Nitrogen-doped fibrous carbon material as well as preparation method and application thereof

Abstract

The invention relates to a nitrogen-doped fibrous carbon material as well as a preparation method and application thereof. According to the preparation method, animal feathers are taken as a raw material, keratin macromolecules are converted from a chain structure to a cross-linked structure through an oxidation-pyrolysis coupling reaction under a mild condition, and the thermal stability of the animal feather material is remarkably improved. On the basis, the animal feather material can maintain a high nitrogen doping level in the subsequent pyrolysis process, and compared with a carbon material obtained by directly pyrolyzing an original animal feather material, the retention rate of nitrogen and carbon is remarkably increased. A lithium-sulfur battery positive electrode modified coating prepared from the keratin-based nitrogen-doped fibrous carbon material prepared by the preparation method disclosed by the invention effectively improves the rate capability and the cycling stability of a lithium-sulfur battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass pyrolysis and lithium-sulfur batteries, and in particular relates to a nitrogen-doped fibrous carbon material and a preparation method and application thereof. Background Art

[0002] Lithium-sulfur batteries are the most promising energy storage systems for the next generation, with high theoretical energy density (2600Whkg -1 ) and lower price. However, the soluble lithium polysulfide produced by its positive electrode active material during the charge and discharge process will cause serious shuttle effect, resulting in poor cycle stability and low energy density of lithium-sulfur batteries, which limits its practical application.

[0003] Nitrogen-doped carbon materials have high specific surface area and conductivity, and can be used to capture polysulfides dissolved on the positive electrode side and reduce the loss of active materials due to the shuttle effect. Nitrogen doping can significantly enhance the interaction between carbon materials and lithium polysulfides, inhibit the shuttle effect of lithium polysulfides, and improve the reaction kinetics on the positive electrode side of lithium-sulfur batteries.

[0004] Protein waste biomass, such as waste animal hair, animal horns, and plant byproducts, has high carbon and nitrogen content and can be used as a precursor for preparing nitrogen-doped carbon materials. However, when the waste biomass is pyrolyzed and carbonized, there is a problem of low retention of carbon and nitrogen in the solid phase product. The resulting carbon material is often at a low nitrogen doping level, making it difficult to effectively enhance the reaction kinetics on the positive electrode side of the lithium-sulfur battery and inhibit its capacity decay, which greatly limits the application potential of protein waste biomass in the preparation of high-performance nitrogen-doped carbon materials. Summary of the invention

[0005] In order to overcome the above problems, the present invention provides a nitrogen-doped fibrous carbon material and a preparation method and application thereof.

[0006] The present invention uses animal feathers as raw materials, and improves the thermal stability of animal feather materials through oxidation-pyrolysis coupling reaction without introducing additional nitrogen sources, so that it can maintain an ultra-high nitrogen doping level after pyrolysis. The obtained nitrogen-doped fibrous carbon material can be used on the positive electrode side of lithium-sulfur batteries to improve their reaction kinetics and inhibit the shuttle effect, significantly improving the rate performance and cycle stability of lithium-sulfur batteries.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] A method for preparing a nitrogen-doped fibrous carbon material comprises the following steps:

[0009] Step 1: Wash the animal feathers, dry them and cut them to obtain cut animal feather materials;

[0010] Step 2: subjecting the animal feather material cut in step 1 to an oxidation-thermal decomposition coupling reaction in an oxygen-containing atmosphere to obtain a cross-linked animal feather material;

[0011] Step 3: Pyrolyze the cross-linked animal feather material obtained in step 2 under a gas protective atmosphere to obtain a nitrogen-doped fibrous carbon material.

[0012] Furthermore, in the step 1, the drying temperature is 50 to 80° C. and the time is 12 to 36 hours.

[0013] Furthermore, in the step 2, the oxidation-thermal decomposition coupling reaction temperature is 200-260°C, the heating rate is 1-5°C / min, the insulation time is 0.5-3h, and after the insulation is completed, it is naturally cooled to room temperature; the oxygen-containing atmosphere is one of air and nitrogen / oxygen mixed gas.

[0014] Furthermore, in the step 3, the pyrolysis temperature is 400-800°C, the heating rate is 1-5°C / min, the insulation time is 1-3h, and after the insulation is completed, it is naturally cooled to 0-40°C, and the gas protection atmosphere is one of nitrogen, argon, and helium.

[0015] The invention also discloses a nitrogen-doped fibrous carbon material, which is prepared according to the above preparation method.

[0016] The invention also discloses an application of the nitrogen-doped fibrous carbon material in preparing a positive electrode modified coating of a lithium-sulfur diaphragm.

[0017] Furthermore, the use of the nitrogen-doped fibrous carbon material in preparing a lithium-sulfur separator positive electrode modified coating comprises the following steps:

[0018] Step 1: mixing nitrogen-doped fibrous carbon material, a conductive agent, a binder, and a solvent to obtain a slurry for a modified coating;

[0019] Step 2: Apply the modified coating slurry described in step 1 on the surface of the lithium-sulfur diaphragm and dry it to obtain a lithium-sulfur diaphragm with a modified coating.

[0020] Furthermore, the mass ratio of the nitrogen-doped fibrous carbon material, the conductive agent, the binder and the solvent in step 1 is 4 to 8:2 to 4:1:99.

[0021] Furthermore, the conductive agent is acetylene black, and the binder is polyvinylidene fluoride;

[0022] The solvent is N-methylpyrrolidone or a mixed solution of polyvinylidene fluoride and N-methylpyrrolidone;

[0023] In the mixed solution of polyvinylidene fluoride and N-methylpyrrolidone, the mass fraction of polyvinylidene fluoride is 0.5-2wt.%;

[0024] The time for mixing the modified coating slurry in step 1 is 12 to 96 hours.

