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

Abstract

The invention provides a modified lithium-rich manganese-based positive electrode material and a preparation method and application thereof, the preparation method comprises the following steps: mixing an initial lithium-rich manganese-based positive electrode material with an organic metal salt coating solution, and then removing a solvent to obtain a mixture; the organic metal salt coating liquid comprises organic alcohol metal salt and an alcohol solvent; and calcining the mixture to obtain the modified lithium-rich manganese-based positive electrode material. The preparation method disclosed by the invention is a composite modification method for overcoming inherent defects in two aspects of the lithium-rich manganese-based positive electrode material, and surface induced structure transformation and metal oxide coating of the lithium-rich manganese-based positive electrode material can be synchronously modified, so that the first coulombic efficiency, the cycling stability and the rate capability of the lithium-rich manganese-based positive electrode material are improved.

Description

Technical Field

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

[0002] Lithium-ion secondary batteries have been rapidly applied and developed in the field of power batteries such as new energy vehicles due to their many advantages such as high energy density, long service life, no memory effect, and adaptability to fast charging and discharging. Among the four major materials of power batteries (cathode material, anode material, electrolyte, and separator material), the importance of the cathode material is particularly prominent, and its electrochemical performance and cost directly determine the overall performance and cost of the battery. At present, traditional cathode materials such as lithium cobaltate, lithium manganate, lithium iron phosphate, and low-nickel ternary materials are rapidly changing to high-nickel ternary materials and lithium-rich manganese-based cathode materials.

[0003] The chemical general formula of the lithium-rich manganese-based cathode material is xLi2MnO3·(1-x)LiMO2 (M = Ni, Co, Mn). Because it has both anion and cation redox reactions at the same time, the specific capacity of the material and the energy density of the battery monomer can reach 296.6 mAh / g (0.1C) and 300 Wh / kg respectively. And due to the substantial increase in the manganese content, the safety and cost of the material have been significantly improved, which is an ideal cathode material for the next generation of power batteries. However, there are still the following problems in the popularization and application of the current lithium-rich manganese-based cathode material:

[0004] (1) The "Li-Li dumbbell" effect in the component Li2MnO3 of the lithium-rich manganese-based cathode material and the poor reaction kinetics at the Mn site lead to a low lithium-ion diffusion coefficient and poor rate performance of the material;

[0005] (2) The loss of lattice oxygen in the lithium-rich manganese-based cathode material during the cycling process leads to irreversible structural transformation, resulting in a low initial Coulomb efficiency and poor cycle stability.

[0006] A large number of studies have found that the structural transformation caused by this lattice oxygen starts from the surface. Therefore, the prior art research on the modification of lithium-rich manganese-based cathode materials mainly focuses on surface modification. In the prior art, lithium-rich manganese-based cathode materials are surface-coated with oxides such as MgO, Al2O3, and ZrO2 to improve the first Coulombic efficiency, rate performance, and cycling performance. However, these are all modifications of lithium-rich manganese-based cathode materials based on the characteristics of the coating layer. Therefore, the improvement of their electrochemical performance is limited, and the inherent defects of lithium-rich manganese-based cathode materials cannot be fundamentally overcome. For example, CN104577101A discloses a preparation method for surface-modifying lithium-rich manganese-based cathode materials for lithium-ion batteries by mixed-air calcination with ammonium salts. This method is similar to the research on surface chemical etching and pre-lithium / oxygen removal using NH4HCO3 and CO(NH2)2 disclosed in recent years. Part of Li2O is removed from the material surface in advance to induce the formation of a spinel phase in the surface layer structure, improving the first Coulombic efficiency and cycling stability of the material. After 50 cycles at 0.1C, the capacity retention rate can reach more than 95%. This type of method overcomes the inherent problem of lattice oxygen loss in lithium-rich manganese-based cathode materials to a certain extent, but ignores another important defect of its poor kinetic behavior (lithium-ion diffusion coefficient). In addition, the washing and drying steps after mixed calcination with ammonium salts increase the processing flow of the material. Therefore, the current lithium-rich manganese-based cathode materials and their modification methods cannot be widely used.

[0007] Based on the above research, aiming at the inherent defects of lithium-rich manganese-based cathode materials, the effect of a single surface modification method is limited. Summary of the Invention

[0008] The purpose of the present invention is to provide a modified lithium-rich manganese-based cathode material, its preparation method and application, especially a lithium-rich manganese-based cathode material with synchronous modification of surface-induced structure transformation and metal oxide coating, its preparation method and application. The preparation method is a composite modification method that overcomes two inherent defects of lithium-rich manganese-based cathode materials, and can synchronously modify the surface-induced structure transformation and metal oxide coating of lithium-rich manganese-based cathode materials, thereby improving the first Coulombic efficiency, cycling stability, and rate performance of lithium-rich manganese-based cathode materials.

