A nitrogen-doped fibrous carbon material, a preparation method and application thereof

Abstract

The present application relates to a kind of nitrogen-doped fibrous carbon materials and its preparation method and application.The preparation method uses animal feather as raw material, and the transformation of keratin macromolecule from chain structure to cross-linked structure is carried out by mild condition oxidation-pyrolysis coupling reaction, which significantly improves the thermal stability of animal feather material.On this basis, the animal hair material can maintain high nitrogen doping level during subsequent pyrolysis process, compared with the carbon material obtained by direct pyrolysis of the original animal feather material, the retention rate of nitrogen and carbon elements is significantly improved.The lithium-sulfur battery positive electrode modification coating prepared by the keratin-based nitrogen-doped fibrous carbon material prepared by the present application effectively improves the rate performance and cycle stability of lithium-sulfur battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of biomass pyrolysis and lithium-sulfur battery, and particularly relates to a nitrogen-doped fibrous carbon material and a preparation method and application thereof. BACKGROUND

[0002] Lithium-sulfur battery is the most potential energy storage system in the next generation, which has high theoretical energy density (2600 Wh kg -1 ) and low price. However, the soluble lithium polysulfide produced by the positive active material in the charging and discharging process will cause serious shuttle effect, resulting in poor cycle stability and low energy density of lithium-sulfur battery, which limits its practical application.

[0003] The nitrogen-doped carbon material has high specific surface area and conductivity, which can be applied to capture the dissolved polysulfide on the positive side, reduce the loss of active material caused by the shuttle effect. Nitrogen doping can significantly improve the interaction between the carbon material and lithium polysulfide, inhibit the shuttle effect of lithium polysulfide, and improve the reaction kinetics on the positive side of lithium-sulfur battery.

[0004] Protein-based waste biomass, such as waste animal hair, animal horn and plant by-products, has the characteristics of high carbon and nitrogen element content, which can be used as a precursor for preparing nitrogen-doped carbon material. However, when the waste biomass is pyrolyzed and carbonized, the retention rate of carbon and nitrogen elements in the solid product is low, and the obtained carbon material is often at a low level of nitrogen doping, which is difficult to effectively enhance the reaction kinetics on the positive side of lithium-sulfur battery and inhibit the capacity decay, greatly limiting the application potential of protein-based waste biomass in preparing high-performance nitrogen-doped carbon material. SUMMARY

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

[0006] The application uses animal hair as raw material, and improves the thermal stability of animal hair material through oxidation-pyrolysis coupling reaction without additional introduction of nitrogen source, so that it can maintain ultra-high nitrogen doping level after pyrolysis. The obtained nitrogen-doped fibrous carbon material can be used on the positive side of lithium-sulfur battery to improve its reaction kinetics and inhibit the shuttle effect, and significantly improve the rate performance and cycle stability of lithium-sulfur battery.

[0007] To achieve the above purpose, the application adopts the following technical solutions:

[0008] A preparation method of a nitrogen-doped fibrous carbon material, comprising the following steps:

[0009] Step 1: washing animal hair, drying and cutting to obtain cut animal hair material;

[0010] Step 2: the clipped animal feather material in step 1 is subjected to an oxidation-pyrolysis coupling reaction in an oxygen-containing atmosphere to obtain a crosslinked animal feather material;

[0011] Step 3: the crosslinked animal feather material obtained in step 2 is subjected to pyrolysis in a gas protection atmosphere to obtain a nitrogen-doped fibrous carbon material.

[0012] Further, in step 1, the drying temperature is 50-80℃, and the time is 12-36h.

[0013] Further, in step 2, the oxidation-pyrolysis coupling reaction temperature is 200-260℃, the heating rate is 1-5℃ / min, the holding time is 0.5-3h, and after the holding time ends, the temperature is naturally cooled to room temperature; the oxygen-containing atmosphere is one of air, nitrogen / oxygen mixed gas.

[0014] Further, in step 3, the pyrolysis temperature is 400-800℃, the heating rate is 1-5℃ / min, the holding time is 1-3h, and after the holding time ends, the temperature is naturally cooled to 0-40℃, and the gas protection atmosphere is one of nitrogen, argon, and helium.

[0015] The application also discloses a nitrogen-doped fibrous carbon material prepared by the above preparation method.

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

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

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

[0019] Step 2: coating and drying the modified coating slurry on the surface of a lithium-sulfur diaphragm to obtain a lithium-sulfur diaphragm with a modified coating.

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

[0021] Further, 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] The mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride and N-methyl pyrrolidone mixed solution is 0.5-2 wt.%.

[0024] The mixing time of the slurry for the modified coating in step 1 is 12-96 h.

[0025] Further, in step 2, the coating height of the modified coating is 60-150 mu m.

