Preparation method of graphene modified ternary positive electrode material
By coating the surface of NCA material with oxides, nitrogen-containing organic binders, and graphene oxide to form a three-layer composite interface structure, the problems of conductivity and interface stability in the modification process of NCA material are solved, achieving efficient electronic conduction and chemical protection, and improving the electrochemical performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- RUICHI NEW ENERGY (XUZHOU) CO LTD
- Filing Date
- 2026-05-14
- Publication Date
- 2026-06-23
AI Technical Summary
During the coating modification process, existing NCA ternary cathode materials have difficulty in balancing conductivity and interfacial structural stability, resulting in low electronic conductivity and decomposition of residual lithium on the surface catalyzing the electrolyte, and volume changes leading to rapid capacity decay.
The preparation method of graphene-modified ternary cathode material involves coating the surface of nickel-cobalt-aluminum ternary cathode material with an oxide layer and introducing nitrogen-containing organic binder and graphene oxide to form a three-layer composite interface structure of "oxide-nitrogen-containing amorphous carbon-reduced graphene oxide", thereby achieving electronic conduction, chemical protection and mechanical buffering.
It significantly improves the electronic conductivity and interfacial structural stability of the material, reduces electrode impedance, prevents microcrack propagation, and enhances the rate performance and cycle stability of the battery.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of secondary battery materials technology. More specifically, it relates to a method for preparing a graphene-modified ternary cathode material. Background Technology
[0002] Nickel-cobalt-aluminum ternary cathode materials (NCA) have become key materials for high-energy-density lithium-ion batteries due to their high specific capacity and good structural stability. However, NCA materials still face two major challenges in practical applications: first, their intrinsic electronic conductivity is low, which limits the rate performance of the battery; second, during high-voltage cycling, residual lithium on the surface is prone to catalyze the decomposition of the electrolyte, and anisotropic volume changes lead to the initiation of microcracks, resulting in rapid capacity decay.
[0003] To overcome the aforementioned drawbacks, surface coating modification has proven to be an effective strategy. Oxide coating can suppress interfacial side reactions, but it introduces an electronic insulating layer; carbon material coating can improve conductivity, but the interfacial bonding is weak and chemical protection is insufficient. In existing technologies, few modification schemes can simultaneously achieve electronic conductivity, chemical stability, and robust interfacial bonding. Therefore, developing a method for preparing NCA cathode materials that can synergistically leverage the advantages of oxide chemical protection and the high conductivity of carbon materials while ensuring interfacial structural stability has significant application value. Summary of the Invention
[0004] The technical problem this invention aims to solve is the difficulty in balancing conductivity and interfacial structural stability during the coating modification process of existing NCA ternary cathode materials. Based on this problem, this invention provides a method for preparing graphene-modified ternary cathode materials.
[0005] The purpose of this invention is to provide a method for preparing graphene-modified ternary cathode materials.
[0006] The above-mentioned objective of this invention is achieved through the following technical solution: A method for preparing a graphene-modified ternary cathode material, the specific preparation steps of which include: An oxide layer is coated on the surface of a nickel-cobalt-aluminum ternary cathode material to obtain an oxide-coated cathode material; A nitrogen-containing organic binder is introduced onto the surface of the oxide-coated cathode material to disperse the nitrogen-containing organic binder on the surface of the oxide layer and in its gaps, thereby obtaining a secondary coated cathode material. Graphene oxide is coated onto the surface of the secondary coated cathode material to obtain a tertiary coated cathode material; The triple-coated cathode material is calcined at high temperature under an inert atmosphere to carbonize the nitrogen-containing organic binder in situ into nitrogen-containing amorphous carbon, and the graphene oxide is thermally reduced to reduced graphene oxide; thus, a graphene-modified ternary cathode material is obtained.
