Lithium-rich manganese-based positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention relates to a lithium-rich manganese-based positive electrode material, a preparation method thereof and a lithium ion battery. The lithium-rich manganese-based positive electrode material comprises a cerium-doped lithium-rich manganese-based positive electrode material core and a coating layer, the coating layer comprises a cobalt boride coating layer and a carbon coating layer which are stacked in sequence, and the cobalt boride coating layer is located on the surface of the cerium-doped lithium-rich manganese-based positive electrode material core. The core of the lithium-rich manganese-based positive electrode material is doped with the cerium element, the crystal structure of the lithium-rich manganese-based positive electrode material can be effectively stabilized, the electronic conductivity and the ion diffusion rate of the material can be improved, meanwhile, the cobalt boride layer and the carbon layer on the surface act synergistically, the lithium-rich manganese-based positive electrode material is coated in all directions, and the lithium-rich manganese-based positive electrode material can be applied to the lithium-rich manganese-based positive electrode material. And doping and coating are adopted for modification at the same time, so that the chemical stability and the electrochemical performance of the lithium-rich manganese-based positive electrode material can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of lithium-rich manganese-based positive electrode materials, and in particular to a lithium-rich manganese-based positive electrode material, a preparation method thereof, and a lithium ion battery. Background Art

[0002] In recent years, the widespread adoption of new energy vehicles has led to an even more urgent demand for lithium-ion batteries. As a key battery component, cathode materials significantly impact battery performance. Among cathode materials, lithium-rich manganese-based cathode materials (LNCMs) offer advantages such as high specific capacity and high output voltage, meeting the demands of high-energy-density batteries. Their high specific capacity stems primarily from the additional capacity provided by the irreversible redox reaction of oxygen anions at high voltages (>4.5V). However, this results in a reduced first coulombic efficiency (ICE) and severe capacity and voltage decay. Furthermore, the loss of lattice oxygen and the migration of transition metals (TMs) can easily lead to a detrimental phase transition from a layered structure to a spinel phase in LNCMs, resulting in reduced cycling performance. Furthermore, the inherently poor lithium-ion diffusion kinetics of LNCMs lead to poor rate capability. These factors hinder their practical application. Therefore, overcoming the inherent limitations of LNCMs and improving their performance remains a key challenge.

[0003] To address the inherent defects of LNCM, three methods are currently commonly used to modify it: size control, surface coating, and ion doping. Ion doping is a simple and effective solution that stabilizes the material's crystal structure by increasing the strength of chemical bonds, inhibiting phase changes during service and improving the material's thermal stability. Crystal structure control can produce materials with specific orientations, exposing specific crystal planes, reducing the ion migration energy barrier, and accelerating electrochemical kinetics. Coating modification forms a protective film on the material's surface to improve its performance. If the material's inherent conductivity is poor, the coating layer is usually made of an ionic or electronic conductor.

[0004] In the existing technology, single element doping or single coating is generally used for modification. Although there are technical solutions using element doping and coating modification, the improvement of the performance of LNCM itself is limited. It is difficult to simultaneously solve problems such as structural stability, microstructure optimization and surface chemical stability to improve the overall performance of LNCM itself. For example, CN117645324A discloses a doped and coated lithium-rich manganese-based positive electrode material and its preparation method and application. Molybdenum and lanthanum are doped in sequence in the lithium-rich manganese-based precursor. Molybdenum is doped at the center of the precursor. Its presence minimizes the primary particle size and maintains the grain structure of the precursor within a wide lithiation temperature range. The lanthanum precursor is doped on the outer side. The La element supports the spatial structure of the precursor and stabilizes the precursor structure. The two act synergistically. A composite coating layer of aluminum and calcium is coated on the surface of the positive electrode material. The ability of the lithium-rich material to release oxygen can be greatly improved to stabilize the surface oxygen of the Li-rich material. The obtained doped and coated lithium-rich manganese-based positive electrode material can produce a battery with a first efficiency of more than 86.9%, an initial discharge capacity of more than 268.6 mAh / g, and a 50-week capacity retention rate of more than 95.3%. Although the above scheme can achieve performance improvement to a certain extent, the improvement effect is limited, and the overall performance has not yet reached a better level.

[0005] Therefore, how to develop a high-performance composite modification strategy to significantly improve the comprehensive performance of lithium-rich manganese-based positive electrode materials is a technical problem that needs to be solved urgently. Summary of the Invention

[0006] To address the above technical problems, the present invention provides a lithium-rich manganese-based cathode material, a preparation method thereof, and a lithium-ion battery. The present invention employs cerium to dope the core of the lithium-rich manganese-based cathode material, effectively stabilizing its crystal structure and improving its electronic conductivity and ion diffusion rate. Simultaneously, the cobalt boride layer and carbon layer on the surface act synergistically to fully coat the lithium-rich manganese-based cathode material, effectively suppressing the occurrence of side reactions. The simultaneous modification of doping and coating effectively improves the chemical stability and electrochemical performance of the lithium-rich manganese-based cathode material.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a lithium-rich manganese-based positive electrode material, wherein the lithium-rich manganese-based positive electrode material comprises a cerium-doped lithium-rich manganese-based positive electrode material core and a coating layer;

[0009] The coating layer comprises a cobalt boride coating layer and a carbon coating layer stacked in sequence, and the cobalt boride coating layer is located on the surface of the core of the cerium-doped lithium-rich manganese-based positive electrode material.

[0010] The lithium-rich manganese-based positive electrode material of the present invention comprises a cerium-doped lithium-rich manganese-based positive electrode material core and a cobalt boride coating layer and a carbon coating layer stacked in sequence. The lithium-rich manganese-based positive electrode material core is doped with cerium (located in the crystal lattice), and the cerium element forms a hybrid with the 3d orbital of the transition metal through its unique 4f electron orbital characteristics, and at the same time, the variable valence state of the cerium ion (Ce 3 + / Ce 4+ ) can effectively inhibit the generation of oxygen vacancies, thereby effectively stabilizing the crystal structure of the lithium-rich manganese-based positive electrode material and improving the electronic conductivity and ion diffusion rate of the material; and the coating layer includes a cobalt boride coating layer and a carbon coating layer, the cobalt boride coating layer is located on the surface of the core of the cerium-doped lithium-rich manganese-based positive electrode material, and the carbon coating layer is located on the surface of the cobalt boride coating layer. The cobalt boride coating layer and the carbon coating layer work together. The cobalt boride coating layer provides a physical barrier to prevent electrolyte corrosion, and the carbon coating layer can further strengthen the physical barrier and improve the electronic conductivity and structural stability of the lithium-rich manganese-based positive electrode material.

[0011] The present invention adopts doping and coating to carry out modification simultaneously, which can effectively improve the chemical stability and electrochemical performance of the lithium-rich manganese-based positive electrode material.