[0009] To achieve the purpose of this invention, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a preparation method for a modified lithium-rich manganese-based cathode material, and the preparation method includes the following steps:

[0011] (1) Mix the initial lithium-rich manganese-based cathode material with an organometallic salt coating solution, and then remove the solvent to obtain a mixture.

[0012] The organometallic salt coating solution includes an organoalcohol metal salt and an alcohol solvent.

[0013] (2) Calcinate the mixture described in step (1) to obtain the modified lithium-rich manganese-based cathode material.

[0014] In the present invention, the initial lithium-rich manganese-based cathode material is mixed with an organometallic salt coating solution, the solvent is removed, and then calcined. During calcination, the organic functional groups of the organoalcohol metal salt decompose under oxygen deficiency, which can induce pre-oxygen removal on the surface of the lithium-rich manganese-based cathode material, thereby realizing the transformation of part of the surface structure of the lithium-rich manganese-based cathode material from a layered structure to a spinel structure, achieving surface-induced structure transformation modification, reducing the irreversible Li loss that occurs during the first charge above 4.5 V, stabilizing the material structure and improving the first Coulombic efficiency; moreover, the oxide formed after calcination of the organoalcohol metal salt uniformly coats the surface of the lithium-rich manganese-based cathode material, realizing metal oxide coating modification, increasing the cycle stability, surface conductivity and lithium ion diffusion coefficient of the material, thereby improving the cycle performance and rate performance, and obtaining a lithium-rich manganese-based cathode material with synchronous modification of surface-induced structure transformation and metal oxide coating.

[0015] In addition, the organometallic salt coating solution in the present invention includes an organoalcohol metal salt and an alcohol solvent, which can effectively prevent the hydrolysis of the organoalcohol metal salt in an aqueous solution, resulting in the problem of uneven coating; at the same time, the organoalcohol metal salt Me-O-H can react with LiOH on the surface of the lithium-rich manganese-based cathode material to remove H2O, making the organoalcohol metal salt tend to be more evenly distributed on the surface of the initial lithium-rich manganese cathode material.

[0016] Preferably, the metal in the organoalcohol metal salt described in step (1) includes any one or a combination of at least two of Mg, Ti, Nb or W.

[0017] The metal oxide obtained after decomposition of the organoalcohol metal salt in step (1) of the present invention has the ability to reduce the surface overpotential or increase the lithium ion conductivity coefficient of the lithium-rich manganese-based cathode material.

[0018] Preferably, the organic group in the organoalcohol metal salt described in step (1) includes an alkoxy group with a carbon atom number ≤ 3, preferably any one or a combination of at least two of methoxy (CH3O-), ethoxy (C2H5O-) or propoxy [(CH3)2CHO- or CH3CH2CH2O-].

[0019] When the organic group in the organoalcohol metal salt of the present invention decomposes, C and H elements can capture the oxygen element on the surface of the lithium-rich manganese cathode material, inducing the transformation of the surface layered structure.

[0020] Preferably, the organoalcohol metal salt described in step (1) includes a methanol metal salt and / or an isopropanol metal salt, preferably a combination of a methanol metal salt and an isopropanol metal salt.

[0021] The metal salts of organic alcohols of the present invention are preferably metal salts of methanol and / or metal salts of isopropanol, and more preferably a combination of metal salts of methanol and metal salts of isopropanol. Since metal salts of methanol are more likely to decompose and are more likely to induce deoxidation on the surface of the initial lithium-rich manganese-based cathode material, the C and H elements of the metal salts of isopropanol can capture more oxygen elements on the surface of the lithium-rich manganese cathode material, promoting continuous deoxidation on the surface of the initial lithium-rich manganese-based cathode material and causing more structural transformations. Therefore, the present invention preferably uses metal salts of methanol and / or metal salts of isopropanol, and further preferably a combination of metal salts of methanol and metal salts of isopropanol.

[0022] Preferably, the molar ratio of the metal salt of methanol to the metal salt of isopropanol is (1 - 3):(1 - 3), for example, it can be 1:1, 1:2, 2:1, 1:3 or 3:1, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0023] Preferably, the metal salts of organic alcohols in step (1) include any one or a combination of at least two of magnesium methoxide, titanium isopropoxide, niobium methoxide or tungsten isopropoxide.

