CN118380574B - Modified hard carbon negative electrode material, preparation method thereof and vehicle - Google Patents

Abstract

The invention discloses a modified hard carbon negative electrode material, a preparation method thereof and a vehicle, and relates to the field of sodium ion battery negative electrode materials. The modified hard carbon negative electrode material is obtained by coating asphalt on hard carbon, pre-oxidizing, carbonizing, mixing with a binder and a conductive agent containing benzenesulfonyl to prepare slurry, and coating the slurry on a current collector; the coating material used in the invention is asphalt, which has rich carbon content and improves the coating effect of the carbon layer; secondly, the coating material is low in cost, so that the cost is reduced, and the market competitiveness is improved; the solvent is a low boiling point solvent, is convenient to dry and collect, and is environment-friendly; in addition, the invention is liquid phase cladding, so that the cladding layer is more uniform and has controllable thickness; in addition, the invention adopts heating in the air to perform pre-oxidation modification on the hard carbon coating layer, so that graphitization phenomenon is avoided at high temperature, and parameters such as temperature, time and the like of the process are easy to control; the hard carbon material prepared by the technical scheme of the invention has the characteristics of high multiplying power, high first efficiency and the like.

Description

A modified hard carbon negative electrode material and preparation method thereof, and a vehicle

Technical Field

The present invention belongs to the field of negative electrode materials for sodium ion batteries, and in particular relates to a modified hard carbon negative electrode material and a preparation method and a vehicle thereof.

Background Art

The application of lithium-ion batteries in large-scale energy storage is limited by the regional limitations and high prices of lithium metal. Compared with lithium metal, sodium metal has similar chemical properties, abundant reserves, and low prices. Therefore, sodium-ion batteries are considered to be a possible alternative to lithium-ion batteries in the field of large-scale energy storage. Negative electrode materials are the key to the development of sodium-ion batteries. Carbon-based materials are the most commonly used. Among them, hard carbon is an amorphous carbon material with a larger interlayer spacing and a higher sodium storage capacity. It is an ideal negative electrode material for sodium-ion batteries. For example, Chinese patent No. CN202211388183.X discloses a sodium-ion battery biomass hard carbon negative electrode material, its preparation method and application. The hard carbon prepared by this method exhibits a higher first charge capacity of 310.5•mAh/g.

The defects and micropores on the surface of hard carbon increase the specific surface area, which will greatly increase the side reactions between hard carbon and the electrolyte, resulting in poor charge and discharge rate performance and low first coulomb efficiency of hard carbon. Surface coating technology is often used to repair the defects and micropores on the surface of hard carbon, thereby improving the electrochemical performance of hard carbon. For example, Chinese Patent No. CN202010809449.8 discloses a preparation method for modified negative electrode materials by coating solid asphalt in liquid phase, which mainly melts the asphalt under heating to achieve the coating of hard carbon. The high viscosity of asphalt in the molten state is not conducive to the coating of the hard carbon surface, and uneven coating is prone to occur. The thickness of the coating layer is difficult to control. Too thin will not repair the surface defects of hard carbon, and too thick will hinder the transmission of sodium ions. In addition, if the surface is not further modified after asphalt coating, graphitization is prone to occur during the high-temperature carbonization process. The graphite layer has a small interlayer spacing, which reduces the kinetics of sodium ion transmission. Therefore, how to achieve rapid and uniform coating on the hard carbon surface and control its thickness, while improving the sodium ion transmission capacity of the hard carbon coating, is an important indicator for evaluating high-quality hard carbon coatings and an important guarantee for hard carbon to achieve high initial efficiency and high rate.

Summary of the invention

The purpose of the present invention is to provide a modified hard carbon negative electrode material and a preparation method and vehicle thereof. The present invention adopts an organic solvent to dissolve asphalt to control the viscosity of the coating liquid, and sprays the coated hard carbon while stirring; in addition, in order to avoid graphitization of the coating layer during the carbonization process, the asphalt coating layer is pre-oxidized and modified to improve the sodium ion transmission capacity of the hard carbon coating layer, so that the hard carbon has the performance of high initial efficiency, high rate and high stability.

The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

A modified hard carbon negative electrode material, comprising an active material layer and a current collector layer stacked in sequence;

The active material layer is made of negative electrode slurry;

The negative electrode slurry comprises modified hard carbon, a binder and carbon nanotubes containing benzenesulfonyl groups.

It should be noted that the modified hard carbon is obtained by pre-oxidation and carbonization of coated hard carbon.

