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

Abstract

The invention provides a lithium-rich manganese-based positive electrode material, a preparation method thereof and a lithium ion battery, and relates to the field of lithium ion batteries. Comprising a base body, a first coating layer and a second coating layer, the chemical general formula of the matrix is LiaNixCoyMnzMwO (1 + a-b) Rb, M comprises one or more of Al, Mg, Mn, Zr, Ti, W, Nb, Ta, Te, Na, La and Sr, R comprises one or more of Cl, N and S, 1.2 < = a < = 1.4, 0 < = b < = 0.1, 0.25 < = x < = 0.4, 0 < = y < = 0.1, 0.6 < = z < = 0.75, 01t, and 0 < = y < = 0.1. W < = 0.02, and x + y + z + w = 1; the first coating layer comprises spinel phase and / or spinel-like phase lithium manganese oxide; the second coating layer includes a Y-containing compound. And the cycling stability and the ionic conductivity of the lithium-rich manganese-based positive electrode material can be effectively improved.

Description

Technical Field

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

[0002] Compared with single-crystal lithium-rich manganese-based positive electrode materials, polycrystalline lithium-rich manganese-based positive electrode materials have better capacity and rate performance, but insufficient cycle stability. In addition, the primary particles of polycrystalline lithium-rich manganese-based positive electrode materials expand and contract during charging and discharging, causing cracks along the grain boundaries during long cycles, which seriously affects the electrochemical performance, structural stability and safety performance of the battery, and shortens the battery life.

[0003] Current research focuses on molten salt-assisted doping / coating of polycrystalline lithium-rich manganese-based cathode materials, but has yet to clearly define the technical effects of molten salt assistance and whether it achieves grain boundary modification, thereby improving their performance. Furthermore, lithium-rich manganese-based cathode materials themselves suffer from low initial efficiency, poor rate capability, and poor cycling performance.

[0004] Based on this, there is an urgent need to provide a lithium-rich manganese-based positive electrode material to solve the above problems. Summary of the Invention

[0005] The purpose of this application is to provide a lithium-rich manganese-based positive electrode material and a preparation method thereof and a lithium-ion battery to solve the above problems.

[0006] To achieve the above objectives, the present application provides a lithium-rich manganese-based positive electrode material in a first aspect, comprising a substrate and a first coating layer and a second coating layer sequentially stacked on the surface of the substrate; The general chemical formula of the matrix is ​​Li a Ni x Co y Mn z M w O (1+a-b) R b , wherein M includes one or more of Al, Mg, Mn, Zr, Ti, W, Nb, Ta, Te, Na, La and Sr, R includes one or more of Cl, N and S, 1.2≤a≤1.4, 0≤b≤0.1, 0.25≤x≤0.4, 0≤y≤0.1, 0.6≤z≤0.75, 0 <w≤0.02,x+y+z+w=1; The first coating layer comprises spinel phase and / or spinel-like phase lithium manganese oxide; The second coating layer includes a Y-containing compound, where Y includes one or more of Li, Al, Zr, Ce, Mg, Ti, W, La, Co, Cr, and Ca.

[0007] Optionally, the lithium-rich manganese-based positive electrode material meets at least one of the following conditions: (1) In the general chemical formula of the matrix, 1.3≤a≤1.38, 0≤b≤0.02, 0≤y≤0.05, 0 <w≤0.01; (2) M includes one or more of W, Nb, Ta and Ti; (3) R includes Cl; (4) Y includes one or more of Zr, Ti, W, and La; (5) The Y-containing compound includes one or more of oxides, fluorides and phosphates containing Li, Al, Zr, Ti, W, La, Co, Cr and Ca.

[0008] Optionally, the lithium-rich manganese-based positive electrode material meets at least one of the following conditions: (1) The M comprises W and Nb or Ta and Ti; (2) The Y includes Zr and / or La.

[0009] Optionally, the lithium-rich manganese-based positive electrode material meets at least one of the following conditions: (1) The D50 of the substrate is 3 μm-12 μm; (2) The thickness of the first coating layer is 10 nm to 30 nm; (3) The thickness of the second coating layer is 5nm-25nm.

[0010] Optionally, the lithium-rich manganese-based positive electrode material meets at least one of the following conditions: (1) The D50 of the substrate is 4 μm-10 μm; (2) The thickness of the first coating layer is 15 nm to 20 nm; (3) The thickness of the second coating layer is 5nm-15nm.

[0011] A second aspect of the present application provides a method for preparing a lithium-rich manganese-based positive electrode material, comprising: performing a first mixing of nickel-cobalt-manganese hydroxide, a lithium salt, an M source, and a flux to obtain a first mixture, and performing a first sintering of the first mixture to obtain a first sintered product; performing a second mixing of the first sintered product and an acid to obtain a second mixture, performing solid-liquid separation on the second mixture to obtain a solid material, and performing a second sintering on the solid material to obtain a second sintered product; The second sintered product and the Y source are mixed for a third time to obtain a third mixture, and the third mixture is sintered for a third time to obtain a lithium-rich manganese-based positive electrode material.