[0024] Preferably, the molar amount of the metal salts of organic alcohols in step (1) is 0.35 - 12.50% of the molar amount of the initial lithium-rich manganese-based cathode material. For example, it can be 0.35%, 1%, 3%, 5%, 7%, 9%, 11% or 12.50%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0025] The present invention preferably has the molar amount of the metal salts of organic alcohols within a suitable range, which can effectively achieve synchronous modification of surface-induced structure transformation and metal oxide coating, and can also avoid a decrease in the energy specific capacity of the material and surface transition reconstruction when too much metal salts of organic alcohols are coated.

[0026] The stoichiometric relationship among the initial lithium-rich manganese-based cathode material, the metal salts of organic alcohols and the alcohol solvent in the present invention is as follows:

[0027] Assume the mass of the initial lithium-rich manganese-based cathode material is m1, the molar mass is M1, and the molar mass of the added metal salts of organic alcohols is M2. Then the mass m2 of the added metal salts of organic alcohols is:

[0028] m2 = m1 / M1 * M2 * (0.35 - 12.50%);

[0029] The mass m0 of the added alcohol solvent is:

[0030] m0 = (2.5 - 5) * (m2 + m1), that is, the liquid-solid ratio of the suspension obtained by mixing in step (1) is 2.5 - 5. For example, it can be 2.5, 3, 3.5, 4, 4.5 or 5, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0031] Preferably, the mass ratio of the alcohol solvent to the metal organic alcohol salt in step (1) is (25 - 500):1. For example, it can be 25:1, 50:1, 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1, 450:1 or 500:1, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0032] Preferably, the alcohol solvent in step (1) includes isopropyl alcohol.

[0033] The alcohol solvent preferably used in the present invention is isopropyl alcohol. Compared with alcohol solvents such as ethanol, it has stronger hydrophobicity and can avoid the influence of moisture on the surface structure during the modification of the material.

[0034] Preferably, the chemical general formula of the initial lithium-rich manganese-based cathode material in step (1) is xLi2MnO3·(1 - x)LiMO2, where M is Ni a , Co b or Mn c or any combination of at least two of them, 0.1 ≤ x < 0.5. For example, it can be 0.11, 0.2, 0.3, 0.4 or 0.49, 0 < a < 1. For example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 0.98, 0 < b < 1. For example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 0.98, 0 < c < 1. For example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 0.98, and a + b + c = 1.

[0035] Preferably, the mixing method in step (1) includes magnetic stirring or mechanical stirring.

[0036] Preferably, the stirring speed of the mixing in step (1) is 500 - 1500 rpm. For example, it can be 500 rpm, 700 rpm, 900 rpm, 1100 rpm, 1300 rpm or 1500 rpm, and the stirring time is 30 - 240 min. For example, it can be 30 min, 50 min, 100 min, 150 min, 200 min or 240 min, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0037] Preferably, the method for removing the solvent in step (1) includes any one or a combination of at least two of a water bath drying-vacuum drying combined method, a forced air drying-vacuum drying combined method, or a rotary evaporation-vacuum drying combined method.

[0038] The temperatures of the water bath drying, forced air drying, and rotary evaporation in the present invention are independently 75-95 °C respectively, for example, they can be 75 °C, 85 °C, or 95 °C. The temperature of the vacuum drying is 80-110 °C, for example, it can be 80 °C, 90 °C, 100 °C, or 110 °C. The time of the vacuum drying is 8-20 h, for example, it can be 8 h, 10 h, 15 h, or 20 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0039] Preferably, the temperature of the calcination in step (2) is 450-750 °C, for example, it can be 450 °C, 550 °C, 650 °C, or 750 °C. The heating rate is 3-10 °C / min, for example, it can be 3 °C / min, 5 °C / min, 7 °C / min, 9 °C / min, or 10 °C / min. The time is 2-7 h, for example, it can be 2 h, 4 h, 6 h, or 7 h, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0040] Preferably, the calcination in step (2) is carried out in a high-stability atmosphere, specifically including nitrogen and / or argon.

[0041] In a second aspect, the present invention provides a modified lithium-rich manganese-based cathode material, and the modified lithium-rich manganese-based cathode material is prepared by the preparation method as described in the first aspect.

[0042] Preferably, the lithium-rich manganese-based cathode material includes an initial lithium-rich manganese-based cathode material and a metal oxide coating layer on the surface of the initial lithium-rich manganese-based cathode material, and the surface of the initial lithium-rich manganese-based cathode material includes a spinel phase structure.

[0043] The spinel phase structure in the present invention is obtained by the oxygen-deficient decomposition of the organic functional groups of the organic alcohol metal salt, inducing the pre-removal of O on the surface of the lithium-rich manganese cathode material, and causing a partial transformation of the surface structure of the material from a layered structure to a spinel structure.

