CN118461309A - A method for preparing a carbon-based negative electrode material for a sodium ion battery - Google Patents

Abstract

The invention discloses a preparation method of a carbon-based negative electrode material for a sodium ion battery, and belongs to the technical field of batteries and battery materials. Firstly, the invention adopts N, P to carry out co-doping modification on the graphene oxide, the interface stability of the material is better, and the impedance is lower; and secondly, the composite carbon fiber and the modified graphene are mixed in equal proportion and then subjected to high-efficiency ball milling, so that stacking and collapse of a layered structure of the graphene are effectively inhibited, a rapid sodium transmission path is provided, and the electrochemical performance of the cathode material is obviously improved. The specific capacity of the sodium ion battery prepared by the negative electrode material is more than 700mAh/g (0.1A/g) after the first charge and discharge cycle, the capacity retention rate is more than 90% after 1000 cycles, and the electrochemical performance is effectively improved.

Description

A method for preparing a carbon-based negative electrode material for a sodium ion battery

Technical Field

The present invention belongs to the technical field of batteries and battery materials, and specifically relates to a method for preparing a carbon-based negative electrode material for a sodium ion battery.

Background Art

Electrochemical energy storage is considered to be an efficient energy storage technology due to its high energy conversion efficiency, relatively compact size, and fast response speed. However, due to the gradual scarcity of lithium resources, lithium-ion batteries (LIBs), as the leader in electrochemical energy storage, are in urgent need of finding a new generation of energy storage batteries that can take over. Sodium has the advantages of abundant resources, low cost, and environmental friendliness, and therefore has attracted the attention of researchers.

There are many types of negative electrode materials for sodium-ion batteries, currently mainly carbon-based materials, titanium-based materials, alloy materials and organic materials. Among them, carbon-based materials are considered to be the most promising candidate materials due to their easy availability and low cost. Carbon-based materials mainly include crystalline carbon and amorphous carbon. Crystalline carbon is natural graphite and artificial graphite, and lithium-ion batteries mainly use this type of negative electrode material. However, when graphite is used as the negative electrode of sodium-ion batteries, sodium ions cannot be embedded, and the specific capacity is too low to meet the requirements. Amorphous carbon materials mainly include hard carbon and soft carbon. Hard carbon exhibits a high initial discharge capacity, good rate performance and structural stability, and has certain electrochemical performance advantages. It is currently the first choice for negative electrode materials.

However, current hard carbon materials are relatively expensive and have disadvantages such as low initial efficiency and poor cycle stability.

For example, Chinese patent application CN202210872497.0, a sodium ion battery negative electrode material, a pole piece and a sodium ion battery, the disclosed negative electrode material contains a negative electrode main material, a conductive agent and a binder, the mass ratio of the negative electrode main material, the conductive agent and the binder is 100:(1-5):(1-5); the negative electrode main material contains a mixture of at least two of graphite, soft carbon and hard carbon, the mass ratio of the graphite, the soft carbon and the hard carbon is (0-5):(0-15):(80-98).

It uses hard carbon as the main negative electrode material, doping some soft carbon and graphene to overcome the defects of the hard carbon material. However, the battery performance of the prepared battery has not been significantly improved, which shows that simple doping cannot effectively solve the inherent defects of the current hard carbon negative electrode.

Therefore, one of the key research directions of negative electrode materials for sodium ion batteries is to continuously explore new materials and construct new morphological structures to obtain negative electrode materials with high energy density and good cycle performance.

Summary of the invention

In view of the problems existing in the prior art, the present invention obtains a new type of carbon negative electrode material with an interpenetrating network structure through element doping and efficient ball milling. The three-dimensional structure of the material effectively solves the stacking and collapse of graphene, and at the same time provides a fast transmission path for sodium ions, thereby effectively improving the battery capacity performance and cycle performance.

