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

Abstract

The application provides a coated lithium-rich manganese-based positive electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a lithium-rich manganese-based precursor with a lithium source, and performing primary roasting and crushing and screening to obtain a lithium-rich manganese-based primary crushed material; mixing the lithium-rich manganese-based primary crushed material with a co-precipitation reaction raw material liquid phase, and performing co-precipitation reaction, wherein the co-precipitation reaction raw material comprises a metal salt solution, a precipitant solution and a complexing agent solution, to obtain a coated lithium-rich manganese-based precursor; mixing the lithium source with the coated lithium-rich manganese-based precursor, and performing secondary roasting to obtain the coated lithium-rich manganese-based positive electrode material. The preparation method can prepare the lithium-rich manganese-based positive electrode material with stable crystal structure by coating the nano-sized spinel material precursor, so that the problem of oxygen loss and voltage attenuation of the Li2MnO3 nano-domain region induced when the continuously accumulated lattice stress of the 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 driving range of vehicle-mounted lithium-ion batteries is a difficult problem for the popularization and application of electric vehicles. In order to improve the energy density of the battery, a high-energy density material that has been studied more at present is the lithium-rich manganese-based layered material. 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, 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 to be an ideal cathode material for the next-generation high-energy lithium-ion batteries.

[0003] However, there are still some problems in the industrial application of lithium-rich manganese-based materials at present, mainly including: side reactions related to the surface and interface caused by the irreversible release of lattice oxygen at high voltages, 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 lithium-rich oxide cathode materials, and this effect causes rapid attenuation of the voltage of the lithium-rich manganese-based layered materials. Through 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 unfavorable 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 lithium-rich manganese-based materials 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 non-uniform 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 lithium-rich manganese-based materials is explained from the perspective of the heterogeneous nanodomain structure of two LiTMO2 phases and Li2MnO3 phases.

[0005] Existing technologies that coat lithium-rich manganese-based materials with metal oxides, metal phosphates, or metal fluorides have limited effectiveness in suppressing oxygen release, metal migration, and dissolution. In recent years, however, technologies that construct integrated surface structures by occupying lithium sites on the surface lattice of lithium-rich manganese-based basal oxides with cations have seen rapid development and have proven highly effective in suppressing irreversible oxygen release and transition metal migration. For example, a general method for treating precursors with nitrates has been disclosed to construct stable integrated surface structures for lithium-rich manganese-based basal oxides, effectively suppressing interfacial reactions and structural evolution, significantly improving the long-cycle performance and voltage stability of the material. Furthermore, theoretical calculations have revealed the influence of different cation-constructed integrated surface structures on electrochemical performance, providing theoretical guidance for future research.

[0006] To improve the voltage decay problem during cycling, CN 113782748A discloses a modified cobalt-free lithium-rich cathode material, its preparation method and application. It is a lithium-rich manganese-based material coated with a lithium metal oxide layer after sintering metal hydrolysate and organic lithium salt by wet coating. Although the lithium metal oxide layer can effectively slow down the phase transition process and voltage decay of Li2MnO3, the lithium metal oxide layer is an inactive coating material, which will reduce the actual capacity of the lithium-rich manganese-based material.

[0007] Based on the above research, there is a need to provide a method for preparing a coated lithium-rich manganese-based cathode material. The coated lithium-rich manganese-based cathode material obtained by the preparation method has reduced lattice stress and significantly alleviates voltage decay during cycling. Summary of the Invention

[0008] The purpose of this invention is to provide a coated lithium-rich manganese-based cathode material, its preparation method, and its application. The preparation method uses a coated nanoscale spinel material precursor to prepare a lithium-rich manganese-based cathode material with a stable crystal structure. This can alleviate the problem of oxygen loss and voltage decay in the Li2MnO3 nanodomain region induced when the lattice stress of the eutectic Li2MnO3 continuously accumulates to a critical value.

[0009] To achieve this objective, the present invention adopts the following technical solution:

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

[0011] (1) A lithium-rich manganese-based precursor is mixed with a lithium source in a solid phase and then calcined once to obtain a lithium-rich manganese-based one-calcined material.

[0012] (2) Mix the metal salt solution, precipitant solution, complexing agent solution and the lithium-rich manganese-based primary roasted material described in step (1) and carry out a co-precipitation reaction to obtain a coated lithium-rich manganese-based precursor.

[0013] (3) The lithium source and the coated lithium-rich manganese-based precursor described in step (2) are mixed in a solid phase and then calcined twice to obtain the coated lithium-rich manganese-based cathode material.

[0014] This invention first sintersects a lithium-rich manganese-based precursor with a lithium source to prepare a lithium-rich manganese-based semi-finished product. Then, a nanoscale spinel material precursor with controllable thickness is coated on its surface by a staged co-precipitation method. Finally, a lithium-rich manganese-based finished material with a stable crystal structure is prepared. In this invention, when the coated spinel phase undergoes delithiation of LiTMO2 at a lower voltage and is accompanied by an increase in interlayer spacing, it can alleviate the oxygen loss and voltage decay problem in the Li2MnO3 nanodomain region induced by the continuous accumulation of lattice stress in the eutectic lattice Li2MnO3 reaching a critical value. Therefore, the lattice stress of the coated lithium-rich manganese-based cathode material prepared by the preparation method of this invention is reduced, and the voltage decay during cycling is significantly alleviated.