[0044] In a third aspect, the present invention provides a lithium-ion battery, and the lithium-ion battery includes the modified lithium-rich manganese-based cathode material as described in the second aspect.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The anoxic decomposition of the organic functional groups of the organometallic salts of the present invention can induce pre-oxygen removal on the surface of the lithium-rich manganese-based cathode material, thereby causing a partial structural transformation of the surface of the lithium-rich manganese-based cathode material from a layered structure to a spinel structure, achieving surface-induced structure transformation modification, reducing the irreversible Li loss that occurs when the first charge reaches above 4.5 V, stabilizing the material structure and improving the first Coulombic efficiency; moreover, the oxides formed after calcining the organometallic salts of alcohols are uniformly coated on the surface of the lithium-rich manganese-based cathode material, achieving metal oxide coating modification, increasing the cycle stability, surface conductivity and lithium ion diffusion coefficient of the material, thereby improving the cycle performance and rate performance, and obtaining a lithium-rich manganese-based cathode material with simultaneous modification of surface-induced structure transformation and metal oxide coating.

[0047] (2) The organometallic salt coating solution of the present invention includes organometallic salts of alcohols and alcohol solvents, which can effectively prevent the hydrolysis of organometallic salts of alcohols in aqueous solutions, resulting in uneven coating; at the same time, the organometallic salt Me-O-H of alcohols can react with LiOH on the surface of the lithium-rich manganese-based cathode material to remove H2O, making the organometallic salts of alcohols tend to be more evenly distributed on the surface of the initial lithium-rich manganese cathode material.

[0048] (3) The preparation method of the present invention improves the comprehensive performance of the lithium-rich manganese-based cathode material, and has a simple process, capable of commercial application and industrial production. Description of the Drawings

[0049] Figure 1 SEM image of the modified lithium-rich manganese-based cathode material obtained in Example 1 at a magnification of 5000 times and the corresponding Mg energy spectrum diagram;

[0050] Figure 2 First charge-discharge cycle curve of the battery prepared from the modified lithium-rich manganese-based cathode material obtained in Example 1 and the initial lithium-rich manganese-based cathode material in Example 1;

[0051] Figure 3 SEM image of the modified lithium-rich manganese-based cathode material obtained in Example 2 at a magnification of 5000 times and the corresponding Ti energy spectrum diagram;

[0052] Figure 4 SEM image of the modified lithium-rich manganese-based cathode material obtained in Example 3 at a magnification of 5000 times and the corresponding Nb energy spectrum diagram;

[0053] Figure 5 SEM image of the modified lithium-rich manganese-based cathode material obtained in Example 4 at a magnification of 5000 times and the corresponding W energy spectrum diagram;

[0054] Figure 6SEM image of the modified Li-rich manganese-based cathode material obtained in Example 5 at 5000-fold magnification and the corresponding W and Nb energy spectrum diagrams. Detailed implementation manners

[0055] The technical solutions of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0056] Example 1

[0057] This example provides a preparation method of a modified Li-rich manganese-based cathode material. The initial Li-rich manganese cathode material used is 0.3Li2MnO3·0.7LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, with a dosage of 10 g; the selected organometallic salt is magnesium methoxide, with the molecular formula of Mg(OCH3)2, and the coating molar amount is 12.5% of the molar amount of the initial Li-rich manganese cathode material. The preparation method includes the following steps:

[0058] (1) Weigh 1.04 g of magnesium methoxide (the final coating molar amount of MgO is 12.5% of the molar amount of the initial Li-rich manganese cathode material, and the coating mass is 4.8% of the mass of the initial Li-rich manganese cathode material). Measure 32 mL of anhydrous isopropanol and place it in a 50 mL beaker. Under magnetic stirring, add magnesium methoxide to anhydrous isopropanol. After adding, continue stirring for 2 h to obtain a magnesium methoxide coating solution.

[0059] (2) Weigh 10 g of the initial Li-rich manganese cathode material and add it to the magnesium methoxide coating solution prepared in step (1) under magnetic stirring. The stirring speed is 500 rpm. After adding, continue stirring for 30 min to obtain a coated suspension; place the above suspension in a 75 °C forced-air drying oven to evaporate and separate isopropanol, and then transfer the beaker to a vacuum drying oven and dry at 80 °C for 20 h.

[0060] (3) Calcinate the mixture obtained in step (2) in a nitrogen atmosphere by programmed temperature control. The calcination temperature is 450 °C, the heating rate is 3 °C / min, and the calcination time is 7 h. Cool it to room temperature to obtain the modified Li-rich manganese-based cathode material with synchronous surface-induced structure transformation and MgO coating.

