CN115744895A

CN115744895A - Nitrogen-doped multi-carbon-coated graphite composite material, composite material and secondary battery

Info

Publication number: CN115744895A
Application number: CN202211523871.2A
Authority: CN
Inventors: 吴凡; 余盛豪; 葛传长; 仰韻霖
Original assignee: Guangdong Kaijin New Energy Technology Co Ltd
Current assignee: Guangdong Kaijin New Energy Technology Co Ltd
Priority date: 2022-11-29
Filing date: 2022-11-29
Publication date: 2023-03-07

Abstract

The invention relates to the technical field of material preparation, and discloses a preparation method of a nitrogen-doped multi-element carbon-coated graphite composite material, the composite material and application thereof. The preparation method comprises the following steps: preparing a coating body; (II) preparing a first precursor; (III) a first carbonization treatment; (IV) acid washing; (V) catalysis; (VI) second carbonization treatment. According to the preparation method of the nitrogen-doped multi-element carbon-coated graphite composite material, the particles containing oxygen groups are used as an activating agent, nitrogen source coating is combined, acid washing, catalysis and carbonization are sequentially carried out, and a hard carbon coating containing nitrogen and carbon nano tubes can be formed.

Description

Nitrogen-doped multi-carbon-coated graphite composite material, composite material and secondary battery

Technical Field

The invention relates to the technical field of material preparation, in particular to a graphite material, and more particularly relates to a nitrogen-doped multi-element carbon-coated graphite composite material, a composite material and a secondary battery.

Background

Since internal combustion engine automobiles have long been a large source of air pollution, the use of clean energy to drive automobiles plays an important role in reducing carbon dioxide emissions. Therefore, electric vehicles using lithium ion batteries as power have been rapidly developed. As is well known, lithium ion batteries occupy a significant position in the digital product and electric vehicle markets due to their high energy density, power density and long life. In recent years, the driving range of electric vehicles has been greatly increased. However, the long charging time still prevents the large-scale application of the electric vehicle. The high energy density lithium battery cannot realize safe and rapid charging due to the unsatisfactory rate performance of the electrode material. Therefore, it is very necessary to improve the performance of the negative electrode material for a fast-charging lithium battery.

Graphite is the most common negative electrode material of lithium batteries, and has various defects such as poor compatibility with electrolyte, low charge and discharge efficiency, unsuitability for large-current rapid charge and discharge and poor cycle stability. The electrode material should have not only a high lithium diffusivity but also high safety during rapid charging. When the lithium ion battery is charged for a long time at a high speed, li in the electrode ⁺ The concentration increases, resulting in an increase in the polarization of the lithium ion battery, and thus a decrease in the voltage of the lithium ion battery. In addition, in the process of rapid charging, the increase of internal resistance causes high thermal effect, causes irreversible reactions such as electrolyte decomposition and gas generation, and reduces the safety and cycle life of the lithium battery. Therefore, manufacturers at home and abroad design the negative electrode material by a series of modification methods, so that the main performances of the electrode, particularly the conductivity of the negative electrode (reduction of the conductivity of the negative electrode)Internal resistance), diffusion (ensuring reaction kinetics), service life, safety and proper processability (specific surface area can not be too large, side reaction is reduced, service safety) are optimized to meet the requirement of high-rate charge and discharge of customers.

The power type artificial graphite used in the current market is mainly composed of graphite coated by soft carbon or hard carbon. During the charge and discharge processes, lithium ions are mainly transported through the soft carbon or the hard carbon on the surface thereof. Although the ion transmission (mass transfer process) is greatly improved, the electron transmission is not improved, and the electron conductivity and the ion diffusivity have profound influence on the quick charge performance of the cathode material. In addition, the heat conducting property of the electrode and the stability of the battery in the long-circulating process are also important concerns in the market.

With the further improvement of the performance requirements of the battery, the development and modification of novel anode materials are still important. Embodied in novel materials and novel structural designs. However, they are still only in the laboratory stage, and when they are applied to commercial batteries, the practical effects (especially rate and cycle performance) may be greatly reduced.

Disclosure of Invention

In view of the above, an object of the present invention is to provide a nitrogen-doped multi-carbon-coated graphite composite material, a composite material and a secondary battery. The obtained nitrogen-doped multi-carbon-coated graphite composite material has high conductivity, better first reversible specific capacity, first coulombic efficiency and cycle performance, and is particularly suitable for being used as a negative electrode material of a market power quick-charging battery.

In order to achieve the above object, a first aspect of the present invention provides a method for preparing a nitrogen-doped multi-component carbon-coated graphite composite material, comprising the steps of:

(I) Preparation of the clad

Grinding and mixing a soft carbon coating agent, an activating agent and a nitrogen source to form a coating body, wherein the activating agent is a particulate matter with an oxygen-containing group on the surface;

(II) preparation of the first precursor

Mixing the cladding body and the artificial graphite precursor to obtain a first precursor;

(III) first carbonization treatment

Carrying out first carbonization treatment on the first precursor in an inert atmosphere to obtain a carbonized product;

(IV) acid washing

Acid washing the carbonized product to obtain a second precursor;

(V) catalysis

Immersing the second precursor into a metal catalyst solution and drying to obtain a third precursor;

(VI) second carbonization treatment

And introducing a carbon source into the third precursor in a reducing atmosphere to perform second carbonization treatment, and performing post-treatment.

The preparation method of the nitrogen-doped multi-element carbon-coated graphite composite material at least comprises the following technical effects:

(1) The invention adopts the particles with oxygen-containing groups on the surface as the activating agent, the oxygen-containing groups can activate the soft carbon coating agent to convert the soft carbon coating agent into a hard carbon structure after carbonization, and volatile substances on the surface and the like are further discharged in the subsequent graphitization process, so that the specific area can be reduced, and the first coulombic efficiency is improved.

(2) After the nitrogen source is carbonized, nitrogen doping can be carried out on the surface of the artificial graphite precursor, so that active sites are provided for the rapid de-intercalation of lithium ions, the conductivity is improved, and meanwhile, the ion permeation potential barrier of the material is reduced, thereby promoting the rapid transmission of electrons and ions and improving the charge and discharge capacity under large current.