It should be noted that the method for preparing the coated hard carbon includes: adding asphalt to an organic solvent to prepare a coating liquid, then spraying the coating liquid on the surface of the hard carbon, adjusting the liquid-solid ratio, drying, and crushing to obtain the coated hard carbon.

It should be noted that the above-mentioned organic solvent includes N,N-dimethylformamide (DMF).

Specifically, the method for preparing the modified hard carbon negative electrode material comprises:

Step 1: crushing the asphalt at 10000-40000 r/min for 1-10 min to obtain asphalt particles;

Step 2: Add asphalt particles into N,N-dimethylformamide (the mass volume ratio of the two is 1g:1-100mL), stir for 10-24h to obtain a coating solution;

Step 3: spraying the coating liquid in the hard carbon while stirring, and controlling the spraying rate at 1 mL/min-10 mL/min to obtain an initial coated hard carbon;

Step 4, initial coating of hard carbon: in sealed stirring, add N,N-dimethylformamide while stirring, adjust the liquid-solid ratio to 30-80wt%, control the stirring speed at 150-500r/min, and stir for 5-24h, then stir and dry the uniformly coated hard carbon negative electrode material under vacuum conditions, at a stirring speed of 20-60r/min, a temperature of 50-100°C, and a drying time of 5-24h, and then perform ultrasonic vibration crushing for 5-12h to obtain coated hard carbon;

Step 5: placing the coated hard carbon in air, heating it to 150-400°C at a heating rate of 1-10°C/min, and pre-oxidizing it for 10-25h to obtain pre-oxidized coated hard carbon;

Step 6: placing the pre-oxidized hard carbon in an inert atmosphere, controlling the gas flow rate at 10-100 sccm, heating the temperature to 1000-1600°C at a heating rate of 1-10°C/min, and heat-treating for 1-5 hours to obtain modified hard carbon;

Step 7: Add ultrapure water to the binder, stir and dissolve, then add the modified hard carbon and carbon nanotubes containing benzenesulfonyl groups, and homogenize for 1-5 hours to obtain a negative electrode slurry;

Step eight, evenly coat the negative electrode slurry on the current collector, dry it in a vacuum environment at 50-100°C for 10-48h (the negative electrode slurry layer after coating and drying is the active material layer), and cool it to room temperature to obtain a modified hard carbon negative electrode material.

The coating material used in the present invention is asphalt, which is rich in carbon content and improves the carbon layer coating effect; secondly, the coating material is cheap, which reduces the cost and improves the market competitiveness; the solvent used is a low-boiling point solvent, which is convenient for drying and collection and is environmentally friendly; in addition, the present invention is liquid phase coating, which makes the coating layer more uniform and the thickness is controllable; and the present invention adopts heating in air to pre-oxidize the coating layer of the hard carbon to avoid graphitization at high temperature, and the temperature, time and other parameters of this process are easy to control; the hard carbon material prepared by the technical solution of the present invention has the characteristics of high rate, high first effect and the like.

It should be noted that the particle size of the above-mentioned asphalt particles is 1-50 μm.

It should be noted that the mass ratio of the coating liquid to the hard carbon is 1:10-30.

It should be noted that the above-mentioned binder is at least one selected from sodium alginate or sodium carboxymethyl cellulose.

It should be noted that the mass ratio of the above-mentioned binder to ultrapure water is 1:10-100.

It should be noted that the mass ratio of the above-mentioned binder to the carbon nanotubes containing benzenesulfonyl groups is 1:0.8-1.2.

It should be noted that the mass ratio of the above binder to the modified hard carbon is 1:1-10.

It should be noted that the thickness of the active material layer is 10-100 μm.

It should be noted that the current collector is selected from a copper foil current collector or an aluminum foil current collector; the thickness of the current collector is 10-100 μm.

Use of a hard carbon negative electrode material in preparing a sodium ion battery, wherein the hard carbon negative electrode material comprises the modified hard carbon negative electrode material.

A battery comprises: a positive electrode plate, a separator, a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises the modified hard carbon negative electrode material.

The invention also discloses the use of the battery in preparing a vehicle.

A method for preparing carbon nanotubes containing benzenesulfonyl groups comprises: subjecting carbon nanotubes to acyl chloride treatment and then subjecting them to substitution reaction with 2-phenylthioethanol to obtain carbon nanotubes containing benzenesulfonyl groups.

