Carbon nanotube reinforced negative electrode material and preparation method thereof

Abstract

The application relates to the field of negative electrode materials, in particular to a carbon nanotube reinforced negative electrode material and a preparation method thereof. The carbon nanotube reinforced negative electrode material comprises the following substances by weight: a carbon nanotube reinforced negative electrode material comprises an artificial graphite inner core, a carbon nanotube coating layer and a pitch coating layer which are sequentially coated from inside to outside, the carbon nanotube coating layer further comprises magnetic modified particles, and the pitch coating layer comprises the following substances by weight: biochar particles 25-35 parts; pitch particles 65-70 parts; dispersing agent 0.1-0.5 parts. The carbon nanotube coating layer can construct a continuous conductive network to improve the electronic transmission efficiency, meanwhile, the pitch coating layer is composed of biochar particles and pitch. The synergistic effect of the three-layer structure can repair the surface defects of the artificial graphite, reduce the electrolyte side reaction, inhibit the volume expansion in the charging and discharging process, and thus comprehensively improve the cycle stability and conductivity of the negative electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of negative electrode materials, and in particular to a carbon nanotube reinforced negative electrode material and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have become the core energy storage devices for new energy vehicles, energy storage systems and portable electronic devices due to high energy density, long cycle life and environmental friendliness. As a key component of lithium ion batteries, the negative electrode material directly affects the rate performance, cycle stability and safety of the battery. At present, artificial graphite occupies a dominant position in commercial negative electrode materials due to its low cost, regular structure and low lithium intercalation potential.

[0003] However, pure artificial graphite has many surface defects and a large irreversible capacity loss in the first cycle. At the same time, its layered structure is prone to volume expansion during long-term charging and discharging, resulting in electrode powdering and peeling. To solve the above problems, researchers generally use surface coating technology to modify artificial graphite. By introducing a carbon coating layer, surface defects are repaired, volume expansion is inhibited, and electrical conductivity is improved.

[0004] In view of the above prior art, the inventors found that pitch, as a traditional coating material, has the characteristics of wide source, high carbon yield and excellent graphitization performance. The amorphous carbon coating layer formed by pyrolysis of pitch can effectively reduce the side reaction between electrolyte and graphite surface. However, the pitch coating layer itself is brittle and prone to cracking during the cycle process. At the same time, the electrical conductivity of pitch is not good, and an additional conductive phase needs to be introduced. At the same time, due to the poor uniformity of pitch material coating, local agglomeration or exposed areas are prone to occur. SUMMARY

[0005] Based on the technical problems existing in the above prior art, the present application provides a carbon nanotube reinforced negative electrode material and a preparation method thereof.

[0006] In a first aspect, the present application provides a carbon nanotube reinforced negative electrode material, which adopts the following technical scheme:

[0007] A carbon nanotube reinforced negative electrode material, characterized in that it comprises an artificial graphite core, a carbon nanotube coating layer and a pitch coating layer coated in turn from the inside out, the carbon nanotube coating layer further comprises magnetic modified particles, and the pitch coating layer comprises the following substances by weight:

[0008] Biochar particles 25-35 parts;

[0009] Pitch particles 65-70 parts;

[0010] Dispersing agent 0.1-0.5 parts.

[0011] By the technical scheme, the performance of the artificial graphite negative electrode material is optimized by designing a three-layer composite structure, the basic lithium intercalation capacity is provided by the artificial graphite core, and a synergistic reinforcing system is formed by sequentially coating the carbon nanotube coating layer and the pitch coating layer. The carbon nanotube coating layer can construct a continuous conductive network to improve the electron transmission efficiency, and the pitch coating layer adjusts the porosity of the coating layer by the compounding of the biochar particles and the pitch, and the dispersant promotes the uniform mixing of the components to avoid agglomeration. The synergistic effect of the three-layer structure can repair the surface defects of the artificial graphite, reduce the electrolyte side reaction, and inhibit the volume expansion in the charging and discharging process, thereby comprehensively improving the cycle stability and conductivity of the negative electrode material.

