Single-crystal lithium-rich manganese-based positive electrode material and preparation method thereof

Abstract

The application belongs to the field of lithium ion battery cathode materials, and provides a single-crystal lithium-rich manganese-based cathode material and a preparation method thereof. The application adopts a composite design of a single-crystal lithium-rich manganese-based layered oxide core particle and a lithium phosphate coating layer, controls the composition (Li 1+x Ni y Co z Mn 1‑x‑y‑z O2, x=0.12-0.22, y=0.06-0.15, z=0.06-0.15), the particle size (D50 is 0.6-1.8 m), and the content (0.6-1.8 wt%) and thickness (4-9 nm) of the surface lithium phosphate coating layer, realizes the synergistic optimization of high tap density (2.6-3.8 g / cm 3 ) of the single-crystal particle with high crystallinity, a suitable specific surface area (0.2-1.5 m 2 / g), and high-voltage interface stability. The application solves the coupling contradiction between single-crystal high density and interface stability, kinetic performance and first-cycle efficiency / storage stability of the existing lithium-rich manganese-based cathode, and has wide application value.

Description

Technical Field

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

[0002] With the rapid development of new energy vehicles and large-scale energy storage systems, higher requirements are being placed on the energy density, power density, cycle life, and safety of lithium-ion battery cathode materials. Lithium-rich manganese-based layered oxide cathode materials (Li1+xNiyCozMn1-xy-zO2 system) have become important candidate materials for next-generation high-energy-density lithium-ion batteries due to their theoretical specific capacity exceeding 300 mAh / g, operating voltage as high as 4.5-4.8V, and relatively low cost. In practical applications, this type of material needs to balance several key performance indicators: highly crystalline single-crystal particles can effectively suppress side reactions and structural collapse at grain boundaries, thereby significantly improving cycle stability; a suitable particle size distribution (D50 in the range of 0.6-1.8) is also crucial. The high tap density (2.6-3.8 g / cm³) is beneficial for improving tap density and processing performance, while ensuring a reasonable specific surface area to optimize lithium-ion transport kinetics at the electrode / electrolyte interface; 3 High volumetric energy density batteries are a prerequisite for achieving high volumetric energy density batteries. Therefore, developing lithium-rich manganese-based cathode materials that simultaneously meet the requirements of high single-crystal crystallinity, suitable particle size distribution, high tap density, and excellent electrochemical performance is of significant practical importance.

[0003] However, existing lithium-rich manganese-based cathode materials face numerous technical challenges in achieving the aforementioned performance targets. For example, Chinese patent application CN116706049A discloses a lithium-rich manganese-based cathode material, but it suffers from side reactions during high-voltage charge and discharge, such as the dissolution of surface transition metal ions, electrolyte decomposition, and the transformation of the surface structure to the spinel phase. These side reactions lead to rapid increases in interfacial impedance, low coulombic efficiency in the first cycle (typically <85%), and severe capacity decay during cycling. Furthermore, Chinese patent application CN118198329B discloses a surfactant-coated modified lithium-rich manganese-based cathode material and its preparation method, but when the coating thickness is not well controlled or the surface coverage is insufficient, it is still difficult to effectively suppress high-voltage side reactions; while when the coating is too thick or too dense, it significantly hinders the rapid transport of lithium ions at the interface, thus sacrificing rate performance and low-temperature performance. Especially for fine-grained single-crystal materials, how to accurately control the interfacial chemical environment, reduce interfacial impedance, improve first-cycle efficiency, and suppress side reactions under high-temperature storage conditions through reasonable surface modification strategies while ensuring the kinetic advantages brought by high specific surface area remains a key technical challenge that urgently needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a single-crystal lithium-rich manganese-based cathode material and its preparation method, which solves the current problem of lithium-rich manganese-based cathodes struggling to achieve high crystallinity and high tap density while simultaneously maintaining high voltage interface stability and low interface impedance, as well as the coupling contradiction between the kinetic advantages brought by fine particle size and high specific surface area and the control of first-cycle efficiency / high-temperature storage side reactions. Furthermore, it overcomes the inherent conflict between lithium-ion transport and rate performance caused by forming a high-coverage nanoscale lithium phosphate protective layer on the surface, thereby achieving a comprehensive balance between processing feasibility, cycle life, and power performance.

[0005] This invention employs a synergistic design of single-crystal lithium-rich manganese-based matrix oxide core particles and a nanoscale lithium phosphate coating layer generated in situ on the surface. This is achieved by precisely controlling the composition of the core particles (Li1+xNiyCozMn1-xy-zO2, x=0.12-0.22, y=0.06-0.15, z=0.06-0.15) and particle size (D50 is 0.6-1.8). The content (0.6-1.8wt%), thickness (4-9nm), and surface coverage (70-88%) of the lithium phosphate coating layer were optimized to achieve synergistic optimization of high tap density, suitable specific surface area, and high voltage interface stability of highly crystalline single crystal particles. This effectively solved the multiple coupling contradictions between high single crystal density and interface impedance control, surface protection and lithium-ion transport, and first-cycle efficiency and cycle stability.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A single-crystal lithium-rich manganese-based cathode material, the single-crystal lithium-rich manganese-based cathode material comprising: A. Single-crystal lithium-rich manganese-based basal oxide core particles; B. A lithium phosphate coating layer covering the surface of the core particle; The stoichiometric formula of the nuclear particles is Li. 1+x Ni y CozMn 1-x-y-z O2, where each subscript indicates a molar ratio, x is 0.12–0.22, y is 0.06–0.15, and z is 0.06–0.15; The lithium phosphate coating is a Li3PO4 coating. The content of the lithium phosphate coating layer is 0.6–1.8 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material; The D50 of the nuclear particles is 0.6–1.8. m.

[0007] Furthermore, no obvious grain boundaries were observed in the single-crystal lithium-rich manganese-based matrix oxide core particles when observed by transmission electron microscopy or scanning electron microscopy.

[0008] Furthermore, the average thickness of the lithium phosphate coating layer is 4–9 nm, which is the local thickness of the coating area measured by transmission electron microscopy; and the surface coverage of the lithium phosphate coating layer on the core particle is 70–88%, which is the area coverage obtained based on the statistical analysis of transmission electron microscopy images.

[0009] Furthermore, the mixed hydroxide precursor used to prepare the core particles is prepared through the following steps: A1. Raw material preparation: Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate are dissolved in deionized water to obtain a mixed metal salt solution; the total concentration of metal ions in the mixed metal salt solution is 1.0–2.0 mol / L; and the molar ratio of the corresponding metal ions of nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate is y:z:1-xyz; A2. Preparation of precipitant solution: Prepare an aqueous solution of sodium hydroxide with a concentration of 2.0–5.0 mol / L; A3. Coprecipitation: At 50–60℃, a mixed solution of metal salts and an aqueous solution of sodium hydroxide are added to the reactor in parallel flow, and the addition rate of the aqueous solution of sodium hydroxide is adjusted to maintain the pH of the reaction system at 10.8–11.5. A4. Aging: Aging at 50–60℃ and pH 10.8–11.5 for 4–8 hours; A5. Post-treatment: Filtration, washing with deionized water until the pH of the filtrate is 7–8, and drying at 100–130℃ for 8–16 h to obtain the mixed hydroxide precursor; The molar ratio of Ni, Co, and Mn metal ions in the mixed hydroxide precursor is y:z:1-xyz, and the relative deviation of the molar ratio of the three metal ions from the target molar ratio y:z:1-xyz does not exceed ±5%.

[0010] Furthermore, the nuclei are prepared through the following steps: B1. Lithium Mixture: A mixed hydroxide precursor is mixed with a lithium source such that the molar ratio of the total number of lithium atoms provided by the lithium source to the total number of metal ions in the mixed hydroxide precursor is 1.45–1.60; the lithium source is lithium carbonate and / or lithium hydroxide. B2. Stepwise sintering: Gradient sintering is performed under an oxygen atmosphere; B3. Cooling and sieving: Cool to room temperature and sieve to obtain core particles; The D50 of the nuclear particles is 0.6–1.8. m.

[0011] Furthermore, the gradient sintering includes the following sintering process: i. Keep warm at 450–550℃ for 3–6 hours; ii. Keep warm at 940–960℃ for 6–8 hours; iii. Hold at 990–1010℃ for 0.5–1.5 hours; iv. Cool to 840–860℃ and hold for 1.5–2.5 hours.

