Single-arm carbon nanotube coated composite cathode material for constructing conductive network and preparation method thereof

Abstract

The application discloses a single-arm carbon nanotube coated composite cathode material for constructing a conductive network and a preparation method thereof, and belongs to the technical field of lithium ion battery electrode materials. The application makes the cathode material carry positive charges and the single-arm carbon nanotube carry negative charges through surface charge modification, then mixes the two in a solvent, drives electrostatic self-assembly by mechanical force provided by high-energy ball milling, makes the single-arm carbon nanotube uniformly and firmly wrap the surface of the cathode material particles, and obtains the composite cathode material through post-processing. The application constructs a long-range, through and stable three-dimensional conductive network by using the single-arm carbon nanotube, significantly reduces the electrode interface resistance, buffers the volume change stress in the charging and discharging process, and greatly improves the rate performance and cycle stability of the cathode material. The method is simple in process, low in cost, easy to scale up, and can be widely applied to the high-performance modification of various lithium ion battery cathode materials.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a composite cathode material with a conductive network constructed by coating single-arm carbon nanotubes and its preparation method. Background Technology

[0002] Guided by the "dual carbon" goals, my country is accelerating the construction of a new power system with new energy sources as the mainstay. The volatility and intermittency of renewable energy, along with the complex characteristics of its loads, pose severe challenges to the power grids of big data centers and new energy power systems, including second / millisecond-level frequency and voltage fluctuations and instantaneous power shortages. Short-duration, high-frequency, high-power energy storage technology, with its millisecond-level response, long cycle life, and high power tolerance, has become a core support for mitigating new energy fluctuations, ensuring grid frequency stability, improving renewable energy absorption, and enhancing the reliability of critical loads.

[0003] Short-duration, high-frequency, high-power energy storage technologies mainly include capacitors, flywheel energy storage, high-power lithium-ion batteries, and hybrid systems. While capacitors and flywheel energy storage offer high power densities (≥20 kW / kg for capacitors, ≥9 kW / kg for flywheel energy storage), their energy densities are typically less than 90 Wh / kg, leading to significant weight and volume issues when applied to energy storage systems. High-power lithium-ion batteries can achieve energy densities exceeding 120 Wh / kg, but their power densities are usually ≤5 kW / kg, making them unsuitable for short-duration, high-frequency applications.

[0004] Currently, most high-power lithium-ion batteries use lithium iron phosphate and lithium titanate as cathode materials. Lithium iron phosphate has poor conductivity and low tap density, affecting the battery's volumetric energy density and power performance; lithium titanate has low energy density (less than 90 Wh / kg), poor low-temperature performance, and its performance is approaching its theoretical limit. Therefore, the development of new high-power lithium-ion battery cathode materials to improve the battery's energy density, power density, and cycle life is urgently needed.

[0005] To improve the power performance and cycle performance of lithium-ion battery cathode materials, carbon coating is considered an effective approach. A uniformly coated carbon layer can reduce interparticle contact resistance, improve electronic conductivity, and simultaneously act as a physical and chemical barrier to inhibit electrolyte oxidation and decomposition, buffering changes in the volume of active particles and improving cycle stability.

[0006] There are already various carbon coating methods in the prior art, such as: Patent CN116845195A proposes a solid-phase dry coating process, but its roughness parameter is highly dependent, its applicability is limited, and the method for testing the coating layer retention rate is complex.

[0007] Patent CN117080388A proposes a double-layer carbon coating structure, but the preparation process is complex, costly, and difficult to control the gradient of graphitization degree, and may peel off during long-term cycling.

[0008] Patent 117393725A proposes a hierarchical porous carbon coating, but the pore structure has poor stability, and the capacity retention rate drops to 90% after 50 cycles.

[0009] Patent CN120674449A proposes fluorine and nitrogen co-doped carbon coating, but the doping position and concentration gradient are difficult to control precisely, and the process is complex.

[0010] Patent CN118745008A proposes a carbon nanotube-coated doped precursor, but the uniformity and binding force of the coating layer depend on physical adsorption, making it easy to fall off, and the type of carbon nanotube is not clearly defined.