[0012] Meanwhile, the magnetic response characteristics of the magnetic particles are utilized, and the external magnetic field is used to induce the directional arrangement of the magnetic particles in the preparation process, and then the ordered conductive network of the carbon nanotubes is guided. The addition of the magnetic particles can also enhance the bonding force between the carbon nanotubes and the graphite matrix through the interfacial interaction, and reduce the interface impedance. In addition, the magnetic particles may have electrochemical activity or catalytic performance, which can synergistically improve the ion transmission efficiency of the coating layer, thereby further optimizing the rate performance and cycle stability of the negative electrode material, and solving the problems of disorder and weak interface bonding of the traditional carbon nanotube coating layer structure.

[0013] Further, the carbon nanotube coating layer is a carbon nanotube aerogel film coating layer.

[0014] By the technical scheme, the carbon nanotube coating layer is limited to a carbon nanotube aerogel film coating layer, and the unique three-dimensional porous network structure of the aerogel film is utilized to realize the uniform dispersion and close combination of the carbon nanotubes on the graphite surface. Compared with the traditional carbon nanotube powder coating, the aerogel film has higher specific surface area and structural integrity, can form a continuous and defect-free coating interface, and enhance the smoothness of the electron conduction path. At the same time, the porous structure of the aerogel film can buffer the volume expansion stress and avoid the cracking of the coating layer, thereby improving the mechanical stability and cycle life of the material, and solving the problems of easy agglomeration and poor uniformity of the carbon nanotube coating.

[0015] Further, the magnetic modified particles are CoFe2O4 magnetic nanoparticles.

[0016] By the technical solution, the magnetic modified particles are CoFe2O4 magnetic nanoparticles, and the CoFe2O4 magnetic nanoparticles have unique superparamagnetic property and chemical stability, and can be precisely arranged under the action of a magnetic field to guide the carbon nanotubes to form a highly ordered coating structure. The nanosize effect of the CoFe2O4 magnetic nanoparticles can increase the contact area with the carbon nanotubes, and the synergistic effect can improve the electron conduction efficiency; at the same time, the oxide property can enhance the chemical stability of the coating layer and reduce the electrolyte corrosion. In addition, the CoFe2O4 magnetic nanoparticles can contribute additional lithium storage capacity through the pseudo-capacitance effect, so as to improve the electrical conductivity and structural stability of the material, and further optimize the electrochemical performance of the negative electrode.

[0017] In a second aspect, the application provides a preparation method of a carbon nanotube reinforced negative electrode material, which adopts the following technical solution:

[0018] The preparation method of the carbon nanotube reinforced negative electrode material includes the following preparation steps:

[0019] CoFe2O4 magnetic nanoparticles and carbon nanotube aerogel membranes are mixed and broken, deionized water and polyvinyl alcohol are added and stirred, ultrasonic dispersion is collected to obtain a suspension;

[0020] The artificial graphite particles are added to a rotating fluidized bed, a magnetic field is applied under a nitrogen atmosphere, and the suspension is sprayed at a spray rate of 2 mL / min at a bed temperature of 80℃;

[0021] After the spraying is completed, formaldehyde vapor is introduced, heated and reacted, and the artificial graphite particles coated with a carbon nanotube coating layer are collected;

[0022] The artificial graphite particles coated with the carbon nanotube coating layer are mixed with pitch and placed in an extruder for extrusion granulation, melt extrusion and cooling to room temperature, and the sieved particles are collected by crushing and sieving;

[0023] The sieved particles are placed in a nitrogen atmosphere, heated and reacted, and then further heated and carbonized, and cooled to room temperature to prepare the carbon nanotube reinforced negative electrode material.

