阅读说明：本技术 一种改性碳纳米管膜/硫复合柔性正极材料的制备方法及在柔性锂硫电池中的应用 (Preparation method of modified carbon nanotube film/sulfur composite flexible positive electrode material and application of modified carbon nanotube film/sulfur composite flexible positive electrode ) 是由 赵奇 李亚利 宋远强 耿浩 吴昊 于 2021-01-27 设计创作，主要内容包括：本发明公开了一种改性碳纳米管膜/硫复合柔性正极材料的制备方法及在柔性锂硫电池中的应用,本发明先制备得到氮掺杂或硼掺杂的多层改性碳纳米管膜正极材料,该正极材料具有导电性高,催化活性好,自支撑的特点,且实现了低成本,连续批量生产,该多层结构以及改性后的碳纳米管膜与硫化合物复合,可以通过物理和化学吸附大量的硫化物,抑制“穿梭效应”,使制备的改性碳纳米管膜/硫复合材料具有优异的电化学性能,用于锂硫电池中,可以提高柔性锂硫电池的性能。(The invention discloses a preparation method of a modified carbon nanotube film/sulfur composite flexible anode material and application thereof in a flexible lithium-sulfur battery.)

1. A preparation method of a modified carbon nanotube film/sulfur composite flexible positive electrode material is characterized by comprising the following steps: the preparation method comprises the following steps:

(1) preparing a boron-doped modified carbon nanotube film by adopting a horizontal three-temperature-zone FCCVD furnace: setting the temperature in a horizontal three-temperature-zone FCCVD furnace, weighing a carbon source, a catalyst and an accelerator according to the mass ratio, mixing the carbon source, the catalyst and the accelerator into a solution, adding a boron source, ultrasonically mixing the solution uniformly to obtain a mixed solution, extracting the mixed solution by using an injector, putting the injector into an injection pump, injecting a precursor solution into the furnace, introducing 800 plus 1800ml/min hydrogen and 0-500ml/min argon, and preparing a continuous boron-doped modified multilayer carbon nanotube film;

(2) preparing a nitrogen-doped modified carbon nanotube film by adopting a horizontal three-temperature-zone FCCVD furnace: setting the temperature in a horizontal three-temperature-zone FCCVD furnace, weighing a carbon source, a catalyst and an accelerant according to the mass ratio, mixing the carbon source, the catalyst and the accelerant into a solution, adding a nitrogen source, carrying out ultrasonic mixing uniformly to obtain a mixed solution, extracting the mixed solution by using an injector, putting the injector into an injection pump, injecting the precursor solution into the furnace, introducing 800-1800ml/min of hydrogen and 0-500ml/min of argon, and preparing the continuous nitrogen-doped modified multilayer carbon nanotube film;

(3) and soaking the continuous boron-doped modified multilayer carbon nanotube film or the continuous nitrogen-doped modified multilayer carbon nanotube film in a sulfur-containing solution, drying in a vacuum drying oven, and treating in an air-blast drying oven to obtain the modified carbon nanotube film/sulfur composite flexible material.

2. The preparation method of the modified carbon nanotube film/sulfur composite flexible cathode material according to claim 1, wherein the preparation method comprises the following steps: the mass ratio of the carbon source, the catalyst and the promoter in the step (1) and the step (2) is 70-75:1-1.5: 0.5-1.

3. The preparation method of the modified carbon nanotube film/sulfur composite flexible cathode material according to claim 1, wherein the preparation method comprises the following steps: the carbon source in the step (1) and the step (2) is one or a mixture of ethanol, methanol and carbonic acid; the catalyst is one or more of ferric oxide, ferrocene, perovskite oxide, cobalt nitrate and phthalocyanine metal; the promoter is thiophene or/and carbon disulfide.

