Lithium-rich manganese-based composite cathode material, preparation method and application thereof

Abstract

The application provides a lithium-rich manganese-based composite positive electrode material and a preparation method and application thereof, relates to the technical field of positive electrode material preparation, and the preparation method of the lithium-rich manganese-based composite positive electrode material comprises the following steps: firstly, a lithium-rich manganese-based material is prepared; then, pyrrole modified graphene oxide is prepared by reacting graphene oxide with pyrrole at 90-100 DEG C for 6-12 h; the lithium-rich manganese-based material and the pyrrole modified graphene oxide are uniformly dispersed in an organic solvent to obtain a mixed solution; the mixed solution is filtered, and the filter residue is dried at 60-80 DEG C for 6-12 h to obtain the lithium-rich manganese-based composite positive electrode material. The prepared lithium-rich manganese-based positive electrode material has excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of cathode material preparation technology, specifically to lithium-rich manganese-based composite cathode materials, their preparation methods, and applications. Background Technology

[0002] Lithium-rich manganese-based (xLiMO2·(1-x)Li2MnO3) cathode materials are considered core materials for next-generation high-energy-density lithium-ion batteries due to their theoretical specific capacity >250mAh / g. However, their application is still limited by bottlenecks such as low initial coulombic efficiency, poor rate performance, and poor cycle stability. The low initial efficiency is due to the low efficiency of Li2MnO3 at a charging voltage ≥4.5V. + With O 2- The irreversible increase in oxygen vacancies and surface phase transitions caused by simultaneous insertion / extraction (first-time efficiency <80%) result in poor rate performance and cycling stability, which is related to Mn. 4+ This results in low intrinsic electronic conductivity (<10). -4 The structure is closely related to the S / cm ratio and the structural distortions caused by the migration of transition metal ions.

[0003] Existing technologies typically employ surface coating strategies to improve the conductivity of lithium-rich manganese-based cathode materials. In existing conductive coating schemes, graphene oxide is used for coating. Although graphene oxide can construct a conductive network, it tends to agglomerate on the surface of the lithium-rich manganese substrate, resulting in an uncontinuous graphene oxide coating layer. Furthermore, the weak bonding between graphene oxide and the lithium-rich manganese substrate leads to the easy detachment of the graphene oxide coating layer during charge and discharge, resulting in an unstable coating layer structure. This allows the electrolyte to attack the substrate from the exposed points of the coating layer, causing numerous side reactions and leading to poor electrochemical performance of the battery. Therefore, providing a lithium-rich manganese-based composite cathode material with a more stable coating layer structure has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a lithium-rich manganese-based composite cathode material, its preparation method, and its application, solving the technical problem of unstable graphene oxide coating structure.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a lithium-rich manganese-based composite cathode material, comprising the following steps:

[0007] S1. Preparation of lithium-rich manganese-based materials;

[0008] S2. Prepare pyrrole-modified graphene oxide by reacting graphene oxide with pyrrole at 90-100℃ for 6-12h.

[0009] S3. The lithium-rich manganese-based material and pyrrole-modified graphene oxide are uniformly dispersed in an organic solvent to obtain a mixed solution. The mixed solution is filtered, and the filter residue is dried at 60-80℃ for 6-12 hours to obtain a lithium-rich manganese-based composite cathode material.

[0010] The above preparation method selects lithium-rich manganese-based materials and pyrrole-modified graphene oxide, and uses an organic solvent dispersion method to prepare lithium-rich manganese-based composite cathode materials. On the one hand, pyrrole-modified graphene oxide exhibits high dispersion uniformity and stability in organic solvents, allowing it to uniformly coat the surface of the lithium-rich manganese-based material, forming a continuous pyrrole-modified graphene oxide coating layer. On the other hand, the pyrrole groups in the pyrrole-modified graphene oxide are positively charged, while the surface of the lithium-rich manganese-based material is negatively charged. The pyrrole-modified graphene oxide coating layer and the lithium-rich manganese-based material are bonded by electrostatic forces, resulting in strong adhesion. Therefore, the prepared lithium-rich manganese-based composite cathode material has higher structural stability of the pyrrole-modified graphene oxide coating layer, which can effectively suppress side reactions in the battery and improve the battery's electrical performance.