[0024] By the technical scheme, the controlled construction of the composite coating layer is realized in multiple steps, the CoFe2O4 magnetic nanoparticles and the carbon nanotube aerogel film are mixed to form a suspension, the artificial graphite particles are uniformly coated by using the rotating fluidized bed under the assistance of a magnetic field, the formaldehyde vapor treatment promotes the solidification of the coating layer, and the final three-layer structure is formed through asphalt mixing, extrusion granulation and carbonization treatment. The whole process combines physical dispersion, magnetic field orientation, chemical solidification and pyrolytic carbonization to ensure that the interfaces of the coating layers are tightly combined and the structure is uniform, effectively inhibiting the problems such as agglomeration and cracking that are prone to occur in traditional coating processes, so as to improve the comprehensive performance of the negative electrode material.

[0025] Further, the carbon nanotube aerogel film is made by the following technical scheme:

[0026] The carbon nanotubes are acidized, an acylating agent is added, and after heating and holding, washing and drying, activated carbon nanotubes are prepared;

[0027] The activated carbon nanotubes, resorcinol and formaldehyde are stirred and mixed, the mixed solution is collected and electrolyzed, the electrolyzed mixed solution is heated and hydrothermally reacted, the reaction gel solution is taken and placed in isopropanol, the solvent is replaced, and the carbon nanotube organic gel solution is collected;

[0028] The carbon nanotube organic gel solution is coated on the surface of the substrate, and then placed in a supercritical drying device, and after supercritical drying treatment, pre-oxidation treatment is carried out by heating, and the carbon nanotube aerogel film material is prepared.

[0029] By the above technical scheme, the surface of the carbon nanotubes is activated by acidizing and acylating treatment, and active functional groups are introduced to enhance the interfacial compatibility with subsequent reactants; then the sol-gel reaction of the resorcinol-formaldehyde system is carried out, the microstructure of the gel network is regulated by electrolysis treatment, the nano-porous structure is retained by solvent replacement and supercritical drying, and finally the thermal stability and mechanical strength of the film material are improved by pre-oxidation treatment.

[0030] Further, the magnetic field applied is an axial magnetic field of 0.7-0.9 T parallel to the rotation axis of the fluidized bed.

[0031] By the technical scheme, the magnetic field is an axial magnetic field parallel to the rotation axis of the fluidized bed. The axial magnetic field has a directional effect, which guides the CoFe2O4 magnetic nanoparticles and the carbon nanotubes with magnetic responsiveness to be arranged in order along the direction of the magnetic field, and forms a "directional conductive channel" distributed radially along the graphite particles. The ordered arrangement can significantly reduce the tortuosity of the electron transport path, and improve the isotropic conductivity of the coating layer. Meanwhile, the axial magnetic field and the rotating fluidized bed can work together to ensure that the graphite particles are uniformly coated during movement, and avoid coating defects caused by uneven local magnetic field strength, thereby further optimizing the consistency and electrochemical performance stability of the material.

[0032] Further, the carbonization treatment includes the following specific steps:

[0033] First, the temperature is raised to 600-650℃ at a rate of 2-5℃ / min and kept for 1-2h, and then the temperature is raised to 800-1000℃ at a rate of 5-8℃ / min and kept for 2-4h.

[0034] By the technical scheme, the microstructure of the coating layer is regulated by a segmented carbonization treatment process. First, the temperature is slowly raised and kept at a lower temperature, so that the organic components in the coating layer are fully decomposed and volatilized, avoiding cracks caused by too fast gas escape due to rapid temperature rise. Then, the temperature is raised to a high temperature at a higher rate and kept, which promotes the graphitization of the carbon material and improves the conductivity and structural density of the coating layer. This step-by-step carbonization strategy can balance the porosity and density of the coating layer, reduce structural defects caused by thermal stress, and enhance the barrier ability of the coating layer to the electrolyte and the buffering effect on volume expansion, thereby improving the cycle stability and safety of the negative electrode material.

[0035] Further, the particle size of the CoFe2O4 magnetic nanoparticles is 10-50 nm.