The invention provides a method for preparing carbon nanotubes containing benzenesulfonyl groups. The carbon nanotubes are subjected to carboxylation treatment by using a strong acid, and then thionyl chloride is added to carry out chlorination treatment, and then 2-phenylthioethanol is added to carry out a substitution reaction. The prepared carbon nanotubes containing benzenesulfonyl groups are used for the preparation of modified hard carbon negative electrode materials, so that the prepared modified hard carbon negative electrode materials have good first coulomb efficiency and cycle stability.

Specifically, the method for preparing the above-mentioned carbon nanotubes containing benzenesulfonyl groups comprises the following steps:

Add carbon nanotubes to the strong acid mixture, react at 53-68°C for 10-20min, cool to room temperature, add deionized water to dilute, filter, wash with deionized water until neutral, and dry to obtain carboxylated carbon nanotubes; add DMF (the mass volume ratio of carboxylated carbon nanotubes to DMF is 1g:17-30mL) to the carboxylated carbon nanotubes, ultrasonically treat for 13-20min, then add thionyl chloride, treat at 68-73°C for 10-20h, cool to room temperature, filter, wash with DMF 3-5 times, then add the filter cake to 2-phenylthioethanol, add triethylamine, react at 47-53°C for 18-27h, cool to room temperature, filter, wash with deionized water 3-5 times, and dry to obtain carbon nanotubes containing benzenesulfonyl groups.

It should be noted that the mass volume ratio of the carbon nanotubes and the strong acid mixed solution is: 1g:25-30mL.

It should be noted that the above-mentioned strong acid mixture contains a sulfuric acid solution with a concentration of 90-98wt% and a nitric acid solution with a concentration of 60-65wt%; the volume ratio of the sulfuric acid solution to the nitric acid solution is 1:0.25-0.38.

It should be noted that the mass volume ratio of the above-mentioned carboxylated carbon nanotubes to thionyl chloride is 1 g:55-68 mL.

It should be noted that the mass volume ratio of the above-mentioned carboxylated carbon nanotubes to 2-phenylthioethanol is 1 g:35-45 mL; the volume ratio of the above-mentioned 2-phenylthioethanol to triethylamine is 1:3.5-4.5.

The invention also discloses the use of the carbon nanotube containing benzenesulfonyl group prepared by the preparation method in preparing hard carbon negative electrode material.

In order to further improve the performance of the modified hard carbon negative electrode material, the present invention also uses a sodium carboxymethyl cellulose derivative to replace sodium carboxymethyl cellulose.

The invention also discloses a method for preparing a sodium carboxymethyl cellulose derivative, comprising: carrying out a graft copolymerization reaction between N-acryloylmorpholine and sodium carboxymethyl cellulose to obtain the sodium carboxymethyl cellulose derivative.

The invention provides a method for preparing a sodium carboxymethyl cellulose derivative. N-acryloylmorpholine is used as a modifier to undergo a graft copolymerization reaction with sodium carboxymethyl cellulose. The prepared sodium carboxymethyl cellulose derivative is then used for preparing a modified hard carbon negative electrode material, so that the prepared modified hard carbon negative electrode material has better first coulomb efficiency, storage stability and cycle stability.

Specifically, the preparation method of the above-mentioned sodium carboxymethyl cellulose derivative comprises the following steps:

Deionized water is added to sodium carboxymethyl cellulose, and the temperature is raised to 80-85°C. Potassium persulfate is added under a nitrogen atmosphere, and the mixture is stirred for 8-15 minutes. N-acryloylmorpholine is added, and the mixture is reacted at a constant temperature for 1-3.5 hours. Anhydrous ethanol is added to break the emulsion, and the mixture is filtered, dried, extracted with Soxhlet, and dried to obtain a sodium carboxymethyl cellulose derivative.

It should be noted that the mass volume ratio of the above sodium carboxymethyl cellulose to deionized water is 1g:25-30mL.

It should be noted that the mass ratio of the above sodium carboxymethyl cellulose to N-acryloylmorpholine is 1:5-7.

It should be noted that the amount of potassium persulfate used is 1.5-2.5wt% of the amount of N-acryloylmorpholine used.

The invention also discloses the use of the sodium carboxymethyl cellulose derivative prepared by the preparation method in preparing hard carbon negative electrode materials.

