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

Abstract

This application relates to the field of lithium battery technology, specifically disclosing a lithium-rich manganese-based cathode material and its preparation method. The lithium-rich manganese-based cathode material includes a precursor and a lithium coating layer covering the surface of the precursor. The precursor is obtained by mixing a nickel source, a cobalt source, a manganese source, and a composite functional metal source, followed by co-precipitation, filtration, washing, and drying. The lithium coating layer is formed by sintering a lithium source. The composite functional metal source is composed of a titanium source, a molybdenum source, and a tungsten source. The preparation method is as follows: the nickel source, cobalt source, manganese source, and composite functional metal source are dissolved in anhydrous ethanol, a precipitant and a surfactant are added, and the mixture is stirred and mixed for co-precipitation. The mixture is then filtered, washed, and dried to obtain the precursor. The precursor is pre-sintered and then mixed with a lithium source for a second sintering treatment. The lithium-rich manganese-based cathode material of this application exhibits excellent cycle stability during application.

Description

Technical Field

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

[0002] Lithium-rich manganese-based cathode materials are the core materials for achieving technological breakthroughs in high energy density of power lithium batteries. They have a specific capacity of up to 300 mAh / g, which far exceeds the discharge specific capacity of currently commercially used cathode materials such as lithium iron phosphate and ternary materials. They are almost twice the actual capacity of currently commercialized cathode materials and have long-term commercial prospects.

[0003] The main components of lithium-rich manganese-based cathode materials are lithium, manganese, and oxygen. Manganese is mainly used to provide lithium-ion storage and transport, while lithium is used to adjust the crystal structure and improve the conductivity of the material. The general chemical formula of lithium-rich manganese-based materials is usually represented as xLi2MnO3·(1-x)LiMO2, where x is a proportionality coefficient (0 < x < 1). The material performance can be optimized by adjusting the value of x. Structurally, it consists of two phases, LiMO2 and Li2MnO3, forming a solid solution or heterogeneous composite structure. In the O3 type structure, oxygen is cubically close-packed, while in the O2 type structure, the oxygen arrangement can inhibit transition metal migration and improve stability. At the same time, Li2MnO3 releases capacity after high-voltage activation, and together with the redox reaction of LiMO2, it contributes to the high specific capacity.

[0004] Regarding the aforementioned technologies, the inventors believe that lithium-rich manganese-based materials rely on anion redox reactions to provide additional capacity. However, during application, oxygen evolution and transition metal migration occur, leading to lattice parameter contraction and structural instability. These changes disrupt lithium-ion diffusion channels, causing voltage decay, and thus the cycle stability of lithium-rich manganese-based cathode materials still needs to be improved. Summary of the Invention

[0005] To improve the cycle stability of lithium-rich manganese-based cathode materials, this application provides a lithium-rich manganese-based cathode material and its preparation method.

[0006] In a first aspect, this application provides a lithium-rich manganese-based cathode material, employing the following technical solution: A lithium-rich manganese-based cathode material includes a precursor and a lithium coating layer covering the surface of the precursor. The precursor is obtained by mixing nickel source, cobalt source, manganese source and composite functional metal source, followed by co-precipitation, filtration, washing and drying. The lithium coating layer is formed by sintering using a lithium source; The composite functional metal source consists of a titanium source, a molybdenum source, and a tungsten source.

[0007] By adopting the above technical solution, nickel is used as the main active element in the precursor design. It provides high capacity and improves energy density through redox reaction, while cobalt can stabilize the layered structure, reduce cation mixing and improve conductivity, and manganese can enhance thermal stability and inhibit high-temperature decomposition. By selecting nickel, cobalt and manganese as the main elements of the precursor, and through the synergistic effect of the three elements, high energy density and controllable thermal runaway risk can be achieved, which is conducive to the performance optimization and balance of lithium battery cathode materials. Meanwhile, the precursor preparation also utilizes a composite functional metal source composed of titanium, molybdenum, and tungsten. Titanium can replace some manganese sites, suppressing lattice shrinkage during charge and discharge, reducing the transformation of layered structures to the spinel phase, and the high Ti-O bond energy can stabilize lattice oxygen, reducing voltage decay caused by oxygen evolution. Molybdenum can improve electronic conductivity, reduce polarization, and synergistically form a Mo-WO network with tungsten, enhancing interlayer bonding strength and suppressing interlayer slip during cycling. The local high-voltage phase formed by tungsten doping can stabilize lithium-ion diffusion channels, alleviate voltage decay, and also inhibit manganese dissolution. Thus, by utilizing the synergy between titanium, molybdenum, and tungsten, a regulatory mechanism of stable lattice, optimized conductivity, and inhibited dissolution can be established, effectively alleviating the problems of lattice shrinkage, voltage decay, and structural instability in lithium-rich manganese-based cathode materials, thereby significantly improving the cycling stability of lithium-rich manganese-based cathode materials.