[0061] The modified Li-rich manganese-based cathode material was tested by scanning electron microscopy and EDS energy spectrum analysis. The results are as Figure 1 shown, indicating that the secondary spherical particle structure of the modified Li-rich manganese-based cathode material is well maintained, and the coated Mg element is uniformly distributed on the surface of the initial Li-rich manganese cathode material.

[0062] Example 2

[0063] This embodiment provides a method for preparing a modified lithium-rich manganese-based cathode material. The initial lithium-rich manganese cathode material used is 0.2Li2MnO3·0.8LiNi 0.5 Co 0.2 Mn 0.3 O2, with a dosage of 10 g; the selected organometallic salt is titanium isopropoxide, with the molecular formula Ti(CH3CH2O)4, and the coating molar amount is 4.0% of the molar amount of the initial lithium-rich manganese cathode material. The specific preparation method is as follows:

[0064] (1) Weigh 0.9 g of titanium isopropoxide (the final coating molar amount of TiO2 is 4.0% of the molar amount of the initial lithium-rich manganese cathode material, and the coating mass is 3.2% of the mass of the initial lithium-rich manganese cathode material). Measure 50 mL of anhydrous isopropanol and place it in a 100 mL beaker. Under magnetic stirring, add titanium isopropoxide to the anhydrous isopropanol. After adding, continue stirring for 2 h to obtain a titanium isopropoxide coating solution.

[0065] (2) Weigh 10 g of the initial lithium-rich manganese cathode material and add it to the titanium isopropoxide coating solution prepared in step (1) under magnetic stirring. The stirring speed is 800 rpm. After adding, continue stirring for 100 min to obtain a suspension before coating; transfer the above suspension to a water bath at 80 °C to evaporate and separate the isopropanol, and then take out the solid and transfer it to a vacuum drying oven for drying at 90 °C for 16 h.

[0066] (3) Calcinate the mixture obtained in step (2) in an argon atmosphere by programmed temperature control. The calcination temperature is 550 °C, the heating rate is 5 °C / min, and the calcination time is 5 h. Cool it to room temperature to obtain the modified lithium-rich manganese-based cathode material with synchronous modification of surface-induced structure transformation and TiO2 coating.

[0067] The modified lithium-rich manganese-based cathode material was tested by scanning electron microscopy and EDS energy spectrum analysis. The results are as Figure 3 shown, indicating that the secondary spherical particle structure of the modified lithium-rich manganese cathode material is well maintained, and the coated Ti element is evenly distributed on the surface of the initial lithium-rich manganese cathode material.

[0068] Example 3

[0069] This embodiment provides a method for preparing a modified lithium-rich manganese-based cathode material. The initial lithium-rich manganese cathode material used is 0.4Li2MnO3·0.6LiNi 0.6 Co 0.2 Mn 0.2 O2, with a dosage of 10 g; the selected organometallic salt is niobium methoxide, with the molecular formula C 10 H5NbO 20 , and the coating molar amount is 1.0% of the molar amount of the initial lithium-rich manganese cathode material. The specific preparation method is as follows:

[0070] (1) Weigh 0.5 g of niobium methoxide Nb(OCH3)5 (the final molar coating amount of Nb2O5 is 0.5% of the molar amount of the initial lithium-rich manganese cathode material, and the coating mass is 2.5% of the mass of the initial lithium-rich manganese cathode material). Measure 57 mL of anhydrous isopropanol and place it in a 100 mL beaker. Under magnetic stirring, add niobium methoxide to the anhydrous isopropanol. After the addition is completed, continue stirring for 2 h to obtain a niobium methoxide coating solution.

[0071] (2) Weigh 10 g of the initial lithium-rich manganese cathode material and add it to the niobium methoxide coating solution prepared in step (1) under mechanical stirring. The stirring speed is 1000 rpm. After the addition is completed, continue stirring for 180 min to obtain a suspension before coating; transfer the above suspension to a rotary evaporator at 90 °C to evaporate and separate isopropanol, and then take out the solid and transfer it to a vacuum drying oven for drying at 100 °C for 12 h.

[0072] (3) Calcinate the mixture obtained in step (2) under a nitrogen atmosphere by programmed temperature control. The calcination temperature is 650 °C, the heating rate is 7 °C / min, and the calcination time is 3 h. Cool it to room temperature to obtain the modified lithium-rich manganese-based cathode material with synchronous modification of surface-induced structure transformation and Nb2O5 coating.

[0073] The modified lithium-rich manganese cathode material was subjected to scanning electron microscopy test and EDS energy spectrum analysis, and the results are as Figure 4 shown, indicating that the secondary spherical particle structure of the modified lithium-rich manganese cathode material is well maintained, and the coated Nb element is evenly distributed on the surface of the initial lithium-rich manganese cathode material.