(3) After the artificial graphite precursor is activated by an activating agent, carbonized for the first time and washed by acid, the surface of the artificial graphite precursor has a plurality of defects, and after the artificial graphite precursor is immersed in a metal catalyst solution, a carbon source is introduced into the solution for carbonization under the catalytic action of a metal catalyst in a reducing atmosphere, so that compact Carbon Nanotubes (CNTs) can grow on the surface of porous hard carbon formed by the defective artificial graphite precursor and a soft carbon coating agent.

(4) The coating layer of the prepared nitrogen-doped multi-element carbon-coated graphite composite material is provided with Carbon Nanotubes (CNTs), the carbon nanotubes have high conductivity and large length-diameter ratio and can improve the electron transmission capability of an electrode material, the carbon nanotubes have a hollow structure which is beneficial to absorbing more electrolyte and improving the migration rate of lithium ions in the electrolyte, so that the reversible degree of the reaction of the electrode material is improved, the kinetic limitation in the charge-discharge process is reduced, the deintercalation of the lithium ions is accelerated, the polarization caused by the local accumulation of the electrons in the electrode is greatly reduced, the large-rate performance of a battery is improved, and the migration rate of the lithium ions in the electrolyte is improved.

(5) The coating layer of the prepared nitrogen-doped multi-element carbon-coated graphite composite material comprises nitrogen doping, carbon nano tubes and hard carbon, and the coating layer can facilitate the transfer of heat inside the battery and improve the cycle stability of the battery.

In some embodiments, the soft carbon-based coating agent is a solid phase asphalt and/or a liquid phase asphalt.

In some embodiments, the soft carbon based coating has a coking value of 10% to 80%.

In some embodiments, the nitrogen source is at least one of melamine, urea, and dopamine.

In some embodiments, the activator is at least one of potassium hydroxide, sodium hydroxide, calcium carbonate, and magnesium oxide.

In some embodiments, the raw materials for preparing the clad body further include a pore-forming assistant, and the pore-forming assistant is at least one of coal tar, resin and aromatic oil.

In some embodiments, the mass ratio of the soft carbon based coating agent, the activator and the nitrogen source is 18.2 to 66.6.

In some embodiments, the equipment used for milling is a ball mill, and the ball milling time is from 8h to 20h.

In some embodiments, the equipment used for mixing in step (I) to prepare the coating is a fusion machine or VC mixer, and the mixing time is from 30min to 180min.

In some embodiments, the artificial graphite precursor is shaped petroleum coke or coal-based coke.

In some embodiments, the artificial graphite precursor has a Dv50 of 2 μm to 50 μm and a carbon content of 99% or more.

In some embodiments, the mass ratio of the clad body to the artificial graphite precursor is 5 to 15.

In some embodiments, the equipment used for mixing in the step (II) preparing the precursor is a fusion machine or a VC mixer, and the mixing time is from 60min to 240min.

In some embodiments, the flow rate of the inert atmosphere is from 0.5L/min to 20.0L/min.

In some embodiments, the inert atmosphere comprises at least one of nitrogen, argon, and helium.

In some embodiments, the first carbonization and the second carbonization are performed using equipment that is independently a roller kiln, a rotary kiln, a box furnace, or a shaft furnace.

In some embodiments, the solution employed for pickling is hydrochloric acid, nitric acid, or hydrofluoric acid.

In some embodiments, the second precursor is subjected to an intermediate treatment after the acid wash and then catalyzed, the intermediate treatment comprising sequentially filtering, drying, and grinding the second precursor.

In some embodiments, the metal catalyst solution is a ferric nitrate solution and has a concentration greater than 0 and equal to or less than 0.5M.

In some embodiments, the time of immersion is 0.5h to 2h.

In some embodiments, the drying conditions are vacuum conditions of 80 ℃ to 150 ℃ for 8h to 20h.

In some embodiments, the reducing atmosphere is a mixed gas of hydrogen and an inert gas, the inert atmosphere comprises at least one of nitrogen, argon, and helium, the flow rate of the inert atmosphere is from 100mL/min to 500mL/min, and the flow rate of hydrogen is from 50mL/min to 100mL/min.

In some embodiments, the carbon source comprises at least one of ethylene, methane, acetylene, acetone, and benzene.

In some embodiments, the flow rate of the carbon source is 1L/min to 10L/min.

In some embodiments, the temperature of the first carbonization and the second carbonization is increased with a gradient, and the maximum temperature is each independently increased to 800 ℃ to 900 ℃.

In some embodiments, the temperature rise rates for the first carbonization and the second carbonization are each independently from 1 ℃/min to 5 ℃/min.

In some embodiments, the temperature of the first carbonization and the second carbonization is increased to 250 ℃ to 300 ℃, then sequentially increased to 300 ℃ to 480 ℃, 480 ℃ to 850 ℃, and then the temperature is maintained.

In some embodiments, the incubation time is from 120min to 300min.

In some embodiments, the post-treatment comprises sequentially purifying, washing, drying, grinding, graphitizing, and sieving the carbonized product obtained after the second carbonization treatment.

In order to achieve the above object, the present invention provides, in a second aspect, a nitrogen-doped multi-carbon coated graphite composite material comprising a graphite core and a multi-carbon layer coating the graphite core, the multi-carbon layer comprising nitrogen-doping, carbon nanotubes and hard carbon. The nitrogen-doped multi-carbon-coated graphite composite material has higher conductivity, better first reversible specific capacity, first coulombic efficiency and cycle performance, and is particularly suitable for serving as a negative electrode material of a market power quick-charging battery.

In some embodiments, the first reversible specific capacity of the nitrogen-doped multi-element carbon-coated graphite composite material is not less than 350mAh/g, and the first coulombic efficiency is not less than 90%.

In order to achieve the above object, a third aspect of the present invention provides a secondary battery, including a positive electrode material and a negative electrode material, where the negative electrode material is a nitrogen-doped multi-component carbon-coated graphite composite material prepared by the foregoing method for preparing a nitrogen-doped multi-component carbon-coated graphite composite material or the foregoing nitrogen-doped multi-component carbon-coated graphite composite material.

Drawings

Fig. 1 is a TEM image of a nitrogen-doped multi-component carbon-coated graphite composite material of example 1.

Detailed Description

The nitrogen-doped multi-carbon-coated graphite composite material can be used as a negative active material to be applied to secondary batteries. The secondary battery includes a positive electrode material and a negative electrode material. The positive electrode material comprises at least one of a lithium cobaltate positive electrode material, a lithium iron phosphate positive electrode material, a lithium nickel cobalt manganese oxide positive electrode material and a lithium nickel cobalt aluminate positive electrode material. The nitrogen-doped multi-element carbon-coated graphite composite material can be used alone as a negative active material, and can also be mixed with other negative active materials (such as silicon-based materials, soft carbon, hard carbon and the like) for use. The nitrogen-doped multi-element carbon-coated graphite composite material has better conductivity, so that a conductive agent can be added or not added according to actual use when a negative pole piece is prepared.

