Lithium oxalate / CNT-coated modified lithium-rich manganese positive electrode material and preparation method thereof

Abstract

This invention discloses a lithium oxalate / CNT-coated modified lithium-rich manganese cathode material and its preparation method. S1: A metal salt solution, a precipitant, and a complexing agent are introduced concurrently into a reaction vessel for a co-precipitation reaction. After the reaction, the mixture is aged, filtered, and dried to obtain a lithium-rich manganese-based cathode material precursor. S2: The lithium-rich manganese-based cathode material precursor and a lithium source are mixed uniformly, and the mixture is heated to 800-900℃ at a rate of 4-6℃ / min and sintered for 8-16 hours to obtain the lithium-rich manganese-based cathode material LMR. S3: Oxalic acid dihydrate, CNTs, and LMR are added to water and heated and stirred until homogeneous to obtain a composite slurry. S4: Lithium hydroxide is dissolved in water and added dropwise to the composite slurry. After continuous stirring, a reaction slurry is obtained. S5: The reaction slurry is filtered and dried to obtain the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material. This invention improves the first-efficiency coulombic efficiency, cycle life, and rate performance of the lithium-rich manganese cathode material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a lithium oxalate / CNT-coated modified lithium-rich manganese cathode material and a preparation method thereof. Background Art

[0002] With the continuous development of electronic devices such as spacecrafts, electric vehicles, medical devices, and communication devices, lithium-ion batteries have become an indispensable part thereof; however, their energy density still needs to be further improved to meet the applications in new energy vehicles.

[0003] The energy density of a single lithium-ion battery is determined by the working voltage and the battery capacity of the battery itself. Therefore, the battery energy density can be improved by increasing the battery working voltage or capacity. The layered lithium-rich manganese-based cathode material xLi2MnO3·(1-x)LiMO2 (0 < x < 1) is composed of LiMO2 (M = Mn, Co, Ni) and Li2MnO3, and the discharge specific capacity at a voltage of 2 - 4.8V can reach 250 - 300 mAh / g, and it is considered an ideal cathode material for high-energy-density lithium-ion batteries. The lithium-rich manganese-based material has a unique anion redox mechanism, which although contributes to a high specific capacity, also causes instability of the crystal structure of the lithium-rich material, oxygen loss, and transition metal migration, etc., thereby causing problems such as voltage and capacity decay during the cycling process, a low first-cycle Coulomb efficiency, and poor cycling performance.

[0004] At present, domestic and foreign researchers usually adopt modification methods such as surface modification, bulk doping, and morphology structure to alleviate problems such as irreversible oxygen loss and phase change during the cycling process of lithium-rich manganese-based materials. Among them, surface modification mainly uses substances such as metal oxides, fluorides, graphene, polymers, etc., and reports on using organic cathode lithium supplement agents are relatively rare. Lithium oxalate (Li2C2O4) is considered one of the most promising lithium compensation materials, which can decompose to generate Li + at about 4.7V, providing a capacity of 440 mAh / g, which can compensate for the lithium loss during the first charge and discharge process of the lithium-rich manganese-based cathode material, thereby improving its first efficiency and energy density; and compared with other lithium supplement materials, organic lithium salts have a lower decomposition potential, a simple preparation method, are stable to air and moisture, and the decomposition products are gases, which can be discharged during the battery preparation process. However, the Li2C2O4 material has poor electronic conductivity and a relatively high decomposition potential (4.7V), which limits its further application. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide a lithium oxalate / CNT-coated modified lithium-rich manganese cathode material and a preparation method thereof, which can not only improve the first-cycle Coulomb efficiency of the lithium-rich manganese cathode material, but also improve its cycling and rate performance.

[0006] The technical solution of this invention is as follows:

[0007] On one hand, the present invention provides a method for preparing a lithium oxalate / CNT-coated modified lithium-rich manganese cathode material, comprising the following steps:

[0008] S1 introduces a metal salt solution, a precipitant, and a complexing agent into a reaction vessel in parallel to carry out a co-precipitation reaction. After the reaction is completed, the mixture is aged, filtered, and dried to obtain a lithium-rich manganese-based cathode material precursor.

[0009] S2 mixes the lithium-rich manganese-based cathode material precursor and lithium source evenly, heats it to 800-900℃ at a rate of 4-6℃ / min, and sinterstens for 8-16h to obtain lithium-rich manganese-based cathode material LMR.

[0010] S3 adds oxalic acid dihydrate, CNT and LMR to water, heats and stirs until uniform to obtain composite slurry;

[0011] S4 dissolves lithium hydroxide in water, adds it dropwise to the composite slurry, and after continuous stirring, obtains the reaction slurry;

[0012] The S5 reaction slurry was filtered and dried to obtain lithium oxalate / CNT coated modified lithium-rich manganese cathode material.