In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

A method for preparing a carbon-based negative electrode material for a sodium ion battery comprises the following preparation steps:

(1) dispersing 100-200 mg of graphene oxide in 100-200 mL of deionized water and ultrasonically treating for 1-2 h to obtain a graphene dispersion;

(2) adding a modifier of the same mass as the graphene oxide to the graphene dispersion, ultrasonically dispersing for 10-20 minutes to mix evenly, placing the mixture in a crucible, and then placing the crucible in a muffle furnace, heating the mixture to 1050-1100° C. at a heating rate of 2-5° C./min in a nitrogen or argon atmosphere and maintaining the temperature for 2 hours, and then naturally cooling the mixture to obtain modified graphene;

(3) dissolving polyacrylonitrile in an organic solvent, magnetically stirring at 50-60° C. for 10-12 hours to obtain a polyacrylonitrile spinning solution with a mass fraction of 10-15%, pumping the spinning solution into an injection syringe, and preparing a composite fiber by an electrospinning method; and then fully drying the obtained composite fiber, oxidizing, carbonizing, and grinding to obtain a composite carbon fiber;

(4) mixing the composite carbon fiber and the modified graphene in a mass ratio of 1:1 and adding the mixture into a ball mill for high-energy ball milling to obtain a modified graphene-carbon fiber composite material;

(5) After the ball milling is completed, the modified graphene-carbon fiber composite material is cooled to room temperature and then dried to finally obtain a powdery final product.

Furthermore, the modifier in step (2) is obtained by mixing urea and diammonium phosphate in a mass ratio of 1:1.

Furthermore, in step (2), the average particle size of the nano-silicon dioxide is 20-30 nm, and the amount added is 1% of the mass of polyacrylonitrile.

Furthermore, the organic solvent in step (3) is one or more of N,N-dimethylformamide, dimethyl sulfoxide, and N,N-dimethylacetamide.

Furthermore, the electrospinning parameters of step (3) are: spinning voltage of 15-30KV, propulsion rate of 1mL/h-2mL/h, receiving distance of 10-18cm, and water bath receiving; the oxidation and carbonization methods are: placing the dried composite fiber in an alumina porcelain boat, and then placing it in a tubular furnace, introducing oxygen into the tubular furnace, heating to 280°C at a heating rate of 1°C/min, keeping the temperature constant for 2h, and naturally cooling to obtain an oxidation product; then introducing protective gas nitrogen into the tubular furnace, heating from room temperature to 650°C at a heating rate of 1°C/min, and then heating to 1000°C at a heating rate of 3°C/min, keeping the temperature for 30min, cooling naturally in the protective gas, and grinding to obtain the composite carbon fiber.

Furthermore, the high-energy ball milling treatment method in step (4) is as follows: the composite carbon fiber and the modified graphene are mixed in a mass ratio of 1:1 and then placed in a grinding jar together with grinding balls, and filled with 1-5 bar nitrogen or argon for protection. The ball-to-material ratio is (20-30):1, and the ball milling process adopts a forward and reverse mode. The forward and reverse mode is set to forward for 5 minutes, stop for 1 minute, and then reverse for 5 minutes as one cycle. The ball milling process runs for a total of 30 cycles; the ball mill speed is 100-200 rpm.

Furthermore, the grinding jar and grinding balls are made of agate.

Furthermore, in step (5), the drying temperature is 50-100° C. and the drying time is 5-10 h.

All raw materials of the present invention are commercially available.

Beneficial effects:

(1) First, the present invention uses N and P to co-dope and modify graphene oxide. The doping of N and P elements, after the two are mixed in equal proportions, has a synergistic effect. On the one hand, it can improve the interlayer spacing and promote the diffusion of sodium ions. On the other hand, it can generate more defect sites and increase the adsorption capacity, thereby improving the electronic conductivity of the material, and the material interface stability is better and the impedance is lower.