[0012] As a preferred technical solution of the present invention, the chemical formula of the core of the cerium-doped lithium-rich manganese-based positive electrode material includes Li 2-x M x Ce y O2, 0<x<1, for example, x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, 0.01x≤y≤0.04x, for example, y can be 0.01x, 0.015x, 0.02x, 0.025x, 0.03x, 0.035x or 0.04x, M includes a first metal and a second metal, the first metal is Mn, and the second metal includes Ni and / or Co.

[0013] Preferably, the thickness of the cobalt boride coating layer is 3 nm to 8 nm, for example, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm or 8 nm.

[0014] In the present invention, the thickness of the cobalt boride coating is controlled to 3nm to 8nm, which effectively blocks electrolyte corrosion while avoiding the obstruction of lithium ion transmission caused by an overly thick coating. If the cobalt boride coating is too thin, the coating will be incomplete, unable to effectively inhibit electrolyte corrosion of the material core, and accelerating the dissolution of transition metals. If the cobalt boride coating is too thick, the lithium ion diffusion path will be extended, increasing the interfacial impedance and reducing the material's rate performance.

[0015] Preferably, the carbon coating layer has a thickness of 1 nm to 5 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm or 5 nm.

[0016] In the present invention, the thickness of the carbon coating layer is adjusted to 1nm to 5nm, which can improve electronic conductivity while maintaining high lithium ion migration efficiency. If the carbon coating layer is too thin, the conductive network will be discontinuous, the electron transport capacity will be insufficient, and the electrochemical performance of the material will be affected. If the carbon coating layer is too thick, the carbon layer will accumulate and densify, hindering lithium ion diffusion and reducing the specific capacity of the material.

[0017] Preferably, the total thickness of the cobalt boride coating layer and the carbon coating layer is 4 nm to 10 nm, for example, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm.

[0018] In the present invention, the thickness of the cobalt boride coating layer and the carbon coating layer is regulated to be 4nm to 10nm. If the total thickness is too thick, it will hinder the transmission of lithium ions, reduce the content of active materials and cause interface cracking, resulting in battery performance degradation.

[0019] In a second aspect, the present invention further provides a method for preparing the lithium-rich manganese-based positive electrode material according to the first aspect, the preparation method comprising the following steps:

[0020] (1) adding a metal salt mixture, a cerium salt solution, a precipitant solution, and a complexing agent solution to a reaction bottom solution in parallel to perform a coprecipitation reaction to obtain a cerium-doped lithium-rich manganese-based precursor;

[0021] (2) uniformly mixing the cerium-doped lithium-rich manganese-based precursor described in step (1) with a lithium source, and performing a first sintering to obtain a cerium-doped lithium-rich manganese-based positive electrode material core;

[0022] (3) mixing and dispersing the cerium-doped lithium-rich manganese-based positive electrode material core described in step (2) with a cobalt-boron-containing coating liquid, and performing a second sintering to obtain a coated intermediate material;

[0023] The cobalt-boron coating solution comprises cobalt salt, boric acid and an organic solvent;

[0024] (4) The coated intermediate material and the coated carbon source described in step (3) are evenly mixed and subjected to a third sintering to obtain a lithium-rich manganese-based positive electrode material.

[0025] The present invention realizes the in-situ uniform recombination of cerium element and metal elements in the metal salt mixture through precise control at the molecular level, breaks through the technical limitations of the traditional post-doping method, realizes the spatial homogeneous distribution of the doping elements in the solution phase, and fundamentally solves the key technical problems such as element segregation and lattice distortion. It can effectively stabilize the crystal structure of lithium-rich manganese-based materials and improve the electronic conductivity and ion diffusion rate of the materials; and then through the double-layer composite coating process of the inner cobalt boride coating layer and the outer carbon coating layer, the two play a synergistic role, inhibit the occurrence of side reactions, and improve the structural stability and cycle performance of the lithium-rich manganese-based positive electrode materials.

[0026] As a preferred technical solution of the present invention, the metal salt mixture in step (1) includes a nickel-cobalt-manganese ternary salt mixture.

[0027] Preferably, the total concentration of the metal salts in the metal salt mixture in step (1) is 1 mol / L to 5 mol / L, for example, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L.

[0028] Preferably, the ratio of the molar amount of cerium element in the cerium salt solution of step (1) to the total molar amount of metal elements in the metal salt mixture of step (1) is (0.01-0.04):1, for example, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1 or 0.04:1, etc.

[0029] In the present invention, the ratio of the molar amount of cerium in the cerium salt solution to the total molar amount of metal elements in the metal salt mixture is regulated to be (0.01-0.04):1, which can ensure the uniform doping of cerium in the crystal lattice, effectively stabilizing the material structure while avoiding lattice distortion caused by excessive doping. If the molar amount of cerium is too low, the doping amount is too low, which will lead to insufficient suppression of oxygen vacancies and difficulty in significantly improving the structural stability and conductivity of the material. If the molar amount of cerium is too high, the doping amount is too high, which will lead to an abnormal increase in the distance between the transition metal layers, destroying the lithium ion transmission channel and possibly forming a cerium oxide impurity phase.

[0030] Preferably, the concentration of the cerium salt solution in step (1) is 0.05 mol / L to 0.4 mol / L, for example, 0.05 mol / L, 0.06 mol / L, 0.075 mol / L, 0.08 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.32 mol / L or 0.4 mol / L, etc.

[0031] Preferably, the reaction base solution in step (1) comprises pure water, a complexing agent solution and a precipitant solution.

[0032] Preferably, the pH of the reaction base solution in step (1) is 10.5 to 10.8, such as 10.5, 10.6, 10.7, 10.8, etc.

[0033] Preferably, in the reaction base solution of step (1), the concentration of the complexing agent solution is 1 g / L to 5 g / L, for example, 1 g / L, 2 g / L, 3 g / L, 4 g / L or 5 g / L.

[0034] Preferably, the volume of the reaction base liquid in step (1) accounts for 20% to 40% of the volume of the reaction container, such as 20%, 25%, 30%, 35% or 40%.

[0035] Preferably, the feed flow rate of the metal salt mixture in step (1) is 5 L / h to 10 L / h, for example, 5 L / h, 6 L / h, 7 L / h, 8 L / h, 9 L / h or 10 L / h.

[0036] Preferably, the feed flow rate of the cerium salt solution in step (1) is 1 L / h to 5 L / h, for example, 1 L / h, 2 L / h, 3 L / h, 4 L / h or 5 L / h.

[0037] Preferably, the feed flow rate of the precipitant solution in step (1) is 5 L / h to 15 L / h, for example, 5 L / h, 8 L / h, 10 L / h, 12 L / h or 15 L / h.

[0038] Preferably, the feed flow rate of the complexing agent solution in step (1) is 1 L / h to 5 L / h, for example, 1 L / h, 2 L / h, 3 L / h, 4 L / h or 5 L / h.