[0011] Preferably, the organic solvent is one or two of N-methylpyrrolidone, N,N-dimethylformamide, acetone, toluene, dibutyl phthalate, dioctyl phthalate, or chloroform.

[0012] Preferably, the preparation method of the pyrrole-modified graphene oxide includes adding the graphene oxide to water, and then subjecting it to ultrasonic treatment for 0.5-2 hours to obtain a concentration of 0.1-1 mg·mL. -1 A stable graphene oxide suspension was prepared by mixing pyrrole with the suspension at a volume ratio of 1:1 to 1:5, stirring continuously in a water bath at 90-100°C for 6-12 hours, filtering, washing the filter residue with deionized water, and freeze-drying for 12-24 hours to obtain pyrrole-modified reduced graphene oxide, i.e., pyrrole-modified graphene oxide. This invention utilizes pyrrole-modified graphene oxide, which possesses good electrical conductivity and can be stably and uniformly dispersed in organic solvents, providing conditions for its uniform coating on lithium-rich manganese-based materials. Furthermore, pyrrole-modified graphene oxide can achieve physical isolation between the electrolyte and the surface of lithium-rich manganese-based particles, thereby mitigating interfacial side reactions. Therefore, the lithium-rich manganese-based cathode material of this invention exhibits excellent electrochemical performance.

[0013] Preferably, the pyrrole-modified graphene oxide accounts for 0.5wt%-1.5wt% of the lithium-rich manganese-based material by mass.

[0014] Preferably, the concentration of the pyrrole-modified graphene oxide in the organic solvent is 0.1-1 mg / mL.

[0015] Preferably, it further includes washing the filter residue with absolute ethanol, and then drying the filter residue at 60-80 °C. By utilizing the exchange between ethanol and organic solvents and combining capillary evaporation drying, during the process of removing the solvent, three-dimensional continuous conductive networks are constructed and capillary shrinkage dense coating is achieved for the pyrrole-modified graphene oxide, improving the interfacial bonding force between the pyrrole-modified graphene oxide and the lithium-rich manganese-based material.

[0016] Preferably, the preparation method of the lithium-rich manganese-based material includes dissolving MnSO4·H2O, NiSO4·H2O, and CoSO4·H2O in water, dropping NaOH aqueous solution and NH3·H2O into the continuously stirred solution, and reacting under nitrogen protection. During the reaction process, the pH of the solution is within the range of 10.5-11. After the reaction is complete, the obtained precipitate is filtered and repeatedly washed with deionized water and ethanol. The precipitate is dried to obtain a nickel-cobalt-manganese hydroxide precursor. The nickel-cobalt-manganese hydroxide precursor is uniformly mixed with lithium carbonate, and then high-temperature solid-phase synthesis is carried out in an air atmosphere to obtain the lithium-rich manganese-based material.

[0017] In a second aspect, the present invention provides a lithium-rich manganese-based composite cathode material prepared by the preparation method described in the first aspect, including:

[0018] A core, where the core includes a lithium-rich manganese-based material;

[0019] A coating layer, where the coating layer includes pyrrole-modified graphene oxide, and the pyrrole-modified graphene oxide coats the surface of the lithium-rich manganese-based material.

[0020] Preferably, the chemical formula of the lithium-rich manganese-based material is xLiMO2·(1-x)Li2MnO3, 0<x<1, M is a transition metal, selected from at least two of Ni, Co, and Mn.