[0012] Optionally, the above-mentioned method for preparing the lithium-rich manganese-based positive electrode material is the method for preparing the lithium-rich manganese-based positive electrode material of the first aspect of the present application.

[0013] Optionally, the method for preparing the lithium-rich manganese-based positive electrode material satisfies at least one of the following conditions: (1) The M source includes one or more oxides, carbonates and organic salts containing Al, Mg, Mn, Zr, Ti, W, Nb, Ta, Te, Na, La and Sr; (2) The flux comprises one or more of chlorides, nitrates and sulfates containing lithium, sodium and potassium; (3) The acid includes one or more of boric acid, oxalic acid, citric acid and acetic acid; (4) The mass concentration of the acid is 2.5%-15%; (5) The Y source includes one or more of oxides, fluorides and phosphates containing Li, Al, Zr, Ti, W, La, Co, Cr and Ca; (6) The molar ratio of the nickel-cobalt-manganese hydroxide, the Li element in the lithium salt, the M source, and the flux is 1:1.2-1.4:0-0.02:0-5, wherein the M source is not 0; (7) The mass ratio of the flux to the nickel-cobalt-manganese hydroxide is 0-10:1; (8) The mass ratio of the acid to the first sintered product is 0.5-3:1; (9) In the lithium-rich manganese-based positive electrode material, the mass of the element from the Y source is 500ppm-2000ppm.

[0014] Optionally, the method for preparing the lithium-rich manganese-based positive electrode material satisfies at least one of the following conditions: (1) The M source includes one or more oxides, carbonates and organic salts containing W, Nb, Ta and Ti; (2) The flux comprises one or more of lithium-containing chlorides, nitrates, and sulfates; (3) The acid comprises boric acid and / or citric acid; (4) The mass concentration of the acid is 2.5%-12%; (5) The Y source includes one or more of oxides, fluorides and phosphates containing Zr, Ti, W and La.

[0015] Optionally, the method for preparing the lithium-rich manganese-based positive electrode material satisfies at least one of the following conditions: (1) The first sintering temperature rise rate is 1°C / min-4°C / min, the end temperature is 850°C-900°C, and the holding time is 12h-18h; (2) The second sintering temperature is increased at a rate of 1°C / min to 4°C / min, the end temperature is 250°C to 400°C, and the holding time is 4h to 6h; (3) The heating rate of the third sintering is 3°C / min-5°C / min, the end temperature is 350°C-450°C, and the holding time is 4h-6h.

[0016] In a third aspect, the present application provides a lithium-ion battery, comprising the lithium-rich manganese-based positive electrode material or the lithium-rich manganese-based positive electrode material prepared by the method for preparing the lithium-rich manganese-based positive electrode material.

[0017] Compared with the prior art, the advantages of this application include: The lithium-rich manganese-based positive electrode material provided by the present application, firstly, by doping the matrix with M and R elements, grain boundary and bulk doping can be achieved, which can reduce the formation of intergranular microcracks and improve the cycle performance on the one hand, and on the other hand, the Li interlayer spacing can be expanded to facilitate the deintercalation of Li ions, and the MO bond inhibits the loss of lattice oxygen, further stabilizing the structure. At the same time, R anions doped into the O site can improve electronic conductivity and Li ion diffusion rate, thereby improving rate performance; secondly, the spinel phase or spinel-like phase of the first coating layer can improve Li + Diffusion dynamics, and hinder the release of surface O2 and side reactions with the electrolyte, thereby improving the cycle stability; then, the second coating layer can isolate the solid-liquid interface side reactions, improve the cycle stability, and increase the ionic conductivity of the material surface, avoiding the inert oxide coating from reducing the electrochemical activity of the material; finally, by giving full play to the synergistic effect of the first coating layer and the second coating layer, the problem of poor oxidation resistance at high voltage caused by only having the first coating layer is avoided, and the problem of its structure being destroyed during the cycle due to oxygen release and interface side reactions is avoided; this is because the second coating layer, as a fast ion conductor, can improve the surface oxidation resistance of the material to a certain extent, and due to its excellent ionic conductivity and electronic conductivity, it can reduce its initial impedance and cycle growth impedance, and the second coating layer can also diffuse into the grain boundary at a certain temperature, alleviating the grain boundary side reactions and grain expansion during the cycle.

[0018] In the preparation method of the lithium-rich manganese-based positive electrode material provided in the present application, the flux reduces the temperature of the first sintering, which is beneficial to saving energy and reducing costs; subsequently, the pickling process can achieve more uniform modification, while removing surface impurities, reducing residual alkali, and further improving the initial efficiency, stability and electrical properties of the material.