[0039] Preferably, the complexing agent solution in step (1) comprises aqueous ammonia.

[0040] Preferably, the concentration of the complexing agent solution in step (1) is 15 wt% to 20 wt%, for example, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt% or 20 wt%.

[0041] Preferably, the precipitant solution in step (1) comprises sodium hydroxide solution.

[0042] Preferably, the concentration of the precipitant solution in step (1) is 15 wt% to 25 wt%, for example, 15 wt%, 18 wt%, 20 wt%, 22 wt% or 25 wt%.

[0043] As a preferred technical solution of the present invention, the temperature of the coprecipitation reaction in step (1) is 55°C to 65°C, for example, 55°C, 58°C, 60°C, 62°C or 65°C.

[0044] Preferably, the pH of the coprecipitation reaction in step (1) is 9.8 to 10.5, for example, 9.8, 9.9, 10, 10.1, 10.2, 10.3, 10.4 or 10.5.

[0045] Preferably, the coprecipitation reaction time in step (1) is 36 h to 72 h, for example, 36 h, 40 h, 44 h, 48 h, 52 h, 56 h, 60 h, 64 h, 68 h or 72 h.

[0046] Preferably, the rotation speed of the coprecipitation reaction in step (1) is 350 rpm to 400 rpm, for example, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm or 400 rpm.

[0047] Preferably, after the coprecipitation reaction in step (1), the process further comprises the steps of solid-liquid separation, washing and drying the obtained precipitated product.

[0048] As a preferred technical solution of the present invention, the molar ratio of the Li element in the lithium source in step (2) to the Mn element in the cerium-doped lithium-rich manganese-based precursor in step (1) is (1 to 1.4):1, for example, 1:1, 1.1:1, 1.2:1, 1.3:1 or 1.4:1, etc.

[0049] Preferably, the lithium source in step (2) comprises lithium hydroxide.

[0050] Preferably, the mixing in step (2) comprises ball milling.

[0051] Preferably, the rotation speed of the ball mill is 200 rpm to 400 rpm, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm or 400 rpm.

[0052] Preferably, the ball milling time is 2 to 6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0053] Preferably, after the mixing in step (2) and before the first sintering, the process further includes drying the obtained mixed product.

[0054] Preferably, the drying temperature is 60°C to 100°C, for example, 60°C, 70°C, 80°C, 90°C or 100°C.

[0055] Preferably, the drying time is 8 h to 16 h, for example, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h or 16 h.

[0056] As a preferred technical solution of the present invention, the first sintering in step (2) includes one-stage sintering and two-stage sintering.

[0057] Preferably, the sintering temperature of the first stage sintering is 300°C to 600°C, for example, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C.

[0058] Preferably, the holding time of the sintering stage is 3 hours to 8 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours.

[0059] Preferably, the heating rate of the second-stage sintering is 2°C / min to 10°C / min, for example, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min.

[0060] Preferably, the sintering temperature of the second stage sintering is 800°C to 1200°C, for example, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1150°C or 1200°C.

[0061] Preferably, the holding time of the second-stage sintering is 8 h to 16 h, for example, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h or 16 h.

[0062] As a preferred technical solution of the present invention, in the cobalt-boron coating solution of step (3), the molar ratio of the cobalt salt to the boric acid is 1:(1-1.4), for example, 1:1, 1:1.15, 1:1.2, 1:25, 1:1.3, 1:35 or 1:4, etc.

[0063] Preferably, in the cobalt-boron coating solution of step (3), the volume ratio of the organic solvent to the total mass of the cobalt nitrate and the boric acid is (8L-12L):1g, for example, 8L:1g, 9L:1g, 10L:1g, 11L:1g or 12L:1g.

[0064] Preferably, in the cobalt-boron coating solution of step (3), the mass ratio of the organic solvent to the cerium-doped lithium-rich manganese-based positive electrode material core of step (2) is (20-50):1, for example, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1, etc.

[0065] In the present invention, the mass ratio of the organic solvent to the cerium-doped lithium-rich manganese-based cathode material core is controlled to be (20-50):1, which can make the cerium-doped lithium-rich manganese-based cathode material core more uniformly dispersed and coated. If the mass of the organic solvent is too low, the cerium-doped lithium-rich manganese-based cathode material core will agglomerate, and uniform coating cannot be achieved. If the mass of the organic solvent is too high, the ultrasonic cavitation effect is weakened, and the cerium-doped lithium-rich manganese-based cathode material core cannot be dispersed or evenly coated.

[0066] Preferably, the cobalt salt in step (3) comprises cobalt nitrate.

[0067] Preferably, the organic solvent in step (3) comprises ethanol.

[0068] The present invention uses a cobalt-boron coating solution to coat the cobalt boride. A cobalt boride precursor (e.g., a Co-BO structure) is formed by reacting a cobalt salt and boric acid in an ethanol solution. This precursor is then uniformly attached to the surface of the cerium-doped lithium-rich manganese-based cathode material core. Subsequently, the precursor is heated to form a uniform cobalt boride coating. Direct coating with a cobalt boride solution can reduce the uniformity of the coating if the cobalt boride is unevenly distributed in the solution, thereby affecting subsequent coating and the performance of the coated material.

[0069] Preferably, the mixing and dispersing in step (3) includes ultrasonic dispersion.

[0070] Preferably, the mixing and dispersing time in step (3) is 0.5 h to 2 h, for example, 0.5 h, 1 h, 1.5 h or 2 h.

[0071] Preferably, the second sintering in step (3) is performed under a protective atmosphere.

[0072] Preferably, the gas used in the protective atmosphere includes nitrogen and / or an inert gas.

[0073] Preferably, the heating rate of the second sintering in step (3) is 1°C / min to 5°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min or 5°C / min.

[0074] Preferably, the sintering temperature of the second sintering in step (3) is 250°C to 350°C, for example, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C or 350°C.

[0075] Preferably, the holding time of the second sintering in step (3) is 1 h to 4 h, such as 1 h, 2 h, 3 h or 4 h.

[0076] Preferably, after the second sintering in step (3), the step further includes washing and drying the sintered product.

[0077] Preferably, the drying temperature is 60°C to 120°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C.

[0078] Preferably, the drying time is 8 hours to 14 hours, for example, 8 hours, 10 hours, 12 hours or 14 hours.

[0079] As a preferred technical solution of the present invention, the mixing in step (4) includes ball milling.

[0080] Preferably, the rotation speed of the ball mill is 300 r / min to 500 r / min, for example, 300 r / min, 350 r / min, 400 r / min, 450 r / min or 500 r / min.

[0081] Preferably, the ball milling time is 3 h to 6 h, such as 3 h, 4 h, 5 h or 6 h.

[0082] Preferably, the coated carbon source in step (4) includes glucose.

[0083] Preferably, the mass ratio of the coated intermediate material in step (3) to the coated carbon source in step (4) is (8-12):1, for example, 8:1, 9:1, 10:1, 11:1 or 12:1.

