Composite lithium-rich manganese-based positive electrode material, preparation method thereof and lithium ion battery containing composite lithium-rich manganese-based positive electrode material

Abstract

The invention provides a composite lithium-rich manganese-based positive electrode material, a preparation method thereof and a lithium ion battery containing the composite lithium-rich manganese-based positive electrode material, and belongs to the field of lithium ion batteries. The composite lithium-rich manganese-based positive electrode material is of a core-shell structure, an inner core of the lithium-rich manganese-based positive electrode material is a phase structure gradient lithium-rich manganese-based positive electrode material, a coating layer of the lithium-rich manganese-based positive electrode material comprises a polymer, the polymer comprises strong negative electricity groups and-NH2 groups, and the strong negative electricity groups comprise-C = O and / or-O-C = O. The composite lithium-rich manganese-based positive electrode material prepared by the invention has excellent long cycle performance in a lithium ion battery containing sulfonyl imino lithium salt.

Description

Technical Field

[0001] This invention provides a composite lithium-rich manganese-based cathode material, its preparation method, and a lithium-ion battery containing the same, belonging to the field of lithium-ion batteries. Background Technology

[0002] With the increasing popularity of pure electric vehicles, the demand for lithium-ion battery energy storage devices is becoming increasingly prominent. Currently, the specific capacity of commercially available graphite anode materials reaches 372 mAh / g, while that of silicon-based anode materials can reach 2000 mAh / g. Compared to anode materials, the specific capacity of cathode materials needs further improvement. Currently, lithium-rich manganese-based cathode materials have received significant attention from the academic community due to their specific capacity (>250 mAh / g), high operating voltage, low cost, and environmental friendliness, making them a promising next-generation lithium-ion battery cathode material. However, during cycling, lithium-rich manganese-based cathode materials suffer from low initial coulombic efficiency, poor rate performance, and capacity and voltage decay, which limits their application.

[0003] In recent years, with the deepening of people's theoretical understanding of lithium-rich manganese-based cathode materials, methods for modifying lithium-rich manganese-based cathode materials have been developed, and a series of important advances have been made.

[0004] CN111634957B discloses a carbon-coated mixed solvate thermally doped lithium-rich manganese material, its preparation method, and its application. Nickel, cobalt, and manganese salts are mixed with salts of doped metals, and an alkaline solution is added to adjust the pH to obtain a mixed solution. The mixed solution is heated, cooled, washed, and dried in a reaction vessel to obtain a metal-doped lithium-rich manganese precursor material. After calcination with lithium salts, a metal-doped lithium-rich manganese cathode material is obtained. The metal-doped lithium-rich manganese cathode material is then mixed uniformly with low-boiling-point long-chain carbon in a mixer, and after calcination, a carbon-coated mixed solution thermally doped lithium-rich manganese material is obtained. However, this method has poor effectiveness in suppressing the reaction between the lithium-rich manganese-based cathode material and the electrolyte.

[0005] CN114256457B discloses a lithium-rich manganese-based cathode material with homogeneous composite coating and its preparation method. The lithium-rich manganese-based cathode material includes a lithium-rich manganese-based material and a homogeneous composite coating layer. The homogeneous composite coating layer is composed of a fast-ion conductor and a three-dimensional carbon network. The fast-ion conductor is uniformly loaded and cross-linked within the three-dimensional carbon network to form a homogeneous composite surface coating layer, which improves the ionic and electronic conductivity of the substrate, effectively reduces interfacial impedance, and avoids the problem of poor electron transport in the fast-ion bulk coating layer and poor lithium-ion transport in the conductive coating layer. However, its cycle performance still needs further improvement.

[0006] Therefore, how to prepare a lithium-rich manganese-based cathode material with excellent electrochemical performance such as long cycle life is an important research direction in this field. Summary of the Invention

[0007] The purpose of the present invention is to provide a composite lithium-rich manganese-based cathode material with long cycle performance and excellent ion transport performance, a preparation method thereof, and a lithium-ion battery containing the same.