[0019] The lithium-ion battery provided in this application has excellent first efficiency and rate performance and good cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0021] Figure 1 Surface SEM image of the lithium-rich manganese-based positive electrode material provided in Example 1; Figure 2 This is a cross-sectional SEM image of the lithium-rich manganese-based positive electrode material provided in Example 1; Figure 3 EDS element distribution diagram of the W element in the lithium-rich manganese-based positive electrode material provided in Example 1; Figure 4 This is the EDS element distribution diagram of the Nb element in the lithium-rich manganese-based positive electrode material provided in Example 1. DETAILED DESCRIPTION

[0022] First, the solution provided in this application is explained in more detail as follows: In a first aspect, the present application provides a lithium-rich manganese-based positive electrode material, comprising a substrate and a first coating layer and a second coating layer sequentially stacked on the surface of the substrate; The general chemical formula of the matrix is ​​Li a Ni x Co y Mn z M w O (1+a-b) R b , wherein M includes one or more of Al, Mg, Mn, Zr, Ti, W, Nb, Ta, Te, Na, La and Sr, R includes one or more of Cl, N and S, 1.2≤a≤1.4, 0≤b≤0.1, 0.25≤x≤0.4, 0≤y≤0.1, 0.6≤z≤0.75, 0 <w≤0.02,x+y+z+w=1; Optionally, the chemical formula of the matrix is ​​Li a Ni x Co y Mn z M w O (1+a-b) R bwherein a may be 1.2, 1.3, 1.4 or any value between 1.2 and 1.4, b may be 0, 0.05, 0.1 or any value between 0 and 0.1, x may be 0.25, 0.3, 0.35, 0.4 or any value between 0.25 and 0.4, y may be 0, 0.05, 0.1 or any value between 0 and 0.1, z may be 0.6, 0.65, 0.7, 0.75 or any value between 0.6 and 0.75, and w may be 0.0001, 0.0005, 0.0006, 0.001, 0.01, 0.02 or any value greater than 0 and less than or equal to 0.02; Preferably, 0.0002≤w≤0.02; more preferably 0.0006≤w≤0.02; The first coating layer comprises spinel phase and / or spinel-like phase lithium manganese oxide; The second coating layer includes a Y-containing compound, where Y includes one or more of Li, Al, Zr, Ce, Mg, Ti, W, La, Co, Cr, and Ca.

[0023] In some embodiments, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions: (1) In the general chemical formula of the matrix, 1.3≤a≤1.38, 0≤b≤0.02, 0≤y≤0.05, 0 <w≤0.01; Optionally, in the chemical formula of the matrix, a may be 1.30, 1.31, 1.32, 1.33, 1.34, 1.35, 1.36, 1.37, 1.38 or any value between 1.3 and 1.38, b may be 0, 0.00001, 0.0001, 0.001, 0.0015, 0.002, 0.01, 0.02 or any value between 0 and 0.02, y may be 0, 0.00001, 0.0001, 0.001, 0.01, 0.02, 0.03, 0.04, 0.05 or any value between 0 and 0.05, and w may be 0.00001, 0.0001, 0.001, 0.005, 0.01 or any value between greater than 0 and equal to 0.0; Preferably, 0.001≤w≤0.006; It should be noted that when w is too small, the doping effect is poor. When w is too large (w is greater than or equal to 0.02), part of M exists in the form of compounds at the grain boundary or surface, which will affect the Li + transmission; (2) M includes one or more of W, Nb, Ta and Ti; Preferably, M includes W, Nb, Ta and Ti. When these four elements are doped, grain boundary and bulk doping can be achieved simultaneously. On the one hand, the formation of intergranular microcracks can be reduced, and the cycle performance can be improved. On the other hand, the Li interlayer spacing can be expanded, which is beneficial to the deintercalation of Li ions. The MO bond also inhibits the loss of lattice oxygen and further stabilizes the structure. (3) R includes Cl; (4) Y includes one or more of Zr, Ti, W, and La; (5) The Y-containing compound includes one or more of oxides, fluorides and phosphates containing Li, Al, Zr, Ti, W, La, Co, Cr and Ca.

[0024] In some embodiments, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions: (1) The M comprises W and Nb or Ta and Ti; It should be noted that Nb and Ta elements can achieve grain boundary doping, reduce the formation of intergranular microcracks, and improve cycle performance; W and Ti elements are easy to form bulk doping, and their ions can expand the Li interlayer spacing, which is beneficial to the deintercalation of Li ions, and the MO bond inhibits the loss of lattice oxygen, further stabilizing the structure; further, when M includes W and Nb, the synergistic effect of W and Nb can be achieved, and the same is true for Ta and Ti; (2) The Y includes Zr and / or La.

[0025] In some embodiments, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions: (1) The D50 of the substrate is 3 μm-12 μm; Optionally, the D50 of the substrate may be 3 μm, 6 μm, 9 μm, 12 μm, or any value between 3 μm and 12 μm; (2) The thickness of the first coating layer is 10 nm to 30 nm; Optionally, the thickness of the first coating layer may be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, or any value between 10 nm and 30 nm; It should be noted that if the thickness of the first coating layer is too thin, the effect is not good. If the thickness of the first coating layer is too thick, the Li + internal diffusion paths and resistance; (3) The thickness of the second coating layer is 5nm-25nm.

[0026] Optionally, the thickness of the second coating layer may be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, or any value between 5 nm and 25 nm.

[0027] It should be noted that when the thickness of the second coating layer is too thin, the cycle stability cannot be effectively improved; when the thickness of the second coating layer is too thick, the Li ion diffusion path will increase, thereby reducing the specific capacity.