[0012] Furthermore, the lithium phosphate coating layer is generated in situ and coated onto the surface of the core particle through the following steps: C1. Dispersion: The nuclear particles are dispersed in deionized water at a solid-liquid mass ratio of 1:5–20; C2. Phosphate reaction: Add a phosphorus source at 20–60℃, and adjust the pH of the reaction system to 5.5–7.5 by adding a 0.5–2.0 mol / L lithium hydroxide aqueous solution and maintain it, and react for 0.5–2.0 h; the phosphorus source is phosphoric acid and / or ammonium dihydrogen phosphate; C3. Solid-liquid separation and washing: Filter and wash with deionized water until the pH of the filtrate is 6–8; C4. Drying and curing: Dry at 80–120℃ for 6–12h, then keep warm at 300–450℃ for 1–3h to form a Li3PO4 coating layer in the coating layer, and obtain a single crystal lithium-rich manganese-based cathode material powder with lithium phosphate surface coating. The content of the lithium phosphate coating is 0.6–1.8 wt% of the total mass of the powder.

[0013] Furthermore, prior to step C2, the nuclear particles undergo surface residual lithium regulation through the following steps: the nuclear particles are slurried and washed in deionized water at a solid-liquid mass ratio of 1:5–30, at a temperature of 20–40°C, for 0.5–2.0 h; filtered and dried at 80–120°C for 6–12 h, in order to regulate and reduce excess residual lithium carbonate and / or lithium hydroxide on the surface of the nuclear particles.

[0014] Furthermore, the average thickness of the lithium phosphate coating layer is 4–9 nm, which is measured by transmission electron microscopy; and the surface coverage of the lithium phosphate coating layer on the core particle is 70–88%, which is the area coverage obtained based on the statistical analysis of transmission electron microscopy images.

[0015] Furthermore, the tap density of the nuclear particles is 2.6–3.8 g / cm³. 3 The tap density was determined according to the GB / T5162 standard method; and the specific surface area of ​​the single-crystal lithium-rich manganese-based cathode material is 0.2–1.5 m². 2 / g, where the specific surface area is measured by the nitrogen adsorption BET method.

[0016] Furthermore, the Li / P molar ratio in the lithium phosphate coating is 2.9–3.15.

[0017] As a concept of this invention, a composite design is employed, consisting of single-crystal lithium-rich manganese-based matrix oxide core particles and a lithium phosphate coating layer primarily composed of Li3PO4. The core particles achieve a highly crystalline single-crystal structure through a gradient sintering process; the composition (Li1+xNiyCozMn1-xy-zO2, x=0.12-0.22, y=0.06-0.15, z=0.06-0.15) and particle size (D50 of 0.6-1.8) are precisely controlled. While ensuring tap density, a suitable specific surface area is obtained. The lithium phosphate coating layer is generated by the in-situ phosphate reaction of residual lithium carbonate and / or lithium hydroxide on the surface of the core particles with a phosphorus source (phosphoric acid and / or ammonium dihydrogen phosphate) in an aqueous phase, followed by heat treatment at 300-450℃ to solidify, forming a Li3PO4 coating layer with a thickness of 4-9 nm and a surface coverage of 70-88%. The coating layer helps to suppress interfacial side reactions under high voltage and, together with the single crystal core particles, improves the electrochemical performance of the material.

[0018] This invention also discloses a method for preparing a single-crystal lithium-rich manganese-based cathode material, comprising the following steps: S1. Preparation of mixed hydroxide precursors by co-precipitation method; S2. The mixed hydroxide precursor is mixed with a lithium source and then subjected to gradient sintering to prepare core particles; S3. The core particles are subjected to a phosphate reaction, followed by drying and heat preservation treatment to form a Li3PO4 coating layer on the surface of the core particles, thereby obtaining a single-crystal lithium-rich manganese-based cathode material.

[0019] Furthermore, the dispersion described in step C1 is carried out under mechanical stirring conditions.

[0020] Furthermore, the mechanical stirring speed is 200–800 rpm, and the stirring time is 10–60 minutes.

[0021] Furthermore, in step C2, the amount of phosphorus source added is such that the content of the resulting lithium phosphate coating layer is 0.6–1.8 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material.

[0022] Furthermore, the concentration of the phosphoric acid is 1.0–5.0 mol / L.

[0023] Furthermore, the concentration of the ammonium dihydrogen phosphate is 0.5–3.0 mol / L.

[0024] Furthermore, in step B3, after cooling to room temperature, depolymerization is performed.

[0025] Furthermore, the depolymerization process includes airflow staging.

[0026] Furthermore, the pressure of the airflow stage is 0.4–0.8 MPa.

[0027] Furthermore, the single-crystal lithium-rich manganese-based basal oxide core particles are single-crystal particles, and no obvious grain boundaries were observed by transmission electron microscopy or scanning electron microscopy.

[0028] Furthermore, the heating rate between each stage in the stepwise sintering is 2–5 °C / min.

[0029] Furthermore, the cooling rate in step B2-iv is 2–5 °C / min.

[0030] Furthermore, the flow rate of the oxygen atmosphere is 2–10 L / min.

[0031] Furthermore, the coprecipitation reaction is carried out under a nitrogen protective atmosphere.

[0032] Furthermore, the heat treatment at 300–450°C in step C4 is carried out in an air atmosphere or an oxygen atmosphere.

[0033] Furthermore, the pulping and washing is carried out under mechanical stirring conditions, with a stirring speed of 100–500 rpm.

[0034] Furthermore, the sieve mesh size is 10–100 μm.

[0035] Furthermore, the lithium phosphate coating layer is tightly bonded to the surface of the core particle, and no obvious delamination was observed during transmission electron microscopy.

[0036] Furthermore, the test conditions for D50 are as follows: using a laser particle size analyzer, with anhydrous ethanol as the dispersion medium, and ultrasonically dispersed for 5–10 minutes.

[0037] Furthermore, when measuring the average thickness using a transmission electron microscope, at least 20 particles are randomly selected for statistical analysis.

[0038] Furthermore, the relative deviation of the molar ratio of metal ions in the mixed hydroxide precursor was calculated by determining the content of each metal element using inductively coupled plasma atomic emission spectrometry.

[0039] Furthermore, the content of the lithium phosphate coating layer was calculated after determining the phosphorus content by inductively coupled plasma atomic emission spectrometry.

[0040] Furthermore, the lithium hydroxide aqueous solution is added dropwise.

[0041] Furthermore, the lithium phosphate coating layer on the surface of the core particle is generated in situ by reacting the residual lithium carbonate and / or lithium hydroxide on the surface of the core particle with a phosphorus source in an aqueous phase.

[0042] Furthermore, the Li / P molar ratio in the lithium phosphate coating is 2.9–3.15.

[0043] Furthermore, the coprecipitation reaction described in step S1 is carried out in a continuous stirred tank reactor.

[0044] Furthermore, the oxygen atmosphere described in step S2 is provided by a tubular furnace or a box furnace.

[0045] Furthermore, the solid-liquid mass ratio in step S3 is determined by controlling the amount of nuclear particles added and the volume of deionized water.

[0046] Furthermore, the pH adjustment described in step C2 is achieved by monitoring and automatically controlling the drop rate of the lithium hydroxide aqueous solution using an online pH meter.

[0047] As another aspect of this invention, the preparation method utilizes a three-step process route of co-precipitation, gradient sintering, and in-situ surface phosphate treatment to achieve compositional control of single-crystal lithium-rich manganese-based cathode materials, preparation of single-crystal core particles, and in-situ generation of a lithium phosphate coating layer. In the co-precipitation stage, a homogeneous mixed hydroxide precursor is synthesized by controlling the molar ratio of Ni, Co, and Mn ions in the metal salt mixed solution, the pH of the reaction system, the temperature, and the aging time. In the gradient sintering stage, core particles are formed by controlling a four-step sintering procedure and the molar ratio of the lithium source to the total number of metal ions in the precursor. In the in-situ surface phosphate treatment stage, the residual lithium carbonate and / or lithium hydroxide on the surface of the core particles react in-situ with the phosphorus source in an aqueous phase, combined with pH control and subsequent heat treatment at 300-450℃, to form a Li3PO4 coating layer with a thickness of 4-9 nm and a surface coverage of 70-88%.

[0048] The synergistic mechanism between the single-crystal lithium-rich manganese-based basal oxide core particles and the nanoscale lithium phosphate coating layer in this invention is analyzed as follows. The main function of the single-crystal core particles is to suppress side reactions such as electrolyte penetration, transition metal ion dissolution, and structural collapse at grain boundaries by eliminating internal grain boundaries, thereby significantly improving cycle stability. Simultaneously, by precisely controlling the composition (x=0.12-0.22, y=0.06-0.15, z=0.06-0.15) and particle size (D50=0.6-1.8), the synergistic effect is further enhanced. m), while ensuring high tap density (2.6-3.8 g / cm³). 3 While achieving a suitable specific surface area (0.2-1.5m²), it is also possible to obtain a suitable specific surface area. 2 / g), thus balancing processing performance and lithium-ion transport kinetics. The main function of the lithium phosphate coating is as an interface passivation layer under high voltage, inhibiting the dissolution of surface transition metal ions, the oxidative decomposition of the electrolyte, and the transformation of the surface structure to the spinel phase, thereby reducing the rate of interface impedance growth, improving the first-cycle coulombic efficiency, and high-temperature storage stability. The synergistic effect of the two is reflected in the following: single crystal nuclei lay the "bulk foundation" for cycle stability by eliminating grain boundary side reactions, while the nanoscale lithium phosphate coating further enhances the "surface protection" through the interface passivation effect; due to the thin coating thickness (4-9nm) and the certain lithium-ion conductivity of Li3PO4, it does not significantly hinder the rapid transport of lithium ions at the interface, thus achieving synergistic optimization between surface protection and lithium-ion transport, cycle stability and rate performance, and ultimately achieving a comprehensive balance between processing feasibility, cycle life and power performance.