4. The preparation method of the modified carbon nanotube film/sulfur composite flexible cathode material according to claim 1, wherein the preparation method comprises the following steps: the boron source is one or a mixture of boric acid, sodium borohydride, potassium borohydride and ethyl borate; the nitrogen source is one or more of urea, pyrrole, pyridine, 1, 2-dimethyl imidazole and 2-methyl imidazole, and the adding amount of the boron source or the nitrogen source is 0.5 to 1.5wt percent of the solution.

5. The preparation method of the modified carbon nanotube film/sulfur composite flexible cathode material according to claim 1, wherein the preparation method comprises the following steps: the number of layers of the multilayer carbon nanotube film is 1000-2000 carbon nanotube films.

6. The preparation method of the modified carbon nanotube film/sulfur composite flexible cathode material according to claim 1, wherein the preparation method comprises the following steps: and (4) drying the carbon nanotube film impregnated in the step (3) in a vacuum drying box at the temperature of 30-45 ℃ for 1-4h, and then treating the carbon nanotube film in an air-blast drying box at the temperature of 155-160 ℃ for 5-20 h.

7. The preparation method of the modified carbon nanotube film/sulfur composite flexible cathode material according to claim 1, wherein the preparation method comprises the following steps: the sulfur-containing solution in the step (3) is CS containing sulfur or sulfide with the concentration of 5-10 percent₂And (3) solution.

8. Use of the modified carbon nanotube film/sulfur composite flexible material prepared according to any one of claims 1 to 7 as a positive electrode material for a lithium-sulfur battery.

Technical Field

The invention belongs to the field of lithium-sulfur battery cathode materials, and particularly relates to a continuous modified multilayer carbon nanotube film prepared by an FCCVD (chemical vapor deposition) method, and a flexible lithium-sulfur battery using the material.

Background

With the development of portable electronic devices, power tools, and electric vehicles, there is an increasing demand for high specific energy flexible batteries. The lithium-sulfur battery takes elemental sulfur (theoretical specific capacity of 1675mAh/g) as a positive electrode and metal lithium as a negative electrode, the theoretical energy density is as high as 2600Wh/kg, which is far higher than that of the currently adopted lithium-ion battery, so the lithium-sulfur battery is widely concerned by scholars at home and abroad.

The lithium-sulfur battery can generate a series of polysulfides during the charging and discharging process, and the polysulfides are very soluble in electrolyte, so that the polysulfides can be diffused to a lithium cathode under the action of concentration gradient, namely a shuttle effect, and finally, irreversible inactivation of partial sulfur and reduction of the utilization rate of lithium are caused, so that the specific capacity and the cycling stability of the lithium-sulfur battery are reduced. In order to solve the problem of the shuttle effect of the sulfur electrode, researchers add different carbon matrixes (porous carbon, graphene/graphite oxide and carbon nanotubes) and the like to sulfur to form a sulfur/polymer composite material, so that the conductivity of sulfur is improved, and the shuttle effect is inhibited. However, the carbon nanotube film is high in preparation cost and difficult to produce in continuous batches, so that industrialization and low-cost production are difficult to realize, the carbon nanotube film is rarely applied to the electrode material of the lithium-sulfur battery at present, and the inventor finds that the carbon nanotube film is not good in compounding effect with the sulfur material, so that the application of the carbon nanotube film to the anode material of the lithium-sulfur battery is influenced.

In order to solve the problems, the invention prepares a modified carbon nanotube film/sulfur positive electrode material which is a flexible electrode material with a self-supporting structure, and the modified carbon nanotube film structure can be uniformly compounded with sulfur, can adsorb polysulfide and inhibit a shuttle effect, thereby improving the specific capacity and the cycling stability of the lithium-sulfur battery. The method can also realize low-cost continuous batch production.

Disclosure of Invention

The invention aims to provide a modified carbon nanotube film/sulfur composite self-supporting positive electrode material with high conductivity and good catalytic activity and application thereof in a flexible lithium-sulfur battery. Research shows that the material is uniformly compounded with sulfur, can be combined with a large amount of polysulfide to inhibit shuttle effect, and has excellent electrochemical performance.