[0028] In some embodiments, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions: (1) The D50 of the substrate is 4 μm-10 μm; Optionally, the D50 of the substrate may be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any value between 4 μm and 10 μm; (2) The thickness of the first coating layer is 15 nm to 20 nm; Optionally, the thickness of the first coating layer may be 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, or any value between 15 nm and 20 nm; (3) The thickness of the second coating layer is 5nm-15nm.

[0029] Optionally, the thickness of the second coating layer may be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm or any value between 5 nm and 15 nm.

[0030] The second aspect of the present application provides a method for preparing the lithium-rich manganese-based positive electrode material, comprising: performing a first mixing of nickel-cobalt-manganese hydroxide, a lithium salt, an M source, and a flux to obtain a first mixture, and performing a first sintering of the first mixture to obtain a first sintered product; performing a second mixing of the first sintered product and an acid to obtain a second mixture, performing solid-liquid separation on the second mixture to obtain a solid material, and performing a second sintering on the solid material to obtain a second sintered product; It should be noted that acid treatment makes H + With some Li + Ion exchange occurs, forming a surface lithium-deficient layered structure, which can be transformed into a spinel phase or a spinel-like phase after a second sintering step; The second sintered product and the Y source are mixed for a third time to obtain a third mixture, and the third mixture is sintered for a third time to obtain a lithium-rich manganese-based positive electrode material.

[0031] In some embodiments, the method for preparing the lithium-rich manganese-based positive electrode material satisfies at least one of the following conditions: (1) The M source includes one or more oxides, carbonates and organic salts containing Al, Mg, Mn, Zr, Ti, W, Nb, Ta, Te, Na, La and Sr; (2) The flux comprises one or more of chlorides, nitrates and sulfates containing lithium, sodium and potassium; It should be noted that molten salt with a low melting point can provide a uniform liquid phase environment for the reaction at a certain dosage and sintering temperature, allowing sufficient contact between the reactants, thereby assisting in the doping of more M sources into the material bulk and grain boundaries; a small amount of flux enters the oxygen site during sintering to replace oxygen and produce a pinning effect on the oxygen element, alleviating excessive oxygen oxidation; after the first sintering treatment, it is cooled to room temperature and the remaining flux is removed by washing with pure water, filtering, and drying; (3) The acid includes one or more of boric acid, oxalic acid, citric acid and acetic acid; It should be noted that when the acid includes boric acid, a shell with cation vacancies can be constructed on the surface of the material. The cation vacancies can activate the lattice oxygen, thereby improving the reversibility of the lattice oxygen during the first charge and discharge, thereby significantly improving the first efficiency. (4) The mass concentration of the acid is 2.5%-15%; Optionally, the mass concentration of the acid can be 2.5%, 3%, 6%, 9%, 12%, 15%, or any value between 2.5% and 15%; It should be noted that when the mass concentration of the acid is lower than 2.5%, the surface ion exchange is too little, resulting in the inability to form a uniform spinel phase; when the mass concentration of the acid is higher than 15%, the material will be over-etched in the acid system, too much active Li will be released, the specific surface area will increase, and the capacity will be affected; after the acid treatment, the material is filtered, washed with water, dried, and then subjected to a second sintering treatment; (5) The Y source includes one or more of oxides, fluorides and phosphates containing Li, Al, Zr, Ti, W, La, Co, Cr and Ca; (6) The molar ratio of the nickel-cobalt-manganese hydroxide, the lithium salt (calculated as Li element), the M source, and the flux is 1:1.2-1.4:0-0.02:0-5, wherein the M source is not 0; Optionally, the molar ratio of nickel cobalt manganese hydroxide, lithium salt (calculated as Li element), M source and flux can be 1:1.2:0.00001:0, 1:1.3:0.00001:0, 1:1.4:0.00001:0, 1:1.2:0.01:0, 1:1.2:0.02:0, 1:1.2:0.001:0.01, 1:1.2:0.001:1, 1:1.2:0.001:5 or any value between 1:1.2-1.4:0-0.02:0-5, wherein the M source is not 0; Preferably, the molar ratio of nickel-cobalt-manganese hydroxide, lithium salt (calculated as Li element), M source and flux is 1:1.2-1.4:0-0.02:3-5; (7) The mass ratio of the flux to the nickel-cobalt-manganese hydroxide is 0-10:1; Optionally, the mass ratio of the flux to the nickel-cobalt-manganese hydroxide may be 0:1, 1:1, 2:1, 4:1, 6:1, 8:1, 10:1, or any value between 0 and 10:1; (8) The mass ratio of the acid to the first sintered product is 0.5-3:1; Optionally, the mass ratio of the acid to the first sintered product may be 0.5:1, 1:1, 2:1, 3:1, or any value between 0.5 and 3:1; It should be noted that when the acid is mixed with the first sintered product, if the acid mass ratio is too small, the surface ion exchange is too small, resulting in the inability to form a uniform spinel phase; In some embodiments, the second mixing time is 10 min-30 min; If the second mixing time is too long, the material will be over-etched in the acid system, and too much active Li will be released, which will increase the specific surface area and affect the capacity. (9) In the lithium-rich manganese-based positive electrode material, the mass of the element from the Y source is 500ppm-2000ppm.