[0036] By the technical scheme, the particle size of the CoFe2O4 magnetic nanoparticles is limited to ensure good magnetic responsiveness and dispersion, avoiding agglomeration caused by too large particles or weakened magnetism caused by too small particles. The appropriate particle size allows the CoFe2O4 magnetic nanoparticles to be uniformly dispersed in the carbon nanotube network, to be precisely arranged under the action of the magnetic field, and to reduce physical barriers to the conductive network of the carbon nanotube. In addition, the nanoparticles with a specific particle size can enhance the interface interaction with the carbon nanotube through size effect, improve the mechanical strength and electrochemical stability of the coating layer, and ensure the synergistic optimization of the magnetic guiding effect and the conductive performance.

[0037] In summary, the present application has the following advantages:

[0038] Firstly, the application realizes the synergistic enhancement of multi-scale performance through the three-layer structure design of artificial graphite core, carbon nanotube aerogel film coating layer and asphalt coating layer. The three-dimensional porous network of carbon nanotube aerogel film can repair the surface defects of graphite, reduce the electrolyte side reaction; the composite system of biochar particles and asphalt in the asphalt coating layer can buffer the volume expansion stress, and the dispersant promotes the uniform mixing of each component to avoid agglomeration. The magnetic modified particles are directionally arranged by magnetic field induction, further enhancing the interfacial bonding force between carbon nanotube and graphite matrix, and inhibiting the cracking of the coating layer. Under the synergistic effect of the three-layer structure, the material exhibits excellent structural stability in long-term charge and discharge cycle, solving the problem of electrode pulverization caused by volume expansion of traditional graphite negative electrode.

[0039] Secondly, the application synergistically constructs an efficient electron transport path through the continuous conductive network of carbon nanotube aerogel film and the directional arrangement of magnetic particles. The high specific surface area and structural integrity of the aerogel film ensure the smoothness of the electron conduction path, and the magnetic particles guide the carbon nanotubes to form an ordered arrangement under the action of the axial magnetic field, reducing the electron transmission impedance. At the same time, the interface interaction between carbon nanotubes and magnetic particles improves the ion diffusion efficiency, and the dense structure of the asphalt coating layer reduces the electrolyte penetration, and the three work together to make the material have high electronic conductivity and ion transport capacity, significantly improving the rate charge and discharge performance and the first coulomb efficiency of the negative electrode.

[0040] Thirdly, in the preparation process, the surface activation treatment of carbon nanotubes enhances the interface compatibility, the sol-gel and supercritical drying process retains the nano-porous structure of the aerogel film; the rotating fluidized bed combined with the magnetic field assisted spraying technology realizes the uniform loading of the coating layer; the segmented carbonization process balances the density and porosity of the coating layer through stepwise temperature control, avoiding thermal stress cracking. These process innovations ensure the controllability and batch consistency of the microstructure of the material, solving the problems of carbon nanotube agglomeration and uneven coating in traditional coating process, providing technical support for the scale production and performance stability of the negative electrode material. DETAILED DESCRIPTION

[0041] The application will be further described in detail below in conjunction with the examples.

[0042] Preparation Example 1

[0043] Asphalt coating layer material 1

[0044] Take 25 kg of biochar particles, 65 kg of asphalt particles and 0.1 kg of sodium dodecylbenzenesulfonate, mix and grind through a 500 mesh sieve to prepare asphalt coating layer material 1.

[0045] Preparation Example 2

[0046] Asphalt coating layer material 2

[0047] Take 30 kg of biochar particles, 67 kg of asphalt particles and 0.2 kg of sodium dodecyl benzene sulfonate, stir and mix and grind through a 500 mesh screen to prepare asphalt coating material 2.

[0048] Preparation Example 3

[0049] Asphalt coating material 3

[0050] Take 35 kg of biochar particles, 70 kg of asphalt particles and 0.5 kg of sodium dodecyl benzene sulfonate, stir and mix and grind through a 500 mesh screen to prepare asphalt coating material 3.