[0025] Furthermore, in the step 2, the coating height of the modified coating is 60-150 μm;

[0026] The drying temperature after coating is 40 to 80° C., and the drying time is 12 to 96 hours.

[0027] The present invention also provides a lithium-sulfur battery, comprising a metal lithium negative electrode, a sulfur positive electrode, a battery shell, an electrolyte, and a diaphragm, wherein the diaphragm is the lithium-sulfur diaphragm with a modified coating in the above solution.

[0028] In the present invention, there is no special requirement for animal feathers, common feathers are sufficient, such as duck feathers, goose feathers, chicken feathers, etc. There is no special requirement for the type of animal feathers, such as down feathers, semi-down feathers, fibrous feathers, etc. In the present invention, the feather shaft and feather root should be cut off during the cutting process of the animal hair used, and the remaining structures such as barbs, barbules, barbules, etc. should be retained.

[0029] In the present invention, in step 1 of the method for preparing nitrogen-doped fibrous carbon materials, the drying temperature may be further preferably 55-65° C.; and the drying time may be preferably 18-30 hours.

[0030] In the present invention, in step 2 of the method for preparing nitrogen-doped fibrous carbon materials, the oxidation-thermal decomposition coupling reaction temperature can be further preferably 220-250°C; the heating rate can be further preferably 2N4°C / min; the insulation time can be further preferably 1-2.5h; and the atmosphere is preferably air.

[0031] In the present invention, in step 3 of the method for preparing nitrogen-doped fibrous carbon materials, the pyrolysis temperature can be further preferably 500-700°C; the heating rate can be further preferably 2N4°C / min; the insulation time can be further preferably 1.5-2.5h; and the atmosphere is preferably nitrogen.

[0032] In the application of the present invention, the mass ratio of the nitrogen-doped fibrous carbon material, the conductive agent, the binder and the solvent in step 1 may further preferably be 5 to 7:2 to 4:1:99.

[0033] In the mixed solution of polyvinylidene fluoride and N-methylpyrrolidone, the mass fraction of polyvinylidene fluoride may be further preferably 0.5 to 1.5 wt.%.

[0034] The mixing time of the modified coating slurry in step 1 may further preferably be 24 to 72 hours.

[0035] In step 2, the coating height of the modified coating can be further 80 to 120 μm; the drying temperature after coating can be further 50 to 70° C., and the drying time can be further 36 to 72 hours.

[0036] The nitrogen-doped fibrous carbon material of the present invention has excellent performance, and its mechanism is:

[0037] The present invention uses animal feathers as raw materials, and transforms keratin macromolecules from a chain structure to a cross-linked ring structure through an oxidation-thermal decomposition coupling reaction under mild conditions, thereby significantly improving the thermal stability of the animal feather material.

[0038] On this basis, the animal feather material can maintain a high nitrogen doping level during the subsequent pyrolysis process. Compared with the carbon material obtained by direct pyrolysis of the original animal feather material, its nitrogen retention rate is increased to greater than 30.00%, and its carbon retention rate is increased to greater than 45.00%.

[0039] At the same time, the obtained carbon material has a high content of pyridine / pyrrole nitrogen structure (relative proportion of 68.5%), which can effectively adjust the electron cloud distribution and density on the surface of the carbon material, improve the kinetics of the redox reaction of polysulfide intermediates, and thus improve the rate performance of lithium-sulfur batteries.

[0040] Furthermore, the nitrogen-doped fibrous carbon material provided by the present invention is applied to a lithium-sulfur battery. By using the nitrogen-doped fibrous carbon material to prepare a modified coating on the positive electrode side of the lithium-sulfur battery, the reaction kinetics of polysulfides can be improved and their shuttle effect can be inhibited, thereby improving the rate performance and cycle stability of the lithium-sulfur battery.

[0041] The present invention has the following beneficial effects:

[0042] 1. The carbon material obtained by the present invention has a high nitrogen doping level, can effectively adsorb polysulfides dissolved in the electrolyte, inhibit the shuttle effect occurring on the positive electrode side, and improve the cycle stability of the lithium-sulfur battery.

[0043] 2. In animal hair, the nitrogen content of keratin-based biomass is about 15%, and the nitrogen content of carbon materials after general treatment methods is usually close to 10%, with low yield and nitrogen retention rate of about 17%. Through the method provided by the present invention, the nitrogen content of the obtained carbon material can be increased to 12-15%, with high yield, and the nitrogen retention rate can be increased to 30%.

[0044] 3. The method provided by the present invention can enhance the utilization efficiency of keratin biomass materials and the added value of the obtained products. Specifically, the method provided by the present invention can effectively regulate the directional migration of nitrogen elements during biomass pyrolysis and reduce the emission of nitrogen and carbon-containing gases. In addition, a nitrogen-doped fibrous carbon material can be prepared, which shows certain practical value in improving the performance of lithium-sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The following is a further description with reference to the accompanying drawings.

[0046] Figure 1 This is an electron microscope characterization image of the nitrogen-doped fibrous carbon material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0047] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0048] In the embodiments of the present invention, unless otherwise defined, all professional terms used hereinafter have the same meanings as those generally understood by those skilled in the art.

[0049] Unless otherwise specified, various reagents and raw materials used in the present invention can be purchased from the market.

[0050] In a specific embodiment of the present invention, a four-sided coater is used to coat the modified coating on the separator, and the separator is preferably a Celgard 2325 separator.

[0051] The present invention has no special requirements on the type of the diaphragm, and commercial diaphragms well known to those skilled in the art may be used.

[0052] In an embodiment of the present invention, the preparation method of the positive electrode sheet is:

[0053] The sublimated sulfur, acetylene black and gelatin solution are mixed evenly, the obtained positive electrode slurry is coated on the surface of aluminum foil, and then dried and sliced ​​in sequence to obtain a positive electrode grade sheet;

[0054] The mass fraction of gelatin in the gelatin aqueous solution is 5%, and the solvent is ultrapure water;

[0055] The mass ratio of sublimated sulfur, acetylene black and gelatin solution is preferably 63:30:7;

[0056] The mixing method is mechanical mixing using a planetary ball mill;

[0057] The coating height of the applicator is 150 μm;

[0058] The drying is preferably carried out in a vacuum drying oven at a temperature of 60° C. for a drying time of 55 h.