[0032] Optionally, the element mass of the Y source can be 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm, 1500ppm, 2000ppm or any value between 500ppm and 2000ppm; preferably 700ppm-1500ppm.

[0033] It should be noted that when the element mass of the Y source is lower than 500ppm, effective island coating cannot be formed; when the element mass of the Y source is higher than 2000ppm, it will lead to an increase in the Li ion diffusion path and reduce the capacity.

[0034] In some embodiments, the method for preparing the lithium-rich manganese-based positive electrode material satisfies at least one of the following conditions: (1) The M source includes one or more oxides, carbonates and organic salts containing W, Nb, Ta and Ti; Preferably, the M source includes one or more of oxides, carbonates and organic salts containing W and Nb or Ta and Ti; (2) The flux comprises one or more of lithium-containing chlorides, nitrates, and sulfates; (3) The acid comprises boric acid and / or citric acid; (4) The mass concentration of the acid is 2.5%-12%; Optionally, the mass concentration of the acid can be 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12% or any value between 2.5% and 12%.

[0035] (5) The Y source includes one or more of oxides, fluorides and phosphates containing Zr, Ti, W and La.

[0036] Preferably, the Y source includes one or more of oxides, fluorides and phosphates containing Zr and / or La.

[0037] Preferably, the Y source comprises LiZr2(PO4)3 and / or Li7La3Zr2O 12 .

[0038] It should be noted that LiZr2(PO4)3 and Li7La3Zr2O 12 As fast ion conductors, they can improve the surface oxidation resistance of the material to a certain extent. At the same time, due to their excellent ionic conductivity and electronic conductivity, they can reduce their initial impedance and cyclic growth impedance. Finally, some fast ion conductors can also diffuse into the grain boundaries at a certain temperature, alleviating grain boundary side reactions and grain expansion during the cycle.

[0039] It should be noted that coating with Y source can inhibit the side reaction between the material surface and the electrolyte, further improving the cycle stability, while hardly affecting the cation vacancies obtained by acid treatment, and maintaining a high first efficiency after coating; In some embodiments, the method for preparing the lithium-rich manganese-based positive electrode material satisfies at least one of the following conditions: (1) The first sintering temperature rise rate is 1°C / min-4°C / min, the end temperature is 850°C-900°C, and the holding time is 12h-18h; Optionally, the heating rate of the first sintering may be 1°C / min, 2°C / min, 3°C / min, 4°C / min, or any value between 1°C / min and 4°C / min; the endpoint temperature may be 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, or any value between 850°C and 900°C; and the holding time may be 12h, 14h, 16h, 18h, or any value between 12h and 18h. It should be noted that when the temperature of the first sintering is too low, sufficient sintering cannot be achieved. If it is too high, it may lead to particle agglomeration and structural densification, hindering Li ion transport, thereby reducing capacity and increasing energy consumption. (2) The second sintering temperature is increased at a rate of 1°C / min to 4°C / min, the end temperature is 250°C to 400°C, and the holding time is 4h to 6h; Optionally, the heating rate of the second sintering may be 1°C / min, 2°C / min, 3°C / min, 4°C / min, or any value between 1°C / min and 4°C / min; the endpoint temperature may be 250°C, 300°C, 350°C, 400°C, or any value between 250°C and 400°C; and the holding time may be 4h, 5h, 6h, or any value between 4h and 6h. It should be noted that when the temperature of the second sintering is too low, the first coating layer cannot be fully formed. If it is too high, the first coating layer will be too thick, which will also affect the crystal structure and be detrimental to the improvement of the first efficiency. In addition, if the temperature is too high, the structure formed by the second sintering will be destroyed. (3) The heating rate of the third sintering is 3°C / min-5°C / min, the end temperature is 350°C-450°C, and the holding time is 4h-6h.

[0040] Optionally, the heating rate of the third sintering can be 3°C / min, 4°C / min, 5°C / min or any value between 3°C / min-5°C / min, the end temperature can be 350°C, 370°C, 390°C, 410°C, 430°C, 450°C or any value between 350°C-450°C, and the holding time can be 4h, 5h, 6h or any value between 4h-6h.

[0041] It should be noted that when the temperature of the third sintering is too low, effective island coating cannot be formed, and when it is too high, it may cause the Li + It diffuses with the transition metal ions in the material, affecting the formation of the second coating layer. At the same time, too high a temperature will affect the original first coating layer. Moreover, within the range of 350℃-450℃, most of the Y source will be retained, so that it can play the role of a fast ion conductor as a whole.

[0042] In a third aspect, the present application provides a lithium-ion battery, comprising the lithium-rich manganese-based positive electrode material or the lithium-rich manganese-based positive electrode material prepared by the method for preparing the lithium-rich manganese-based positive electrode material.

[0043] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0044] Example 1 This embodiment provides a lithium-rich manganese-based positive electrode material and a preparation method thereof, and the specific preparation steps include: S1: Ni 0.30 Co 0.05 Mn 0.65 (OH)2 precursor, Li2CO3 (calculated as Li element), WO3, Nb2O5 and LiCl are mixed in a molar ratio of 1:1.36:0.004:0.001:4, and then the resulting mixture is subjected to a first sintering treatment in an air atmosphere, heated to 885°C at 3°C / min and kept warm for 14 hours, cooled to room temperature, washed with pure water, filtered, and dried to obtain a W- and Nb-doped first sintered product.