[0084] Preferably, the mixed raw materials in step (4) also include deionized water.

[0085] Preferably, after the mixing in step (4) and before the third sintering, the process further includes drying the obtained mixed product.

[0086] Preferably, the drying temperature is 60°C to 120°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C.

[0087] Preferably, the drying time is 8 hours to 14 hours, for example, 8 hours, 10 hours, 12 hours or 14 hours.

[0088] Preferably, the third sintering in step (4) is performed under a protective atmosphere.

[0089] Preferably, the gas used in the protective atmosphere includes nitrogen and / or an inert gas.

[0090] Preferably, the heating rate of the third sintering in step (4) is 2°C / min to 10°C / min, for example, 2°C / min, 4°C / min, 6°C / min, 8°C / min or 10°C / min.

[0091] Preferably, the sintering temperature of the third sintering in step (4) is 400°C to 650°C, for example, 400°C, 420°C, 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, 600°C, 620°C or 650°C.

[0092] Preferably, the holding time of the third sintering in step (4) is 2 hours to 8 hours, for example, 2 hours, 4 hours, 6 hours or 8 hours.

[0093] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0094] (1) adding a metal salt mixture, a cerium salt solution, a precipitant solution, and a complexing agent solution to a reaction base solution having a pH of 10.5 to 10.8 in parallel, and performing a co-precipitation reaction at 55° C. to 65° C., a pH of 9.8 to 10.5, and a rotation speed of 350 rpm to 400 rpm for 36 to 72 hours, and performing solid-liquid separation, washing, and drying on the obtained precipitated product to obtain a cerium-doped lithium-rich manganese-based precursor;

[0095] The metal salt mixture comprises a nickel-cobalt-manganese ternary salt mixture; the total concentration of the metal salts in the metal salt mixture is 1 mol / L to 5 mol / L; the ratio of the molar amount of cerium element in the cerium salt solution to the total molar amount of metal elements in the metal salt mixture is (0.01 to 0.04):1; the reaction base liquid comprises pure water, a complexing agent solution with a concentration of 15 wt% to 20 wt% and a precipitant solution with a concentration of 15 wt% to 25 wt%; the concentration of the complexing agent solution in the reaction base liquid is 1 g / L to 5 g / L; the volume of the reaction base liquid accounts for 20% to 40% of the volume of the reaction container; the feed flow rate of the metal salt mixture is 5 L / h to 10 L / h; the feed flow rate of the cerium salt solution is 1 L / h to 5 L / h; the feed flow rate of the precipitant solution is 5 L / h to 15 L / h; and the feed flow rate of the complexing agent solution is 1 L / h to 5 L / h.

[0096] (2) The cerium-doped lithium-rich manganese-based precursor of step (1) is uniformly mixed with a lithium source, dried at 60°C to 100°C for 8h to 16h, and then subjected to a first sintering process, wherein the first sintering process is carried out at 300°C to 600°C for 3h to 8h, and then the second sintering process is carried out at 800°C to 1200°C for 8h to 16h at a heating rate of 2°C / min to 10°C / min to obtain a cerium-doped lithium-rich manganese-based positive electrode material core;

[0097] The molar ratio of the Li element in the lithium source to the Mn element in the cerium-doped lithium-rich manganese-based precursor in step (1) is (1-1.4):1;

[0098] (3) The cerium-doped lithium-rich manganese-based positive electrode material core of step (2) is mixed and dispersed with the cobalt-boron coating liquid for 0.5 h to 2 h, and a second sintering is performed at 250 ° C to 350 ° C for 1 h to 4 h at a heating rate of 1 ° C / min to 5 ° C / min under a protective atmosphere, and the obtained sintered product is washed and dried at 60 ° C to 120 ° C for 8 h to 14 h to obtain a coated intermediate material;

[0099] The cobalt-boron coating solution comprises a cobalt salt, boric acid and an organic solvent. In the cobalt-boron coating solution, the molar ratio of the cobalt salt to the boric acid is 1:(1-1.4), the volume of the organic solvent to the total mass ratio of the cobalt nitrate and the boric acid is (8L-12L):1g, and the mass ratio of the organic solvent to the cerium-doped lithium-rich manganese-based positive electrode material core in step (2) is (20-50):1;

[0100] (4) uniformly mixing the coated intermediate material of step (3) with the coated carbon source and deionized water, drying the resulting mixed product at 60° C. to 120° C. for 8 h to 14 h, and then performing a third sintering at 400° C. to 650° C. under a protective atmosphere at a heating rate of 2° C. / min to 10° C. / min for 2 h to 8 h to obtain a lithium-rich manganese-based positive electrode material;

[0101] The mass ratio of the coated intermediate material to the coated carbon source in step (3) is (8-12):1.

[0102] In a third aspect, the present invention further provides a lithium-ion battery, comprising the lithium-rich manganese-based positive electrode material as described in the first aspect, or the lithium-rich manganese-based positive electrode material prepared by the preparation method as described in the second aspect.

[0103] Compared with the prior art, the present invention has at least the following beneficial effects:

[0104] 1) The core of the lithium-rich manganese-based cathode material of the present invention is doped with cerium (located in the crystal lattice). The cerium element forms a hybrid with the 3d orbital of the transition metal through its unique 4f electron orbital characteristics. At the same time, the variable valence state of the cerium ion (Ce 3+ / Ce 4+ ) can effectively inhibit the generation of oxygen vacancies, thereby effectively stabilizing the crystal structure of lithium-rich manganese-based materials and improving the electronic conductivity and ion diffusion rate of the materials.

[0105] 2) The coating layer in the lithium-rich manganese-based positive electrode material of the present invention includes a cobalt boride coating layer and a carbon coating layer. The cobalt boride coating layer is located on the surface of the core of the cerium-doped lithium-rich manganese-based positive electrode material, and the carbon coating layer is located on the surface of the cobalt boride coating layer. The cobalt boride coating layer and the carbon coating layer work synergistically. The cobalt boride coating layer provides a physical barrier to prevent electrolyte corrosion, and the carbon coating layer can further strengthen the physical barrier and improve the electronic conductivity and structural stability of the lithium-rich manganese-based positive electrode material.

[0106] 3) The present invention achieves in-situ uniform recombination of cerium elements with metal elements in a metal salt mixture through precise control at the molecular level, breaking through the technical limitations of the traditional post-doping method and achieving spatially homogenized distribution of doping elements in the solution phase. It fundamentally solves key technical problems such as element segregation and lattice distortion, and can effectively stabilize the crystal structure of lithium-rich manganese-based materials and improve the electronic conductivity and ion diffusion rate of the materials. DETAILED DESCRIPTION

[0107] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0108] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0109] Example 1

[0110] This embodiment provides a lithium-rich manganese-based positive electrode material, which includes a cerium-doped lithium-rich manganese-based positive electrode material core, the chemical formula of which is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 Ce 0.016 The surface of the core of the O2, cerium-doped lithium-rich manganese-based positive electrode material is sequentially coated with a cobalt boride coating layer with a thickness of 5 nm and a carbon coating layer with a thickness of 3 nm.