(2) Secondly, the present invention mixes composite carbon fiber and modified graphene in equal proportions and then conducts efficient ball milling. The appropriate amount of carbon fiber and modified graphene are combined and subjected to low-speed ball milling with alternating forward and reverse rotations. The carbon fiber effectively disrupts the graphene layer structure and realizes the conversion of the graphene two-dimensional structure to a three-dimensional structure. As a result, the stacking and collapse of the graphene layer structure are effectively suppressed, providing a fast sodium transmission path. At the same time, the specific surface area of the carbon material is greatly increased, so that its wettability to the electrolyte is greatly enhanced, and the macroscopic performance is that the electrochemical performance of the negative electrode material is significantly improved;

(3) Finally, the specific capacity of the sodium ion battery prepared using the negative electrode material of the present invention after the first charge and discharge cycle is above 700 mAh/g (0.1 A/g). After 1000 cycles, the capacity retention rate is above 90%, and the electrochemical performance is effectively improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a first cycle charge and discharge curve of negative electrode material in Embodiment 3 of the present invention;

FIG2 is a scanning electron microscope image of the negative electrode materials obtained in Example 3 of the present invention and Comparative Examples 4-6, wherein the scale size is 10 μm;

FIG3 is a cycle performance diagram of a sodium ion battery obtained from the negative electrode material obtained in Example 3 of the present invention;

FIG. 4 is an AC impedance spectrum of the electrode materials of Example 3 of the present invention and Comparative Examples 1-3.

DETAILED DESCRIPTION

The technical solution of the present invention is further described below in conjunction with specific embodiments, but is not limited thereto.

Example 1

A method for preparing a carbon-based negative electrode material for a sodium ion battery comprises the following preparation steps:

(1) Dispersing 100 mg of graphene oxide in 200 mL of deionized water and ultrasonically treating for 1 h to obtain a graphene dispersion;

(2) adding a modifier of the same mass as the graphene oxide to the graphene dispersion, ultrasonically dispersing for 10 min to mix evenly, placing the mixture in a crucible, and then placing the crucible in a muffle furnace, heating the mixture to 1050-1100° C. at a heating rate of 2° C./min in a nitrogen or argon atmosphere and maintaining the temperature for 2 h, and then naturally cooling the mixture to obtain modified graphene;

(3) dissolving polyacrylonitrile in an organic solvent, and magnetically stirring at 50-60° C. for 10 h to obtain a polyacrylonitrile spinning solution with a mass fraction of 10%, and pumping the spinning solution into an injection syringe to prepare a composite fiber by an electrospinning method; and then fully drying the obtained composite fiber, and then oxidizing, carbonizing, and grinding to obtain a composite carbon fiber;

(4) mixing the composite carbon fiber and the modified graphene in a mass ratio of 1:1 and adding the mixture into a ball mill for high-energy ball milling to obtain a modified graphene-carbon fiber composite material;

(5) After the ball milling is completed, the modified graphene-carbon fiber composite material is cooled to room temperature and then dried to finally obtain a powdery final product.

The modifier is obtained by mixing urea and diammonium phosphate in a mass ratio of 1:1.

The average particle size of the nano-silicon dioxide in step (2) is 20-30 nm, and the amount added is 1% of the mass of polyacrylonitrile.

The organic solvent in step (3) is N,N-dimethylformamide.

The electrospinning parameters of step (3) are as follows: spinning voltage is 15KV, propulsion rate is 1mL/h, receiving distance is 10cm, and water bath receiving is adopted; the oxidation and carbonization methods are as follows: the dried composite fiber is placed in an alumina porcelain boat, and then placed in a tubular furnace, oxygen is introduced into the tubular furnace, and heated to 280°C at a heating rate of 1°C/min, kept at a constant temperature for 2h, and cooled naturally to obtain an oxidation product; then, protective gas nitrogen is introduced into the tubular furnace, and the temperature is increased from room temperature to 650°C at a heating rate of 1°C/min, and then increased to 1000°C at a heating rate of 3°C/min, and kept warm for 30min, and naturally cooled in the protective gas, and the composite carbon fiber is obtained after grinding.