[0011] In summary, there is currently a lack of a method in the technology to efficiently prepare carbon-coated cathode materials for lithium-ion batteries that possess both high rate capability and high cycle stability. Summary of the Invention

[0012] This invention aims to address the problems of uneven dispersion, weak bonding, and complex processes in existing cathode materials by providing a composite cathode material with a conductive network constructed by coating with single-arm carbon nanotubes and its preparation method. By using a ball milling-driven electrostatic self-assembly process, the single-arm carbon nanotubes are uniformly and firmly coated on the surface of the cathode material, thereby constructing a highly efficient three-dimensional conductive network and improving the rate performance and cycle stability of the material.

[0013] Firstly, to achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a single-arm carbon nanotube-coated composite cathode material, comprising the following steps: (1) Surface charge modification steps: a. Surface modification of lithium-ion battery cathode material particles to make their surface positively charged; b. Acidification treatment is applied to the single-arm carbon nanotubes to make their surface negatively charged; (2) Ball mill driven electrostatic self-assembly steps: The positively charged cathode material obtained in step (1) and the negatively charged single-arm carbon nanotubes are dispersed together in an organic solvent to form a mixed slurry; then the mixed slurry is subjected to high-energy ball milling together with grinding balls; the mechanical force provided by the ball milling process drives the positively charged cathode material particles with opposite charges to collide strongly and frequently with the single-arm carbon nanotubes, promoting their binding through electrostatic attraction, thereby coating the surface of the cathode material particles with single-arm carbon nanotubes; (3) Post-processing steps: The ball-milled slurry was separated, dried, and heat-treated to obtain the single-arm carbon nanotube-coated composite cathode material.

[0014] Preferably, as an improvement, in step (1)a, the method of making the surface of the positive electrode material positively charged is: immersing the positive electrode material in an aqueous solution containing a positively charged modifier and stirring, then washing and drying; the positively charged modifier is selected from at least one of positively charged surfactants, polymers or polyelectrolytes.

[0015] Preferably, as an improvement, the positively charged surfactant is hexadecyltrimethylammonium bromide or hexadecylpyridinium chloride; the positively charged polymer is polyethyleneimine, imidazolium salt polymer or polyvinyl alcohol with quaternary ammonium salt groups introduced; and the positively charged polyelectrolyte is polydiallyldimethylammonium chloride.

[0016] Preferably, as an improvement, the aqueous solution of the positively charged modifier has a mass-volume concentration of 0.05% to 2% and a pH value of 3.0 to 10.0; the solid-liquid ratio of the positive electrode material to the aqueous solution is 1 g : (10 to 50) mL; and the stirring time is 0.5 to 2 hours.

[0017] Preferably, as an improvement, in step (1)b, the acidification treatment is as follows: the single-arm carbon nanotube is placed in aqua regia and ultrasonically treated at 50~70℃ for 1~4 hours, then washed with deionized water until neutral and dried; the aqua regia is a mixture of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3.

[0018] Preferably, as an improvement, in step (2), the mass ratio of the single-arm carbon nanotube to the cathode material is 0.5% to 3%.

[0019] Preferably, as an improvement, in step (2), the organic solvent is N-methylpyrrolidone; the mixed slurry is mechanically stirred and dispersed before ball milling, and the stirring conditions include: stirring at 30~50 rpm and 300~500 rpm for 15~20 min, and then stirring at 40~60 rpm and 2000~3000 rpm for 90~120 min.

[0020] Preferably, as an improvement, in step (2), the parameters of the high-energy ball mill are: the mass ratio of grinding balls to mixed slurry is 10:1 to 20:1, the ball milling speed is 200 to 400 rpm, and the ball milling time is 2 to 8 hours; in step (3), the heat treatment is carried out in an inert atmosphere at a temperature of 150°C to 300°C for 2 to 4 hours.

[0021] Preferably, as an improvement, the positive electrode material of the lithium-ion battery is LiCoO2, LiMn2O4, LiFePO4, or LiNi. 1-x-y Co y Mn x O2, LiNi 1-x-y Co y Al x O2 or LiM x Mn 2-x At least one of O4, wherein M is Fe or Co.

[0022] Secondly, the present invention provides a composite cathode material with a conductive network constructed by coating single-arm carbon nanotubes obtained by any of the above-mentioned preparation methods. The composite cathode material includes cathode material particles and a single-arm carbon nanotube layer coated on the surface of the particles. The single-arm carbon nanotube layer is uniformly, discretely, and seamlessly distributed, forming a long-range interconnected three-dimensional conductive network between adjacent particles.

