Coated lithium-rich manganese-based positive electrode material as well as preparation method and application thereof

Abstract

The invention provides a coated lithium-rich manganese-based positive electrode material and a preparation method and application thereof.The preparation method comprises the following steps that a lithium-rich manganese-based precursor and a lithium source are mixed and subjected to primary roasting, smashing and sieving, and a lithium-rich manganese-based primary smashed material is obtained; the lithium-rich manganese-based primary crushed material and a coprecipitation reaction raw material liquid phase are mixed for a coprecipitation reaction, coprecipitation reaction raw materials comprise a metal salt solution, a precipitator solution and a complexing agent solution, and a coated lithium-rich manganese-based precursor is obtained; a lithium source and the coated lithium-rich manganese-based precursor are mixed and subjected to secondary roasting, and the coated lithium-rich manganese-based positive electrode material is obtained. According to the preparation method, the lithium-rich manganese-based positive electrode material with a stable crystal structure can be prepared by coating a nanoscale spinel material precursor, so that the problem that oxygen loss and voltage attenuation in a Li2MnO3 nano domain region are induced when lattice stress continuously accumulated by co-lattice Li2MnO3 reaches a critical value can be relieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to a coated lithium-rich manganese-based cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] The long cruising range of vehicle-mounted lithium-ion batteries is a problem for the popularization and application of electric vehicles. In order to improve the energy density of the batteries, a lithium-rich manganese-based layered material, which is a high-energy density material that has been studied a lot currently, is used. The lithium-rich manganese-based layered oxide material (the molecular formula can be abbreviated as Li 1+x TM 1-x O2, or can also be written as xLi2MnO3·(1-x)LiTMO2 according to its structural composition, where TM represents transition metal elements such as Ni, Co, or Mn, and 0 < x < 1) has attracted extensive research and attention due to its high capacity (>250 mAh / g) and low cost (less content of expensive metals Co and Ni), and is considered as an ideal cathode material for the next generation of high-energy lithium-ion batteries.

[0003] However, there are still some problems in the industrial application of the current lithium-rich manganese-based materials, mainly including: side reactions related to the surface and interface caused by the irreversible release of lattice oxygen under high voltage, such as oxygen vacancies, migration and dissolution of transition metal ions, structural evolution, and electrolyte consumption, etc., which will cause rapid attenuation of the capacity and voltage of the lithium-rich manganese-based layered cathode material, seriously affecting its practical application.

[0004] Although the voltage attenuation problem leads to continuous energy loss and hinders commercialization, the prerequisite driving force for this phenomenon still has no scientific explanation. In the prior art, through in-situ X-ray coherent diffraction imaging technology at the nanoscale, it is revealed that nanoscale strain and lattice displacement are the original driving forces for the structural degradation and oxygen loss of the lithium-rich oxide cathode material, and this effect causes rapid voltage attenuation of the lithium-rich manganese-based layered material. By performing micro-to-macro scale characterization at the atomic structure, primary particle, secondary particle, and electrode levels, it is proved that the heterogeneous structure of the lithium-rich manganese-based material inevitably leads to adverse phase displacement / strain, which cannot be solved by conventional doping or coating methods. The research proposes that the oxygen loss and voltage attenuation problems of the lithium-rich manganese-based material can be fundamentally solved by eliminating structural heterogeneity, such as designing a crystal structure strategy of O2 type with homogeneous atomic arrangement to reduce lattice displacement and uneven electrochemical / structural evolution, so as to achieve stable voltage and capacity distribution. It is found that lattice strain / displacement is of outstanding importance in causing voltage attenuation, and the failure mechanism of the lithium-rich manganese-based material is explained from the perspective of the heterogeneous nanodomain structure of two LiTMO2 phases and Li2MnO3 phases.

[0005] In the prior art, the surface coating of lithium-rich manganese-based materials by metal oxides, metal phosphates or metal fluorides has little effect on inhibiting oxygen release, metal migration and dissolution. In recent years, the technology of constructing a surface integrated structure by partially occupying the surface lattice lithium sites of lithium-rich manganese-based layered oxides by cations has made rapid progress, and it has been found that it has significant effects in inhibiting irreversible oxygen release and transition metal migration. For example, the prior art discloses a general method for treating precursors with nitrates to construct a stable surface integrated structure for lithium-rich manganese-based layered oxides, effectively inhibiting interfacial reactions and structural evolution, significantly improving the long-cycle performance and voltage stability of the material, and combining theoretical calculations to reveal the law of the influence of surface integrated structures constructed by different cations on electrochemical performance, providing theoretical guidance for subsequent research.

[0006] In order to improve the problem of voltage decay during the cycle process, CN 113782748A discloses a modified cobalt-free lithium-rich positive electrode material, its preparation method and application. The material is a lithium-rich manganese-based material coated with a lithium metal acid layer formed by sintering a metal hydrolyzate and an organic lithium salt through a wet coating method. Although the lithium metal acid layer can effectively slow down the phase change process of Li2MnO3 and the voltage decay problem, the lithium metal acid layer is an inactive coating material and will reduce the actual capacity of the lithium-rich manganese-based material.

[0007] Based on the above research, it is necessary to provide a method for preparing a coated lithium-rich manganese-based positive electrode material. The coated lithium-rich manganese-based positive electrode material obtained by the preparation method has reduced lattice stress and significantly alleviated voltage decay during the cycle process. Summary of the invention

[0008] The purpose of the present invention is to provide a coated lithium-rich manganese-based positive electrode material and a preparation method and application thereof. The preparation method can prepare a lithium-rich manganese-based positive electrode material with a stable crystal structure through a coated nanoscale spinel material precursor, thereby alleviating the problem of oxygen loss and voltage attenuation in the Li2MnO3 nanodomain area induced by the lattice stress of the Li2MnO3 in the eutectic lattice that continuously accumulates and reaches a critical value.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for preparing a coated lithium-rich manganese-based positive electrode material, the preparation method comprising the following steps:

[0011] (1) solid-phase mixing a lithium-rich manganese-based precursor with a lithium source and once calcining to obtain a lithium-rich manganese-based primary calcined material;

[0012] (2) mixing a metal salt solution, a precipitant solution, a complexing agent solution and the lithium-rich manganese-based primary calcined material of step (1) to carry out a coprecipitation reaction to obtain a coated lithium-rich manganese-based precursor;

[0013] (3) solid-phase mixing and secondary calcining of the lithium source and the coated lithium-rich manganese-based precursor of step (2) to obtain the coated lithium-rich manganese-based positive electrode material.

[0014] The present invention first sintered a lithium-rich manganese-based precursor with a lithium source to prepare a lithium-rich manganese-based semi-finished product, and coated a nanoscale spinel material precursor with controllable thickness on its surface by a staged co-precipitation method, and finally prepared a lithium-rich manganese-based finished material with a stable crystal structure. Among them, when the coated spinel new phase delithiation occurs in LiTMO2 at a relatively low voltage and the interlayer spacing increases, the oxygen loss and voltage attenuation problems in the Li2MnO3 nanodomain area induced by the lattice stress of the eutectic Li2MnO3 continuously accumulating to reach a critical value can be alleviated. Therefore, the lattice stress of the coated lithium-rich manganese-based positive electrode material prepared by the preparation method of the present invention is reduced, and the voltage decay during the cycle process is significantly alleviated.

[0015] Preferably, the surface of the coated lithium-rich manganese-based precursor in step (2) is coated with a metal hydroxide, and the molar ratio of lithium ions in the lithium source in step (3) to the total metal ions in the metal hydroxide is (0.4-0.6):1, for example, it can be 0.4:1, 0.45:1, 0.5:1, 0.55:1 or 0.6:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] The molecular formula of the metal hydroxide coated on the surface of the coated lithium-rich manganese-based precursor of the present invention is TM(OH)2, wherein TM represents any combination of two or three of the transition metal elements Ni, Co, Mn, Fe or Cr, preferably Ni 0.25 Mn 0.75 (OH)2 or Ni 0.225 Mn 0.725 Co 0.05 (OH)2.