[0008] Preferably, in the composite functional metal source, the molar ratio of titanium, molybdenum and tungsten is (5-6):(2-3):1, and the total molar amount of titanium, molybdenum and tungsten is 1-5% of the total molar amount of nickel, cobalt and manganese.

[0009] By adopting the above technical solution, the molar ratio of titanium, molybdenum and tungsten is (5-6):(2-3):1, which can ensure that the three form an excellent and stable coordination mechanism. Under this premise, controlling the total molar amount of titanium, molybdenum and tungsten to 1-5% of the total molar amount of nickel, cobalt and manganese can not only avoid excessive doping from damaging the integrity of the layered structure, but also form a uniform and stable combination, thereby exerting excellent corresponding effects and finally obtaining a high-quality and stable lithium-rich manganese-based cathode material.

[0010] Preferably, the molar ratio of nickel, cobalt and manganese in the nickel source, cobalt source and manganese source is (8-10):1:(20-25).

[0011] By adopting the above technical solutions, the above proportion of nickel can significantly improve the specific capacity of the cathode material and achieve ultra-high energy density; while cobalt has a higher cost, the above proportion can reasonably control the composition while achieving the required effect; and the higher proportion of manganese can achieve a better balance between structural stability and safety; at the same time, in addition to playing the above excellent role, the above proportions of nickel, cobalt and manganese have good compatibility and adaptability, and have a better combination and cooperation effect with related elements in the composite functional metal source, which is conducive to finally obtaining a lithium-rich manganese-based cathode material with excellent cycle stability.

[0012] Preferably, the molar ratio of lithium in the lithium source to the total molar amounts of titanium, molybdenum, tungsten, nickel, cobalt and manganese in the precursor is (1.2-1.5):1.

[0013] By adopting the above technical solution, the lithium source is sintered to form a coating layer, which can suppress electrolyte erosion and reduce interfacial impedance. Within the above ratio range, the solid-state reaction kinetics between the precursor and the lithium source can ensure the full formation of the layered structure, and facilitate the decomposition of the lithium source during high-temperature sintering, releasing lithium ions to embed into the lattice structure of the cathode material, forming a stable crystal structure and exhibiting excellent electrochemical performance. This results in the lithium-rich manganese-based cathode material having excellent cycle stability during application.

[0014] Secondly, this application provides a method for preparing a lithium-rich manganese-based cathode material, employing the following technical solution: A method for preparing a lithium-rich manganese-based cathode material includes the following steps: (1) Take nickel source, cobalt source, manganese source and composite functional metal source, dissolve them in anhydrous ethanol, add precipitant and surfactant, stir and mix, and then carry out co-precipitation reaction. After filtration, washing and drying, the precursor is obtained. (2) After pre-sintering the precursor obtained in step (1), it is mixed with the lithium source and sintered again to obtain lithium-rich manganese-based cathode material.

[0015] By adopting the above technical solution, the metal ions provided by the nickel, cobalt, and manganese sources form the basic framework of the lithium-rich manganese-based cathode material, while the doping of the composite functional metal source can play an optimization role. Dissolving the nickel, cobalt, manganese, and composite functional metal sources in anhydrous ethanol facilitates uniform dispersion. Subsequently, a precipitant is used to promote the co-precipitation of metal ions, and a uniform precursor is formed under the control of a surfactant. Then, pre-sintering is performed to remove organic residues and water of crystallization in the precursor, forming a stable metal oxide framework that provides active sites for the subsequent lithiation reaction. Finally, a secondary sintering treatment is performed to decompose the lithium source at high temperature, providing lithium ions to intercalate into the precursor lattice, forming a layered lithium-rich manganese-based cathode material.