[0015] Preferably, the surface of the coated lithium-rich manganese-based precursor in step (2) is coated with metal hydroxide, and the molar ratio of lithium ions in the lithium source to the total metal ions in the metal hydroxide in step (3) 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. Other unlisted values ​​within the range are also applicable.

[0016] The metal hydroxide coated on the surface of the lithium-rich manganese-based precursor of the present invention has the molecular formula 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] The present invention describes a process where, after 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 cathode material. The purpose of adding a small amount of lithium source is to generate a nanoscale spinel coating layer with high electronic conductivity of the same element. If the amount of lithium source added is too small, a lithium-poor spinel structure is formed with low electronic conductivity. If the amount of lithium source added is too large, a non-spinel structure is formed, which is inconsistent with the design.

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

[0019] Preferably, after the secondary roasting in step (3), the material is further crushed and sieved.

[0020] Preferably, the sieve mesh size is 200-500 mesh, for example, it can be 200 mesh, 300 mesh, 400 mesh or 500 mesh, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

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

[0022] The time of the co-precipitation reaction in step (2) of this invention will affect the thickness of the coating layer. If the co-precipitation reaction time is too short, the coating layer will be too thin and the advantages of the spinel coating layer cannot be effectively utilized. If the co-precipitation reaction time is too long, the coating layer will be too thick, which will cause obvious grain boundaries to form between the lithium-rich manganese-based substrate and the spinel coating layer, resulting in uneven lithium insertion / extraction during charging and discharging and grain stress cracks.

[0023] Preferably, the mixing in step (2) includes mixing the lithium-rich manganese-based primary calcined material from step (1) with the bottom liquid, and then introducing the metal salt solution, precipitant solution and complexing agent solution from step (2) for 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. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the first 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 1-5 hours, for example, 1 hour, 3 hours or 5 hours, and then raising the temperature to 700-1000°C, for example, 700°C, 800°C or 1000°C, and continuing to calcinate for 2-20 hours, for example, 2 hours, 5 hours, 10 hours, 15 hours or 20 hours, but not limited to the listed values, and other unlisted values ​​within the 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) includes a lithium-rich manganese-based carbonate precursor.

[0030] The lithium-rich manganese-based carbonate precursor of this invention comprises TMCO3, wherein TM indicates 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 ≤15μm, for example, it can be 15μm, 10μm, 5μm, 3μm or 2μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 2-12μm.

[0032] Preferably, the tap density of the lithium-rich manganese-based precursor in step (1) is ≥0.4 g / cm³. 3 For example, it could be 0.4 g / cm³. 3 0.5g / cm 3 0.6g / cm 3 0.7g / cm 3 or 0.8g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range also apply, with ≥0.5 g / cm³ being preferred. 3 .

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

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

[0035] (i) Pass the metal salt solution and alkaline solution into the bottom liquid to carry out a co-precipitation reaction, then stop the feed and perform a declaratory liquid removal operation;

[0036] (ii) After the declaratory liquid operation described in step (i) is completed, continue to pass metal salt solution and alkaline solution to carry out co-precipitation reaction, then stop feeding and carry out declaratory liquid operation;

[0037] (iii) After the declaratory liquid operation described in step (ii) is completed, continue to pass metal salt solution and alkali solution to carry out co-precipitation reaction, then stop feeding and carry out declaratory liquid operation to obtain the lithium-rich manganese-based carbonate precursor.

[0038] The preparation method of the lithium-rich manganese-based precursor in step (1) of this invention adopts a stepwise co-precipitation method. Compared with the conventional one-step co-precipitation, the stepwise co-precipitation corresponds to the nucleation stage, the low-speed growth stage, and the fast growth stage, respectively. First, it can improve the nucleation density and avoid the formation of hollow structures. Second, the addition of a low-speed growth stage in the nucleation stage and the fast growth stage can make the grain growth 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 grain.

[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 alkaline solution in step (i) is greater than that in step (ii) and less than that in step (iii).

[0041] In this invention, step (i) is the nucleation stage, and steps (ii) and (iii) are the growth stages. The flow rates of the metal salt solution and the alkali solution in steps (i), (ii), and (iii) are different and have a specific relationship. The nucleation rate can be controlled by the ultra-low flow rate of the metal salt and the alkali solution (the ratio of alkali solution flow rate to metal salt flow rate is 3) in step (i), the slow growth rate of the initial grains can be controlled by the low flow rate of the metal salt and the alkali solution (the ratio of alkali solution flow rate to metal salt flow rate is 1.3) in step (ii), and the rapid growth rate of the later grains can be controlled by the high flow rate of the metal salt and the alkali solution (the ratio of alkali solution flow rate to 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 not limited to the listed values. Other unlisted values ​​within the 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. Other unlisted values ​​within the 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 not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the alkaline solutions described in steps (i), (ii), and (iii) each independently comprise a carbonate or a bicarbonate.

[0046] Preferably, the substrate in step (i) includes a complexing agent and metaphosphate, and the pH of the substrate is 9-10, for example, it can be 9, 9.5 or 10, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] In the staged preparation of lithium-rich manganese-based precursors of the present invention, metaphosphate is added to the bottom solution to play a dispersing role. Since step (i) is the nucleation stage, the addition of metaphosphate avoids the rapid growth of particles.

