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

Abstract

This application provides a lithium-rich manganese-based cathode material, its preparation method, and a lithium-ion battery, relating to the field of lithium-ion batteries. It includes a substrate and a first coating layer and a second coating layer sequentially stacked on the surface of the substrate; the substrate has the general chemical formula 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

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and more particularly to a lithium-rich manganese-based cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Compared to monocrystalline lithium-rich manganese-based cathode materials, polycrystalline lithium-rich manganese-based cathode materials have better capacity and rate performance, but insufficient cycle stability. Furthermore, during charge and discharge, the expansion and contraction of polycrystalline lithium-rich manganese-based cathode materials can cause 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's lifespan.

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

[0004] Therefore, there is an urgent need to provide a lithium-rich manganese-based cathode material to solve the above problems. Summary of the Invention

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

[0006] To achieve the above objectives, the first aspect of this application provides a lithium-rich manganese-based cathode material, comprising a substrate and a first coating layer and a second coating layer sequentially stacked on the surface of the substrate;

[0007] 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;

[0008] The first coating layer comprises lithium manganese oxide of spinel phase and / or spinel-like phase;

[0009] The second coating layer includes a Y-containing compound, wherein Y includes one or more of Li, Al, Zr, Ce, Mg, Ti, W, La, Co, Cr, and Ca.

[0010] Optionally, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0011] (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;

[0012] (2) M includes one or more of W, Nb, Ta and Ti;

[0013] (3) The R includes Cl;

[0014] (4) The Y includes one or more of Zr, Ti, W, and La;

[0015] (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.

[0016] Optionally, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0017] (1) M includes W and Nb or Ta and Ti;

[0018] (2) The Y includes Zr and / or La.

[0019] Optionally, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0020] (1) The D50 of the matrix is ​​3μm-12μm;

[0021] (2) The thickness of the first coating layer is 10nm-30nm;

[0022] (3) The thickness of the second coating layer is 5nm-25nm.

[0023] Optionally, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0024] (1) The D50 of the matrix is ​​4μm-10μm;

[0025] (2) The thickness of the first coating layer is 15nm-20nm;

[0026] (3) The thickness of the second coating layer is 5nm-15nm.

[0027] A second aspect of this application provides a method for preparing a lithium-rich manganese-based cathode material, comprising:

[0028] Nickel-cobalt-manganese hydroxide, lithium salt, M source and flux are first mixed to obtain a first mixture, and the first mixture is first sintered to obtain a first sintered product;

[0029] The first sintered product and acid are mixed for a second time to obtain a second mixture. The second mixture is then subjected to solid-liquid separation to obtain a solid material. The solid material is then subjected to a second sintering to obtain a second sintered product.

[0030] The second sintered product and the Y source are mixed in a third way to obtain a third mixture, and the third mixture is sintered in a third way to obtain a lithium-rich manganese-based cathode material.

[0031] Optionally, the method for preparing the lithium-rich manganese-based cathode material described above is the method for preparing the lithium-rich manganese-based cathode material according to the first aspect of this application.

[0032] Optionally, the method for preparing the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0033] (1) The M source includes one or more of oxides, carbonates and organic salts containing Al, Mg, Mn, Zr, Ti, W, Nb, Ta, Te, Na, La and Sr;

[0034] (2) The flux includes one or more of the following: lithium, sodium and potassium chlorides, nitrates and sulfates;

[0035] (3) The acid includes one or more of boric acid, oxalic acid, citric acid and acetic acid;

[0036] (4) The mass concentration of the acid is 2.5%-15%;

[0037] (5) The Y source includes one or more of the following: oxides, fluorides and phosphates containing Li, Al, Zr, Ti, W, La, Co, Cr and Ca;

[0038] (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;

[0039] (7) The mass ratio of the flux to the nickel-cobalt-manganese hydroxide is 0-10:1;

[0040] (8) The mass ratio of the acid to the first sintered product is 0.5-3:1;

[0041] (9) In the lithium-rich manganese-based cathode material, the mass of the element from the Y source is 500ppm-2000ppm.

[0042] Optionally, the method for preparing the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0043] (1) The M source includes one or more of oxides, carbonates and organic salts containing W, Nb, Ta and Ti;

[0044] (2) The flux includes one or more of lithium-containing chlorides, nitrates and sulfates;

[0045] (3) The acids include boric acid and / or citric acid;

[0046] (4) The mass concentration of the acid is 2.5%-12%;

[0047] (5) The Y source includes one or more of oxides, fluorides and phosphates containing Zr, Ti, W and La.