[0059] The present invention has no special requirements for the tabletting, and the sulfur positive electrode tablets can be pressed into specific sizes according to actual needs;

[0060] In a specific embodiment of the present invention, when the diameter of the aluminum foil is 12 mm, the sulfur loading on the surface of the aluminum foil is preferably 1.0 to 2.0 mg; in a specific embodiment of the present invention, the sulfur positive electrode sheet is preferably a round sheet with a diameter of 10 to 15 mm.

[0061] In an embodiment of the present invention, the preparation method of the electrolyte is as follows:

[0062] The electrolyte used includes a solvent and a solute.

[0063] The solvent is a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether, with a volume ratio of 1:1;

[0064] The solutes include lithium bis(trifluoromethanesulfonyl)imide and anhydrous lithium nitrate, and the concentrations thereof are 1 mol / L and 0.4 mol / L, respectively.

[0065] In an embodiment of the present invention, the test of the assembled design battery is as follows:

[0066] A button cell was assembled with a metal lithium negative electrode, a sulfur positive electrode, a 2025 button cell housing, an electrolyte, and a separator, and the resulting button cell was preferably left to stand for 12 to 36 hours, more preferably for 20 to 28 hours. A charge-discharge cycle test was then performed at a rate of 1C (1C = 1675 mAh / g).

[0067] Example 1

[0068] (1) Preparation of nitrogen-doped fibrous carbon materials:

[0069] Wash the duck feathers and place them in a blast drying oven at 60°C for 24 hours. Cut the dried duck feathers, remove the feather shaft and feather root, and keep the remaining barbs, barbules, barbules and other structures.

[0070] The sheared duck feathers were subjected to an oxidation-thermal decomposition coupling reaction in the air to obtain a cross-linked keratin material. The oxidation-thermal decomposition coupling reaction temperature was 240°C, the heating rate was 3°C / min, the insulation time was 1h, and after the insulation was completed, they were naturally cooled to room temperature.

[0071] The cross-linked keratin material was pyrolyzed in nitrogen at a pyrolysis temperature of 600°C, a heating rate of 5°C / min, and a holding time of 2h. After the holding period, the material was naturally cooled to 25°C to obtain a nitrogen-doped fibrous carbon material.

[0072] from Figure 1It can be seen that thanks to the above oxidation-pyrolysis reaction, the thermal stability of keratin is effectively improved, and the resulting carbon material presents a fibrous structure on a macro scale, maintaining the intrinsic morphology of animal hair. This feature is conducive to the construction of a long-range conductive carbon material network.

[0073] It can be seen from the data in Table 1 that the nitrogen content in the biomass raw material is 14.60%, and the nitrogen content of the carbon material prepared by the present invention is 13.62wt.%. In comparison, the nitrogen content of the carbon material prepared by the conventional method is usually around 10%. The above method greatly increases the nitrogen content in the biomass carbon material, which is very close to the nitrogen content of the biomass itself. The nitrogen retention rate is increased to 34.80%, with an increase rate of 98.17%; the carbon retention rate is increased to 51.61%, with an increase rate of 48.39%.

[0074] Its nitrogen element mainly exists in the form of pyridinic nitrogen and pyrrolic nitrogen, accounting for a total of 68.5%, which can provide abundant lone pair electrons for the surface of carbon materials, effectively improving its ability to anchor and catalyze the conversion of polysulfides.

[0075] (2) Preparation of modified coating:

[0076] Accurately weigh 9.90 g of N-methylpyrrolidone and 0.10 g of polyvinylidene fluoride, add them to the above liquid, stir magnetically for 24 h, set the rotation speed to 1200 rpm, and use the obtained solution as a binder solution for later use.

[0077] 5.00 g of the binder solution, 0.30 g of the nitrogen-doped fibrous carbon material, and 0.15 g of acetylene black were accurately weighed, so that the mass ratio of the nitrogen-doped fibrous carbon material, the conductive agent, and the binder was 6:3:1.

[0078] The slurry was magnetically stirred for 36 h with a rotation speed set at 1200 rpm to obtain a uniformly mixed slurry, which was then coated on a Celgard 2325 separator using a four-sided coater with a height of 90 μm to form a modified coating.

[0079] The coated diaphragm was placed in a fume hood to dry naturally at room temperature for 24 hours, and then transferred to a vacuum drying oven to dry for 24 hours to ensure that all the solvents were volatilized. The drying temperature was 60°C.

[0080] After being completely dried, the diaphragm was cut into discs with a diameter of 19 mm using a cutting machine.

[0081] (3) Assembling lithium-sulfur batteries

[0082] The above-mentioned diaphragm, a common metal lithium negative electrode sheet and a sulfur positive electrode sheet were assembled into a button battery in a glove box protected by an argon environment. The model of the battery shell was CR2025.

[0083] The electrolyte is a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether, preferably in a volume ratio of 1:1; the solute includes lithium bis(trifluoromethanesulfonyl)imide and anhydrous lithium nitrate, preferably in concentrations of 1 mol / L and 0.4 mol / L, respectively. The assembled battery is left to stand for 12 hours.

[0084] Accurately weigh 9.80 g of ultrapure water and 0.20 g of gelatin and add them to the above liquid. Let the resulting solution stand for 20 min and then stand in a 60°C water environment for 20 min. Stir evenly and set aside as a binder solution.

[0085] 3.50 g of the binder solution, 0.63 g of sublimated sulfur, and 0.30 g of acetylene black were accurately weighed, so that the mass ratio of the sublimated sulfur, acetylene black, and gelatin was 63:30:7.