1. The modified carbon nanotube film is prepared by adopting a horizontal three-temperature-zone FCCVD furnace, the sealing mode is box sealing, and the liquid injection mode adopts a medical needle tube to extract precursor liquid and carries out liquid injection through a medical injection pump. Firstly, introducing inert gas to exhaust oxygen in the furnace, turning on a power switch of the furnace, setting a temperature-raising program of the furnace, and then starting heating, wherein the three temperature zones are sequentially from a liquid inlet to the tail part of the furnace, and the temperatures of the three temperature zones are set to be 1000-.

2. Weighing a carbon source, a catalyst and an accelerator according to a mass ratio of 70-75:1-1.5:0.5-1, mixing the carbon source, the catalyst and the accelerator to obtain a solution, adding 0.5-1.5 wt.% of boron source, uniformly mixing the solution by ultrasonic to obtain a mixed solution, pumping the mixed solution by using an injector, putting the injector into an injection pump, injecting the precursor solution into the center of the front end of a furnace tube through a needle tube, inserting the injector into a flange plate at the front end of the furnace when the furnace reaches a set temperature, opening the injection pump, opening a proton flow meter, introducing 1800ml/min hydrogen and 0-500ml/min argon. After the liquid injection is started for 1min, the precursor liquid is vaporized at the front end of the furnace tube, a carbon source grows on catalyst particles, hydrogen and an accelerant promote the growth of carbon nanotubes, the macroscopic phenomenon is that a white cylinder is formed at the center of the front end of the furnace tube, the white cylinder slowly approaches the rear end of the furnace tube under the action of airflow, the white cylinder extends into the sealed box body by hands, the continuous white cylinder is placed on the roller through simple mechanical winding, the speed of the roller is 20r/min, a stepping motor is fixed below the roller, the stepping motor has a certain speed, reciprocating motion is realized, and the continuous modified multilayer carbon nanotube film is prepared.

The number of layers of the multilayer carbon nanotube film is determined according to the liquid injection time, the liquid injection time is half an hour, and about 1000-2000 layers of carbon nanotube films are prepared. The multilayer carbon nanotube film is formed under the action of Van der Waals force and macroscopic extrusion force, and the bonding force between layers is strong.

3. Weighing a carbon source, a catalyst and an accelerator according to the mass ratio of 70-75:1-1.5:0.5-1, mixing to obtain a solution, adding 0.5-1.5 wt.% of nitrogen source into the solution, and preparing the continuous modified multilayer carbon nanotube film in the same way.

Further, the carbon source is one or more of ethanol, methanol and carbonic acid; the catalyst is one or more of ferric oxide, ferrocene, perovskite oxide, cobalt nitrate and phthalocyanine metal; the promoter is thiophene or/and carbon disulfide; the nitrogen source is one or more of urea, pyrrole, pyridine, 1, 2-dimethyl imidazole and 2-methyl imidazole.

The boron source is one or a mixture of boric acid, sodium borohydride, potassium borohydride and ethyl borate.

Among them, the doping amount of 0.5-1.5 wt.% is preferable, and when the doping amount is higher than 1.5 wt.%, the continuity of the carbon nanotube film is not favorable, and the conductivity of the carbon nanotube film is not only reduced, but also the performance of the battery after application is not favorable.

4. Soaking carbon nanotube membrane in CS containing sulfur or sulfide with concentration of 5-10%₂Drying the solution in a vacuum drying oven at 30-45 deg.C for 1-4 hr for 0.5-1 hr to remove toxic CS on the membrane₂And then the carbon nanotube film is treated for 5 to 20 hours in a blast drying box at the temperature of 155 ℃ and 160 ℃ to obtain the modified carbon nanotube film/sulfur composite flexible material.