[0007] The beneficial effects of the above technical solution include: The above technical solution involves coating the surface of NCA with an oxide coating layer to physically isolate the electrolyte from direct contact with NCA and suppress side reactions catalyzed by residual lithium on the surface. Then, a nitrogen-containing organic binder is used to fill the gaps in the oxide layer before calcination, forming nitrogen-containing amorphous carbon after carbonization. The nitrogen in the amorphous carbon can form coordination bonds or hydrogen bonds with the oxide surface, and simultaneously form π-π conjugation with graphene, firmly connecting the originally chemically poor oxide with graphene. The modulus of the amorphous carbon is between that of rigid oxide and flexible graphene, which can absorb the stress generated by the volume expansion of NCA and prevent interlayer delamination. Nitrogen doping improves the electronic conductivity of the amorphous carbon, providing a "fast channel" for electrons to pass from graphene through the oxide layer into NCA. The outer layer of reduced graphene oxide constructs a three-dimensional conductive network with surface contact, significantly reducing electrode impedance. At the same time, the high modulus of the reduced graphene oxide provides radial compressive stress, suppressing the propagation of microcracks in NCA from the outside.
[0008] Compared with existing single oxide coating or single carbon coating technologies, this scheme is the first to propose a three-layer composite interface structure of "oxide-nitrogen-amorphous carbon-reduced graphene oxide". Through the interfacial bridging effect of amorphous carbon, the technical challenges of poor chemical affinity, mismatch of mechanical modulus and discontinuous electron transport between oxide and graphene are solved, and the synergistic enhancement of chemical protection, electronic conduction and mechanical buffering is achieved.
[0009] Furthermore, the material of the oxide layer is selected from any one of alumina, yttrium oxide, zirconium oxide, LiNbO3, and Li2ZrO3; and the thickness of the oxide layer is 1-10 nm.
[0010] When the thickness is less than 1 nm, the oxide layer is difficult to form a continuous coverage, resulting in exposed sites that lead to electrolyte erosion. When the thickness is greater than 10 nm, the Li⁺ crossing distance is too long, and electrons need to tunnel through a thicker insulating layer, resulting in a significant increase in interfacial impedance. The 1-10 nm range ensures dense coverage while avoiding excessive blocking.
[0011] Furthermore, the nitrogen-containing organic binder is selected from any one of polypyrrole, polydopamine, and polyaniline.
[0012] Furthermore, the specific preparation steps also include: Aluminum isopropoxide was used as the aluminum source and dissolved in anhydrous ethanol to form an aluminum isopropoxide solution with a mass fraction of 4-6%. Add deionized water dropwise to the aluminum isopropoxide solution at a rate of 10-20 mL / min, wherein the amount of deionized water is 10-15% of the volume of the aluminum isopropoxide solution; The pH was then adjusted to 4.5-5.0, and the mixture was stirred for 1 hour at a temperature of 4-8℃ and a stirring speed of 300-500 r / min. Then, 15-20% of the mass of aluminum isopropoxide solution of nickel-cobalt-aluminum ternary cathode material was added, and the mixture was stirred continuously at a temperature of 80-90℃ until the solvent was completely evaporated. Finally, the mixture was calcined in air at a temperature of 500-600℃ for 4-6 hours to obtain oxide-coated cathode material.
[0013] Furthermore, the D50 of the nickel-cobalt-aluminum ternary cathode material is 3-5 μm, and the sphericity of the nickel-cobalt-aluminum ternary cathode material is 0.8-0.9.
[0014] NCA particles with a D50 of 3-5 μm have a suitable specific surface area. Excessive surface area (>10 μm) leads to an overly long Li⁺ diffusion path, affecting the scaling factor; conversely, excessive surface area (<1 μm) exacerbates side reactions and requires a large amount of coating layer. A sphericity of 0.8-0.9 (approximately spherical) facilitates the uniform spreading of the precursor liquid film on the particle surface during the sol-gel process, preventing excessive coating or exposure at depressions or protrusions.
[0015] Furthermore, the specific preparation steps also include: The oxide-coated cathode material is dispersed in water, and 6-8% by weight of ferric chloride is added. After stirring and dissolving, a dispersion is obtained. Under stirring, a pyrrole ethanol solution of 50-60% by mass of the dispersion is slowly added dropwise to the dispersion. After the addition is complete, the ultrasonic reaction is continued, and then the mixture is allowed to stand for aging, so that the nitrogen-containing organic binder is dispersed on the surface of the oxide layer and in its gaps, thus obtaining an aging solution.
[0016] When the pyrrole ethanol solution is slowly dripped in, the pyrrole monomers come into contact with the Fe³⁺ adsorbed on the particle surface, undergoing oxidative polymerization to generate polypyrrole chains. Because the Fe³⁺ is anchored on the particle surface, the polypyrrole preferentially grows on the oxide layer surface and naturally fills the tiny gaps between the oxide particles. This achieves selective and uniform distribution of the nitrogen-containing organic binder (polypyrrole) on the oxide layer surface and in its gaps, avoiding the formation of free polypyrrole precipitation and laying the structural foundation for the subsequent carbonization to form a continuous amorphous carbon interface layer.