[0016] Preferably, step (2) is specifically set as follows: after pre-sintering the precursor obtained in step (1), it is mixed with lithium source and functional additives and then sintered again to obtain lithium-rich manganese-based cathode material; The functional additive is a carbon nanotube composite material uniformly coated with boron nitride, and is prepared by the following method: S1. Take carbon nanotube raw material, immerse it in acid solution for ultrasonic treatment, and then take it out and dry it to obtain pretreated carbon nanotubes. S2. The pretreated carbon nanotubes obtained in step S1 are added to ethanol along with boric acid, melamine, and surfactant. After ultrasonic treatment, filtration, and drying, the mixture is sintered to obtain the functional additive.

[0017] By adopting the above technical solution, in operation S1, impurities on the surface of carbon nanotube raw materials can be removed and active sites can be introduced to enhance the subsequent chemical bonding with boron nitride. In operation S2, boron nitride is generated by reacting boric acid with melamine, and the boron nitride uniformly coats the carbon nanotube composite material. In the application of functional additives, the high thermal conductivity and chemical inertness of boron nitride can suppress the side reactions between the electrode material and the electrolyte, reduce the dissolution of transition metals, and buffer volume changes through boron nitride molecules to maintain lattice integrity. At the same time, carbon nanotubes can not only provide a three-dimensional conductive network, improve the electron transport rate, and reduce electrode polarization, but also adapt to stress changes during the charging and discharging process through their flexible structure, reducing the generation of microcracks. Therefore, when boron nitride and carbon nanotubes are used in combination in the above manner, they can achieve excellent synergistic compounding effect, forming a multi-enhancement mechanism of mechanical support, conductive enhancement, and interface protection, thereby significantly improving the cycle stability of lithium-rich manganese-based cathode materials.

[0018] Preferably, the weight ratio of boron nitride to carbon nanotubes in the functional additive is 1:(3-5).

[0019] By adopting the above technical solution, if the ratio exceeds the above range, although the proportion of carbon nanotubes is higher, the conductive network is denser, and the electron transport efficiency is improved, the boron nitride coating layer is thinner, and the effect of inhibiting the dissolution of transition metals is limited; if the ratio is lower than the above range, the proportion of carbon nanotubes is lower, and boron nitride will be over-coated, making it difficult for both to exert excellent synergistic effects; while the ratio of boron nitride and carbon nanotubes within the above range makes the corresponding improvement effect brought about by the functional additives after application better.

[0020] Preferably, the amount of the functional additive is 3-5% of the total mass of the precursor and lithium source.

[0021] By adopting the above technical solution, the functional additives with the above dosage ratio have better compatibility. They can form a continuous conductive network, avoid excessive dosage which would lead to sintering difficulties or a decrease in material density, and can stably exert their corresponding improvement effects. In this way, the optimal balance is achieved between conductivity, structural stability and cost, which is ultimately conducive to obtaining high-quality lithium-rich manganese-based cathode materials.

[0022] Preferably, in step (2), the pre-sintering temperature is 350-500℃ and the pre-sintering time is 4-7h.

[0023] By adopting the above technical solution, under the above pre-sintering conditions, the surfactants, water and other organic impurities in the precursor can be effectively removed, avoiding carbon residue during high-temperature sintering that leads to a decrease in the conductivity of the material, and ensuring that the components inside the precursor react uniformly, promoting the lattice recombination of metal oxides, and providing active sites for subsequent lithiation reactions.

[0024] Preferably, in step (2), the operation of re-sintering is as follows: first sintering at 650-750℃ for 6-10h, and then sintering at 800-900℃ for 8-12h.

[0025] By adopting the above technical solution, sintering is first carried out at 650-750℃ for 6-10 hours to promote the initial solid-state reaction between the lithium source and the precursor, followed by sintering at 800-900℃ for 8-12 hours to complete the uniform embedding of lithium ions in the layered structure, forming a stable lithium-rich manganese-based cathode material. This two-stage sintering operation can suppress lattice defects and optimize the layered structure, which is beneficial for achieving the excellent cycle stability of the lithium-rich manganese-based cathode material.