[0026] The drying temperature after coating is 40-80 DEG C, and the drying time is 12-96 h.

[0027] The application also provides a lithium-sulfur battery, comprising a metal lithium negative electrode, a sulfur positive electrode, a battery shell, an electrolyte, and a separator.

[0028] In the application, there is no special requirement for the animal feathers, and common feathers can be used, which can be duck feathers, goose feathers, chicken feathers, etc.

[0029] In the application, in step 1 of the preparation method of the nitrogen-doped fibrous carbon material, the drying temperature can be further preferably 55-65 DEG C; and the time is preferably 18-30 h.

[0030] In the application, in step 2 of the preparation method of the nitrogen-doped fibrous carbon material, the oxidation-pyrolysis coupling reaction temperature can be further preferably 220-250 DEG C; the heating rate can be further preferably 2N4 DEG C / min; the holding time can be further preferably 1-2.5 h; and the atmosphere is preferably air.

[0031] In the application, in step 3 of the preparation method of the nitrogen-doped fibrous carbon material, the pyrolysis temperature can be further preferably 500-700 DEG C; the heating rate can be further preferably 2N4 DEG C / min; the holding time can be further preferably 1.5-2.5 h; and the atmosphere is preferably nitrogen.

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

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

[0034] The mixing time of the slurry for the modified coating in step 1 can be further preferably 24-72 h.

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

[0036] The nitrogen-doped fibrous carbon material has excellent performance, and the mechanism is that:

[0037] The present application uses animal feathers as raw materials, and through mild oxidation-pyrolysis coupling reaction, the keratin macromolecules are transformed from chain structure to cross-linked ring structure, which significantly improves the thermal stability of animal feather materials.

[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 directly pyrolyzing the original animal feather material, the nitrogen element retention rate is increased to more than 30.00%, and the carbon element retention rate is increased to more 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 of the surface of the carbon material, improve the kinetics of the oxidation-reduction reaction of polysulfide intermediates, and further improve the rate performance of lithium-sulfur batteries.

[0040] Further, the nitrogen-doped fibrous carbon material provided by the present application is applied to lithium-sulfur batteries, and by using the nitrogen-doped fibrous carbon material to prepare a modified coating on the positive side of the lithium-sulfur battery, the reaction kinetics of polysulfide can be improved and the shuttle effect can be inhibited, and the rate performance and cycle stability of the lithium-sulfur battery can be improved.

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

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

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

[0044] 3、The method provided by the application can enhance the utilization efficiency of keratin biomass materials and the added value of the obtained products. Specifically, the method provided by the application can effectively regulate the directional migration of nitrogen elements in the biomass pyrolysis process, reduce the emission of nitrogen-containing and carbon-containing gases, and prepare a nitrogen-doped fibrous carbon material, which exhibits certain practical value in improving the performance of lithium-sulfur batteries. BRIEF DESCRIPTION OF DRAWINGS

[0045] Further description will be given in combination with the drawings.

[0046] Figure 1 An electron microscope characterization diagram of the nitrogen-doped fibrous carbon material prepared for the embodiment 1 of the application. DETAILED DESCRIPTION

[0047] The application will be further described in combination with the drawings and embodiments:

[0048] In the embodiments of the application, unless otherwise defined, all the professional terms used in the following have the same meaning as generally understood by those skilled in the art.

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

[0050] In the specific embodiments of the application, a four-sided coater is used to coat a modified coating layer on the separator, and the separator is preferably a Celgard2325 separator.

[0051] The application does not have special requirements for the type of the separator, and a commercial separator well known to those skilled in the art can be used.

[0052] In the embodiments of the application, the preparation method of the positive electrode sheet is:

[0053] The sublimed sulfur, acetylene black and gelatin solution are uniformly mixed, the obtained positive electrode slurry is coated on the surface of an aluminum foil, and then drying and slicing are sequentially performed to obtain a positive electrode 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 the sublimed 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 coater is 150 mu m;

[0058] The drying is preferably performed in a vacuum drying oven, the temperature is 60 DEG C, and the drying time is 55 h.

[0059] The invention has no special requirements for the tablet, and the sulfur positive electrode tablet of a specific size can be pressed according to actual needs.

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

[0061] In the embodiment of the present application, 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, and the volume ratio is 1:1;

[0064] The solute includes lithium bistrifluoromethanesulfonimide and anhydrous lithium nitrate, and the concentrations are 1 mol / L and 0.4 mol / L, respectively.

[0065] In the embodiment of the present application, the test of assembling a designed battery is as follows:

[0066] The metal lithium negative electrode, the sulfur positive electrode, the 2025 button cell shell, the electrolyte, and the diaphragm are assembled into a button cell, and the standing time of the obtained button cell is preferably 12-36 h, and more preferably 20-28 h. Then, the charge-discharge cycle test is carried out under the condition of a rate of 1C (1C=1675 mAh / g).