[0017] Furthermore, the slow addition is performed at a rate of 3-5 mL / s, and the concentration of pyrrole in the pyrrole ethanol solution is 0.3-0.5 mol / L.
[0018] Furthermore, the specific preparation steps also include: Nano-graphene oxide (0.8-1.2% by weight of the oxide-coated cathode material) was added to the aging solution. After ultrasonic reaction, the mixture was filtered, washed, and dried to obtain a triple-coated cathode material. The D50 of the nano-graphene oxide is 30-60 nm.
[0019] Furthermore, the high-temperature calcination is as follows: heating to 750-800℃ at a rate of 1-3℃ / min and holding at that temperature for 4-6 hours; the inert atmosphere is selected from either argon or nitrogen. Detailed Implementation
[0020] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.
[0021] Unless otherwise specified, all reagents and materials used in the following examples are commercially available. Example 1
[0022] Oxide layer coating (sol-gel method) Aluminum isopropoxide was used as the aluminum source and dissolved in anhydrous ethanol to prepare a 5% (w / w) aluminum isopropoxide solution. Deionized water was added dropwise to this solution at a rate of 15 mL / min, with the amount of deionized water being 12% of the volume of the aluminum isopropoxide solution. The pH was then adjusted to 4.8 with dilute nitric acid, and the mixture was stirred for 1 h at 6 °C and 400 r / min. 18% (w / w) of nickel-cobalt-aluminum ternary cathode material (NCA, D50 of 4 μm, sphericity of 0.85) was added to the aluminum isopropoxide solution, and the mixture was stirred continuously at 85 °C until the solvent was completely evaporated. The resulting product was calcined in air at 550 °C for 5 h to obtain an oxide (Al₂O₃) coated cathode material with a coating thickness of approximately 5 nm.
[0023] Introduction of nitrogen-containing organic binders (in-situ polymerization method) The above-mentioned oxide-coated cathode material was dispersed in deionized water, and 7% (by weight) of ferric chloride (FeCl3·6H2O) was added. After stirring and dissolving, a dispersion was obtained. A pyrrole ethanol solution with a pyrrole concentration of 0.4 mol / L was prepared. Under stirring, a 55% (by weight) pyrrole ethanol solution was slowly added dropwise to the dispersion at a rate of 4 mL / s. After the addition was complete, the reaction was continued with sonication for 10 min, followed by aging for 2 h to allow polypyrrole to disperse on the surface of the oxide layer and in its gaps, resulting in an aged solution.
[0024] Graphene oxide coating Add 1.0% by weight of nano-graphene oxide (D50 of 45nm) to the above aging solution, sonicate for 15 min, filter, wash three times alternately with deionized water and anhydrous ethanol, and vacuum dry at 100℃ for 12 h to obtain triple-coated cathode material.
[0025] High-temperature calcination The above-mentioned three-coated cathode material was placed in a tube furnace and heated to 780°C at a rate of 2°C / min under an argon atmosphere. The temperature was then maintained for 5 hours to allow polypyrrole to be carbonized in situ into nitrogen-containing amorphous carbon and graphene oxide to be thermally reduced into reduced graphene oxide, thus obtaining the graphene-modified ternary cathode material. Example 2
[0026] This embodiment is basically the same as Embodiment 1, except that the oxide material in step (1) is replaced with Y2O3. Specifically: Yttrium nitrate (Y(NO3)3·6H2O) is dissolved in anhydrous ethanol, citric acid is added as a complexing agent, and a Y2O3 layer is coated on the NCA surface using the sol-gel method. The coating layer thickness is approximately 6 nm. The remaining steps are the same as in Embodiment 1. Example 3
[0027] This embodiment is basically the same as Embodiment 1, except that the nitrogen-containing organic binder in step (2) is replaced with polydopamine. Specifically: the oxide-coated cathode material is dispersed in Tris buffer (pH=8.5), and dopamine monomer (5% of the mass of the oxide-coated cathode material) is added. The mixture is stirred at room temperature for 24 h to allow dopamine to self-polymerize on the surface of the oxide layer to form a polydopamine coating layer. The remaining steps are the same as in Embodiment 1.