[0049] Beneficial technical effects 1. Improved Cyclic Stability and High-Voltage Interface Stability: The composite design of single-crystal lithium-rich manganese-based basal oxide core particles and nanoscale lithium phosphate coating suppresses side reactions from both bulk and surface dimensions. The single-crystal structure helps reduce side reactions at grain boundaries within the particles; the nanoscale Li3PO4 coating helps suppress the dissolution of surface transition metal ions, oxidative decomposition of the electrolyte, and the transformation of the surface structure to the spinel phase, thus helping the material maintain good cycling stability within a voltage window of 2.0–4.8V.

[0050] 2. Balancing Initial Coulombic Efficiency and Reversible Specific Capacity: This invention precisely controls the thickness of the lithium phosphate coating and the Li / P molar ratio to ensure effective interface protection while avoiding excessive obstruction of lithium-ion transport by the coating. Due to the thin coating and the lithium-ion conductivity of Li3PO4, lithium ions can be transported to the core particle surface through the coating, thus improving the initial coulombic efficiency. Simultaneously, a suitable specific surface area helps to balance reversible specific capacity and interface stability.

[0051] 3. It is beneficial to balance the tap density and powder compaction performance: By precisely controlling the particle size and single crystal structure of the core particles, a high tap density is achieved while ensuring high crystallinity, which is beneficial to the powder compaction performance and processing feasibility of the material.

[0052] 4. Simple preparation process and controllable cost: The present invention adopts a three-step process route of co-precipitation-gradient sintering-in-situ surface phosphate treatment. All raw materials used are commercially available conventional chemical reagents. The preparation process is simple, reproducible, and easy to scale up. In particular, the in-situ generation process of lithium phosphate coating does not require additional complex equipment or harsh process conditions, thereby significantly reducing manufacturing costs.

[0053] 5. Good stability of the coating layer: The Li3PO4 coating layer has good chemical and thermal stability, which is beneficial to the surface stabilization of the material. Attached Figure Description

[0054] Figure 1 The XRD patterns are those of Example 1, Comparative Example 1, and Comparative Example 2.

[0055] Figure 2 The XPS P2p fine spectra of Example 1, Comparative Example 4, and Comparative Example 8 are shown.

[0056] Figure 3 The XPS Li1s fine spectra of Example 1, Comparative Example 4, and Comparative Example 8 are shown.

[0057] Figure 4 ECDF statistical diagrams showing the TEM coating thickness distribution of Example 1 and Comparative Example 7.

[0058] Figure 5 The image shows the scanning electron microscope (SEM) morphology of the Li3PO4-coated single-crystal lithium-rich manganese-based cathode material powder prepared in Example 1.

[0059] Figure 6 This is a low-magnification bright-field transmission electron microscope image of the Li3PO4-coated single-crystal lithium-rich manganese-based cathode material prepared in Example 1 of the present invention.

[0060] Figure 7 This is a macroscopic optical photograph of the single-crystal lithium-rich manganese-based cathode material powder from Example 1. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0062] Example 1 This embodiment provides a single-crystal lithium-rich manganese-based cathode material, comprising single-crystal lithium-rich manganese-based crystalline oxide core particles and a lithium phosphate coating layer covering the surface of the core particles. The stoichiometric formula of the core particles is Li1.17Ni0.105Co0.105Mn0.62O2, where x is 0.17, y is 0.105, and z is 0.105. The lithium phosphate coating layer is a Li3PO4 coating layer, and the content of the lithium phosphate coating layer is 1.0 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material. The D50 of the core particles is 1.0. The particle size was measured using a laser particle size analyzer. The particles were ultrasonically dispersed for 8 minutes using anhydrous ethanol as the dispersion medium. The core particles were single-crystal particles, and no obvious grain boundaries were observed during transmission electron microscopy.

[0063] The mixed hydroxide precursor for preparing nuclear particles is prepared through the following steps: First, raw materials are prepared by dissolving nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate in deionized water to obtain a mixed metal salt solution. The total concentration of metal ions in the mixed metal salt solution is 1.5 mol / L, and the molar ratio of the corresponding metal ions in nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate is 0.105:0.105:0.62. Then, a precipitant solution is prepared by preparing an aqueous sodium hydroxide solution with a concentration of 3.5 mol / L. Next, a coprecipitation reaction is carried out. Under a nitrogen atmosphere, the mixed metal salt solution and the aqueous sodium hydroxide solution are added concurrently to a continuous stirred tank reactor at 55°C, and the addition rate of the aqueous sodium hydroxide solution is adjusted to maintain the pH of the reaction system at 11.15. After the coprecipitation reaction is completed, aging is performed at 55°C and pH 11.15 for 6 hours. After aging, post-treatment was performed, including filtration, washing with deionized water until the pH of the filtrate reached 7.5, and drying at 115℃ for 12 hours to obtain a mixed hydroxide precursor. The molar ratio of Ni, Co, and Mn ions in the mixed hydroxide precursor was 0.105:0.105:0.62, and the relative deviation of the molar ratio of the three metal ions from the target molar ratio of 0.105:0.105:0.62 did not exceed ±5%. The content of each metal element was determined by inductively coupled plasma atomic emission spectrometry and then calculated.

[0064] The nuclei were prepared through the following steps: First, lithium mixing was performed, in which a mixed hydroxide precursor was mixed with a lithium source, such that the molar ratio of the total number of lithium atoms provided by the lithium source to the total number of metal ions in the mixed hydroxide precursor was 1.525. The lithium source was lithium carbonate. Then, stepwise sintering was performed in a gradient sintering atmosphere provided by a tube furnace at a flow rate of 6 L / min. The gradient sintering consisted of the following sintering procedure: the first stage was held at 500°C for 4.5 hours (between 450°C and 550°C); the second stage was held at 950°C for 7 hours (between 940°C and 960°C); the third stage was held at 1000°C for 1 hour (between 990°C and 1010°C); and the fourth stage was cooled to 850°C (between 840°C and 860°C) and held for 2 hours. The heating rate between each stage was 3.5°C / min, and the cooling rate in the fourth stage was 3.5°C / min. After sintering, the particles are cooled and sieved. After cooling to room temperature, a deagglomeration process is performed, including airflow staged at a pressure of 0.6 MPa. The deagglomerated particles are then sieved through a 50 μm mesh to obtain the core particles. The D50 of the core particles is 1.0. m.

[0065] Surface residual lithium in the core particles was controlled before the formation of the lithium phosphate coating: the core particles were slurried and washed in deionized water at a solid-liquid mass ratio of 1:17, determined by controlling the amount of core particles added and the volume of deionized water. Slurry washing was performed under mechanical stirring at 300 rpm and 30°C for 1.2 hours. After slurry washing, the particles were filtered and dried at 100°C for 9 hours to reduce residual lithium carbonate on the surface of the core particles.

[0066] The lithium phosphate coating was generated in situ and coated onto the surface of the core particles through the following steps: First, dispersion was performed by adding the core particles to deionized water at a solid-liquid mass ratio of 1:12. Dispersion was carried out under mechanical stirring at 500 rpm for 30 minutes. Then, a phosphate reaction was performed by adding phosphoric acid (3.0 mol / L) at 40°C. The amount of phosphoric acid added was such that the content of the resulting lithium phosphate coating was 1.0 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material. The pH of the reaction system was adjusted to 6.5 and maintained by adding a 1.25 mol / L lithium hydroxide aqueous solution. pH adjustment was achieved by monitoring with an online pH meter and automatically controlling the dropping rate of the lithium hydroxide aqueous solution. The reaction lasted 1.25 hours. After the reaction was completed, solid-liquid separation and washing were performed. The solution was filtered and washed with deionized water until the pH of the filtrate reached 7. The material was then dried and cured, first at 100°C for 9 hours, followed by holding at 375°C in air for 2 hours to form Li3PO4 in the coating layer, resulting in a single-crystal lithium-rich manganese-based cathode material powder coated with lithium phosphate. The lithium phosphate coating content was 1.0 wt% of the total powder mass, calculated by determining the phosphorus content using inductively coupled plasma atomic emission spectrometry. The lithium source for the lithium phosphate coating mainly came from the residual lithium carbonate on the surface of the core particles, supplemented by the dropwise addition of an aqueous lithium hydroxide solution. This lithium carbonate reacted with the phosphorus source in the aqueous phase to form a lithium phosphate precursor layer in situ, which was then converted into a Li3PO4 coating layer after heat treatment in step C4.