[0067] Example 1

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

[0069] The washed duck primary feather is dried in a forced air drying oven, the temperature is set to 60℃, and the time should be 24h. The obtained dried duck primary feather is cut, the feather shaft and feather are cut off, and the remaining feather branch, feather twig, feather hook and the like are retained.

[0070] The cut duck primary feather is subjected to an oxidation-pyrolysis coupling reaction in air, and a crosslinked keratin material is obtained, the oxidation-pyrolysis coupling reaction temperature is 240℃, the heating rate is 3℃ / min, and the holding time is 1h. After the holding is completed, it is naturally cooled to room temperature.

[0071] The crosslinked keratin material is pyrolyzed in nitrogen, the pyrolysis temperature is 600℃, the heating rate is 5℃ / min, and the holding time is 2h. After the holding is completed, it is naturally cooled to 25℃, and a nitrogen-doped fibrous carbon material is obtained.

[0072] From Figure 1As can be seen, thanks to the above oxidation-pyrolysis reaction, the thermal stability of keratin is effectively improved, and the obtained carbon material macroscopically presents a fibrous structure, maintaining the intrinsic morphology of animal hair. This feature is conducive to building a long-range conductive carbon material network.

[0073] As can be seen from the data in Table 1, the nitrogen element content in the biomass raw material is 14.60%, and the nitrogen element content in the carbon material prepared by the present application is 13.62wt.%. In contrast, the nitrogen element content of the carbon material prepared by the ordinary method is usually about 10%, and the above method greatly improves the nitrogen element content of the biomass carbon material, which is very close to the nitrogen element content of the biomass itself. The retention rate of nitrogen element is improved to 34.80%, and the improvement rate is 98.17%; the retention rate of carbon element is improved to 51.61%, and the improvement rate is 48.39%.

[0074] The nitrogen element mainly exists in the form of pyridine nitrogen and pyrrole nitrogen, accounting for a total of 68.5%, which can provide abundant lone pair electrons on the surface of the carbon material, effectively improving its anchoring and catalytic conversion ability to polysulfides.

[0075] (2) Preparation of modified coating:

[0076] Accurately weigh 9.90g of N-methyl pyrrolidone and 0.10g of polyvinylidene fluoride into the above liquid, magnetically stir for 24h, and set the stirring speed to 1200rpm. The obtained solution is used as a binder solution.

[0077] Accurately weigh 5.00g of the above binder solution, 0.30g of the fibrous carbon material doped with nitrogen, and 0.15g of acetylene black, so that the mass ratio of the nitrogen-doped fibrous carbon material, the conductive agent, and the binder is 6:3:1.

[0078] Magnetic stirring of the above slurry is carried out for 36h at a stirring speed of 1200rpm to obtain a uniformly mixed slurry, and a four-sided coater with a height of 90μm is used to coat the Celgard2325 separator with a modified coating.

[0079] After the obtained coated separator is naturally air-dried at room temperature for 24h in a fume hood, it is transferred to a vacuum drying oven for drying for 24h to ensure that the solvent is completely volatilized, and the drying temperature is 60℃.

[0080] After complete drying, the separator is cut into a circular piece with a diameter of 19mm using a dicing machine.

[0081] (3) Assembly of lithium-sulfur battery

[0082] The above separator, ordinary metal lithium sheet negative electrode, and sulfur positive electrode sheet are assembled into a button cell in an argon environment protection glove box, and the battery shell is of CR2025 type.

[0083] The electrolyte is a mixed solvent of 1,3-dioxolane and ethylene glycol dimethyl ether, the volume ratio of which is preferably 1:1; the solute includes lithium bistrifluoromethanesulfonylimide and anhydrous lithium nitrate, the concentrations of which are preferably 1 mol / L and 0.4 mol / L respectively. The assembled battery is left for 12 h.

[0084] Accurately weigh 9.80 g of ultrapure water and 0.20 g of gelatin into the above liquid, and after the obtained solution is left for 20 min and then left for 20 min in a water bath environment at 60℃, it is stirred uniformly and used as an adhesive solution.

[0085] Accurately weigh 3.50 g of the above adhesive solution, 0.63 g of sublimed sulfur and 0.30 g of acetylene black, so that the mass ratio of the sublimed sulfur, acetylene black and gelatin is 63:30:7.

[0086] The above slurry is placed in a planetary ball mill for mechanical stirring for 8 h at a rotation speed of 250 rpm to obtain a uniformly mixed slurry, and a four-side coater with a height of 150 μm is used to coat the slurry on an aluminum foil.