[0111] The preparation method comprises the following steps:

[0112] (1) First, NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O with a Ni:Co:Mn molar ratio of 0.13:0.13:0.54 were dissolved in deionized water to obtain a nickel-cobalt-manganese ternary salt mixture with a total metal concentration of 2 mol / L; a cerium nitrate solution with a concentration of 0.075 mol / L was prepared, and the ratio of the molar amount of cerium element in the cerium nitrate solution to the total molar amount of Ni, Co, and Mn in the nickel-cobalt-manganese ternary salt mixture was 0.02:1; pure water, 20 wt% sodium hydroxide solution, and 18 wt% ammonia water were mixed to obtain a reaction base solution with a pH of 10.8, and the ammonia concentration in the reaction base solution was 3 g / L;

[0113] Add 30% of the total volume of the reaction vessel to the reaction vessel. Then, add 7 L / h of nickel-cobalt-manganese ternary salt mixture, 3 L / h of cerium nitrate solution, 3 L / h of 18 wt% ammonia water, and 10 L / h of 20 wt% sodium hydroxide solution to the reaction vessel in parallel through a metering pump. Maintain the speed at 380 rpm, the temperature at 58°C, and the pH value of the reaction system at 10.2 for a co-precipitation reaction of 48 hours. After the reaction is completed, the obtained precipitated product is subjected to solid-liquid separation, and the obtained solid is washed multiple times and dried to obtain a cerium-doped lithium-rich manganese-based precursor.

[0114] (2) The cerium-doped lithium-rich manganese-based precursor and lithium hydroxide were ball-milled at a speed of 400 rpm for 4 hours to mix, the molar ratio of the Li element in the lithium hydroxide to the Mn element in the cerium-doped lithium-rich manganese-based precursor was 1.2:1, and after drying at 80°C for 12 hours, the first sintering was performed, first at 500°C for 5 hours for a first sintering, and then at 900°C for 12 hours at a heating rate of 5°C / min for a second sintering to obtain the core of the cerium-doped lithium-rich manganese-based positive electrode material;

[0115] (3) Cobalt nitrate, boric acid and ethanol are mixed to prepare a cobalt-boron coating solution, wherein the molar ratio of cobalt nitrate and boric acid is 1:1, and the volume ratio of ethanol to the total mass of cobalt nitrate and boric acid is 10L:1g; the core of the cerium-doped lithium-rich manganese-based positive electrode material is added to the cobalt-boron coating solution, wherein the mass ratio of ethanol to the core of the cerium-doped lithium-rich manganese-based positive electrode material is 25:1, and ultrasonic dispersion is performed for 1 hour to uniformly disperse the core of the cerium-doped lithium-rich manganese-based positive electrode material in the cobalt-boron coating solution, and the dispersion is transferred to a three-necked flask, and heated to 300°C at a heating rate of 2°C / min under nitrogen protection and kept warm for 3 hours for a second sintering. After the reaction is completed, it is naturally cooled to room temperature, washed with ethanol several times to remove excess reactants, and dried in a vacuum drying oven at 100°C for 12 hours to obtain a coated intermediate material;

[0116] (4) The coated intermediate material and glucose were mixed in a mass ratio of 10:1, and an appropriate amount of deionized water (enough to cover the raw materials) was added for ball milling. The ball milling was carried out at a speed of 400 r / min for 4 h so that the glucose was evenly coated on the surface of the material. The ball-milled product was dried at 80 ° C for 12 h to remove moisture. The dried product was then placed under argon protection and heated to 600 ° C at a heating rate of 5 ° C / min for 5 h for the third sintering to obtain a lithium-rich manganese-based positive electrode material (cerium doped-cobalt boride and carbon double layer coating).

[0117] Example 2

[0118] This embodiment provides a lithium-rich manganese-based positive electrode material. The difference between the lithium-rich manganese-based positive electrode material and the embodiment 1 is that the chemical formula of the core of the cerium-doped lithium-rich manganese-based positive electrode material is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 Ce 0.008 O2, the rest of the structure and parameters remain the same as in Example 1.

[0119] The difference between the preparation method and Example 1 is that the ratio of the molar amount of cerium element in the cerium nitrate solution to the total molar amount of Ni, Co and Mn in the nickel-cobalt-manganese ternary salt mixture is 0.01:1, and the other preparation methods and parameters are consistent with Example 1.

[0120] Example 3

[0121] This embodiment provides a lithium-rich manganese-based positive electrode material. The difference between the lithium-rich manganese-based positive electrode material and the embodiment 1 is that the chemical formula of the core of the cerium-doped lithium-rich manganese-based positive electrode material is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 Ce 0.024 O2, the rest of the structure and parameters remain the same as in Example 1.

[0122] The difference between the preparation method and Example 1 is that the ratio of the molar amount of cerium element in the cerium nitrate solution to the total molar amount of Ni, Co and Mn in the nickel-cobalt-manganese ternary salt mixture is 0.03:1, and the other preparation methods and parameters are consistent with Example 1.

[0123] Example 4

[0124] This embodiment provides a lithium-rich manganese-based positive electrode material, which includes a cerium-doped lithium-rich manganese-based positive electrode material core, the chemical formula of which is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 Ce 0.032The surface of the core of the O2, cerium-doped lithium-rich manganese-based positive electrode material is sequentially coated with a cobalt boride coating layer with a thickness of 3 nm and a carbon coating layer with a thickness of 1 nm.

[0125] The preparation method comprises the following steps:

[0126] (1) First, NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O with a Ni:Co:Mn molar ratio of 0.13:0.13:0.54 were dissolved in deionized water to obtain a nickel-cobalt-manganese ternary salt mixture with a total metal concentration of 2 mol / L; a cerium nitrate solution with a concentration of 0.32 mol / L was prepared, and the ratio of the molar amount of cerium element in the cerium nitrate solution to the total molar amount of Ni, Co, and Mn in the nickel-cobalt-manganese ternary salt mixture was 0.04:1; pure water, 20 wt% sodium hydroxide solution, and 18 wt% ammonia water were mixed to obtain a reaction base solution with a pH of 10.5, and the ammonia concentration in the reaction base solution was 3 g / L;

[0127] Add 20% of the total volume of the reaction vessel to the reaction vessel. Then, add 5 L / h of nickel-cobalt-manganese ternary salt mixture, 1 L / h of cerium nitrate solution, 1 L / h of 18 wt% ammonia water, and 5 L / h of 20 wt% sodium hydroxide solution to the reaction vessel in parallel through a metering pump. Maintain the speed at 350 rpm, the temperature at 55°C, and the pH value of the reaction system at 9.8 for 36 hours of co-precipitation reaction. After the reaction is completed, the obtained precipitated product is subjected to solid-liquid separation, and the obtained solid is washed multiple times and dried to obtain a cerium-doped lithium-rich manganese-based precursor.