[0017] According to the present invention, after the co-precipitation coating, a small amount of lithium source is added to react with the coated lithium-rich manganese-based precursor to obtain a coated lithium-rich manganese-based positive electrode material. The role of adding a small amount of lithium source is to generate a nanoscale spinel coating layer with high electron conductivity of the same element. If the amount of lithium source added is too little, a lithium-poor spinel structure is formed with low electron conductivity. If the amount of lithium source added is too much, a non-spinel structure is formed, which is inconsistent with the design.

[0018] Preferably, the temperature of the secondary calcination in step (3) is 500-1100°C, for example, 500°C, 800°C, 1000°C or 1100°C, the time is 5-20h, for example, 5h, 10h, 15h or 20h, and the atmosphere includes air or oxygen atmosphere.

[0019] Preferably, the secondary roasting in step (3) is followed by crushing and screening.

[0020] Preferably, the mesh number of the sieving is 200-500 mesh, for example, it can be 200 mesh, 300 mesh, 400 mesh or 500 mesh, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, the coprecipitation reaction time in step (2) is 3-6 h, for example, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] The time of the coprecipitation reaction in step (2) of the present invention will affect the thickness of the coating layer. If the time of the coprecipitation reaction is too short, the thickness of the coating layer will be too thin and the advantages of the spinel coating layer cannot be effectively exerted. If the time of the coprecipitation reaction is too long, the thickness of the coating layer will be too thick, which will cause obvious grain boundaries to form between the base lithium-rich manganese-based material and the spinel material of the coating layer, resulting in uneven lithium deintercalation during the charge and discharge process and the generation of grain stress cracks.

[0023] Preferably, the mixing in step (2) comprises first mixing the lithium-rich manganese-based primary calcined material in step (1) with the base liquid, and then introducing the metal salt solution, precipitant solution and complexing agent solution in step (2) to carry out a co-precipitation reaction.

[0024] Preferably, the pH of the coprecipitation reaction in step (2) is maintained in the range of 12-12.8, which means that the lowest pH of the coprecipitation reaction in step (2) is above 12, for example, it can be 12, 12.1, 12.2 or 12.3, and the highest pH is below 12.8, for example, it can be 12.8, 12.7, 12.6 or 12.8, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0025] Preferably, the primary calcination in step (1) is carried out in an air or oxygen atmosphere, including first calcining at 200-600°C, for example, 200°C, 400°C or 600°C, for 1-5h, for example, 1h, 3h or 5h, and then heating to 700-1000°C, for example, 700°C, 800°C or 1000°C, and continuing calcining for 2-20h, for example, 2h, 5h, 10h, 15h or 20h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the molar ratio of lithium ions in the lithium source in step (1) to the total metal ions in the lithium-rich manganese-based precursor is (1.1-1.9):1. For example, it can be 1.1:1, 1.5:1 or 1.9:1, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0027] After the first calcination in step (1) of the present invention, crushing and classification with a frequency of 1-20 Hz are also carried out. For example, it can be 1 Hz, 5 Hz, 10 Hz, 15 Hz or 20 Hz, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0028] The molecular formula of the lithium-rich manganese-based primary calcined material in step (1) of the present invention is Li 1+x TM 1-x O2 or xLi2MnO3·(1-x)LiTMO2, where TM represents a combination of one or at least two of the transition metal elements Ni, Co, and Mn, 0<x<1. For example, it can be 0.1, 0.3, 0.5, 0.7, 0.8 or 0.9; preferably a cobalt-free lithium-rich manganese-based cathode material, with a composition of Li 1.05 Ni 0.43 Mn 0.52 O2(0.1Li2MnO3·0.9LiNi 0.5 Mn 0.5 O2), Li 1.09 Ni 0.36 Mn 0.55 O2(0.2Li2MnO3·0.8LiNi 0.5 Mn 0.5 O2), Li 1.13 Ni 0.3 Mn 0.57 O2(0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2), Li 1.17 Ni 0.25 Mn 0.58 O2(0.4Li2MnO3·0.6LiNi 0.5 Mn 0.5 O2), Li 1.20 Ni 0.2 Mn 0.6 O2(0.5Li2MnO3·0.5LiNi 0.5 Mn 0.5 O2), Li 1.23 Ni 0.15 Mn 0.62 O2(0.6Li2MnO3·0.4LiNi 0.5 Mn 0.5 O2), Li1.26 Ni 0.11 Mn 0.63 O2(0.7Li2MnO3·0.3LiNi 0.5 Mn 0.5 O2)、Li 1.29 Ni 0.07 Mn 0.64 O2(0.8Li2MnO3·0.2LiNi 0.5 Mn 0.5 O2)、Li 1.31 Ni 0.03 Mn 0.66 O2(0.9Li2MnO3·0.1LiNi 0.5 Mn 0.5 O2).

[0029] Preferably, the lithium-rich manganese-based precursor in step (1) comprises a lithium-rich manganese-based carbonate precursor.

[0030] The lithium-rich manganese-based carbonate precursor of the present invention comprises TMCO3, wherein TM represents any one or a combination of at least two of the transition metal elements Ni, Co, and Mn; preferably, a low-cost, cobalt-free lithium-rich manganese-based carbonate precursor is composed of Ni 0.45 Mn 0.55 CO3(Li 1.05 Ni 0.43 Mn 0.52 O2 precursor), Ni 0.4 Mn 0.6 CO3(Li 1.09 Ni 0.36 Mn 0.55 O2 precursor), Ni 0.35 Mn 0.65 CO3(Li 1.13 Ni 0.3 Mn 0.57 O2 precursor), Ni 0.3 Mn 0.7 CO3(Li 1.17 Ni 0.25 Mn 0.58 O2 precursor), Ni 0.25 Mn 0.75 CO3(Li 1.20 Ni 0.2 Mn 0.6 O2 precursor), Ni 0.2 Mn 0.8 CO3(Li 1.23 Ni 0.15 Mn 0.62 O2 precursor), Ni 0.15 Mn0.85 CO3(Li 1.26 Ni 0.11 Mn 0.63 O2 precursor), Ni 0.1 Mn 0.9 CO3(Li 1.29 Ni 0.07 Mn 0.64 O2 precursor), Ni 0.05 Mn 0.95 CO3(Li 1.31 Ni 0.03 Mn 0.66 O2 precursor).

[0031] Preferably, the median particle size of the lithium-rich manganese-based precursor in step (1) is ≤15 μm, for example, it can be 15 μm, 10 μm, 5 μm, 3 μm or 2 μm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 2-12 μm.

[0032] Preferably, the tap density of the lithium-rich manganese-based precursor in step (1) is ≥ 0.4 g / cm 3 , for example, it can be 0.4 g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 or 0.8g / cm 3 , but not limited to the listed values, other values ​​not listed in the numerical range are also applicable, preferably ≥ 0.5 g / cm 3 .

[0033] The lithium source used in the present invention includes lithium carbonate and / or lithium hydroxide, and is preferably battery grade. The lithium carbonate preferably has a purity of ≥95%, and the lithium hydroxide preferably has a purity of ≥55%. The lithium carbonate preferably has a powder particle with a median particle size of 3 to 30 μm; the lithium hydroxide preferably has a micro-powder-grade powder particle with a median particle size of 1 to 10 μm.

[0034] Preferably, the method for preparing the lithium-rich manganese-based carbonate precursor comprises:

[0035] (i) introducing a metal salt solution and an alkali solution into the bottom liquid to carry out a coprecipitation reaction, then stopping the feeding and removing the supernatant liquid;

[0036] (ii) after the removal of the supernatant in step (i) is completed, the metal salt solution and the alkali solution are continued to be introduced for coprecipitation reaction, and then the feeding is stopped and the supernatant is removed;

[0037] (iii) After the removal of the supernatant in step (ii) is completed, the metal salt solution and the alkali solution are continuously introduced to carry out a coprecipitation reaction, and then the feeding is stopped and the supernatant is removed to obtain the lithium-rich manganese-based carbonate precursor.