[0013] Preferably, in step S1, the metal salt in the metal salt solution is a manganese salt, a nickel salt, and a cobalt salt, with a molar ratio of (5-8):(1-4):(0-2), and the concentration of the metal salt solution is 0.5-4 mol / L; wherein the manganese salt is at least one of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate; the nickel salt is at least one of nickel sulfate, manganese nitrate, nickel chloride, and nickel acetate; and the cobalt salt is at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate.

[0014] Preferably, in step S1, the precipitant is at least one of sodium carbonate solution and sodium hydroxide solution, with a concentration of 0.5-4 mol / L; the complexing agent is at least one of ammonia water, ammonium bicarbonate solution and ammonium carbonate solution, with a concentration of 0.5-2 mol / L.

[0015] Preferably, in step S1, the pH of the coprecipitation reaction is 7-11, the reaction temperature is 50-60℃, and the aging time is 12-24h.

[0016] Preferably, in step S1, the particle size D50 of the lithium-rich manganese-based cathode material precursor is 4-6 μm.

[0017] Preferably, in step S2, the lithium source is at least one of lithium carbonate and lithium hydroxide, and the molar ratio of the lithium source to the lithium-rich manganese-based cathode material precursor is (1.2-1.3):1.

[0018] Preferably, in step S3, the mass of the dihydrated oxalic acid is in the mass ratio of the generated lithium oxalate, CNT and LMR as (1-5):(1-5):100; and the mixture is heated to 50-80°C.

[0019] Preferably, in step S4, the molar ratio of lithium hydroxide to oxalic acid dihydrate is (2-2.05):1; lithium hydroxide is used to control the reaction pH to 7-7.5 and the reaction time to 10-40 min.

[0020] Preferably, in step S5, the drying temperature is 130-160℃ and the drying time is 3-5 hours.

[0021] On the other hand, the present invention provides a lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared by the above-described method for preparing lithium oxalate / CNT-coated modified lithium-rich manganese cathode material.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared by this invention exhibits a lithium oxalate coating layer that provides lithium replenishment, improving the initial coulombic efficiency and energy density of the LMR cathode material. Simultaneously, the CNT coating layer not only effectively reduces the decomposition voltage of the lithium replenishing agent and improves the lithium replenishment efficiency, but also acts as an inert protective layer to safeguard the LMR cathode material. This enhances the material's conductivity while reducing material distortion during lithium-ion insertion / extraction, suppressing oxygen release and structural phase transitions, and effectively improving the battery's cycle stability. Attached Figure Description

[0024] Figure 1 This is a SEM image of the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared in Example 1 of this invention.

[0025] Figure 2 This is a SEM image of the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared in Example 2 of this invention.

[0026] Figure 3 This is a SEM image of the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared in Example 3 of this invention.

[0027] Figure 4 This is a SEM image of the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared in Example 4 of this invention.

[0028] Figure 5 This is a SEM image of the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared in Example 5 of this invention.

[0029] Figure 6This is a SEM image of the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared in Example 6 of this invention.

[0030] Figure 7 These are the charging dQ / dV curves of the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared in Example 1 of this invention and the lithium-rich manganese cathode material prepared in Comparative Example 2. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0032] Example 1

[0033] The preparation method of the lithium oxalate / CNT coated modified lithium-rich manganese cathode material in this embodiment includes the following steps:

[0034] S1: Manganese sulfate, nickel sulfate, and cobalt sulfate were weighed out in a Mn:Ni:Co molar ratio of 6:2:2 and dissolved in water to prepare a metal salt solution with a total concentration of 2 mol / L. A certain amount of sodium carbonate was weighed out and a precipitant with a concentration of 2 mol / L was prepared. A certain amount of ammonia water was weighed out and a complexing agent with a concentration of 1 mol / L was prepared. The three solutions were added dropwise to the reactor for co-precipitation reaction, and the reaction temperature was controlled at 55℃ and the pH at 7.8. When the particle size of the generated reactants reached 4-6 μm, the feed was stopped. After aging for 12 hours, the mixture was filtered and dried to obtain the lithium-rich manganese-based cathode material precursor.