The invention soaks the modified carbon nano-tube membrane structure in sulfur-containing solution, and dries the membrane structure for 1 to 4 hours in a vacuum drying oven at 30 to 45 ℃ by processing at different temperatures, so as to remove toxic CS on the membrane₂And then heat treatment is carried out at the temperature of 155-160 ℃ for 5-20h, sulfur can be immersed into the carbon nanotube film structure and chemisorbed in the temperature range, and the bonding effect of the modified carbon nanotube film and sulfide can be reduced when the temperature is higher than 160 ℃ or lower than 155 ℃. Experiments prove that the temperature of 160 ℃ is the optimal temperature, the uniform compounding of sulfur and the membrane can be realized, the combination effect is optimal, and the optimal electrochemical performance is shown. The modified carbon nanotube film and the sulfur compound prepared by the method effectively inhibit shuttle effect through physical adsorption and chemical adsorption, and show excellent performanceElectrochemical performance.

5. Cutting the modified carbon nanotube film/sulfur composite material into a required shape and size, or directly manufacturing the modified carbon nanotube film/sulfur composite material into a flexible lithium-sulfur battery cathode material with a specific size.

The flexible modified carbon nanotube film/sulfur composite material prepared by the invention is applied as the anode of a lithium-sulfur battery.

Compared with the prior art, the invention has the following beneficial effects:

1. compared with the integral technology, the method has the advantages that the transverse three-temperature-zone CVD furnace is used, the box body is sealed, the continuous multilayer modified carbon nanotube film is prepared by the FCCVD method, and the method has the characteristics of high conductivity and good catalytic activity.

2. The modified carbon nanotube film/sulfur composite material is prepared by an impregnation method, and is uniformly compounded with sulfur because the surface performance of the carbon nanotube is changed by doping of the heteroatom, and the dispersibility of sulfur particles is further improved.

3. The flexible lithium-sulfur battery prepared by the method has excellent electrochemical performance, and the self-supporting material has the advantages of high specific capacity, good rate capability, long cycle life, high energy density and the like.

Drawings

FIG. 1 is a diagram of a modified carbon nanotube film prepared in step (2) of example 1 according to the present invention;

fig. 2 is a flexible display diagram of a modified carbon nanotube film/sulfur composite cathode material prepared in example 1 of the present invention;

fig. 3a is a SEM image of the surface of the modified carbon nanotube film/sulfur composite flexible positive electrode material prepared in example 1 of the present invention, and fig. 3b is a cross-sectional SEM image of the modified carbon nanotube film/sulfur composite flexible positive electrode material prepared in example 1 of the present invention;

fig. 4 is a raman test chart of the modified carbon nanotube film/sulfur composite flexible positive electrode material prepared by the present invention;

fig. 5 is a rate performance diagram of the modified carbon nanotube film/sulfur composite flexible cathode material prepared by the present invention.

Detailed Description

The invention is described in further detail below with reference to the figures and specific embodiments.

Example 1

1. The invention adopts a horizontal three-temperature-zone FCCVD furnace, the sealing mode is box sealing, and the liquid injection mode adopts a medical needle tube to extract precursor liquid and carries out liquid injection through a medical injection pump. Firstly, introducing inert gas to exhaust oxygen in the furnace, turning on a power switch of the furnace, setting a temperature-raising program of the furnace, and then starting heating, wherein the three temperature zones are arranged from a liquid inlet to the tail of the furnace, and the temperatures of the three temperature zones are respectively set to 1175 ℃, 1165 ℃ and 980 ℃.