[0028] Comparative Example 1 This comparative example provides an NCA cathode material with only an oxide layer, and its preparation method is as follows: Following the oxide layer coating method in Example 1, an Al2O3 layer (approximately 5 nm thick) was coated onto the surface of NCA to obtain a single oxide-coated NCA cathode material. Steps (2)-(4) of introducing nitrogen-containing binders, coating with graphene oxide, and high-temperature calcination were not performed.
[0029] Comparative Example 2 This comparative example provides an NCA cathode material coated only with reduced graphene oxide, and its preparation method is as follows: (1) Disperse the NCA cathode material (same as in Example 1) in ethanol, add 1.0% of NCA by mass of graphene oxide (D50 45 nm), and ultrasonically disperse for 30 min; (2) After the solvent is evaporated, the temperature is increased to 780℃ at 2℃ / min under an argon atmosphere for 5 h to thermally reduce graphene oxide to reduced graphene oxide, thus obtaining NCA cathode material coated with single graphene.
[0030] Comparative Example 3 This comparative example provides an oxide-graphene bilayer coated NCA cathode material (excluding nitrogen-containing amorphous carbon layer), and its preparation method is as follows: (1) Following the method in step (1) of Example 1, an Al2O3 layer (approximately 5 nm thick) was coated on the surface of NCA to obtain an oxide-coated cathode material; (2) The above oxide-coated cathode material is coated with graphene oxide and calcined at high temperature according to the method of Comparative Example 2 (directly coated with graphene oxide without the step of introducing nitrogen-containing organic binder) to obtain the oxide-graphene double-layer coated NCA cathode material.
[0031] Comparative Example 4 This comparative example provides an NCA cathode material coated only with nitrogen-containing amorphous carbon, and its preparation method is as follows: (1) Follow the method of step (1) in Example 1, but replace the NCA cathode material with bare NCA without any coating; (2) Following the method of step (2) in Example 1 (introducing polypyrrole by in-situ polymerization); (3) The material obtained in step (2) is heated to 780°C for 5 h in an argon atmosphere at a rate of 2°C / min to carbonize the polypyrrole into nitrogen-containing amorphous carbon, thus obtaining the NCA cathode material with nitrogen-containing amorphous carbon monolayer coating.
[0032] Electrochemical performance testing: The materials obtained in Examples 1-3 and Comparative Examples 1-4 were assembled into CR2032 coin cells, and their electrochemical performance was tested. The test conditions were as follows: Positive electrode preparation: Active material, conductive carbon black and PVDF are mixed in a mass ratio of 8:1:1, NMP is added and ground into a slurry, which is then coated on aluminum foil, vacuum dried and cut into electrode sheets with a diameter of 12 mm.
[0033] Battery assembly: Using lithium foil as the counter electrode, Celgard 2400 as the separator, and 1 mol / L LiPF6 dissolved in EC / DMC / EMC (volume ratio 1:1:1) as the electrolyte, coin cells were assembled in an argon glove box.
[0034] Test conditions: voltage range 2.8-4.3 V, charge / discharge rate 0.5C / 0.5C (1C = 180 mAh / g), cycle test temperature 25℃.
[0035] The relevant test results are shown in Table 1; Table 1: Product Performance Test Results
[0036] The 0.5C initial discharge specific capacity, 100-cycle capacity retention, and 5C rate performance of Examples 1-3 are significantly better than all comparative examples. This indicates that the three-layer composite interface structure of "oxide layer-nitrogen-containing amorphous carbon-reduced graphene oxide" can effectively synergistically exert chemical protection, electronic conduction, and mechanical buffering effects.
[0037] The comparison between Example 1 and Comparative Examples 1-3 shows that: Comparative Example 1 (oxide only) has a large interfacial impedance and poor rate performance; Comparative Example 2 (graphene only) has insufficient cycle stability; Comparative Example 3 (oxide + graphene, no interfacial layer) has performance between the two but is significantly worse than Example 1. This proves that nitrogen-containing amorphous carbon plays a key role as an "interfacial bridge" between oxide and graphene.