[0045] S2: A boric acid solution with a mass concentration of 12% is obtained by heating and dissolving, and the obtained boric acid solution and the first sintered product are added to a stirrer at a mass ratio of 1.5:1. After being fully stirred, the mixture is filtered, washed with pure water, and filtered, and then placed in a vacuum oven at 120°C for 10 hours. The mixture is then subjected to a second sintering treatment, heated to 350°C at a rate of 3°C / min, and kept at this temperature for 4 hours. After cooling, a surface-modified second sintered product is obtained. S3: The obtained second sintered product is mixed with LiZr2(PO4)3 to obtain a mixture, and then the mixture is subjected to a third sintering treatment, the temperature is increased to 400°C at 4°C / min and kept warm for 6 hours, and after cooling, a lithium-rich manganese-based positive electrode material with an element mass ratio of 987ppm from the Y source is obtained.

[0046] The surface SEM of the lithium-rich manganese-based positive electrode material is shown in Figure 1 shown.

[0047] The SEM cross-section of the lithium-rich manganese-based cathode material is as follows Figure 2 shown.

[0048] The EDS element distribution of W element in the cross section of the lithium-rich manganese-based positive electrode material is as follows Figure 3 shown.

[0049] The EDS element distribution of Nb element in the cross section of the lithium-rich manganese-based positive electrode material is as follows Figure 4 shown.

[0050] Example 2 This embodiment provides a lithium-rich manganese-based positive electrode material and a preparation method thereof, and the specific preparation steps include: S1: Ni 0.30 Co 0.05 Mn 0.65A (OH)2 precursor, Li2CO3 (calculated as Li element), WO3, Nb2O5 and LiCl were mixed in a molar ratio of 1:1.40:0.01:0.01:5, and the resulting mixture was subjected to a first sintering treatment in an air atmosphere, heated to 900°C at a rate of 4°C / min, kept at that temperature for 18 hours, cooled to room temperature, washed with pure water, filtered, and dried to obtain a W- and Nb-doped first sintered product; S2: A boric acid solution with a mass concentration of 15% is obtained by heating and dissolving, and the obtained boric acid solution and the above-mentioned first sintered product are added to a stirrer at a mass ratio of 3:1. After sufficient stirring, the mixture is filtered, washed with pure water, and filtered, and then placed in a vacuum oven at 120°C for 10 hours. Then, a second sintering treatment is performed, the temperature is increased to 400°C at 4°C / min, and the temperature is maintained for 6 hours. After cooling, a surface-modified second sintered product is obtained; S3: The obtained second sintered product is mixed with LiZr2(PO4)3 to obtain a mixture, and then the mixture is subjected to a third sintering treatment, the temperature is increased to 450°C at 5°C / min and kept warm for 6 hours, and after cooling, a lithium-rich manganese-based positive electrode material with an element mass ratio of 1013ppm from the Y source is obtained.

[0051] Example 3 This embodiment provides a lithium-rich manganese-based positive electrode material and a preparation method thereof, and the specific preparation steps include: S1: Ni 0.30 Co 0.05 Mn 0.65 A (OH)2 precursor, Li2CO3 (calculated as Li element), WO3, and Nb2O5 were mixed in a molar ratio of 1:1.2:0.0003:0.0003, and the resulting mixture was subjected to a first sintering treatment in an air atmosphere, heated to 850°C at a rate of 1°C / min, kept at that temperature for 12 hours, cooled to room temperature, washed with pure water, filtered, and dried to obtain a W- and Nb-doped first sintered product; S2: A boric acid solution with a mass concentration of 2.5% is obtained by heating and dissolving, and the obtained boric acid solution and the above-mentioned first sintered product are added to a stirrer at a mass ratio of 0.5:1. After sufficient stirring, the mixture is filtered, washed with pure water, and filtered, and then placed in a vacuum oven at 120°C for 10 hours. Then, a second sintering treatment is performed, and the temperature is increased to 250°C at 1°C / min and kept at this temperature for 4 hours. After cooling, a surface-modified second sintered product is obtained; S3: The obtained second sintered product is mixed with LiZr2(PO4)3 to obtain a mixture, and then the mixture is subjected to a third sintering treatment, the temperature is increased to 350°C at 3°C / min and kept warm for 4 hours, and after cooling, a lithium-rich manganese-based positive electrode material with an element mass ratio of 996ppm from the Y source is obtained.

[0052] Example 4 The difference from Example 1 is that in step S1, WO3 and Nb2O5 are replaced by TiO2 and Ta2O5 respectively.

[0053] Example 5 The difference from Example 1 is that in step S1, Ti and Ta doping are added, specifically: Ni 0.30 Co 0.05 Mn 0.65 (OH)2 precursor, Li2CO3 (calculated as Li element), WO3, Nb2O5, TiO2, Ta2O5 and LiCl are mixed in a molar ratio of 1:1.36:0.001:0.001:0.001:0.001:4.