2. Weighing ethanol, ferrocene and thiophene according to the mass ratio of 74:1.5:1, and mixing to obtain a solution. Then 0.5 wt.% of ethyl borate, based on the mass of the solution, was added. 50ml of liquid was withdrawn with a syringe, which was placed in a syringe pump. When the furnace reaches the set temperature, the injector is inserted into a flange at the front end of the furnace, the needle tube of the injector is inserted into the flange about 4cm, the injection pump is started and set to be 18ml/h, the proton flow meter is started, the hydrogen flow is set to be 1800ml/min, and the argon is 200 ml/min. After the liquid injection is started for 1min, the boron-doped carbon nanotube film in the furnace tube is slowly close to the rear end of the furnace tube under the action of airflow, the boron-doped carbon nanotube film is stretched into the sealing box body by hands, the continuous boron-doped carbon nanotube film is placed on the roller through simple mechanical winding, and a stepping motor is fixed below the roller. The physical diagram of the prepared modified carbon nanotube film is shown in FIG. 1, the modified carbon nanotube film has a length of 19cm, a width of 12cm, a thickness of 80 μm (about 1-2 kilo-layers) and an electrical conductivity of 705S/m.

3. Placing the carbon nanotube membrane in a container immersed in CS containing sulfur at a concentration of 5%₂And (3) soaking the solution for 30min, drying the solution in a vacuum drying oven at the temperature of 45 ℃ for 4h, and then treating the solution in an air-blast drying oven at the temperature of 160 ℃ for 20h to obtain the modified carbon nanotube film/sulfur composite flexible material. The prepared modified carbon nanotube film/sulfur composite flexible cathode material is shown in fig. 2.

The modified carbon nanotube film/sulfur composite flexible positive electrode material (B-CNT positive electrode) prepared in this example was tested, and the results are as follows:

and (3) testing by a scanning electron microscope:

as shown in fig. 3, fig. 3a is an SEM image of the surface of the modified carbon nanotube film/sulfur composite flexible cathode material, from which fig. 3a it can be seen that the carbon nanotubes are uniformly composited with sulfur, and fig. 3b is an SEM image of the cross section of the material, and the thickness of the composite material is 96 μm measured by SEM.

Raman testing:

as shown in fig. 4: at 100cm^-1To 500cm^-1In the middle, the Raman spectrum of the unmodified carbon nanotube film @ S anode (CNT anode) has three peaks corresponding to C-S and S-S stretching vibration and corresponding to the Raman peak of sulfur element. The modified carbon nanotube film @ S positive electrode (B-CNT positive electrode and N-CNT positive electrode) does not have a Raman peak of sulfur, and the modified carbon nanotube film is proved to be capable of being uniformly combined with sulfur, so that the shuttle effect is favorably inhibited, and the performance of the flexible lithium-sulfur battery is improved.

3. Assembling the flexible lithium-sulfur battery:

the battery is assembled in a glove box filled with argon, the moisture and oxygen content is lower than 0.1ppm, the anode material is the modified carbon nanotube film/sulfur flexible anode material prepared by the invention, the cathode is a lithium sheet, the electrolyte is 1mol/L of ethylene glycol dimethyl ether of lithium bistrifluoromethylsulfonate imide and 1, 3-dioxolane solution, and 1.0 wt% of 1mol/L lithium nitrate is added; wherein the volume ratio of the ethylene glycol dimethyl ether to the 1, 3-dioxolane is 1: 1, the diaphragm is a lithium ion battery diaphragm. And assembling the positive plate, the negative electrode, the diaphragm, the electrolyte and the flexible packaging bag into a flexible lithium-sulfur battery for electrochemical test.

And (3) testing the rate capability of the lithium-sulfur battery:

as shown in fig. 5, at current densities of 0.1C, 0.2C, 0.5C and 1C, the B-CNT positive electrode showed discharge capacities of 1497.6, 984.9, 864.5 and 715.5mAh/g, respectively, and when the current density was returned to 0.1C again, the B-CNT positive electrode discharge capacity reached 1263.1 mAh/g.

