Biomass carbon for lithium-sulfur battery cathode and preparation method and application thereof

Abstract

The application belongs to the technical field of secondary battery positive electrode materials. More specifically, it relates to a biomass carbon for lithium-sulfur battery positive electrodes, and a preparation method and application thereof. The specific preparation steps include: low-temperature carbonization: rice husks are subjected to low-temperature pyrolysis treatment at 200-300 DEG C under an inert atmosphere to obtain a primary carbonization product; morphology screening: the obtained primary carbonization product is crushed and sieved to screen out ellipsoidal carbon particles with a sphericity of 0.5-0.6; gas-phase impregnation and hydrolysis: the obtained ellipsoidal carbon particles are contacted with organic aluminum source vapor in a reaction device, and then water vapor is introduced to perform a hydrolysis reaction, so that the generated aluminum oxide is deposited in the pores of the ellipsoidal carbon particles in situ to obtain a composite material; high-temperature carbonization: the treated composite material is subjected to high-temperature carbonization treatment at 800-1000 DEG C under an inert atmosphere to obtain the biomass carbon for lithium-sulfur battery positive electrodes.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of secondary battery positive electrode materials. More specifically, it relates to a biomass carbon for lithium-sulfur battery positive electrode and a preparation method and application thereof. BACKGROUND

[0002] In recent years, biomass carbon materials have attracted extensive attention due to their wide sources, renewability, low cost and inherent heteroatoms (such as N, O, S, etc.) and natural porous structure. Using wood, straw, cellulose, chitin and other biomass waste as carbon source, porous carbon is prepared by pyrolysis carbonization, which is considered as a green and sustainable strategy. However, the existing biomass carbon materials still have some limitations when used in lithium-sulfur batteries:

[0003] Insufficient pore structure adaptability: the pore structure (mainly macropores and micropores) of many natural biomass carbons is not effectively regulated, and it is difficult to achieve efficient physical confinement and chemical adsorption of polysulfides. Effective host materials need to have hierarchical pore structure, in which micropores are used to confine small molecule sulfur, mesopores are used to load sulfur and provide ion transmission channels, and macropores are used as electrolyte reservoirs.

[0004] Weak intrinsic adsorption activity: most pure carbon materials have weak chemical affinity for lithium polysulfides, mainly relying on physical confinement, which cannot completely solve the shuttle effect. It is necessary to dope carbon materials with heteroatoms (such as N, S, B, etc.) to introduce polar sites and enhance the chemical anchoring effect of polysulfides.

[0005] Therefore, it is of great significance to develop a biomass carbon material with simple process, low cost and environmental friendliness, which can simultaneously realize good electrical conductivity, adaptive pore structure and strong chemical adsorption sites, for promoting the practical application of high-performance lithium-sulfur batteries. SUMMARY

[0006] The technical problem to be solved by the present application is that the existing positive electrode material for lithium-sulfur batteries has weak intrinsic adsorption of sparks and weak limitation of the shuttle effect of polysulfides during battery use. Based on the above problems, the present application provides a biomass carbon for lithium-sulfur battery positive electrode and a preparation method and application thereof.

[0007] The purpose of the present application is to provide a biomass carbon for lithium-sulfur battery positive electrode.

[0008] Another purpose of the present application is to provide a preparation method of a biomass carbon for lithium-sulfur battery positive electrode.

[0009] Another purpose of the present application is to provide a method for applying a biomass carbon for lithium-sulfur battery positive electrode.

[0010] The above purposes of the present application are achieved by the following technical solutions:

[0011] A preparation method of biomass carbon for lithium-sulfur battery cathode, the specific preparation steps comprising:

[0012] S1. Low-temperature carbonization: rice husk is treated by low-temperature pyrolysis at 200-300℃ under inert atmosphere to obtain primary carbonization product;

[0013] S2. Morphology screening: the primary carbonization product obtained in step S1 is crushed and sieved to screen out ellipsoidal carbon particles with sphericity of 0.5-0.6;

[0014] S3. Gas-phase impregnation and hydrolysis: the ellipsoidal carbon particles obtained in step S2 are contacted with organic aluminum source vapor in a reaction device, followed by introduction of water vapor for hydrolysis reaction, so that the generated aluminum oxide is deposited in the pores of the ellipsoidal carbon particles in situ to obtain a composite material;

[0015] S4. High-temperature carbonization: the composite material treated in step S3 is treated by high-temperature carbonization at 800-1000℃ under inert atmosphere to obtain the biomass carbon for lithium-sulfur battery cathode.