[0035] S2 involves uniformly mixing a lithium-rich manganese-based cathode material precursor and lithium carbonate at a molar ratio of 1:1.2, transferring the mixture to a muffle furnace, heating it to 850°C at a rate of 5°C / min, sintering for 12 hours with air purging throughout, and then removing it after cooling to obtain Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material (i.e., LMR);

[0036] S3 is calculated based on the generated lithium oxalate, CNT, and LMR in a mass ratio of 1:5:100. Weigh 1.24g of oxalic acid, 2.5g of CNT, and 50g of LMR, add them to 500mL of deionized water, heat to 60℃, and stir continuously until homogeneous to obtain a composite slurry.

[0037] S4 weighed lithium hydroxide at a molar ratio of lithium hydroxide to oxalic acid dihydrate of 2.02:1 and dispersed it in 20 mL of deionized water to obtain a lithium hydroxide solution. The lithium hydroxide solution was slowly added dropwise to the composite slurry. The final pH was controlled to be 7.5 using the lithium hydroxide solution. The reaction was stirred continuously for 30 min to obtain the reaction slurry.

[0038] S5 The reaction slurry was filtered and dried in an oven at 130°C for 5 hours to obtain Li2C2O4 / CNT coated Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material, denoted as L@C@LMR-1.

[0039] Example 2

[0040] The difference from Example 1 is that in step S3, the mass ratio of lithium oxalate, CNT, and LMR is 2:5:100, and the final material is denoted as L@C@LMR-2.

[0041] Example 3

[0042] The difference from Example 1 is that in step S3, the mass ratio of lithium oxalate, CNT, and LMR is 3:5:100, and the final material is denoted as L@C@LMR-3.

[0043] Example 4

[0044] The difference from Example 1 is that in step S3, the mass ratio of lithium oxalate, CNT, and LMR is 4:5:100, and the final material is denoted as L@C@LMR-4.

[0045] Example 5

[0046] The preparation method of the lithium oxalate / CNT coated modified lithium-rich manganese cathode material in this embodiment includes the following steps:

[0047] S1: Manganese sulfate, nickel sulfate, and cobalt sulfate were weighed out in a Mn:Ni:Co molar ratio of 6:2:2 and dissolved in water to prepare a metal salt solution with a total concentration of 2 mol / L. A certain amount of sodium carbonate was weighed out and a precipitant with a concentration of 2 mol / L was prepared. A certain amount of ammonia water was weighed out and a complexing agent with a concentration of 1 mol / L was prepared. The three solutions were added dropwise to the reactor for co-precipitation reaction, and the reaction temperature was controlled at 55℃ and the pH at 7.8. When the particle size of the generated reactants reached 4-6 μm, the feed was stopped. After aging for 12 hours, the mixture was filtered and dried to obtain the lithium-rich manganese-based cathode material precursor.

[0048] S2: A lithium-rich manganese-based cathode material precursor and lithium carbonate were uniformly mixed at a molar ratio of 1:1.2, transferred to a muffle furnace, heated to 900°C at a rate of 5°C / min, and sintered for 8 hours with air purging throughout. After cooling, the mixture was removed to obtain Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material (i.e., LMR);

[0049] S3 is calculated based on the generated lithium oxalate, CNT, and LMR mass ratio of 2:4:100. Weigh 2.48g of oxalic acid, 2g of CNT, and 50g of LMR, add them to 500mL of deionized water, heat to 60℃, and stir continuously until homogeneous to obtain the composite slurry.

[0050] S4 Weigh lithium hydroxide at a molar ratio of lithium hydroxide to oxalic acid dihydrate of 2.02:1 and disperse it in 20 mL of deionized water to obtain a lithium hydroxide solution. Slowly add the lithium hydroxide solution dropwise to the composite slurry and use the lithium hydroxide solution to control the final pH to 7.2. Stir continuously for 30 min to obtain the reaction slurry.

[0051] S5 The reaction slurry was filtered and dried in an oven at 130°C for 5 hours to obtain Li2C2O4 / CNT coated Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material, denoted as L@C@LMR-5.

[0052] Example 6

[0053] The preparation method of the lithium oxalate / CNT coated modified lithium-rich manganese cathode material in this embodiment includes the following steps:

[0054] S1: Manganese sulfate and nickel sulfate were weighed according to a Mn:Ni molar ratio of 6:2 and dissolved in water to prepare a metal salt solution with a total concentration of 2 mol / L. A certain amount of sodium hydroxide was weighed and prepared as a precipitant with a concentration of 4 mol / L. A certain amount of ammonia water was weighed and prepared as a complexing agent with a concentration of 1 mol / L. The three solutions were added dropwise to the reactor for co-precipitation reaction. Nitrogen gas was introduced for protection, and the reaction temperature was controlled at 55℃ and the pH at 11. When the particle size of the generated reactants reached 4-6 μm, the feed was stopped. After aging for 12 hours, the mixture was filtered and dried to obtain the lithium-rich manganese-based cathode material precursor.