[0021] In a third aspect, the present invention provides a lithium-ion battery, and the lithium-ion battery includes the lithium-rich manganese-based composite cathode material described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0023] Figure 1 SEM image of the lithium-rich manganese-based composite cathode material prepared for Example 1;

[0024] Figure 2SEM image of the composite cathode material prepared in Comparative Example 1;

[0025] Figure 3 X-ray diffraction pattern of the lithium-rich manganese-based composite cathode material prepared in Example 1;

[0026] Figure 4 The first-cycle charge-discharge curves of the lithium-rich manganese-based composite cathode material prepared in Example 1 at 0.1C (2.0-4.8V);

[0027] Figure 5 The graphs show the cycle performance of the batteries corresponding to Example 1 and Comparative Example 1 at 1C (2.0-4.5V).

[0028] Figure 6 The graphs show the rate performance of the batteries corresponding to Example 1 and Comparative Example 1 at different current densities (2.0-4.5V). Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0031] I. Preparation Method

[0032] Example 1

[0033] This embodiment provides a method for preparing a lithium-rich manganese-based composite cathode material, including the following steps:

[0034] S1. Preparation of lithium-rich manganese-based materials: MnSO4·H2O, NiSO4·H2O, and CoSO4·H2O were weighed out according to a molar ratio of Mn:Ni:16.25:16.25 and dissolved in deionized water. Then, NaOH aqueous solution and NH3·H2O were slowly added dropwise to the metal salt solution, which was continuously stirred in a 60°C water bath under nitrogen protection. The pH of the solution was maintained within the range of 10.5-11 throughout the precipitation process. After the reaction was complete, the precipitate was filtered and repeatedly washed with deionized water and ethanol. The precipitate was dried at 100°C to obtain a nickel-cobalt-manganese hydroxide precursor. The nickel-cobalt-manganese hydroxide precursor was uniformly mixed with lithium carbonate at a molar ratio of Li:TM (transition metals) of 1.2:0.8, and then subjected to high-temperature solid-phase synthesis in air to obtain the lithium-rich manganese-based material Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2.

[0035] S2. Preparation of pyrrole-modified graphene oxide: Commercial graphene oxide powder (Changzhou Sixth Element Materials Technology Co., Ltd., model SE2431) was added to deionized water and ultrasonically treated for 0.5 hours to obtain a concentration of 1 mg·mL⁻¹. -1 A homogeneous and stable graphene oxide suspension (GO suspension) was obtained. Pyrrole and GO suspension were mixed at a volume ratio of 1:1 and stirred continuously in a 100°C water bath for 6 hours. The mixed suspension was then filtered and washed with a large amount of deionized water to remove excess pyrrole. The resulting powder was freeze-dried for 24 hours to obtain pyrrole-modified reduced graphene oxide, i.e., pyrrole-modified graphene oxide.

[0036] S3. Using lithium-rich manganese-based material as the matrix, pyrrole-modified graphene oxide accounts for 0.5 wt% of the matrix material. The lithium-rich manganese-based matrix material and pyrrole-modified graphene oxide are dispersed in the organic solvent N-methylpyrrolidone, with the concentration of pyrrole-modified graphene oxide in the organic solvent being 0.1 mg / mL. The mixture is then stirred for 1 hour using a high-speed disperser at a speed of 20,000 r / min to obtain a homogeneous mixed solution. Subsequently, the mixed solution is filtered and washed multiple times with a large amount of anhydrous ethanol. The material on the filter membrane is collected and placed in a 60℃ oven for drying for 12 hours. The obtained sample is a pyrrole-modified graphene oxide-coated lithium-rich manganese-based cathode material, i.e., a lithium-rich manganese-based composite cathode material. By utilizing the exchange between ethanol and organic solvent, combined with capillary evaporation drying, the pyrrole-modified graphene oxide achieves the construction of a three-dimensional continuous conductive network and capillary shrinkage dense coating during the solvent removal process.