[0087] The obtained coated separator is left to dry naturally in a fume hood at room temperature for 24 h and then transferred to a vacuum drying oven for drying for 24 h to ensure that all the solvent is volatilized, and the drying temperature is 60℃. After complete drying, the separator is cut into a circular piece with a diameter of 12 mm by using a film cutting machine, and the sulfur loading on the surface of the aluminum foil is about 1.5 mg.

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

[0089] The lithium-sulfur battery is subjected to a cycle performance test on a charge-discharge device, and the test conditions are 1C (1C = 1675 mAh / g).

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

[0091] It is illustrated that the nitrogen-doped fibrous carbon material of the present application can effectively inhibit the shuttle effect of polysulfides and effectively improve the rate performance and cycle stability of the lithium-sulfur battery.

[0092] Example 2

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

[0094] The washed duck quill is dried in a forced air drying oven, the temperature of which is set to 50℃, and the time is 36 h. The obtained dried duck quill is cut, the quill shaft and quill are cut off and the remaining quill branches, quill twigs, quill hooks and the like are retained.

[0095] The sheared duck contour feather was subjected to oxidation-pyrolysis coupling reaction in air to obtain a crosslinked keratin material, the oxidation-pyrolysis coupling reaction temperature was 200℃, the heating rate was 1℃ / min, and the holding time was 0.5 h, and after the holding was completed, the sample was naturally cooled to room temperature.

[0096] The crosslinked keratin material was subjected to pyrolysis in nitrogen, the pyrolysis temperature was 600℃, the heating rate was 1℃ / min, and the holding time was 1 h, and after the holding was completed, the sample was naturally cooled to room temperature to obtain a nitrogen-doped fibrous carbon material.

[0097] As can be seen from the data in Table 1, the nitrogen element content of the carbon material prepared in this example was 12.54 wt.%. In comparison, the carbon material prepared in Comparative Example 1 had an improved nitrogen element content.

[0098] (2) Preparation of the modified coating:

[0099] Accurately weighed 9.90 g of N-methyl pyrrolidone and 0.10 g of polyvinylidene fluoride was added to the above-mentioned liquid, and the resulting solution was used as a binder solution.

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

[0101] The above-mentioned slurry was subjected to magnetic stirring for 96 h at a speed of 1200 rpm to obtain a uniformly mixed slurry, and a four-sided applicator with a height of 60 μm was used to coat the Celgard 2325 separator with the modified coating.

[0102] The coated separator was placed in a fume hood and naturally air-dried at room temperature for 52 h, and then transferred to a vacuum drying oven for drying for 20 h to ensure that the solvent was completely volatilized, and the drying temperature was 70℃.

[0103] After complete drying, the separator was cut into a circular piece with a diameter of 19 mm using a dicing machine.

[0104] (3) Assembly of lithium-sulfur batteries

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

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

[0107] Accurately weigh 9.80 g of ultrapure water, and weigh 0.20 g of gelatin into the above liquid, and after the obtained solution is placed for 20 min, it is placed in a water environment at 60°C for 20 min, and after being stirred uniformly, it is used as an adhesive solution.

[0108] Accurately weigh 3.50 g of the above adhesive solution, 0.63 g of sublimed sulfur, and 0.30 g of acetylene black, so that the mass ratio of the sublimed sulfur, acetylene black, and gelatin is 63:30:7.

[0109] The above slurry is placed in a planetary ball mill for mechanical stirring for 8 h, the stirring speed is set to 250 rpm, a uniformly mixed slurry is obtained, and a four-sided coater with a height of 150 μm is used to coat the slurry on an aluminum foil.

[0110] The obtained coated separator is placed in a fume hood for natural air drying at room temperature for 24 h, and then transferred to a vacuum drying oven for drying for 24 h to ensure that the solvent is completely volatilized, and the drying temperature is 60°C. After complete drying, the separator is cut into a circular piece with a diameter of 12 mm using a film cutting machine, and the sulfur loading on the surface of the aluminum foil is about 1.5 mg.

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

[0112] The lithium-sulfur battery is tested for cycle performance on a charge-discharge device, and the test conditions are 1C (1C = 1675 mAh / g). The test results show that, compared with a lithium-sulfur battery using a common separator, a lithium-sulfur battery assembled using the modified separator prepared by the application has a higher discharge specific capacity and a more stable cycle efficiency.

[0113] Example 3

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

[0115] The duck primary feather is washed and then placed in an air drying oven for drying, the temperature is set to 80°C, and the time should be 12 h. The obtained dried duck primary feather is cut, the feather shaft and feather are cut off, and the remaining feather branches, feather twigs, feather hooks, etc. are retained.

[0116] The cut duck primary feather is subjected to an oxidation-pyrolysis coupling reaction in air to obtain a crosslinked keratin material, the oxidation-pyrolysis coupling reaction temperature is 220°C, the heating rate is 3°C / min, and the holding time is 1 h, after the holding is completed, the temperature is naturally cooled to room temperature.