[0128] (2) The cerium-doped lithium-rich manganese-based precursor and lithium hydroxide were ball-milled at a speed of 400 rpm for 4 hours to mix, the molar ratio of the Li element in the lithium hydroxide to the Mn element in the cerium-doped lithium-rich manganese-based precursor was 1.2:1, and after drying at 80°C for 12 hours, the first sintering was performed, first at 300°C for 8 hours for a first sintering, and then at 800°C for 16 hours at a heating rate of 5°C / min for a second sintering to obtain the core of the cerium-doped lithium-rich manganese-based positive electrode material;

[0129] (3) Cobalt nitrate, boric acid and ethanol are mixed to prepare a cobalt-boron coating solution, wherein the molar ratio of cobalt nitrate to boric acid is 1:1.4, and the volume ratio of ethanol to the total mass of cobalt nitrate and boric acid is 10L:1g; the core of the cerium-doped lithium-rich manganese-based positive electrode material is added to the cobalt-boron coating solution, wherein the mass ratio of ethanol to the core of the cerium-doped lithium-rich manganese-based positive electrode material is 20:1, and ultrasonic dispersion is performed for 1 hour to uniformly disperse the core of the cerium-doped lithium-rich manganese-based positive electrode material in the cobalt-boron coating solution, and the dispersion is transferred to a three-necked flask, and heated to 250°C at a heating rate of 2°C / min under nitrogen protection and kept warm for 4 hours for a second sintering. After the reaction is completed, it is naturally cooled to room temperature, washed with ethanol several times to remove excess reactants, and dried in a vacuum drying oven at 100°C for 12 hours to obtain a coated intermediate material;

[0130] (4) The coated intermediate material and glucose were mixed in a mass ratio of 8:1, and an appropriate amount of deionized water (enough to cover the raw materials) was added for ball milling. The ball milling was carried out at a speed of 400 r / min for 4 h so that the glucose was evenly coated on the surface of the material. The ball-milled product was dried at 80 ° C for 12 h to remove moisture. The dried product was then placed under argon protection and heated to 400 ° C at a heating rate of 5 ° C / min for 8 h for the third sintering to obtain a lithium-rich manganese-based positive electrode material (cerium doped-cobalt boride and carbon double layer coating).

[0131] Example 5

[0132] This embodiment provides a lithium-rich manganese-based positive electrode material, which includes a cerium-doped lithium-rich manganese-based positive electrode material core, the chemical formula of which is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 Ce 0.012 The surface of the core of the O2, cerium-doped lithium-rich manganese-based positive electrode material is sequentially coated with a cobalt boride coating layer with a thickness of 8 nm and a carbon coating layer with a thickness of 2 nm.

[0133] The preparation method comprises the following steps:

[0134] (1) First, NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O with a Ni:Co:Mn molar ratio of 0.13:0.13:0.54 were dissolved in deionized water to obtain a nickel-cobalt-manganese ternary salt mixture with a total metal concentration of 2 mol / L; a cerium nitrate solution with a concentration of 0.06 mol / L was prepared, and the ratio of the molar amount of cerium element in the cerium nitrate solution to the total molar amount of Ni, Co, and Mn in the nickel-cobalt-manganese ternary salt mixture was 0.015:1; pure water, 20 wt% sodium hydroxide solution, and 18 wt% ammonia water were mixed to obtain a reaction base solution with a pH of 10.6, and the ammonia concentration in the reaction base solution was 3 g / L;

[0135] A reaction bottom solution (40% of the total volume of the reactor) was added to the reactor. A metering pump was used to add 10 L / h of a nickel-cobalt-manganese ternary salt mixture, 5 L / h of a cerium nitrate solution, 5 L / h of 18 wt% ammonia water, and 15 L / h of a 20 wt% sodium hydroxide solution to the reaction bottom solution. The speed was maintained at 400 rpm, the temperature was 65°C, and the pH value of the reaction system was 10.5. The co-precipitation reaction was carried out for 72 hours. After the reaction was completed, the precipitated product was subjected to solid-liquid separation, and the obtained solid was washed multiple times and dried to obtain a cerium-doped lithium-rich manganese-based precursor.

[0136] (2) The cerium-doped lithium-rich manganese-based precursor and lithium hydroxide were ball-milled at a speed of 400 rpm for 4 hours to mix, the molar ratio of the Li element in the lithium hydroxide to the Mn element in the cerium-doped lithium-rich manganese-based precursor was 1.2:1, and after drying at 80°C for 12 hours, the first sintering was performed, first at 600°C for 3 hours for a first sintering, and then at 1200°C for 8 hours at a heating rate of 5°C / min for a second sintering to obtain the core of the cerium-doped lithium-rich manganese-based positive electrode material;

[0137] (3) Cobalt nitrate, boric acid and ethanol are mixed to prepare a cobalt-boron coating solution, wherein the molar ratio of cobalt nitrate to boric acid is 1:1.2, and the volume ratio of ethanol to the total mass of cobalt nitrate and boric acid is 10L:1g; the core of the cerium-doped lithium-rich manganese-based positive electrode material is added to the cobalt-boron coating solution, wherein the mass ratio of ethanol to the core of the cerium-doped lithium-rich manganese-based positive electrode material is 50:1, and ultrasonic dispersion is performed for 1 hour to uniformly disperse the core of the cerium-doped lithium-rich manganese-based positive electrode material in the cobalt-boron coating solution, and the dispersion is transferred to a three-necked flask, and heated to 350°C at a heating rate of 2°C / min under nitrogen protection and kept warm for 1 hour for a second sintering. After the reaction is completed, it is naturally cooled to room temperature, washed with ethanol several times to remove excess reactants, and dried in a vacuum drying oven at 100°C for 12 hours to obtain a coated intermediate material;

[0138] (4) The coated intermediate material and glucose were mixed in a mass ratio of 12:1, and an appropriate amount of deionized water (enough to cover the raw materials) was added for ball milling. The ball milling was carried out at a speed of 400 r / min for 4 h to uniformly coat the glucose on the surface of the material. The ball-milled product was dried at 80 ° C for 12 h to remove moisture. The dried product was then placed under argon protection and heated to 650 ° C at a heating rate of 5 ° C / min for 2 h for the third sintering to obtain a lithium-rich manganese-based positive electrode material (cerium doped-cobalt boride and carbon double layer coating).

[0139] Example 6

[0140] This embodiment provides a lithium-rich manganese-based positive electrode material. The difference between the lithium-rich manganese-based positive electrode material and the embodiment 1 is that the chemical formula of the core of the cerium-doped lithium-rich manganese-based positive electrode material is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 Ce 0.004 O2, the rest of the structure and parameters remain the same as in Example 1.