[0048] Optionally, the method for preparing the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0049] (1) The heating rate of the first sintering is 1℃ / min-4℃ / min, the final temperature is 850℃-900℃, and the holding time is 12h-18h;

[0050] (2) The heating rate of the second sintering is 1℃ / min-4℃ / min, the final temperature is 250℃-400℃, and the holding time is 4h-6h;

[0051] (3) The heating rate of the third sintering is 3℃ / min-5℃ / min, the final temperature is 350℃-450℃, and the holding time is 4h-6h.

[0052] A third aspect of this application provides a lithium-ion battery, comprising the aforementioned lithium-rich manganese-based cathode material or a lithium-rich manganese-based cathode material prepared by the aforementioned method.

[0053] Compared with the prior art, the beneficial effects of this application include:

[0054] The lithium-rich manganese-based cathode material provided in this application, firstly, achieves grain boundary and bulk phase doping through matrix doping with M and R elements. This reduces the formation of intergranular microcracks and improves cycle performance, while also widening the Li interlayer spacing, which facilitates Li ion insertion / extraction. Furthermore, the M and R bonds suppress lattice oxygen loss, further stabilizing the structure. Simultaneously, R anion doping to the O sites improves electronic conductivity and Li ion diffusion rate, thereby improving rate performance. Secondly, the spinel or spinel-like phase in the first coating layer can enhance Li... + The diffusion kinetics are improved, and the surface O2 release and side reactions with the electrolyte are hindered, thereby improving cycling stability. Then, the second coating layer can isolate solid-liquid interface side reactions, improve cycling stability, and increase the ionic conductivity of the material surface, avoiding the reduction of electrochemical activity by inert oxide coating. Finally, by leveraging the synergistic effect of the first and second coating layers, the problem of poor oxidation resistance at high voltage and structural damage due to oxygen release and interface side reactions during cycling, which is caused by only having the first coating layer, 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. At the same time, due to its excellent ionic and electronic conductivity, it can reduce its initial impedance and cycle growth impedance. Furthermore, the second coating layer can diffuse into the grain boundaries at certain temperatures, alleviating grain boundary side reactions and grain expansion during cycling.

[0055] The method for preparing lithium-rich manganese-based cathode material provided in this application uses a flux to lower the temperature of the first sintering, which helps to save energy and reduce costs. Subsequently, the acid washing process can achieve more uniform modification, while removing surface impurities and reducing residual alkali, further improving the material's initial efficiency, stability and electrical performance.

[0056] The lithium-ion battery provided in this application has excellent initial efficiency and rate performance, and good cycle stability. Attached Figure Description

[0057] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0058] Figure 1 The surface SEM image of the lithium-rich manganese-based cathode material provided in Example 1;

[0059] Figure 2 A cross-sectional SEM image of the lithium-rich manganese-based cathode material provided in Example 1;

[0060] Figure 3 EDS elemental distribution diagram of W element in the lithium-rich manganese-based cathode material provided in Example 1;

[0061] Figure 4 The image shows the EDS elemental distribution of Nb in the lithium-rich manganese-based cathode material provided in Example 1. Detailed Implementation

[0062] First, the solution provided in this application will be explained in more detail as follows:

[0063] The first aspect of this application provides a lithium-rich manganese-based cathode material, comprising a substrate and a first coating layer and a second coating layer sequentially stacked on the surface of the substrate;

[0064] 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;

[0065] Optionally, in the matrix with the general chemical formula Li a Ni x Co y Mn z M w O (1+a-b) R b In this context, a can be any value between 1.2, 1.3, 1.4, or 1.2-1.4; b can be any value between 0, 0.05, 0.1, or 0-0.1; x can be any value between 0.25, 0.3, 0.35, 0.4, or 0.25-0.4; y can be any value between 0, 0.05, 0.1, or 0-0.1; z can be any value between 0.6, 0.65, 0.7, 0.75, or 0.6-0.75; and w can be any value between 0.0001, 0.0005, 0.0006, 0.001, 0.01, 0.02, or greater than 0 and less than or equal to 0.02.

[0066] Preferably, 0.0002 ≤ w ≤ 0.02; more preferably, 0.0006 ≤ w ≤ 0.02.