[0026] In summary, this application has the following beneficial effects: 1. This application uses a composite functional metal source composed of titanium, molybdenum and tungsten sources in the preparation of the precursor. By utilizing the synergy between titanium, molybdenum and tungsten, a control mechanism of stable lattice-optimized conductivity-inhibited dissolution can be established, which can effectively alleviate the problems of lattice shrinkage, voltage decay and structural instability of lithium-rich manganese-based cathode materials, and thus significantly improve the cycle stability of lithium-rich manganese-based cathode materials. 2. This application utilizes functional additives simultaneously in the application of lithium sources, and employs a carbon nanotube composite material uniformly coated with boron nitride to enable boron nitride and carbon nanotubes to synergistically build a multi-enhancement mechanism of mechanical support, conductivity enhancement, and interface protection, thereby significantly improving the cycle stability of lithium-rich manganese-based cathode materials. Detailed Implementation

[0027] The present application will be further described in detail below with reference to preparation examples, embodiments and comparative examples.

[0028] Unless otherwise specified, all raw materials used in the preparation examples, embodiments and comparative examples of this application are commercially available.

[0029] The carbon nanotube raw material was purchased from Beijing Deco Island Gold Technology Co., Ltd., and the model number was CNT-202.

[0030] Preparation examples of raw materials and / or intermediates Preparation Example 1 A functional additive is a carbon nanotube composite material uniformly coated with boron nitride, and is prepared by the following method: S1. Take carbon nanotube raw material, immerse it in acid solution and sonicate it for 2 hours, then take it out and dry it to obtain pretreated carbon nanotubes. S2. The pretreated carbon nanotubes obtained in step S1 are added to ethanol along with boric acid, melamine, and surfactant. After ultrasonic treatment for 30 min, filtration, and drying, the mixture is sintered at 1100℃ for 2.5 h to obtain the functional additive.

[0031] Note: The acid solution used in step S1 is obtained by mixing nitric acid and sulfuric acid in a volume ratio of 1:3; the surfactant in step S2 is polyvinylpyrrolidone K30, and its amount is 10% of the mass of the pretreated carbon nanotubes. At the same time, in the obtained functional additives, the weight ratio of boron nitride to carbon nanotubes is 1:4.

[0032] Preparation Example 2 A functional additive, which differs from Preparation Example 1 in that the weight ratio of boron nitride to carbon nanotubes in the functional additive is 1:3.

[0033] Preparation Example 3 A functional additive, which differs from Preparation Example 1 in that the weight ratio of boron nitride to carbon nanotubes in the functional additive is 1:5.

[0034] Preparation Example 4 A functional additive, which differs from Preparation Example 1 in that the weight ratio of boron nitride to carbon nanotubes in the functional additive is 1:2.5.

[0035] Preparation Example 5 A functional additive, which differs from Preparation Example 1 in that the weight ratio of boron nitride to carbon nanotubes in the functional additive is 1:5.5.

[0036] Example Example 1

[0037] A lithium-rich manganese-based cathode material includes a precursor and a lithium coating layer on the surface of the precursor. The precursor is obtained by mixing a nickel source, a cobalt source, a manganese source, and a composite functional metal source, followed by co-precipitation, filtration, washing, and drying. The lithium coating layer is formed by sintering using a lithium source. The lithium-rich manganese-based cathode material is specifically prepared through the following steps: (1) Take nickel source, cobalt source, manganese source and composite functional metal source, dissolve them in anhydrous ethanol, add precipitant and surfactant, stir and mix, and then carry out co-precipitation reaction. After filtration, washing and drying, the precursor is obtained. (2) After pre-sintering the precursor obtained in step (1), it is mixed with the lithium source and sintered again to obtain lithium-rich manganese-based cathode material.