[0117] The crosslinked keratin material is pyrolyzed in nitrogen, the pyrolysis temperature is 600°C, the heating rate is 3°C / min, and the holding time is 2 h, after the holding is completed, the temperature is 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 obtained carbon material macroscopically presents a fibrous structure, maintaining the intrinsic morphology of animal hair. This feature is conducive to the construction of a long-range conductive carbon material network.

[0119] As can be seen from the data in Table 1, the nitrogen content of the carbon material prepared in this embodiment is 12.46wt.%. In contrast, the nitrogen content of the carbon material prepared in Comparative Example 1 is improved.

[0120] (2) Preparation of modified coating:

[0121] Accurately weigh 9.90g of N-methyl pyrrolidone and 0.10g of polyvinylidene fluoride into the above liquid, magnetically stir for 24h, and set the stirring speed to 1200rpm. The obtained solution is used as the binder solution.

[0122] Accurately weigh 5.00g of the above binder solution, 0.30g of the fibrous carbon material doped with nitrogen, and 0.15g of acetylene black, so that the mass ratio of the nitrogen-doped fibrous carbon material, the conductive agent, and the binder is 6:3:1.

[0123] Magnetic stirring of the above slurry is carried out for 36h at a stirring speed of 1200rpm to obtain a uniformly mixed slurry, and a four-sided applicator with a height of 150pm is used to coat the Celgard2325 separator with a modified coating.

[0124] After the obtained coated separator is naturally air-dried at room temperature for 30h in a fume hood, it is transferred to a vacuum drying oven for drying for 40h to ensure that the solvent is completely volatilized, and the drying temperature is 50°C.

[0125] After complete drying, the separator is cut into a circular piece with a diameter of 19mm using a dicing machine.

[0126] (3) Assembly of lithium-sulfur battery

[0127] The above separator, a common metal lithium sheet negative electrode, and a sulfur positive electrode sheet are assembled into a button cell in an argon environment-protected glove box, and the battery shell is of CR2025 type.

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

[0129] Accurately weigh 9.80g of ultrapure water and 0.20g of gelatin into the above liquid, and the obtained solution is allowed to stand for 20min, then is allowed to stand in a 60°C water bath environment for 20min. After stirring uniformly, the solution is used as the binder solution.

[0130] Accurately weigh 3.50 g of the above binder solution, 0.63 g of sublimed sulfur and 0.30 g of acetylene black, so that the mass ratio of the sublimed sulfur, acetylene black and gelatin is 63:30:7.

[0131] The above slurry is placed in a planetary ball mill for mechanical stirring for 8 h at a rotation speed of 250 rpm to obtain a uniformly mixed slurry, which is coated on an aluminum foil using a four-sided applicator with a height of 150 μm.

[0132] The obtained coated separator is naturally air-dried in a fume hood at room temperature for 24 h and then transferred to a vacuum drying oven for drying for 24 h to ensure complete evaporation of the solvent, with a drying temperature of 60 °C. After complete drying, the separator is cut into a circular piece with a diameter of 12 mm using a film cutting machine, and the sulfur loading on the surface of the aluminum foil is about 1.5 mg.

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

[0134] The lithium-sulfur battery is subjected to a cycle performance test on a charge-discharge device, with a test condition of 1C (1C = 1675 mAh / g). The test results show that, compared with a lithium-sulfur battery using a common separator, a lithium-sulfur battery assembled using the modified separator prepared by the application has a higher discharge specific capacity and a more stable cycle efficiency.

[0135] Example 4

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

[0137] The washed duck primary feather is dried in a forced air drying oven, with a temperature setting of 80 °C and a drying time of 12 h. The obtained dried duck primary feather is cut, and the feather shaft and feather vanes are cut off, and the remaining feather branches, feather twigs, feather hooks and the like are retained.

[0138] The cut duck primary feather is subjected to an oxidation-pyrolysis coupling reaction in air to obtain a crosslinked keratin material, with an oxidation-pyrolysis coupling reaction temperature of 260 °C, a heating rate of 5 °C / min and a holding time of 3 h. After the holding time ends, the sample is naturally cooled to room temperature.

[0139] The crosslinked keratin material is pyrolyzed in nitrogen, with a pyrolysis temperature of 400 °C, a heating rate of 1 °C / min and a holding time of 3 h. After the holding time ends, the sample is 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-methyl pyrrolidone and 0.10 g of polyvinylidene fluoride, and add them to the above liquid. The obtained solution is used as a binder solution after magnetic stirring for 96 h at a rotation speed of 1200 rpm.