[0055] S2 involves uniformly mixing a lithium-rich manganese-based cathode material precursor and lithium carbonate at a molar ratio of 1:1.2, transferring the mixture to a muffle furnace, heating it to 800°C at a rate of 5°C / min, sintering for 16 hours with air purging throughout, and then removing it after cooling to obtain Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material (i.e., LMR);

[0056] S3 is calculated based on the generated lithium oxalate, CNT, and LMR in a mass ratio of 3:3:100. Weigh 3.72g of oxalic acid, 1.5g of CNT, and 50g of LMR, add them to 500mL of deionized water, heat to 60℃, and stir continuously until homogeneous to obtain a composite slurry.

[0057] S4 Weigh lithium hydroxide at a molar ratio of lithium hydroxide to oxalic acid dihydrate of 2.02:1 and disperse it in 20 mL of deionized water to obtain a lithium hydroxide solution. Slowly add the lithium hydroxide solution dropwise to the composite slurry, and use the lithium hydroxide solution to control the final pH to 7. Stir continuously for 30 min to obtain the reaction slurry.

[0058] S5 The reaction slurry was filtered and dried in an oven at 130°C for 5 hours to obtain Li2C2O4 / CNT coated Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material, denoted as L@C@LMR-6.

[0059] SEM images of the lithium oxalate / CNT-coated modified lithium-rich manganese cathode materials prepared in Examples 1-6 are shown below. Figure 1-6 As shown, the prepared lithium oxalate / CNT coated modified lithium-rich manganese cathode material has a uniform particle size distribution and a uniform coating layer on its surface.

[0060] Comparative Example 1

[0061] The difference from Example 1 is that steps S3-S5 are omitted, and Li is ultimately obtained. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material (i.e., LMR).

[0062] Comparative Example 2

[0063] The difference from Example 1 is that in step S3, CNTs are not added, and Li2C2O4 coated with Li is finally obtained. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material, denoted as L@LMR-1.

[0064] Comparative Example 3

[0065] The difference from Example 1 is that oxalic acid is not added in step S3, resulting in CNT-coated Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material, denoted as C@LMR-1.

[0066] Comparative Example 4

[0067] The difference from Example 1 is that in step S3, based on the generated lithium oxalate, CNT, and LMR mass ratio of 1:6:100, 1.24g of oxalic acid, 3g of CNT, and 50g of LMR were weighed and added to 500mL of deionized water. The mixture was heated to 60°C and stirred continuously until homogeneous to obtain a composite slurry. Finally, Li₂C₂O₄ / CNT-coated Li₂ was obtained. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material.

[0068] Comparative Example 5

[0069] The difference from Example 1 is that in step S4, a lithium hydroxide solution is used to control the final pH to 8.

[0070] Electrochemical performance tests were performed on the cathode materials prepared in Examples 1-6 and Comparative Examples 1-5:

[0071] The positive electrode material, acetylene black, and polyvinylidene fluoride (PVDF) binder were mixed evenly at a mass ratio of 94:3:3, and then dispersed in an N-methylpyrrolidone (NMP) solution to obtain a paste-like mixture. The mixture was coated onto aluminum foil and vacuum dried overnight at 90°C. Li / Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 The assembly of the O2 button cell (model 2016) was carried out in a glove box filled with high-purity argon gas.

[0072] Using lithium metal sheets as the negative electrode and a polypropylene membrane as the separator, 1 mol of LiPF6 was dissolved in ethyl carbonate / dimethyl carbonate (EC / DMC, volume ratio 1:1) as the electrolyte to synthesize a Li-containing electrolyte. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material electrodes were used as the positive electrode material of the battery. The charging and discharging performance of the lithium-ion battery was tested at room temperature on a Blue Electric testing system, with a test voltage range of 2-4.8V.

[0073] The electrochemical performance test results of the cathode materials prepared in Examples 1-6 and Comparative Examples 1-5 are shown in Table 1:

[0074] Table 1. Electrochemical performance test results of the cathode materials prepared in Examples 1-6 and Comparative Examples 1-5.