[0067] In the single-crystal lithium-rich manganese-based cathode material prepared in this embodiment, the average thickness of the lithium phosphate coating layer is 6 nm. The average thickness was measured using transmission electron microscopy (TEM), with at least 20 randomly selected particles analyzed. The lithium phosphate coating layer covers 78% of the surface of the core particles, a percentage determined based on area coverage from TEM images. The lithium phosphate coating layer is tightly bonded to the surface of the core particles, and no obvious delamination was observed during TEM. The tap density of the core particles is 3.2 g / cm³. 3 The tap density was determined according to the standard method of GB / T5162. The specific surface area of ​​the single-crystal lithium-rich manganese-based cathode material is 0.8 m². 2 / g, specific surface area was measured by nitrogen adsorption BET method. The Li / P molar ratio in the lithium phosphate coating is 3.0.

[0068] This embodiment is applicable to power battery application scenarios that have high requirements for cycle stability and rate performance. It is particularly suitable for mainstream models of new energy vehicles with long driving range, and can provide good cycle life and safety performance while ensuring energy density.

[0069] Example 2 This embodiment provides a single-crystal lithium-rich manganese-based cathode material, comprising single-crystal lithium-rich manganese-based crystalline oxide core particles and a lithium phosphate coating layer covering the surface of the core particles. The stoichiometric formula of the core particles is Li1.14Ni0.08Co0.12Mn0.66O2, where x is 0.14, y is 0.08, and z is 0.12. The lithium phosphate coating layer is mainly composed of Li3PO4, and its content is 0.6 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material. The D50 of the core particles is 0.6. The particle size was measured using a laser particle size analyzer. The particles were ultrasonically dispersed for 7 minutes using anhydrous ethanol as the dispersion medium. The core particles were single-crystal particles, and no obvious grain boundaries were observed during transmission electron microscopy.

[0070] The mixed hydroxide precursor for preparing nuclear particles was prepared through the following steps: First, raw materials were prepared by dissolving nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate in deionized water to obtain a mixed metal salt solution. The total concentration of metal ions in the mixed metal salt solution was 1.3 mol / L, and the molar ratio of the corresponding metal ions in nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate was 0.08:0.12:0.66. Then, a precipitant solution was prepared by preparing an aqueous sodium hydroxide solution with a concentration of 3.0 mol / L. Next, a co-precipitation reaction was carried out. Under a nitrogen atmosphere, the mixed metal salt solution and the aqueous sodium hydroxide solution were added concurrently to a continuous stirred tank reactor at 52°C, and the addition rate of the aqueous sodium hydroxide solution was adjusted to maintain the pH of the reaction system at 11.0. After the co-precipitation reaction was completed, aging was performed at 52°C and pH 11.0 for 5 hours. After aging, post-processing was performed, including filtration, washing with deionized water until the pH of the filtrate reached 7.3, and drying at 105℃ for 10 hours to obtain a mixed hydroxide precursor. The molar ratio of Ni, Co, and Mn ions in the mixed hydroxide precursor was 0.08:0.12:0.66, and the relative deviation of the molar ratio of the three metal ions from the target molar ratio of 0.08:0.12:0.66 did not exceed ±5%. The content of each metal element was determined by inductively coupled plasma atomic emission spectrometry and then calculated.

[0071] The nuclei were prepared through the following steps: First, lithium mixing was performed, in which a mixed hydroxide precursor was mixed with a lithium source, such that the molar ratio of the total number of lithium atoms provided by the lithium source to the total number of metal ions in the mixed hydroxide precursor was 1.48. The lithium source was lithium hydroxide. Then, stepwise sintering was performed in a gradient sintering atmosphere provided by a box furnace at a flow rate of 4 L / min. The gradient sintering consisted of the following sintering procedure: the first stage was held at 470°C for 4 hours (between 450°C and 550°C); the second stage was held at 945°C for 6.5 hours (between 940°C and 960°C); the third stage was held at 995°C for 0.8 hours (between 990°C and 1010°C); and the fourth stage was cooled to 845°C (between 840°C and 860°C) and held for 1.8 hours. The heating rate between each stage was 2.5°C / min, and the cooling rate in the fourth stage was 2.5°C / min. After sintering, the particles are cooled and sieved. After cooling to room temperature, a deagglomeration process is performed, including airflow staged at a pressure of 0.5 MPa. The deagglomerated particles are then sieved through a 30 μm mesh to obtain the core particles. The D50 of the core particles is 0.6. m.

[0072] Surface residual lithium in the core particles was controlled before the formation of the lithium phosphate coating: the core particles were slurried and washed in deionized water at a solid-liquid mass ratio of 1:8, determined by controlling the amount of core particles added and the volume of deionized water. Slurry washing was performed under mechanical stirring at 200 rpm, 25°C, and for 0.8 hours. After slurry washing, the particles were filtered and dried at 90°C for 8 hours to reduce residual lithium hydroxide on the surface of the core particles.

[0073] The lithium phosphate coating layer was generated in situ and coated onto the surface of the core particles through the following steps: First, dispersion was performed by adding the core particles to deionized water and dispersing them at a solid-liquid mass ratio of 1:8. Dispersion was carried out under mechanical stirring at a speed of 300 rpm for 20 minutes. Then, a phosphate reaction was carried out by adding a phosphorus source, ammonium dihydrogen phosphate, at a concentration of 1.5 mol / L at 30°C. The amount of phosphorus source added was such that the content of the resulting lithium phosphate coating layer was 0.6 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material. The pH of the reaction system was adjusted to 6.0 and maintained by adding a 0.8 mol / L lithium hydroxide aqueous solution. pH adjustment was achieved by monitoring with an online pH meter and automatically controlling the dropping rate of the lithium hydroxide aqueous solution. The reaction was carried out for 0.8 hours. After the reaction was completed, solid-liquid separation and washing were performed, and the solution was filtered and washed with deionized water until the pH of the filtrate was 6.5. The material was then dried and cured at 90°C for 8 hours, followed by heating at 330°C for 1.5 hours in an oxygen atmosphere to form Li3PO4 in the coating layer, resulting in a single-crystal lithium-rich manganese-based cathode material powder coated with lithium phosphate. The lithium phosphate coating content was 0.6 wt% of the total powder mass, calculated by determining the phosphorus content using inductively coupled plasma atomic emission spectrometry. The lithium source for the lithium phosphate coating mainly came from the residual lithium hydroxide on the surface of the core particles, which could be supplemented by the dropwise addition of an aqueous lithium hydroxide solution. It reacted with the phosphorus source in the aqueous phase to generate a lithium phosphate precursor layer in situ, which was then converted into a Li3PO4 coating layer after heat treatment in step C4.

[0074] In the single-crystal lithium-rich manganese-based cathode material prepared in this embodiment, the average thickness of the lithium phosphate coating layer is 4 nm. The average thickness was measured using transmission electron microscopy (TEM), with at least 20 randomly selected particles analyzed. The lithium phosphate coating layer covers 70% of the surface of the core particles, a percentage determined based on area coverage from TEM images. The lithium phosphate coating layer is tightly bonded to the surface of the core particles, and no obvious delamination was observed during TEM. The tap density of the core particles is 2.9 g / cm³. 3 The tap density was determined according to the standard method of GB / T5162. The specific surface area of ​​the single-crystal lithium-rich manganese-based cathode material is 1.1 m². 2 / g, specific surface area was measured by nitrogen adsorption BET method. The Li / P molar ratio in the lithium phosphate coating layer is 2.9.

[0075] This embodiment is suitable for application scenarios with high requirements for safety and cost control, and is particularly suitable for energy storage systems and commercial vehicle power batteries. Its high manganese content and small particle size design can provide excellent thermal stability and structural stability, while the low nickel content helps to reduce material costs.

[0076] Example 3 This embodiment provides a single-crystal lithium-rich manganese-based cathode material, comprising single-crystal lithium-rich manganese-based crystalline oxide core particles and a lithium phosphate coating layer covering the surface of the core particles. The stoichiometric formula of the core particles is Li1.20Ni0.13Co0.08Mn0.59O2, where x is 0.20, y is 0.13, and z is 0.08. The lithium phosphate coating layer is mainly composed of Li3PO4, and its content is 1.4 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material. The D50 of the core particles is 1.5. The particle size was measured using a laser particle size analyzer. The particles were ultrasonically dispersed for 9 minutes using anhydrous ethanol as the dispersion medium. The core particles were single-crystal particles, and no obvious grain boundaries were observed during transmission electron microscopy.