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

[0143] Magnetic stir the above slurry for 96 h at a rotation speed of 1200 rpm to obtain a uniformly mixed slurry, and use a four-sided applicator with a height of 60 pm to coat the Celgard 2325 separator with a modified coating.

[0144] After the obtained coated separator is naturally air-dried in a fume hood at room temperature for 36 h, it is transferred to a vacuum drying oven for drying for 96 h to ensure that all the solvent is volatilized, and the drying temperature is 40 °C.

[0145] After complete drying, the separator is cut into a circular piece with a diameter of 19 mm using a film cutting machine.

[0146] (3) Assembling a lithium-sulfur battery

[0147] The above separator, a common metal lithium sheet negative electrode, and a sulfur positive electrode sheet are assembled into a button cell in an argon environment protection glove box, and the battery shell is of a CR2025 type.

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

[0149] Accurately weigh 9.80 g of ultrapure water and 0.20 g of gelatin, and add them to the above liquid. After the obtained solution is left to stand for 20 min, it is left to stand in a water bath environment at 60 °C for 20 min, and is uniformly stirred to serve as a binder solution.

[0150] Accurately weigh 3.50 g of the above binder solution, 0.63 g of sulfur, and 0.30 g of acetylene black, so that the mass ratio of the sulfur, the acetylene black, and the gelatin is 63:30:7.

[0151] Mechanically stir the above slurry in a planetary ball mill for 8 h at a rotation speed of 250 rpm to obtain a uniformly mixed slurry, and use a four-sided applicator with a height of 150 pm to coat an aluminum foil.

[0152] After the obtained coated separator is naturally air-dried in a fume hood at room temperature for 24 h, it is transferred to a vacuum drying oven for drying for 24 h to ensure that all the solvent is volatilized, and the drying temperature is 60 °C. After complete drying, the separator is cut into a circular piece with a diameter of 12 mm using a film cutting machine, and the sulfur loading on the surface of the aluminum foil is about 1.5 mg.

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

[0154] The lithium-sulfur battery was tested for cycle performance on a charge-discharge device, and the test conditions were 1C (1C = 1675 mAh / g). The test results showed that, compared with the lithium-sulfur battery using a common separator, the lithium-sulfur battery assembled using the modified separator prepared by the application had higher discharge specific capacity and more stable cycle efficiency.

[0155] Example 5

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

[0157] The duck rectrices were washed and then dried in a forced air drying oven, with the temperature set to 80°C and the time being 12 h. The obtained dried duck rectrices were cut, and the quill and vanes were cut off and the remaining branch, small branch, small hook and other structures were retained.

[0158] The cut duck rectrices were subjected to an oxidation-pyrolysis coupling reaction in air, with the oxidation-pyrolysis coupling reaction temperature being 240°C, the heating rate being 5°C / min, and the holding time being 3 h. After the holding time ended, the sample was naturally cooled to room temperature.

[0159] The crosslinked keratin material was pyrolyzed in nitrogen, with the pyrolysis temperature being 800°C, the heating rate being 1°C / min, and the holding time being 3 h. After the holding time ended, the sample was naturally cooled to room temperature to obtain a nitrogen-doped fibrous carbon material.

[0160] (2) Preparation of modified coating:

[0161] 9.90 g of N-methylpyrrolidone and 0.10 g of polyvinylidene fluoride were accurately weighed and added to the above-mentioned liquid, which was then subjected to magnetic stirring for 96 h at a speed of 1200 rpm. The obtained solution was used as an adhesive solution.

[0162] 5.00 g of the above-mentioned adhesive 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 adhesive was 6:3:1.

[0163] The above-mentioned slurry was subjected to magnetic stirring for 96 h at a speed of 1200 rpm to obtain a uniformly mixed slurry, which was then coated with a modified coating on a Celgard2325 separator using a four-sided applicator with a height of 60 μm.

[0164] The obtained coated separator was naturally air-dried at room temperature for 2 h in a fume hood, and then transferred to a vacuum drying oven for drying for 12 h to ensure that all the solvent was volatilized. The drying temperature was 80°C.

[0165] After complete drying, the separator is cut into a 19 mm diameter disc using a disc cutter.

[0166] (3) Assembling the lithium-sulfur battery

[0167] The separator is assembled into a button cell with a common lithium metal negative electrode and a sulfur positive electrode in an argon environment glove box, and the battery shell is of CR2025 type.

[0168] The electrolyte is a mixed solvent of 1,3 dioxolane and ethylene glycol dimethyl ether, and the volume ratio is preferably 1:1; the solute includes lithium bis-trifluoromethanesulfonimide and anhydrous lithium nitrate, and the concentration is preferably 1 mol / L and 0.4 mol / L, respectively. The assembled battery is left for 12 h.