[0037] The morphology of the prepared lithium-rich manganese-based composite cathode material is as follows: Figure 1As shown, its X-ray diffraction pattern is as follows: Figure 3 As shown. In this embodiment, graphene oxide is modified by pyrrole. Pyrrole reduces graphene oxide in situ, generating pyrrole oligomers on the graphene surface. Figure 1 It can be seen that pyrrole-modified graphene oxide uniformly covers the surface of the lithium-rich manganese-based substrate material in solution. (From...) Figure 3 It is known that lithium-rich manganese-based materials have good crystallinity, and the coating process does not introduce other impurity phases.

[0038] Example 2

[0039] This embodiment provides a method for preparing a lithium-rich manganese-based cathode material with a surface coating, including the following steps:

[0040] MnSO4·H2O, NiSO4·H2O, and CoSO4·H2O were weighed out in a molar ratio of Mn:Ni:Co of 67.5:16.25:16.25 and dissolved in deionized water. Then, NaOH aqueous solution and NH3·H2O were slowly added dropwise to the metal salt solution, which was continuously stirred in a 60°C water bath under nitrogen protection. The pH of the solution was maintained between 10.5 and 11 throughout the precipitation process. After the reaction was complete, the precipitate was filtered and repeatedly washed with deionized water and ethanol. The precipitate was dried at 100°C to obtain a nickel-cobalt-manganese hydroxide precursor. This precursor was then uniformly mixed with lithium carbonate in a Li:TM (transition metal) molar ratio of 1.2:0.8, and then subjected to high-temperature solid-state synthesis in air to obtain the desired lithium-rich manganese-based matrix material, Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2.

[0041] A concentration of 0.1 mg·mL⁻¹ was obtained by adding commercial graphene oxide powder to deionized water and then sonicating it for 2 hours. -1 A homogeneous and stable graphene oxide (GO) suspension was prepared. Pyrrole was mixed with the GO suspension at a volume ratio of 1:5 and stirred continuously in a water bath at 90-100℃ for 12 hours. The suspension was then filtered and washed with a large amount of deionized water to remove excess pyrrole. The resulting powder was freeze-dried for 12 hours to finally obtain pyrrole-modified reduced graphene oxide, i.e., pyrrole-modified graphene oxide.

[0042] A lithium-rich manganese-based material was used as the matrix material, with pyrrole-modified graphene oxide accounting for 0.5 wt% of the matrix material. The lithium-rich manganese-based matrix material and pyrrole-modified graphene oxide were dispersed in the organic solvent N-methylpyrrolidone, with the concentration of pyrrole-modified graphene oxide in the organic solvent being 0.5 mg / mL. The mixture was then stirred for 1 hour using a high-speed disperser at 30,000 rpm to obtain a homogeneous solution. Subsequently, the above solution was filtered and washed multiple times with a large amount of anhydrous ethanol. The material on the filter membrane was collected and placed in an oven at 80°C for drying for 10 hours. The resulting sample is the pyrrole-modified graphene oxide-coated lithium-rich manganese-based cathode material.

[0043] Example 3

[0044] This embodiment provides a method for preparing a lithium-rich manganese-based cathode material with a surface coating, including the following steps:

[0045] MnSO4·H2O and NiSO4·H2O were weighed out in a Mn:Ni molar ratio of 3:1 and dissolved in deionized water. Then, NaOH aqueous solution and NH3·H2O were slowly added dropwise to the metal salt solution, which was continuously stirred in a 60°C water bath under nitrogen protection. The pH of the solution was maintained between 10.5 and 11 throughout the precipitation process. After the reaction was complete, the precipitate was filtered and repeatedly washed with deionized water and ethanol. The precipitate was dried at 100°C to obtain a nickel-cobalt-manganese hydroxide precursor. This precursor was then uniformly mixed with lithium carbonate in a Li:TM (transition metal) molar ratio of 1.2:0.8, and then subjected to high-temperature solid-state synthesis in air to obtain the desired lithium-rich manganese-based matrix material, Li. 1.2 Mn 0.6 Ni 0.2 O2.