[0038] The preparation method of the lithium-rich manganese-based precursor in step (1) of the present invention adopts a step-by-step co-precipitation method. Compared with the conventional one-step co-precipitation, due to the use of step-by-step co-precipitation, which corresponds to the nucleation stage, the low-speed growth stage, and the rapid growth stage, firstly, the nucleation density can be improved to avoid the formation of hollow structures. Secondly, adding a low-speed growth stage to the nucleation stage and the rapid growth stage can make the growth of the grains uniform and dense, greatly improve the tap density of the lithium-rich manganese-based precursor, and avoid the occurrence of faults and a large number of grain boundaries in the grains.

[0039] Preferably, the flow rate of the metal salt solution in step (i) is less than the flow rate of the metal salt solution in step (ii), and the flow rate of the metal salt solution in step (ii) is less than the flow rate of the metal salt solution in step (iii);

[0040] Preferably, the flow rate of the alkali solution in step (i) is greater than the flow rate of the alkali solution in step (ii), and less than the flow rate of the alkali solution in step (iii).

[0041] According to the present invention, step (i) is a nucleation stage, and step (ii) and step (iii) are growth stages. The flow rates of the metal salt solution and the alkali solution in step (i), step (ii) and step (iii) are different and have a specific relationship. The nucleation rate can be controlled by ultra-low metal salt flow rate and alkali solution flow rate (the ratio of alkali solution flow rate: metal salt flow rate is 3) in step (i), the slow growth rate of the initial grains can be controlled by low metal salt flow rate and alkali solution flow rate (the ratio of alkali solution flow rate: metal salt flow rate is 1.3) in step (ii), and the fast growth rate of the later grains can be controlled by high metal salt flow rate and alkali solution flow rate (the ratio of alkali solution flow rate: metal salt flow rate is 1.3) in step (iii).

[0042] Preferably, the flow rate of the metal salt solution in step (i) is 1-3 mL / min, for example, 1 mL / min, 2 mL / min or 3 mL / min, and the flow rate of the alkali solution in step (i) is 5-7 mL / min, for example, 5 mL / min, 6 mL / min or 7 mL / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] Preferably, the flow rate of the metal salt solution in step (ii) is 2.5-3.5 mL / min, for example, 2.5 mL / min, 3 mL / min or 3.5 mL / min, and the flow rate of the alkali solution in step (ii) is 3.5-4.5 mL / min, for example, 3.5 mL / min, 4 mL / min or 4.5 mL / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] Preferably, the flow rate of the metal salt solution in step (iii) is 5-7 mL / min, for example, 6 mL / min, 6.5 mL / min or 7 mL / min, and the flow rate of the alkali solution in step (iii) is 6.5-9 mL / min, for example, 8 mL / min, 8.5 mL / min or 9 mL / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the alkali solutions in step (i), step (ii) and step (iii) respectively and independently comprise carbonate or bicarbonate.

[0046] Preferably, the base solution in step (i) comprises a chelating agent and a metaphosphate, and the pH of the base solution is 9-10, for example, 9, 9.5 or 10, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] When the lithium-rich manganese-based precursor is prepared in stages, metaphosphate is added to the base liquid to play a dispersing role. Since step (i) is a nucleation stage, the addition of metaphosphate prevents the rapid growth of particles.

[0048] Preferably, the metaphosphate includes sodium hexametaphosphate, and the complexing agent includes aqueous ammonia.

[0049] Preferably, the pH of the coprecipitation reaction in step (i) is maintained in the range of 8-8.5, which means that the pH of the coprecipitation reaction in step (i) is at least 8, for example, 8, 8.1 or 8.2, and at least 8.5, for example, 8.5, 8.4 or 8.3, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0050] Preferably, after the coprecipitation reaction in step (i) has been carried out for 5-6 hours, for example, 5 hours, 5.5 hours or 6 hours, the feeding is stopped and the supernatant is removed.

[0051] Preferably, the operations of removing the supernatant in step (i), step (ii) and step (iii) respectively and independently include stirring, standing, stratification, pumping water and alkali supplementation operations performed in sequence.

[0052] Preferably, the pH of the coprecipitation reaction in step (ii) is maintained in the range of 7.1-7.4, which means that the lowest pH of the coprecipitation reaction in step (ii) is above 7.1, for example, it can be 7.1, 7.15 or 7.2, and the highest pH is below 7.4, for example, it can be 7.4, 7.35 or 7.3, but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0053] Preferably, the supernatant removal operation in step (ii) is repeated until the particle size D50 is 2.5-3 μm, for example, 2.5 μm, 2.8 μm or 3 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0054] Preferably, the supernatant removal operation in step (ii) is repeated every 5-6 hours of the coprecipitation reaction, for example, 5 hours, 5.5 hours or 6 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0055] The supernatant removal operation described in the present invention is repeated every 5-6 hours of the coprecipitation reaction, which means that after 5-6 hours of the coprecipitation reaction, the supernatant removal operation is performed, and then the metal salt solution and alkali solution are continued to be introduced for coprecipitation reaction. After the coprecipitation reaction is carried out for another 5-6 hours, the supernatant removal operation is performed, and this is repeated until the particle size reaches the target particle size.

[0056] Preferably, the pH of the coprecipitation reaction in step (iii) is maintained in the range of 7.1-7.5, which means that the lowest pH of the coprecipitation reaction in step (ii) is above 7.1, for example, 7.1, 7.15 or 7.2, and the highest pH is below 7.5, for example, 7.5, 7.45 or 7.4, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0057] Preferably, the supernatant removal operation in step (iii) is repeated until the particle size D50 is 4.3-5 μm, for example, 4.3 μm, 4.5 μm or 5 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0058] Preferably, the supernatant removal operation in step (iii) is repeated after every 2-3 hours of the coprecipitation reaction, for example, 2 hours, 2.5 hours or 3 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0059] The supernatant removal operation described in the present invention is repeated every 2-3 hours of the coprecipitation reaction, which means that after 2-3 hours of the coprecipitation reaction, the supernatant removal operation is performed, and then the metal salt solution and alkali solution are continued to be introduced for coprecipitation reaction. After the coprecipitation reaction is carried out for another 2-3 hours, the supernatant removal operation is performed, and this is repeated until the particle size reaches the target particle size.

[0060] The temperature of the coprecipitation reaction of the present invention is 35-60°C, for example, 35°C, 45°C, 50°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0061] The reactor sizes used in the coprecipitation reaction of the present invention include 5L, 50L, 100L, 1m 3 、5m 3 or 10m 3 .

[0062] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

[0063] (1) mixing a lithium-rich manganese-based precursor with a lithium source in a solid phase, and then calcining at 200-600° C. for 1-5 hours in an air or oxygen atmosphere, and then heating to 700-1000° C. and continuing to calcine for 2-20 hours, and then crushing and sieving to obtain a lithium-rich manganese-based primary crushed material;

[0064] The lithium-rich manganese-based precursor includes a lithium-rich manganese-based carbonate precursor, and the method for preparing the lithium-rich manganese-based carbonate precursor includes:

[0065] (i) passing a metal salt solution and an alkali solution into a base liquid for a coprecipitation reaction, wherein the pH of the coprecipitation reaction is maintained in the range of 8-8.5, and after 5-6 hours of the coprecipitation reaction, the feeding is stopped and a clear liquid removal operation is performed;

[0066] The base liquid includes a complexing agent and a metaphosphate, and the pH of the base liquid is 9-10;

[0067] (ii) After the removal of the supernatant in step (i) is completed, the metal salt solution and the alkali solution are continued to be introduced for coprecipitation reaction, and the pH of the coprecipitation reaction is maintained in the range of 7.1-7.4, and then the feeding is stopped and the supernatant removal operation is performed, and the supernatant removal operation is repeated every 5-6 hours of the coprecipitation reaction until the particle size D50 is 2.5-3 μm;