The high-energy ball milling treatment method in step (4) is as follows: the composite carbon fiber and the modified graphene are mixed in a mass ratio of 1:1 and then placed in a grinding jar together with grinding balls, and 1 bar of nitrogen or argon is filled for protection. The ball-to-material ratio is 20:1. The ball milling process adopts a forward and reverse mode. The forward and reverse mode is set to forward for 5 minutes, stop for 1 minute, and then reverse for 5 minutes as one cycle. The ball milling process runs for 30 cycles in total. The ball mill speed is 100 revolutions per minute.

The grinding jar and grinding balls are made of agate.

The drying temperature in step (5) is 50°C and the drying time is 10 h.

Example 2

A method for preparing a carbon-based negative electrode material for a sodium ion battery comprises the following preparation steps:

(1) dispersing 150 mg of graphene oxide in 100 mL of deionized water and ultrasonically treating for 1.5 h to obtain a graphene dispersion;

(2) adding a modifier of the same mass as the graphene oxide to the graphene dispersion, ultrasonically dispersing for 20 minutes to mix evenly, placing the mixture in a crucible, and then placing the crucible in a muffle furnace, heating the mixture to 1050-1100° C. at a heating rate of 3° C./min under a nitrogen or argon atmosphere and maintaining the temperature for 2 hours, and then naturally cooling the mixture to obtain modified graphene;

(3) dissolving polyacrylonitrile in an organic solvent, and magnetically stirring at 50-60° C. for 10 h to obtain a polyacrylonitrile spinning solution with a mass fraction of 13%, and pumping the spinning solution into an injection syringe to prepare a composite fiber by an electrospinning method; and then fully drying the obtained composite fiber, and then oxidizing, carbonizing, and grinding to obtain a composite carbon fiber;

(4) mixing the composite carbon fiber and the modified graphene in a mass ratio of 1:1 and adding the mixture into a ball mill for high-energy ball milling to obtain a modified graphene-carbon fiber composite material;

(5) After the ball milling is completed, the modified graphene-carbon fiber composite material is cooled to room temperature and then dried to finally obtain a powdery final product.

The modifier is obtained by mixing urea and diammonium phosphate in a mass ratio of 1:1.

The average particle size of the nano-silicon dioxide in step (2) is 20-30 nm, and the amount added is 1% of the mass of polyacrylonitrile.

The organic solvent in step (3) is dimethyl sulfoxide.

The electrospinning parameters of step (3) are as follows: spinning voltage is 20 KV, propulsion rate is 1 mL/h, receiving distance is 15 cm, and water bath receiving is adopted; the oxidation and carbonization methods are as follows: the dried composite fiber is placed in an alumina porcelain boat, and then placed in a tubular furnace, oxygen is introduced into the tubular furnace, and heated to 280°C at a heating rate of 1°C/min, kept at a constant temperature for 2 hours, and cooled naturally to obtain an oxidation product; then, protective gas nitrogen is introduced into the tubular furnace, and the temperature is increased from room temperature to 650°C at a heating rate of 1°C/min, and then increased to 1000°C at a heating rate of 3°C/min, and kept warm for 30 minutes, and naturally cooled in the protective gas, and the composite carbon fiber is obtained after grinding.

The high-energy ball milling treatment method in step (4) is as follows: the composite carbon fiber and the modified graphene are mixed in a mass ratio of 1:1 and then placed in a grinding jar together with grinding balls, and 3 bar of nitrogen or argon is filled for protection. The ball-to-material ratio is 25:1. The ball milling process adopts a forward and reverse mode. The forward and reverse mode is set to forward for 5 minutes, stop for 1 minute, and then reverse for 5 minutes as one cycle. The ball milling process runs for 30 cycles in total. The ball mill speed is 100 revolutions per minute.