[0075]

[0076] As can be seen from Examples 1-4 and Comparative Example 1, with the increase of lithium oxalate / CNT coating amount, the discharge capacity, initial coulombic efficiency, and cycle capacity retention all increase. This is because the coating provides an additional lithium source during charge and discharge, not only offsetting irreversible lithium loss and reducing problems such as irreversible lithium metal deposition, but also acting as an inert protective layer to protect the LMR cathode material, improving the material conductivity while reducing material distortion during lithium-ion insertion / extraction, inhibiting oxygen release and structural phase transitions, ultimately improving the material's charge / discharge efficiency, energy density, and cycle life. As can be seen from Examples 1 and Comparative Example 2, Comparative Example 2, without CNT coating, showed a decrease in both discharge capacity and initial coulombic efficiency of the cathode material, but the cycle capacity retention decreased most significantly, indicating that the addition of CNTs helps improve the lithium replenishment efficiency of the lithium oxalate supplementer and enhances the material's stability. As can be seen from Examples 1 and Comparative Example 3, the addition of lithium oxalate supplementer helps improve discharge capacity and initial coulombic efficiency. Furthermore, the charging dQ / dV curves of the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared in Example 1 and the lithium-rich manganese cathode material prepared in Comparative Example 2 are as follows: Figure 7 As shown, by Figure 7 It can be seen that the clear characteristic peak appearing near 4.21V in Example 1 indicates that a significant electrochemical reaction occurred at that point, while no obvious characteristic peak appeared in Comparative Example 2 between 4 and 4.4V, indicating that no chemical reaction occurred within that voltage range; this shows that the addition of CNTs can reduce the decomposition voltage of the lithium supplement to about 4.2V.

Claims

1. A method for preparing lithium oxalate / CNT-coated modified lithium-rich manganese cathode material, characterized in that, Includes the following steps: S1 introduces a metal salt solution, a precipitant, and a complexing agent into a reaction vessel in parallel to carry out a co-precipitation reaction. After the reaction is completed, the mixture is aged, filtered, and dried to obtain a lithium-rich manganese-based cathode material precursor. S2 mixes the lithium-rich manganese-based cathode material precursor and lithium source evenly, heats it to 800-900℃ at a rate of 4-6℃ / min, and sinterstens for 8-16h to obtain lithium-rich manganese-based cathode material LMR. S3 adds oxalic acid dihydrate, CNT and LMR to water, heats and stirs until uniform to obtain composite slurry; S4 dissolves lithium hydroxide in water, adds it dropwise to the composite slurry, and after continuous stirring, obtains the reaction slurry; The S5 reaction slurry was filtered and dried to obtain lithium oxalate / CNT coated modified lithium-rich manganese cathode material.

2. The method for preparing the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material as described in claim 1, characterized in that, In step S1, the metal salt solution contains manganese salt, nickel salt, and cobalt salt, with a molar ratio of (5-8):(1-4):(0-2), and a concentration of 0.5-4 mol / L. The manganese salt is at least one of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate; the nickel salt is at least one of nickel sulfate, manganese nitrate, nickel chloride, and nickel acetate; and the cobalt salt is at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate.

3. The preparation method of the lithium oxalate / CNT coated modified lithium-rich manganese cathode material as described in claim 1, characterized in that, In step S1, the precipitant is at least one of sodium carbonate solution and sodium hydroxide solution, with a concentration of 0.5-4 mol / L; the complexing agent is at least one of ammonia water, ammonium bicarbonate solution and ammonium carbonate solution, with a concentration of 0.5-2 mol / L.

4. The preparation method of the lithium oxalate / CNT coated modified lithium-rich manganese cathode material as described in claim 1, characterized in that, In step S1, the pH of the coprecipitation reaction is 7-11, the reaction temperature is 50-60℃, and the aging time is 12-24h.

5. The method for preparing the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material as described in claim 1, characterized in that, In step S1, the particle size D50 of the lithium-rich manganese-based cathode material precursor is 4-6 μm.

6. The method for preparing the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material as described in claim 1, characterized in that, In step S2, the lithium source is at least one of lithium carbonate and lithium hydroxide, and the molar ratio of the lithium source to the lithium-rich manganese-based cathode material precursor is (1.2-1.3):

1.

7. The method for preparing the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material as described in claim 1, characterized in that, The mass ratio of lithium oxalate, CNT and LMR is (1-5):(1-5):100, and the mass of oxalic acid dihydrate is calculated based on the generated lithium oxalate; heat to 50-80℃.

8. The method for preparing the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material as described in claim 1, characterized in that, In step S4, the molar ratio of lithium hydroxide to oxalic acid dihydrate is (2-2.05):1; lithium hydroxide is used to control the reaction pH to 7-7.5 and the reaction time to 10-40 min.

9. The method for preparing the lithium oxalate / CNT-coated modified lithium-rich manganese cathode material as described in claim 1, characterized in that, In step S5, the drying temperature is 130-160℃ and the drying time is 3-5 hours.

10. The lithium oxalate / CNT-coated modified lithium-rich manganese cathode material prepared by the method for preparing lithium oxalate / CNT-coated modified lithium-rich manganese cathode material according to any one of claims 1-9.

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