[0054] Example 6 The difference from Example 1 is that in step S1, Nb2O5 is not added.

[0055] Example 7 The difference from Example 1 is that LiZr2(PO4)3 in step S3 is replaced by Li7La3Zr2O 12 .

[0056] Comparative Example 1 The difference from Example 1 is that in step S1, WO3 and Nb2O5 are not added.

[0057] Comparative Example 2 The difference from Example 1 is that in step S1, WO3 and Nb2O5 are replaced by CeO2 and ZrO2.

[0058] Comparative Example 3 The difference from Example 4 is that in step S1, TiO2 and Ta2O5 are replaced by MgO and La2O3.

[0059] Comparative Example 4 The difference from Example 1 is that step S2 is not performed, the first sintered product and LiZr2(PO4)3 are directly mixed, and the third sintering treatment is performed.

[0060] Comparative Example 5 The difference from Example 1 is that step S3 is not performed.

[0061] Comparative Example 6 The difference from Example 1 is that the preparation order of step S2 and step S3 is replaced.

[0062] Comparative Example 7 The difference from Example 1 is that LiZr2(PO4)3 is replaced by Li3PO4.

[0063] Comparative Example 8 The difference from Example 1 is that in step S2, the terminal heating temperature of the second sintering treatment is 500° C. and the holding time is 4 hours.

[0064] The relevant parameters of the lithium-rich manganese-based positive electrode materials prepared in the above examples and comparative examples are shown in Table 1.

[0065]

[0066] The lithium-rich manganese-based positive electrode materials prepared in the above examples and comparative examples were respectively used to assemble electrode sheets and lithium-ion batteries. The specific method was as follows: the lithium-rich manganese-based positive electrode materials prepared in the above examples and comparative examples, the conductive agent SuperP, the binder polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) were mixed and stirred uniformly in a mass ratio of 90:5:5 to prepare a positive electrode slurry, which was coated on a current collector aluminum foil, dried at 105°C, and then rolled at room temperature to a surface density of 2.8-3.3 g / cm 3 , then punched and cut into φ14mm discs to make positive electrode sheets. Then, button cells are assembled in a glove box in the order of "negative electrode shell-nickel foam-lithium sheet-electrolyte-diaphragm-electrolyte-positive electrode sheet-positive electrode shell". The electrolyte consists of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), containing 1.0M LiPF6; the diameter of the lithium sheet is 18mm, the diameter of the diaphragm is 22mm, and the size of the positive and negative electrode shells is 24mm. The assembled button cell is placed in the mold of the hydraulic sealing machine and a pressure of >450kg / cm is applied. 2 , that is, a sealed button battery is obtained.

[0067] The button batteries prepared in the above examples and comparative examples were subjected to electrochemical performance tests, including initial coulombic efficiency and cycle capacity retention tests. The specific test results are shown in Table 2.

[0068] Among them, the button battery charge and discharge cycle is carried out at 25 ° C, and the blue electric test cabinet is used to detect the charge and discharge cycle characteristics of the button battery. First, the test is carried out in the voltage range of 2.3V-4.52V at a charge and discharge rate of 0.1C. Specifically, it is charged to 4.52V at a constant current of 0.1C, and then charged to a cut-off current of 0.02C at a voltage of 4.52V. After standing for 5 minutes, it is discharged to 2.3V at 0.1C, and the first charge and discharge capacity is recorded. Then, a cycle test is carried out at a charge and discharge rate of 1C. Specifically, it is charged to 4.52V at a constant current of 1C, and then charged to a cut-off current of 0.02C at a voltage of 4.52V. After standing for 5 minutes, it is discharged to 2.3V at 0.1C and stood for 5 minutes. This cycle is repeated for 100 weeks, and the charge and discharge capacity of the 100th cycle is recorded to obtain the battery's first coulombic efficiency and 100-week cycle capacity retention rate. The calculation formula is as follows: Cycle capacity retention (%) = (100th cycle discharge capacity / 1st cycle discharge capacity) × 100%.

[0069]

[0070] analyze: It can be seen from the above tests that the lithium-rich manganese-based positive electrode material provided by the present invention achieves higher discharge capacity, first efficiency, cycle capacity retention rate, etc. through molten salt-assisted doping and double-layer coating under certain reactants and reaction conditions. Among them, comparative examples 1-3 show that it is difficult to achieve better bulk and grain boundary doping without or replacing the doping elements, which in turn affects the discharge capacity and cycle performance; comparative examples 4-8 show that the first coating layer of the spinel / spinel-like phase and the second coating layer formed by the fast ion conductor are indispensable, and changes in the coating, reaction temperature or coating order will be unfavorable for improving the first efficiency, rate and cycle performance.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

[0072] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and to form different embodiments. For example, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this application and should not be construed as an admission or any implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A lithium-rich manganese-based positive electrode material, characterized in that It comprises a base body and a first coating layer and a second coating layer sequentially stacked on the surface of the base body; The general chemical formula of the matrix is ​​Li a Ni x Co y Mn z M w O (1+a-b) R b , wherein M includes one or more of Al, Mg, Mn, Zr, Ti, W, Nb, Ta, Te, Na, La and Sr, R includes one or more of Cl, N and S, 1.2≤a≤1.4, 0≤b≤0.1, 0.25≤x≤0.4, 0≤y≤0.1, 0.6≤z≤0.75, 0 <w≤0.02,x+y+z+w=1; The first coating layer comprises spinel phase and / or spinel-like phase lithium manganese oxide; The second coating layer includes a Y-containing compound, where Y includes one or more of Li, Al, Zr, Ce, Mg, Ti, W, La, Co, Cr, and Ca.