[0051] Preparation Example 4

[0052] Carbon nanotube aerogel film

[0053] Take multi-walled carbon nanotubes and add them to a mixture of 1 mol / L concentrated nitric acid and 1 mol / L concentrated sulfuric acid in a volume ratio of 1:3, reflux at 80°C for 4h, filter and wash to neutral, and then dry; add acylation agent acetic anhydride to the acidified carbon nanotubes, heat at 120°C for 3h, wash and dry again to obtain activated carbon nanotubes; take the activated carbon nanotubes, resorcinol and formaldehyde in a mass ratio of 1:2:3, stir and mix, collect the mixture and place it in an electrolytic cell with platinum electrode as anode and graphite as cathode, electrolyze at 20V for 1h; transfer the electrolyzed mixture to a hydrothermal reactor, hydrothermal reaction at 180°C for 12h, take the reaction gel and place it in isopropanol for 48h to replace the solvent, and obtain carbon nanotube organic gel. Coating the gel on the surface of a PET substrate, placing it in a supercritical drying device, using CO2 as medium, drying at 40°C and 8MPa for 10h, then pre-oxidizing at 250°C in air atmosphere for 3h, and peeling off to obtain carbon nanotube aerogel film.

[0054] Example 1

[0055] Take CoFe2O4 magnetic nanoparticles with a particle size of 10-50 nm and carbon nanotube aerogel film in a mass ratio of 1:5, mechanically crush to a particle size of ≤10μm, and collect the mixed particles; take the mixed particles and add them to a 5% polyvinyl alcohol solution in a mass ratio of 1:6, stir and mix, and collect the suspension after ultrasonic dispersion at 200W.

[0056] Add D50 15μm artificial graphite particles to a rotating fluidized bed, apply an axial magnetic field of 0.7T parallel to the rotation axis of the fluidized bed in a nitrogen atmosphere, and spray the suspension at a spray rate of 2 mL / min at a bed temperature of 80°C;

[0057] After spraying, introduce formaldehyde vapor at a flow rate of 5L / min, heat to 120°C and keep for 2-3h, and collect the artificial graphite particles coated with a carbon nanotube coating layer;

[0058] The artificial graphite particles coated with the carbon nanotube coating layer and the pitch coating material 1 were mixed at a mass ratio of 1:5, placed in an extruder, and melt-extruded at 200°C to form granules. After cooling, the granules were crushed through a 200-mesh sieve, allowed to stand and cool to room temperature, crushed and sieved to collect the sieved particles.

[0059] The sieved particles were placed in a nitrogen atmosphere, first heated at a rate of 2°C / min to 600°C and held for 1 h, then heated at a rate of 5°C / min to 800°C and held for 2 h, allowed to stand and cool to room temperature, to prepare the carbon nanotube-reinforced negative electrode material.

[0060] Example 2

[0061] CoFe2O4 magnetic nanoparticles with a particle size of 10-50 nm and carbon nanotube aerogel membranes were mixed at a mass ratio of 1:5, mechanically broken to a particle size of ≤10 μm, and the mixed particles were collected. The mixed particles were added to a 5% polyvinyl alcohol solution at a mass ratio of 1:8, stirred and mixed, and the suspension was collected by ultrasonic dispersion at 250 W.

[0062] The D50 of the artificial graphite particles was 15 μm. The particles were added to a rotating fluidized bed, a 0.8T axial magnetic field parallel to the rotation axis of the fluidized bed was applied under a nitrogen atmosphere, and the suspension was sprayed at a rate of 2 mL / min at a bed temperature of 80°C.

[0063] After spraying, formaldehyde vapor was introduced at a flow rate of 5 L / min, and the temperature was raised to 120°C and held for 2 h to collect the artificial graphite particles coated with the carbon nanotube coating layer.

[0064] The artificial graphite particles coated with the carbon nanotube coating layer and the pitch coating material 1 were mixed at a mass ratio of 1:5, placed in an extruder, and melt-extruded at 200°C to form granules. After cooling, the granules were crushed through a 200-mesh sieve, allowed to stand and cool to room temperature, crushed and sieved to collect the sieved particles.