[0008] To achieve the purpose of this invention, the following technical solutions are adopted:

[0009] One of the purposes of the present invention is to provide a composite lithium-rich manganese-based cathode material. The composite lithium-rich manganese-based cathode material has a core-shell structure. The core of the lithium-rich manganese-based cathode material is a phase-structure gradient lithium-rich manganese-based cathode material, and the coating layer of the lithium-rich manganese-based cathode material includes a polymer. The polymer includes a strongly negatively charged group and -NH2 group, and the strongly negatively charged group includes -C=O and / or -O-C=O.

[0010] The core of the composite lithium-rich manganese-based cathode material of the present invention is a phase-structure gradient lithium-rich manganese-based cathode material. -O-C=O in the coating polymer can anchor transition metal ions on the surface of the lithium-rich manganese-based cathode material, generating a complexing effect. On the one hand, it can reduce the reaction of Mn ions while inhibiting the activation process of Li2MnO3, thereby inhibiting the release of oxygen. On the other hand, it can achieve the stable adhesion of the organic coating layer to the lithium-rich manganese-based cathode material during the cycling process.

[0011] As a preferred technical solution of the present invention, the general formula of the core is xLi2MnO3·(1-x)LiTMO2-yLi2MnO3·(1-y)LiTMO2, 0 < y < x < 1, TM is selected from any one or at least two combinations of Ni, Co or Mn. The phase-structure gradient lithium-rich manganese-based cathode material includes a monoclinic Li2MnO3 phase and a rhombic LiTMO2 phase. The content of the monoclinic Li2MnO3 phase decreases sequentially from the inside to the outside, and the content of the rhombic LiTMO2 phase increases sequentially from the inside to the outside.

[0012] The core of the lithium-rich manganese-based cathode material of the present invention is a phase-structure gradient lithium-rich cathode material. The phase-structure gradient lithium-rich cathode material can regulate the cycling stability, discharge specific capacity and safety and other properties of the composite lithium-rich cathode material in the lithium-ion battery, effectively improving the electrochemical performance of the composite lithium-rich cathode material.

[0013] Preferably, the coating layer includes a polymer shown in Formula 1, n≥2, where the value of n can be 2, 4, 6, 10, 20, 40, 60, 80, 100, 200, 400, 600, 800, 1000, 10000 or 20000, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0014]

[0015] The core of this invention's composite lithium-rich manganese-based cathode material is a phase-gradient lithium-rich manganese-based cathode material. The coating layer includes a polymer as shown in Formula 1, which is obtained by polymerizing an acetyl group with an ester group linked to the vinyl resin backbone with isocyanate. In the polymer of Formula 1, -OC=O can anchor transition metal ions on the surface of the lithium-rich manganese-based cathode material, generating a complexation effect. Firstly, this can reduce the reaction of Mn ions while inhibiting the activation process of Li2MnO3, thereby suppressing the release of oxygen. Secondly, it can achieve stable adhesion of the organic coating layer to the lithium-rich manganese-based cathode material during cycling.

[0016] As a preferred technical solution of the present invention, the thickness of the coating layer is 5 to 30 nm, wherein the thickness can be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm or 30 nm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0017] In this invention, if the coating layer is too thick or too thin, the electrochemical performance of the composite lithium-rich cathode material will decrease. A polymer coating layer of suitable thickness can reduce the volume expansion and contraction of the cathode material during charge and discharge, thereby improving the corrosion resistance of the cathode material. It can also act as a protective barrier, reducing direct contact between the electrolyte and the cathode material, suppressing side reactions, and thus improving the battery's cycle performance and capacity retention. Furthermore, the polymer coating layer can remove HF, mitigate the chemical erosion of the electrolyte, reduce transition metal dissolution, and enhance the corrosion resistance of the cathode material.

[0018] A second objective of this invention is to provide a method for preparing the composite lithium-rich manganese-based cathode material as described in one objective, the method comprising the following steps:

[0019] The composite lithium-rich manganese-based cathode material is obtained by mixing organic chelating material monomers, isocyanate, initiator, solvent and phase structure gradient lithium-rich manganese-based cathode material.

[0020] As a preferred embodiment of the present invention, the organic chelating material monomer includes ethylene glycol acetoacetate methacrylate and / or cyanoethyl acrylate, preferably ethylene glycol acetoacetate methacrylate.