[0068] (iii) After the end of step (ii), continue to introduce the metal salt solution and the alkali solution for coprecipitation reaction. The pH of the coprecipitation reaction is maintained within the range of 7.1 - 7.5, and then the feeding is stopped for supernatant removal operation. The supernatant removal operation is repeated every 2 - 3 h after the coprecipitation reaction until the particle size D50 is 4.3 - 5 μm, and the lithium-rich manganese-based carbonate precursor is obtained;

[0069] (2) First, mix the lithium-rich manganese-based primary crushed material described in step (1) with the bottom liquid phase, and then introduce the metal salt solution, the precipitant solution, and the complexing agent solution for coprecipitation reaction. The pH of the coprecipitation reaction is maintained within the range of 12 - 12.8, and the time is 3 - 6 h to obtain the coated lithium-rich manganese-based precursor;

[0070] (3) Solid-phase mix the lithium source and the coated lithium-rich manganese-based precursor described in step (2), and then perform secondary calcination at a temperature of 500 - 1100 °C for 5 - 20 h in an air or oxygen atmosphere. After pulverization and screening, the coated lithium-rich manganese-based cathode material is obtained;

[0071] The surface of the coated lithium-rich manganese-based precursor is coated with metal hydroxide. The molar ratio of lithium ions in the lithium source described in step (3) to the total metal ions in the metal hydroxide is (0.4 - 0.6):1.

[0072] In a second aspect, the present invention provides a coated lithium-rich manganese-based cathode material, which is prepared by using the preparation method described in the first aspect.

[0073] The chemical general formula of the coating layer in the present invention is LiNi 0.5-x / 2 Mn 1.5-x / 2 Co x O4, where 0 ≤ x ≤ 0.1. For example, it can be 0, 0.03, 0.05, 0.07, 0.09, or 0.1. When x = 0, the chemical formula of the coating layer is cobalt-free spinel LiNi 0.5 Mn 1.5 O4. When 0 < x ≤ 0.1, the chemical formula of the coating layer is cobalt-doped spinel LiNi 0.5-x / 2 Mn 1.5-x / 2 Co x O4.

[0074] Preferably, the thickness of the coating layer is 10 - 30 nm. For example, it can be 10 nm, 20 nm, or 30 nm, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0075] In a third aspect, the present invention provides a lithium-ion battery, which includes the coated lithium-rich manganese-based cathode material described in the second aspect.

[0076] Compared with the prior art, the present invention has the following beneficial effects:

[0077] The present invention uses a single-step co-precipitation method to coat the lithium-rich manganese-based material with a nano-spinel structure material with controllable thickness, so that the electrochemically active ions partially occupy the surface lithium sites, which can not only inhibit the migration of transition metal ions, but also serve as a pillar to improve the structural stability of the oxygen framework, slow down the irreversible release of oxygen, improve the redox reversibility of anions, and effectively reduce the voltage decay problem; in addition, the coated lithium-rich manganese-based positive electrode material of the present invention can also isolate the active ingredients from the electrolyte to avoid direct contact between the two, thereby inhibiting interface side reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 The charge and discharge curves of the battery made of the coated lithium-rich manganese-based positive electrode materials described in Examples 1-3 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0079] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0080] Example 1

[0081] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material, the preparation method comprising the following steps:

[0082] (1) Preparation of lithium-rich manganese-based carbonate precursor Ni 0.3 Mn 0.7 CO3: (i) Preparation of metal salt solution: Dissolve two metal salts, NiSO4·6H2O and MnSO4·H2O, in 5L pure water to prepare mixed metal salt solution A, where the molar concentrations of the metal salts are 0.6mol / L NiSO4·6H2O and 1.4mol / L MnSO4·H2O, respectively; (ii) Preparation of reaction base solution: Add 30ml of concentrated ammonia water with a molar concentration of 10mol / L to 2L pure water and stir for 30 minutes, then add 4g of sodium hexametaphosphate and continue stirring for 10 minutes. Measure the pH value to be 9.5 to obtain reaction base solution B; (iii) Preparation of alkaline solution: Dissolve 200g of monoammonium bicarbonate in 1L pure water and stir for 20 minutes to prepare 2.53mol / L monoammonium bicarbonate alkaline solution C;

[0083] The first stage: the metal salt solution A and the alkali solution C are pumped into the reaction bottom liquid B of the 5L reactor by a peristaltic pump. One hour after the reaction starts, the pH is stabilized at 8-8.5. The flow rate of the mixed metal salt solution A is controlled to be 2ml / min, the flow rate of the alkali solution C is controlled to be 6ml / min, the reactor temperature is 40°C, and the stirring speed is 1000rpm. After the reaction is carried out for 6 hours, the feeding is stopped and the stirring is continued for 30 minutes. Then, the stirring is turned off and the upper clear liquid is allowed to stand for another 3 hours. The lower precipitate and the upper clear liquid are obviously separated. 3L of the supernatant is pumped out, and 0.3L of the alkali solution C is added to the reactor to form the reaction bottom liquid D. The series of operations of stirring, standing, stratification, pumping out water, and adding alkali are called "full reactor clear liquid removal operation";

[0084] The second stage: the metal salt solution A and the alkaline solution C are pumped into the reaction bottom liquid D of the 5L reactor by a peristaltic pump. One hour after the reaction starts, the pH is stabilized at 7.1-7.4. The flow rate of the mixed metal salt solution A is controlled to be 3.2 ml / min, the flow rate of the alkaline solution C is 4.3 ml / min, the reactor temperature is 40°C, and the stirring speed is 1000 rpm. After the reaction is carried out for 6 hours, the feeding is stopped and the stirring is continued for 30 minutes. Then the stirring is turned off and the lower layer precipitation and the upper layer clear liquid are separated. 3L of supernatant is pumped out, and 0.3L of alkaline solution C is added to the reactor to form the reaction bottom liquid E. Repeat the second stage until the lower layer precipitation D 50 Reach 2.7μm, during which time "full kettle to remove supernatant liquid operation" is performed every 6 hours, and when the particle size reaches the required value, reaction bottom liquid F is formed;

[0085] The third stage: metal salt solution A and alkaline solution C were pumped into the reaction bottom liquid F of the 5L reactor by a peristaltic pump. The pH was stabilized at 7.1-7.5 0.5 hours after the reaction started. The flow rate of the mixed metal salt solution A was controlled at 6.4 ml / min, the flow rate of the alkaline solution C was controlled at 8.6 ml / min, the reactor temperature was 40°C, the stirring speed was 1000 rpm, and the "full reactor clear liquid removal operation" was performed every 3 hours during the reaction process until the lower layer of the precipitate D 50 When the design requirement of 4.5 μm is reached, the feeding and stirring are stopped, and the reactor is allowed to stand for 1 hour. The lower precipitate and the upper clear liquid are clearly separated. 3 L of water is pumped out of the supernatant, and then the lower precipitate is filtered, washed with water, and dried to obtain a lithium-rich manganese-based carbonate precursor.