The nitrogen-doped multi-carbon-coated graphite composite material comprises a graphite core and a multi-carbon layer coating the graphite core, wherein the multi-carbon layer comprises nitrogen doping, carbon nano tubes and hard carbon. The carbon nano-tube and the hard carbon are carbon materials, so the coating layer is a multi-carbon layer. The first reversible specific capacity of the nitrogen-doped multi-carbon-coated graphite composite material is not less than 350mAh/g, and specifically, but not limited to 350mAh/g, 351mAh/g, 352mAh/g, 353mAh/g, 354mAh/g, 355mAh/g, 356mAh/g, 357mAh/g and 358mAh/g. The first coulombic efficiency is more than or equal to 90 percent, and can be specifically but not limited to 90 percent, 91 percent, 92 percent, 93 percent, 94 percent and 95 percent.

The preparation method of the nitrogen-doped multi-element carbon-coated graphite composite material comprises the steps of (I) preparing a coating body, (II) preparing a first precursor, step (III) carrying out first carbonization treatment, step (IV) carrying out acid washing, step (V) carrying out catalysis and step (VI) carrying out second carbonization treatment.

The preparation of the coating body in the step (I) comprises the step of grinding and mixing a soft carbon coating agent, an activating agent and a nitrogen source to form the coating body, wherein the activating agent is a particle with an oxygen-containing group on the surface.

The mass ratio of the soft carbon coating agent to the nitrogen source is, by way of example, from.

In one embodiment, the soft carbon coating is solid phase asphalt and/or liquid phase asphalt and has a coking value of 10% to 80%, in certain embodiments 30% to 80%, and in certain embodiments 50% to 80%. The coking values may be, but are not limited to, specifically 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%.

As an embodiment, the nitrogen source is at least one of melamine, urea and dopamine, the nitrogen-containing substances can form a three-dimensional network structure before carbonization, and nitrogen atoms are combined in a complex mesh structure after sintering, so that the conductivity of the material can be improved, and the prepared nitrogen-doped multi-element carbon-coated graphite composite material has better first coulombic efficiency.

As an embodiment, the activator is at least one of potassium hydroxide, sodium hydroxide, calcium carbonate, and magnesium oxide, and as an example, the activator is potassium hydroxide. In the preparation process of the material, surface groups, such as oxygen-containing groups such as phenol groups, ether groups, carbonyl groups and the like, which are inevitably existed in the particles, and some acid groups exist, so that the material can be used as an activator for providing an oxygen component to help the soft carbon coating agent to be converted into a hard carbon structure from soft carbon after carbonization.

As an embodiment, the preparation raw material of the clad body further comprises a pore-forming assistant, wherein the pore-forming assistant is at least one of coal tar, resin and aromatic oil. The substances form a hard carbon material before carbonization, and can play a pore-forming role in the activation process so as to improve the porosity of the prepared nitrogen-doped multi-element carbon-coated graphite composite material and further improve the dynamic performance of the material.

In one embodiment, the apparatus used for milling is a ball mill, and the milling time is 8h to 20h, and specifically, but not limited to, 8h, 10h, 12h, 14h, 16h, 18h, and 20h.

As an embodiment, the equipment used for mixing in the preparation of the encapsulates in step (I) is a fusion machine or VC mixer, and the fusion machine can be a normal temperature fusion machine or a heating fusion machine, including but not necessarily limited to a VC mixer. The mixing time is 30 min-180 min, and specifically, but not limited to, 30min, 50min, 70min, 90min, 110min, 130min, 150min, 170min, 180min.

The step (II) of preparing the first precursor comprises mixing the cladding body and the artificial graphite precursor.

As an embodiment, the artificial graphite precursor is shaped petroleum coke or coal coke, and the shaping equipment can be a spheroidizing shaper. The Dv50 of the artificial graphite precursor is from 2 μm to 50 μm, and in some embodiments, the Dv50 of the artificial graphite precursor is from 2 μm to 30 μm, and in some embodiments, the Dv50 of the artificial graphite precursor is from 8 μm to 11 μm. The Dv50 of the artificial graphite precursor may specifically, but not limited to, be 2 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 16 μm, 20 μm, 24 μm, 28 μm, 30 μm, 35 μm, 40 μm, 43 μm, 48 μm, 50 μm. The carbon content of the artificial graphite precursor is 99% or more, and as some embodiments, the carbon content of the artificial graphite precursor is 99.9% or more. The carbon content of the artificial graphite precursor may specifically, but not limited to, be 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, 99.91%, 99.92%, 99.93%, 99.94%, 99.95%, 99.96%, 99.97%, 99.98%, 99.99%.

As an embodiment, the mass ratio of the clad body to the artificial graphite precursor is 5 to 15, and may be, but not limited to, 5.

As an embodiment, the mixing equipment used in the step (II) of preparing the first precursor is a fusion machine or a VC mixer, and the fusion machine can be a normal temperature fusion machine or a heating fusion machine, including but not necessarily limited to a VC mixer. The mixing time is 60 min-240 min, and specifically, but not limited to, 60min, 80min, 100min, 120min, 140min, 160min, 180min, 200min, 220min, and 240min.

And (III) performing first carbonization treatment on the first precursor in an inert atmosphere to obtain a carbonized product.

As an embodiment, the inert atmosphere comprises at least one of nitrogen, argon and helium. The flow rate of the inert atmosphere is 0.5L/min to 20.0L/min, and specifically, but not limited to, 0.5L/min, 1.5L/min, 2.5L/min, 3.5L/min, 4.5L/min, 5.5L/min, 6.5L/min, 7.5L/min, 8.5L/min, 9.5L/min, 11.0L/min, 13.0L/min, 15.0L/min, 17.0L/min, 19.0L/min, 20.0L/min.

As an embodiment, the first carbonization is performed by using a roller kiln, a rotary kiln, a box furnace or a vertical kettle, and as an example, the first carbonization is performed by using a roller kiln.