[0023] The core of this invention lies in proposing a composite process of "ball milling-driven electrostatic self-assembly" to solve the technical problems of uneven coating, weak bonding, and easy agglomeration of single-arm carbon nanotubes (SWCNTs) on the surface of cathode materials. Its unique working principle and the resulting significant technical effects constitute a fundamental difference from existing technologies.

[0024] The principle of this invention: In existing technologies, electrostatic self-assembly (ESA) relies on the Brownian motion of particles in solution to randomly collide and combine, which is inefficient and has limited ability to overcome the agglomeration problem caused by the high specific surface area and strong van der Waals forces of nanomaterials; while high-energy ball milling (BM) can provide strong mechanical force to achieve physical mixing, it usually cannot achieve precise and orderly coating at the nanoscale and is prone to damage to the crystal structure of materials.

[0025] This invention creatively couples the two, and its working principle can be divided into three collaborative stages: Pre-positioning stage (surface charge modification): By introducing positively charged groups into the cathode material and acidifying SWCNT to introduce negatively charged groups, both surfaces carry stable, opposite charges. This is not a simple dispersion process, but rather creates an electrostatic potential difference for subsequent precise bonding, resulting in an inherent tendency for the two materials to attract each other when they approach each other.

[0026] Driving and bonding stage (ball mill-driven electrostatic self-assembly): This stage is the key difference of this invention. The materials with opposite charges are mixed in a solvent and then subjected to high-energy ball milling.

[0027] The core function of ball milling: The intense mechanical energy provided by ball milling is not used for simple crushing or mixing, but is converted into directional kinetic energy, which forces positively charged particles to collide with negatively charged SWCNTs at high frequency and with high energy.

[0028] Synergistic Mechanism: In each collision, mechanical force overcomes the spatial resistance and van der Waals repulsion between particles, greatly shortening the effective range of electrostatic forces. Once the distance reaches the nanoscale, the pre-set strong electrostatic attraction quickly dominates, "pulling" SWCNTs and firmly anchoring them to the surface of the cathode particles. The "force" of ball milling and the "field" of electrostatics work synergistically here. Ball milling solves the problem of insufficient electrostatic self-assembly power (low collision frequency and energy), while electrostatic action guides the orderliness and precision of ball milling composites (avoiding disordered physical damage).

[0029] Curing stage (post-treatment): Subsequent low-temperature heat treatment further removes residual modifiers and solvents under an inert atmosphere, and may promote the formation of more stable chemical connections (such as esterification reaction) between SWCNTs and functional groups on the surface of the cathode material, thereby curing the initial coating structure formed by electrostatic interaction and enhancing its thermodynamic stability.

[0030] The beneficial effects of this invention are as follows: Based on the aforementioned unique working principle, this invention, compared to simple electrostatic self-assembly or mechanical ball milling mixing methods, produces a synergistic and beneficial effect: (1) This invention enables SWCNTs to be coated along the surface of cathode material particles through the directional guidance of electrostatic force, rather than through random and agglomerated mixing. The uniform shear force and collision provided by ball milling ensure that all particles undergo a similar composite process, thereby obtaining a composite cathode material with uniform coating thickness and high coverage, overcoming the problems of uneven dispersion and loose structure in traditional coating methods.

[0031] (2) In traditional physical mixing, the bonding between carbon nanotubes and active materials mainly relies on van der Waals forces, resulting in weak bonding. In this invention, strong electrostatic bonds are first formed through chemical modification, then compacted by the mechanical force of ball milling, and finally the interface is further stabilized through heat treatment, forming a strong interface with physical anchoring and synergistic chemical bonding (electrostatic and possibly covalent bonds). This makes the coating layer less likely to fall off during the volume expansion / contraction process of battery charging and discharging.

[0032] (3) Effectively constructs a three-dimensional conductive network with excellent electrochemical performance: High conductivity: The uniform and firmly coated SWCNTs form a continuous and efficient electronic conduction path on the surface of the positive electrode particles and between the particles, which greatly reduces the ohmic resistance and charge transfer impedance of the electrode.

[0033] Improved rate performance: The excellent conductive network enables faster transport of lithium ions and electrons in the electrodes, thus the composite material exhibits excellent high-rate charge and discharge capabilities.

[0034] Enhanced cycle stability: The robust SWCNT network acts like an "elastic skeleton," buffering the structural stress of the cathode material during cycling and inhibiting particle pulverization and crack propagation. At the same time, its good conductivity ensures the full utilization of active materials, reducing local overcharging / over-discharging, thereby significantly extending the battery's cycle life.