[0048] Preferably, the metaphosphate comprises sodium hexametaphosphate, and the complexing agent comprises 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 above 8, for example, it can be 8, 8.1 or 8.2, and at least below 8.5, for example, it can be 8.5, 8.4 or 8.3, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

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

[0051] Preferably, the declaratory liquid operations described in steps (i), (ii), and (iii) each independently include sequentially performed stirring, settling, stratification, water extraction, and alkali replenishment operations.

[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 is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] Preferably, the declaratory liquid removal operation described in step (ii) is repeated until the particle size D50 is 2.5-3 μm, for example, it can be 2.5 μm, 2.8 μm or 3 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] Preferably, the declaratory liquid removal operation described in step (ii) is repeated every 5-6 hours after the coprecipitation reaction, for example, 5 hours, 5.5 hours or 6 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] The declaratory liquid removal operation described in this invention is repeated every 5-6 hours after the coprecipitation reaction. This means that after 5-6 hours of coprecipitation reaction, the declaratory liquid removal operation is performed, and then the metal salt solution and alkali solution are continuously introduced to carry out the coprecipitation reaction. After another 5-6 hours of coprecipitation reaction, the declaratory liquid removal operation is performed again. This process 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, it can be 7.1, 7.15 or 7.2, and the highest pH is below 7.5, for example, it can be 7.5, 7.45 or 7.4, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0057] Preferably, the declaratory liquid removal operation described in step (iii) is repeated until the particle size D50 is 4.3-5 μm, for example, it can be 4.3 μm, 4.5 μm or 5 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

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

[0059] The declaratory liquid removal operation described in this invention is repeated every 2-3 hours after the coprecipitation reaction. This means that after 2-3 hours of coprecipitation reaction, the declaratory liquid removal operation is performed, and then the metal salt solution and alkali solution are continuously introduced to carry out the coprecipitation reaction. After another 2-3 hours of coprecipitation reaction, the declaratory liquid removal operation is performed again. This process is repeated until the particle size reaches the target particle size.

[0060] The temperature of the coprecipitation reaction described in this invention is 35-60℃, for example, it can be 35℃, 45℃, 50℃ or 60℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] The coprecipitation reaction described in this invention uses reaction vessels of sizes including 5L, 50L, 100L, and 1m. 3 5m 3 or 10m 3 .

[0062] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0063] (1) The lithium-rich manganese-based precursor is mixed with the lithium source in a solid phase, and then calcined at 200-600℃ for 1-5 hours in an air or oxygen atmosphere. Then the temperature is raised to 700-1000℃ and calcined for 2-20 hours. After crushing and sieving, the lithium-rich manganese-based primary crushed material is obtained.

[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) A metal salt solution and an alkaline solution are passed into the bottom liquid to carry out a co-precipitation reaction. The pH of the co-precipitation reaction is maintained in the range of 8-8.5. After the co-precipitation reaction is carried out for 5-6 hours, the feed is stopped and the supernatant is removed.

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

[0067] (ii) After the declaratory liquid operation described in step (i) is completed, continue to pass metal salt solution and alkaline solution to carry out coprecipitation reaction. The pH of the coprecipitation reaction is maintained in the range of 7.1-7.4. Then stop feeding and carry out declaratory liquid operation. The declaratory liquid operation is repeated every 5-6 hours after the coprecipitation reaction until the particle size D50 is 2.5-3μm.

[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, and the supernatant removal operation is carried out. 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 to carry out the 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 carry out 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 the second aspect, the present invention provides a coated lithium-rich manganese-based cathode material, and the coated lithium-rich manganese-based cathode material 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 [[ID= / / 19]]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, and other unlisted values within the numerical range are equally applicable.

[0075] In the third aspect, the present invention provides a lithium-ion battery, and the lithium-ion battery 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] This invention utilizes a single-step co-precipitation method to coat lithium-rich manganese-based materials with a nano-spinel structure material of controllable thickness. This allows electrochemically active ions to occupy surface lithium sites, which not only inhibits the migration of transition metal ions but also acts as a support 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 voltage decay. Furthermore, the coated lithium-rich manganese-based cathode material of this invention can also isolate the active components from the electrolyte, avoiding direct contact between the two and thus suppressing interfacial side reactions. Attached Figure Description

[0078] Figure 1 The charge-discharge curves are for batteries made from the coated lithium-rich manganese-based cathode material described in Examples 1-3 and Comparative Example 1. Detailed Implementation

[0079] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0080] Example 1

[0081] This embodiment provides a method for preparing a coated lithium-rich manganese-based cathode material, the 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 of pure water to prepare mixed metal salt solution A. 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 solution with a molar concentration of 10mol / L to 2L of pure water and stir for 30 minutes. Then add 4g of sodium hexametaphosphate and continue stirring for 10 minutes. The pH is measured to be 9.5, and reaction base solution B is obtained; (iii) Preparation of alkaline solution: Dissolve 200g of ammonium bicarbonate in 1L of pure water and stir for 20 minutes to prepare 2.53mol / L ammonium bicarbonate alkaline solution C;

[0083] First stage: Metal salt solution A and alkali solution C are pumped into the reaction base liquid B of a 5L reactor using a peristaltic pump. After 1 hour of reaction, the pH stabilizes at 8-8.5. The flow rate of mixed metal salt solution A is controlled at 2 ml / min, the flow rate of alkali solution C at 6 ml / min, the reactor temperature at 40℃, and the stirring speed at 1000 rpm. After 6 hours of reaction, the feed is stopped and stirring is continued for 30 minutes. Then the stirring is turned off and the mixture is allowed to stand for 3 hours. The lower precipitate and the upper clear liquid are clearly separated. 3L of water is pumped out of the upper clear liquid, and 0.3L of alkali solution C is added to the reactor to form the reaction base liquid D. The series of operations of stirring, standing, separation, pumping out water, and adding alkali is called "full reactor declaring clear liquid operation".