As an embodiment, the temperature of the first carbonization is increased by gradient, and the maximum temperature is increased to 800 ℃ to 900 ℃, and the maximum temperature can be, but is not limited to, 800 ℃, 820 ℃, 840 ℃, 860 ℃, 880 ℃, 900 ℃. The adoption of gradient temperature rise is beneficial to the conversion of the soft carbon coating agent from soft carbon to hard carbon. The temperature rise rate of carbonization is 1 ℃/min to 5 ℃/min, and the temperature rise rate can be but is not limited to 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min and 5 ℃/min. The carbonization temperature can be increased by four gradients, for example, the carbonization temperature is increased to 250 ℃ to 300 ℃, then sequentially increased to 300 ℃ to 480 ℃ and 480 ℃ to 850 ℃, and then heat preservation is carried out for 120min to 300min, and specifically, but not limited to, 120min, 130min, 150min, 170min, 190min, 210min, 230min, 250min, 270min, 290min and 300min.

And (IV) acid washing comprises the step of carrying out acid washing on the carbonized product to obtain a second precursor.

In one embodiment, the solution used for the acid cleaning is hydrochloric acid, nitric acid or hydrofluoric acid, or a diluted solution of hydrochloric acid, nitric acid or hydrofluoric acid, and the acid cleaning is performed to remove residual ions.

As an embodiment, after the acid washing, the second precursor is subjected to intermediate treatment and then catalyzed, wherein the intermediate treatment comprises sequentially filtering, drying and grinding the second precursor. The filtration includes suction filtration, centrifugation or filter pressing. The filtration mode is suction filtration, centrifugation or filter pressing. The drying equipment is oven or drier, the temperature for drying is 80 deg.C-160 deg.C, and the drying temperature can be, but is not limited to, 80 deg.C, 100 deg.C, 120 deg.C, 140 deg.C, 160 deg.C. The drying time is 1h to 36h, and the drying time can be specifically but not limited to 1h, 5h, 10h, 15h, 20h, 25h, 30h and 36h. The equipment adopted for grinding is a ball mill, and the ball milling time is 10h to 20h, and specifically, but not limited to, 10h, 11h, 13h, 15h, 17h, 19h and 20h.

And the step (V) of catalyzing comprises the step of immersing the second precursor into a metal catalyst solution and drying to obtain a third precursor.

In one embodiment, the metal catalyst solution is an iron nitrate solution and has a concentration of 0M or more and 0.5M or less. By way of example, the concentration of the ferric nitrate solution may be, but is not limited to, 0.01M, 0.05M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M.

As an embodiment, the second precursor is immersed in the metal catalyst solution for 0.5h to 2h, and the immersion time may be, but is not limited to, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, as examples.

As an embodiment, the drying condition is vacuum environment and heat preservation is carried out for 8h to 20h at the temperature of 80 ℃ to 150 ℃. As an example, the drying temperature may be, but is not limited to, 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃. The holding time can be, but is not limited to, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h.

And (VI) introducing a carbon source into the third precursor in a reducing atmosphere to perform second carbonization treatment, and performing post-treatment.

In one embodiment, the reducing atmosphere is a mixture of hydrogen and an inert gas. The inert atmosphere comprises at least one of nitrogen, argon and helium. The flow rate of the inert atmosphere is 100mL/min to 500mL/min, and by way of example, the flow rate of the inert atmosphere can be, but is not limited to, 100mL/min, 150mL/min, 200mL/min, 250mL/min, 300mL/min, 350mL/min, 400mL/min, 450mL/min, 500mL/min. The flow rate of hydrogen is 50mL/min to 100mL/min, and the flow rate of hydrogen may be, but is not limited to, 50mL/min, 60mL/min, 70mL/min, 80mL/min, 90mL/min, 100mL/min, as examples.

As an embodiment, the second carbonization is performed by using a roller kiln, a rotary kiln, a box furnace or a vertical kettle, and as an example, the second carbonization is performed by using a roller kiln.

In one embodiment, the temperature of the second carbonization is increased by gradient, and the maximum temperature is increased to 800 ℃ to 900 ℃, and the maximum temperature can be, but is not limited to, 800 ℃, 820 ℃, 840 ℃, 860 ℃, 880 ℃, 900 ℃. The adoption of gradient temperature rise is beneficial to the conversion of the soft carbon coating agent from soft carbon to hard carbon. The temperature rise rate of carbonization is 1 ℃/min to 5 ℃/min, and the temperature rise rate can be but is not limited to 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min and 5 ℃/min. The carbonization temperature can be increased by four gradients, for example, the carbonization temperature is increased to 250 ℃ to 300 ℃, then sequentially increased to 300 ℃ to 480 ℃ and 480 ℃ to 850 ℃, and then heat preservation is carried out for 120min to 300min, and specifically, but not limited to, 120min, 130min, 150min, 170min, 190min, 210min, 230min, 250min, 270min, 290min and 300min.

As an embodiment, the carbon source includes at least one of ethylene, methane, acetylene, acetone, and benzene. The flow rate of the carbon source is 1L/min to 10L/min, and may be, for example, but not limited to, 1L/min, 2L/min, 3L/min, 4L/min, 5L/min, 6L/min, 7L/min, 8L/min, 9L/min, 10L/min.

As an embodiment, the post-treatment comprises purifying, washing, drying, grinding, graphitizing and sieving the carbonized product obtained after the second carbonization treatment in sequence. The solution used for purification is 50 to 80wt.% HNO ₃ By way of example, HNO ₃ The concentration of (d) may be, but is not limited to, 50wt.%, 55wt.%, 60wt.%, 65wt.%, 70wt.%, 75wt.%, 80wt.%. The time for purification is 0.5h to 2h, and the time for purification may not be limited to 0.5h, 0.7h, 0.9h, 1.1h, 1.3h, 1.5h, 1.7h, 1.9h, 2h, as an example. As an example, the solvent for washing is water, ethanol, or a mixture of water and ethanol. The drying equipment is an oven or a dryer, and the drying temperature is 60 ℃ to 160 ℃, for example, the drying temperature can be, but is not limited to, 60 ℃, 80 ℃, 100 ℃, 120 ℃, 140 ℃ and 160 ℃. The drying time is 1h to 48h, and as an example, the drying time may be specifically, but not limited to, 1h, 5h, 10h, 15h, 20h, 25h, 30h, 36h, 40h, 44h, 48h. The equipment adopted for grinding is a ball mill, and the ball milling time is 8h to 20h, and specifically, but not limited to, 8h, 10h, 11h, 13h, 15h, 17h, 19h and 20h. The graphitization equipment can adopt AchesonThe graphitization furnace can adopt a 400-mesh screen for sieving.