Example 2

1. A horizontal three-temperature-zone FCCVD furnace is adopted, the sealing mode is box sealing, and the liquid injection mode adopts a medical needle tube to extract precursor liquid and carries out liquid injection through a medical injection pump. Firstly, introducing inert gas to exhaust oxygen in the furnace, turning on a power switch of the furnace, setting a temperature-raising program of the furnace, and then starting heating, wherein the three temperature zones are arranged from a liquid inlet to the tail of the furnace, and the temperatures of the three temperature zones are respectively set to 1175 ℃, 1165 ℃ and 980 ℃.

Weighing ethanol, ferrocene and thiophene according to the mass ratio of 74:1.5:1, and mixing to obtain a solution. Then 0.5 wt.% of 1, 2-dimethyl imidazole is added. 50ml of liquid was withdrawn with a syringe, which was placed in a syringe pump. When the furnace reaches the set temperature, the injector is inserted into a flange at the front end of the furnace, the needle tube of the injector is inserted into the flange about 2cm, the injection pump is started and set to be 30ml/h, the proton flow meter is started, and the argon flow is set to be 500 ml/min. After the liquid injection is started for 1min, the nitrogen-doped carbon nanotube film in the furnace tube is slowly close to the rear end of the furnace tube under the action of the airflow, the sealed box body is stretched into by hands, the continuous nitrogen-doped carbon nanotube film is placed on the roller through simple mechanical winding, and a stepping motor is fixed below the roller. The prepared modified carbon nanotube film is 15cm in width and 10cm in thickness, the thickness is 80 microns, and the conductivity is 484S/m.

2. Placing the carbon nanotube membrane in a container immersed in CS containing sulfur at a concentration of 5%₂And (3) soaking the solution for 30min, drying the solution in a vacuum drying oven at the temperature of 45 ℃ for 4h, and then treating the solution in an air-blast drying oven at the temperature of 160 ℃ for 20h to obtain the modified carbon nanotube film/sulfur composite flexible material (N-CNT positive electrode). The thickness of the composite material was 96 μm.

3. The composite material is assembled into a flexible lithium-sulfur battery

The battery is assembled in a glove box filled with argon, the moisture and oxygen content is lower than 0.1ppm, the cathode material is the modified carbon nanotube film/sulfur flexible cathode material prepared by the invention, the cathode is a lithium sheet, the electrolyte is 1mol/L of ethylene glycol dimethyl ether of lithium bistrifluoromethylsulfonate imide and 1, 3-dioxolane solution, 1.0 wt% of 1mol/L lithium nitrate is added, wherein the volume ratio of the ethylene glycol dimethyl ether to the 1, 3-dioxolane is 1: 1, the diaphragm is a lithium ion battery diaphragm. And assembling the positive plate, the negative electrode, the diaphragm, the electrolyte and the flexible packaging bag into a flexible lithium-sulfur battery for electrochemical test.

The rate capability is shown in fig. 5.

At current densities of 0.1C, 0.2C, 0.5C and 1C, the N-CNT positive electrode respectively shows discharge capacities of 1136.9, 857.9, 703.9 and 610.0mAh/g, and when the current density returns to 0.1C again, the discharge capacity of the N-CNT positive electrode can reach 1053.3 mAh/g.

Comparative example 1

A horizontal three-temperature-zone FCCVD furnace is used, the sealing mode is box sealing, and the liquid injection mode adopts a medical needle tube to extract precursor liquid and carries out liquid injection through a medical injection pump. Firstly, introducing inert gas to exhaust oxygen in the furnace, turning on a power switch of the furnace, setting a temperature-raising program of the furnace, and then starting heating, wherein the three temperature zones are arranged from a liquid inlet to the tail of the furnace, and the temperatures of the three temperature zones are respectively set to 1175 ℃, 1165 ℃ and 980 ℃.