[0084] Second stage: Metal salt solution A and alkali solution C are pumped into the reaction base liquid D of a 5L reactor using a peristaltic pump. After 1 hour of reaction, the pH stabilizes at 7.1-7.4. The flow rate of mixed metal salt solution A is controlled at 3.2 ml / min, the flow rate of alkali solution C at 4.3 ml / min, the reactor temperature at 40℃, and the stirring speed at 1000 rpm. After 6 hours of reaction, the feed is stopped, and stirring continues for 30 minutes. Then, the stirring is turned off, and the mixture is allowed to stand for 3 hours. The lower precipitate and the upper clear liquid are clearly separated. 3L of the upper clear liquid is pumped out, and 0.3L of alkali solution C is added to the reactor to form the reaction base liquid E. The second stage is repeated until the lower precipitate D is formed. 50 The particle size reaches 2.7 μm. During this period, a "full-bottle declaratory liquid operation" is performed every 6 hours. When the particle size is reached, the reaction bottom liquid F is formed.

[0085] Third stage: Metal salt solution A and alkali solution C are pumped into the reaction base liquid F of a 5L reactor using a peristaltic pump. After 0.5 hours of reaction, the pH stabilizes at 7.1-7.5. The flow rate of mixed metal salt solution A is controlled at 6.4 ml / min, and the flow rate of alkali solution C is controlled at 8.6 ml / min. The reactor temperature is 40℃, and the stirring speed is 1000 rpm. A "full reactor declaratory cleaning operation" is performed every 3 hours until the lower precipitate D is obtained. 50 Once the design requirement of 4.5μm is reached, feeding and stirring are stopped, and the mixture is allowed to stand in the reactor for 1 hour. The lower precipitate and the upper clear liquid are clearly separated. 3L of water is pumped from the upper clear liquid, and then the lower precipitate is filtered, washed with water, and dried to obtain the lithium-rich manganese-based carbonate precursor.

[0086] (2) Preparation of lithium-rich manganese-based primary pulverized material: Based on the lithium-rich manganese-based cathode material Li 1.17 Ni 0.25 Mn 0.58 The composition of O2, with median particle size D 50 =4.4μm, tap density 0.5g / cm³ 3 Lithium-rich manganese-based carbonate precursor and median particle size D 50Battery-grade lithium carbonate with a particle size of 20 μm and a purity of 99.6% was uniformly mixed at a molar ratio of lithium ions to metal ions of 1.4:1. The mixed material was then calcined in an air atmosphere at a platform of 300°C in a roller kiln for 3 hours, followed by a further increase in temperature to a platform of 900°C for 10 hours to obtain lithium-rich manganese-based primary calcined material. After further pulverization and grading at a frequency of 18 Hz, lithium-rich manganese-based primary pulverized material I was obtained.

[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 of pure water to prepare mixed metal salt solution G, with molar concentrations of 0.6mol / L NiSO4·6H2O and 1.8mol / L MnSO4·H2O, respectively; (ii) Preparation of reaction base solution: Add 5ml of concentrated ammonia solution with a molar concentration of 10mol / L to 2L of pure water and stir for 30 minutes, then add NaOH and continue stirring for 10 minutes, adjusting the pH to 12.4-12.6 to 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 solution with a molar concentration of 10mol / L in 1L of pure water to form a 2mol / L dilute ammonia solution K;

[0088] First, 1 kg of lithium-rich manganese-based primary pulverized material I was added to the bottom liquid H of a 5 L reactor and stirred for 10 minutes. Then, metal salt solution G and alkali solution J were pumped into the bottom liquid H of the 5 L reactor using a peristaltic pump. After 0.5 hours of reaction, the pH stabilized at 12.3–12.5. The flow rate of mixed metal salt solution G was controlled at 5 ml / min, the flow rate of dilute ammonia solution K at 0.3 ml / min, and the flow rate of alkali solution J was automatically adjusted online according to the pH value. The reactor temperature was 50℃, and the stirring speed was 1200 rpm. After 6 hours of reaction, the feeding was stopped, and stirring continued for 30 minutes. Then, the feeding and stirring were stopped, and the mixture was allowed to stand in the reactor for 1 hour. The lower precipitate and the upper clear liquid were clearly separated. 3 L of the upper clear liquid was pumped out, and the lower precipitate was filtered, washed with water, and dried to obtain Ni-coated material. 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 are combined. 50Battery-grade lithium carbonate with a particle size of 6 μm and a purity of 99.7% was uniformly mixed with lithium ions at a molar ratio of 0.5:1 to the total amount of metal ions in the hydroxide coating to obtain a coated lithium-rich manganese-based lithium salt mixture S. This mixture was then 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. After pulverization and 200-mesh sieving, the coated lithium-rich manganese-based cathode material was obtained.