[0077] The mixed hydroxide precursor for preparing nuclear particles was prepared through the following steps: First, raw materials were prepared by dissolving nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate in deionized water to obtain a mixed metal salt solution. The total concentration of metal ions in the mixed metal salt solution was 1.7 mol / L, and the molar ratio of the corresponding metal ions in nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate was 0.13:0.08:0.59. Then, a precipitant solution was prepared by preparing an aqueous sodium hydroxide solution with a concentration of 4.0 mol / L. Next, a coprecipitation reaction was carried out. Under a nitrogen atmosphere, the mixed metal salt solution and the aqueous sodium hydroxide solution were added concurrently to a continuous stirred tank reactor at 58°C, and the addition rate of the aqueous sodium hydroxide solution was adjusted to maintain the pH of the reaction system at 11.3. After the coprecipitation reaction was completed, aging was performed at 58°C and pH 11.3 for 7 hours. After aging, post-treatment was performed, including filtration, washing with deionized water until the pH of the filtrate reached 7.8, and drying at 122℃ for 14 hours to obtain a mixed hydroxide precursor. The molar ratio of Ni, Co, and Mn ions in the mixed hydroxide precursor was 0.13:0.08:0.59, and the relative deviation of the molar ratio of the three metal ions from the target molar ratio of 0.13:0.08:0.59 did not exceed ±5%. The content of each metal element was determined by inductively coupled plasma atomic emission spectrometry and then calculated.

[0078] The nuclei were prepared through the following steps: First, lithium mixing was performed, in which a mixed hydroxide precursor was mixed with a lithium source, such that the molar ratio of the total number of lithium atoms provided by the lithium source to the total number of metal ions in the mixed hydroxide precursor was 1.555. The lithium source was a mixture of 70% lithium carbonate and 30% lithium hydroxide by mass. Then, stepwise sintering was performed in a gradient sintering atmosphere provided by a tube furnace at a flow rate of 8 L / min. The gradient sintering consisted of the following sintering procedure: the first stage was held at 530°C for 5.5 hours (between 450°C and 550°C); the second stage was held at 955°C for 7.5 hours (between 940°C and 960°C); the third stage was held at 1005°C for 1.3 hours (between 990°C and 1010°C); and the fourth stage was cooled to 855°C (between 840°C and 860°C) and held for 2.3 hours. The heating rate between each stage was 4.2℃ / min, and the cooling rate in the fourth stage was also 4.2℃ / min. After sintering, cooling and sieving were performed. After cooling to room temperature, deagglomeration was carried out, including airflow staged at a pressure of 0.7 MPa. After deagglomeration, the particles were sieved through a 70 μm mesh to obtain core particles. The D50 of the core particles was 1.5. m.

[0079] Surface residual lithium in the core particles was controlled before the formation of the lithium phosphate coating: the core particles were slurried and washed in deionized water at a solid-liquid mass ratio of 1:25, determined by controlling the amount of core particles added and the volume of deionized water. Slurry washing was performed under mechanical stirring at 400 rpm, 35°C, and for 1.6 hours. After slurry washing, the particles were filtered and dried at 110°C for 10 hours to reduce residual lithium carbonate and lithium hydroxide on the surface of the core particles.

[0080] The lithium phosphate coating was generated in situ and coated onto the surface of the core particles through the following steps: First, dispersion was performed by adding the core particles to deionized water at a solid-liquid mass ratio of 1:16. Dispersion was carried out under mechanical stirring at a speed of 650 rpm for 45 minutes. Then, a phosphate reaction was carried out by adding a phosphoric acid source at 50°C. The phosphoric acid source was 4.0 mol / L. The amount of phosphoric acid source added was such that the content of the resulting lithium phosphate coating was 1.4 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material. The pH of the reaction system was adjusted to 7.0 by adding a 1.6 mol / L lithium hydroxide aqueous solution and maintained thereafter. pH adjustment was achieved by monitoring with an online pH meter and automatically controlling the dropping rate of the lithium hydroxide aqueous solution. The reaction was carried out for 1.5 hours. After the reaction was completed, solid-liquid separation and washing were performed. The solution was filtered and washed with deionized water until the pH of the filtrate was 7.5. The material was then dried and cured, first at 110°C for 10 hours, followed by holding at 410°C in air for 2.5 hours to form Li3PO4 in the coating layer, resulting in a single-crystal lithium-rich manganese-based cathode material powder coated with lithium phosphate. The lithium phosphate coating content was 1.4 wt% of the total powder mass, calculated by determining the phosphorus content using inductively coupled plasma atomic emission spectrometry. The lithium source for the lithium phosphate coating mainly came from residual lithium carbonate and / or lithium hydroxide on the surface of the core particles, and could be supplemented by dropwise added lithium hydroxide aqueous solution. It reacted with the phosphorus source in the aqueous phase to generate a lithium phosphate precursor layer in situ, which was then converted into a Li3PO4 coating layer after heat treatment in step C4.

[0081] In the single-crystal lithium-rich manganese-based cathode material prepared in this embodiment, the average thickness of the lithium phosphate coating layer is 8 nm. The average thickness was measured using transmission electron microscopy (TEM), with at least 20 randomly selected particles analyzed. The lithium phosphate coating layer covers 85% of the surface of the core particles, a percentage determined based on area coverage from TEM images. The lithium phosphate coating layer is tightly bonded to the surface of the core particles, and no obvious delamination was observed during TEM. The tap density of the core particles is 3.5 g / cm³. 3 The tap density was determined according to the standard method of GB / T5162. The specific surface area of ​​the single-crystal lithium-rich manganese-based cathode material is 0.5 m². 2 / g, specific surface area was measured by nitrogen adsorption BET method. The Li / P molar ratio in the lithium phosphate coating layer is 3.1.

[0082] This embodiment is suitable for high-end application scenarios with extremely high requirements for energy density and volumetric energy density, and is particularly suitable for high-end electric vehicles and long-range models. Its high-nickel and high-lithium formulation can provide excellent specific capacity and energy density, and the thicker coating layer and high coverage ensure the cycling stability and safety of the material under high voltage.

[0083] Example 4 This embodiment provides a single-crystal lithium-rich manganese-based cathode material, comprising single-crystal lithium-rich manganese-based crystalline oxide core particles and a lithium phosphate coating layer covering the surface of the core particles. The stoichiometric formula of the core particles is Li1.21Ni0.07Co0.14Mn0.58O2, where x is 0.21, y is 0.07, and z is 0.14. The lithium phosphate coating layer is mainly composed of Li3PO4, and its content is 1.8 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material. The D50 of the core particles is 1.8. The particle size was measured using a laser particle size analyzer. The particles were ultrasonically dispersed for 10 minutes using anhydrous ethanol as the dispersion medium. The core particles were single-crystal particles, and no obvious grain boundaries were observed during transmission electron microscopy.

[0084] The mixed hydroxide precursor for preparing nuclear particles was prepared through the following steps: First, raw material preparation was carried out by dissolving nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate in deionized water to obtain a mixed metal salt solution. The total concentration of metal ions in the mixed metal salt solution was 1.85 mol / L, and the molar ratio of the corresponding metal ions in nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate was 0.07:0.14:0.58. Then, a precipitant solution was prepared by preparing an aqueous sodium hydroxide solution with a concentration of 4.6 mol / L. Next, a coprecipitation reaction was carried out. Under a nitrogen atmosphere, the mixed metal salt solution and the aqueous sodium hydroxide solution were added concurrently to a continuous stirred tank reactor at 59°C, and the addition rate of the aqueous sodium hydroxide solution was adjusted to maintain the pH of the reaction system at 11.4. After the coprecipitation reaction was completed, aging was performed at 59°C and pH 11.4 for 4.5 hours. After aging, post-treatment was performed, including filtration, washing with deionized water until the pH of the filtrate reached 7.7, and drying at 127℃ for 15 hours to obtain a mixed hydroxide precursor. The molar ratio of Ni, Co, and Mn ions in the mixed hydroxide precursor was 0.07:0.14:0.58, and the relative deviation of the molar ratio of the three metal ions from the target molar ratio of 0.07:0.14:0.58 did not exceed ±5%. The content of each metal element was determined by inductively coupled plasma atomic emission spectrometry and then calculated.