[0021] Preferably, the ethylene glycol acetoacetate methacrylate accounts for 0.5 to 50 wt% of the mass fraction of the phase structure gradient lithium-rich manganese-based cathode material. The mass fraction can be 0.5 wt%, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 2 to 5 wt%.

[0022] Preferably, the molar ratio of ethylene glycol acetoacetate methacrylate to isocyanate is (1-5):1, wherein the molar ratio can be 1:1, 2:1, 3:1, 4:1 or 5:1, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0023] As a preferred embodiment of the present invention, the initiator includes any one or a combination of at least two of azobisisobutyronitrile, cyclohexane peroxide, or tert-butyl hydroperoxide. Typical but non-limiting examples of such combinations include: a combination of azobisisobutyronitrile and cyclohexane peroxide, a combination of cyclohexane peroxide and tert-butyl hydroperoxide, or a combination of azobisisobutyronitrile and tert-butyl hydroperoxide, etc.

[0024] Preferably, the solvent includes any one or a combination of at least two of tetrahydrofuran, dimethylformamide, acetone, or anhydrous acetonitrile, wherein typical but non-limiting examples of the combination include: a combination of tetrahydrofuran and dimethylformamide, a combination of dimethylformamide and acetone, a combination of acetone and anhydrous acetonitrile, or a combination of tetrahydrofuran and anhydrous acetonitrile, etc.

[0025] Preferably, the mass ratio of the solvent to the phase structure gradient lithium-rich manganese-based cathode material is (3-8):1, wherein the mass ratio can be 3:1, 4:1, 5:1, 6:1, 7:1 or 8:1, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0026] As a preferred technical solution of the present invention, the mixing method includes: first mixing the initiator, solvent and phase structure gradient lithium-rich manganese-based cathode material, and then sequentially adding organic chelating material monomer and isocyanate for a second mixing to obtain the composite lithium-rich manganese-based cathode material.

[0027] As a preferred technical solution of the present invention, the temperature of the first mixing is 5 to 25°C, wherein the temperature can be 5°C, 8°C, 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, 22°C, 24°C or 25°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] Preferably, the first mixed atmosphere comprises an inert atmosphere.

[0029] Preferably, the first mixing time is 5 to 30 minutes, wherein the time can be 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] Preferably, the temperature of the second mixture is 40 to 80°C, wherein the temperature can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] Preferably, the second mixed atmosphere comprises an inert atmosphere.

[0032] Preferably, the second mixing time is 1 to 15 hours, wherein the time can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] A third objective of this invention is to provide a lithium-ion battery, which includes a positive electrode, an electrolyte, and a negative electrode, wherein the active material of the positive electrode includes the composite lithium-rich manganese-based positive electrode material as described in one objective.

[0034] In the lithium-ion battery of this invention, polymer coating reduces the direct contact between the positive electrode material and the electrolyte, thereby inhibiting the corrosion of the positive electrode material surface by the electrolyte.

[0035] As a preferred embodiment of the present invention, the electrolyte comprises a lithium salt, wherein the lithium salt is a sulfonylimino lithium salt.

[0036] Preferably, the lithium sulfonylimide salt comprises lithium bis(trifluoromethanesulfonylimide) and / or lithium bis(fluoromethanesulfonylimide).

[0037] The positive electrode sheet prepared by this invention is combined with an electrolyte containing lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluoromethanesulfonyl)imide. The N in lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluoromethanesulfonyl)imide can react with the -NH2 group in the composite lithium-rich manganese-based positive electrode material, thereby promoting the dissolution of lithium salt.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The polymer-coated phase-gradient lithium-rich manganese-based cathode material of the present invention has the advantages of both polymer coating layer and phase-gradient lithium-rich manganese-based cathode material. The phase-gradient lithium-rich cathode material can regulate the cycle stability, discharge specific capacity and safety of the composite lithium-rich cathode material in lithium-ion battery, and can effectively improve the electrochemical performance of lithium-rich cathode material. The -OC=O bond of the polymer in the polymer coating layer can anchor the transition metal ions on the surface of the lithium-rich manganese-based cathode material and generate a complexation effect, which can reduce the reaction of Mn ions and suppress the activation process of Li2MnO3, thereby suppressing the release of oxygen. At the same time, it can stabilize the adhesion of the lithium-rich manganese-based cathode material during long cycle.