[0065] The sieved particles were placed in a nitrogen atmosphere, first heated at a rate of 2°C / min to 600°C and held for 1 h, then heated at a rate of 5°C / min to 800°C and held for 2 h, allowed to stand and cool to room temperature, to prepare the carbon nanotube-reinforced negative electrode material.

[0066] Example 3

[0067] CoFe2O4 magnetic nanoparticles with a particle size of 10-50 nm and carbon nanotube aerogel membranes were mixed at a mass ratio of 1:5, mechanically broken to a particle size of ≤10 μm, and the mixed particles were collected. The mixed particles were added to a 5% polyvinyl alcohol solution at a mass ratio of 1:8, stirred and mixed, and the suspension was collected by ultrasonic dispersion at 250 W.

[0068] D50 of 15 μm artificial graphite particles were added to a rotating fluidized bed, an axial magnetic field of 0.9 T parallel to the rotation axis of the fluidized bed was applied under a nitrogen atmosphere, and the suspension was sprayed at a spray rate of 2 mL / min at a bed temperature of 80℃;

[0069] After spraying, formaldehyde vapor was introduced at a flow rate of 5 L / min, the temperature was raised to 120℃ and maintained for 3 h, and artificial graphite particles coated with a carbon nanotube coating layer were collected;

[0070] The artificial graphite particles coated with a carbon nanotube coating layer were mixed with pitch coating material 1 at a mass ratio of 1:15, placed in an extruder, melted and extruded at 200℃, crushed through a 200 mesh sieve after cooling, and collected after sieving and cooling to room temperature.

[0071] The sieved particles were placed in a nitrogen atmosphere, first heated to 650℃ at a rate of 5℃ / min and maintained for 2 h, then heated to 1000℃ at a rate of 8℃ / min and maintained for 4 h, and cooled to room temperature to prepare a carbon nanotube reinforced negative electrode material.

[0072] Example 4

[0073] CoFe2O4 magnetic nanoparticles with a particle size of 10-50 nm and carbon nanotube aerogel film were mixed at a mass ratio of 1:5, mechanically broken to a particle size of ≤10 μm, and collected as mixed particles. The mixed particles were added to a 5% polyvinyl alcohol solution at a mass ratio of 1:7, stirred and mixed, and ultrasonically dispersed at 250 W to collect a suspension.

[0074] D50 of 15 μm artificial graphite particles were added to a rotating fluidized bed, an axial magnetic field of 0.8 T parallel to the rotation axis of the fluidized bed was applied under a nitrogen atmosphere, and the suspension was sprayed at a spray rate of 2 mL / min at a bed temperature of 80℃;

[0075] After spraying, formaldehyde vapor was introduced at a flow rate of 5 L / min, the temperature was raised to 120℃ and maintained for 2 h, and artificial graphite particles coated with a carbon nanotube coating layer were collected;

[0076] The artificial graphite particles coated with a carbon nanotube coating layer were mixed with pitch coating material 2 at a mass ratio of 1:10, placed in an extruder, melted and extruded at 200℃, crushed through a 200 mesh sieve after cooling, and collected after sieving and cooling to room temperature.

[0077] The sieved particles were placed in a nitrogen atmosphere, first heated to 625℃ at a rate of 3℃ / min and maintained for 1 h, then heated to 900℃ at a rate of 6℃ / min and maintained for 3 h, and cooled to room temperature to prepare a carbon nanotube reinforced negative electrode material.

[0078] Example 5

[0079] CoFe2O4 magnetic nanoparticles with a particle size of 10-50 nm and carbon nanotube aerogel membranes were mixed in a mass ratio of 1:5, mechanically broken to a particle size of ≤10 μm, and then the mixed particles were collected. The mixed particles were added to a 5% polyvinyl alcohol solution in a mass ratio of 1:7, stirred and mixed, and a suspension was collected by ultrasonic dispersion at 250 W.