[0074] Example 4

[0075] This example provides a preparation method of a modified lithium-rich manganese-based cathode material. The initial lithium-rich manganese cathode material used is 0.1Li2MnO3·0.9LiNi 0.4 Co 0.2 Mn 0.4 O2, with a dosage of 10 g; the selected organometallic salt is tungsten isopropoxide, with the molecular formula C 12 H 30 O6W, and the coating molar amount is 0.35% of the molar amount of the initial lithium-rich manganese cathode material. The specific preparation method is as follows:

[0076] (1) Weigh 0.16 g of tungsten isopropoxide (the final molar coating amount of WO3 is 0.35% of the molar amount of the initial lithium-rich manganese cathode material, and the coating mass is 0.81% of the mass of the initial lithium-rich manganese cathode material). Measure 64.4 mL of anhydrous isopropanol and place it in a 100 mL beaker. Under mechanical stirring, add tungsten isopropoxide to the anhydrous isopropanol. After the addition is completed, continue stirring for 2 h to obtain a tungsten isopropoxide coating solution.

[0077] (2) Weigh 10 g of the initial lithium-rich manganese cathode material and add it to the tungsten isopropoxide coating solution prepared in step (1) under mechanical stirring at a stirring speed of 1500 rpm. After the addition, continue stirring for 240 min to obtain a suspension before coating. Transfer the above suspension to a rotary evaporator at 95 °C to evaporate and separate isopropanol, then take out the solid and transfer it to a vacuum drying oven, and dry at 110 °C for 8 h.

[0078] (3) Calcinate the mixture obtained in step (2) under a nitrogen atmosphere by programmed temperature control. The calcination temperature is 750 °C, the heating rate is 10 °C / min, and the calcination time is 2 h. Cool it to room temperature to obtain the modified lithium-rich manganese-based cathode material with synchronous modification of surface-induced structure transformation and WO3 coating.

[0079] The modified lithium-rich manganese cathode material was subjected to scanning electron microscopy testing and EDS energy spectrum analysis, and the results are as Figure 5 shown, indicating that the secondary spherical particle structure of the modified lithium-rich manganese cathode material is well maintained, and the coated W element is evenly distributed on the surface of the initial lithium-rich manganese cathode material.

[0080] Example 5

[0081] This example provides a preparation method of a modified lithium-rich manganese-based cathode material. The initial lithium-rich manganese cathode material used is 0.1Li2MnO3·0.9LiNi 0.4 Co 0.2 Mn 0.4 O2, with a dosage of 10 g; the selected organometallic salts are a mixture of niobium methanolate and tungsten isopropoxide with a molar ratio of 1:1, and the total molar amount of coating is 0.7% of the molar amount of the initial lithium-rich manganese cathode material. The specific preparation method is as follows:

[0082] (1) Weigh 0.16 g of tungsten isopropoxide (the final molar amount of WO3 coating is 0.35% of the molar amount of the initial lithium-rich manganese cathode material, and the coating mass is 0.81% of the mass of the initial lithium-rich manganese cathode material) and 0.175 g of niobium methanolate (the final molar amount of Nb2O5 coating is 0.175% of the molar amount of the initial lithium-rich manganese cathode material, and the coating mass is 0.875% of the mass of the initial lithium-rich manganese cathode material). Measure 50 mL of anhydrous isopropanol and place it in a 100 mL beaker. Add tungsten isopropoxide and niobium methanolate to the anhydrous isopropanol under mechanical stirring. After the addition, continue stirring for 2 h to obtain a coating solution of tungsten isopropoxide and niobium methanolate.

[0083] (2) Weigh 10 g of the lithium-rich manganese cathode material and add it to the tungsten isopropoxide and niobium methoxide coating solution prepared in step (1) under mechanical stirring at a stirring speed of 1200 rpm. After the addition is completed, continue stirring for 180 min to obtain a pre-coating suspension; transfer the above suspension to a rotary evaporator at 80 °C to evaporate and separate the isopropanol, then take out the solid and transfer it to a vacuum drying oven for drying at 90 °C for 16 h.

[0084] (3) Calcinate the mixture obtained in step (2) under a nitrogen atmosphere with a programmable temperature control. The calcination temperature is 650 °C, the heating rate is 10 °C / min, and the calcination time is 3 h. Cool it to room temperature to obtain the modified lithium-rich manganese-based cathode material with synchronous modification of surface-induced structure transformation and Nb2O5 and WO3 coating.

[0085] Perform scanning electron microscopy testing and EDS energy spectrum analysis on the modified lithium-rich manganese cathode material, and the results are as Figure 6 shown, indicating that the secondary spherical particle structure of the modified lithium-rich manganese cathode material is well maintained, and the coated Nb and W elements are evenly distributed on the surface of the initial lithium-rich manganese cathode material.