[0040] (2) The electrolyte of the lithium-ion battery of the present invention contains lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluoromethanesulfonyl)imide, wherein the N atom can react with the -NH2 group in the composite lithium-rich manganese-based cathode material, thereby promoting the dissolution of lithium salt.

[0041] (3) The lithium-ion battery prepared by the present invention can maintain a capacity retention rate of up to 94% or more after 200 cycles at a 1C rate. Attached Figure Description

[0042] Figure 1 This is a structural diagram of the composite lithium-rich manganese-based cathode material prepared in Example 1 of the present invention. Detailed Implementation

[0043] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0044] Example 1

[0045] This embodiment provides a method such as Figure 1 The composite lithium-rich manganese-based cathode material shown is a core-shell structure with a coating layer. The core of the lithium-rich manganese-based cathode material is a phase-gradient lithium-rich manganese-based cathode material with the chemical formula 0.5Li₂MnO₃·0.5Li(Ni)₂. 0.42 Mn 0.42 Co 0.16 O2, the surface layer has the chemical formula 0.3Li2MnO3·0.7Li(Ni) 0.42 Mn 0.42 Co 0.16 O2. The general formula for the coating layer is shown in Formula 1, and the thickness is 15 nm.

[0046]

[0047] This embodiment also provides a method for preparing the above-mentioned composite lithium-rich manganese-based cathode material, the method comprising the following steps:

[0048] 0.001 g of azobisisobutyronitrile, 15 ml of anhydrous acetonitrile, and 5 g of phase-gradient lithium-rich manganese-based cathode material were stirred at 20 °C for 20 min under an argon protective atmosphere. Then, 0.1 g of ethylene glycol acetoacetate methacrylate and isocyanate in a molar ratio of 1:3 were added sequentially and stirred at 60 °C for 4 h. The organically coated powder was collected using a rotary evaporator and dried under vacuum for 12 h to obtain the composite lithium-rich manganese-based cathode material.

[0049] This embodiment also provides a coin cell battery, which includes a positive electrode material, an electrolyte, and a negative electrode material. The preparation method of the positive electrode material includes: mixing the above-mentioned composite lithium-rich manganese-based positive electrode material, acetylene black, and PVDF in a mass ratio of 8:1:1 to prepare a positive electrode slurry; uniformly coating the positive electrode slurry onto an aluminum foil current collector; drying and then stamping and rolling to obtain a positive electrode sheet; using lithium sheet as the negative electrode material; using lithium bis(trifluoromethanesulfonylimide)-lithium hexafluorophosphate / EC+DEC (Klude) as the electrolyte; assembling the positive electrode sheet, lithium salt, separator, and electrolyte in a battery case to form a 2032 coin cell battery; and allowing the battery to stand for 8-12 hours after preparation.

[0050] Example 2

[0051] This embodiment provides a composite lithium-rich manganese-based cathode material. The composite lithium-rich manganese-based cathode material has a core-shell structure with a coating layer. The core of the lithium-rich manganese-based cathode material is a phase-gradient lithium-rich manganese-based cathode material, with the central chemical formula 0.5Li₂MnO₃·0.5Li(Ni)₂. 0.42 Mn 0.42 Co 0.16 O2, the surface layer has the chemical formula 0.3Li2MnO3·0.7Li(Ni) 0.42 Mn 0.42 Co 0.16 O2. The general formula for the coating layer is shown in Formula 1, and the thickness is 5 nm.

[0052]

[0053] This embodiment also provides a method for preparing the above-mentioned composite lithium-rich manganese-based cathode material, the method comprising the following steps:

[0054] 0.001 g of cyclohexane peroxide, 80 ml of tetrahydrofuran, and 5 g of lithium-rich manganese-based cathode material with phase gradient were stirred at 5 °C for 30 min under an argon protective atmosphere. Then, 0.1 g of ethylene glycol acetoacetate methacrylate and isocyanate in a molar ratio of 1:1 were added sequentially and stirred at 60 °C for 4 h. The organically coated powder was collected using a rotary evaporator and dried under vacuum for 12 h to obtain the composite lithium-rich manganese-based cathode material.