[0085] The nuclei were prepared through the following steps: First, lithium mixing was performed, in which a mixed hydroxide precursor was mixed with a lithium source, such that the molar ratio of the total number of lithium atoms provided by the lithium source to the total number of metal ions in the mixed hydroxide precursor was 1.58. The lithium source was a mixture of 50% lithium carbonate and 50% lithium hydroxide by mass. Then, stepwise sintering was performed in a gradient sintering atmosphere provided by a tube furnace at a flow rate of 9 L / min. The gradient sintering consisted of the following sintering procedure: the first stage was held at 540°C for 3.5 hours (between 450°C and 550°C); the second stage was held at 958°C for 7.8 hours (between 940°C and 960°C); the third stage was held at 1008°C for 0.6 hours (between 990°C and 1010°C); and the fourth stage was cooled to 858°C (between 840°C and 860°C) and held for 2.4 hours. The heating rate between each stage was 4.5℃ / min, and the cooling rate in the fourth stage was also 4.5℃ / min. After sintering, cooling and sieving were performed. After cooling to room temperature, deagglomeration was carried out, including airflow staged at a pressure of 0.75 MPa. After deagglomeration, the particles were sieved through an 85 μm sieve to obtain core particles. The D50 of the core particles was 1.8. m.

[0086] Surface residual lithium in the core particles was controlled before the formation of the lithium phosphate coating: the core particles were slurried and washed in deionized water at a solid-liquid mass ratio of 1:28, determined by controlling the amount of core particles added and the volume of deionized water. Slurry washing was performed under mechanical stirring at 150 rpm, 22°C, and for 0.7 hours. After slurry washing, the particles were filtered and dried at 118°C for 11 hours to reduce residual lithium carbonate and lithium hydroxide on the surface of the core particles.

[0087] The lithium phosphate coating was generated in situ and coated onto the surface of the core particles through the following steps: First, dispersion was performed by adding the core particles to deionized water and dispersing them at a solid-liquid mass ratio of 1:18. Dispersion was carried out under mechanical stirring at a speed of 700 rpm for 55 minutes. Then, a phosphate reaction was carried out by adding a phosphorus source at 26°C. The phosphorus source was a mixture of phosphoric acid and ammonium dihydrogen phosphate, with a phosphoric acid concentration of 4.5 mol / L and an ammonium dihydrogen phosphate concentration of 2.5 mol / L, representing mass percentages of 60% and 40%, respectively. The amount of phosphorus source added resulted in a lithium phosphate coating content of 1.8 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material. The pH of the reaction system was adjusted to 7.3 by adding a 1.85 mol / L lithium hydroxide aqueous solution and maintained thereafter. pH adjustment was achieved by monitoring with an online pH meter and automatically controlling the dropping rate of the lithium hydroxide aqueous solution. The reaction was carried out for 1.8 hours. After the reaction was completed, solid-liquid separation and washing were performed. The solution was filtered and washed with deionized water until the pH of the filtrate reached 7.8. The material was then dried and cured, first at 118°C for 11 hours, followed by heating at 435°C for 2.8 hours in an oxygen atmosphere to form Li3PO4 in the coating layer, resulting in a single-crystal lithium-rich manganese-based cathode material powder coated with lithium phosphate. The lithium phosphate coating content was 1.8 wt% of the total powder mass, calculated by determining the phosphorus content using inductively coupled plasma atomic emission spectrometry. The lithium source for the lithium phosphate coating mainly came from residual lithium carbonate and / or lithium hydroxide on the surface of the core particles, and could be supplemented by dropwise added lithium hydroxide aqueous solution. It reacted with the phosphorus source in the aqueous phase to generate a lithium phosphate precursor layer in situ, which was then converted into a Li3PO4 coating layer after heat treatment in step C4.

[0088] In the single-crystal lithium-rich manganese-based cathode material prepared in this embodiment, the average thickness of the lithium phosphate coating layer is 9 nm. The average thickness was measured using transmission electron microscopy (TEM), with at least 20 randomly selected particles analyzed. The lithium phosphate coating layer covers 88% of the surface of the core particles, a percentage determined based on area coverage from TEM images. The lithium phosphate coating layer is tightly bonded to the surface of the core particles, and no obvious delamination was observed during TEM. The tap density of the core particles is 3.65 g / cm³. 3 The tap density was determined according to the standard method of GB / T5162. The specific surface area of ​​the single-crystal lithium-rich manganese-based cathode material is 0.35 m². 2 / g, specific surface area was measured by nitrogen adsorption BET method. The Li / P molar ratio in the lithium phosphate coating layer is 3.15.

[0089] This embodiment is suitable for special application scenarios with stringent requirements for volumetric energy density, compaction density, and processing performance. It is particularly suitable for high-end energy storage systems and power batteries in the aerospace field. Its large-particle-size single-crystal structure and high tap density can provide excellent compaction performance and volumetric energy density. The thick coating layer and high coverage ensure the structural stability and electrochemical performance of the material under extreme conditions.

[0090] Performance testing: Experiment 1: First Coulomb Efficiency Test Test Subject: The initial charge-discharge performance of single-crystal lithium-rich manganese-based cathode material in lithium-ion batteries. Test Objective: To evaluate the lithium-ion insertion / extraction efficiency of the material during the first charge-discharge cycle, reflecting the ratio of reversible to irreversible capacity. This indicator is directly related to the core challenge of controlling the initial cycle efficiency. Test Principle: The coulombic efficiency is calculated by measuring the ratio of the initial charge capacity (lithium extraction) to the initial discharge capacity (lithium insertion), reflecting the reversibility of the material's crystal structure and the degree of side reactions. Experimental Method: The cathode material, conductive agent, and binder are mixed at a mass ratio of 8:1:1, coated onto an aluminum foil current collector, dried, and then stamped into coin cell half-cells (with lithium metal as the negative electrode). Constant current charge-discharge testing is used, charging to 4.8V and discharging to 2.0V, with a current density of 0.1C and a test temperature of 25±2℃. Key Parameters: Charging cut-off voltage 4.8V, discharging cut-off voltage 2.0V, current density 0.1C, test temperature 25℃, and humidity controlled in a dry environment below the dew point temperature of -40℃. Data processing: Initial coulombic efficiency (%) = (initial discharge capacity / initial charge capacity) × 100%. Each sample group should test no less than 3 batteries and take the average value ± standard deviation.

[0091] Experiment 2: Reversible specific capacity test Test Subject: Reversible lithium-ion storage capacity of single-crystal lithium-rich manganese-based cathode material. Test Objective: To evaluate the amount of lithium-ions reversibly transported during charge and discharge, reflecting the material's energy density potential. This indicator is related to the core objective of balancing high energy density and power performance. Test Principle: The discharge capacity per unit mass of the material is measured under constant current conditions, reflecting the material's lithium-ion storage capacity. Experimental Method: Using the same battery assembly method as Experiment 1, constant current charge-discharge tests are conducted under constant temperature conditions of 25±2℃, with a voltage range of 2.0-4.8V. The first cycle uses a 0.1C rate, and the second cycle uses a 0.2C rate. The discharge specific capacity of stable cycles is recorded. Key Parameters: Test rate 0.2C, voltage window 2.0-4.8V, temperature 25℃, humidity controlled below the dew point of -40℃. Data Processing: Reversible specific capacity (mAh / g) = discharge capacity / mass of cathode active material. At least three batteries are tested for each sample group. The average value ± standard deviation is used, and the average value of the 2nd-5th cycles is adopted.

[0092] Experiment 3: Cyclic Stability Test Test Subject: Capacity retention rate of single-crystal lithium-rich manganese-based cathode material during long-term cycling. Test Objective: To evaluate the structural stability and electrochemical performance degradation of the material during repeated charge-discharge cycles, directly verifying the effectiveness of addressing the core challenges of high-voltage interface stability and cycle life. Test Principle: Through continuous constant-current charge-discharge cycling, the change in discharge capacity with the number of cycles is monitored, and the capacity retention rate is calculated to reflect the material's cycle life. Experimental Method: Using the same battery assembly method as Experiment 1, under constant temperature conditions of 25±2℃, the first 3 cycles were activated at a 0.1C rate, followed by constant-current charge-discharge cycling tests at a 1C rate within a voltage range of 2.0-4.8V, for 200 cycles. Key Parameters: Cycle rate 1C, voltage window 2.0-4.8V, number of cycles 200, test temperature 25℃. Data Processing: Cycle capacity retention rate (%) = (200th discharge capacity / 4th discharge capacity) × 100%. At least 3 batteries were tested per sample group, and the average value ± standard deviation was used.

[0093] Experiment 4: Compacted Density Test Test Object: Compaction characteristics of single-crystal lithium-rich manganese-based cathode material powder. Test Objective: To evaluate the densification ability of the material during the compaction process, reflecting its processing performance and volumetric energy density potential. This indicator is related to the core challenge of processing feasibility. Test Principle: By applying standard pressure to the powder, the volume and mass after compaction are measured, and the compaction density is calculated, reflecting the packing efficiency and deformation resistance of the material particles. Experimental Method: The cathode material powder is loaded into a 13mm diameter mold, and a hydraulic press is used to apply 3t / cm² pressure. 2 Maintain pressure for 30 seconds, then release the pressure and remove the compacted tablet. Measure the tablet thickness using calipers, weigh it using an electronic balance, and calculate the compacted density. Key parameter: Compaction pressure 3t / cm³ 2 The pressure holding time was 30 seconds, the mold diameter was 13mm, the test environment temperature was 20-25℃, and the humidity was <50%RH. Data processing: compacted density (g / cm³) 3 = Tablet mass / Tablet volume. Each sample group should test no less than 5 tablets, take the average value ± standard deviation, and remove outliers.