[0080] Artificial graphite particles with a D50 of 15 μm were added to a rotating fluidized bed, an axial magnetic field of 0.8 T parallel to the rotation axis of the fluidized bed was applied under a nitrogen atmosphere, and a suspension was sprayed at a spraying rate of 2 mL / min at a bed temperature of 80℃;

[0081] After spraying was completed, formaldehyde vapor was introduced at a flow rate of 5 L / min, and the temperature was raised to 120℃ and maintained for 2 h. Artificial graphite particles coated with a carbon nanotube coating layer were collected.

[0082] The artificial graphite particles coated with a carbon nanotube coating layer were mixed with pitch coating material 3 in a mass ratio of 1:10 and placed in an extruder, melted and extruded at 200℃, crushed through a 200-mesh sieve after cooling, and left to cool to room temperature. The sieved particles were collected by crushing and sieving.

[0083] The sieved particles were placed in a nitrogen atmosphere, first heated to 625℃ at a rate of 3℃ / min and maintained for 1 h, then heated to 900℃ at a rate of 6℃ / min and maintained for 3 h, and left to cool to room temperature. A carbon nanotube reinforced negative electrode material was prepared.

[0084] Comparative Example 1

[0085] Comparative Example 1 used an equal mass of carbon nanotubes instead of carbon nanotube aerogel membranes, and the remaining preparation steps and parameters were the same as those of Example 1.

[0086] Comparative Example 2

[0087] Comparative Example 2 did not add carbon nanotube aerogel membranes, and the remaining preparation steps and parameters were the same as those of Example 1.

[0088] Performance Testing

[0089] First coulombic efficiency: Artificial graphite negative electrode material as working electrode, lithium metal sheet as counter electrode, 1 mol / L LiPF6-EC / DEC (volume ratio 1:1) as electrolyte, CR2032 button half-cell was assembled; at 25℃ constant temperature environment, 0.1C (1C=372mAh / g) current density was used for first charge-discharge test, voltage range 0.01-3.0V.

[0090] Cycling stability test: 0.5C charge-discharge cycle for 500 times, the ratio of the 500th discharge specific capacity to the first discharge specific capacity was calculated.

[0091] Rate performance: discharge at 2C current density, record the discharge specific capacity at different rates. The results are shown in Table 1 below:

[0092] Table 1 Performance test table

[0093]

[0094] From the above Examples 1-5 and Comparative Examples 1-2 in combination with Table 1 test results, it can be found that:

[0095] In combination with Examples 1-5 and Comparative Examples 1-2, it is further illustrated that the technical scheme of the present application designs a three-layer composite structure to optimize the performance of the artificial graphite negative electrode material, uses the inner core of artificial graphite to provide basic lithium intercalation capacity, and successively coats the outer layer with a carbon nanotube coating layer and a pitch coating layer to form a synergistic reinforcement system. At the same time, the technical scheme of the present application utilizes the superparamagnetic property and chemical stability of CoFe2O4 magnetic nanoparticles to realize precise directional arrangement under the action of a magnetic field, guiding the carbon nanotubes to form a highly ordered coating structure. The nanosize effect of CoFe2O4 magnetic nanoparticles can increase the contact area with the carbon nanotubes, and through synergistic effect, the electron conduction efficiency is improved; at the same time, the oxide property of CoFe2O4 magnetic nanoparticles can enhance the chemical stability of the coating layer, reducing electrolyte corrosion. In addition, CoFe2O4 magnetic nanoparticles can contribute additional lithium storage capacity through pseudo-capacitance effect, thereby improving the electrical conductivity and structural stability of the material, and further optimizing the electrochemical performance of the negative electrode.

[0096] The present application has been described in detail based on the specific embodiments and exemplary examples, but these descriptions cannot be understood as limiting the present application. Those skilled in the art understand that various equivalent substitutions, modifications or improvements can be made to the technical scheme of the present application and its embodiments without departing from the spirit and scope of the present application, and these all fall within the scope of the present application. The protection scope of the present application is subject to the appended claims.

[0097] All publications, patent applications, patents and other references mentioned in this specification are hereby incorporated by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meaning commonly understood by one of ordinary skill in the art. In case of conflict, the present specification will control.