[0038] Note: In the above operations, the nickel source is nickel sulfate, the cobalt source is cobalt sulfate, and the manganese source is manganese sulfate. The molar ratio of nickel, cobalt, and manganese in the nickel, cobalt, and manganese sources is 9:1:22.5. The composite functional metal source consists of titanium, molybdenum, and tungsten sources. The titanium source is titanium tetrachloride, the molybdenum source is ammonium molybdate, and the tungsten source is sodium tungstate. The molar ratio of titanium, molybdenum, and tungsten in the composite functional metal source is 5.5:2.5:1, and the total molar amount of titanium, molybdenum, and tungsten is 3% of the total molar amount of nickel, cobalt, and manganese. The precipitant is oxalic acid, and the molar ratio of oxalic acid to the total metal ions in the nickel, cobalt, manganese, and composite functional metal sources is 2.5:1. The surfactant is hexadecyltrimethylammonium bromide, and the amount of surfactant used is 3% of the total mass of the nickel, cobalt, manganese, and composite functional metal sources. The lithium source is lithium hydroxide, and the molar ratio of lithium in the lithium source to the total molar amount of titanium, molybdenum, tungsten, nickel, cobalt, and manganese in the precursor is 1.35:1. In step (2), the pre-sintering temperature is 425℃ and the pre-sintering time is 5.5h; the operation for re-sintering is: first sintering at 700℃ for 8h, and then sintering at 850℃ for 10h. Example 2

[0039] A lithium-rich manganese-based cathode material differs from Example 1 in that the molar ratio of titanium, molybdenum, and tungsten in the composite functional metal source is 5:2:1, and the total molar amount of titanium, molybdenum, and tungsten is 1% of the total molar amount of nickel, cobalt, and manganese. Example 3

[0040] A lithium-rich manganese-based cathode material differs from Example 1 in that the molar ratio of titanium, molybdenum, and tungsten in the composite functional metal source is 6:3:1, and the total molar amount of titanium, molybdenum, and tungsten is 5% of the total molar amount of nickel, cobalt, and manganese. Example 4

[0041] A lithium-rich manganese-based cathode material differs from Example 1 in that the molar ratio of nickel, cobalt, and manganese in the nickel source, cobalt source, and manganese source is 8:1:20. Example 5

[0042] A lithium-rich manganese-based cathode material differs from Example 1 in that the molar ratio of nickel, cobalt, and manganese in the nickel source, cobalt source, and manganese source is 10:1:25. Example 6

[0043] A lithium-rich manganese-based cathode material differs from Example 1 in that the molar ratio of lithium in the lithium source to the total molar amounts of titanium, molybdenum, tungsten, nickel, cobalt, and manganese in the precursor is 1.2:1. Example 7

[0044] A lithium-rich manganese-based cathode material differs from Example 1 in that the molar ratio of lithium in the lithium source to the total molar amounts of titanium, molybdenum, tungsten, nickel, cobalt, and manganese in the precursor is 1.5:1. Example 8

[0045] A lithium-rich manganese-based cathode material differs from Example 1 in that, in step (2), the pre-sintering temperature is 350°C and the pre-sintering time is 7h. Example 9

[0046] A lithium-rich manganese-based cathode material differs from Example 1 in that, in step (2), the pre-sintering temperature is 500°C and the pre-sintering time is 4 hours. Example 10

[0047] A lithium-rich manganese-based cathode material differs from Example 1 in that, in step (2), the re-sintering process is performed by first sintering at 650°C for 10 hours and then sintering at 900°C for 8 hours. Example 11

[0048] A lithium-rich manganese-based cathode material differs from Example 1 in that, in step (2), the re-sintering process is performed by first sintering at 750°C for 6 hours and then sintering at 800°C for 12 hours. Example 12

[0049] A lithium-rich manganese-based cathode material differs from Example 1 in that step (2) is specifically set as follows: after pre-sintering the precursor obtained in step (1), it is mixed with a lithium source and functional additives and then sintered again to obtain the lithium-rich manganese-based cathode material; the functional additives are obtained from Preparation Example 1. Example 13

[0050] A lithium-rich manganese-based cathode material, which differs from Example 12 in that the functional additives are obtained from Preparation Example 2. Example 14

[0051] A lithium-rich manganese-based cathode material differs from Example 12 in that the functional additives are obtained from Preparation Example 3. Example 15

[0052] A lithium-rich manganese-based cathode material, which differs from Example 12 in that the functional additives are obtained from Preparation Example 4. Example 16

[0053] A lithium-rich manganese-based cathode material, which differs from Example 12 in that the functional additives are obtained from Preparation Example 5. Example 17

[0054] A lithium-rich manganese-based cathode material differs from Example 12 in that the functional additives are replaced by a mixture of boron nitride particles and carbon nanotubes, and the mass and corresponding ratio of boron nitride particles and carbon nanotubes are the same.