[0046] A concentration of 1 mg·mL⁻¹ was obtained by adding commercial graphene oxide powder to deionized water and then sonicating it for 0.5–2 hours. -1 A homogeneous and stable graphene oxide (GO) suspension was obtained. Pyrrole was mixed with the GO suspension at a volume ratio of 1:3 and stirred continuously in a 95°C water bath for 10 hours. The suspension was then filtered and washed with a large amount of deionized water to remove excess pyrrole. The resulting powder was freeze-dried for 20 hours to finally obtain pyrrole-modified reduced graphene oxide, i.e., pyrrole-modified graphene oxide.

[0047] A lithium-rich manganese-based material was used as the matrix material, with pyrrole-modified graphene oxide accounting for 1.5 wt% of the matrix material. The lithium-rich manganese-based matrix material and pyrrole-modified graphene oxide were dispersed in the organic solvent N,N-dimethylformamide, with the concentration of pyrrole-modified graphene oxide in the organic solvent being 1 mg / mL. The mixture was then stirred for 0.5 h using a high-speed disperser at 30,000 r / min to obtain a homogeneous mixed solution. Subsequently, the above mixed solution was filtered and washed multiple times with a large amount of anhydrous ethanol. The material on the filter membrane was collected and placed in an 80℃ oven for drying for 12 h. The obtained sample is the pyrrole-modified graphene oxide-coated lithium-rich manganese-based cathode material.

[0048] Example 4

[0049] This embodiment provides a method for preparing a lithium-rich manganese-based cathode material with a surface coating, including the following steps:

[0050] MnSO4·H2O and NiSO4·H2O were weighed out at a molar ratio of Mn:Ni of 3:1 and dissolved in deionized water. Then, NaOH aqueous solution and NH3·H2O were slowly added dropwise to the metal salt solution, which was continuously stirred in a 60°C water bath under nitrogen protection. The pH of the solution was maintained between 10.5 and 11 throughout the precipitation process. After the reaction was complete, the precipitate was filtered and repeatedly washed with deionized water and ethanol. The precipitate was dried at 100°C to obtain a nickel-cobalt-manganese hydroxide precursor. This precursor was then uniformly mixed with lithium carbonate at a molar ratio of Li:TM (transition metals) of 1.2:0.8, and then subjected to high-temperature solid-state synthesis in air to obtain the desired lithium-rich manganese-based matrix material, Li. 1.2 Mn 0.6 Ni 0.2 O2.

[0051] A concentration of 0.5 mg·mL⁻¹ was obtained by adding commercial graphene oxide powder to deionized water and then sonicating it for 1 hour. -1 A homogeneous and stable graphene oxide (GO) suspension was prepared. Pyrrole was mixed with the GO suspension at a volume ratio of 1:5 and stirred continuously in a 90°C water bath for 12 hours. The suspension was then filtered and washed with a large amount of deionized water to remove excess pyrrole. The resulting powder was freeze-dried for 20 hours to finally obtain pyrrole-modified reduced graphene oxide, i.e., pyrrole-modified graphene oxide.

[0052] A lithium-rich manganese-based material was used as the matrix material, with pyrrole-modified graphene oxide accounting for 1 wt% of the matrix material. The lithium-rich manganese-based matrix material and pyrrole-modified graphene oxide were dispersed in the organic solvent acetone, with the concentration of pyrrole-modified graphene oxide in the organic solvent being 1 mg / mL. The mixture was then stirred for 1 hour using a high-speed disperser at a speed of 20,000 rpm to obtain a homogeneous mixed solution. Subsequently, the above mixed solution was filtered and washed multiple times with a large amount of anhydrous ethanol. The material on the filter membrane was collected and placed in a 60°C oven for drying for 12 hours. The obtained sample is the pyrrole-modified graphene oxide-coated lithium-rich manganese-based cathode material.