The beneficial effects of the present invention include:

The present invention obtains a modified hard carbon negative electrode material, which is prepared by coating hard carbon with asphalt, pre-oxidizing and carbonizing, and then mixing with a binder and a conductive agent containing a benzenesulfonyl group to prepare a slurry, and then coating the slurry on a current collector; the coating material used in the present invention is asphalt, which is rich in carbon content and improves the carbon layer coating effect; secondly, the coating material is cheap, which reduces the cost and improves the market competitiveness; the solvent used is a low-boiling point solvent, which is convenient for drying and collection and is environmentally friendly; in addition, the present invention is liquid phase coating, which makes the coating layer more uniform and the thickness is controllable; and the present invention adopts heating in air to pre-oxidize the coating layer of hard carbon to avoid graphitization at high temperature, and the temperature, time and other parameters of this process are easy to control; the hard carbon material prepared by the technical scheme of the present invention has the characteristics of high rate, high first efficiency and the like.

Therefore, the present invention provides a method for preparing a modified hard carbon negative electrode material. The present invention uses an organic solvent to dissolve asphalt to control the viscosity of the coating liquid, and sprays the coated hard carbon while stirring; in addition, in order to avoid graphitization of the coating layer during the carbonization process, the asphalt coating layer is pre-oxidized and modified to improve the sodium ion transmission capacity of the hard carbon coating layer, so that the hard carbon has the performance of high initial efficiency, high rate and high stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is an electron microscope image of the modified hard carbon and hard carbon obtained in Example 1;

FIG2 is a graph showing the benzenesulfonyl-containing carbon nanotubes prepared in Example 3 and the infrared spectrum test results of the carbon nanotubes;

FIG3 is an infrared spectrum test result of the sodium carboxymethyl cellulose derivative and sodium carboxymethyl cellulose obtained in Example 6;

FIG4 is a rate performance test result of the modified hard carbon negative electrode material and the hard carbon negative electrode material prepared in Example 1;

FIG5 is a charge-discharge diagram of the first cycle of the modified hard carbon negative electrode material and the hard carbon negative electrode material obtained in Example 1;

FIG6 is the first effect test results of the modified hard carbon negative electrode materials and the hard carbon negative electrode materials prepared in Examples 1 to 9;

FIG7 is a test result of storage stability of modified hard carbon negative electrode materials and hard carbon negative electrode materials prepared in Examples 1 to 9;

FIG8 is the test results of the cycle stability of the modified hard carbon negative electrode materials and the hard carbon negative electrode materials prepared in Examples 1 to 9.

DETAILED DESCRIPTION

In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention is further described in detail below in conjunction with specific implementation methods:

Embodiment 1:

A method for preparing a modified hard carbon negative electrode material, comprising:

Step 1: Weigh 100 g of asphalt, use a powder mill with a capacity of 250 g and a rotation speed of 20,000 r/min, work for 5 minutes, and sieve to obtain asphalt particles with an average particle size of 25 μm;

Step 2: Add 10 g of asphalt particles into a beaker, then add 50 mL of N,N-dimethylformamide and stir for 10 hours to obtain a coating solution;

Step 3, weigh 100g of hard carbon and put it into a sealed stirrer, and the mass ratio of hard carbon to coating liquid is controlled at 10:1; spray the coating liquid while stirring, and control the coating liquid spraying rate at 5mL/min to obtain initial coated hard carbon;

Step 4: Place the initial coated hard carbon in a sealed agitator, add N,N-dimethylformamide while stirring to adjust the liquid-solid ratio to 80wt%, control the stirring speed at 300r/min, and stir for 10h, then start the vacuum and heating functions of the sealed agitator, control the temperature at 80°C, stir at the same time, control the speed at 50r/min, and control the time at 10h, then crush under ultrasonic vibration, and control the crushing time at 6h until complete separation to obtain coated hard carbon;

Step 5: heating the coated hard carbon in air to perform surface pre-oxidation modification, the heating temperature is controlled at 300° C., the heating rate is controlled at 5° C./min, and the pre-oxidation time is controlled at 10 h to obtain pre-oxidation coated hard carbon;

Step 6: put the pre-oxidized coated hard carbon into a tube furnace, and carbonize it at high temperature under the protection of inert Ar, with the gas flow rate controlled at 50 sccm, the heating rate controlled at 5°C/min, the insulation temperature controlled at 1100°C, and the insulation time controlled at 2h. After the end, cool it to room temperature to modify the hard carbon;

Step 7: First, weigh 1 g of sodium alginate as a binder and completely dissolve it in 100 g of ultrapure water, then add 8 g of modified hard carbon and 1 g of carbon nanotubes, and homogenize them in a homogenizer for 2 h to obtain a negative electrode slurry;

Step 8. Then, the negative electrode slurry is evenly coated on an aluminum foil current collector with a thickness of 20 μm using an automatic coater, dried in a vacuum environment at 80°C for 24 hours, and cooled to room temperature to obtain a modified hard carbon negative electrode material with an active material layer thickness of 20 μm. Finally, a punching machine is used to cut negative electrode sheets with a diameter of 15 mm.