[0090] The cobalt-free lithium-rich manganese-based cathode material Li prepared in this embodiment 1.17 Ni 0.25 Mn 0.58 The O2 nano-spinel structure material, with a coating thickness of 30 nm, allows electrochemically active ions Ni and Mn to partially occupy surface lithium sites. This not only inhibits the migration of transition metal ions but also acts as a support to improve the structural stability of the oxygen framework, slowing down irreversible oxygen release and improving the redox reversibility of anions, effectively reducing voltage drop by 0.06 V. Furthermore, this design isolates the active components from the electrolyte, preventing direct contact between the two and thus suppressing interfacial side reactions.

[0091] Example 2

[0092] This embodiment provides a method for preparing a coated lithium-rich manganese-based cathode material, the 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 of 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 solution with a molar concentration of 10mol / L to 2L of pure water and stir for 30 minutes. Then add 4g of sodium hexametaphosphate and continue stirring for 10 minutes. The pH is measured to be 9, and the reaction base solution B is obtained; (iii) Preparation of alkaline solution: Dissolve 200g of ammonium bicarbonate in 1L of pure water and stir for 20 minutes to prepare 2.53mol / L ammonium bicarbonate alkaline solution C.

[0094] First stage: Metal salt solution A and alkali solution C are pumped into the reaction base liquid B of a 5L reactor using a peristaltic pump. After 0.5 to 1 hour of reaction, the pH stabilizes at 8 to 8.5. The flow rate of mixed metal salt solution A is controlled at 2.3 ml / min, the flow rate of alkali solution C is controlled at 6.9 ml / min, the reactor temperature is 40℃, and the stirring speed is 1000 rpm. After 6 hours of reaction, the feed is stopped and stirring is continued for 30 minutes. Then the stirring is turned off and the mixture is allowed to stand for 3 hours. The lower precipitate and the upper clear liquid are clearly separated. 3L of water is pumped out of the supernatant, and 0.3L of alkali solution C is added to the reactor to form the reaction base liquid D. The series of operations of stirring, standing, separation, pumping water, and adding alkali is named "full reactor declaring operation".

[0095] Second stage: Metal salt solution A and alkali solution C are pumped into the reaction base liquid D of a 5L reactor using a peristaltic pump. After 0.5 hours of reaction, the pH stabilizes at 7.1-7.4. The flow rate of mixed metal salt solution A is controlled at 3.5 ml / min, the flow rate of alkali solution C at 4.5 ml / min, the reactor temperature at 40℃, and the stirring speed at 1000 rpm. After 6 hours of reaction, the feed is stopped, and stirring continues for 30 minutes. Then, the stirring is turned off, and the mixture is allowed to stand for 3 hours. The lower precipitate and the upper clear liquid are clearly separated. 3L of the upper clear liquid is pumped out, and 0.3L of alkali solution C is added to the reactor to form the reaction base liquid E. The second stage is repeated until the lower precipitate D is formed. 50 The particle size reaches 3.0 μm. During this period, a "full-bottle declaratory liquid operation" is performed every 6 hours. When the particle size is reached, the reaction bottom liquid F is formed.

[0096] Third stage: Metal salt solution A and alkali solution C are pumped into the reaction base liquid F of a 5L reactor using a peristaltic pump. After 1 hour of reaction, the pH stabilizes at 7.1-7.5. The flow rate of mixed metal salt solution A is controlled at 7 ml / min, and the flow rate of alkali solution C is controlled at 9 ml / min. The reactor temperature is 40℃, and the stirring speed is 1000 rpm. A "full reactor declaratory cleaning operation" is performed every 3 hours until the lower precipitate D is obtained. 50 Once the design requirement of 5.0 μm is reached, feeding and stirring are stopped, and the mixture is allowed to stand in the reactor for 1 hour. The lower precipitate and the upper clear liquid are clearly separated. 3 L of water is pumped from the upper clear liquid, and then the lower precipitate is filtered, washed with water, and dried to obtain the lithium-rich manganese-based carbonate precursor.

[0097] (2) Preparation of lithium-rich manganese-based primary pulverized material: Based on the lithium-rich manganese-based cathode material Li 1.20 Ni 0.2 Mn 0.6 The composition of O2, with median particle size D 50 =5.0μm, tap density 0.6g / cm³ 3 Lithium-rich manganese-based carbonate precursor and median particle size D 50Battery-grade lithium carbonate with a particle size of 6μm and a purity of 99.5% was uniformly mixed at a molar ratio of lithium ions to metal ions of 1.5:1. The mixed material was then calcined in a roller kiln at 400℃ for 2 hours under an oxygen atmosphere, and then calcined at 850℃ for 15 hours to obtain lithium-rich manganese-based primary calcined material. After being pulverized and graded at a frequency of 15Hz, lithium-rich manganese-based primary pulverized material I was obtained.