[0053] Example 5

[0054] This embodiment provides a method for preparing a lithium-rich manganese-based cathode material with a surface coating, including the following steps:

[0055] MnSO4·H2O, NiSO4·H2O, and CoSO4·H2O were weighed out in a molar ratio of Mn:Ni:Co of 67.5:16.25:16.25 and dissolved in deionized water. Then, NaOH aqueous solution and NH3·H2O were slowly added dropwise to the metal salt solution, which was continuously stirred in a 60°C water bath under nitrogen protection. The pH of the solution was maintained between 10.5 and 11 throughout the precipitation process. After the reaction was complete, the precipitate was filtered and repeatedly washed with deionized water and ethanol. The precipitate was dried at 100°C to obtain a nickel-cobalt-manganese hydroxide precursor. This precursor was then uniformly mixed with lithium carbonate in a Li:TM (transition metal) molar ratio of 1.2:0.8, and then subjected to high-temperature solid-state synthesis in air to obtain the desired lithium-rich manganese-based matrix material, Li. 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2.

[0056] A concentration of 1 mg·mL⁻¹ was obtained by adding commercial graphene oxide powder to deionized water and then sonicating it for 1.5 hours. -1 A homogeneous and stable graphene oxide (GO) suspension was prepared. Pyrrole was mixed with the GO suspension at a volume ratio of 1:1 and stirred continuously in a 95°C water bath for 10 hours. The suspension was then filtered and washed with a large amount of deionized water to remove excess pyrrole. The resulting powder was freeze-dried for 24 hours to finally obtain pyrrole-modified reduced graphene oxide, i.e., pyrrole-modified graphene oxide.

[0057] A lithium-rich manganese-based material was used as the matrix material, with pyrrole-modified graphene oxide accounting for 1.5 wt% of the matrix material. The lithium-rich manganese-based matrix material and pyrrole-modified graphene oxide were dispersed in the organic solvent N-methylpyrrolidone, with the concentration of pyrrole-modified graphene oxide in the organic solvent being 0.1 mg / mL. The mixture was then stirred for 1 hour using a high-speed disperser at 30,000 rpm to obtain a homogeneous solution. Subsequently, the above solution was filtered and washed multiple times with a large amount of anhydrous ethanol. The material on the filter membrane was collected and placed in a 70°C oven for drying for 12 hours. The resulting sample is the pyrrole-modified graphene oxide-coated lithium-rich manganese-based cathode material.

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 1 is that this comparative example does not include S2, the preparation of pyrrole-modified graphene oxide, and in S3, commercial graphene oxide powder is used instead of pyrrole-modified graphene oxide; otherwise, it is the same as Example 1. That is, this comparative example does not modify commercial graphene oxide powder, but uses commercial graphene oxide powder to replace pyrrole-modified graphene oxide to prepare lithium-rich manganese-based composite cathode material.

[0060] The composite cathode materials prepared in Example 1 and Comparative Example 1 were assembled into batteries, and the assembly method is as follows.

[0061] Electrode slurry preparation: The binder is PVDF and the conductive agent is conductive carbon black. The above materials are uniformly dispersed in the organic solvent NMP according to the mass ratio of composite positive electrode material: binder: conductive agent = 9:0.5:0.5 to obtain the electrode slurry.

[0062] The obtained electrode slurry was coated onto the current collector aluminum foil, then dried, rolled, sliced, and assembled into half-cells. The entire assembly process was carried out in a glove box with low water and oxygen content (<0.1ppm). Lithium foil was used as the electrode, Celgard polypropylene film was used as the separator, and 1 M LiPF6 was used as the electrolyte (the solvent was a 1:1 volume ratio of ethylene carbonate / diethyl carbonate mixed solvent).