Embodiment 2:

The difference between the method for preparing a modified hard carbon negative electrode material and Example 1 is that sodium carboxymethyl cellulose is used instead of sodium alginate.

Embodiment 3:

The difference between the method for preparing a modified hard carbon negative electrode material and Example 2 is that carbon nanotubes containing benzenesulfonyl groups are used instead of carbon nanotubes.

The method for preparing carbon nanotubes containing benzenesulfonyl groups comprises the following steps:

Add carbon nanotubes to the strong acid mixture, react at 53°C for 20 minutes, cool to room temperature, add deionized water to dilute, filter, wash with deionized water until neutral, and dry to obtain carboxylated carbon nanotubes; add DMF (the mass volume ratio of carboxylated carbon nanotubes to DMF is 1g:17mL) to the carboxylated carbon nanotubes, ultrasonically treat for 13 minutes, then add dichlorothionyl, treat at 68°C for 20 hours, cool to room temperature, filter, wash with DMF three times, then add the filter cake to 2-phenylthioethanol, add triethylamine, react at 47°C for 27 hours, cool to room temperature, filter, wash with deionized water three times, and dry to obtain carbon nanotubes containing benzenesulfonyl groups. Among them, the mass volume ratio of carbon nanotubes and strong acid mixture is: 1g:25mL, the above-mentioned strong acid mixture contains sulfuric acid solution with a concentration of 90wt% and nitric acid solution with a concentration of 60wt%; the volume ratio of sulfuric acid solution to nitric acid solution is 1:0.25; the mass volume ratio of carboxylated carbon nanotubes to dichloride is 1g:55mL, the mass volume ratio of carboxylated carbon nanotubes to 2-phenylthioethanol is 1g:35mL; the volume ratio of the above-mentioned 2-phenylthioethanol to triethylamine is 1:3.5.

Embodiment 4:

The difference between the method for preparing a modified hard carbon negative electrode material and Example 3 is that the method for preparing the carbon nanotubes containing benzenesulfonyl groups is different.

The difference between the preparation method of carbon nanotubes containing benzenesulfonyl groups and Example 3 is as follows: the mass volume ratio of carbon nanotubes to the strong acid mixture is: 1g:30mL, the above-mentioned strong acid mixture contains a sulfuric acid solution with a concentration of 98wt% and a nitric acid solution with a concentration of 65wt%; the volume ratio of the sulfuric acid solution to the nitric acid solution is 1:0.38; the mass volume ratio of carboxylated carbon nanotubes to dichloride is 1g:68mL, the mass volume ratio of carboxylated carbon nanotubes to 2-phenylthioethanol is 1g:45mL; the volume ratio of the above-mentioned 2-phenylthioethanol to triethylamine is 1:4.5.

Embodiment 5:

The difference between the method for preparing a modified hard carbon negative electrode material and Example 3 is that the method for preparing the carbon nanotubes containing benzenesulfonyl groups is different.

The difference between the preparation method of carbon nanotubes containing benzenesulfonyl groups and Example 3 is as follows: the mass volume ratio of carbon nanotubes to the strong acid mixture is: 1g:28mL, the above-mentioned strong acid mixture contains a sulfuric acid solution with a concentration of 95wt% and a nitric acid solution with a concentration of 62wt%; the volume ratio of the sulfuric acid solution to the nitric acid solution is 1:0.3; the mass volume ratio of carboxylated carbon nanotubes to dichloride is 1g:60mL, the mass volume ratio of carboxylated carbon nanotubes to 2-phenylthioethanol is 1g:40mL; the volume ratio of the above-mentioned 2-phenylthioethanol to triethylamine is 1:4.

Embodiment 6:

The difference between the method for preparing a modified hard carbon negative electrode material and Example 2 is that a sodium carboxymethyl cellulose derivative is used instead of sodium carboxymethyl cellulose.