[0067] The first coating layer comprises lithium manganese oxide of spinel phase and / or spinel-like phase;

[0068] The second coating layer includes a Y-containing compound, wherein Y includes one or more of Li, Al, Zr, Ce, Mg, Ti, W, La, Co, Cr, and Ca.

[0069] In some embodiments, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0070] (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;

[0071] Optionally, in the general chemical formula of the matrix, a can be any value between 1.30, 1.31, 1.32, 1.33, 1.34, 1.35, 1.36, 1.37, 1.38 or 1.3-1.38; b can be any value between 0, 0.00001, 0.0001, 0.001, 0.0015, 0.002, 0.01, 0.02 or 0-0.02; y can be any value between 0, 0.00001, 0.0001, 0.001, 0.01, 0.02, 0.03, 0.04, 0.05 or 0-0.05; and w can be any value between 0.00001, 0.0001, 0.001, 0.005, 0.01 or greater than 0 and less than or equal to 0.0.

[0072] Preferably, 0.001 ≤ w ≤ 0.006;

[0073] It is important to note that when w is too low, the doping effect is poor; when w is too high (w ≥ 0.02), some M exists as compounds at grain boundaries or surfaces, which can affect the reaction of Li. + The transmission;

[0074] (2) M includes one or more of W, Nb, Ta and Ti;

[0075] Preferably, M includes W, Nb, Ta and Ti. When these four elements are doped, grain boundary and bulk phase doping can be achieved simultaneously. On the one hand, it can reduce the formation of intergranular microcracks and improve cycle performance. On the other hand, it can expand the Li interlayer spacing, which is conducive to the insertion and extraction of Li ions. Moreover, the MO bond inhibits the loss of lattice oxygen and further stabilizes the structure.

[0076] (3) The R includes Cl;

[0077] (4) The Y includes one or more of Zr, Ti, W, and La;

[0078] (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.

[0079] In some embodiments, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0080] (1) M includes W and Nb or Ta and Ti;

[0081] It is worth noting that Nb and Ta elements can achieve grain boundary doping, reducing the formation of intergranular microcracks and improving cycle performance; W and Ti elements are easy to form bulk doping, and their ions can expand the Li interlayer spacing, which is conducive to the insertion and extraction of Li ions, and the MO bond inhibits the loss of lattice oxygen, further stabilizing the structure; furthermore, when M includes W and Nb, the synergistic effect of W and Nb can be achieved, and the same applies to Ta and Ti.

[0082] (2) The Y includes Zr and / or La.

[0083] In some embodiments, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0084] (1) The D50 of the matrix is ​​3μm-12μm;

[0085] Optionally, the D50 of the substrate can be any value between 3μm, 6μm, 9μm, 12μm, or 3μm-12μm;

[0086] (2) The thickness of the first coating layer is 10nm-30nm;

[0087] Optionally, the thickness of the first coating layer can be any value between 10nm, 15nm, 20nm, 25nm, 30nm, or 10nm-30nm;

[0088] It should be noted that if the first coating layer is too thin, the effect will be poor; if the first coating layer is too thick, it will increase the Li... + Inward diffusion paths and resistance;

[0089] (3) The thickness of the second coating layer is 5nm-25nm.

[0090] Optionally, the thickness of the second coating layer can be any value between 5nm, 10nm, 15nm, 20nm, 25nm, or 5nm-25nm.

[0091] It should be noted that when the thickness of the second coating layer is too thin, it cannot effectively improve the cycling stability; when the thickness of the second coating layer is too thick, it will lead to an increase in the diffusion path of Li ions, thereby reducing the specific capacity.

[0092] In some embodiments, the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0093] (1) The D50 of the matrix is ​​4μm-10μm;

[0094] Optionally, the D50 of the substrate can be any value between 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or 4μm-10μm;

[0095] (2) The thickness of the first coating layer is 15nm-20nm;

[0096] Optionally, the thickness of the first coating layer can be any value between 15nm, 16nm, 17nm, 18nm, 19nm, 20nm or 15nm-20nm;

[0097] (3) The thickness of the second coating layer is 5nm-15nm.

[0098] Optionally, the thickness of the second coating layer can be any value between 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, or 5nm-15nm.

[0099] A second aspect of this application provides a method for preparing the lithium-rich manganese-based cathode material, comprising:

[0100] Nickel-cobalt-manganese hydroxide, lithium salt, M source and flux are first mixed to obtain a first mixture, and the first mixture is first sintered to obtain a first sintered product;

[0101] The first sintered product and acid are mixed for a second time to obtain a second mixture. The second mixture is then subjected to solid-liquid separation to obtain a solid material. The solid material is then subjected to a second sintering to obtain a second sintered product.