[0055] Comparative Example Comparative Example 1 A lithium-rich manganese-based cathode material differs from Example 1 in that it does not use the titanium or molybdenum source found in composite functional metal sources.

[0056] Comparative Example 2 A lithium-rich manganese-based cathode material differs from Example 1 in that it does not use the titanium or tungsten source in the composite functional metal source.

[0057] Comparative Example 3 A lithium-rich manganese-based cathode material differs from Example 1 in that it does not use the molybdenum or tungsten source in the composite functional metal source.

[0058] Comparative Example 4 A lithium-rich manganese-based cathode material differs from Example 1 in that it does not use the titanium source in the composite functional metal source.

[0059] Comparative Example 5 A lithium-rich manganese-based cathode material differs from Example 1 in that it does not use the molybdenum source from the composite functional metal source.

[0060] Comparative Example 6 A lithium-rich manganese-based cathode material differs from Example 1 in that it does not use the tungsten source in the composite functional metal source.

[0061] Comparative Example 7 A lithium-rich manganese-based cathode material differs from Example 1 in that it does not use a composite functional metal source.

[0062] Performance testing Test samples: The lithium-rich manganese-based cathode materials obtained in Examples 1-17 were selected as test samples 1-17, and the lithium-rich manganese-based cathode materials obtained in Comparative Examples 1-7 were selected as control samples 1-7.

[0063] Experimental method: Using N-methylpyrrolidone as a dispersant, lithium-rich manganese-based cathode material, carbon black, and PVDF (polyvinylidene fluoride) were mixed at a mass ratio of 80:10:10 to prepare a cathode slurry. The cathode slurry was then uniformly coated onto carbon-coated aluminum foil with a coating density of 3 cm³. 2 / mg, dried in an oven at 80℃ for 2h to obtain the positive electrode; under an argon atmosphere in a glove box, using a Celgard 2500 separator, lithium metal sheet as the negative electrode, and 1mol / L electrolyte (EC, EMC and DMC in a volume ratio of 1:1:1); CR2032 button half-cells were assembled in the order of negative electrode, electrolyte, separator, electrolyte, and positive electrode.

[0064] The capacity retention rate of the battery was tested after 300 charge-discharge cycles under a current density of 0.5C (1C = 200mAh g-1). After performing the above tests on test samples 1-17 and control samples 1-7, the test results are recorded in Table 1.

[0065] Table 1. Test results of test samples 1-17 and control samples 1-7 sample Capacity retention rate (%) Test sample 1 96.2 Test sample 2 95.4 Test sample 3 95.0 Test sample 4 95.2 Test sample 5 95.1 Test sample 6 95.3 Test sample 7 95.5 Test sample 8 95.8 Test sample 9 95.6 Test sample 10 95.9 Test sample 11 95.7 Test sample 12 98.4 Test sample 13 98.1 Test sample 14 98.2 Test sample 15 97.4 Test sample 16 97.3 Test sample 17 96.8 Control sample 1 86.7 Control sample 2 87.6 Control sample 3 87.0 Control sample 4 90.0 Control sample 5 89.4 Control sample 6 90.3 Control sample 7 84.3 As can be seen from Example 1 and Comparative Examples 1-7, and Table 1, using a composite functional metal source composed of titanium, molybdenum, and tungsten sources in the preparation of the precursor can significantly improve the cycle stability of lithium-rich manganese-based cathode materials, and the capacity retention rate obtained in the above tests is significantly improved. While using only one or two of the titanium, molybdenum, and tungsten sources can bring about corresponding improvements, the improvement is limited, and the effects of any two sources are merely a simple additive effect. Only when titanium, molybdenum, and tungsten work synergistically can a significant synergistic effect be achieved.