The grinding jar and grinding balls are made of agate.

The drying temperature in step (5) is 100°C and the drying time is 5h.

Example 3

A method for preparing a carbon-based negative electrode material for a sodium ion battery comprises the following preparation steps:

(1) Dispersing 200 mg of graphene oxide in 120 mL of deionized water and ultrasonically treating for 2 h to obtain a graphene dispersion;

(2) adding a modifier of the same mass as the graphene oxide to the graphene dispersion, ultrasonically dispersing for 20 minutes to mix evenly, placing the mixture in a crucible, and then placing the crucible in a muffle furnace. In a nitrogen or argon atmosphere, heating the mixture to 1050-1100° C. at a heating rate of 5° C./min and maintaining the temperature for 2 hours, and then naturally cooling the mixture to obtain the modified graphene.

(3) dissolving polyacrylonitrile in an organic solvent, and magnetically stirring at 50-60° C. for 12 hours to obtain a polyacrylonitrile spinning solution with a mass fraction of 15%, and pumping the spinning solution into a syringe to prepare a composite fiber by an electrospinning method; and then fully drying the obtained composite fiber, and then oxidizing, carbonizing, and grinding to obtain a composite carbon fiber;

(4) mixing the composite carbon fiber and the modified graphene in a mass ratio of 1:1 and adding the mixture into a ball mill for high-energy ball milling to obtain a modified graphene-carbon fiber composite material;

(5) After the ball milling is completed, the modified graphene-carbon fiber composite material is cooled to room temperature and then dried to finally obtain a powdery final product.

The modifier is obtained by mixing urea and diammonium phosphate in a mass ratio of 1:1.

The organic solvent in step (3) is N,N-dimethylacetamide.

The average particle size of the nano-silicon dioxide in step (2) is 20-30 nm, and the amount added is 1% of the mass of polyacrylonitrile.

The electrospinning parameters of step (3) are as follows: spinning voltage is 30 KV, propulsion rate is 2 mL/h, receiving distance is 18 cm, and water bath receiving is adopted; the oxidation and carbonization methods are as follows: the dried composite fiber is placed in an alumina porcelain boat, and then placed in a tubular furnace, oxygen is introduced into the tubular furnace, and heated to 280°C at a heating rate of 1°C/min, kept at a constant temperature for 2 hours, and cooled naturally to obtain an oxidation product; then, protective gas nitrogen is introduced into the tubular furnace, and the temperature is increased from room temperature to 650°C at a heating rate of 1°C/min, and then increased to 1000°C at a heating rate of 3°C/min, and kept warm for 30 minutes, and naturally cooled in the protective gas, and the composite carbon fiber is obtained after grinding.

The high-energy ball milling treatment method in step (4) is as follows: the composite carbon fiber and the modified graphene are mixed in a mass ratio of 1:1 and then placed in a grinding jar together with grinding balls, and 5 bar of nitrogen or argon is filled for protection. The ball-to-material ratio is 30:1. The ball milling process adopts a forward and reverse mode. The forward and reverse mode is set to forward for 5 minutes, stop for 1 minute, and then reverse for 5 minutes as one cycle. The ball milling process runs for 30 cycles in total. The ball mill speed is 200 revolutions per minute.

The grinding jar and grinding balls are made of agate.

The drying temperature in step (5) is 80°C and the drying time is 8h.

Comparative Example 1

A method for preparing a carbon-based negative electrode material for a sodium ion battery comprises the following preparation steps:

(1) Dispersing 200 mg of graphene oxide in 120 mL of deionized water and ultrasonically treating for 2 h to obtain a graphene dispersion;

(2) adding a modifier of the same mass as the graphene oxide to the graphene dispersion, ultrasonically dispersing for 20 minutes to mix evenly, placing the mixture in a crucible, and then placing the crucible in a muffle furnace, heating the mixture to 1050-1100° C. at a heating rate of 5° C./min under a nitrogen or argon atmosphere, and maintaining the temperature for 2 hours. After natural cooling, the modified graphene can be obtained.