[0102] It should be noted that acid treatment causes H to... + With some Li + Ion exchange occurs, forming a lithium-deficient layered structure on the surface, which can be further transformed into a spinel phase or a spinel-like phase through a second sintering process;

[0103] The second sintered product and the Y source are mixed in a third way to obtain a third mixture, and the third mixture is sintered in a third way to obtain a lithium-rich manganese-based cathode material.

[0104] In some embodiments, the method for preparing the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0105] (1) The M source includes one or more of oxides, carbonates and organic salts containing Al, Mg, Mn, Zr, Ti, W, Nb, Ta, Te, Na, La and Sr;

[0106] (2) The flux includes one or more of the following: lithium, sodium and potassium chlorides, nitrates and sulfates;

[0107] It is important to note that molten salts with lower melting points, when used in a certain amount and at a certain sintering temperature, can provide a uniform liquid phase environment for the reaction, allowing the reactants to come into full contact, thereby assisting the M source to be doped more into the bulk phase and grain boundaries of the material; a small portion of the flux enters the oxygen sites through sintering to replace oxygen and exerts a pinning effect on the oxygen element, thus alleviating the excessive oxidation of oxygen; after the first sintering treatment, the mixture is cooled to room temperature and then washed with pure water, filtered, and dried to remove the remaining flux;

[0108] (3) The acid includes one or more of boric acid, oxalic acid, citric acid and acetic acid;

[0109] It should be noted that when the acid includes boric acid, it can create a shell with cation vacancies on the material surface. The cation vacancies can activate lattice oxygen, which improves the reversibility of lattice oxygen during the first charge and discharge, thereby significantly improving the first efficiency.

[0110] (4) The mass concentration of the acid is 2.5%-15%;

[0111] Optionally, the mass concentration of the acid can be 2.5%, 3%, 6%, 9%, 12%, 15%, or any value between 2.5% and 15%.

[0112] It should be noted that when the mass concentration of acid is below 2.5%, the surface ion exchange is too small, resulting in the inability to form a uniform spinel phase; when the mass concentration of acid is above 15%, it will cause the material to be over-etched in the acid system, resulting in too much active Li being extracted, increasing the specific surface area, and affecting the capacity. After acid treatment, the material is filtered, washed with water, dried, and then subjected to a second sintering treatment.

[0113] (5) The Y source includes one or more of the following: oxides, fluorides and phosphates containing Li, Al, Zr, Ti, W, La, Co, Cr and Ca;

[0114] (6) The molar ratio of the nickel-cobalt-manganese hydroxide, the lithium salt (calculated based on 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;

[0115] Optionally, the molar ratio of nickel cobalt manganese hydroxide, lithium salt (based on Li element), M source and flux can be any value between 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 1:1.2-1.4:0-0.02:0-5, wherein the M source is not 0;

[0116] Preferably, the molar ratio of nickel cobalt manganese hydroxide, lithium salt (based on Li element), M source and flux is 1:1.2-1.4:0-0.02:3-5;

[0117] (7) The mass ratio of the flux to the nickel-cobalt-manganese hydroxide is 0-10:1;

[0118] Optionally, the mass ratio of flux to nickel cobalt manganese hydroxide can be 0:1, 1:1, 2:1, 4:1, 6:1, 8:1, 10:1 or any value between 0 and 10:1;

[0119] (8) The mass ratio of the acid to the first sintered product is 0.5-3:1;

[0120] Optionally, the mass ratio of acid to the first sintered product can be any value between 0.5:1, 1:1, 2:1, 3:1, or 0.5:3:1;

[0121] It should be noted that when the acid is mixed with the first sintering product, if the mass ratio of the acid is too small, there will be too little surface ion exchange, which will prevent the formation of a uniform spinel phase.

[0122] In some embodiments, the second mixing time is 10 min-30 min;

[0123] If the second mixing time is too long, it will cause the material to be over-etched in the acid system, resulting in too much active Li being extracted, increasing the specific surface area, and affecting the capacity performance.

[0124] (9) In the lithium-rich manganese-based cathode material, the mass of the element from the Y source is 500ppm-2000ppm.

[0125] Optionally, the elemental mass of the Y source can be any value between 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm, 1500ppm, 2000ppm or 500ppm-2000ppm; preferably 700ppm-1500ppm.