[0063] Performance Tests and Results

[0064] 1. The composite cathode material prepared in Example 1 includes a pyrrole-modified graphene oxide coating layer and a lithium-rich manganese matrix. Figure 1 It is its SEM image, by Figure 1 It can be seen that the composite cathode material prepared in Example 1 has fewer and smaller pyrrole-modified graphene oxide agglomerates formed on the lithium-rich manganese substrate, and the pyrrole-modified graphene oxide coating layer is more continuous; the composite cathode material prepared in Comparative Example 1 includes a graphene oxide coating layer and a lithium-rich manganese substrate. Figure 2 It is its SEM image, by Figure 2It can be seen that unmodified graphene oxide has a large number of graphene oxide agglomerates on the lithium-rich manganese matrix, and the continuity of the graphene oxide coating layer is poor.

[0065] 2. The electrochemical performance of the assembled half-cells was tested using the following methods:

[0066] (1) First-cycle discharge specific capacity and first-cycle coulombic efficiency: 0.1C, 2.0-4.8V;

[0067] (2) Capacity after 100 cycles: 1C, 2.0-4.5V;

[0068] (3) Rate performance: 5C / 0.1C, 2.0-4.5V.

[0069] Table 1 Performance test results of composite cathode materials

[0070]

[0071] As shown in Table 1, the performance of the half-cell assembled with the composite cathode material of Example 1 is superior to that of Comparative Example 1. This is because the pyrrole-modified graphene oxide coating layer of the composite cathode material prepared in Example 1 is more continuous, while the graphene oxide coating layer of the composite cathode material prepared in Comparative Example 1 has poor continuity. The uniform and continuous pyrrole-modified graphene oxide coating layer has the largest effective contact area and stable physical contact with the substrate material. Furthermore, since the pyrrole groups of the pyrrole-modified graphene oxide are positively charged and the surface of the lithium-rich manganese-based material is negatively charged, the pyrrole-modified graphene oxide coating layer and the lithium-rich manganese-based material are bonded by strong electrostatic forces. This results in higher structural stability of the pyrrole-modified graphene oxide coating layer of the prepared lithium-rich manganese-based composite cathode material, which can effectively suppress side reactions in the battery and improve the battery's electrical performance.

[0072] Figure 4 The first-cycle charge-discharge curves (voltage range 2.0-4.8V) of the battery assembled using the lithium-rich manganese-based composite cathode material prepared in Example 1 are shown in Table 1. Figure 4 It can be seen that the first-cycle discharge specific capacity of the lithium-rich manganese-based composite cathode material is 247 mAh / g, and the first-cycle coulombic efficiency is 85.69%.

[0073] Figure 5 Table 1 shows the cycle performance curves (voltage range 2.0-4.5V) of batteries assembled from the lithium-rich manganese-based composite cathode materials prepared in Example 1 and Comparative Example 1 at 1C. (Table 1 and...) Figure 5It can be seen that the battery assembled with the lithium-rich manganese-based composite cathode material prepared in Example 1 has a capacity of 176.5 mAh / g after 100 cycles, while the capacity of the lithium-rich manganese-based material in Comparative Example 1 after 100 cycles is 173.1 mAh / g. During the cycling process, the capacity of the lithium-rich manganese-based composite cathode material prepared in Example 1 is always higher than that of Comparative Example 1.

[0074] Figure 6 The graph shows the rate performance of batteries assembled from the lithium-rich manganese-based composite cathode materials prepared in Example 1 and Comparative Example 1 at different current densities (0.1C, 0.33C, 1C, 2C, 5C, voltage range 2.0-4.5V). Figure 6 It is known that the lithium-rich manganese-based composite cathode material has a discharge specific capacity of 223.3 mAh / g at 0.1C and 130.9 mAh / g at 5C current density. The lithium-rich manganese-based composite cathode material prepared in Comparative Example 1 has a discharge specific capacity of 209.6 mAh / g at 0.1C and only 124.8 mAh / g at 5C.