To better illustrate the objects, technical solutions and advantages of the present invention, the present invention will be further described with reference to specific examples. It should be noted that the following implementation of the method is a further explanation of the present invention, and should not be taken as a limitation of the present invention.

Example 1

The preparation method of the nitrogen-doped multi-element carbon-coated graphite composite material of the embodiment includes the following steps.

(I) Preparation of the clad

13.2kg of liquid phase asphalt (the softening point is 280 ℃ and the coking value is 70 percent), 6.6kg of KOH and 2.2kg of melamine are ground for 12 hours by a ball mill and then mixed for 90 minutes at the rotating speed of 200r/min by a VC100 mixer to form a coating body.

(II) preparation of the first precursor

Mixing 22kg of coating body and 200kg of shaped petroleum coke A (Dv 50 is 10 mu m, and the carbon content is more than or equal to 99 percent) in VC500 for 120min to obtain a first precursor.

(III) first carbonization treatment

And (3) putting the precursor into a carbonization crucible, putting the carbonization crucible into a roller kiln for carbonization, and reacting according to the following heating mode under the condition of introducing 5L/min of nitrogen to obtain a carbonized product.

A heating mode: (1) a first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) a second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is increased to 850 ℃, and the heating rate is 2.06 ℃/min; (4) a fourth warming step: keeping the temperature at 850 ℃ for 180min.

(IV) acid washing

And soaking the carbonized product in 1M hydrochloric acid for 24h, performing ultrasonic treatment for 12h by using an ultrasonic device, repeatedly washing the carbonized product with deionized water for 10 times until the carbonized product is neutral, performing suction filtration, drying the carbonized product in a drying machine at 100 ℃ for 10h, and grinding the dried product for 15h by using a ball mill to obtain a second precursor.

(V) catalysis

And soaking the second precursor in 0.5mol/L ferric nitrate solution for 2h, and then preserving heat at 100 ℃ in a vacuum environment for 12h to obtain a third precursor.

(VI) second carbonization treatment

Transferring the third precursor into a rotary furnace, and introducing Ar/H ₂ Introducing 6L/min of ethylene gas into the mixed gas (the flow rates are respectively 300mL/min/70 mL/min), and reacting according to the following heating mode to obtain a carbonized product.

A heating mode: (1) first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is raised to 850 ℃, and the heating rate is 2.06 ℃/min; (4) fourth warming step: keeping the temperature at 850 ℃ for 180min.

(VII) post-treatment

Cooling the obtained carbonized product to room temperature, and then sequentially carrying out 65wt.% of HNO ₃ Purifying for 1h, washing with deionized water, drying in an oven at 100 ℃ for 10h, grinding by a ball mill for 5h, graphitizing by an Acheson graphitizing furnace, and sieving by a 400-mesh sieve.

The result of the examination of the nitrogen-doped multi-component carbon-coated graphite composite material prepared in example 1 by XRD is shown in fig. 1, and it can be seen from fig. 1 that the nitrogen-doped multi-component carbon-coated graphite composite material includes a graphite core and a multi-component carbon layer coating the graphite core, and the multi-component carbon layer includes nitrogen-doped carbon nanotubes and hard carbon.

Example 2

The preparation method of the nitrogen-doped multi-element carbon-coated graphite composite material of the embodiment comprises the following steps.

(I) Preparation of the clad

13.2kg of coal tar (the softening point is 280 ℃ and the coking value is 70 percent), 6.6kg of KOH and 2.2kg of urea are ground for 12 hours by a ball mill, and then are mixed for 90 minutes at the rotating speed of 200r/min by a VC100 mixer to form a coating body.

(II) preparation of the first precursor

(III) first carbonization treatment

And (3) putting the precursor into a carbonization crucible, putting the carbonization crucible into a roller kiln for carbonization, and reacting in a heating mode under the condition of introducing nitrogen gas of 5L/min to obtain a carbonized product.

A heating mode: (1) first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is raised to 850 ℃, and the heating rate is 2.06 ℃/min; (4) a fourth warming step: keeping the temperature at 850 ℃ for 180min.

(IV) acid washing

(V) catalysis

(VI) second carbonization treatment

A heating mode: (1) a first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) a second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is increased to 850 ℃, and the heating rate is 2.06 ℃/min; (4) fourth warming step: keeping the temperature at 850 ℃ for 180min.

(VII) post-treatment

Cooling the obtained carbonized product to room temperature, and sequentially carrying out 65wt.% of HNO ₃ Purifying for 1h, washing with deionized water, drying in an oven at 100 ℃ for 10h, grinding in a ball mill for 5h, graphitizing in an Acheson graphitizing furnace, and sieving with a 400-mesh sieve.

Example 3

(I) Preparation of the clad

13.2kg of liquid phase asphalt (the softening point is 280 ℃, the coking value is 70 percent), 6.6kg of KOH and 2.2kg of dopamine are ground for 12 hours by a ball mill, and then are mixed for 90 minutes at the rotating speed of 200r/min by a VC100 mixer to form a coating body.

(II) preparation of the first precursor

(III) first carbonization treatment

(IV) acid washing

And soaking the carbonized product in 1M hydrochloric acid for 24 hours, performing ultrasonic treatment for 12 hours by using an ultrasonic device, repeatedly washing with deionized water for 10 times until the carbonized product is neutral, performing suction filtration, drying in a drying machine at 100 ℃ for 10 hours, and grinding for 15 hours by using a ball mill to obtain a second precursor.

(V) catalysis

And soaking the second precursor in 0.5mol/L ferric nitrate solution for 2h, and then preserving heat for 12h at 100 ℃ in a vacuum environment to obtain a third precursor.

(VI) second carbonization treatment

(VII) post-treatment

Example 4

(I) Preparation of the clad

13.2kg of solid phase asphalt (the softening point is 250 ℃ and the coking value is 77 percent), 6.6kg of KOH and 2.2kg of melamine are ground for 12 hours by a ball mill, and then are mixed for 90 minutes by a VC100 mixer at the rotating speed of 200r/min to form a coating body.

(II) preparation of the first precursor

(III) first carbonization treatment

A heating mode: (1) first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) a second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is raised to 850 ℃, and the heating rate is 2.06 ℃/min; (4) fourth warming step: keeping the temperature at 850 ℃ for 180min.