2. The lithium-rich manganese-based positive electrode material according to claim 1, characterized in that At least one of the following conditions is met: (1) In the general chemical formula of the matrix, 1.3≤a≤1.38, 0≤b≤0.02, 0≤y≤0.05, 0 <w≤0.01; (2) M includes one or more of W, Nb, Ta and Ti; (3) R includes Cl; (4) Y includes one or more of Zr, Ti, W, and La; (5) The Y-containing compound includes one or more of oxides, fluorides and phosphates containing Li, Al, Zr, Ti, W, La, Co, Cr and Ca.

3. The lithium-rich manganese-based positive electrode material according to claim 2, characterized in that At least one of the following conditions is met: (1) The M comprises W and Nb or Ta and Ti; (2) The Y includes Zr and / or La.

4. The lithium-rich manganese-based positive electrode material according to any one of claims 1 to 3, characterized in that At least one of the following conditions is met: (1) The D50 of the substrate is 3 μm-12 μm; (2) The thickness of the first coating layer is 10 nm to 30 nm; (3) The thickness of the second coating layer is 5nm-25nm.

5. The lithium-rich manganese-based positive electrode material according to claim 4, characterized in that At least one of the following conditions is met: (1) The D50 of the substrate is 4 μm-10 μm; (2) The thickness of the first coating layer is 15 nm to 20 nm; (3) The thickness of the second coating layer is 5nm-15nm.

6. A method for preparing a lithium-rich manganese-based positive electrode material, characterized in that: include: performing a first mixing of nickel-cobalt-manganese hydroxide, a lithium salt, an M source, and a flux to obtain a first mixture, and performing a first sintering of the first mixture to obtain a first sintered product; performing a second mixing of the first sintered product and an acid to obtain a second mixture, performing solid-liquid separation on the second mixture to obtain a solid material, and performing a second sintering on the solid material to obtain a second sintered product; The second sintered product and the Y source are mixed for a third time to obtain a third mixture, and the third mixture is sintered for a third time to obtain a lithium-rich manganese-based positive electrode material.

7. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 6, characterized in that: At least one of the following conditions is met: (1) The M source includes one or more oxides, carbonates and organic salts containing Al, Mg, Mn, Zr, Ti, W, Nb, Ta, Te, Na, La and Sr; (2) The flux comprises one or more of chlorides, nitrates and sulfates containing lithium, sodium and potassium; (3) The acid includes one or more of boric acid, oxalic acid, citric acid and acetic acid; (4) The mass concentration of the acid is 2.5%-15%; (5) The Y source includes one or more of oxides, fluorides and phosphates containing Li, Al, Zr, Ti, W, La, Co, Cr and Ca; (6) The molar ratio of the nickel-cobalt-manganese hydroxide, the Li element in the lithium salt, the M source, and the flux is 1:1.2-1.4:0-0.02:0-5, wherein the M source is not 0; (7) The mass ratio of the flux to the nickel-cobalt-manganese hydroxide is 0-10:1; (8) The mass ratio of the acid to the first sintered product is 0.5-3:1; (9) In the lithium-rich manganese-based positive electrode material, the mass of the element from the Y source is 500ppm-2000ppm.

8. The method for preparing a lithium-rich manganese-based positive electrode material according to claim 7, characterized in that: At least one of the following conditions is met: (1) The M source includes one or more oxides, carbonates and organic salts containing W, Nb, Ta and Ti; (2) The flux comprises one or more of lithium-containing chlorides, nitrates, and sulfates; (3) The acid comprises boric acid and / or citric acid; (4) The mass concentration of the acid is 2.5%-12%; (5) The Y source includes one or more of oxides, fluorides and phosphates containing Zr, Ti, W and La.

9. The method for preparing a lithium-rich manganese-based positive electrode material according to any one of claims 6 to 8, characterized in that: At least one of the following conditions is met: (1) The first sintering temperature rise rate is 1°C / min-4°C / min, the end temperature is 850°C-900°C, and the holding time is 12h-18h; (2) The second sintering temperature is increased at a rate of 1°C / min to 4°C / min, the end temperature is 250°C to 400°C, and the holding time is 4h to 6h; (3) The heating rate of the third sintering is 3°C / min-5°C / min, the end temperature is 350°C-450°C, and the holding time is 4h-6h.

10. A lithium ion battery, characterized in that: The invention relates to a lithium-rich manganese-based positive electrode material according to any one of claims 1 to 5 or a lithium-rich manganese-based positive electrode material prepared by the method for preparing a lithium-rich manganese-based positive electrode material according to any one of claims 6 to 9.

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