[0016] The beneficial effects of the above technical solution are:

[0017] Firstly, the above technical solution adopts a low-temperature interval of 200-300℃ for carbonization, which is the temperature window for the main pyrolysis of hemicellulose and cellulose in rice husk. Through reactions such as dehydrogenation, dehydration or decarboxylation, oxygen and hydrogen elements are removed in the form of water, carbon monoxide and carbon dioxide, forming a solid precursor rich in aromatic ring structure. This process maximizes the preservation of the macroscopic morphology of biomass carbon, and at the same time, the overflow of small molecule gases realizes the preliminary pore formation, forming rich initial diffusion channels for subsequent reactions;

[0018] Secondly, through mechanical crushing and sieving, ellipsoidal particles with sphericity of 0.5-0.6 are selectively obtained according to the intrinsic brittle fracture behavior of the carbonized material. Compared with irregularly shaped particles, ellipsoidal particles have better flowability and packing characteristics. They can be arranged more closely during coating and rolling, forming an electrode layer with lower porosity and higher density. In particular, when manufacturing the electrode sheet, after rolling, the electrode structure formed by ellipsoidal particles is more stable and less likely to rebound and powder. In addition, due to the roughness and non-perfect symmetry of its surface, it can form a stronger mechanical interlocking with the conductive agent and binder in the electrode slurry, which is beneficial to maintaining the integrity of the electrode structure during long cycle process. Even if a small amount of polysulfide dissolves and penetrates into the micro-pores of a particle, it will immediately enter the macro-pores formed by the close packing of numerous ellipsoidal particles, which have high tortuosity, making it difficult to migrate to the negative electrode, thereby greatly increasing the difficulty of polysulfide escaping from the whole positive electrode;

[0019] The reason for choosing rice husk as the raw material is that the rice husk itself contains a certain amount of Si, which can cooperate with the subsequently introduced alumina to support the internal pore structure; prevent the collapse of the pore during the subsequent high-temperature carbonization process; and alumina and silicon dioxide can also play a role in adsorbing lithium polysulfide.

[0020] Further, the rice husk is subjected to acid pickling before the low-temperature carbonization:

[0021] The rice husk is soaked in an acid solution, and under the conditions of a temperature of 60-90℃ and a stirring speed of 200-300r / min, the acid pickling is continuously stirred for 8-12h, then filtered, the filter cake is collected and washed with water until neutral, and then dried, thereby completing the acid pickling of the rice husk.

[0022] The concentration of the acid solution is 0.5-0.8mol / L.

[0023] The acid solution is selected from any one of hydrochloric acid, sulfuric acid or nitric acid.

[0024] Further, the low-temperature carbonization further comprises:

[0025] The acid-pickled rice husk is heated to 200-300℃ at a rate of 1-2℃ / min in an argon atmosphere, and after low-temperature pyrolysis treatment for 6-8h, the furnace is cooled to room temperature, the material is discharged, and the primary carbonization product is obtained.

[0026] The pyrolysis of biomass is a complex series reaction network. A very slow heating rate ensures a quasi-equilibrium process of heat transfer from the outside to the inside of the particle, minimizing the temperature gradient of the entire rice husk particle. This enables components such as hemicellulose and cellulose to undergo depolymerization, cyclization, aromatization and other reactions simultaneously and smoothly, maximizing the release of small molecule gases (CO, CO2, CH4, etc.) in a controllable manner, thereby forming an initial pore network with good connectivity and concentrated pore size distribution.

[0027] Further, the particle size Dv50 of the ellipsoidal carbon particles is 8-12μm.

[0028] In the preparation of the electrode, the size of the active material particles directly determines the pore tortuosity and electrolyte wettability of the electrode. A Dv50 of 8-12μm is an optimal value: the electrode formed by the accumulation of particles of this size has a pore size that can ensure the rapid capillary penetration of the electrolyte, and will not reduce the effective diffusion coefficient of Li⁺ due to excessively large pores; the combination of size and morphology enables the particles to form a stable arch structure during the coating and drying process, resisting the capillary shrinkage force of the binder and reducing electrode curling and cracking.