[0086] The slurry was placed in a planetary ball mill and mechanically stirred for 8 h with the rotation speed set to 250 rpm to obtain a uniformly mixed slurry, which was then coated on an aluminum foil using a four-sided coater with a height of 150 μm.

[0087] The coated membrane was placed in a fume hood and dried naturally in the shade for 24 hours at room temperature, and then transferred to a vacuum drying oven for 24 hours to ensure that the solvent was completely volatilized, and the drying temperature was 60° C. After complete drying, the membrane was cut into discs with a diameter of 12 mm using a cutting machine, and the sulfur loading on the surface of the aluminum foil was about 1.5 mg.

[0088] (4) Electrochemical performance test of lithium-sulfur batteries

[0089] The cycle performance of the lithium-sulfur battery was tested on a charge and discharge device, and the test condition was 1C (1C = 1675 mAh / g).

[0090] It can be seen from the test data that the lithium-sulfur battery assembled using the modified diaphragm prepared by the present invention has a higher discharge specific capacity and a more stable cycle efficiency than the lithium-sulfur battery assembled using the commercial diaphragm.

[0091] This indicates that the nitrogen-doped fibrous carbon material of the present invention can effectively inhibit the shuttling effect of polysulfides and effectively improve the rate performance and cycle stability of lithium-sulfur batteries.

[0092] Example 2

[0093] (1) Preparation of nitrogen-doped fibrous carbon materials:

[0094] Wash the duck feathers and place them in a blast drying oven, set the temperature to 50℃, and dry them for 36 hours. Cut the dried duck feathers, cut off the feather shaft and feather root, and keep the remaining barbs, barbules, barbules and other structures.

[0095] The sheared duck feathers are subjected to an oxidation-thermal decomposition coupling reaction in the air to obtain a cross-linked keratin material. The oxidation-thermal decomposition coupling reaction temperature is 200°C, the heating rate is 1°C / min, the insulation time is 0.5h, and after the insulation is completed, it is naturally cooled to room temperature.

[0096] The cross-linked keratin material was pyrolyzed in nitrogen at a pyrolysis temperature of 600°C, a heating rate of 1°C / min, and a holding time of 1 hour. After the holding period, the material was naturally cooled to room temperature to obtain a nitrogen-doped fibrous carbon material.

[0097] It can be seen from the data in Table 1 that the nitrogen content of the carbon material prepared in this example is 12.54 wt.%. In comparison, the nitrogen content of the carbon material prepared in Comparative Example 1 is increased.

[0098] (2) Preparation of modified coating:

[0099] Accurately weigh 9.90 g of N-methylpyrrolidone and 0.10 g of polyvinylidene fluoride, add them to the above liquid, stir magnetically for 96 h, set the rotation speed to 1200 rpm, and use the obtained solution as a binder solution for later use.

[0100] 5.00 g of the binder solution, 0.20 g of the nitrogen-doped fibrous carbon material, and 0.20 g of acetylene black were accurately weighed, so that the mass ratio of the nitrogen-doped fibrous carbon material, the conductive agent, and the binder was 4:4:1.

[0101] The slurry was magnetically stirred for 96 h with a rotation speed set at 1200 rpm to obtain a uniformly mixed slurry, which was then coated on a Celgard 2325 separator using a four-sided coater with a height of 60 μm to form a modified coating.

[0102] The coated diaphragm was placed in a fume hood to dry naturally at room temperature for 52 hours, and then transferred to a vacuum drying oven to dry for 20 hours to ensure that all the solvents were volatilized. The drying temperature was 70°C.

[0103] After being completely dried, the diaphragm was cut into discs with a diameter of 19 mm using a cutting machine.

[0104] (3) Assembling lithium-sulfur batteries

[0105] The above-mentioned diaphragm, a common metal lithium negative electrode sheet and a sulfur positive electrode sheet were assembled into a button battery in a glove box protected by an argon environment. The model of the battery shell was CR2025.

[0106] The electrolyte is a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether, preferably in a volume ratio of 1:1; the solute includes lithium bis(trifluoromethanesulfonyl)imide and anhydrous lithium nitrate, preferably in concentrations of 1 mol / L and 0.4 mol / L, respectively. The assembled battery is left to stand for 12 hours.

[0107] Accurately weigh 9.80 g of ultrapure water and 0.20 g of gelatin and add them to the above liquid. Let the resulting solution stand for 20 min and then stand in a 60°C water environment for 20 min. Stir evenly and set aside as a binder solution.

[0108] 3.50 g of the binder solution, 0.63 g of sublimated sulfur, and 0.30 g of acetylene black were accurately weighed, so that the mass ratio of the sublimated sulfur, acetylene black, and gelatin was 63:30:7.

[0109] The slurry was placed in a planetary ball mill and mechanically stirred for 8 h with the rotation speed set to 250 rpm to obtain a uniformly mixed slurry, which was then coated on an aluminum foil using a four-sided coater with a height of 150 μm.

[0110] The coated membrane was placed in a fume hood and dried naturally in the shade for 24 hours at room temperature, and then transferred to a vacuum drying oven for 24 hours to ensure that the solvent was completely volatilized, and the drying temperature was 60° C. After complete drying, the membrane was cut into discs with a diameter of 12 mm using a cutting machine, and the sulfur loading on the surface of the aluminum foil was about 1.5 mg.

[0111] (4) Electrochemical performance test of lithium-sulfur batteries

[0112] The lithium-sulfur battery was tested for cycle performance on a charge-discharge device under the test condition of 1C (1C = 1675 mAh / g). The test results show that compared with lithium-sulfur batteries using ordinary diaphragms, lithium-sulfur batteries assembled using the modified diaphragm prepared by the present invention have higher discharge specific capacity and more stable cycle efficiency.