[0086] (2) Preparation of lithium-rich manganese-based primary crushed material: According to the lithium-rich manganese-based positive electrode material Li 1.17 Ni 0.25 Mn 0.58 The composition of O2 is the median particle size D 50 =4.4μm, tap density 0.5g / cm 3 Lithium-rich manganese-based carbonate precursor and median particle size D 50=20μm, 99.6% pure battery-grade lithium carbonate, uniformly mixed at a molar ratio of lithium ions to metal ions of 1.4:1, calcined in a roller kiln at 300°C for 3 hours under air atmosphere, then continued to heat to 900°C for 10 hours to obtain a lithium-rich manganese-based primary roasted material, which was then crushed and classified at a frequency of 18 Hz to obtain a lithium-rich manganese-based primary crushed material I;

[0087] (3) Preparation of coated lithium-rich manganese-based precursor: (i) Preparation of metal salt solution: Dissolve two metal salts, NiSO4·6H2O and MnSO4·H2O, in 5L pure water to prepare a mixed metal salt solution G, the molar concentrations of the metal salts are 0.6mol / LNiSO4·6H2O and 1.8mol / LMnSO4·H2O respectively; (ii) Preparation of reaction base solution: Add 5ml of concentrated ammonia water with a molar concentration of 10mol / L into 2L pure water and stir for 30 minutes, then add NaOH and continue stirring for 10 minutes, adjust the pH to 12.4-12.6, and obtain reaction base solution H; (iii) Preparation of alkaline solution: Purchase commercially available sodium hydroxide alkaline solution J with a molar concentration of 10mol / L and use it directly. (iv) Preparation of dilute ammonia solution: Dissolve 200ml of concentrated ammonia water with a molar concentration of 10mol / L in 1L pure water to form a 2mol / L dilute ammonia solution K;

[0088] First, 1 kg of lithium-rich manganese-based primary crushed material I was added to a 5L reactor bottom liquid H and stirred for 10 minutes, and then the metal salt solution G and the alkaline solution J were pumped into the reaction bottom liquid H of the 5L reactor through a peristaltic pump. 0.5 hours after the reaction started, the pH was stabilized at 12.3-12.5, the flow rate of the mixed metal salt solution G was controlled to be 5 ml / min, the flow rate of the dilute ammonia solution K was 0.3 ml / min, and the flow rate of the alkaline solution J was automatically adjusted online according to the pH value. The reactor temperature was 50°C, the stirring speed was 1200 rpm, the feeding was stopped after the reaction for 6 hours, and the stirring was continued for 30 minutes, and then the feeding and stirring were stopped, and the reactor was allowed to stand for 1 hour. The lower precipitate and the upper clear liquid were obviously separated, and 3L of water was pumped from the supernatant, and then the lower precipitate was filtered, washed with water, and dried to obtain a coated Ni 0.25 Mn 0.75 (OH)2-type lithium-rich manganese-based precursor II;

[0089] (4) Preparation of coated lithium-rich manganese-based finished product: The coated lithium-rich manganese-based precursor II and the median particle size D 50=6μm, 99.7% pure battery-grade lithium carbonate, at a molar ratio of lithium ions to the total amount of metal ions in the hydroxide coating of 0.5:1, is uniformly mixed to obtain a coated lithium-rich manganese-based lithium salt mixture S; calcined in an air atmosphere at 500°C in a roller kiln for 15 hours to obtain a coated lithium-rich manganese-based secondary calcined material, which is then crushed and sieved through 200 meshes to obtain the coated lithium-rich manganese-based positive electrode material;

[0090] The cobalt-free lithium-rich manganese-based positive electrode material Li 1.17 Ni 0.25 Mn 0.58 O2, the nano-spinel structure material coating thickness is 30nm, so that the electrochemically active ions Ni and Mn partially occupy the surface lithium site, which can not only inhibit the migration of transition metal ions, but also serve as a pillar to improve the structural stability of the oxygen framework, slow down the irreversible release of oxygen, improve the redox reversibility of anions, and effectively reduce the voltage decay by 0.06V. In addition, this design can also isolate the active ingredients from the electrolyte to avoid direct contact between the two, thereby inhibiting interface side reactions.

[0091] Example 2

[0092] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material, the preparation method comprising the following steps:

[0093] (1) Preparation of lithium-rich manganese-based carbonate precursor Ni 0.25 Mn 0.75 CO3: (i) Preparation of metal salt solution: Dissolve two metal salts, NiSO4·6H2O and MnSO4·H2O, in 5L pure water to prepare mixed metal salt solution A. The molar concentrations of the metal salts are 0.6mol / L NiSO4·6H2O and 1.8mol / L MnSO4·H2O, respectively; (ii) Preparation of reaction base solution: Add 30ml of concentrated ammonia water with a molar concentration of 10mol / L into 2L pure water and stir for 30 minutes. Then add 4g of sodium hexametaphosphate and continue stirring for 10 minutes. The pH value is measured to be 9 to obtain reaction base solution B; (iii) Preparation of alkaline solution: Dissolve 200g of monoammonium bicarbonate in 1L pure water and stir for 20 minutes to prepare 2.53mol / L monoammonium bicarbonate alkaline solution C.

[0094] The first stage: the metal salt solution A and the alkaline solution C are pumped into the reaction bottom liquid B of the 5L reactor by a peristaltic pump. The pH is stabilized at 8-8.5 after 0.5-1 hour after the reaction starts. The flow rate of the mixed metal salt solution A is controlled to be 2.3 ml / min, the flow rate of the alkaline solution C is 6.9 ml / min, the reactor temperature is 40°C, and the stirring speed is 1000 rpm. After the reaction is carried out for 6 hours, the feeding is stopped and the stirring is continued for 30 minutes. Then the stirring is turned off and the lower layer precipitation and the upper layer clear liquid are obviously separated. 3L of the supernatant is pumped out, and 0.3L of alkaline solution C is added to the reactor to form the reaction bottom liquid D. The series of operations of stirring, standing, separation, pumping out water, and adding alkali are named "full reactor clear liquid removal operation";

[0095] The second stage: the metal salt solution A and the alkaline solution C are pumped into the reaction bottom liquid D of the 5L reactor by a peristaltic pump. The pH is stabilized at 7.1-7.4 0.5 hours after the reaction starts. The flow rate of the mixed metal salt solution A is controlled to be 3.5 ml / min, the flow rate of the alkaline solution C is controlled to be 4.5 ml / min, the reactor temperature is 40°C, and the stirring speed is 1000 rpm. After the reaction is carried out for 6 hours, the feeding is stopped and the stirring is continued for 30 minutes. Then the stirring is turned off and the lower layer precipitation and the upper layer clear liquid are separated. 3L of the supernatant is pumped out, and 0.3L of alkaline solution C is added to the reactor to form the reaction bottom liquid E. The second stage is repeated until the lower layer precipitation D 50 Reach 3.0μm, during which time "full kettle to remove supernatant liquid operation" is performed every 6 hours, and when the particle size reaches 3.0μm, reaction bottom liquid F is formed;

[0096] The third stage: metal salt solution A and alkaline solution C were pumped into the reaction bottom liquid F of the 5L reactor by a peristaltic pump. The pH was stabilized at 7.1-7.5 one hour after the reaction started. The flow rate of the mixed metal salt solution A was controlled to be 7ml / min, the flow rate of the alkaline solution C was controlled to be 9ml / min, the reactor temperature was 40℃, the stirring speed was 1000rpm, and the "full reactor clear liquid removal operation" was performed every 3 hours during the reaction process until the lower layer of sediment D 50 When the design requirement of 5.0 μm is reached, the feeding and stirring are stopped, and the reactor is allowed to stand for 1 hour. The lower precipitate and the upper clear liquid are clearly separated. 3 L of water is pumped out of the supernatant, and then the lower precipitate is filtered, washed with water, and dried to obtain a lithium-rich manganese-based carbonate precursor.