[0126] It should be noted that when the elemental mass of the Y source is below 500 ppm, effective island-like coating cannot be formed; when the elemental mass of the Y source is above 2000 ppm, the excessively high concentration will increase the diffusion path of Li ions and reduce the capacity.

[0127] In some embodiments, the method for preparing the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0128] (1) The M source includes one or more of oxides, carbonates and organic salts containing W, Nb, Ta and Ti;

[0129] Preferably, the M source comprises one or more of oxides, carbonates, and organic salts containing W and Nb or Ta and Ti;

[0130] (2) The flux includes one or more of lithium-containing chlorides, nitrates and sulfates;

[0131] (3) The acids include boric acid and / or citric acid;

[0132] (4) The mass concentration of the acid is 2.5%-12%;

[0133] 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%.

[0134] (5) The Y source includes one or more of oxides, fluorides and phosphates containing Zr, Ti, W and La.

[0135] Preferably, the Y source includes one or more of oxides, fluorides, and phosphates containing Zr and / or La.

[0136] Preferably, the Y source includes LiZr2(PO4)3 and / or Li7La3Zr2O 12 .

[0137] It should be noted that LiZr2(PO4)3 and Li7La3Zr2O 12As fast ion conductors, they can improve the oxidation resistance of material surfaces to a certain extent. At the same time, due to their excellent ionic and electronic conductivity, they can reduce the initial impedance and cyclic growth impedance. Finally, some fast ion conductors can diffuse into the grain boundaries at certain temperatures, alleviating grain boundary side reactions and grain expansion during the cycling process.

[0138] It should be noted that coating with Y source and other substances can suppress side reactions between the material surface and the electrolyte, further improve cycle stability, and at the same time hardly affect the cation vacancies obtained by acid treatment, maintaining a high initial efficiency after coating.

[0139] In some embodiments, the method for preparing the lithium-rich manganese-based cathode material satisfies at least one of the following conditions:

[0140] (1) The heating rate of the first sintering is 1℃ / min-4℃ / min, the final temperature is 850℃-900℃, and the holding time is 12h-18h;

[0141] Optionally, the heating rate of the first sintering can be any value between 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min or 1℃ / min-4℃ / min, the final temperature can be any value between 850℃, 860℃, 870℃, 880℃, 890℃, 900℃ or 850℃-900℃, and the holding time can be any value between 12h, 14h, 16h, 18h or 12h-18h.

[0142] It should be noted that if the temperature of the first sintering is too low, sintering cannot be fully completed, while if it is too high, it may lead to particle agglomeration and structural densification, which will hinder the transport of Li ions, thereby reducing capacity and increasing energy consumption.

[0143] (2) The heating rate of the second sintering is 1℃ / min-4℃ / min, the final temperature is 250℃-400℃, and the holding time is 4h-6h;

[0144] Optionally, the heating rate of the second sintering can be any value between 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min or 1℃ / min-4℃ / min, the final temperature can be any value between 250℃, 300℃, 350℃, 400℃ or 250℃-400℃, and the holding time can be any value between 4h, 5h, 6h or 4h-6h.

[0145] It should be noted that when the temperature of the second sintering is too low, the first coating layer cannot be fully formed; when it is too high, the first coating layer becomes too thick, which also affects the crystal structure and is not conducive to improving the first effect. Furthermore, excessively high temperature will destroy the structure formed by the second sintering.

[0146] (3) The heating rate of the third sintering is 3℃ / min-5℃ / min, the final temperature is 350℃-450℃, and the holding time is 4h-6h.

[0147] Optionally, the heating rate of the third sintering can be any value between 3℃ / min, 4℃ / min, 5℃ / min or 3℃ / min-5℃ / min, the final temperature can be any value between 350℃, 370℃, 390℃, 410℃, 430℃, 450℃ or 350℃-450℃, and the holding time can be any value between 4h, 5h, 6h or 4h-6h.

[0148] It is important to note that if the third sintering temperature is too low, an effective island-like coating cannot be formed; if it is too high, it may cause the Li in the fast ion conductor to saturate. + Interdiffusion with transition metal ions in the material affects the formation of the second coating layer, while excessively high temperatures can affect the original first coating layer; furthermore, within the temperature range of 350℃-450℃, most of the Y source is retained, thus enabling it to function as a fast ion conductor as a whole.