[0113] Example 3

[0114] (1) Preparation of nitrogen-doped fibrous carbon materials:

[0115] Wash the duck feathers and place them in a blast drying oven, set the temperature to 80℃, and dry them for 12 hours. Cut the dried duck feathers, cut off the feather shaft and feather root, and keep the remaining barbs, barbules, barbules and other structures.

[0116] The sheared duck feathers were subjected to an oxidation-thermal decomposition coupling reaction in the air to obtain a cross-linked keratin material. The oxidation-thermal decomposition coupling reaction temperature was 220°C, the heating rate was 3°C / min, the insulation time was 1h, and after the insulation was completed, they were naturally cooled to room temperature.

[0117] The cross-linked keratin material was pyrolyzed in nitrogen at a pyrolysis temperature of 600°C, a heating rate of 3°C / min, and a holding time of 2h. After the holding period, the material was naturally cooled to room temperature to obtain a nitrogen-doped fibrous carbon material.

[0118] from Figure 1It can be seen that thanks to the above oxidation-pyrolysis reaction, the thermal stability of keratin is effectively improved, and the resulting carbon material presents a fibrous structure on a macro scale, maintaining the intrinsic morphology of animal hair. This feature is conducive to the construction of a long-range conductive carbon material network.

[0119] It can be seen from the data in Table 1 that the nitrogen content of the carbon material prepared in this example is 12.46 wt.%. In comparison, the nitrogen content of the carbon material prepared in Comparative Example 1 is increased.

[0120] (2) Preparation of modified coating:

[0121] Accurately weigh 9.90 g of N-methylpyrrolidone and 0.10 g of polyvinylidene fluoride, add them to the above liquid, stir magnetically for 24 h, set the rotation speed to 1200 rpm, and use the obtained solution as a binder solution for later use.

[0122] 5.00 g of the binder solution, 0.30 g of the nitrogen-doped fibrous carbon material, and 0.15 g of acetylene black were accurately weighed, so that the mass ratio of the nitrogen-doped fibrous carbon material, the conductive agent, and the binder was 6:3:1.

[0123] The slurry was magnetically stirred for 36 h with a rotation speed set at 1200 rpm to obtain a uniformly mixed slurry, which was then coated on a Celgard 2325 separator using a four-sided coater with a height of 150 μm to form a modified coating.

[0124] The coated diaphragm was placed in a fume hood to dry naturally at room temperature for 30 hours, and then transferred to a vacuum drying oven to dry for 40 hours to ensure that all the solvents were volatilized. The drying temperature was 50°C.

[0125] After being completely dried, the diaphragm was cut into discs with a diameter of 19 mm using a cutting machine.

[0126] (3) Assembling lithium-sulfur batteries

[0127] The above-mentioned diaphragm, a common metal lithium negative electrode sheet and a sulfur positive electrode sheet were assembled into a button battery in a glove box protected by an argon environment. The model of the battery shell was CR2025.

[0128] The electrolyte is a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether, preferably in a volume ratio of 1:1; the solute includes lithium bis(trifluoromethanesulfonyl)imide and anhydrous lithium nitrate, preferably in concentrations of 1 mol / L and 0.4 mol / L, respectively. The assembled battery is left to stand for 12 hours.

[0129] Accurately weigh 9.80 g of ultrapure water and 0.20 g of gelatin and add them to the above liquid. Let the resulting solution stand for 20 min and then stand in a 60°C water environment for 20 min. Stir evenly and set aside as a binder solution.

[0130] 3.50 g of the binder solution, 0.63 g of sublimated sulfur, and 0.30 g of acetylene black were accurately weighed, so that the mass ratio of the sublimated sulfur, acetylene black, and gelatin was 63:30:7.

[0131] The slurry was placed in a planetary ball mill and mechanically stirred for 8 h with the rotation speed set to 250 rpm to obtain a uniformly mixed slurry, which was then coated on an aluminum foil using a four-sided coater with a height of 150 μm.

[0132] The coated membrane was placed in a fume hood and dried naturally in the shade for 24 hours at room temperature, and then transferred to a vacuum drying oven for 24 hours to ensure that the solvent was completely volatilized, and the drying temperature was 60° C. After complete drying, the membrane was cut into discs with a diameter of 12 mm using a cutting machine, and the sulfur loading on the surface of the aluminum foil was about 1.5 mg.

[0133] (4) Electrochemical performance test of lithium-sulfur batteries

[0134] The lithium-sulfur battery was tested for cycle performance on a charge-discharge device under the test condition of 1C (1C = 1675 mAh / g). The test results show that compared with lithium-sulfur batteries using ordinary diaphragms, lithium-sulfur batteries assembled using the modified diaphragm prepared by the present invention have higher discharge specific capacity and more stable cycle efficiency.

[0135] Example 4

[0136] (1) Preparation of nitrogen-doped fibrous carbon materials:

[0137] Wash the duck feathers and place them in a blast drying oven, set the temperature to 80℃, and dry them for 12 hours. Cut the dried duck feathers, cut off the feather shaft and feather root, and keep the remaining barbs, barbules, barbules and other structures.

[0138] The sheared duck feathers were subjected to an oxidation-thermal decomposition coupling reaction in the air to obtain a cross-linked keratin material. The oxidation-thermal decomposition coupling reaction temperature was 260°C, the heating rate was 5°C / min, the insulation time was 3h, and after the insulation was completed, they were naturally cooled to room temperature.

[0139] The cross-linked keratin material was pyrolyzed in nitrogen at a pyrolysis temperature of 400°C, a heating rate of 1°C / min, and a holding time of 3 hours. After the holding period, the material was naturally cooled to room temperature to obtain a nitrogen-doped fibrous carbon material.

[0140] (2) Preparation of modified coating:

[0141] Accurately weigh 9.90 g of N-methylpyrrolidone and 0.10 g of polyvinylidene fluoride, add them to the above liquid, stir magnetically for 96 h, set the rotation speed to 1200 rpm, and use the obtained solution as a binder solution for later use.