[0035] (4) While promoting the composite process, the ball milling process also simultaneously achieves efficient secondary dispersion of SWCNTs in the slurry due to its strong shear force, preventing their re-agglomeration, which is difficult to achieve with simple static self-assembly. The "ball milling electrostatic self-assembly method" organically combines mechanical dispersion with electrostatic directional assembly, solving the two core bottlenecks of uneven dispersion and weak interfacial contact of single-arm carbon nanotubes in cathode materials. It has the advantages of low cost, high efficiency and easy scale-up production. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating the principle of preparing single-arm carbon nanotube-coated composite cathode materials using the ball milling electrostatic self-assembly method of the present invention. Figure 2 This is a SEM image of the single-arm carbon nanotube-coated lithium cobalt oxide composite cathode material prepared in Example 1 of the present invention; Figure 3 SEM image of the conductive carbon black-coated lithium cobalt oxide composite cathode material prepared in Comparative Example 2; Figure 4 EIS diagrams of the materials in Examples 1, 2, and 3 and Comparative Examples 1 and 2; Figure 5 This is a comparison chart of the rate performance of the materials in Examples 1, 2, and 3 with those in Comparative Examples 1 and 2. Figure 6 The graph shows a comparison of the cycling performance of the materials in Examples 1, 2, and 3 with those in Comparative Examples 1 and 2. Figure 7 , Figure 8 The images shown are SEM images of the electrode sheets after 100 cycles in Example 1 and Comparative Example 2, respectively. Detailed Implementation

[0037] The following detailed description illustrates the specific implementation method: Example 1: Preparation of single-arm carbon nanotube-coated lithium cobalt oxide composite cathode material (1) Surface charge modification: ① Weigh 0.25 g of hexadecyltrimethylammonium bromide into 500 mL of deionized water and stir to obtain a 0.05% (mass / volume) aqueous solution. Adjust the pH to 8.0. Weigh 50 g of lithium cobalt oxide (LiCoO2) cathode material and add it to the above aqueous solution. Stir at room temperature for 1 hour. After stirring, the suspension is centrifuged, washed three times with deionized water, and dried under vacuum at 120℃ for 10 hours to obtain positively charged LiCoO2.

[0038] ② Weigh 5g of single-arm carbon nanotubes and place them in 50mL of aqua regia (concentrated sulfuric acid:concentrated nitric acid = 3:1). Sonicate at 60℃ for 2h to introduce functional groups such as carboxyl and hydroxyl groups. Wash with deionized water until neutral and vacuum dry at 120℃ for 10h to obtain negatively charged single-arm carbon nanotubes.

[0039] (2) Ball mill driven electrostatic self-assembly: ① Preparation of mixed slurry: Weigh 0.201g of negatively charged single-arm carbon nanotubes and 40g of positively charged LiCoO2, add them to 50g of N-methylpyrrolidone, stir at low speed for 20 min (30 rpm / min revolution, 300 rpm / min dispersion), and then stir at medium speed for 120 min (40 r / min revolution, 2000 r / min dispersion) to form a suspension slurry.

[0040] ② Ball milling: Weigh 80g of mixed slurry and 800g of stainless steel balls and put them into a ball mill jar. Mill at 300 r / min for 6 hours.

[0041] (3) Post-processing: After ball milling, the slurry was passed through a 200-mesh standard sieve, the solid composite was collected by centrifugation, vacuum dried at 120℃ for 10h, and then heat-treated at low temperature at 200℃ under nitrogen atmosphere for 4h to obtain a single-arm carbon nanotube coated LiCoO2 composite cathode material, labeled as SWCNTs@LiCoO2.

[0042] Example 2: Preparation of single-arm carbon nanotube-coated lithium nickel cobalt manganese oxide composite cathode material (1) Surface charge modification: ① Weigh 0.5g of polyethyleneimine into 500mL of deionized water to obtain a 0.1% aqueous solution, and adjust the pH to 7.0. Weigh 50g of lithium nickel cobalt manganese oxide (NCM523) positive electrode material and add it, stir at room temperature for 1 hour, centrifuge, wash, and vacuum dry at 120℃ for 10 hours to obtain positively charged NCM523.

[0043] ② The acidification treatment of single-arm carbon nanotubes is the same as in Example 1.