Weighing ethanol, ferrocene and thiophene according to the mass ratio of 74:1.5:1, and mixing to obtain a solution. 50ml of liquid was withdrawn with a syringe, which was placed in a syringe pump. When the furnace reaches the set temperature, the injector is inserted into a flange at the front end of the furnace, the needle tube of the injector is inserted into the flange about 4cm, the injection pump is started and set to be 18ml/h, the proton flow meter is started, the hydrogen flow is set to be 1800ml/min, and the argon is 200 ml/min. The carbon nanotube film slowly approaches the rear end of the furnace tube under the action of airflow, stretches into the sealing box body by hand, puts the continuous carbon nanotube film into the roller through simple mechanical winding, and fixes a stepping motor under the roller. A continuous carbon nanotube film was prepared, and a carbon nanotube film/sulfur composite flexible material (CNT positive electrode) was obtained by the same impregnation method as in example 1.

The composite material is assembled into a flexible lithium-sulfur battery to be subjected to electrochemical tests (same as example 1), the rate performance is shown in figure 5, the CNT positive electrode respectively shows discharge capacities of 965.8, 726.9, 621.2 and 556.4mAh/g under current densities of 0.1C, 0.2C, 0.5C and 1C, and when the current density returns to 0.1C again, the discharge capacity of the CNT positive electrode can reach 900.5 mAh/g.

Comparative example 2

Comparative example 2 differs from example 1 in that: and adding 2.0 wt.% of ethyl borate for boron doping, and preparing the boron-doped modified carbon nanotube film under the same other operating conditions as in example 1.

And then, preparing the boron-doped modified carbon nanotube film/sulfur composite flexible material by adopting the same method and conditions as in the embodiment 1 and adopting a dipping method and sulfur composite.

The conductivity of the boron-doped modified carbon nanotube film prepared in the comparative example 2 is 96S/m;

comparative example 2 the prepared boron-doped modified carbon nanotube film/sulfur flexible cathode material was assembled into a flexible lithium-sulfur battery and subjected to electrochemical testing (same as example 1).

The rate capability is that the positive electrode material respectively shows discharge capacities of 1000.7, 832.3, 685.6 and 580.0mAh/g under the current densities of 0.1C, 0.2C, 0.5C and 1C, and when the current density returns to 0.1C again, the discharge capacity of the positive electrode material can reach 908.4 mAh/g.

Comparative example 3

Comparative example 3 differs from example 1 in that: the impregnation method is different:

the boron-doped modified carbon nanotube film prepared in example 1 was immersed in CS containing sulfur at a concentration of 5%₂And (3) putting the solution in a vacuum drying oven at 45 ℃ for drying for 4 hours for 30min, and fully drying to obtain the modified carbon nanotube film/sulfur composite flexible material.

Comparative example 3a flexible lithium-sulfur battery was assembled from the boron-doped modified carbon nanotube film/sulfur flexible positive electrode material and subjected to electrochemical testing (same as example 1).

The positive electrode material showed discharge capacities of 713.6, 557.4, 403.9 and 310.5mAh/g at current densities of 0.1C, 0.2C, 0.5C and 1C, respectively, and the discharge capacity of the positive electrode material reached 580.3mAh/g when the current density returned to 0.1C.

Comparative example 4

Comparative example 4 is different from example 1 in that: the impregnation method is different:

the boron-doped modified carbon nanotube film prepared in example 1 was immersed in CS containing sulfur at a concentration of 5%₂Dissolving in the solution for 30min, drying in a vacuum drying oven at 45 deg.C for 4 hr, and treating in a forced air drying oven at 150 deg.C for 20 hr to obtainThe boron-doped modified carbon nanotube film/sulfur composite flexible material.

Comparative example 4 a flexible lithium-sulfur battery was assembled from the boron-doped modified carbon nanotube film/sulfur flexible positive electrode material and subjected to electrochemical testing (same as example 1).

The positive electrode material showed discharge capacities of 1100.4, 832.7, 703.4 and 605.3mAh/g at current densities of 0.1C, 0.2C, 0.5C and 1C, respectively, and the discharge capacity of the positive electrode material reached 1042.3mAh/g when the current density returned to 0.1C.