[0141] The difference between the preparation method and Example 1 is that the ratio of the molar amount of cerium element in the cerium nitrate solution to the total molar amount of Ni, Co and Mn in the nickel-cobalt-manganese ternary salt mixture is 0.005:1, and the other preparation methods and parameters are consistent with Example 1.

[0142] Example 7

[0143] This embodiment provides a lithium-rich manganese-based positive electrode material. The difference between the lithium-rich manganese-based positive electrode material and the embodiment 1 is that the chemical formula of the core of the cerium-doped lithium-rich manganese-based positive electrode material is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 Ce 0.036 O2, the rest of the structure and parameters remain the same as in Example 1.

[0144] The difference between the preparation method and Example 1 is that the ratio of the molar amount of cerium element in the cerium nitrate solution to the total molar amount of Ni, Co and Mn in the nickel-cobalt-manganese ternary salt mixture is 0.045:1, and the other preparation methods and parameters are consistent with Example 1.

[0145] Example 8

[0146] This embodiment provides a lithium-rich manganese-based positive electrode material. The lithium-rich manganese-based positive electrode material differs from that of Example 1 in that the thickness of the cobalt boride coating layer is 10 nm, and the remaining structures and parameters are consistent with those of Example 1.

[0147] The difference between the preparation method and Example 1 is that the content of the cerium-doped lithium-rich manganese-based positive electrode material core and the cobalt-boron coating liquid are adaptively adjusted so that the thickness of the obtained cobalt boride coating layer is 10 nm. The rest of the preparation methods and parameters are consistent with Example 1.

[0148] Example 9

[0149] This embodiment provides a lithium-rich manganese-based positive electrode material. The lithium-rich manganese-based positive electrode material differs from that of Example 1 in that the thickness of the carbon coating layer is 1 nm, and the remaining structures and parameters remain the same as those of Example 1.

[0150] The difference between the preparation method and Example 1 is that the contents of the coating intermediate material and glucose are adaptively adjusted so that the thickness of the obtained carbon coating layer is 1 nm. The other preparation methods and parameters are consistent with Example 1.

[0151] Comparative Example 1

[0152] This comparative example provides a lithium-rich manganese-based positive electrode material. The lithium-rich manganese-based positive electrode material differs from Example 1 in that the cobalt boride coating layer is omitted, and the remaining structures and parameters remain the same as Example 1.

[0153] The difference between the preparation method and Example 1 is that step (3) is omitted and the core of the cerium-doped lithium-rich manganese-based positive electrode material is directly carbon-coated. The remaining preparation methods and parameters are consistent with Example 1.

[0154] Comparative Example 2

[0155] This comparative example provides a lithium-rich manganese-based positive electrode material. The lithium-rich manganese-based positive electrode material differs from Example 1 in that the carbon coating layer is omitted, and the remaining structures and parameters remain the same as Example 1.

[0156] The difference between the preparation method and Example 1 is that step (4) is omitted, and the remaining preparation methods and parameters are consistent with Example 1.

[0157] The lithium-rich manganese-based positive electrode materials prepared in Examples 1-9 and Comparative Examples 1-2 were prepared as positive electrode sheets, and button cells were assembled using lithium metal sheets as negative electrode sheets and 1 mol / L LiPF6 as electrolyte for electrochemical performance testing (voltage range 2.0-4.8 V vs. Li + / Li), and the specific test results are shown in Table 1.

[0158] Table 1

[0159] project <![CDATA[Initial discharge specific capacity at 0.1C (mAh·g -1 )]]> Capacity retention rate after 200 cycles at 1C rate (%) Example 1 280.58 94.7 Example 2 265.30 88.3 Example 3 272.80 90.2 Example 4 270.54 91.9 Example 5 264.89 88.5 Example 6 235.40 78.5 Example 7 248.70 75.4 Example 8 230.10 72.8 Example 9 245.60 82.6 Comparative Example 1 201.90 62.1 Comparative Example 2 255.20 70.5

[0160] The test results show that:

[0161] (1) It can be seen from Examples 1 to 5 that the present invention uses cerium to dope the core of the lithium-rich manganese-based positive electrode material, which can effectively stabilize the crystal structure of the lithium-rich manganese-based material and improve the electronic conductivity and ion diffusion rate of the material. At the same time, the cobalt boride layer and the carbon layer double coating on the surface work together to fully coat the lithium-rich manganese-based positive electrode material, effectively suppressing the occurrence of side reactions. The simultaneous modification of doping and coating can effectively improve the chemical stability and electrochemical performance of the lithium-rich manganese-based positive electrode material. Specifically, the 0.1C first discharge specific capacity is 264.89mAh·g -1 ~280.58mAh·g -1 The capacity retention rate after 200 cycles at 1C rate is between 88.3% and 94.7%. Among them, in Example 1, when Ce is 0.0016, the cobalt boride coating layer is 5nm, and the carbon coating layer is 3nm, the first discharge capacity can reach 280.58mAh / g, which is mainly attributed to the precise control of cerium doping and the double-layer coating of cobalt boride coating and carbon coating layer, which significantly improves the interface stability.

[0162] (2) It can be seen from Examples 1 and 6 to 7 that the present invention regulates the ratio of the molar amount of cerium element in the cerium salt solution to the total molar amount of metal elements in the metal salt mixture to be (0.01 to 0.04):1, which can ensure the uniform doping of cerium element in the lattice, effectively stabilize the material structure, and avoid lattice distortion caused by excessive doping. In Example 6, the cerium doping content is too low, which will result in insufficient suppression of oxygen vacancies and lead to Mn 3+The dissolution amount increases and the capacity retention rate decreases. In Example 7, the cerium doping content is too high, and the excess cerium occupies the transition metal sites, which reduces the lithium ion diffusion coefficient and the first discharge specific capacity. CeO2 nanodomains may also be generated, which blocks the lithium channel and reduces the capacity retention rate.

[0163] (3) It can be seen from Examples 1 and 8 to 9 that the present invention regulates the thickness of the cobalt boride coating layer to be 3nm to 8nm, the thickness of the carbon coating layer to be 1nm to 5nm, and the total thickness of the cobalt boride coating layer and the carbon coating layer to be 4nm to 10nm, which can achieve better overall performance of the material. In Example 8, the cobalt boride coating layer is too thick, which makes the total thickness of the cobalt boride coating layer and the carbon coating layer also too thick, resulting in increased interface impedance and decreased first discharge specific capacity. In Example 9, the carbon coating layer is too thin, the electronic conductivity is reduced, and the electrolyte penetration is aggravated, resulting in a reduced capacity retention rate.