[0097] (2) Preparation of lithium-rich manganese-based primary crushed material: According to the lithium-rich manganese-based positive electrode material Li 1.20 Ni 0.2 Mn 0.6 The composition of O2 is the median particle size D 50 =5.0μm, tap density 0.6g / cm 3 Lithium-rich manganese-based carbonate precursor and median particle size D 50=6μm, 99.5% pure battery-grade lithium carbonate, uniformly mixed at a molar ratio of lithium ions to metal ions of 1.5:1, calcined in a roller kiln at 400°C for 2 hours under an oxygen atmosphere, then continued to heat to 850°C for 15 hours to obtain a lithium-rich manganese-based primary calcined material, which was then crushed and classified at a frequency of 15 Hz to obtain a lithium-rich manganese-based primary crushed material I;

[0098] (3) Preparation of coated lithium-rich manganese-based precursor: (i) Preparation of metal salt solution: Dissolve two metal salts, NiSO4·6H2O and MnSO4·H2O, in 5L pure water to prepare a mixed metal salt solution G, the molar concentrations of the metal salts are 0.6mol / LNiSO4·6H2O and 1.8mol / LMnSO4·H2O respectively; (ii) Preparation of reaction base solution: Add 5ml of concentrated ammonia water with a molar concentration of 10mol / L into 2L pure water and stir for 30 minutes, then add NaOH and continue stirring for 10 minutes, adjust the pH to 12.6, and obtain reaction base solution H; (iii) Preparation of alkaline solution: Purchase commercially available sodium hydroxide alkaline solution J with a molar concentration of 10mol / L and use it directly. (iv) Preparation of dilute ammonia solution: Dissolve 200ml of concentrated ammonia water with a molar concentration of 10mol / L in 1L pure water to form a 2mol / L dilute ammonia solution K;

[0099] First, 1 kg of lithium-rich manganese-based primary crushed material I was added to a 5L reactor bottom liquid H and stirred for 10 minutes, and then the metal salt solution G and the alkaline solution J were pumped into the reaction bottom liquid H of the 5L reactor through a peristaltic pump. 0.5 hours after the reaction started, the pH was stabilized at 12.3-12.5, the flow rate of the mixed metal salt solution G was controlled to be 5 ml / min, the flow rate of the dilute ammonia solution K was 0.3 ml / min, and the flow rate of the alkaline solution J was automatically adjusted online according to the pH value. The reactor temperature was 50°C, the stirring speed was 1200 rpm, the feeding was stopped after the reaction for 6 hours and the stirring was continued for 30 minutes, and then the feeding and stirring were stopped, and the reactor was allowed to stand for 1 hour. The lower precipitate and the upper clear liquid were obviously separated, and 3L of water was pumped from the supernatant, and then the lower precipitate was filtered, washed with water, and dried to obtain a coated Ni 0.25 Mn 0.75 (OH)2-type lithium-rich manganese-based precursor II;

[0100] (4) Preparation of coated lithium-rich manganese-based finished product: The coated lithium-rich manganese-based precursor II and the median particle size D 50=5μm, battery-grade lithium hydroxide monohydrate with a lithium hydroxide purity of 55%, and uniformly mixed at a molar ratio of lithium ions to the total amount of metal ions of the hydroxide coating of 0.52:1 to obtain a coated lithium-rich manganese-based lithium salt mixture S; calcined in a roller kiln at 700°C in an air atmosphere for 10 hours to obtain a coated lithium-rich manganese-based secondary calcined material, and then crushed and sieved with 300 meshes to obtain a final product, a coated lithium-rich manganese-based finished product;

[0101] The coated cobalt-free lithium-rich manganese-based positive electrode material Li 1.20 Ni 0.2 Mn 0.6 O2, the nano-spinel structure material coating thickness is 20nm, and the voltage attenuation is effectively reduced by 0.09V.

[0102] Example 3

[0103] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material, comprising the following steps:

[0104] 1) Preparation of lithium-rich manganese-based carbonate precursor Ni 0.3 Co 0.12 Mn 0.58 CO3: (i) Preparation of metal salt solution: Dissolve three metal salts, NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O, in 5L pure water to prepare mixed metal salt solution A. The molar concentrations of the metal salts are 0.6mol / L NiSO4·6H2O, 0.24mol / L CoSO4·7H2O and 1.16mol / L MnSO4·H2O, respectively; (ii) Preparation of reaction base solution: Add 30ml of concentrated ammonia water with a molar concentration of 10mol / L into 2L pure water and stir for 30 minutes. Then add 4g of sodium hexametaphosphate and continue stirring for 10 minutes. The pH value is 10 to obtain reaction base solution B; (iii) Preparation of alkaline solution: Dissolve 200g of ammonium bicarbonate in 1L pure water and stir for 20 minutes to prepare 2.53mol / L ammonium bicarbonate alkaline solution C.

[0105] The first stage: the metal salt solution A and the alkali solution C are pumped into the reaction bottom liquid B of the 5L reactor by a peristaltic pump. One hour after the reaction starts, the pH is stabilized at 8-8.5. The flow rate of the mixed metal salt solution A is controlled to be 1.8 ml / min, the flow rate of the alkali solution C is 5.4 ml / min, the reactor temperature is 40°C, and the stirring speed is 1000 rpm. After the reaction is carried out for 6 hours, the feeding is stopped and the stirring is continued for 30 minutes. Then the stirring is turned off and the lower layer precipitation and the upper layer clear liquid are separated obviously. 3L of the supernatant is pumped out, and 0.3L of the alkali solution C is added to the reactor to form the reaction bottom liquid D. The series of operations of stirring, standing, stratification, pumping out water, and adding alkali are named "full reactor clear liquid removal operation";

[0106] The second stage: the metal salt solution A and the alkaline solution C are pumped into the reaction bottom liquid D of the 5L reactor by a peristaltic pump. One hour after the reaction starts, the pH is stabilized at 7.1-7.4. The flow rate of the mixed metal salt solution A is controlled to be 3 ml / min, the flow rate of the alkaline solution C is controlled to be 4 ml / min, the reactor temperature is 40°C, and the stirring speed is 1000 rpm. After the reaction is carried out for 6 hours, the feeding is stopped and the stirring is continued for 30 minutes. Then the stirring is turned off and the lower layer precipitation and the upper layer clear liquid are separated. 3L of the supernatant is pumped out, and 0.3L of alkaline solution C is added to the reactor to form the reaction bottom liquid E. The second stage is repeated until the lower layer precipitation D 50 Reach 2.8μm, during which time "full kettle to remove supernatant liquid operation" is performed every 6 hours, and when the particle size reaches the required value, reaction bottom liquid F is formed;

[0107] The third stage: metal salt solution A and alkaline solution C were pumped into the reaction bottom liquid F of the 5L reactor by a peristaltic pump. The pH was stabilized at 7.1-7.5 0.5 hours after the reaction started. The flow rate of the mixed metal salt solution A was controlled at 6 ml / min, the flow rate of the alkaline solution C was controlled at 8 ml / min, the reactor temperature was 40°C, the stirring speed was 1000 rpm, and the "full reactor clear liquid removal operation" was performed every 3 hours during the reaction process until the lower layer of sediment D 50 When the design requirement of 4.3 μm is reached, the feeding and stirring are stopped, and the reactor is allowed to stand for 1 hour. The lower precipitate and the upper clear liquid are clearly separated. 3 L of water is pumped out of the supernatant, and then the lower precipitate is filtered, washed with water, and dried to obtain a lithium-rich manganese-based carbonate precursor.

[0108] (2) Preparation of lithium-rich manganese-based primary crushed material: According to the lithium-rich manganese-based positive electrode material Li 1.17 Ni 0.25 Co 0.1 Mn 0.48 The composition of O2 is the median particle size D 50 =3.4μm, tap density 0.4g / cm 3 Lithium-rich manganese-based carbonate precursor and median particle size D 50 =3.5μm, 99.6% pure battery-grade lithium carbonate, uniformly mixed at a molar ratio of lithium ions to metal ions of 1.4:1, calcined in a roller kiln at 600°C for 2 hours under air atmosphere, then continued to heat to 1000°C for 8 hours to obtain a lithium-rich manganese-based primary calcined material, which was then crushed and classified at a frequency of 10 Hz to obtain a lithium-rich manganese-based primary crushed material I;