[0169] Accurately weigh 9.80 g of ultrapure water, and weigh 0.20 g of gelatin and add to the above liquid, and the obtained solution is left for 20 min in a 60℃ water environment, and after stirring uniformly, it is used as an adhesive solution.

[0170] Accurately weigh 3.50 g of the above adhesive solution, 0.63 g of sublimed sulfur, and 0.30 g of acetylene black, so that the mass ratio of the sublimed sulfur, acetylene black and gelatin is 63:30:7.

[0171] The above slurry is placed in a planetary ball mill for mechanical stirring for 8 h, and the stirring speed is set to 250 rpm, to obtain a uniformly mixed slurry, and a four-sided coater with a height of 150 μm is used to coat the aluminum foil.

[0172] The obtained coated separator is left to naturally dry in a fume hood at room temperature for 24 h, and then transferred to a vacuum drying oven for drying for 24 h to ensure that the solvent is completely volatilized, and the drying temperature is 60℃. After complete drying, the separator is cut into a 12 mm diameter disc using a disc cutter, and the sulfur loading on the surface of the aluminum foil is about 1.5 mg.

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

[0174] The lithium-sulfur battery is tested for cycle performance on a charge-discharge device, and the test conditions are 1C (1C = 1675 mAh / g). The test results show that, compared with the lithium-sulfur battery using a common separator, the lithium-sulfur battery assembled using the modified separator prepared by the present application has higher discharge specific capacity and more stable cycle efficiency.

[0175] Comparative Example 1

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

[0177] The duck primary feather is washed and dried in a blast drying oven, the temperature is set to 60℃, and the time should be 24h. The obtained dried duck primary feather is cut, the feather shaft and feather are cut off, and the remaining feather branch, feather twig, feather hook and the like are retained.

[0178] The above keratin-based carbon material is pyrolyzed in nitrogen, the pyrolysis temperature is 600℃, the heating rate is 5℃ / min, the holding time is 2h, and after the holding is completed, it is naturally cooled to 25℃ to obtain a nitrogen-doped fibrous carbon material.

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

[0180] (2) Preparation of modified coating:

[0181] Accurately weigh 9.90g of N-methyl pyrrolidone and 0.10g of polyvinylidene fluoride into the above liquid, magnetically stir for 24h, and set the stirring speed to 1200rpm. The obtained solution is used as a binder solution.

[0182] Accurately weigh 5.00g of the above binder solution, 0.30g of keratin-based carbon material, and 0.15g of acetylene black, so that the mass ratio of the keratin-based carbon material, the conductive agent, and the binder is 6:3:1.

[0183] The above slurry is magnetically stirred for 36h at a stirring speed of 1200rpm to obtain a uniformly mixed slurry, and a four-sided coater with a height of 90μm is used to coat the Celgard2325 separator with a modified coating.

[0184] The obtained coated separator is placed in a fume hood and naturally air-dried at room temperature for 24h, then transferred to a vacuum drying oven and dried for 24h to ensure that the solvent is completely volatilized, and the drying temperature is 60℃.

[0185] After complete drying, the separator is cut into a circular piece with a diameter of 19mm using a cutting machine.

[0186] (3) Assembly of lithium-sulfur battery

[0187] The above separator, ordinary metal lithium sheet negative electrode, and sulfur positive electrode sheet are assembled into a button cell in an argon environment protection glove box, and the battery shell is of CR2025 type.

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

[0189] Accurately weigh 9.80 g of ultrapure water, and weigh 0.20 g of gelatin into the above liquid, and after the obtained solution is placed for 20 min, it is placed in a water bath environment at 60°C for 20 min, and after being stirred uniformly, it is used as an adhesive solution.

[0190] Accurately weigh 3.50 g of the above adhesive solution, 0.63 g of sulfur sublimation, and 0.30 g of acetylene black, so that the mass ratio of the sulfur sublimation, acetylene black, and gelatin is 63:30:7.

[0191] The above slurry is placed in a planetary ball mill for mechanical stirring for 8 h, the stirring speed is set to 250 rpm, a uniformly mixed slurry is obtained, and a four-sided coater with a height of 150 μm is used to coat on an aluminum foil.

[0192] The obtained coated separator is placed in a fume hood for natural air drying at room temperature for 24 h, and then transferred to a vacuum drying oven for drying for 24 h to ensure that the solvent is completely volatilized, and the drying temperature is 60°C. After complete drying, the separator is cut into a circular piece with a diameter of 12 mm using a film cutting machine, and the sulfur loading on the surface of the aluminum foil is about 1.5 mg.

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

[0194] The lithium-sulfur battery is tested for cycle performance on a charge-discharge device, and the test conditions are 1C (1C = 1675 mAh / g). As shown in Table 2, compared with Example 1, it exhibits weaker electrochemical performance.