[0038] The comparison between Example 1 and Comparative Example 4 shows that when nitrogen-containing amorphous carbon is used alone, its performance is even worse than that of a single oxide coating due to the lack of chemical protection from the oxide layer and the conductive network of the graphene layer. This indicates that each layer in the three-layer structure is indispensable, and optimal performance is achieved through the synergy of all three.
[0039] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.
Claims
1. A method for preparing a graphene-modified ternary cathode material, characterized in that, The specific preparation steps include: An oxide layer is coated on the surface of a nickel-cobalt-aluminum ternary cathode material to obtain an oxide-coated cathode material; A nitrogen-containing organic binder is introduced onto the surface of the oxide-coated cathode material to disperse the nitrogen-containing organic binder on the surface of the oxide layer and in its gaps, thereby obtaining a secondary coated cathode material. Graphene oxide is coated onto the surface of the secondary coated cathode material to obtain a tertiary coated cathode material; The triple-coated cathode material is calcined at high temperature under an inert atmosphere to carbonize the nitrogen-containing organic binder in situ into nitrogen-containing amorphous carbon, and the graphene oxide is thermally reduced to reduced graphene oxide; thus, a graphene-modified ternary cathode material is obtained.
2. The method for preparing a graphene-modified ternary cathode material according to claim 1, characterized in that, The oxide layer is made of any one of aluminum oxide, yttrium oxide, zirconium oxide, LiNbO3, and Li2ZrO3; and the thickness of the oxide layer is 1-10 nm.
3. The method for preparing a graphene-modified ternary cathode material according to claim 1, characterized in that, The nitrogen-containing organic binder is selected from any one of polypyrrole, polydopamine, and polyaniline.
4. The method for preparing a graphene-modified ternary cathode material according to claim 1, characterized in that, The specific preparation steps also include: Aluminum isopropoxide was used as the aluminum source and dissolved in anhydrous ethanol to form an aluminum isopropoxide solution with a mass fraction of 4-6%. Add deionized water dropwise to the aluminum isopropoxide solution at a rate of 10-20 mL / min, wherein the amount of deionized water is 10-15% of the volume of the aluminum isopropoxide solution; The pH was then adjusted to 4.5-5.0, and the mixture was stirred for 1 hour at a temperature of 4-8℃ and a stirring speed of 300-500 r / min. Then, 15-20% of the mass of aluminum isopropoxide solution of nickel-cobalt-aluminum ternary cathode material was added, and the mixture was stirred continuously at a temperature of 80-90℃ until the solvent was completely evaporated. Finally, the mixture was calcined in air at a temperature of 500-600℃ for 4-6 hours to obtain oxide-coated cathode material.
5. The method for preparing a graphene-modified ternary cathode material according to claim 4, characterized in that, The D50 of the nickel-cobalt-aluminum ternary cathode material is 3-5 μm, and the sphericity of the nickel-cobalt-aluminum ternary cathode material is 0.8-0.
9.
6. A method for preparing a graphene-modified ternary cathode material according to any one of claims 1 or 3, characterized in that, The specific preparation steps also include: The oxide-coated cathode material is dispersed in water, and 6-8% by weight of ferric chloride is added. After stirring and dissolving, a dispersion is obtained. Under stirring, a pyrrole ethanol solution of 50-60% by mass of the dispersion is slowly added dropwise to the dispersion. After the addition is complete, the ultrasonic reaction is continued, and then the mixture is allowed to stand for aging, so that the nitrogen-containing organic binder is dispersed on the surface of the oxide layer and in its gaps, thus obtaining an aging solution.
7. The method for preparing a graphene-modified ternary cathode material according to claim 6, characterized in that, The slow addition is performed at a rate of 3-5 mL / s, and the concentration of pyrrole in the pyrrole ethanol solution is 0.3-0.5 mol / L.
8. The method for preparing a graphene-modified ternary cathode material according to claim 6, characterized in that, The specific preparation steps also include: Nano-graphene oxide (0.8-1.2% by weight of the oxide-coated cathode material) was added to the aging solution. After ultrasonic reaction, the mixture was filtered, washed, and dried to obtain a triple-coated cathode material. The D50 of the nano-graphene oxide is 30-60 nm.
9. The method for preparing a graphene-modified ternary cathode material according to claim 1, characterized in that, The high-temperature calcination is performed by heating to 750-800℃ at a rate of 1-3℃ / min and holding the temperature for 4-6 hours; the inert atmosphere is selected from either argon or nitrogen.