The preparation method of sodium carboxymethyl cellulose derivative comprises the following steps:

Deionized water was added to sodium carboxymethyl cellulose, and the temperature was raised to 80°C. Potassium persulfate was added under a nitrogen atmosphere, and the mixture was stirred for 8 minutes. N-acryloylmorpholine was added, and the mixture was reacted at a constant temperature for 1 hour. Anhydrous ethanol was added to break the emulsion, and the mixture was filtered and dried. Soxhlet extraction was performed and the mixture was dried to obtain a sodium carboxymethyl cellulose derivative. The mass volume ratio of sodium carboxymethyl cellulose to deionized water was 1 g:25 mL. The mass ratio of sodium carboxymethyl cellulose to N-acryloylmorpholine was 1:5. The amount of potassium persulfate used was 1.5 wt% of the amount of N-acryloylmorpholine used.

Embodiment 7:

The difference between a method for preparing a modified hard carbon negative electrode material and Example 6: the preparation method of sodium carboxymethyl cellulose derivative is different.

The preparation method of sodium carboxymethyl cellulose derivative is different from that of Example 6: deionized water is added to sodium carboxymethyl cellulose, the temperature is raised to 85°C, potassium persulfate is added under a nitrogen atmosphere, the mixture is stirred for 15 minutes, N-acryloylmorpholine is added, the mixture is reacted at a constant temperature for 3.5 hours, anhydrous ethanol is added to demulsify, the mixture is filtered, dried, extracted with Soxhlet, and dried to obtain a sodium carboxymethyl cellulose derivative; the mass volume ratio of sodium carboxymethyl cellulose to deionized water is 1 g:30 mL; the mass ratio of sodium carboxymethyl cellulose to N-acryloylmorpholine is 1:7; the amount of potassium persulfate used is 2.5 wt% of the amount of N-acryloylmorpholine used.

Embodiment 8:

The difference between a method for preparing a modified hard carbon negative electrode material and Example 6: the preparation method of sodium carboxymethyl cellulose derivative is different.

The preparation method of sodium carboxymethyl cellulose derivative is different from that of Example 6: deionized water is added to sodium carboxymethyl cellulose, the temperature is raised to 82° C., potassium persulfate is added under a nitrogen atmosphere, the mixture is stirred for 10 min, N-acryloylmorpholine is added, the mixture is reacted at a constant temperature for 2 h, anhydrous ethanol is added to demulsify, the mixture is filtered, dried, Soxhlet extraction is performed, and dried to obtain a sodium carboxymethyl cellulose derivative; the mass volume ratio of sodium carboxymethyl cellulose to deionized water is 1 g:28 mL; the mass ratio of sodium carboxymethyl cellulose to N-acryloylmorpholine is 1:6; the amount of potassium persulfate used is 2 wt % of the amount of N-acryloylmorpholine used.

Embodiment 9:

The difference between the method for preparing a modified hard carbon negative electrode material and Example 3 is that a sodium carboxymethyl cellulose derivative is used instead of sodium carboxymethyl cellulose.

The preparation method of sodium carboxymethyl cellulose derivative is the same as that in Example 6.

Test example:

1. Scanning electron microscope test

The samples were tested using a scanning electron microscope (S4800) produced by Hitachi, Japan.

The above test was performed on the modified hard carbon and the hard carbon (i.e., the hard carbon without coating treatment) obtained in Example 1, and the results are shown in Figure 1. As can be seen from Figure 1 (a) before coating with the technical solution of the present invention, the surface of the hard carbon particles is rough and has obvious micropores, and as can be seen from Figure 1 (b) after coating with the technical solution of the present invention, the surface of the hard carbon particles becomes smooth and has no micropores. This example shows that after coating with the technical solution of the present invention, the microstructure of the hard carbon is significantly changed.

2. Infrared spectrum test

The measurement was carried out using a VECTOR-22 Fourier infrared spectrometer produced by the German BRUKER company. The sample powder and potassium bromide were fully mixed in a ratio of 1:100, pressed into tablets, and then tested.

The above test was performed on the carbon nanotubes containing benzenesulfonyl groups and the carbon nanotubes prepared in Example 3, and the results are shown in Figure 2. As shown in Figure 2, compared with the infrared spectrum of the carbon nanotubes, the infrared spectrum of the carbon nanotubes containing benzenesulfonyl groups has an infrared characteristic absorption peak of the C=O bond in the ester group at 1738cm ^-1 ; an infrared characteristic absorption peak of the COC bond in the ester group at 1177cm ^-1 ; and an infrared characteristic absorption peak of the CS bond at 1045cm ^-1 , indicating that 2-phenylthioethanol participates in the formation reaction of the carbon nanotubes containing benzenesulfonyl groups.