[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 of pure water to prepare mixed metal salt solution G, with molar concentrations of 0.6mol / L NiSO4·6H2O and 1.8mol / L MnSO4·H2O, respectively; (ii) Preparation of reaction base solution: Add 5ml of concentrated ammonia solution with a molar concentration of 10mol / L to 2L of pure water and stir for 30 minutes, then add NaOH and continue stirring for 10 minutes, adjust the pH to 12.6 to 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 solution with a molar concentration of 10mol / L in 1L of pure water to form a 2mol / L dilute ammonia solution K;

[0099] First, 1 kg of lithium-rich manganese-based primary pulverized material I was added to the bottom liquid H of a 5 L reactor and stirred for 10 minutes. Then, metal salt solution G and alkali solution J were pumped into the bottom liquid H of the 5 L reactor using a peristaltic pump. After 0.5 hours of reaction, the pH stabilized at 12.3–12.5. The flow rate of mixed metal salt solution G was controlled at 5 ml / min, the flow rate of dilute ammonia solution K at 0.3 ml / min, and the flow rate of alkali solution J was automatically adjusted online according to the pH value. The reactor temperature was 50℃, and the stirring speed was 1200 rpm. After 6 hours of reaction, the feeding was stopped and stirring continued for 30 minutes. Then, the feeding and stirring were stopped, and the mixture was allowed to stand in the reactor for 1 hour. The lower precipitate and the upper clear liquid were clearly separated. 3 L of water was pumped from the upper clear liquid, and the lower precipitate was filtered, washed with water, and dried to obtain Ni-coated material. 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 are combined. 50Battery-grade lithium hydroxide monohydrate with a purity of 55% and a particle size of 5μm was uniformly mixed with lithium ions at a molar ratio of 0.52:1 to obtain a coated lithium-rich manganese-based lithium salt mixture S. This mixture was then calcined in an air atmosphere at 700℃ in a roller kiln for 10 hours to obtain a coated lithium-rich manganese-based secondary calcined material. After pulverization and sieving through a 300-mesh sieve, the final product, a coated lithium-rich manganese-based finished product, was obtained.

[0101] The coated cobalt-free lithium-rich manganese-based cathode material Li prepared in this embodiment 1.20 Ni 0.2 Mn 0.6 With O2 and a 20nm thick coating of nano-spinel structure material, the voltage drop was effectively reduced by 0.09V.

[0102] Example 3

[0103] This embodiment provides a method for preparing a coated lithium-rich manganese-based cathode material, including 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 solutions: Dissolve three metal salts, NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O, in 5L of 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 solution with a molar concentration of 10mol / L to 2L of pure water and stir for 30 minutes. Then add 4g of sodium hexametaphosphate and continue stirring for 10 minutes. The pH is measured to be 10, and the reaction base solution B is obtained; (iii) Preparation of alkaline solution: Dissolve 200g of ammonium bicarbonate in 1L of pure water and stir for 20 minutes to prepare a 2.53mol / L ammonium bicarbonate alkaline solution C.

[0105] First stage: Metal salt solution A and alkali solution C are pumped into the reaction base liquid B of a 5L reactor using a peristaltic pump. After 1 hour of reaction, the pH stabilizes at 8-8.5. The flow rate of mixed metal salt solution A is controlled at 1.8 ml / min, the flow rate of alkali solution C is controlled at 5.4 ml / min, the reactor temperature is 40℃, and the stirring speed is 1000 rpm. After 6 hours of reaction, the feed is stopped and stirring is continued for 30 minutes. Then the stirring is turned off and the mixture is allowed to stand for 3 hours. The lower precipitate and the upper clear liquid are clearly separated. 3L of water is pumped out of the supernatant, and 0.3L of alkali solution C is added to the reactor to form the reaction base liquid D. The series of operations including stirring, standing, separation, pumping out water, and adding alkali is named "full reactor declaring operation".

[0106] Second stage: Metal salt solution A and alkali solution C are pumped into the reaction base liquid D of a 5L reactor using a peristaltic pump. After 1 hour of reaction, the pH stabilizes at 7.1-7.4. The flow rate of mixed metal salt solution A is controlled at 3 ml / min, the flow rate of alkali solution C at 4 ml / min, the reactor temperature at 40℃, and the stirring speed at 1000 rpm. After 6 hours of reaction, the feed is stopped, and stirring continues for 30 minutes. Then, the stirring is turned off, and the mixture is allowed to stand for 3 hours. The lower precipitate and the upper clear liquid are clearly separated. 3L of the upper clear liquid is pumped out, and 0.3L of alkali solution C is added to the reactor to form the reaction base liquid E. The second stage is repeated until the lower precipitate D is formed. 50 The particle size reaches 2.8 μm. During this period, a "full-bottle declaratory liquid operation" is performed every 6 hours. When the particle size is reached, the reaction bottom liquid F is formed.

[0107] Third stage: Metal salt solution A and alkali solution C are pumped into the reaction base liquid F of a 5L reactor using a peristaltic pump. After 0.5 hours of reaction, the pH stabilizes at 7.1-7.5. The flow rate of mixed metal salt solution A is controlled at 6 ml / min, and the flow rate of alkali solution C is controlled at 8 ml / min. The reactor temperature is 40℃, and the stirring speed is 1000 rpm. A "full reactor declaratory cleaning operation" is performed every 3 hours until the lower precipitate D is obtained. 50 Once the design requirement of 4.3μm is reached, feeding and stirring are stopped, and the mixture is allowed to stand in the reactor for 1 hour. The lower precipitate and the upper clear liquid are clearly separated. 3L of water is pumped from the upper clear liquid, and then the lower precipitate is filtered, washed with water, and dried to obtain the lithium-rich manganese-based carbonate precursor.