[0055] The method for preparing the button cell in this embodiment is the same as that in Example 1.

[0056] Example 3

[0057] This embodiment provides a composite lithium-rich manganese-based cathode material. The composite lithium-rich manganese-based cathode material has a core-shell structure with a coating layer. The core of the lithium-rich manganese-based cathode material is a phase-gradient lithium-rich manganese-based cathode material, with the central chemical formula 0.5Li₂MnO₃·0.5Li(Ni)₂. 0.42 Mn 0.42 Co 0.16 O2, the surface layer has the chemical formula 0.3Li2MnO3·0.7Li(Ni) 0.42 Mn 0.42 Co 0.16 O2. The general formula for the coating layer is shown in Formula 1, and the thickness is 30 nm.

[0058]

[0059] This embodiment also provides a method for preparing the above-mentioned composite lithium-rich manganese-based cathode material, the method comprising the following steps:

[0060] 0.001 g of tert-butyl hydrogen peroxide, 25 ml of acetone, and 5 g of phase-gradient lithium-rich manganese-based cathode material were stirred at 25 °C for 5 min under an argon protective atmosphere. Then, 0.1 g of ethylene glycol acetoacetate methacrylate and isocyanate in a molar ratio of 1:5 were added sequentially and stirred at 60 °C for 4 h. The organically coated powder was collected using a rotary evaporator and dried under vacuum for 12 h to obtain the composite lithium-rich manganese-based cathode material.

[0061] The method for preparing the button cell in this embodiment is the same as that in Example 1.

[0062] Example 4

[0063] In this embodiment, all conditions are the same as in Example 1, except that the molar ratio of ethylene glycol acetoacetate methacrylate and isocyanate is replaced with 8:1.

[0064] Example 5

[0065] In this embodiment, all conditions are the same as in Example 1, except that the molar ratio of ethylene glycol acetoacetate methacrylate and isocyanate is replaced with 0.5:1.

[0066] Example 6

[0067] In this embodiment, all conditions are the same as in Example 1, except that stirring at 60°C for 4 hours is replaced with stirring at 25°C for 4 hours.

[0068] Example 7

[0069] In this embodiment, all conditions are the same as in Example 1, except that stirring at 60°C for 4 hours is replaced with stirring at 100°C for 4 hours.

[0070] Comparative Example 1

[0071] The conditions for this comparative example are the same as those for Example 1, except that isocyanate is not added.

[0072] Comparative Example 2

[0073] The only difference between this comparative example and Example 1 is that the electrolyte was replaced with lithium hexafluorophosphate / EC+DEC (Klude).

[0074] Comparative Example 3

[0075] Except for the use of lithium-rich manganese-based cathode material with phase structure gradient as the active material, all other conditions in this comparative example are the same as in Example 1.

[0076] The cycle performance of the batteries prepared in Examples 1-7 and Comparative Examples 1-3 was tested, and the test results are shown in Table 1.

[0077] Cyclic performance test conditions: Capacity retention rate after 200 cycles at 1C rate.

[0078] Table 1

[0079]

[0080]

[0081] Table 1 shows that the batteries prepared in Examples 1-3 of this invention have excellent electrochemical performance. In Examples 4-5, the cycle performance of the batteries decreased when the molar ratio of isocyanate was too high or too low. If the isocyanate was too low, the solubility of lithium salt in the electrolyte decreased, resulting in a decrease in battery cycle performance. If the isocyanate was too high, the battery impedance increased, resulting in a decrease in battery cycle performance. In Examples 6-7, if the reaction temperature was too high or too low, the polymerization effect of isocyanate and ethylene glycol acetoacetate methacrylate decreased, resulting in a decrease in battery cycle performance. In Comparative Example 1, without the addition of isocyanate, the solubility of lithium salt in the electrolyte decreased, resulting in a decrease in battery cycle performance. In Comparative Example 2, without the use of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte, the solubility of lithium salt decreased, resulting in a decrease in battery cycle performance. In Comparative Example 3, without modification of the phase gradient lithium-rich manganese-based cathode material, the battery cycle performance was poor.