[0044] (2) Ball mill driven electrostatic self-assembly: ① Weigh 0.201g of negatively charged single-arm carbon nanotubes and 40g of positively charged NCM523, add 50g of N-methylpyrrolidone, stir at low speed for 15 min (40 rpm / min revolution, 400 rpm / min dispersion), and then stir at medium speed for 90 min (50 r / min revolution, 2000 r / min dispersion).

[0045] ② Ball milling: Weigh 80g of mixed slurry and 1200g of stainless steel balls, and ball mill at 200 r / min for 8 hours.

[0046] (3) Post-treatment: Same as in Example 1, but the low-temperature heat treatment temperature is 300℃ and the time is 2h. SWCNTs@NCM523 is obtained.

[0047] Example 3: Preparation of single-arm carbon nanotube-coated lithium iron phosphate composite cathode material (1) Surface charge modification: ① Weigh 0.5g of polydiallyldimethylammonium chloride into 500mL of deionized water to obtain a 0.1% aqueous solution, and adjust the pH to 7.0. Weigh 50g of lithium iron phosphate (LiFePO4) cathode material and add it, stir at room temperature for 1 hour, centrifuge, wash, and vacuum dry at 120℃ for 10 hours to obtain positively charged LiFePO4.

[0048] ② The acidification treatment of single-arm carbon nanotubes is the same as in Example 1.

[0049] (2) Ball mill driven electrostatic self-assembly: ① Weigh 0.201g of negatively charged single-arm carbon nanotubes and 40g of positively charged LiFePO4, add 50g of N-methylpyrrolidone, stir at low speed for 20 min (50 rpm / min revolution, 500 rpm / min dispersion), and then stir at medium speed for 120 min (60 r / min revolution, 3000 r / min dispersion).

[0050] ② Ball milling: Weigh 80g of mixed slurry and 1000g of stainless steel balls, and ball mill at 400 r / min for 4 hours.

[0051] (3) Post-processing: Same as in Example 2 (300℃, 2h), to obtain SWCNTs@LiFePO4.

[0052] Comparative Example 1: Commercial LiCoO2 cathode material Commercial LiCoO2 cathode material was used directly without any coating treatment.

[0053] Comparative Example 2: Preparation of conductive carbon black-coated lithium cobalt oxide composite cathode material (1) Surface charge modification: Same as in Example 1, but replace the single-arm carbon nanotubes with conductive carbon black (SP), and also perform aqua regia acidification treatment to introduce negative charge.

[0054] (2) Ball milling driven electrostatic self-assembly: The process parameters are the same as in Example 1, but negatively charged conductive carbon black and positively charged LiCoO2 are used for ball milling.

[0055] (3) Post-processing: Same as in Example 1, to obtain conductive carbon black coated LiCoO2 composite cathode material, labeled as SP@LiCoO2.

[0056] Performance testing The materials from Examples 1-3 and Comparative Examples 1-2 were assembled into button cells, and their rate performance and 1C cycle performance were tested in the voltage range of 4.4-3.0V.

[0057] Figure 2 SEM images show that in Example 1, single-arm carbon nanotubes are uniformly coated on the lithium cobalt oxide material, forming conductive pathways between the particles and constructing a long-range, interconnected, and stable three-dimensional conductive network. This ensures efficient synergistic transport of electrons and ions, which can greatly improve the rate performance and cycle stability of the material.

[0058] Figure 3 The results show that the coating effect of conductive carbon black on lithium cobalt oxide in Comparative Example 2 is not ideal. Only a small amount of carbon black particles are coated, and the carbon black agglomerates and scatters, failing to form a continuous conductive network, which is not conducive to improving the rate performance of the material.

[0059] Figure 4 The EIS plots show that the charge transfer impedance (Rct) values ​​of Examples 1-3 are significantly lower than those of Comparative Example 1 (uncoated) and Comparative Example 2 (coated with conductive carbon black), indicating that the single-arm carbon nanotube coating in the electrode forms a denser conductive network, thereby reducing the electron transport impedance. Figure 5 The rate performance comparison shows that the rate performance of Examples 1-3 is significantly higher than that of Comparative Examples 1 and 2, and the 20C rate discharge capacity retention rate is increased from less than 80% in Comparative Examples 1 and 2 to more than 85%. Figure 6 The comparison of the cycling performance shows that the cycling stability of Examples 1-3 is also significantly better than that of Comparative Examples 1 and 2.