[0108] (2) Preparation of lithium-rich manganese-based primary pulverized material: Based on the lithium-rich manganese-based cathode material Li 1.17 Ni 0.25 Co 0.1 Mn 0.48 The composition of O2, with median particle size D 50 =3.4μm, tap density 0.4g / cm³ 3 Lithium-rich manganese-based carbonate precursor and median particle size D 50 Battery-grade lithium carbonate with a particle size of 3.5 μm and a purity of 99.6% was uniformly mixed at a molar ratio of lithium ions to metal ions of 1.4:1. The mixed material was then calcined in an air atmosphere at a plateau temperature of 600°C for 2 hours, followed by calcination at a plateau temperature of 1000°C for 8 hours to obtain lithium-rich manganese-based primary calcined material. After further pulverization and grading at a frequency of 10 Hz, lithium-rich manganese-based primary pulverized material I was obtained.

[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 of pure water to prepare 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 to 2L of pure water and stir for 30 minutes. Then add NaOH and continue stirring for 10 minutes. Adjust the pH to 12.4~12.6 to 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 200 ml of concentrated ammonia solution with a molar concentration of 10 mol / L 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 pulverized material I was added to the bottom liquid H of a 5 L reactor and stirred for 10 minutes. Then, metal salt solution G and alkali solution J were pumped into the bottom liquid H of the 5 L reactor using a peristaltic pump. After 0.5 hours of reaction, the pH stabilized at 12.3–12.5. The flow rate of mixed metal salt solution G was controlled at 5 ml / min, the flow rate of dilute ammonia solution K at 0.3 ml / min, and the flow rate of alkali solution J was automatically adjusted online according to the pH value. The reactor temperature was 50℃, and the stirring speed was 1200 rpm. After 6 hours of reaction, the feeding was stopped and stirring continued for 30 minutes. Then, the feeding and stirring were stopped, and the mixture was allowed to stand in the reactor for 1 hour. The lower precipitate and the upper clear liquid were clearly separated. 3 L of water was pumped from the upper clear liquid, and the lower precipitate was filtered, washed with water, and dried to obtain Ni-coated material. 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 are combined. 50 Battery-grade lithium carbonate with a particle size of 6μm and a purity of 99.7% was uniformly mixed with lithium ions at a molar ratio of 0.47:1 to obtain a coated lithium-rich manganese-based lithium salt mixture S. The coated lithium-rich manganese-based secondary calcined material was obtained by calcining it in an air atmosphere at 900℃ for 5 hours in a roller kiln. After pulverization and sieving through a 400-mesh sieve, the final product, coated lithium-rich manganese-based finished product, was obtained.

[0112] The coated lithium-rich manganese-based cathode material Li prepared in this embodiment has a cobalt coating. 1.17 Ni 0.25 Co 0.1 Mn 0.48The O2 nano-spinel structure material coating thickness is 10nm, which effectively reduces the voltage drop by 0.10V.

[0113] Example 4

[0114] This embodiment provides a method for preparing a coated lithium-rich manganese-based cathode material. Except for step (4), in which the molar ratio of lithium ions to the total amount of metal ions in the hydroxide coating is 0.4:1, the preparation method is the same as in Example 1.

[0115] Example 5

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

[0117] Example 6

[0118] This embodiment provides a method for preparing a coated lithium-rich manganese-based cathode material. Except for step (4), in which the molar ratio of lithium ions to the total amount of metal ions in the hydroxide coating is 0.3:1, the preparation method is the same as in Example 1.

[0119] Example 7

[0120] This embodiment provides a method for preparing a coated lithium-rich manganese-based cathode material. Except for step (4), in which the molar ratio of lithium ions to the total amount of metal ions in the hydroxide coating is 0.7:1, the preparation method is the same as in Example 1.

[0121] Example 8

[0122] This embodiment provides a method for preparing a coated lithium-rich manganese-based cathode material. Except for stopping the feeding after the reaction in step (3) is carried out for 3 hours, the preparation method is the same as in Example 1.

[0123] Example 9

[0124] This embodiment provides a method for preparing a coated lithium-rich manganese-based cathode material. Except for stopping the feeding after the reaction in step (3) is carried out for 1.5 hours, the preparation method is the same as in Example 1.

[0125] Example 10

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

[0127] Example 11

[0128] This embodiment provides a method for preparing a coated lithium-rich manganese-based cathode material. The preparation method is the same as that in Example 1, except that step (1) is prepared by one-step co-precipitation instead of three-stage co-precipitation.

[0129] Step (1) of this embodiment 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 of pure water to prepare mixed metal salt solution A. 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 solution with a molar concentration of 10mol / L to 2L of pure water and stir for 30 minutes. Then add 4g of sodium hexametaphosphate and continue stirring for 10 minutes. The pH is measured to be 9.5, and reaction base solution B is obtained; (iii) Preparation of alkaline solution: Dissolve 200g of ammonium bicarbonate in 1L of pure water and stir for 20 minutes to prepare 2.53mol / L ammonium bicarbonate alkaline solution C;

[0131] One-step coprecipitation: Metal salt solution A and alkali solution C are pumped into the reaction base liquid B of a 5L reactor using a peristaltic pump. After 1 hour of reaction, the pH stabilizes at 8-8.5. The flow rate of mixed metal salt solution A is controlled at 3.2 ml / min, the flow rate of alkali solution C at 4.3 ml / min, the reactor temperature at 40℃, and the stirring speed at 1000 rpm. After 6 hours of reaction, the feed is stopped, and stirring continues for 30 minutes. Then, the stirring is turned off and the mixture is allowed to stand for 3 hours. The lower precipitate and the upper clear liquid are clearly separated. 3L of the upper clear liquid is pumped out, and 0.3L of alkali solution C is added to the reactor to form the reaction base liquid D. The series of operations of stirring, standing, separation, pumping out water, and adding alkali is called "full reactor declaring clear liquid operation". The above coprecipitation reaction operation is repeated until the lower precipitate D is formed. 50 Once the design requirement of 4.5μm is reached, feeding and stirring are stopped, and the mixture is allowed to stand in the reactor for 1 hour. The lower precipitate and the upper clear liquid are clearly separated. 3L of water is pumped from the upper clear liquid, and then the lower precipitate is filtered, washed with water, and dried to obtain the lithium-rich manganese-based carbonate precursor.