[0149] A third aspect of this application provides a lithium-ion battery, comprising the aforementioned lithium-rich manganese-based cathode material or a lithium-rich manganese-based cathode material prepared by the aforementioned method.

[0150] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0151] Example 1

[0152] This embodiment provides a lithium-rich manganese-based cathode material and its preparation method, the specific preparation steps of which include:

[0153] S1: Ni 0.30 Co 0.05 Mn 0.65 (OH)2 precursor, Li2CO3 (based on Li element), WO3, Nb2O5 and LiCl were mixed in a molar ratio of 1:1.36:0.004:0.001:4. The resulting mixture was then subjected to a first sintering treatment in air atmosphere. The temperature was increased to 885℃ at 3℃ / min and held for 14h. After cooling to room temperature, the mixture was washed with pure water, filtered, and dried to obtain the W and Nb doped first sintered product.

[0154] S2: A boric acid solution with a mass concentration of 12% was obtained by heating and dissolving. The obtained boric acid solution and the first sintering product were added to a stirrer at a mass ratio of 1.5:1. After thorough stirring, the mixture was filtered, washed with pure water, and vacuum filtered. Then, it was placed in a vacuum oven at 120°C and dried for 10 hours. Then, a second sintering treatment was performed. The temperature was increased to 350°C at 3°C / min and held for 4 hours. After cooling, a second sintering product with surface modification was obtained.

[0155] S3: The obtained second sintering product is mixed with LiZr2(PO4)3 to obtain a mixture. The mixture is then subjected to a third sintering treatment. The temperature is increased to 400℃ at 4℃ / min and held for 6h. After cooling, a lithium-rich manganese-based cathode material with an element mass ratio of 987ppm from the Y source is obtained.

[0156] Surface SEM images of the lithium-rich manganese-based cathode material are shown below. Figure 1 As shown.

[0157] SEM images of the cross-section of the lithium-rich manganese-based cathode material are shown below. Figure 2 As shown.

[0158] The EDS elemental distribution of W in the cross-section of this lithium-rich manganese-based cathode material is as follows: Figure 3 As shown.

[0159] The EDS elemental distribution of Nb in the cross section of this lithium-rich manganese-based cathode material is as follows: Figure 4 As shown.

[0160] Example 2

[0161] This embodiment provides a lithium-rich manganese-based cathode material and its preparation method, the specific preparation steps of which include:

[0162] S1: Ni 0.30 Co 0.05 Mn 0.65 (OH)2 precursor, Li2CO3 (based on Li element), WO3, Nb2O5 and LiCl were mixed in a molar ratio of 1:1.40:0.01:0.01:5. The resulting mixture was then subjected to a first sintering treatment in air atmosphere. The temperature was increased to 900℃ at 4℃ / min and held for 18h. After cooling to room temperature, the mixture was washed with pure water, filtered, and dried to obtain the first sintered product doped with W and Nb.

[0163] S2: A boric acid solution with a mass concentration of 15% is obtained by heating and dissolving. The obtained boric acid solution is added to the stirrer with the first sintering product at a mass ratio of 3:1. After thorough stirring, the product is filtered, washed with pure water, and vacuum filtered. Then, it is placed in a vacuum oven at 120°C and dried for 10 hours. Then, a second sintering treatment is performed. The temperature is increased to 400°C at 4°C / min and held for 6 hours. After cooling, a surface-modified second sintering product is obtained.

[0164] S3: The obtained second sintering product is mixed with LiZr2(PO4)3 to obtain a mixture. The mixture is then subjected to a third sintering treatment. The temperature is increased to 450℃ at 5℃ / min and held for 6h. After cooling, a lithium-rich manganese-based cathode material with an element mass ratio of 1013ppm from the Y source is obtained.

[0165] Example 3

[0166] This embodiment provides a lithium-rich manganese-based cathode material and its preparation method, the specific preparation steps of which include:

[0167] S1: Ni 0.30 Co 0.05 Mn 0.65 (OH)2 precursor, Li2CO3 (based on Li element), WO3 and Nb2O5 were mixed in a molar ratio of 1:1.2:0.0003:0.0003. The resulting mixture was then subjected to a first sintering treatment in air atmosphere. The temperature was increased to 850℃ at 1℃ / min and held for 12h. After cooling to room temperature, the mixture was washed with pure water, filtered, and dried to obtain the first sintered product doped with W and Nb.