[0195] Comparative Example 2

[0196] (1) Assembly of lithium-sulfur battery

[0197] The above separator is assembled into a button cell with a common metal lithium sheet negative electrode and a sulfur positive electrode sheet in an argon gas environment protection glove box, and the battery shell is of CR2025 type.

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

[0199] Accurately weigh 9.80 g of ultrapure water, and weigh 0.20 g of gelatin into the above liquid, and after the obtained solution is placed for 20 min, it is placed in a water bath environment at 60°C for 20 min, and after being stirred uniformly, it is used as an adhesive solution.

[0200] Accurately weigh 3.50 g of the above adhesive solution, 0.63 g of sulfur sublimation, and 0.30 g of acetylene black, so that the mass ratio of the sulfur sublimation, acetylene black, and gelatin is 63:30:7.

[0201] The slurry was placed in a planetary ball mill for mechanical stirring for 8 h at a rotation speed of 250 rpm to obtain a uniformly mixed slurry, and a four-sided coater with a height of 150 μm was used to coat the slurry on an aluminum foil.

[0202] After the coated separator was naturally air-dried in a fume hood at room temperature for 24 h, it was transferred to a vacuum drying oven for drying for 24 h to ensure complete evaporation of the solvent, and the drying temperature was 60℃. After complete drying, the separator was cut into a circular piece with a diameter of 12 mm using a film 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 battery

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

[0205] The elemental analysis results of the nitrogen-doped fibrous carbon material and the biomass raw material 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 battery prepared in Example 1 and Comparative Example 1 is shown in Table 2:

[0209] Table 2

[0210]

[0211] The preparation method of the present application uses animal feathers as raw material, and through mild condition oxidation-pyrolysis coupling reaction, the keratin macromolecule is 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 level of nitrogen doping during the subsequent pyrolysis process. Compared with the carbon material obtained by directly pyrolyzing the original animal feather material, the retention rate of nitrogen and carbon elements is greatly improved. The positive electrode modification coating of the lithium-sulfur battery prepared by using the nitrogen-doped fibrous carbon material prepared by the present application can effectively adsorb the dissolved polysulfides 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 above has been described by way of example with reference to the accompanying drawings. Obviously, the implementation of the present application is not limited to the above-described manner. Any improvement or direct application of the inventive concept and technical solution to other occasions without modification is within the scope of protection of the present application.

Claims

1. Use of nitrogen-doped fibrous carbon material in the preparation of a modified coating layer of a lithium-sulfur separator cathode, comprising the following steps: Step 1: mixing a nitrogen-doped fibrous carbon material, a conductive agent, a binder, and a solvent to obtain a slurry for the modified coating layer; Step 2: coating the slurry for the modified coating layer on the surface of a lithium-sulfur separator and drying to obtain a lithium-sulfur battery separator with a modified coating layer; The preparation method of the nitrogen-doped fibrous carbon material comprises the following steps: Step 1: washing, drying, and cutting animal feathers to obtain cut animal feather material; Step 2: performing an oxidation-pyrolysis coupling reaction on the cut animal feather material in an oxygen-containing atmosphere to obtain cross-linked animal feather material; Step 3: performing pyrolysis on the cross-linked animal feather material in a gas protection atmosphere to obtain nitrogen-doped fibrous carbon material with high nitrogen content; In step 1 of the preparation method, the drying temperature is 50-80°C, and the time is 12-36 h; In step 2 of the preparation method, the oxidation-pyrolysis coupling reaction temperature is 200-260°C, the heating rate is 1-5°C / min, the holding time is 0.5-3 h, and after the holding time ends, the material is naturally cooled to room temperature; In step 3 of the preparation method, the pyrolysis temperature is 400-800°C, the heating rate is 1-5°C / min, the holding time is 1-3 h, and after the holding time ends, the material is naturally cooled to room temperature.

2. The use according to claim 1, wherein: In step 2 of the preparation method, the oxygen-containing atmosphere is one of air, nitrogen / oxygen mixed gas.

3. The use according to claim 1, wherein: In step 3 of the preparation method, the gas protection atmosphere is one of nitrogen, argon, and helium.

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

99.

5. The use according to claim 1, wherein: The conductive agent is acetylene black, and the binder is polyvinylidene fluoride; The solvent is N-methyl pyrrolidone or a mixed solution of polyvinylidene fluoride and N-methyl pyrrolidone; In the mixed solution of polyvinylidene fluoride and N-methyl pyrrolidone, the mass fraction of polyvinylidene fluoride is 0.5-2 wt.%; In step 1, the mixing time of the slurry for the modified coating layer is 12-96 h.

6. The use according to claim 1, wherein: In step 2, the coating height of the modified coating layer is 60-150 μm; After coating and drying, the temperature is 40-80°C, and the drying time is 12-96 h.

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