[0132] Comparative Example 1

[0133] This embodiment provides a method for preparing a lithium-rich manganese-based cathode material. The preparation method is the same as that in Example 1 except that steps (3) and (4) are not performed.

[0134] The cathode materials obtained in the above embodiments and comparative examples were used to fabricate 2032-type coin cells and tested. The charge / discharge cutoff voltage was 2.3-4.55V. The charge / discharge curves of the batteries made from the coated lithium-rich manganese-based cathode materials described in Examples 1-3 and Comparative Example 1 are shown in the figure. Figure 1 As shown, the obtained electrochemical performance data are presented in Table 1 below:

[0135] Table 1

[0136]

[0137]

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

[0139] In summary, this invention provides a coated lithium-rich manganese-based cathode material, its preparation method, and its application. The preparation method uses a coated nanoscale spinel precursor to prepare a lithium-rich manganese-based cathode material with a stable crystal structure. This can alleviate the problem of oxygen loss and voltage decay in the Li2MnO3 nanodomain region when the lattice stress of the eutectic Li2MnO3 continuously accumulates to a critical value.

[0140] The above description is only a specific embodiment 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 conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection 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) mixing a lithium-rich manganese-based precursor with a lithium source by solid phase mixing, then calcining at 200-600°C for 1-5h in an air or oxygen atmosphere, then raising the temperature to 700-1000°C and continuing to calcine for 2-20h, then crushing and sieving to obtain a lithium-rich manganese-based primary crushed material; The lithium-rich manganese-based precursor comprises a lithium-rich manganese-based carbonate precursor, and a method for preparing the lithium-rich manganese-based carbonate precursor comprises: (i) introducing a metal salt solution and a lye into a bottom liquid to perform a co-precipitation reaction, the pH of the co-precipitation reaction being maintained within a range of 8-8.5, the feeding being stopped after the co-precipitation reaction is performed for 5-6h, and a supernatant removal operation is performed; The bottom liquid comprises a complexing agent and a metaphosphate, and the pH of the bottom liquid is 9-10; (ii) after the supernatant removal operation in step (i) is completed, the co-precipitation reaction is continued by continuously introducing a metal salt solution and a lye, the pH of the co-precipitation reaction being maintained within a range of 7.1-7.4, then the feeding is stopped, and a supernatant removal operation is performed, the supernatant removal operation being repeatedly performed every 5-6h after the co-precipitation reaction is performed, until the particle size D50 is 2.5-3μm; (iii) after step (ii) is completed, the co-precipitation reaction is continued by continuously introducing a metal salt solution and a lye, the pH of the co-precipitation reaction being maintained within a range of 7.1-7.5, then the feeding is stopped, and a supernatant removal operation is performed, the supernatant removal operation being repeatedly performed every 2-3h after the co-precipitation reaction is performed, until the particle size D50 is 4.3-5μm, to obtain the lithium-rich manganese-based carbonate precursor; (2) mixing the lithium-rich manganese-based primary crushed material in step (1) with a bottom liquid by liquid phase mixing, then introducing a metal salt solution, a precipitant solution and a complexing agent solution to perform a co-precipitation reaction, the pH of the co-precipitation reaction being maintained within a range of 12-12.8, and the time being 3-6h, to obtain a coated lithium-rich manganese-based precursor; (3) mixing a lithium source and the coated lithium-rich manganese-based precursor in step (2) by solid phase mixing, then performing secondary calcination at a temperature of 500-1100°C for 5-20h in an air or oxygen atmosphere, then crushing and sieving to obtain the coated lithium-rich manganese-based positive electrode material; The surface of the coated lithium-rich manganese-based precursor is coated with a metal hydroxide, and the molar ratio of lithium ions in the lithium source in step (3) to total metal ions in the metal hydroxide is (0.4-0.6):

1.

2. The production method according to claim 1, characterized by, 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.

3. The preparation method according to claim 1, characterized in that, The flow rate of the metal salt solution introduced in step (i) is less than the flow rate of the metal salt solution introduced in step (ii), and the flow rate of the metal salt solution introduced in step (ii) is less than the flow rate of the metal salt solution introduced in step (iii).

4. The method of claim 1, wherein, The flow rate of the lye introduced in step (i) is greater than the flow rate of the lye introduced in step (ii), and less than the flow rate of the lye introduced in step (iii).

5. The preparation method according to claim 1, characterized in that, The supernatant removal operations in steps (i), (ii) and (iii) each independently comprise stirring, standing, layering, water pumping and alkali supplementing operations performed in sequence.

6. 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 in any one of claims 1-5.

7. A lithium-ion battery, characterized by The lithium ion battery comprises the coated lithium-rich manganese-based positive electrode material in claim 6.

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