[0060] Figure 7 and Figure 8 The images are SEM images of the electrode sheets after 100 cycles for Example 1 and Comparative Example 2, respectively. It can be seen that the electrode sheet prepared by the material in Example 1 still maintains the complete active material particle structure, while the material particles of the electrode sheet prepared by the material in Comparative Example 2 have been significantly broken.

[0061] The above results demonstrate that the single-arm carbon nanotube-coated composite cathode material prepared by ball milling-driven electrostatic self-assembly in this invention can effectively improve the rate performance and cycle life of lithium-ion batteries.

[0062] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a composite cathode material with a conductive network constructed by coating single-arm carbon nanotubes, characterized in that, Includes the following steps: (1) Surface charge modification steps: a. Surface modification of lithium-ion battery cathode material particles to make their surface positively charged; b. Acidification treatment is applied to the single-arm carbon nanotubes to make their surface negatively charged; (2) Ball mill driven electrostatic self-assembly steps: The positively charged cathode material obtained in step (1) and the negatively charged single-arm carbon nanotubes are dispersed together in an organic solvent to form a mixed slurry; then the mixed slurry is subjected to high-energy ball milling together with grinding balls; the mechanical force provided by the ball milling process drives the positively charged cathode material particles with opposite charges to collide strongly and frequently with the single-arm carbon nanotubes, promoting their binding through electrostatic attraction, thereby coating the surface of the cathode material particles with single-arm carbon nanotubes; (3) Post-processing steps: The ball-milled slurry was separated, dried, and heat-treated to obtain the single-arm carbon nanotube-coated composite cathode material.

2. The preparation method according to claim 1, characterized in that, In step (1)a, the method for making the surface of the positive electrode material positively charged is as follows: the positive electrode material is immersed in an aqueous solution containing a positively charged modifier and stirred, and then washed and dried; the positively charged modifier is selected from at least one of positively charged surfactants, polymers or polyelectrolytes.

3. The preparation method according to claim 2, characterized in that, The positively charged surfactant is hexadecyltrimethylammonium bromide or hexadecylpyridinium chloride; the positively charged polymer is polyethyleneimine, imidazolium salt polymer or polyvinyl alcohol with quaternary ammonium salt groups introduced; the positively charged polyelectrolyte is polydiallyldimethylammonium chloride.

4. The preparation method according to claim 2 or 3, characterized in that, The aqueous solution of the positively charged modifier has a mass-volume concentration of 0.05% to 2% and a pH value of 3.0 to 10.0; the solid-liquid ratio of the positive electrode material to the aqueous solution is 1 g : (10 to 50) mL; and the stirring time is 0.5 to 2 hours.

5. The preparation method according to claim 1, characterized in that, In step (1)b, the acidification treatment is as follows: the single-arm carbon nanotube is placed in aqua regia and ultrasonically treated at 50~70℃ for 1~4 hours, then washed with deionized water until neutral and dried; the aqua regia is a mixture of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:

3.

6. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the single-arm carbon nanotube to the cathode material is 0.5% to 3%.

7. The preparation method according to claim 1, characterized in that, In step (2), the organic solvent is N-methylpyrrolidone; the mixed slurry is mechanically stirred and dispersed before ball milling, and the stirring conditions include: stirring at 30~50 rpm and 300~500 rpm for 15~20 min, and then stirring at 40~60 rpm and 2000~3000 rpm for 90~120 min.

8. The preparation method according to claim 1, characterized in that, In step (2), the parameters of the high-energy ball mill are: the mass ratio of grinding balls to mixed slurry is 10:1 to 20:1, the ball milling speed is 200 to 400 rpm, and the ball milling time is 2 to 8 hours; in step (3), the heat treatment is carried out in an inert atmosphere at a temperature of 150℃ to 300℃ for 2 to 4 hours.

9. The preparation method according to claim 1, characterized in that, The positive electrode material of the lithium-ion battery is LiCoO2, LiMn2O4, LiFePO4, or LiNi. 1-x-y Co y Mn x O2, LiNi 1-x-y Co y Al x O2 or LiM x Mn 2-x At least one of O4, wherein M is Fe or Co.

10. A composite cathode material in which a conductive network is constructed by coating single-arm carbon nanotubes, characterized in that, The composite cathode material prepared according to any one of claims 1 to 3 and 5 to 9 comprises cathode material particles and a single-arm carbon nanotube layer coated on the surface of the particles. The single-arm carbon nanotube layer is uniformly, discretely, and seamlessly distributed, and forms a long-range interconnected three-dimensional conductive network between adjacent particles.

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