[0094] Experiment 5: X-ray diffraction (XRD) structural characterization Test Object: Crystal structure and phase composition of single-crystal lithium-rich manganese-based cathode material. Test Objective: To characterize the material's phase purity, lattice parameters, and single-crystal characteristics, verifying the integrity of the layered oxide structure. This characterization can be exported as CSV data for Origin plotting and analysis. Test Principle: Utilizing the diffraction phenomenon of X-rays in crystals, the position and intensity of diffraction peaks are analyzed according to the Bragg equation to determine the material's crystal structure information. Experimental Method: X-ray diffractometer was used for testing, employing a CuKα radiation source (λ=1.5406). The scanning range was 10-80° (2θ), the scanning step size was 0.02°, the scanning rate was 5° / min, the tube voltage was 40kV, and the tube current was 40mA. The sample preparation adopted the back pressure loading method to ensure the flatness of the powder surface and eliminate the influence of preferred orientation. Key parameters: CuKα radiation, scanning range 10-80°, step size 0.02°, rate 5° / min, room temperature test. Data processing: phase analysis and lattice parameter refinement were performed by Jade or HighScore software, the (003) / (104) peak intensity ratio was calculated to evaluate the layered order, and the data was exported in CSV format (2θ, intensity).

[0095] Experiment 6: X-ray photoelectron spectroscopy (XPS) analysis of surface chemical states Test Object: Surface chemical composition and elemental chemical states of the lithium phosphate coating layer of a single-crystal lithium-rich manganese-based cathode material. Test Objective: To characterize the formation of Li3PO4 and the distribution of surface elemental valence states in the coating layer, verifying the chemical structure of the lithium phosphate coating layer. This characterization can export CSV data for quantitative analysis. Test Principle: X-rays are used to excite inner-shell electrons of the sample surface atoms, and the binding energy of the photoelectrons is measured. The elemental type, chemical state, and content are determined based on the binding energy position and peak shape. Experimental Method: X-ray photoelectron spectroscopy is used with an AlKα ray source (hν = 1486.6 eV) and a vacuum level better than 5 × 10⁻⁶. -7 Pa, with C1s (284.8 eV) as the internal standard to correct for the charging effect. The test area was selected on the material surface, and Li1s, P2p, O1s, Ni2p, Co2p, and Mn2p spectra were collected. The data acquisition pass energy was 80 eV, the fine spectrum acquisition pass energy was 20 eV, and the step size was 0.05 eV. Key parameters: AlKα rays, vacuum degree <5 × 10⁻⁶. -7 Pa, C1s corrected to 284.8 eV, fine spectrum passing energy 20 eV. Data processing: Peak separation and fitting were performed using CasaXPS or Avantage software to calculate the relative abundance and chemical state distribution of each element. Data were exported in CSV format (binding energy, intensity).

[0096] Figure 1 shows the XRD patterns of Example 1, Comparative Examples 1 and 2. The XRD patterns were characterized by X-ray diffraction and the intensities were normalized to the 10⁴ peak before being superimposed for comparison. The horizontal axis represents 2θ, and the vertical axis represents the normalized intensity I / I(10⁴). The figure shows that different samples exhibit differences in the peak position, shape, and relative intensity of characteristic peaks such as 003 and 10⁴.

[0097] Figure 2 XPS fine spectra of P2p from Example 1 and Comparative Examples 4 and 8 are presented. P2p was finely scanned and compared using X-ray photoelectron spectroscopy. The basic parameters were the binding energy (129-137 eV) on the x-axis and the inverse x-axis (intensity) on the y-axis, as is customary in XPS. Variable parameters included sample type (Example 1, Comparative Examples 4, and 8) and differences in peak position, relative intensity, and peak shape of the P2p characteristic peaks. The results showed that the P2p signal of Example 1 was more consistent and the peak shape more representative, while the comparative examples showed more obvious shifts or additional component characteristics. This indicates that the phosphorus-related chemical environment on the surface of Example 1 was more stable and controllable, demonstrating the rationality of the process design from a surface chemical perspective.

[0098] Figure 3 The XPS fine spectra of Li1s in Example 1 and Comparative Examples 4 and 8 are shown. Fine scanning and comparison of Li1s were performed using X-ray photoelectron spectroscopy. The basic parameters are the binding energy (52-60 eV) on the x-axis and the intensity on the y-axis. Variable parameters include sample type (Example 1, Comparative Example 4, Comparative Example 8) and changes in Li1s peak position, peak shape, and relative intensity. The results show that the Li1s peak shape in Example 1 is more concentrated and has smaller differences, while the comparative samples show a more obvious shift or shoulder peak trend. This indicates that the lithium-related species on the surface of Example 1 are more stable and the surface inhomogeneity related to side reactions is lower, thus supporting the rationality of this scheme in interfacial chemical regulation.

[0099] Figure 4 The TEM statistical graphs of the coating thickness distribution in Example 1 and Comparative Example 7 are presented. The particle-level coating thickness was measured using transmission electron microscopy and represented by empirical cumulative distribution curves. The basic parameters are thickness in nanometers on the horizontal axis and cumulative percentage on the vertical axis, ranging from 0 to 100. The variable parameters are sample type (Example 1 and Comparative Example 7) and the overall offset and dispersion of the particle-level thickness distribution. The results show that the cumulative distribution curve of Example 1 is steeper and concentrated in a narrower thickness range, while the distribution of Comparative Example 7 is more dispersed. This indicates that the coating thickness of Example 1 has better consistency and is easier to achieve a stable interface. Statistically, this proves that the scheme has repeatability and reasonable structural control capabilities.

[0100] Figure 5 This is a scanning electron microscope (SEM) image of the single-crystal lithium-rich manganese-based cathode material powder with lithium phosphate surface coating prepared in this embodiment. Figure 5 (a) is a low-magnification scanning electron microscope (SEM) image of the single-crystal lithium-rich manganese-based cathode material from Example 1. This image shows the overall particle distribution and dispersion state of the sample under low magnification, with the basic parameter being a micrometer-level field of view. Observation shows that the powder consists of near-equiaxed particles with diameters concentrated in the sub-micrometer to micrometer range. The particles are predominantly discrete individuals, with only a small number of soft agglomerates and no large micrometer-sized hard agglomerates. This result is consistent with the preset D50 particle size index, demonstrating the effectiveness of the precursor sintering and subsequent airflow classification process in controlling particle size distribution and achieving good dispersibility. Figure 5 (b) is a medium-magnification scanning electron microscope image of the single-crystal lithium-rich manganese-based cathode material of Example 1. This image focuses on characterizing the structural unit morphology and particle packing mode of the powder. It is clearly visible that individual particles exhibit well-developed polyhedral or truncated polyhedral single-crystal characteristics, with flat crystal faces and sharp edges, rather than being polycrystalline secondary particles composed of small primary particles. The particles mainly exhibit point or line contact, confirming that the high-temperature solid-state reaction promotes preferential grain growth to form single crystals, and that the deagglomeration process effectively avoids severe inter-particle sintering and adhesion. Figure 5 (c) is a high-magnification scanning electron microscope (SEM) image of the single-crystal lithium-rich manganese-based cathode material of Example 1. This image aims to reveal the microscopic details, density, and coating morphology of the single-particle surface. At high resolution, the particle surface appears dense and smooth overall, with few defects and pores. Nanoscale roughness differences are also observed on the surface, with some areas covered by extremely thin granular or island-like materials. This corresponds to the surface morphology changes caused by the nanoscale Li3PO4 coating layer, thus demonstrating the successful implementation of the surface coating scheme at the microscale.

[0101] Figure 6 The image shown is a low-magnification bright-field transmission electron microscope (BTEM) image of the Li3PO4-coated single-crystal lithium-rich manganese-based cathode material prepared in Example 1 of this invention. Under low-magnification bright-field transmission mode, the particles exhibit a typical core-shell structure morphology. The internal core region shows a deep contrast due to its large mass and thickness, and the overall color is uniform. No obvious polycrystalline grain boundaries are observed, which is consistent with the characteristics of single-crystal particles. The particle surface is covered with a thin layer with shallow contrast, uniform thickness, and continuity, corresponding to the Li3PO4 coating layer. This proves that the liquid-phase coating and subsequent heat treatment process used in this scheme successfully constructed a complete coating structure on the surface of the single-crystal particles.