[0109] (3) Preparation of coated lithium-rich manganese-based precursor: (i) Preparation of metal salt solution: Dissolve three metal salts, NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O, in 5L pure water to prepare a mixed metal salt solution G, the molar concentrations of the metal salts are 0.6mol / L NiSO4·6H2O, 1.93mol / L MnSO4·H2O and 0.13mol / L CoSO4·7H2O respectively; (ii) Preparation of reaction base solution: Add 5ml of concentrated ammonia water with a molar concentration of 10mol / L into 2L pure water and stir for 30 minutes, then add NaOH and continue stirring for 10 minutes, adjust the pH to 12.4-12.6, and obtain reaction base solution H; (iii) Preparation of alkaline solution: Purchase commercially available sodium hydroxide alkaline solution J with a molar concentration of 10mol / L and use it directly. (iv) preparing a dilute ammonia solution: dissolving 200 ml of 10 mol / L concentrated ammonia solution in 1 L of pure water to form a 2 mol / L dilute ammonia solution K;

[0110] First, 1 kg of lithium-rich manganese-based primary crushed material I was added to a 5L reactor bottom liquid H and stirred for 10 minutes, and then the metal salt solution G and the alkaline solution J were pumped into the reaction bottom liquid H of the 5L reactor through a peristaltic pump. 0.5 hours after the reaction started, the pH was stabilized at 12.3-12.5, the flow rate of the mixed metal salt solution G was controlled to be 5 ml / min, the flow rate of the dilute ammonia solution K was 0.3 ml / min, and the flow rate of the alkaline solution J was automatically adjusted online according to the pH value. The reactor temperature was 50°C, the stirring speed was 1200 rpm, the feeding was stopped after the reaction for 6 hours and the stirring was continued for 30 minutes, and then the feeding and stirring were stopped, and the reactor was allowed to stand for 1 hour. The lower precipitate and the upper clear liquid were obviously separated, and 3L of water was pumped from the supernatant, and then the lower precipitate was filtered, washed with water, and dried to obtain a coated Ni 0.225 Mn 0.725 Co 0.05 (OH)2-type lithium-rich manganese-based precursor II;

[0111] (4) Preparation of coated lithium-rich manganese-based finished product: The coated lithium-rich manganese-based precursor II and the median particle size D 50 =6μm, 99.7% pure battery-grade lithium carbonate, at a molar ratio of lithium ions to the total amount of metal ions of the hydroxide coating of 0.47:1, is uniformly mixed to obtain a coated lithium-rich manganese-based lithium salt mixture S; calcined in a roller kiln at 900°C in an air atmosphere for 5 hours to obtain a coated lithium-rich manganese-based secondary calcined material, which is then crushed and sieved with 400 meshes to obtain a final product, a coated lithium-rich manganese-based finished product;

[0112] The coated cobalt-rich lithium manganese-based positive electrode material Li 1.17 Ni 0.25 Co 0.1 Mn 0.48O2, the coating thickness of the nano-spinel structure material is 10nm, and the voltage attenuation is effectively reduced by 0.10V.

[0113] Example 4

[0114] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material. The preparation method is the same as that of Embodiment 1 except that the molar ratio of lithium ions to the total amount of metal ions in the hydroxide coating in step (4) is 0.4:1.

[0115] Example 5

[0116] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material. The preparation method is the same as that of Example 1 except that the molar ratio of lithium ions to the total amount of metal ions in the hydroxide coating in step (4) is 0.6:1.

[0117] Example 6

[0118] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material. The preparation method is the same as that of Embodiment 1 except that the molar ratio of lithium ions to the total amount of metal ions in the hydroxide coating in step (4) is 0.3:1.

[0119] Example 7

[0120] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material. The preparation method is the same as that of Embodiment 1 except that the molar ratio of lithium ions to the total amount of metal ions in the hydroxide coating in step (4) is 0.7:1.

[0121] Example 8

[0122] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material. The preparation method is the same as that of Embodiment 1, except that the feeding is stopped after the reaction in step (3) is carried out for 3 hours.

[0123] Example 9

[0124] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material. The preparation method is the same as that of Embodiment 1, except that the feeding is stopped after the reaction in step (3) is carried out for 1.5 hours.

[0125] Example 10

[0126] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material. The preparation method is the same as that of Example 1 except that sodium hexametaphosphate is not added to the reaction base liquid in step (1).

[0127] Embodiment 11

[0128] This embodiment provides a method for preparing a coated lithium-rich manganese-based positive electrode material. The preparation method is the same as that of Embodiment 1 except that step (1) does not adopt a three-stage co-precipitation but a one-step co-precipitation preparation.

[0129] In this embodiment, step (1) includes the following steps:

[0130] (1) Preparation of lithium-rich manganese-based carbonate precursor Ni 0.3 Mn 0.7 CO3: (i) Preparation of metal salt solution: Dissolve two metal salts, NiSO4·6H2O and MnSO4·H2O, in 5L pure water to prepare mixed metal salt solution A, where the molar concentrations of the metal salts are 0.6mol / L NiSO4·6H2O and 1.4mol / L MnSO4·H2O, respectively; (ii) Preparation of reaction base solution: Add 30ml of concentrated ammonia water with a molar concentration of 10mol / L to 2L pure water and stir for 30 minutes, then add 4g of sodium hexametaphosphate and continue stirring for 10 minutes. Measure the pH value to be 9.5 to obtain reaction base solution B; (iii) Preparation of alkaline solution: Dissolve 200g of monoammonium bicarbonate in 1L pure water and stir for 20 minutes to prepare 2.53mol / L monoammonium bicarbonate alkaline solution C;

[0131] One-step co-precipitation: metal salt solution A and alkali solution C are pumped into the reaction bottom liquid B of the 5L reactor through a peristaltic pump. One hour after the reaction starts, the pH is stabilized at 8-8.5. The flow rate of the mixed metal salt solution A is controlled to be 3.2 ml / min, the flow rate of the alkali solution C is 4.3 ml / min, the reactor temperature is 40°C, and the stirring speed is 1000 rpm. After the reaction is carried out for 6 hours, the feeding is stopped and stirring is continued for 30 minutes. Then, the stirring is turned off and the upper clear liquid is allowed to stand for 3 hours. The lower precipitate and the upper clear liquid are obviously separated. 3L of the supernatant is pumped out, and 0.3L of the alkali solution C is added to the reactor to form a reaction bottom liquid D. The series of operations of stirring, standing, stratification, pumping, and alkali supplementation is called "full reactor clear liquid removal operation". Repeat the above co-precipitation reaction operation until the lower precipitate D is formed. 50 When the design requirement of 4.5μm is reached, the feeding and stirring are stopped, and the reaction vessel is allowed to stand for 1 hour. The lower precipitate and the upper clear liquid are clearly separated. 3L of the supernatant is pumped out, and then the lower precipitate is filtered, washed with water, and dried to obtain a lithium-rich manganese-based carbonate precursor.

[0132] Comparative Example 1

[0133] This embodiment provides a method for preparing a lithium-rich manganese-based positive electrode material. The preparation method is the same as that of Embodiment 1 except that step (3) and step (4) are not performed.

[0134] The positive electrode materials obtained in the above embodiments and comparative examples were made into 2032 button batteries and tested, and the charge and discharge cut-off voltage was 2.3-4.55V. The charge and discharge curves of the batteries made of the coated lithium-rich manganese-based positive electrode materials described in embodiments 1-3 and comparative example 1 are as shown in FIG. Figure 1 As shown, the electrochemical performance data obtained are shown in Table 1 below:

[0135] Table 1

[0136]

[0137]

[0138] The button cell made of the coated lithium-rich manganese-based positive electrode material obtained by the present invention has improved coulombic efficiency and discharge platform voltage, the 0.1C first charge specific capacity can reach more than 284.9 mAh / g, the 0.1C first discharge specific capacity can reach more than 213.7 mAh / g, the first efficiency can be brought to more than 80%, and the voltage decay phenomenon is effectively reduced; and it can be seen from Example 1 and Comparative Example 1 that the specific coating of the present invention can significantly improve the electrochemical performance; it can be seen from Example 1 and Examples 6-7 that the molar ratio of the lithium ions in step (4) to the total amount of metal ions in the hydroxide coating affects the formation of the spinel structure coating layer; it can be seen from Example 1 and Examples 8-9 that the coating time affects the thickness of the coating layer, thereby affecting the material performance; it can be seen from Example 1 and Examples 10-11 that the specific base solution of the present invention and the three-stage co-precipitation method can further improve the material performance.