[0142] 5.00 g of the binder solution, 0.40 g of the nitrogen-doped fibrous carbon material, and 0.10 g of acetylene black were accurately weighed, so that the mass ratio of the nitrogen-doped fibrous carbon material, the conductive agent, and the binder was 8:2:1.

[0143] The slurry was magnetically stirred for 96 h with a rotation speed set at 1200 rpm to obtain a uniformly mixed slurry, which was then coated on a Celgard 2325 separator using a four-sided coater with a height of 60 μm to form a modified coating.

[0144] The coated diaphragm was placed in a fume hood for natural drying at room temperature for 36 hours, and then transferred to a vacuum drying oven for drying for 96 hours to ensure that all the solvents were volatilized. The drying temperature was 40°C.

[0145] After being completely dried, the diaphragm was cut into discs with a diameter of 19 mm using a cutting machine.

[0146] (3) Assembling lithium-sulfur batteries

[0147] The above-mentioned diaphragm, a common metal lithium negative electrode sheet and a sulfur positive electrode sheet were assembled into a button battery in a glove box protected by an argon environment. The model of the battery shell was CR2025.

[0148] The electrolyte is a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether, preferably in a volume ratio of 1:1; the solute includes lithium bis(trifluoromethanesulfonyl)imide and anhydrous lithium nitrate, preferably in concentrations of 1 mol / L and 0.4 mol / L, respectively. The assembled battery is left to stand for 12 hours.

[0149] Accurately weigh 9.80 g of ultrapure water and 0.20 g of gelatin and add them to the above liquid. Let the resulting solution stand for 20 min and then stand in a 60°C water environment for 20 min. Stir evenly and set aside as a binder solution.

[0150] 3.50 g of the binder solution, 0.63 g of sublimated sulfur, and 0.30 g of acetylene black were accurately weighed, so that the mass ratio of the sublimated sulfur, acetylene black, and gelatin was 63:30:7.

[0151] The slurry was placed in a planetary ball mill and mechanically stirred for 8 h with the rotation speed set to 250 rpm to obtain a uniformly mixed slurry, which was then coated on an aluminum foil using a four-sided coater with a height of 150 μm.

[0152] The coated membrane was placed in a fume hood and dried naturally in the shade for 24 hours at room temperature, and then transferred to a vacuum drying oven for 24 hours to ensure that the solvent was completely volatilized, and the drying temperature was 60° C. After complete drying, the membrane was cut into discs with a diameter of 12 mm using a cutting machine, and the sulfur loading on the surface of the aluminum foil was about 1.5 mg.

[0153] (4) Electrochemical performance test of lithium-sulfur batteries

[0154] The lithium-sulfur battery was tested for cycle performance on a charge-discharge device under the test condition of 1C (1C = 1675 mAh / g). The test results show that compared with lithium-sulfur batteries using ordinary diaphragms, lithium-sulfur batteries assembled using the modified diaphragm prepared by the present invention have higher discharge specific capacity and more stable cycle efficiency.

[0155] Example 5

[0156] (1) Preparation of nitrogen-doped fibrous carbon materials:

[0157] Wash the duck feathers and place them in a blast drying oven, set the temperature to 80℃, and dry them for 12 hours. Cut the dried duck feathers, cut off the feather shaft and feather root, and keep the remaining barbs, barbules, barbules and other structures.

[0158] The sheared duck feathers are subjected to an oxidation-thermal decomposition coupling reaction in the air to obtain a cross-linked keratin material. The oxidation-thermal decomposition coupling reaction temperature is 240°C, the heating rate is 5°C / min, and the insulation time is 3h. After the insulation is completed, the duck feathers are naturally cooled to room temperature.

[0159] The cross-linked keratin material was pyrolyzed in nitrogen at a pyrolysis temperature of 800°C, a heating rate of 1°C / min, and a holding time of 3 hours. After the holding period, the material was naturally cooled to room temperature to obtain a nitrogen-doped fibrous carbon material.

[0160] (2) Preparation of modified coating:

[0161] Accurately weigh 9.90 g of N-methylpyrrolidone and 0.10 g of polyvinylidene fluoride, add them to the above liquid, stir magnetically for 96 h, set the rotation speed to 1200 rpm, and use the obtained solution as a binder solution for later use.

[0162] 5.00 g of the binder solution, 0.40 g of the nitrogen-doped fibrous carbon material, and 0.10 g of acetylene black were accurately weighed, so that the mass ratio of the nitrogen-doped fibrous carbon material, the conductive agent, and the binder was 6:3:1.

[0163] The slurry was magnetically stirred for 96 h with a rotation speed set at 1200 rpm to obtain a uniformly mixed slurry, which was then coated on a Celgard 2325 separator using a four-sided coater with a height of 60 μm to form a modified coating.

[0164] The coated diaphragm was placed in a fume hood to dry naturally at room temperature for 2 h, and then transferred to a vacuum drying oven to dry for 12 h to ensure that all the solvents were volatilized. The drying temperature was 80°C.

[0165] After being completely dried, the diaphragm was cut into discs with a diameter of 19 mm using a cutting machine.

[0166] (3) Assembling lithium-sulfur batteries

[0167] The above-mentioned diaphragm, a common metal lithium negative electrode sheet and a sulfur positive electrode sheet were assembled into a button battery in a glove box protected by an argon environment. The model of the battery shell was CR2025.

[0168] The electrolyte is a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether, preferably in a volume ratio of 1:1; the solute includes lithium bis(trifluoromethanesulfonyl)imide and anhydrous lithium nitrate, preferably in concentrations of 1 mol / L and 0.4 mol / L, respectively. The assembled battery is left to stand for 12 hours.

[0169] Accurately weigh 9.80 g of ultrapure water and 0.20 g of gelatin and add them to the above liquid. Let the resulting solution stand for 20 min and then stand in a 60°C water environment for 20 min. Stir evenly and set aside as a binder solution.