[0168] S2: A boric acid solution with a mass concentration of 2.5% was obtained by heating and dissolving. The obtained boric acid solution and the first sintering product were added to a stirrer at a mass ratio of 0.5:1. After thorough stirring, the mixture was filtered, washed with pure water, and vacuum filtered. Then, it was placed in a vacuum oven at 120°C and dried for 10 hours. Then, a second sintering treatment was performed. The temperature was increased to 250°C at 1°C / min and held for 4 hours. After cooling, a second sintering product with surface modification was obtained.

[0169] S3: The obtained second sintering product is mixed with LiZr2(PO4)3 to obtain a mixture. The mixture is then subjected to a third sintering treatment. The temperature is increased to 350℃ at 3℃ / min and held for 4h. After cooling, a lithium-rich manganese-based cathode material with an element mass ratio of 996ppm from the Y source is obtained.

[0170] Example 4

[0171] The difference from Example 1 is that in step S1, WO3 and Nb2O5 are replaced with TiO2 and Ta2O5, respectively.

[0172] Example 5

[0173] The difference from Example 1 is that in step S1, Ti and Ta doping are added, specifically: Ni is doped with... 0.30 Co 0.05 Mn 0.65The (OH)2 precursor, Li2CO3 (based on Li element), WO3, Nb2O5, TiO2, Ta2O5 and LiCl were mixed in a molar ratio of 1:1.36:0.001:0.001:0.001:0.001:4.

[0174] Example 6

[0175] The difference from Example 1 is that Nb2O5 is not added in step S1.

[0176] Example 7

[0177] The difference from Example 1 is that LiZr2(PO4)3 in step S3 is replaced with Li7La3Zr2O. 12 .

[0178] Comparative Example 1

[0179] The difference from Example 1 is that WO3 and Nb2O5 are not added in step S1.

[0180] Comparative Example 2

[0181] The difference from Example 1 is that in step S1, WO3 and Nb2O5 are replaced with CeO2 and ZrO2.

[0182] Comparative Example 3

[0183] The difference from Example 4 is that in step S1, TiO2 and Ta2O5 are replaced with MgO and La2O3.

[0184] Comparative Example 4

[0185] The difference from Example 1 is that step S2 is omitted, and the first sintering product and LiZr2(PO4)3 are directly mixed and then subjected to a third sintering treatment.

[0186] Comparative Example 5

[0187] The difference from Example 1 is that step S3 is not performed.

[0188] Comparative Example 6

[0189] The difference from Example 1 is that the preparation order of steps S2 and S3 is replaced.

[0190] Comparative Example 7

[0191] The difference from Example 1 is that LiZr2(PO4)3 is replaced with Li3PO4.

[0192] Comparative Example 8

[0193] The difference from Example 1 is that in step S2, the final heating temperature of the second sintering treatment is 500°C and the holding time is 4 hours.

[0194] The relevant parameters of the lithium-rich manganese-based cathode materials prepared in the above embodiments and comparative examples are shown in Table 1.

[0195]

[0196] The lithium-rich manganese-based cathode materials prepared in the above examples and comparative examples were used to assemble electrode sheets and lithium-ion batteries, respectively. Specifically, the lithium-rich manganese-based cathode 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 evenly at a mass ratio of 90:5:5 to form a cathode slurry. This slurry was coated onto a current collector aluminum foil, dried at 105°C, and then rolled at room temperature until the areal density reached 2.8-3.3 g / cm³. 3 Then, the cells are punched and cut into φ14mm round pieces to form the positive electrode. Next, the coin cells are assembled in a glove box in the following order: negative electrode shell - nickel foam - lithium sheet - electrolyte - separator - 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 lithium sheet diameter is 18mm, the separator diameter is 22mm, and the positive and negative electrode shells are 24mm in size. The assembled coin cells are placed in the mold cavity of a hydraulic sealing machine and pressure >450kg / cm² is applied. 2 This results in a sealed button cell battery.

[0197] The coin cells 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.