[0139] In summary, the present invention provides a coated lithium-rich manganese-based positive electrode material and a preparation method and application thereof. The preparation method can prepare a lithium-rich manganese-based positive electrode material with a stable crystal structure through a coated nanoscale spinel material precursor, thereby alleviating the problem of oxygen loss and voltage attenuation in the Li2MnO3 nanodomain area induced by the lattice stress continuously accumulated in the eutectic lattice of Li2MnO3 reaching a critical value.

[0140] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a coated lithium-rich manganese-based positive electrode material, characterized in that: The preparation method comprises the following steps: (1) solid-phase mixing a lithium-rich manganese-based precursor with a lithium source and once calcining to obtain a lithium-rich manganese-based primary calcined material; (2) mixing a metal salt solution, a precipitant solution, a complexing agent solution and the lithium-rich manganese-based primary calcined material of step (1) to carry out a coprecipitation reaction to obtain a coated lithium-rich manganese-based precursor; (3) solid-phase mixing and secondary calcining of the lithium source and the coated lithium-rich manganese-based precursor of step (2) to obtain the coated lithium-rich manganese-based positive electrode material.

2. The preparation method according to claim 1, characterized in that: The surface of the coated lithium-rich manganese-based precursor in step (2) is coated with a metal hydroxide, and the molar ratio of lithium ions in the lithium source to total metal ions in the metal hydroxide in step (3) is (0.4-0.6):1; Preferably, the temperature of the secondary calcination in step (3) is 500-1100° C., the time is 5-20 h, and the atmosphere includes air or oxygen atmosphere; Preferably, the secondary roasting in step (3) is followed by crushing and screening.

3. The preparation method according to claim 1 or 2, characterized in that: The coprecipitation reaction time in step (2) is 3-6 hours; Preferably, the mixing in step (2) comprises first mixing the lithium-rich manganese-based primary calcined material in step (1) with the base liquid, and then introducing the metal salt solution, precipitant solution and complexing agent solution in step (2) to carry out a co-precipitation reaction; Preferably, the pH of the coprecipitation reaction in step (2) is maintained in the range of 12-12.8; Preferably, the primary calcination in step (1) is carried out in an air or oxygen atmosphere, including first calcining at 200-600° C. for 1-5 h, then heating to 700-1000° C., and continuing calcining for 2-20 h; Preferably, the molar ratio of lithium ions in the lithium source in step (1) to total metal ions in the lithium-rich manganese-based precursor is (1.1-1.9):

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The lithium-rich manganese-based precursor in step (1) includes a lithium-rich manganese-based carbonate precursor; Preferably, the method for preparing the lithium-rich manganese-based carbonate precursor comprises: (i) introducing a metal salt solution and an alkali solution into the bottom liquid to carry out a coprecipitation reaction, then stopping the feeding and removing the supernatant liquid; (ii) after the removal of the supernatant in step (i) is completed, the metal salt solution and the alkali solution are continued to be introduced for coprecipitation reaction, and then the feeding is stopped and the supernatant is removed; (iii) After the removal of the supernatant in step (ii) is completed, the metal salt solution and the alkali solution are continuously introduced to carry out a coprecipitation reaction, and then the feeding is stopped and the supernatant is removed to obtain the lithium-rich manganese-based carbonate precursor.

5. The preparation method according to claim 4, characterized in that: The flow rate of the metal salt solution in step (i) is less than the flow rate of the metal salt solution in step (ii), and the flow rate of the metal salt solution in step (ii) is less than the flow rate of the metal salt solution in step (iii); Preferably, the flow rate of the alkali solution in step (i) is greater than the flow rate of the alkali solution in step (ii), and less than the flow rate of the alkali solution in step (iii).

6. The preparation method according to claim 4 or 5, characterized in that: The base solution in step (i) comprises a complexing agent and a metaphosphate, and the pH of the base solution is 9-10; Preferably, the pH of the coprecipitation reaction in step (i) is maintained in the range of 8-8.5; Preferably, after the coprecipitation reaction in step (i) is carried out for 5-6 hours, the feeding is stopped and the supernatant is removed; Preferably, the operations of removing the supernatant in step (i), step (ii) and step (iii) respectively and independently include stirring, standing, stratification, pumping water and alkali supplementation operations performed in sequence.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The pH of the coprecipitation reaction in step (ii) is maintained in the range of 7.1-7.4; Preferably, the supernatant removal operation in step (ii) is repeated until the particle size D50 is 2.5-3 μm; Preferably, the supernatant removal operation in step (ii) is repeated every 5-6 hours after the coprecipitation reaction is carried out; Preferably, the pH of the coprecipitation reaction in step (iii) is maintained in the range of 7.1-7.5; Preferably, the supernatant removal operation in step (iii) is repeated until the particle size D50 is 4.3-5 μm; Preferably, the supernatant removal operation in step (iii) is repeated after every 2-3 hours of coprecipitation reaction.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: (1) mixing a lithium-rich manganese-based precursor with a lithium source in a solid phase, and then calcining at 200-600° C. for 1-5 hours in an air or oxygen atmosphere, and then heating to 700-1000° C. and continuing to calcine for 2-20 hours, and then crushing and sieving to obtain a lithium-rich manganese-based primary crushed material; The lithium-rich manganese-based precursor includes a lithium-rich manganese-based carbonate precursor, and the method for preparing the lithium-rich manganese-based carbonate precursor includes: (i) passing a metal salt solution and an alkali solution into a base liquid for a coprecipitation reaction, wherein the pH of the coprecipitation reaction is maintained in the range of 8-8.5, and after 5-6 hours of the coprecipitation reaction, the feeding is stopped and a clear liquid removal operation is performed; The base liquid includes a complexing agent and a metaphosphate, and the pH of the base liquid is 9-10; (ii) After the removal of the supernatant in step (i) is completed, the metal salt solution and the alkali solution are continued to be introduced for coprecipitation reaction, and the pH of the coprecipitation reaction is maintained in the range of 7.1-7.4, and then the feeding is stopped and the supernatant removal operation is performed, and the supernatant removal operation is repeated every 5-6 hours of the coprecipitation reaction until the particle size D50 is 2.5-3 μm; (iii) After step (ii), continue to introduce the metal salt solution and the alkali solution to carry out the coprecipitation reaction, the pH of the coprecipitation reaction is maintained in the range of 7.1-7.5, then stop feeding, and remove the supernatant liquid, the supernatant liquid removal operation is repeated every 2-3 hours of the coprecipitation reaction until the particle size D50 is 4.3-5 μm, to obtain the lithium-rich manganese-based carbonate precursor; (2) mixing the lithium-rich manganese-based primary crushed material of step (1) with the bottom liquid phase, and then introducing a metal salt solution, a precipitant solution and a complexing agent solution to carry out a coprecipitation reaction, wherein the pH of the coprecipitation reaction is maintained in the range of 12-12.8 and the reaction time is 3-6 hours to obtain a coated lithium-rich manganese-based precursor; (3) solid-phase mixing the lithium source and the coated lithium-rich manganese-based precursor of step (2), and then secondary calcining at a temperature of 500-1100° C. for 5-20 h in air or oxygen atmosphere, and then crushing and screening to obtain the coated lithium-rich manganese-based positive electrode material; The surface of the coated lithium-rich manganese-based precursor is coated with metal hydroxide, and the molar ratio of lithium ions in the lithium source in step (3) to the total metal ions in the metal hydroxide is (0.4-0.6):

1.

9. A coated lithium-rich manganese-based positive electrode material, characterized in that: The coated lithium-rich manganese-based positive electrode material is prepared by the preparation method according to any one of claims 1 to 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the coated lithium-rich manganese-based positive electrode material as claimed in claim 9.

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