[0086] Example 6

[0087] This example provides a preparation method of a modified lithium-rich manganese-based cathode material. Except that magnesium methoxide is replaced with an equimolar combination of magnesium methoxide and titanium isopropoxide (the molar ratio of magnesium methoxide to titanium isopropoxide is 1:1), the rest are the same as in Example 1.

[0088] Example 7

[0089] This example provides a preparation method of a modified lithium-rich manganese-based cathode material. Except that magnesium methoxide is replaced with magnesium ethoxide in an equimolar amount, the rest are the same as in Example 1.

[0090] Example 8

[0091] This example provides a preparation method of a modified lithium-rich manganese-based cathode material. Except that magnesium methoxide is replaced with titanium ethoxide in an equimolar amount, the rest are the same as in Example 2.

[0092] Example 9

[0093] This example provides a preparation method of a modified lithium-rich manganese-based cathode material. Except that the coating molar amount of the organometallic salt is 0.15% of the molar amount of the initial lithium-rich manganese cathode material, the rest are the same as in Example 1.

[0094] Example 10

[0095] This embodiment provides a method for preparing a modified lithium-rich manganese-based cathode material. Except that the coating molar amount of the organometallic salt is 15% of the molar amount of the initial lithium-rich manganese cathode material, the rest are the same as in Example 1.

[0096] Example 11

[0097] This embodiment provides a method for preparing a modified lithium-rich manganese-based cathode material. Except that isopropanol is replaced with ethanol in equal volume, the rest are the same as in Example 1.

[0098] Comparative Example 1

[0099] This comparative example provides a method for preparing a modified lithium-rich manganese-based cathode material. Except that magnesium methoxide is replaced with magnesium nitrate hexahydrate in equal molar amount, the rest are the same as in Example 1.

[0100] Comparative Example 2

[0101] This comparative example provides a method for preparing a modified lithium-rich manganese-based cathode material. Except that isopropanol is replaced with distilled water in equal volume, the rest are the same as in Example 1.

[0102] Due to the hydrolysis of magnesium methoxide in this comparative example, a lithium-rich manganese cathode material with uniform MgO coating was not obtained.

[0103] The modified lithium-rich manganese-based cathode materials obtained in the above examples and comparative examples are mixed evenly with acetylene black and PVDF (polyvinylidene fluoride) in a mass ratio of 90:5:5. This mixture is made into a slurry with NMP (N-methylpyrrolidone), evenly coated on an aluminum foil, dried in a forced-air drying oven at 80 °C for 4 h, taken out, rolled, punched into a pole piece, and vacuum dried at 85 °C for 24 h to obtain the pole pieces of the example samples. Using a lithium sheet as the counter electrode, a solution of 1.15 M LiPF6 in ethyl carbonate + dimethyl carbonate (volume ratio 1:1) as the electrolyte, and celgard2400 as the separator, a CR2032 type coin cell is assembled in a glove box filled with an argon atmosphere.

[0104] The first charge-discharge cycle test is carried out on the above coin cell. The test conditions are: the charge-discharge voltage range is 2.2~4.8 V, the charge-discharge current is 0.1 C (1 C = 240 mA / g, the same below). The first Coulombic efficiency is shown in Table 1. At the same time, the first charge-discharge cycle curve of the battery prepared from the modified lithium-rich manganese-based cathode material obtained in Example 1 and the initial lithium-rich manganese-based cathode material in Example 1 is as Figure 2 shown.

[0105] The rate performance of the above-mentioned button battery was tested under the following conditions: the charge-discharge voltage range was 2.2 - 4.8 V. After activating for 5 cycles with a charge-discharge current of 0.1C each, charge-discharge cycles were carried out at 0.2C, 0.5C, 1C, 2C, 5C, and 10C respectively. Each rate cycle was repeated 5 times, and the discharge capacity at 3C is shown in Table 1. The cycle stability of the above-mentioned button battery was tested under the following conditions: the charge-discharge voltage range was 2.2 - 4.8 V. After activating for 5 cycles with a charge-discharge current of 0.1C each, a 100-cycle stability test was carried out at 0.5C, and the results are shown in Table 1.