[0098] When the specification derives material, substances, methods, steps, devices or components, etc. with the lead word "known to the person skilled in the art", "prior art" or similar, the objects derived with the lead word encompass those which are conventionally used in the art at the time of the present application, but also those which are not yet conventionally used, but will become generally recognized in the art as suitable for analogous purposes.

[0099] In the context of the present specification, any matter or item not mentioned in addition to the explicitly stated matters or items applies directly to those known in the art without any change, unless explicitly stated otherwise.

Claims

1. A carbon nanotube-reinforced negative electrode material, characterized by comprising: a carbon nanotube; and a metal oxide, wherein the metal oxide is supported on the carbon nanotube. The carbon nanotube gas reinforced negative electrode material comprises an artificial graphite core, a carbon nanotube aerogel film coating layer and a pitch coating layer from inside to outside, wherein the carbon nanotube aerogel film coating layer further comprises CoFe2O4 magnetic nanoparticles, and the pitch coating layer is formed by mixing 25-35 parts by weight of biochar particles, 65-70 parts by weight of pitch particles and 0.1-0.5 parts by weight of a dispersing agent and then carbonizing the mixture. The preparation method of the carbon nanotube gas reinforced negative electrode material comprises the following steps: CoFe2O4 magnetic nanoparticles and carbon nanotube aerogel film are mixed and crushed, deionized water and polyvinyl alcohol are added and stirred, and the mixture is ultrasonically dispersed to obtain a suspension; Artificial graphite particles are added to a rotating fluidized bed, a magnetic field is applied under a nitrogen atmosphere, and the suspension is sprayed into the bed at a spraying rate of 2 mL / min at a bed temperature of 80℃; After spraying is completed, formaldehyde vapor is introduced, and the mixture is heated and reacted, and then the artificial graphite particles coated with the carbon nanotube aerogel film coating layer are collected; The artificial graphite particles coated with the carbon nanotube aerogel film coating layer are mixed with biochar particles, pitch particles and a dispersing agent, and then extruded in an extruder to form granules, melt-extruded and cooled to room temperature, and then crushed and sieved to obtain sieved particles; The sieved particles are placed in a nitrogen atmosphere, heated and reacted, and then carbonized at an increased temperature, and then cooled to room temperature to obtain the carbon nanotube gas reinforced negative electrode material.

2. The carbon nanotube reinforced anode material of claim 1, wherein the carbon nanotube reinforced anode material is a carbon nanotube reinforced silicon anode material. The carbon nanotube aerogel film is prepared by the following method: Activated carbon nanotubes are prepared by acidizing carbon nanotubes, adding an acylating agent, heating and reacting, and then washing and drying; Activated carbon nanotubes, resorcinol and formaldehyde are stirred and mixed, the mixture is electrolyzed, the electrolyzed mixture is heated and hydrothermally reacted, the reaction gel is collected and placed in isopropyl alcohol to replace the solvent, and then the carbon nanotube organic gel is collected; The carbon nanotube aerogel film material is prepared by coating the carbon nanotube organic gel on the surface of a substrate, placing it in a supercritical drying device for supercritical drying treatment, and then heating and pre-oxidizing.

3. The carbon nanotube reinforced anode material of claim 2, wherein the carbon nanotube reinforced anode material is characterized by: The magnetic field is an axial magnetic field parallel to the rotating axis of the fluidized bed with a strength of 0.7-0.9 T.

4. The carbon nanotube reinforced anode material of claim 3, wherein the carbon nanotube reinforced anode material is characterized by: The carbonization treatment comprises the following steps: First, the temperature is increased to 600-650℃ at a rate of 2-5℃ / min and maintained for 1-2h, and then the temperature is increased to 800-1000℃ at a rate of 5-8℃ / min and maintained for 2-4h.

5. The carbon nanotube reinforced anode material of claim 4, wherein the carbon nanotube reinforced anode material is characterized by: The CoFe2O4 magnetic nanoparticles have a particle size of 10-50 nm.

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