(IV) acid washing

(V) catalysis

(VI) second carbonization treatment

A heating mode: (1) first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) a second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is increased to 850 ℃, and the heating rate is 2.06 ℃/min; (4) a fourth warming step: keeping the temperature at 850 ℃ for 180min.

(VII) post-treatment

Example 5

(I) Preparation of the clad

13.2kg of liquid phase asphalt (the softening point is 280 ℃ and the coking value is 70 percent), 6.6kg of calcium carbonate and 2.2kg of melamine are ground for 12 hours by a ball mill, and then are mixed for 90 minutes at the rotating speed of 200r/min by a VC100 mixer to form a coating body.

(II) preparation of the first precursor

(III) first carbonization treatment

(IV) acid washing

(V) catalysis

(VI) second carbonization treatment

Transferring the third precursor into a rotary furnace, and introducing Ar/H ₂ Introducing 6L/min of ethylene gas into the mixed gas (the flow is respectively 300mL/min/70 mL/min), and reacting according to the following heating mode to obtain a carbonized product.

(VII) post-treatment

Example 6

(I) Preparation of the clad

13.2kg of liquid phase asphalt (the softening point is 280 ℃ and the coking value is 70 percent), 6.6kg of magnesium oxide and 2.2kg of melamine are ground for 12 hours by a ball mill and then mixed for 90 minutes at the rotating speed of 200r/min by a VC100 mixer to form a coating body.

(II) preparation of the first precursor

(III) first carbonization treatment

(IV) acid washing

(V) catalysis

(VI) second carbonization treatment

(VII) post-treatment

Example 7

(I) Preparation of the clad

11kg of liquid phase asphalt (the softening point is 280 ℃ and the coking value is 70 percent), 2.2kg of coal tar (the coking value is 66 percent), 6.6kg of KOH and 2.2kg of melamine are ground by a ball mill for 12 hours and then mixed by a VC100 mixer for 90 minutes at the rotating speed of 200r/min to form a coating body.

(II) preparation of the first precursor

(III) first carbonization treatment

A heating mode: (1) a first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) a second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is raised to 850 ℃, and the heating rate is 2.06 ℃/min; (4) a fourth warming step: keeping the temperature at 850 ℃ for 180min.

(IV) acid washing

(V) catalysis

(VI) second carbonization treatment

Transferring the third precursor into a rotary furnace, and introducingInto Ar/H ₂ Introducing 6L/min of ethylene gas into the mixed gas (the flow rates are respectively 300mL/min/70 mL/min), and reacting according to the following heating mode to obtain a carbonized product.

(VII) post-treatment

Example 8

(I) Preparation of the clad

14.6kg of liquid phase asphalt (the softening point is 280 ℃ and the coking value is 70 percent), 8.2kg of KOH and 2.5kg of melamine are ground for 10 hours by a ball mill, and then are mixed for 90 minutes by a VC100 mixer at the rotating speed of 200r/min to form a coating body.

(II) preparation of the first precursor

30kg of the cladding and 160kg of the shaped coal-based coke A (Dv 50 is 20 μm, carbon content is more than or equal to 99%) are mixed in VC500 for 120min to obtain a first precursor.

(III) first carbonization treatment

A heating mode: (1) a first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is raised to 850 ℃, and the heating rate is 2.06 ℃/min; (4) fourth warming step: keeping the temperature at 850 ℃ for 180min.

(IV) acid washing

And soaking the carbonized product in 1M nitric acid for 24h, performing ultrasonic treatment for 12h by using an ultrasonic device, repeatedly washing with deionized water for 10 times until the carbonized product is neutral, performing suction filtration, drying in a drying machine at 100 ℃ for 10h, and grinding for 15h by using a ball mill to obtain a second precursor.

(V) catalysis

And soaking the second precursor in 0.35mol/L ferric nitrate solution for 2h, and then preserving heat at 100 ℃ in a vacuum environment for 12h to obtain a third precursor.

(VI) second carbonization treatment

A heating mode: (1) a first warming step: the temperature in the room is increased to 280 ℃, and the heating rate is 2.65 ℃/min; (2) second warming step: the temperature is raised to 400 ℃, and the temperature raising rate is 1.55 ℃/min; (3) a third warming step: the temperature is raised to 400 ℃, and the temperature raising rate is 1.55 ℃/min; (4) a fourth warming step: keeping the temperature at 800 ℃ for 200min.

(VII) post-treatment

Cooling the obtained carbonized product to room temperature, and then sequentially carrying out 65wt.% of HNO ₃ Purifying for 2h, washing with deionized water, drying in an oven at 120 ℃ for 12h, grinding in a ball mill for 8h, graphitizing in an Acheson graphitizing furnace, and sieving with a 400-mesh sieve.

Example 9

(I) Preparation of the clad

15.2kg of liquid phase asphalt (the softening point is 280 ℃, the coking value is 70 percent), 7.8kg of KOH and 2.2kg of dopamine are ground for 10 hours by a ball mill, and then mixed for 80 minutes at the rotating speed of 150r/min by a fusion machine to form a cladding body.

(II) preparation of the first precursor

Mixing 22kg of coating body and 230kg of shaped petroleum coke A (Dv 50 is 10 mu m, and the carbon content is more than or equal to 99 percent) in VC500 for 120min to obtain a first precursor.

(III) first carbonization treatment

And (3) putting the precursor into a carbonization crucible, then putting the carbonization crucible into a rotary furnace for carbonization, and reacting according to the following heating mode under the condition of introducing argon gas of 10L/min to obtain a carbonized product.

A heating mode: (1) a first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) a second warming step: the temperature is increased to 480 ℃, and the heating rate is 2.25 ℃/min; (3) a third warming step: the temperature is raised to 850 ℃, and the heating rate is 2.60 ℃/min; (4) a fourth warming step: keeping the temperature at 850 ℃ for 180min.

(IV) acid washing

And soaking the carbonized product in 1M hydrochloric acid for 20h, performing ultrasonic treatment for 10h by using an ultrasonic device, repeatedly washing the carbonized product with deionized water for 12 times until the carbonized product is neutral, performing suction filtration, drying the carbonized product in a drying machine at the temperature of 120 ℃ for 8h, and grinding the dried product for 13h by using a ball mill to obtain a second precursor.

(V) catalysis

And soaking the second precursor in 0.5mol/L ferric nitrate solution for 1.5h, and then preserving heat at 130 ℃ in a vacuum environment for 15h to obtain a third precursor.