(3) dissolving polyacrylonitrile in an organic solvent, magnetically stirring at 50-60° C. for 12 h to obtain a polyacrylonitrile spinning solution with a mass fraction of 15%, pumping the spinning solution into an injection syringe, and preparing a composite fiber by an electrospinning method; and then fully drying the obtained composite fiber, oxidizing, carbonizing, and grinding to obtain a composite carbon fiber;

(4) mixing the composite carbon fiber and the modified graphene in a mass ratio of 1:1 and adding the mixture into a ball mill for high-energy ball milling to obtain a modified graphene-carbon fiber composite material;

(5) After the ball milling is completed, the modified graphene-carbon fiber composite material is cooled to room temperature and then dried to finally obtain a powdery final product.

The modifier is urea.

In this comparative example, except that only urea is used as the modifier, other raw materials and process steps are the same as those in Example 3.

Comparative Example 2

In this comparative example, except that only ammonium dihydrogen phosphate was used as the modifier, other raw materials and process steps were the same as those in Example 3.

Comparative Example 3

A method for preparing a carbon-based negative electrode material for a sodium ion battery comprises the following preparation steps:

(1) dispersing 200 mg of graphene oxide in 120 mL of deionized water and ultrasonically treating for 2 h to obtain a graphene dispersion;

(2) Put the graphene dispersion into a crucible, then put the crucible into a muffle furnace, and heat it to 1050-1100°C at a heating rate of 5°C/min under a nitrogen or argon atmosphere and keep it for 2 hours. After natural cooling, high-temperature treated graphene can be obtained;

(3) dissolving polyacrylonitrile in an organic solvent, magnetically stirring at 50-60° C. for 12 h to obtain a polyacrylonitrile spinning solution with a mass fraction of 15%, pumping the spinning solution into an injection syringe, and preparing a composite fiber by an electrospinning method; and then fully drying the obtained composite fiber, oxidizing, carbonizing, and grinding to obtain a composite carbon fiber;

(4) mixing the composite carbon fiber and the graphene obtained in step (2) in a mass ratio of 1:1 and adding the mixture into a ball mill for high-energy ball milling to obtain a graphene-carbon fiber composite material;

After the ball milling is completed, the modified graphene-carbon fiber composite material is cooled to room temperature and then dried to finally obtain a powdery final product.

In this comparative example, except that the graphene modification treatment is not performed, the other raw materials and preparation methods are the same as those of Example 3.

Comparative Example 4

In this comparative example, except for changing the composition ratio of the composite carbon fiber and the modified graphene, the other raw materials and preparation method are the same as those in Example 3.

That is, the high-energy ball milling treatment method in step (4) is as follows: the composite carbon fiber and the modified graphene are mixed in a mass ratio of 2:1 and then placed in a grinding jar together with grinding balls, and 5 bar of nitrogen or argon is filled for protection. The ball-to-material ratio is 30:1, and the ball milling process adopts a forward and reverse mode. The forward and reverse mode is set to forward for 5 minutes, stop for 1 minute, and then reverse for 5 minutes as one cycle. The ball milling process runs for 30 cycles in total; the ball mill speed is 200 rpm.

Comparative Example 5

In this comparative example, except for changing the composition ratio of the composite carbon fiber and the modified graphene, the other raw materials and preparation method are the same as those in Example 3.

That is, the high-energy ball milling treatment method in step (4) is as follows: the composite carbon fiber and the modified graphene are mixed in a mass ratio of 1:2 and then placed in a grinding jar together with grinding balls, and 5 bar of nitrogen or argon is filled for protection. The ball-to-material ratio is 30:1, and the ball milling process adopts a forward and reverse mode. The forward and reverse mode is set to forward for 5 minutes, stop for 1 minute, and then reverse for 5 minutes as one cycle. The ball milling process runs for 30 cycles in total; the ball mill speed is 500 rpm.