The above test was performed on the sodium carboxymethyl cellulose derivative and sodium carboxymethyl cellulose obtained in Example 6, and the results are shown in Figure 3. As shown in Figure 3, compared with the infrared spectrum of sodium carboxymethyl cellulose, the infrared spectrum of the sodium carboxymethyl cellulose derivative has an infrared characteristic absorption peak of C=O bond at 1657cm ^-1 ; and an infrared characteristic absorption peak of COC at 1179cm ^-1 , indicating that N-acryloylmorpholine participates in the formation reaction of the sodium carboxymethyl cellulose derivative.

3. Rate performance test

Battery assembly: A sodium sheet with the same size as the negative electrode is used as the positive electrode material. In a glove box under an argon atmosphere, the positive electrode shell, the negative electrode shell, the glass fiber separator, the sodium sheet and the nickel foam are assembled into a CR2025 button battery. The electrolyte uses 1MNaPF ₆ as an electrolyte dissolved in a mixed solution with a volume ratio of ethylene carbonate (EC): diethyl carbonate (DEC) = 1:1 Vol%, and the assembled battery is packaged (the control sample uses a hard carbon negative electrode material prepared from uncoated hard carbon, and the other preparation conditions of the hard carbon negative electrode material are the same as in Example 1). The LAND CT3002A battery performance tester produced by Wuhan Landian Electronics Co., Ltd. is used to test the electrochemical performance of the battery. The test voltage range is 0.001~2.5V, and the rate performance of the composite hard carbon material sample is tested at different rates (1C=279mAh•g ^-1 ).

The above test was performed on the modified hard carbon negative electrode material and the hard carbon negative electrode material prepared in Example 1, and the results are shown in Figure 4. As shown in Figure 4, the specific capacity of the hard carbon negative electrode material before coating is around 20 mAh•g ^-1 at a 3C rate, while the specific capacity of the hard carbon negative electrode material after coating prepared by the technical solution of the present invention is around 148 mAh•g ^-1 at a 3C rate. The above results show that the performance of the coated hard carbon negative electrode material prepared by the technical solution of the present invention is significantly improved.

4. First Coulombic efficiency test

The preparation method of the battery is the same as that of Experiment 3. The LANDCT3002A battery performance tester produced by Wuhan Landian Electronics Co., Ltd. is used to test the electrochemical performance of the battery. The test voltage range is 0.001~2.5V. The first cycle is cycled at a current density of 0.1C, and the first coulombic efficiency (first efficiency) of the battery is calculated. The calculation formula is as follows:

First coulombic efficiency = (first cycle charge specific capacity/first cycle discharge specific capacity) × 100%.

The above test was performed on the modified hard carbon negative electrode material and the hard carbon negative electrode material prepared in Example 1, and the results are shown in Figure 5. As shown in Figure 5, the first coulombic efficiency of the hard carbon negative electrode material before coating is 75.40%, and the first coulombic efficiency of the hard carbon negative electrode material after coating prepared by the technical solution of the present invention is 80.54%, and the first efficiency is significantly improved.

The above test was performed on the modified hard carbon negative electrode materials and hard carbon negative electrode materials obtained in Examples 1 to 9, and the results are shown in Figure 6. As can be seen from Figure 6, compared with Example 2, Example 3 and Example 6, Example 9, the first coulombic efficiency is significantly improved, indicating that the carbon nanotubes modified by 2-phenylthioethanol and then the obtained carbon nanotubes containing benzenesulfonyl groups are used for the preparation of modified hard carbon negative electrode materials, so that the prepared modified hard carbon negative electrode materials have good first coulombic efficiency; compared with Example 2 and Example 3, Example 6 and Example 2, Example 9 and Example 3, the first coulombic efficiency is also increased, indicating that the sodium carboxymethyl cellulose derivative is modified by N-acryloylmorpholine, and then the sodium carboxymethyl cellulose derivative is used for the preparation of modified hard carbon negative electrode materials, so that the prepared modified hard carbon negative electrode materials have good first coulombic efficiency.

5. Storage stability test

The preparation method of the battery is the same as that of Test Example 3. The battery is placed at 60°C, charged to 3.8V at 0.33C constant current, then charged to 0.05C at 3.8V constant voltage, and charged to 2.0V at 1C constant current, and the discharge capacity is recorded as R1. Then, the battery is charged to 3.8V at 0.33C constant current, and then charged to 0.05C at 3.8V constant voltage. After the battery is stored at a constant temperature for 7 days, it is discharged to 2.0V at 1C constant current, and the discharge capacity is recorded as R2. The capacity recovery rate M is calculated as follows:

M/%=(R2/R1)×100%.