[0075] Therefore, the performance of the half-cell assembled with the composite cathode material in Example 1 is superior to that of Comparative Example 1.

[0076] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0078] The present invention has been illustrated with the above embodiments to describe the detailed process flow of the present invention. However, the present invention is not limited to the above detailed process flow, that is, it does not mean that the present invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a lithium-rich manganese-based composite cathode material, characterized in that, It includes the following steps: S1. Prepare the lithium-rich manganese-based material; S2. React graphene oxide with pyrrole at 90 - 100 °C for 6 - 12 h to prepare pyrrole-modified graphene oxide; S3. The lithium-rich manganese-based material and pyrrole-modified graphene oxide are uniformly dispersed in an organic solvent to obtain a mixed solution. Filter the mixed solution, and dry the filter residue at 60 - 80 °C for 6 - 12 h to obtain the lithium-rich manganese-based composite cathode material.

2. The preparation method of the lithium-rich manganese-based composite cathode material as described in claim 1, characterized in that, The organic solvent is one or two of N-methylpyrrolidone, N,N-dimethylformamide, acetone, toluene, dibutyl phthalate, dioctyl phthalate or chloroform.

3. The method for preparing the lithium-rich manganese-based composite cathode material as described in claim 1, characterized in that, The preparation method of the pyrrole-modified graphene oxide includes adding the graphene oxide to water, and then subjecting it to ultrasonic treatment for 0.5-2 hours to obtain a concentration of 0.1-1 mg·mL. -1 The graphene oxide suspension was prepared by mixing pyrrole with the suspension at a volume ratio of 1:1 to 1:5, reacting at 90-100℃ for 6-12 hours, filtering, washing the filter residue with deionized water, and freeze-drying for 12-24 hours to obtain pyrrole-modified graphene oxide.

4. The method for preparing the lithium-rich manganese-based composite cathode material as described in claim 1, characterized in that, The mass ratio of the pyrrole-modified graphene oxide to the lithium-rich manganese-based material is 0.5 wt% - 1.5 wt%.

5. The method for preparing the lithium-rich manganese-based composite cathode material as described in claim 1, characterized in that, The concentration of the pyrrole-modified graphene oxide in the organic solvent is 0.1 - 1 mg / mL.

6. The method for preparing the lithium-rich manganese-based composite cathode material as described in claim 1, characterized in that, It also includes washing the filter residue with absolute ethanol, and then drying the filter residue at 60 - 80 °C.

7. The method for preparing the lithium-rich manganese-based composite cathode material as described in claim 1, characterized in that, The preparation method of the lithium-rich manganese-based material includes dissolving MnSO4·H2O, NiSO4·H2O, and CoSO4·H2O in water, adding an aqueous NaOH solution and NH3·H2O to the solution at 50 - 70 °C, and reacting under nitrogen protection. During the reaction, the pH of the solution is within the range of 10.5 - 11. After the reaction is complete, filter the obtained precipitate, and wash the precipitate with deionized water and ethanol. The precipitate is dried at 100 - 110 °C to obtain a nickel-cobalt-manganese hydroxide precursor. The nickel-cobalt-manganese hydroxide precursor is uniformly mixed with lithium carbonate, and then high-temperature solid-phase synthesis is carried out in an air atmosphere to obtain the lithium-rich manganese-based material.

8. A lithium-rich manganese-based composite cathode material prepared by the preparation method according to any one of claims 1-7, characterized in that, It includes: A core, the core includes a lithium-rich manganese-based material; A coating layer, the coating layer includes pyrrole-modified graphene oxide, and the pyrrole-modified graphene oxide is coated on the surface of the lithium-rich manganese-based material.

9. The lithium-rich manganese-based composite cathode material according to claim 8, characterized in that, The chemical formula of the lithium-rich manganese-based material is xLi2MnO3·(1 - x)LiMO2, 0 < x < 1, M is a transition metal, selected from at least two of Ni, Co, and Mn.

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

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