(VI) second carbonization treatment

Transferring the third precursor to a rotary furnace, and introducing N ₂ /H ₂ Introducing 8L/min methane gas into the mixed gas (the flow is respectively 400mL/min/80 mL/min), and reacting according to the following heating mode to obtain the carbonized product.

A heating mode: (1) a first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is raised to 850 ℃, and the heating rate is 2.06 ℃/min; (4) a fourth warming step: keeping the temperature at 850 ℃ for 180min.

(VII) post-treatment

Cooling the obtained carbonized product to room temperature, and sequentially carrying out 70wt.% of HNO ₃ Purifying for 1h, washing with deionized water, drying in an oven at 100 ℃ for 13h, grinding by a ball mill for 5h, graphitizing by an Acheson graphitizing furnace, and sieving by a 400-mesh sieve.

Example 10

(I) Preparation of the clad

(II) preparation of the first precursor

(III) first carbonization treatment

And putting the precursor into a carbonization crucible, putting the carbonization crucible into a roller kiln for carbonization, heating the precursor from room temperature to 850 ℃ under the condition of introducing 5L/min of nitrogen, wherein the heating rate is 2.5 ℃/min, and preserving the heat for 180min for reaction to obtain a carbonized product.

(IV) acid washing

(V) catalysis

(VI) second carbonization treatment

A heating mode: (1) first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is increased to 850 ℃, and the heating rate is 2.06 ℃/min; (4) a fourth warming step: keeping the temperature at 850 ℃ for 180min.

(VII) post-treatment

Comparative example 1

(I) Preparation of the first precursor

Mixing 22kg of liquid phase asphalt (softening point of 280 ℃ and coking value of 70%) and 200kg of shaped petroleum coke A (Dv 50 of 10 μm, carbon content of more than or equal to 99%) in VC500 for 90min to obtain a first precursor.

(II) first carbonization treatment

(III) acid washing

(IV) catalysis

(V) second carbonization treatment

A heating mode: (1) a first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is increased to 850 ℃, and the heating rate is 2.06 ℃/min; (4) a fourth warming step: keeping the temperature at 850 ℃ for 180min.

(VI) post-treatment

Comparative example 2

(I) Preparation of the clad

19.8kg of liquid-phase asphalt (the softening point is 280 ℃ and the coking value is 70%) and 2.2kg of melamine are ground by a ball mill for 12 hours and then mixed by a VC100 mixer at the rotating speed of 200r/min for 90min to form the coating body.

(II) preparation of the first precursor

(III) first carbonization treatment

(IV) acid washing

(V) catalysis

(VI) second carbonization treatment

(VII) post-treatment

Cooling the obtained carbonized product to room temperature, and then sequentially carrying out 65wt.% of HNO ₃ Purifying for 1h, washing with deionized water, drying in an oven at 100 ℃ for 10h, grinding in a ball mill for 5h, graphitizing in an Acheson graphitizing furnace, and sieving with a 400-mesh sieve.

Comparative example 3

(I) Preparation of the clad

13.2kg of liquid phase asphalt (the softening point is 280 ℃ and the coking value is 70 percent) and 6.6kg of KOH are ground for 12 hours by a ball mill and then mixed for 90 minutes by a VC100 mixer at the rotating speed of 200r/min to form a coating body.

(II) preparation of the first precursor

(III) first carbonization treatment

(IV) acid washing

(V) catalysis

(VI) second carbonization treatment

(VII) post-treatment

Cooling the obtained carbonized product to room temperature, and sequentially carrying out 65wt.% of HNO ₃ Purifying for 1h, washing with deionized water, drying in an oven at 100 ℃ for 10h, grinding by a ball mill for 5h, graphitizing by an Acheson graphitizing furnace, and sieving by a 400-mesh sieve.

Comparative example 4

(I) Preparation of the clad

13.2kg of liquid phase asphalt (the softening point is 280 ℃ and the coking value is 70 percent), 6.6kg of KOH and 2.2kg of melamine are ground for 12 hours by a ball mill, and then are mixed for 90 minutes by a VC100 mixer at the rotating speed of 200r/min to form a coating body.

(II) preparation of the first precursor

(III) first carbonization treatment

(IV) acid washing

(V) second carbonization treatment

A heating mode: (1) a first warming step: the temperature in the room is increased to 300 ℃, and the heating rate is 3 ℃/min; (2) second warming step: the temperature is increased to 480 ℃, and the heating rate is 1.25 ℃/min; (3) a third warming step: the temperature is increased to 850 ℃, and the heating rate is 2.06 ℃/min; (4) fourth warming step: keeping the temperature at 850 ℃ for 180min.

(VI) post-treatment

Cooling the obtained carbonized product to room temperature, and then sequentially carrying out 65wt.% of HNO ₃ Purifying for 1h, washing with deionized water, and drying in oven at 100 deg.C 1Grinding for 0h by using a ball mill for 5h, graphitizing by using an Acheson graphitizing furnace, and sieving by using a 400-mesh sieve.

The nitrogen-doped multi-component carbon-coated graphite composite materials obtained in examples 1 to 10 and comparative examples 1 to 4 were measured for average particle size Dv50 using a particle size analyzer, specific surface area using a macbeck specific surface area analyzer 3020, and conductivity using a conductivity meter, respectively, and the results are shown in table 1.

The nitrogen-doped multi-element carbon-coated graphite composite materials obtained in examples 1 to 10 and comparative examples 1 to 4 are respectively used as negative electrode active materials, uniformly mixed with polyvinylidene fluoride and conductive carbon black Super-P according to a mass ratio of 70.

The metal lithium sheet is used as a counter electrode, and the electrolyte is 1M LiPF ₆ DEC and DMC = l:1 (volume ratio), and a CR2032 type button cell is assembled in a glove box filled with inert gas by using a polypropylene microporous membrane as a diaphragm. The charging and discharging test of the button cell is carried out on a cell test system of blue-electricity electronic products, inc. in Wuhan city, under the condition of normal temperature, the constant current charging and discharging is carried out at 0.1C, the charging and discharging voltage is limited to 0.005V to 1.5V, the first reversible specific capacity, the first coulombic efficiency and the cycle performance of the button cell are tested, and the test results are shown in Table 1.

