th cycle, and a voltage retention rate of 96.8-98%. In contrast, the lithium-rich manganese-based cathode materials prepared in Comparative Examples 1-4 exhibit a capacity retention rate of 80.1-92.5% after 100 cycles at 1C, an average discharge voltage (V) of 3.35-3.48V after the 100th cycle, and a voltage retention rate of 92-95.5%. Therefore, the lithium-rich manganese-based cathode materials prepared in Examples 1-6 of this invention demonstrate high capacity and voltage retention rates.

[0058] In summary, the positive electrode sheet made from the lithium-rich manganese-based positive electrode material provided by this invention has high capacity retention and high voltage retention.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A lithium-rich manganese-based cathode material, comprising a lithium-rich manganese-based material body and a yttrium oxide layer, a lithium yttrium phosphate transition layer, and a lithium phosphate layer sequentially coated on the surface of the lithium-rich manganese-based material body; The molecular formula of the lithium-rich manganese-based material is Li. 1.2x [Ni a Mn b Co c Al d O2, of which, 1.05≤x≤1.15, 0.08≤a≤0.25, 0.4≤b≤0.75, 0.05≤c≤0.18, 0.02≤d≤0.12, and a+b+c+d=1.

2. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, The mass of the yttrium oxide layer is 0.5 to 2.5% of the mass of the lithium-rich manganese-based material.

3. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, The mass of the lithium phosphate layer is 0.5 to 3.5% of the total mass of the lithium-rich manganese-based material body and the yttrium oxide layer.

4. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, The mass of the lithium yttrium phosphate transition layer is 0.25 to 1.5% of the total mass of the lithium-rich manganese-based material body and the yttrium oxide layer.

5. A method for preparing the lithium-rich manganese-based cathode material according to any one of claims 1 to 4, comprising the following steps: After mixing cobalt aluminum hydroxide with nickel manganese carbonate and lithium salt, the first sintering and the second sintering were carried out in sequence to obtain lithium-rich manganese-based material body; The lithium-rich manganese-based material bulk material is mixed with yttrium oxide powder and then subjected to a third sintering to obtain an intermediate. The intermediate was mixed with phosphate powder and then subjected to a fourth sintering process to obtain a lithium-rich manganese-based cathode material.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the cobalt aluminum hydroxide to the nickel manganese carbonate is 1:(1~4).

7. The preparation method according to claim 5, characterized in that, The mass ratio of the lithium-rich manganese-based material to the yttrium oxide powder is 100:(0.5~2.5).

8. The preparation method according to claim 5, characterized in that, The mass ratio of the intermediate to the phosphate powder is 100:(0.5~3.5).

9. The preparation method according to claim 5, characterized in that, The first sintering temperature is 480~550℃ and the first sintering time is 4~6h; the second sintering temperature is 880~950℃ and the second sintering time is 10~15h.

10. The preparation method according to claim 5, characterized in that, The third sintering temperature is 600~750℃, and the third sintering time is 4~8h; the fourth sintering temperature is 350~550℃, and the fourth sintering time is 2~5h.

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