[0198] The button cell charge-discharge cycle test was conducted at 25°C using a Blue Electric test cabinet to examine its charge-discharge cycle characteristics. First, the test was performed at a charge-discharge rate of 0.1C within a voltage range of 2.3V-4.52V. Specifically, the battery was charged at a constant current of 0.1C to 4.52V, then charged at a constant voltage of 4.52V to a cutoff current of 0.02C. After a 5-minute rest, the battery was discharged at 0.1C to 2.3V, and the initial charge-discharge capacity was recorded. Then, the cycle test was performed at a charge-discharge rate of 1C. Specifically, the battery was charged at a constant current of 1C to 4.52V, then charged at a constant voltage of 4.52V to a cutoff current of 0.02C. After a 5-minute rest, the battery was discharged at 0.1C to 2.3V, and rested for another 5 minutes. This cycle was repeated 100 times, and the charge-discharge capacity of the 100th cycle was recorded. The initial coulombic efficiency and the 100-cycle capacity retention rate were calculated using the following formulas:

[0199] Cycle capacity retention (%) = (Discharge capacity of the 100th cycle / Discharge capacity of the 1st cycle) × 100%.

[0200]

[0201] analyze:

[0202] As can be seen from the above tests, the lithium-rich manganese-based cathode material provided by the present invention achieves high discharge capacity, first efficiency, and cycle capacity retention through molten salt-assisted doping and double-layer coating under certain reactant and reaction conditions. Comparative Examples 1-3 show that it is difficult to achieve good bulk phase and grain boundary doping effects by lacking or replacing doping elements, which in turn affects discharge capacity and cycle performance. Comparative Examples 4-8 show that the first coating layer of spinel / spinel-like phase and the second coating layer formed by fast ion conductor are indispensable. Changes in the coating material, reaction temperature, or coating sequence will be detrimental to improving first efficiency, rate capability, and cycle performance.

[0203] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0204] Furthermore, those skilled in the art will understand 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 form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A lithium-rich manganese-based cathode material, characterized in that, It includes 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 Where M includes one or more of Ti, W, Nb, and Ta, 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 lithium manganese oxide of spinel phase and / or spinel-like phase; The second coating layer comprises a Y-containing compound, wherein the Y includes Zr and / or La; and the Y further includes lithium; The second coating layer serves as a fast ion conductor; The preparation method of the lithium-rich manganese-based cathode material includes: Nickel-cobalt-manganese hydroxide, lithium salt, M source and flux are first mixed to obtain a first mixture, and the first mixture is first sintered to obtain a first sintered product; The first sintered product and acid are mixed for a second time to obtain a second mixture. The second mixture is then subjected to solid-liquid separation to obtain a solid material. The solid material is then subjected to a second sintering to obtain a second sintered product. The second sintered product and the Y source are mixed in a third way to obtain a third mixture, and the third mixture is sintered in a third way to obtain a lithium-rich manganese-based cathode material. The flux includes one or more of lithium, sodium, and potassium chlorides and sulfates; The heating rate of the first sintering is 1℃ / min-4℃ / min, the final temperature is 850℃-900℃, and the holding time is 12h-18h. The heating rate of the second sintering is 1℃ / min-4℃ / min, the final temperature is 250℃-400℃, and the holding time is 4h-6h. The heating rate of the third sintering is 3℃ / min-5℃ / min, the final temperature is 350℃-450℃, and the holding time is 4h-6h.

2. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, At least one of the following conditions must be 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) The R includes Cl; (3) The Y-containing compound includes one or more of the following: oxides, fluorides and phosphates containing Zr and La.

3. The lithium-rich manganese-based cathode material according to claim 1 or 2, characterized in that, At least one of the following conditions must be met: (1) The D50 of the matrix is ​​3μm-12μm; (2) The thickness of the first coating layer is 10nm-30nm; (3) The thickness of the second coating layer is 5nm-25nm.

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

5. The lithium-rich manganese-based cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The M source includes one or more of oxides, carbonates and organic salts containing Ti, W, Nb and Ta; (2) The acid includes one or more of boric acid, oxalic acid, citric acid and acetic acid; (3) The mass concentration of the acid is 2.5%-15%; (4) The Y source includes one or more of the following: oxides, fluorides and phosphates containing Zr and La; (5) 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; (6) The mass ratio of the flux to the nickel-cobalt-manganese hydroxide is 0-10:1; (7) The mass ratio of the acid to the first sintered product is 0.5-3:1; (8) In the lithium-rich manganese-based cathode material, the mass of the element from the Y source is 500ppm-2000ppm.

6. The lithium-rich manganese-based cathode material according to claim 5, characterized in that, At least one of the following conditions must be met: (1) The acid includes boric acid and / or citric acid; (2) The mass concentration of the acid is 2.5%-12%.

7. A lithium-ion battery, characterized in that, Includes the lithium-rich manganese-based cathode material according to any one of claims 1-6.

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