[0102] Figure 7This is a macroscopic optical photograph of the single-crystal lithium-rich manganese-based cathode material powder from Example 1. The image shows the natural packing state of the powder against a white background, with the basic parameters being the finished powder after high-temperature sintering and airflow classification. The photograph shows that the sample exhibits a uniform dark gray appearance, without obvious discolored spots or macroscopic agglomerates. This macroscopic morphology verifies the effectiveness of the material preparation process in controlling particle dispersion and coating uniformity, and its dark gray tone is consistent with the expected dense single-crystal structure and intrinsic absorption characteristics of transition metal elements.

[0103] Table 1 Performance comparison between the examples and comparative examples

[0104] As can be seen from the performance of the embodiments and comparative examples in Table 1, the four embodiments of the present invention are significantly superior to all comparative examples in key performance indicators such as initial coulombic efficiency, reversible specific capacity, cycle stability, and compaction density. Comparative Example 1, due to its excessively low x-value resulting in insufficient lithium content, exhibited a significant decrease in reversible capacity and cycle stability, with an initial coulombic efficiency of only 82.3%. Comparative Example 2, with its excessively high x-value, although improving some capacity, suffered from compromised structural stability, resulting in a cycle retention rate of only 87.5%. Comparative Example 3, while increasing the specific surface area to 1.85 m² due to its extremely small particle size, also showed improvement. 2 / g, but the side reactions are exacerbated and the tap density is only 2.50g / cm³. 3 The insufficient coating content in Comparative Example 4 failed to effectively protect the core particle surface, resulting in a significant drop in cycle stability to 83.2%. In Comparative Example 5, the insufficient lithium molar ratio led to incomplete lithiation, resulting in low material capacity and efficiency. In Comparative Example 6, the excessively high pH of the co-precipitation caused irregular precursor morphology, affecting subsequent sintering quality and causing a comprehensive decline in all performance characteristics. In Comparative Example 7, the lack of surface residual lithium control resulted in uneven reaction between residual lithium carbonate and lithium hydroxide and the phosphorus source, leading to poor coating quality and the worst initial efficiency and cycle performance. In Comparative Example 8, the excessively low pH of the phosphate reaction resulted in incomplete Li3PO4 formation, poor coating protection, and a cycle stability of only 79.2%. In contrast, Examples 1-4, through precise control of various parameters, achieved an initial coulombic efficiency of 86.5-89.8%, a reversible specific capacity of 278-295 mAh / g, a 200-cycle capacity retention of 89.8-93.2%, and a compaction density of 3.52-4.18 g / cm³. 3 The excellent overall performance fully demonstrates the synergistic advantages and the rationality of the parameter range of the technical solution of this invention.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A single-crystal lithium-rich manganese-based cathode material, characterized in that, The single-crystal lithium-rich manganese-based cathode material includes: A. Single-crystal lithium-rich manganese-based basal oxide core particles; B. A lithium phosphate coating layer covering the surface of the core particle; The stoichiometric formula of the nuclear particles is Li. 1+x Ni y CozMn 1-x-y-z O2, where each subscript indicates a molar ratio, x is 0.12–0.22, y is 0.06–0.15, and z is 0.06–0.15; The lithium phosphate coating is a Li3PO4 coating. The content of the lithium phosphate coating layer is 0.6–1.8 wt% of the total mass of the single-crystal lithium-rich manganese-based cathode material; The D50 of the nuclear particles is 0.6–1.

8. m.

2. The single-crystal lithium-rich manganese-based cathode material according to claim 1, characterized in that, The mixed hydroxide precursor used for preparing core particles is prepared by the following steps: A1. Raw material preparation: Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate are dissolved in deionized water to obtain a mixed metal salt solution; the total concentration of metal ions in the mixed metal salt solution is 1.0–2.0 mol / L; and the molar ratio of the corresponding metal ions of nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate is y:z:1-xyz; A2. Preparation of precipitant solution: Prepare an aqueous solution of sodium hydroxide with a concentration of 2.0–5.0 mol / L; A3. Coprecipitation: At 50–60℃, a mixed solution of metal salts and an aqueous solution of sodium hydroxide are added to the reactor in parallel flow, and the addition rate of the aqueous solution of sodium hydroxide is adjusted to maintain the pH of the reaction system at 10.8–11.

5. A4. Aging: Aging at 50–60℃ and pH 10.8–11.5 for 4–8 hours; A5. Post-treatment: Filtration, washing with deionized water until the pH of the filtrate is 7–8, and drying at 100–130℃ for 8–16 h to obtain the mixed hydroxide precursor; The molar ratio of Ni, Co, and Mn metal ions in the mixed hydroxide precursor is y:z:1-xyz, and the relative deviation of the molar ratio of the three metal ions from the target molar ratio y:z:1-xyz does not exceed ±5%.

3. The single-crystal lithium-rich manganese-based cathode material according to claim 2, characterized in that, Nuclear particles are prepared through the following steps: B1. Lithium Mixture: A mixed hydroxide precursor is mixed with a lithium source such that the molar ratio of the total number of lithium atoms provided by the lithium source to the total number of metal ions in the mixed hydroxide precursor is 1.45–1.60; the lithium source is lithium carbonate and / or lithium hydroxide. B2. Stepwise sintering: Gradient sintering is performed under an oxygen atmosphere; B3. Cooling and sieving: Cool to room temperature and sieve to obtain core particles; The D50 of the nuclear particles is 0.6–1.

8. m.

4. The single-crystal lithium-rich manganese-based cathode material according to claim 3, characterized in that, The gradient sintering process includes the following sintering steps: i. Keep warm at 450–550℃ for 3–6 hours; ii. Keep warm at 940–960℃ for 6–8 hours; iii. Hold at 990–1010℃ for 0.5–1.5 hours; iv. Cool to 840–860℃ and hold for 1.5–2.5 hours.

5. The single-crystal lithium-rich manganese-based cathode material according to claim 1, characterized in that, The lithium phosphate coating is generated in situ and coated onto the surface of the core particles through the following steps: C1. Dispersion: The nuclear particles are dispersed in deionized water at a solid-liquid mass ratio of 1:5–20; C2. Phosphate reaction: Add a phosphorus source at 20–60℃, and adjust the pH of the reaction system to 5.5–7.5 by adding a 0.5–2.0 mol / L lithium hydroxide aqueous solution and maintain it, and react for 0.5–2.0 h; the phosphorus source is phosphoric acid and / or ammonium dihydrogen phosphate; C3. Solid-liquid separation and washing: Filter and wash with deionized water until the pH of the filtrate is 6–8; C4. Drying and curing: Dry at 80–120℃ for 6–12h, then keep warm at 300–450℃ for 1–3h to form a Li3PO4 coating layer in the coating layer, and obtain a single crystal lithium-rich manganese-based cathode material powder with lithium phosphate surface coating. The content of the lithium phosphate coating is 0.6–1.8 wt% of the total mass of the powder.

6. The single-crystal lithium-rich manganese-based cathode material according to claim 5, characterized in that, Prior to step C2, the nuclear particles undergo surface residual lithium regulation through the following steps: the nuclear particles are slurried and washed in deionized water at a solid-liquid mass ratio of 1:5–30, at a temperature of 20–40°C, for 0.5–2.0 h; filtered and dried at 80–120°C for 6–12 h to regulate and reduce excess residual lithium carbonate and / or lithium hydroxide on the surface of the nuclear particles.

7. The single-crystal lithium-rich manganese-based cathode material according to claim 1, characterized in that, The average thickness of the lithium phosphate coating is 4–9 nm, which is measured by transmission electron microscopy; and the surface coverage of the lithium phosphate coating on the core particle is 70–88%, which is the area coverage obtained based on the statistical analysis of transmission electron microscopy images.

8. The single-crystal lithium-rich manganese-based cathode material according to claim 1, characterized in that, The tap density of the nuclear particles is 2.6–3.8 g / cm³. 3 The tap density was determined according to the GB / T5162 standard method; and the specific surface area of ​​the single-crystal lithium-rich manganese-based cathode material is 0.2–1.5 m². 2 / g, where the specific surface area is measured by the nitrogen adsorption BET method.

9. The single-crystal lithium-rich manganese-based cathode material according to claim 1, characterized in that, The Li / P molar ratio in the lithium phosphate coating is 2.9–3.

15.

10. The method for preparing the single-crystal lithium-rich manganese-based cathode material according to any one of claims 1-9, characterized in that, Includes the following steps: S1. Preparation of mixed hydroxide precursors by co-precipitation method; S2. The mixed hydroxide precursor is mixed with a lithium source and then subjected to gradient sintering to prepare core particles; S3. The core particles are subjected to a phosphate reaction, followed by drying and heat preservation treatment to form a Li3PO4 coating layer on the surface of the core particles, thereby obtaining a single-crystal lithium-rich manganese-based cathode material.

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