[0066] Combining Examples 1 and 12-14 with Table 1, it can be seen that by simultaneously using functional additives in the application of lithium sources, the cycle stability of lithium-rich manganese-based cathode materials can be further improved by utilizing the boron nitride-coated carbon nanotube composite material, and the capacity retention rate obtained in the above tests is also further improved. Furthermore, combining Examples 15-16 with Table 1, it can be seen that when the weight ratio of boron nitride to carbon nanotubes in the functional additive is 1:(3-5), the corresponding improvement effect brought about by the functional additive after application is better. When it is lower or higher than the above range, a significant loss of the corresponding improvement effect will occur. Furthermore, combining Example 17 with Table 1, it can be seen that if the functional additive is replaced by an equal mass of a mixture of boron nitride particles and carbon nanotubes, the capacity retention rate obtained in the test will also show a significant loss. Therefore, it is evident that the boron nitride-coated carbon nanotube composite material combined in a specific ratio and in a special manner can bring about a significantly superior improvement in the corresponding effect.

[0067] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A lithium-rich manganese-based positive electrode material, characterized in that, Includes a precursor and a lithium coating layer covering the surface of the precursor; The precursor is obtained by mixing nickel source, cobalt source, manganese source and composite functional metal source, followed by co-precipitation, filtration, washing and drying. The lithium coating layer is formed by sintering using a lithium source; The composite functional metal source consists of a titanium source, a molybdenum source, and a tungsten source.

2. The lithium-rich manganese-based cathode material according to claim 1, characterized in that: In the composite functional metal source, the molar ratio of titanium, molybdenum and tungsten is (5-6):(2-3):1, and the total molar amount of titanium, molybdenum and tungsten is 1-5% of the total molar amount of nickel, cobalt and manganese.

3. The lithium-rich manganese-based cathode material according to claim 1, characterized in that: The molar ratio of nickel, cobalt and manganese in the nickel source, cobalt source and manganese source is (8-10):1:(20-25).

4. The lithium-rich manganese-based cathode material according to claim 1, characterized in that: The molar ratio of lithium in the lithium source to the total molar amounts of titanium, molybdenum, tungsten, nickel, cobalt, and manganese in the precursor is (1.2-1.5):

1.

5. The method for preparing the lithium-rich manganese-based cathode material according to claim 1, characterized in that: Includes the following steps: (1) Take nickel source, cobalt source, manganese source and composite functional metal source, dissolve them in anhydrous ethanol, add precipitant and surfactant, stir and mix, and then carry out co-precipitation reaction. After filtration, washing and drying, the precursor is obtained. (2) After pre-sintering the precursor obtained in step (1), it is mixed with the lithium source and sintered again to obtain lithium-rich manganese-based cathode material.

6. The method for preparing lithium-rich manganese-based cathode material according to claim 5, characterized in that: Step (2) is specifically set as follows: after pre-sintering the precursor obtained in step (1), it is mixed with lithium source and functional additives and then sintered again to obtain lithium-rich manganese-based cathode material; The functional additive is a carbon nanotube composite material uniformly coated with boron nitride, and is prepared by the following method: S1. Take carbon nanotube raw material, immerse it in acid solution for ultrasonic treatment, and then take it out and dry it to obtain pretreated carbon nanotubes. S2. The pretreated carbon nanotubes obtained in step S1 are added to ethanol along with boric acid, melamine, and surfactant. After ultrasonic treatment, filtration, and drying, the mixture is sintered to obtain the functional additive.

7. The method for preparing lithium-rich manganese-based cathode material according to claim 6, characterized in that: In the functional additives, the weight ratio of boron nitride to carbon nanotubes is 1:(3-5).

8. The method for preparing lithium-rich manganese-based cathode material according to claim 6, characterized in that: The amount of the functional additive is 3-5% of the total mass of the precursor and lithium source.

9. The method for preparing lithium-rich manganese-based cathode material according to claim 5, characterized in that: In step (2), the pre-sintering temperature is 350-500℃ and the pre-sintering time is 4-7h.

10. The method for preparing the lithium-rich manganese-based cathode material according to claim 5, characterized in that: In step (2), the operation of re-sintering is as follows: first sinter at 650-750℃ for 6-10h, and then sinter at 800-900℃ for 8-12h.