[0106] Table 1

[0107]

[0108]

[0109] As can be seen from Table 1:

[0110] (1) It can be seen from Examples 1 - 5 and Comparative Examples 1 - 2 that the method for simultaneously modifying the lithium-rich manganese cathode material by surface-induced structure transformation and metal oxide coating provided by the present invention, by selecting an organometallic salt as the coating precursor material and isopropanol as the solvent, through liquid-phase homogeneous mixing and high-temperature sintering under a high-stability atmosphere, can obtain a lithium-rich manganese cathode material with surface-induced structure transformation and metal oxide coating simultaneously modified, and will not damage the morphology and structure of the initial lithium-rich manganese cathode material. The first Coulombic efficiency, rate performance, and cycle stability of the obtained surface-composite modified lithium-rich manganese cathode material are all significantly improved.

[0111] (2) It can be seen from Example 1 and Example 6 that the organometallic salt of the present invention is preferably a combination of metal methanol salt and metal isopropanol salt, which can simultaneously improve the first efficiency, rate performance, and cycle stability of the battery; it can be seen from Examples 1 - 2 and Examples 7 - 8 that the present invention preferably uses metal methanol salt and / or metal isopropanol salt, which has a higher matching degree with the preparation method of the present invention and is more likely to cause surface structure transformation of the material, thereby further improving the comprehensive performance of the battery; it can be seen from Example 1 and Examples 9 - 10 that the present invention preferably has a coating amount within a suitable range; it can be seen from Example 1 and Example 11 that the solvent of the present invention is preferably isopropanol, which has a higher adaptability with the preparation method of the present invention and promotes the dehydration reaction between Me-O-H and LiOH on the surface of the lithium-rich manganese cathode material.

[0112] The above are only specific embodiments 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 fall within the protection scope and disclosure scope of the present invention.

Claims

1. A preparation method of a modified lithium-rich manganese-based cathode material, characterized in that, The preparation method comprises the following steps: (1) Mix the initial lithium-rich manganese-based cathode material with an organometallic salt coating solution, and then remove the solvent to obtain a mixture; The organometallic salt coating solution includes an organoalcohol metal salt and an alcohol solvent; (2) Calcinate the mixture obtained in step (1) to obtain the modified lithium-rich manganese-based cathode material.

2. The preparation method according to claim 1, characterized in that, The metal in the organoalcohol metal salt in step (1) includes any one or a combination of at least two of Mg, Ti, Nb or W; Preferably, the organic group in the organoalcohol metal salt in step (1) includes an alkoxy group with a carbon atom number ≤ 3, preferably any one or a combination of at least two of methoxy, ethoxy or propoxy.

3. The preparation method according to claim 1 or 2, characterized in that, The organoalcohol metal salt in step (1) includes a methanol metal salt and / or an isopropanol metal salt, preferably a combination of a methanol metal salt and an isopropanol metal salt; Preferably, the organoalcohol metal salt in step (1) includes any one or a combination of at least two of magnesium methoxide, titanium isopropoxide, niobium methoxide or tungsten isopropoxide.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The molar amount of the organoalcohol metal salt in step (1) is 0.35-12.50% of the molar amount of the initial lithium-rich manganese-based cathode material; Preferably, the mass ratio of the alcohol solvent to the organoalcohol metal salt in step (1) is (25-500):1; Preferably, the alcohol solvent in step (1) includes isopropanol.

5. The preparation method according to any one of claims 1-4, characterized in that, The chemical general formula of the initial lithium-rich manganese-based cathode material described in step (1) is xLi2MnO3·(1-x)LiMO2, where M is Ni a , Co b or Mn c Any one or a combination of at least two of them, 0.1 ≤ x < 0.5, 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1; Preferably, the stirring speed of the mixing in step (1) is 500-1500 rpm, and the stirring time is 30-240 min.

6. The preparation method according to any one of claims 1-5, characterized in that, The method for removing the solvent in step (1) includes any one or a combination of at least two of a water bath drying-vacuum drying combined method, a hot air drying-vacuum drying combined method or a rotary evaporation-vacuum drying combined method.

7. The preparation method according to any one of claims 1-6, characterized in that, The temperature of the calcination in step (2) is 450-750 °C, the heating rate is 3-10 °C / min, and the time is 2-7 h; Preferably, the atmosphere of the calcination in step (2) includes nitrogen and / or argon.

8. A modified lithium-rich manganese-based cathode material, characterized in that, The modified lithium-rich manganese-based cathode material is prepared by the preparation method as described in any one of claims 1-7.

9. The modified lithium-rich manganese-based cathode material according to claim 8, wherein, The lithium-rich manganese-based cathode material includes the initial lithium-rich manganese-based cathode material and a metal oxide coating layer on the surface of the initial lithium-rich manganese-based cathode material, and the surface of the initial lithium-rich manganese-based cathode material includes a spinel phase structure.

10. A lithium-ion battery, characterized in that, The lithium ion battery includes the modified lithium-rich manganese-based cathode material as described in claim 8 or 9.

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