[0029] It should be noted that the particle size range (e.g. 18-38 μm) determined by sieving in step S2 of the present application is based on the geometric size of the sieve mesh aperture, while the Dv50 of 8-12 μm is the equivalent spherical particle size measured by a laser particle size analyzer. Since the specific screened particles of the present application are ellipsoidal particles that are not perfect spheres, the size of the long axis direction is greater than the equivalent volume particle size, so the above two parameter ranges are not contradictory; and in the process of multiple sieving, the Dv50 of the particles obtained may reasonably fluctuate within the above range.

[0030] Further, the gas phase impregnation and hydrolysis further comprises:

[0031] The ellipsoidal carbon particles obtained in step S2 are transferred to a reaction device, preheated to 140-160°C, then the system pressure is adjusted to 0.4-0.5 atm, then isopropyl alcohol aluminum vapor is introduced into the reaction device at a flow rate of 40-60 sccm of nitrogen as a carrier, so that the isopropyl alcohol aluminum vapor contacts in the reaction device for 2-3 h, then cooled to 100-105°C, continue to bubble in deionized water vapor at a temperature of 95°C with nitrogen as a carrier at a flow rate of 40-60 sccm, to introduce water vapor for hydrolysis reaction for 3-5 h, so that the generated aluminum oxide is deposited in the pores of the ellipsoidal carbon particles in situ, after the reaction is completed, stop bubbling in water vapor, continue to blow with nitrogen for 1 h, to obtain a composite material.

[0032] Further, the high-temperature carbonization treatment further comprises:

[0033] The composite material treated by step S3 is heated to 500-600°C at a rate of 8-10°C / min under an argon atmosphere, and after carbonization for 40-60 min, the temperature is further increased to 800-1000°C at a rate of 2-4°C / min, and high-temperature carbonization treatment is carried out for 80-120 min, and the furnace is cooled to room temperature, and the material is discharged, to obtain the biomass carbon for lithium-sulfur battery anodes.

[0034] The above technical solution is carbonized in two stages:

[0035] First stage (500-600°C): This stage is the key to the carbonization process. At this temperature, residual alkanes and oxygen-containing, nitrogen-containing heteroatom functional groups can be completely removed in a controllable manner. Slow heating and stable holding avoid the rapid thermal decomposition of these components to produce a large internal gas pressure, thereby preventing the generation of internal microcracks in the material;

[0036] The second stage (slowly heating to 800-1000℃): this stage is the graphitization budding stage. Slow heating (2-4℃ / min) allows carbon atoms to have enough time to rearrange, at high temperature, sp2carbon heterocycles begin to merge with each other, forming small graphite crystallites, the size and number of these crystallites directly determine the conductivity of the material. Long time holding promotes the further growth and ordering of the crystallites, significantly reduces the Fermi level of the material, and greatly improves its electronic conductivity. At the same time, high temperature makes Al2O3 and carbon interface have stronger interaction, forming a stable composite.

[0037] Further, the crushing in step S2 comprises:

[0038] Under the condition of shear rotation speed of 100-140r / min, low-speed shearing crushing for 15-20min.

[0039] The carbonized rice husk is a typical brittle material, and its fracture behavior is mainly controlled by internal defects and cracks. Low-speed shearing provides a kind of quasi-static, continuous shearing force and extrusion stress, rather than high-energy impact. This stress mode allows the cracks to have enough time to expand and penetrate along the inherent structural weak plane of the material (such as cell wall boundary), so as to cause the material to fracture according to its intrinsic structure, and naturally form ellipsoidal particles. High-speed impact will cause random and violent crushing, resulting in a large amount of irregular shape and fine powder.

[0040] Further, the screening in step S2 comprises:

[0041] The crushed particles are placed on a 400-mesh screen for screening, and the fine powder passing through the 400-mesh screen is collected;

[0042] The fine powder is placed on an 800-mesh screen for screening, and the particles remaining on the 800-mesh screen are collected.