Comparative Example 6

This comparative example uses the same raw materials and preparation method as Example 3 except that the ball milling method is used in a single direction.

That is, the high-energy ball milling treatment method in step (4) is as follows: the composite carbon fiber and the modified graphene are mixed in a mass ratio of 1:1 and then placed in a grinding jar together with grinding balls, and 5 bar of nitrogen or argon is filled for protection. The ball-to-material ratio is 30:1. The ball milling process adopts a forward rotation mode. The forward rotation mode is set to rotate forward for 5 minutes, stop for 1 minute, and then rotate forward for 5 minutes as one cycle. The ball milling process runs for 30 cycles in total. The ball mill speed is 200 rpm.

Performance Testing

Material morphology: The material morphology was analyzed and characterized using Hitachi's SU8010 cold field emission scanning electron microscope (SEM).

Battery assembly: The negative electrode materials obtained in the embodiment and the comparative example were used as experimental samples to prepare batteries for performance testing. The negative electrode material was used as the active material, and it was mixed and ground with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1 to prepare a slurry, which was evenly coated on the current collector copper foil and vacuum dried at 120°C for 12 hours to prepare a working electrode.

Electrochemical experiments were performed using standard CR2032 batteries, with pure sodium metal sheets as counter electrodes, glass fibers as separators, and 1 mol/L sodium hexafluorophosphate dissolved in a mixture of ethylene carbonate and dimethyl carbonate (volume ratio of 1:1) as the electrolyte. The battery was aged for 12 h before the electrochemical test. Constant current charge and discharge tests were performed at different current densities in the voltage window of 0.01~3.00 V using the CT2001 Blue Battery Test System. Electrochemical impedance spectroscopy (EIS) was measured using the same electrochemical workstation by applying an AC voltage with an amplitude of 10 mV in the frequency range of 100 kHz-100 MHz.

Table 1 Performance test results

From the data in Table 1, we can also see that the negative electrode material of the embodiment of the present invention has good specific capacity and cycle performance. This is because the appropriate proportion of carbon fiber and graphene are mixed, combined with the efficient ball milling method of forward and reverse combination, which can promote the full combination of carbon fiber and graphene. The carbon fiber plays a role in supporting the graphene sheet structure. The three-dimensional structure formed thereby effectively alleviates the stacking and collapse of the layered structure of graphene and provides a fast sodium transmission path; at the same time, the co-doping of N and P, the interaction between the two can produce more defect sites and increase the adsorption capacity, and the interface stability is good. Therefore, macroscopically, the impedance of the material is reduced and the electrochemical performance is improved. However, in Comparative Examples 1-6, in which the process parameters are changed, both the capacity performance and the cycle performance are significantly weakened. In Comparative Examples 1-3, in which the element doping is changed, the doping of the element will not have a significant effect on the microstructure, but more on the surface performance of the material. The lack of N and P doped negative electrode materials leads to an increase in charge transfer impedance and a decrease in interface stability, which leads to a decrease in the electrochemical performance of the material (as shown in Figure 4). However, in Comparative Examples 4-6, which changed the carbon fiber graphene composition and the ball milling method, the improvement effect of the carbon fiber on the graphene sheet structure decreased and could not play an effective supporting role, thus resulting in a decrease in material performance (as shown in Figure 2).