TABLE 1 physical and electrochemical Properties of the graphite-based negative electrode materials obtained in the examples

As can be seen from the results in table 1, compared with comparative examples 1 to 4, in the preparation method of the nitrogen-doped multi-component carbon-coated graphite composite material according to embodiments 1 to 10 of the present invention, the hard carbon coating layer containing nitrogen and carbon nanotubes can be formed by using the particulate matter containing oxygen groups as an activator, coating the particulate matter with a nitrogen source, and then sequentially performing acid washing, catalysis, and carbonization, and the prepared material has a low specific surface area, high conductivity, and good first reversible specific capacity, first coulombic efficiency, and cycle performance.

It is understood from comparative examples 1 to 3 that the nitrogen-containing compound is melamine, which is more excellent in recycling performance, and this may be associated with a higher nitrogen content per unit mass of melamine. It can be seen from comparison examples 1, 5 and 6 that when the activating agent is KOH, the cycle performance of the material is better, which may be related to the KOH chemically reacting with the asphalt surface and combining to form more stable oxygen-containing groups, so as to make the produced hard carbon structure most stable. As can be seen by comparing example 1 and example 10, the materials produced using a gradient temperature increase during carbonization performed better, probably because the gradient temperature increase facilitates the conversion of the soft carbon coating agent from soft carbon to hard carbon.

It should be finally noted that the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to the embodiments, and it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. The preparation method of the nitrogen-doped multi-carbon-coated graphite composite material is characterized by comprising the following steps:

(I) Preparation of the clad

(II) preparation of the first precursor

(III) first carbonization treatment

(IV) acid washing

Acid washing is carried out on the carbonized product to obtain a second precursor;

(V) catalysis

(VI) second carbonization treatment

2. The method for producing a nitrogen-doped multi-carbon-coated graphite composite material according to claim 1, characterized by comprising at least one of the following features (1) to (23):

(1) The soft carbon coating agent is solid-phase asphalt and/or liquid-phase asphalt;

(2) The coking value of the soft carbon coating agent is 10 to 80 percent;

(3) The nitrogen source is at least one of melamine, urea and dopamine;

(4) The activating agent is at least one of potassium hydroxide, sodium hydroxide, calcium carbonate and magnesium oxide;

(5) The preparation raw material of the cladding body also comprises a pore-forming auxiliary agent, wherein the pore-forming auxiliary agent is at least one of coal tar, resin and aromatic oil;

(6) The mass ratio of the soft carbon coating agent, the activating agent and the nitrogen source is 18.2-66.6;

(7) The grinding equipment is a ball mill, and the ball milling time is 8-20 h;

(8) The equipment adopted for mixing in the step (I) of preparing the coating body is a fusion machine or a VC mixer, and the mixing time is 50-180 min;

(9) The artificial graphite precursor is shaped petroleum coke or coal-based coke;

(10) The Dv50 of the artificial graphite precursor is 2-50 mu m, and the carbon content is more than or equal to 99 percent;

(11) The mass ratio of the cladding body to the artificial graphite precursor is 5-15;

(12) In the step (II), the mixing equipment used in the preparation of the first precursor is a fusion machine or a VC mixer, and the mixing time is 60-240 min;

(13) The flow rate of the inert atmosphere is 0.5L/min to 20.0L/min;

(14) The inert atmosphere comprises at least one of nitrogen, argon and helium;

(15) The equipment adopted for the first carbonization and the second carbonization are respectively and independently a roller kiln, a rotary furnace, a box furnace or a vertical kettle;

(16) The solution adopted by the acid cleaning is hydrochloric acid, nitric acid or hydrofluoric acid;

(17) After the acid washing, carrying out intermediate treatment on the second precursor, and then carrying out the catalysis, wherein the intermediate treatment comprises filtering, drying and grinding the second precursor in sequence;

(18) The metal catalyst solution is ferric nitrate solution, and the concentration is more than 0 and less than or equal to 0.5M;

(19) The immersion time is 0.5h to 2h;

(20) The drying condition is that the vacuum environment is kept for 8 to 20 hours at a temperature of between 80 and 150 ℃;

(21) The reducing atmosphere is a mixed gas of hydrogen and inert gas, the inert atmosphere comprises at least one of nitrogen, argon and helium, the flow rate of the inert atmosphere is 100mL/min to 500mL/min, and the flow rate of the hydrogen is 50mL/min to 100mL/min;

(22) The carbon source comprises at least one of ethylene, methane, acetylene, acetone and benzene;

(23) The flow rate of the carbon source is 1L/min to 10L/min.

3. The method for preparing the nitrogen-doped multi-component carbon-coated graphite composite material according to claim 1, wherein the temperatures of the first carbonization and the second carbonization are increased by gradient temperature, and the maximum temperatures are independently increased to 800 ℃ to 900 ℃.

4. The method of preparing the nitrogen-doped multi-component carbon-coated graphite composite material according to claim 1, wherein the temperature increase rates of the first carbonization and the second carbonization are each independently 1 ℃/min to 5 ℃/min.

5. The method for preparing the nitrogen-doped multi-element carbon-coated graphite composite material according to claim 3, wherein the temperature of the first carbonization and the second carbonization is increased to 250 ℃ to 300 ℃, then sequentially increased to 300 ℃ to 480 ℃, and then increased to 480 ℃ to 850 ℃, and then the temperature is maintained.

6. The method for preparing the nitrogen-doped multi-element carbon-coated graphite composite material according to claim 5, wherein the heat preservation time is 120min to 300min.

7. The method for preparing the nitrogen-doped multi-element carbon-coated graphite composite material according to claim 1, wherein the post-treatment comprises the steps of sequentially purifying, washing, drying, grinding, graphitizing and sieving the carbonized product obtained after the second carbonization treatment.

8. The nitrogen-doped multi-carbon-coated graphite composite material is characterized by comprising a graphite core and a multi-carbon layer coating the graphite core, wherein the multi-carbon layer comprises nitrogen doping, carbon nano tubes and hard carbon.

9. The nitrogen-doped multi-element carbon-coated graphite composite material according to claim 8, wherein the first reversible specific capacity is not less than 350mAh/g, and the first coulombic efficiency is not less than 90%.

10. A secondary battery comprising a positive electrode material and a negative electrode material, wherein the negative electrode material is the nitrogen-doped multi-component carbon-coated graphite composite material prepared by the method for preparing the nitrogen-doped multi-component carbon-coated graphite composite material according to any one of claims 1 to 7 or the nitrogen-doped multi-component carbon-coated graphite composite material according to any one of claims 8 to 9.