[0170] 3.50 g of the binder solution, 0.63 g of sublimated sulfur, and 0.30 g of acetylene black were accurately weighed, so that the mass ratio of the sublimated sulfur, acetylene black, and gelatin was 63:30:7.

[0171] The slurry was placed in a planetary ball mill and mechanically stirred for 8 h with the rotation speed set to 250 rpm to obtain a uniformly mixed slurry, which was then coated on an aluminum foil using a four-sided coater with a height of 150 μm.

[0172] The coated membrane was placed in a fume hood and dried naturally in the shade for 24 hours at room temperature, and then transferred to a vacuum drying oven for 24 hours to ensure that the solvent was completely volatilized, and the drying temperature was 60° C. After complete drying, the membrane was cut into discs with a diameter of 12 mm using a cutting machine, and the sulfur loading on the surface of the aluminum foil was about 1.5 mg.

[0173] (4) Electrochemical performance test of lithium-sulfur batteries

[0174] The lithium-sulfur battery was tested for cycle performance on a charge-discharge device under the test condition of 1C (1C = 1675 mAh / g). The test results show that compared with lithium-sulfur batteries using ordinary diaphragms, lithium-sulfur batteries assembled using the modified diaphragm prepared by the present invention have higher discharge specific capacity and more stable cycle efficiency.

[0175] Comparative Example 1

[0176] (1) Preparation of keratin-based carbon materials:

[0177] Wash the duck feathers and place them in a blast drying oven at 60°C for 24 hours. Cut the dried duck feathers, remove the feather shaft and feather root, and keep the remaining barbs, barbules, barbules and other structures.

[0178] The keratin-based carbon material was pyrolyzed in nitrogen at a pyrolysis temperature of 600°C, a heating rate of 5°C / min, and a holding time of 2h. After the holding period, the material was naturally cooled to 25°C to obtain a nitrogen-doped fibrous carbon material.

[0179] It can be seen from the data in Table 1 that the nitrogen content is only 10.21%, the nitrogen retention rate is increased to 17.56%, and the carbon retention rate is only 39.26%.

[0180] (2) Preparation of modified coating:

[0181] Accurately weigh 9.90 g of N-methylpyrrolidone and 0.10 g of polyvinylidene fluoride, add them to the above liquid, stir magnetically for 24 h, set the rotation speed to 1200 rpm, and use the obtained solution as a binder solution for later use.

[0182] 5.00 g of the binder solution, 0.30 g of keratin-based carbon material, and 0.15 g of acetylene black were accurately weighed, so that the mass ratio of the keratin-based carbon material, the conductive agent, and the binder was 6:3:1.

[0183] The slurry was magnetically stirred for 36 h with a rotation speed set at 1200 rpm to obtain a uniformly mixed slurry, which was then coated on a Celgard 2325 separator using a four-sided coater with a height of 90 μm to form a modified coating.

[0184] The coated diaphragm was placed in a fume hood to dry naturally at room temperature for 24 hours, and then transferred to a vacuum drying oven to dry for 24 hours to ensure that all the solvents were volatilized. The drying temperature was 60°C.

[0185] After being completely dried, the diaphragm was cut into discs with a diameter of 19 mm using a cutting machine.

[0186] (3) Assembling lithium-sulfur batteries

[0187] The above-mentioned diaphragm, a common metal lithium negative electrode sheet and a sulfur positive electrode sheet were assembled into a button battery in a glove box protected by an argon environment. The model of the battery shell was CR2025.

[0188] The electrolyte is a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether, preferably in a volume ratio of 1:1; the solute includes lithium bis(trifluoromethanesulfonyl)imide and anhydrous lithium nitrate, preferably in concentrations of 1 mol / L and 0.4 mol / L, respectively. The assembled battery is left to stand for 12 hours.

[0189] Accurately weigh 9.80 g of ultrapure water and 0.20 g of gelatin and add them to the above liquid. Let the resulting solution stand for 20 min and then stand in a 60°C water environment for 20 min. Stir evenly and set aside as a binder solution.

[0190] 3.50 g of the binder solution, 0.63 g of sublimated sulfur, and 0.30 g of acetylene black were accurately weighed, so that the mass ratio of the sublimated sulfur, acetylene black, and gelatin was 63:30:7.

[0191] The slurry was placed in a planetary ball mill and mechanically stirred for 8 h with the rotation speed set to 250 rpm to obtain a uniformly mixed slurry, which was then coated on an aluminum foil using a four-sided coater with a height of 150 μm.

[0192] The coated membrane was placed in a fume hood and dried naturally in the shade for 24 hours at room temperature, and then transferred to a vacuum drying oven for 24 hours to ensure that the solvent was completely volatilized, and the drying temperature was 60° C. After complete drying, the membrane was cut into discs with a diameter of 12 mm using a cutting machine, and the sulfur loading on the surface of the aluminum foil was about 1.5 mg.

[0193] (4) Electrochemical performance test of lithium-sulfur batteries

[0194] The lithium-sulfur battery was subjected to a cycle performance test on a charge-discharge device, and the test condition was 1C (1C=1675 mAh / g). As shown in Table 2, the electrochemical performance was weaker than that of Example 1.

[0195] Comparative Example 2

[0196] (1) Assembling lithium-sulfur batteries

[0197] The above-mentioned diaphragm, a common metal lithium negative electrode sheet and a sulfur positive electrode sheet were assembled into a button battery in a glove box protected by an argon environment. The model of the battery shell was CR2025.

[0198] The electrolyte is a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether, preferably in a volume ratio of 1:1; the solute includes lithium bis(trifluoromethanesulfonyl)imide and anhydrous lithium nitrate, preferably in concentrations of 1 mol / L and 0.4 mol / L, respectively. The assembled battery is left to stand for 12 hours.