The above test was performed on the modified hard carbon negative electrode materials and hard carbon negative electrode materials obtained in Examples 1 to 9, and the results are shown in Figure 7. As can be seen from Figure 7, compared with Example 2, Example 6 and Example 6, the capacity recovery rate of Example 3 has no significant improvement, indicating that the carbon nanotubes modified by 2-phenylthioethanol and then the obtained carbon nanotubes containing benzenesulfonyl groups are used for the preparation of modified hard carbon negative electrode materials, which has no negative effect on the storage stability of the prepared modified hard carbon negative electrode materials; compared with Example 2, Example 6 and Example 3, the capacity recovery rate of Example 9 has increased, indicating that the sodium carboxymethyl cellulose derivative modified by N-acryloylmorpholine and then the sodium carboxymethyl cellulose derivative is used for the preparation of modified hard carbon negative electrode materials, so that the prepared modified hard carbon negative electrode materials have good storage stability.

6. Cyclic stability test

The preparation method of the battery is the same as that of Experimental Example 3. The electrochemical performance of the battery is tested using a LANDCT3002A battery performance tester produced by Wuhan Landian Electronics Co., Ltd. At a current density of 0.1C, the capacity retention rate after 1000 cycles of charge and discharge is recorded.

The above test was performed on the modified hard carbon negative electrode materials and hard carbon negative electrode materials obtained in Examples 1 to 9, and the results are shown in Figure 8. As can be seen from Figure 8, compared with Example 2, Example 6 and Example 9, the capacity retention rate is significantly improved, indicating that the carbon nanotubes modified by 2-phenylthioethanol and then the obtained carbon nanotubes containing benzenesulfonyl groups are used for the preparation of modified hard carbon negative electrode materials, so that the prepared modified hard carbon negative electrode materials have good cycle stability; compared with Example 2 and Example 3, the capacity retention rate of Example 6 is also increased, indicating that the sodium carboxymethyl cellulose derivative is modified by N-acryloylmorpholine, and then the sodium carboxymethyl cellulose derivative is used for the preparation of modified hard carbon negative electrode materials, so that the prepared modified hard carbon negative electrode materials have good cycle stability.

The conventional techniques in the above embodiments are prior arts known to those skilled in the art, and thus will not be described in detail here.

The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (7)

1. A modified hard carbon negative electrode material is characterized in that: the modified hard carbon anode material comprises an active material layer and a current collector layer which are sequentially laminated; the active material layer is made of negative electrode slurry; the negative electrode slurry comprises modified hard carbon, a binder and carbon nanotubes containing benzenesulfonyl;

the modified hard carbon is obtained by pre-oxidizing and carbonizing coated hard carbon; the coated hard carbon is obtained by adopting asphalt through liquid phase coating;

The process conditions of the pre-oxidation include: heating to 150-400 ℃ in air at a heating rate of 1-10 ℃/min, and performing pre-oxygen treatment for 10-25 h;

The carbonization process conditions include: under the protection of inert atmosphere, the gas flow rate is controlled at 10-100sccm, the temperature is raised to 1000-1600 ℃ at the heating rate of 1-10 ℃/min, and the heat preservation treatment is carried out for 1-5h.

2. The modified hard carbon negative electrode material according to claim 1, wherein: the preparation method of the coated hard carbon comprises the following steps: adding asphalt into an organic solvent to prepare coating liquid, then spraying the coating liquid on the surface of the hard carbon, adjusting the liquid-solid ratio, drying and crushing to obtain the coated hard carbon.

3. The modified hard carbon negative electrode material according to claim 2, characterized in that: the spraying rate of the coating liquid is controlled to be 1mL/min-10mL/min.

4. The modified hard carbon negative electrode material according to claim 2, characterized in that: the liquid-solid ratio is 30-80wt%.

5. The modified hard carbon negative electrode material according to claim 1, wherein: the preparation method of the carbon nano tube containing the benzenesulfonyl group comprises the following steps: and (3) performing acyl chlorination on the carbon nano tube, and then performing substitution reaction on the carbon nano tube and 2-thiophenylethanol to obtain the carbon nano tube containing benzenesulfonyl.

6. A battery, the battery comprising: a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, the negative electrode sheet comprising the modified hard carbon negative electrode material of claim 1.

7. Use of the battery of claim 6 in the manufacture of a vehicle.