It should be noted that the above embodiments are only some embodiments of the preferred methods of implementing the present invention, rather than all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

Claims (8)

1. The preparation method of the carbon-based negative electrode material for the sodium ion battery is characterized by comprising the following preparation steps of:

(1) Dispersing 100-200mg of graphene oxide in 100-200mL of deionized water, and carrying out ultrasonic treatment for 1-2 hours to obtain graphene dispersion liquid;

(2) Adding a modifier with the same mass as graphene oxide into the graphene dispersion liquid, carrying out ultrasonic dispersion for 10-20min, mixing uniformly, then placing the mixture into a crucible, then placing the crucible into a muffle furnace, heating to 1050-1100 ℃ at a heating rate of 2-5 ℃/min under nitrogen or argon atmosphere, and keeping for 2h, and naturally cooling to obtain modified graphene;

(3) Dissolving polyacrylonitrile in an organic solvent, adding a small amount of nano silicon dioxide, magnetically stirring for 10-12 hours at 50-60 ℃ to obtain a polyacrylonitrile spinning solution with the mass fraction of 10-15%, pumping the spinning solution into a syringe, and preparing composite fibers by an electrostatic spinning method; fully drying the obtained composite fiber, and oxidizing, carbonizing and grinding to obtain the composite carbon fiber;

(4) The composite carbon fiber and the modified graphene are mixed according to the mass ratio of 1:1, mixing and then adding the mixture into a ball milling tank for high-energy ball milling treatment to obtain a modified graphene-carbon fiber composite material;

(5) And after ball milling is finished, cooling the modified graphene-carbon fiber composite material to room temperature, and drying to finally obtain a powdery final product.

2. The preparation method of the carbon-based anode material for the sodium ion battery according to claim 1, wherein the modifier in the step (2) is obtained by mixing urea and ammonium dihydrogen phosphate according to a mass ratio of 1:1.

3. The method for preparing a carbon-based anode material for sodium ion batteries according to claim 1, wherein the average particle size of the nano silicon dioxide in the step (2) is 20-30nm, and the addition amount is 1% of the mass of the polyacrylonitrile.

4. The method for preparing a carbon-based anode material for sodium ion batteries according to claim 1, wherein the organic solvent in the step (3) is one or more of N, N-dimethylformamide, dimethyl sulfoxide and N, N-dimethylacetamide.

5. The method for preparing a carbon-based anode material for sodium ion battery according to claim 1, wherein the electrostatic spinning parameters in step (3) are as follows: spinning voltage is 15-30KV, propulsion rate is 1-2 mL/h, receiving distance is 10-18cm, and water bath is adopted for receiving; the oxidation and carbonization method comprises the following steps: placing the dried composite fibers in an alumina porcelain boat, then placing the alumina porcelain boat in a tube furnace, introducing oxygen into the tube furnace, heating to 280 ℃ at a heating rate of 1 ℃/min, keeping the temperature for 2 hours, and naturally cooling to obtain an oxidation product; and then introducing protective gas nitrogen into the tubular furnace, raising the temperature from room temperature to 650 ℃ at a heating rate of 1 ℃/min, raising the temperature to 1000 ℃ at a heating rate of 3 ℃/min, preserving the temperature for 30min, naturally cooling in the protective gas, and grinding to obtain the composite carbon fiber.

6. The method for preparing a carbon-based anode material for sodium ion batteries according to claim 1, wherein the high-energy ball milling treatment method in the step (4) is as follows: the mass ratio of the composite carbon fiber to the modified graphene is 1:1 mixing, putting the mixture and grinding balls into a grinding tank, filling 1-5bar of nitrogen or argon for protection, wherein the ball-material ratio is (20-30), 1, the ball milling process adopts a positive and reverse rotation mode, the positive and reverse rotation mode is set to be positive rotation for 5 minutes, then stop for 1 minute, and then reverse rotation for 5 minutes is set as a period, and the ball milling process is operated for 30 periods in total; the revolution of the ball mill is 100-200 revolutions per minute.

7. The method for preparing a carbon-based negative electrode material for a sodium ion battery according to claim 5, wherein the grinding pot and the grinding ball are made of agate.

8. The method for preparing a carbon-based anode material for sodium ion battery according to claim 1, wherein the drying temperature in step (5) is 50-100 ℃ and the drying time is 5-10h.