[0082] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite lithium-rich manganese-based cathode material, characterized in that, The composite lithium-rich manganese-based cathode material has a core-shell structure. The core of the lithium-rich manganese-based cathode material is a phase-structure gradient lithium-rich manganese-based cathode material. The coating layer of the lithium-rich manganese-based cathode material includes a polymer, and the polymer includes a strongly negatively charged group and -NH2 group. The strongly negatively charged group includes -C=O and / or -O-C=O.

2. The composite lithium-rich manganese-based cathode material according to claim 1, characterized in that, The general formula of the core is xLi2MnO3·(1-x)LiTMO2-yLi2MnO3·(1-y)LiTMO2, where 0 < y < x < 1, and TM is selected from any one or at least two combinations of Ni, Co or Mn. The phase-structure gradient lithium-rich manganese-based cathode material includes a monoclinic Li2MnO3 phase and a rhombic LiTMO2 phase. The content of the monoclinic Li2MnO3 phase decreases sequentially from the inside to the outside, and the content of the rhombic LiTMO2 phase increases sequentially from the inside to the outside. Preferably, the coating layer includes a polymer shown in Formula 1, where n≥2.

3. The composite lithium-rich manganese-based cathode material according to claim 1 or 2, characterized in that, The thickness of the coating layer is 5 - 30 nm.

4. A method for preparing a composite lithium-rich manganese-based cathode material as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: Mix an organic chelating material monomer, isocyanic acid, an initiator, a solvent and a phase-structure gradient lithium-rich manganese-based cathode material to obtain the composite lithium-rich manganese-based cathode material.

5. The preparation method according to claim 4, characterized in that, The organic chelating material monomer includes ethylene glycol methacrylate acetoacetate and / or 2-cyanoethyl acrylate, preferably ethylene glycol methacrylate acetoacetate. Preferably, the mass fraction of ethylene glycol methacrylate acetoacetate in the phase-structure gradient lithium-rich manganese-based cathode material is 0.5 - 50 wt%, preferably 2 - 5 wt%. Preferably, the molar ratio of ethylene glycol methacrylate acetoacetate to isocyanic acid is (1 - 5):

1.

6. The preparation method according to claim 4 or 5, characterized in that, The initiator includes any one or at least two combinations of azobisisobutyronitrile, cyclohexanone peroxide or tert-butyl hydroperoxide. Preferably, the solvent includes any one or at least two combinations of tetrahydrofuran, dimethylformamide, acetone or anhydrous acetonitrile. Preferably, the mass ratio of the solvent to the phase-structure gradient lithium-rich manganese-based cathode material is (3 - 8):

1.

7. The preparation method according to any one of claims 4-6, characterized in that, The mixing method includes: first mixing the initiator, the solvent and the phase-structure gradient lithium-rich manganese-based cathode material, and then sequentially adding the organic chelating material monomer and isocyanic acid for second mixing to obtain the composite lithium-rich manganese-based cathode material.

8. The preparation method according to claim 7, characterized in that, The temperature of the first mixing is 5 - 25 °C. Preferably, the atmosphere of the first mixing includes an inert atmosphere. Preferably, the time of the first mixing is 5 - 30 min. Preferably, the temperature of the second mixing is 40 - 80 °C. Preferably, the atmosphere of the second mixing includes an inert atmosphere. Preferably, the time of the second mixing is 1 - 15 h.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode plate, an electrolyte and a negative electrode plate. The active material of the positive electrode plate includes the composite lithium-rich manganese-based cathode material according to any one of claims 1 - 3.

10. The lithium-ion battery according to claim 9, characterized in that, The electrolyte includes a lithium salt, and the lithium salt is a sulfonyl imide lithium salt. Preferably, the sulfonyl imide lithium salt includes lithium bis(trifluoromethanesulfonyl)imide and / or lithium difluoromethylsulfonylimide.

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