[0164] (4) It can be seen from Example 1 and Comparative Examples 1-2 that the cobalt boride coating layer of the present invention is located on the surface of the core of the cerium-doped lithium-rich manganese-based positive electrode material, and the carbon coating layer is located on the surface of the cobalt boride coating layer. The cobalt boride coating layer and the carbon coating layer work synergistically. The cobalt boride coating layer provides a physical barrier to prevent electrolyte corrosion, and the carbon coating layer can further strengthen the physical barrier and improve the electronic conductivity and structural stability of the lithium-rich manganese-based positive electrode material. In Comparative Example 1, the cobalt boride coating was not performed, and the capacity retention rate was greatly reduced due to electrolyte corrosion. In Comparative Example 2, the carbon layer was not coated, and the capacity retention rate was still greatly reduced due to the increase in polarization voltage. In summary, the present invention uses cerium element to dope the core of the lithium-rich manganese-based positive electrode material, which can effectively stabilize the crystal structure of the lithium-rich manganese-based positive electrode material and improve the electronic conductivity and ion diffusion rate of the material. At the same time, the double coating layers of cobalt boride layer and carbon layer on the surface work synergistically to fully coat the lithium-rich manganese-based positive electrode material, effectively inhibiting the occurrence of side reactions. The simultaneous modification of doping and coating can effectively improve the chemical stability and electrochemical properties of the lithium-rich manganese-based positive electrode material.

[0165] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A lithium-rich manganese-based positive electrode material, characterized in that The lithium-rich manganese-based positive electrode material comprises a cerium-doped lithium-rich manganese-based positive electrode material core and a coating layer; The coating layer comprises a cobalt boride coating layer and a carbon coating layer stacked in sequence, and the cobalt boride coating layer is located on the surface of the core of the cerium-doped lithium-rich manganese-based positive electrode material.

2. The lithium-rich manganese-based positive electrode material according to claim 1, characterized in that The chemical formula of the core of the cerium-doped lithium-rich manganese-based positive electrode material includes Li 2-x M x Ce y O2, 0<x<1, 0.01x≤y≤0.04x, M includes a first metal and a second metal, the first metal is Mn, and the second metal includes Ni and / or Co; Preferably, the thickness of the cobalt boride coating layer is 3 nm to 8 nm; Preferably, the thickness of the carbon coating layer is 1 nm to 5 nm; Preferably, the total thickness of the cobalt boride coating layer and the carbon coating layer is 4 nm to 10 nm.

3. A method for preparing a lithium-rich manganese-based positive electrode material according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: (1) adding a metal salt mixture, a cerium salt solution, a precipitant solution, and a complexing agent solution to a reaction bottom solution in parallel to perform a coprecipitation reaction to obtain a cerium-doped lithium-rich manganese-based precursor; (2) uniformly mixing the cerium-doped lithium-rich manganese-based precursor described in step (1) with a lithium source, and performing a first sintering to obtain a cerium-doped lithium-rich manganese-based positive electrode material core; (3) mixing and dispersing the cerium-doped lithium-rich manganese-based positive electrode material core described in step (2) with a cobalt-boron-containing coating liquid, and performing a second sintering to obtain a coated intermediate material; The cobalt-boron coating solution comprises cobalt salt, boric acid and an organic solvent; (4) The coated intermediate material and the coated carbon source described in step (3) are evenly mixed and subjected to a third sintering to obtain a lithium-rich manganese-based positive electrode material.

4. The preparation method according to claim 3, characterized in that The metal salt mixture in step (1) comprises a nickel-cobalt-manganese ternary salt mixture; Preferably, the total concentration of the metal salt in the metal salt mixture in step (1) is 1 mol / L to 5 mol / L; Preferably, the ratio of the molar amount of cerium element in the cerium salt solution of step (1) to the total molar amount of metal elements in the metal salt mixture of step (1) is (0.01-0.04):1; Preferably, the reaction base solution in step (1) comprises pure water, a complexing agent solution and a precipitant solution; Preferably, the pH of the reaction base solution in step (1) is 10.5 to 10.8; Preferably, in the reaction base solution of step (1), the concentration of the complexing agent solution is 1 g / L to 5 g / L; Preferably, the volume of the reaction base liquid in step (1) accounts for 20% to 40% of the volume of the reaction container; Preferably, the feed flow rate of the metal salt mixture in step (1) is 5 L / h to 10 L / h; Preferably, the feed flow rate of the cerium salt in step (1) is 1 L / h to 5 L / h; Preferably, the feed flow rate of the precipitant solution in step (1) is 5 L / h to 15 L / h; Preferably, the feed flow rate of the complexing agent solution in step (1) is 1 L / h to 5 L / h.

5. The preparation method according to claim 3 or 4, characterized in that The temperature of the coprecipitation reaction in step (1) is 55° C. to 65° C.; Preferably, the pH of the coprecipitation reaction in step (1) is 9.8 to 10.5; Preferably, the coprecipitation reaction time in step (1) is 36h to 72h; Preferably, the rotation speed of the coprecipitation reaction in step (1) is 350 rpm to 400 rpm.

6. The preparation method according to any one of claims 3 to 5, characterized in that The molar ratio of the Li element in the lithium source of step (2) to the Mn element in the cerium-doped lithium-rich manganese-based precursor of step (1) is (1-1.4):1; Preferably, the mixing in step (2) comprises ball milling.

7. The preparation method according to any one of claims 3 to 6, characterized in that Step (2) the first sintering includes a first stage sintering and a second stage sintering; Preferably, the sintering temperature of the first stage sintering is 300° C. to 600° C.; Preferably, the holding time of the sintering stage is 3h to 8h; Preferably, the sintering temperature of the second stage sintering is 800° C. to 1200° C.; Preferably, the holding time of the second-stage sintering is 8 hours to 16 hours.

8. The preparation method according to any one of claims 3 to 7, characterized in that In the cobalt-boron coating solution of step (3), the molar ratio of the cobalt salt to the boric acid is 1:(1-1.4); Preferably, in the cobalt-boron coating solution of step (3), the mass ratio of the organic solvent to the cerium-doped lithium-rich manganese-based positive electrode material core of step (2) is (20-50):1; Preferably, the second sintering in step (3) is carried out under a protective atmosphere; Preferably, the sintering temperature of the second sintering in step (3) is 250° C. to 350° C.; Preferably, the holding time of the second sintering in step (3) is 1 hour to 4 hours.

9. The preparation method according to any one of claims 3 to 8, characterized in that The mixing in step (4) includes ball milling; Preferably, the coated carbon source in step (4) comprises glucose; Preferably, the mass ratio of the coating intermediate material in step (3) to the coating carbon source in step (4) is (8-12):1; Preferably, the third sintering in step (4) is carried out under a protective atmosphere; Preferably, the sintering temperature of the third sintering in step (4) is 400° C. to 650° C.; Preferably, the holding time of the third sintering in step (4) is 2h to 8h.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the lithium-rich manganese-based positive electrode material according to claim 1 or 2, or the lithium-rich manganese-based positive electrode material prepared by the preparation method according to any one of claims 3 to 9.