[0199] Accurately weigh 9.80 g of ultrapure water and 0.20 g of gelatin and add them to the above liquid. Let the resulting solution stand for 20 min and then stand in a 60°C water environment for 20 min. Stir evenly and set aside as a binder solution.

[0200] 3.50 g of the binder solution, 0.63 g of sublimated sulfur, and 0.30 g of acetylene black were accurately weighed, so that the mass ratio of the sublimated sulfur, acetylene black, and gelatin was 63:30:7.

[0201] The slurry was placed in a planetary ball mill and mechanically stirred for 8 h with the rotation speed set to 250 rpm to obtain a uniformly mixed slurry, which was then coated on an aluminum foil using a four-sided coater with a height of 150 μm.

[0202] The coated membrane was placed in a fume hood and dried naturally in the shade for 24 hours at room temperature, and then transferred to a vacuum drying oven for 24 hours to ensure that the solvent was completely volatilized, and the drying temperature was 60° C. After complete drying, the membrane was cut into discs with a diameter of 12 mm using a cutting machine, and the sulfur loading on the surface of the aluminum foil was about 1.5 mg.

[0203] (2) Electrochemical performance test of lithium-sulfur batteries

[0204] The lithium-sulfur battery was tested for cycle performance on a charge-discharge device under the test condition of 1C (1C=1675 mAh / g). As shown in Table 2, compared with Example 1 and Comparative Example 1, both showed weaker electrochemical performance.

[0205] The elemental analysis results of the nitrogen-doped fibrous carbon materials and biomass raw materials prepared in Example 1, Example 2, Example 3 and Comparative Example 1 are shown in Table 1:

[0206] Table 1

[0207]

[0208] The electrochemical performance of the batteries prepared in Example 1 and Comparative Example 1 is shown in Table 2:

[0209] Table 2

[0210]

[0211] The preparation method of the present invention uses animal feathers as raw materials, and through a mild oxidation-pyrolysis coupling reaction, the keratin macromolecules are transformed from a chain structure to a cross-linked ring structure, which significantly improves the thermal stability of the animal feather material. On this basis, the animal hair material can maintain a high nitrogen doping level during the subsequent pyrolysis process, and the retention rate of nitrogen and carbon elements is greatly improved compared to the carbon material obtained by direct pyrolysis of the original animal feather material. The lithium-sulfur battery positive electrode modified coating prepared using the nitrogen-doped fibrous carbon material prepared by the present invention can effectively adsorb polysulfides dissolved in the electrolyte, inhibit the shuttle effect occurring on the positive electrode side, and significantly improve the rate performance and cycle stability of the lithium-sulfur battery.

[0212] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the implementation of the present invention is not limited to the above-mentioned method. As long as various improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a nitrogen-doped fibrous carbon material, characterized in that: The following steps are involved: Step 1: Wash the animal feathers, dry them and cut them to obtain cut animal feather materials; Step 2: subjecting the animal feather material cut in step 1 to an oxidation-thermal decomposition coupling reaction in an oxygen-containing atmosphere to obtain a cross-linked animal feather material; Step 3: Pyrolyze the cross-linked animal feather material obtained in step 2 under a gas protective atmosphere to obtain a nitrogen-doped fibrous carbon material having a high nitrogen content.

2. The method for preparing nitrogen-doped fibrous carbon material according to claim 1, characterized in that: In the step 1, the drying temperature is 50 to 80° C. and the drying time is 12 to 36 hours.

3. The method for preparing nitrogen-doped fibrous carbon material according to claim 1, characterized in that: In the step 2, the oxidation-thermal decomposition coupling reaction temperature is 200-260°C, the heating rate is 1-5°C / min, the insulation time is 0.5-3h, and after the insulation is completed, it is naturally cooled to room temperature; the oxygen-containing atmosphere is one of air and nitrogen / oxygen mixed gas.

4. The method for preparing the nitrogen-doped fibrous carbon material according to claim 1, characterized in that: In the step 3, the pyrolysis temperature is 400-800°C, the heating rate is 1-5°C / min, the insulation time is 1-3h, and after the insulation is completed, it is naturally cooled to room temperature. The gas protection atmosphere is one of nitrogen, argon and helium.

5. A nitrogen-doped fibrous carbon material, characterized in that: The nitrogen-doped fibrous carbon material is prepared according to the preparation method described in any one of claims 1-4.

6. Use of the nitrogen-doped fibrous carbon material according to claim 5 in preparing a positive electrode modified coating for a lithium-sulfur separator.

7. The use of the nitrogen-doped fibrous carbon material according to claim 6 in preparing a positive electrode modified coating of a lithium-sulfur separator, characterized in that: The following steps are involved: Step 1: mixing nitrogen-doped fibrous carbon material, a conductive agent, a binder, and a solvent to obtain a slurry for a modified coating; Step 2: Apply the modified coating slurry described in step 1 on the surface of the lithium-sulfur diaphragm and dry it to obtain a lithium-sulfur battery diaphragm with a modified coating.

8. The use according to claim 7, characterized in that: The mass ratio of the nitrogen-doped fibrous carbon material, the conductive agent, the binder and the solvent described in step 1 is 4 to 8:2 to 4:1:

99.

9. The use according to claim 7, characterized in that: The conductive agent is acetylene black, and the binder is polyvinylidene fluoride; The solvent is N-methylpyrrolidone or a mixed solution of polyvinylidene fluoride and N-methylpyrrolidone; In the mixed solution of polyvinylidene fluoride and N-methylpyrrolidone, the mass fraction of polyvinylidene fluoride is 0.5-2wt.%; The time for mixing the modified coating slurry in step 1 is 12 to 96 hours.

10. The use according to claim 7, characterized in that: In the step 2, the coating height of the modified coating is 60-150 μm; The drying temperature after coating is 40 to 80° C., and the drying time is 12 to 96 hours.

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