[0043] By screening with screens of certain mesh number, large particles and long strip impurities that are not completely crushed, and fine powder are removed, so that particles with corresponding sphericity and size are obtained by cooperating with the aforementioned low-speed shearing crushing process.

[0044] A biomass carbon for lithium-sulfur battery anode is prepared by the preparation method described above.

[0045] A method for applying biomass carbon for lithium-sulfur battery, the biomass carbon for lithium-sulfur battery prepared by the preparation method described above is used as a carrier, loaded with sulfur, and used as an anode material for lithium-sulfur battery. DETAILED DESCRIPTION

[0046] The application will be further described in conjunction with specific examples, but the examples do not limit the application in any form. Unless otherwise specified, the reagents, methods and equipment used in the application are conventional reagents, methods and equipment in the art.

[0047] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0048] Example 1

[0049] S1. Low-temperature carbonization:

[0050] The rice husks were soaked in an acid solution, and continuously stirred for 8 h at a temperature of 60℃ and a stirring speed of 200 r / min. After stirring, the filter cake was collected and washed with water until neutral, and then dried to complete the acid pickling and impurity removal of the rice husks, obtaining pretreated rice husks;

[0051] The concentration of the acid solution was 0.5 mol / L, and the acid solution was selected from hydrochloric acid.

[0052] The pretreated rice husks were heated to 200℃ at a rate of 1℃ / min under an argon atmosphere, and then cooled to room temperature after low-temperature pyrolysis treatment for 8 h. The primary carbonized product was obtained by discharging the material.

[0053] S2. Morphology screening:

[0054] The primary carbonized product was broken by low-speed shearing for 20 min at a shearing speed of 140 r / min. The broken particles were then sieved on a 400-mesh sieve, and the fine powder passing through the 400-mesh sieve was collected.

[0055] The fine powder was sieved on an 800-mesh sieve, and the particles remaining on the 800-mesh sieve were collected.

[0056] Obtaining ellipsoidal carbon particles with a sphericity of 0.5 and a Dv50 of 8 μm.

[0057] S3. Gas-phase impregnation and hydrolysis:

[0058] The ellipsoidal carbon particles obtained in step S2 were transferred to a reaction device, preheated to 140℃, and then the system pressure was adjusted to 0.4 atm. Subsequently, while maintaining the system pressure constant, isopropyl aluminum alcohol vapor was introduced into the reaction device by using nitrogen gas with a flow rate of 40 sccm as a carrier, so that the isopropyl alcohol aluminum vapor was in contact with the reaction device for 2 h. Then, the temperature was lowered to 100℃, and the nitrogen gas with a flow rate of 40 sccm was continued to be used as a carrier to bubble in the deionized water vapor with a temperature of 95℃ to introduce water vapor for hydrolysis reaction for 3 h. The generated aluminum oxide was deposited in the pores of the ellipsoidal carbon particles in situ. After the reaction was completed, the water vapor was stopped, and the nitrogen gas was continued to be used for 1 h to obtain a composite material.

[0059] S4. High temperature carbonization:

[0060] The composite material after step S3 is heated to 500℃ at a rate of 8℃ / min under an argon atmosphere, and after carbonization for 40min, it is heated to 800℃ at a rate of 2℃ / min, and high temperature carbonization is performed for 80min. The furnace is cooled to room temperature, and the material is discharged to obtain the biomass carbon for the lithium-sulfur battery cathode.

[0061] Example 2

[0062] S1. Low temperature carbonization:

[0063] The rice husks are soaked in an acid solution, and after stirring for 10h at a temperature of 70℃ and a stirring speed of 260r / min, the filter cake is collected and washed with water until it is neutral, and then dried to complete the acid cleaning of the rice husks, and obtain pretreated rice husks;

[0064] The concentration of the acid solution is 0.6mol / L, and the acid solution is selected from hydrochloric acid;

[0065] The pretreated rice husks are heated to 260℃ at a rate of 1.5℃ / min under an argon atmosphere, and after low temperature pyrolysis for 7h, the furnace is cooled to room temperature, and the material is discharged to obtain the primary carbonization product;

[0066] S2. Morphology screening:

[0067] The primary carbonization product is broken by low speed shearing for 18min at a shearing speed of 120r / min, and then the broken particles are sieved through a 400mesh sieve, and the fine powder passing through the 400mesh sieve is collected;

[0068] The fine powder is sieved through an 800mesh sieve, and the particles remaining on the 800mesh sieve are collected;

[0069] Obtaining ellipsoidal carbon particles with a sphericity of 0.55 and a Dv50 of 11μm;

[0070] S3. Gas phase impregnation and hydrolysis:

[0071] The ellipsoidal carbon particles obtained in step S2 were transferred to a reaction device, preheated to 150°C, and then the system pressure was adjusted to 0.4 atm. Subsequently, isopropyl alcohol aluminum vapor was introduced into the reaction device at a flow rate of 50 sccm of nitrogen gas as a carrier while keeping the system pressure constant, so that the isopropyl alcohol aluminum vapor was contacted in the reaction device for 2.5 h. Subsequently, the temperature was lowered to 102°C, and nitrogen gas at a flow rate of 50 sccm was continued to be used as a carrier to bubble in deionized water vapor at a temperature of 95°C to introduce water vapor for hydrolysis reaction for 4 h, so that the generated aluminum oxide was deposited in situ in the pores of the ellipsoidal carbon particles. After the reaction was completed, the water vapor was stopped, and nitrogen gas was continued to be used for purging for 1 h to obtain a composite material.

[0072] S4. High-temperature carbonization:

[0073] The composite material treated in step S3 was heated to 560°C at a rate of 9°C / min under an argon atmosphere, and after holding for carbonization for 50 min, the temperature was continued to be increased to 900°C at a rate of 3°C / min for high-temperature carbonization treatment for 100 min. The furnace was cooled to room temperature, and the material was discharged to obtain the biomass carbon for the lithium-sulfur battery cathode.

[0074] Example 3

[0075] S1. Low-temperature carbonization:

[0076] The rice husk was soaked in an acid solution, and after continuous stirring for acid washing for 12 h at a temperature of 90°C and a stirring speed of 300 r / min, the filter cake was collected by filtration, washed with water until neutral, and then dried to complete the acid washing and impurity removal of the rice husk to obtain pretreated rice husk.

[0077] The concentration of the acid solution was 0.8 mol / L, and the acid solution was selected from hydrochloric acid.

[0078] The pretreated rice husk was heated to 300°C at a rate of 2°C / min under an argon atmosphere, and after low-temperature pyrolysis treatment for 6 h, the material was cooled to room temperature, and discharged to obtain a primary carbonization product.

[0079] S2. Morphology screening:

[0080] The primary carbonization product was broken by low-speed shearing for 15 min at a shearing speed of 100 r / min. Then the broken particles were sieved on a 400-mesh sieve, and the fine powder passing through the 400-mesh sieve was collected.

[0081] The fine powder was sieved on an 800-mesh sieve, and the particles remaining on the 800-mesh sieve were collected.

[0082] Ellipsoidal carbon particles with a sphericity of 0.6 and a Dv50 of 12 μm were obtained.

[0083] S3. Gas phase impregnation and hydrolysis:

[0084] The ellipsoidal carbon particles obtained in step S2 were transferred to a reaction device, preheated to 160°C, and then the system pressure was adjusted to 0.5 atm. Subsequently, isopropyl alcohol aluminum vapor was introduced into the reaction device at a flow rate of 60 sccm of nitrogen as a carrier while maintaining the system pressure constant, so that the isopropyl alcohol aluminum vapor was contacted in the reaction device for 3 h. Subsequently, the temperature was lowered to 105°C, and nitrogen at a flow rate of 60 sccm was continued to be used as a carrier to bubble in deionized water vapor at a temperature of 95°C to introduce water vapor for hydrolysis reaction for 5 h, so that the generated aluminum oxide was deposited in situ in the pores of the ellipsoidal carbon particles. After the reaction was completed, the water vapor was stopped, and nitrogen was continued to be purged for 1 h to obtain a composite material.

[0085] S4. High temperature carbonization:

[0086] The composite material treated in step S3 was heated to 600°C at a rate of 10°C / min under an argon atmosphere, and after holding for carbonization for 60 min, the temperature was continued to be increased to 1000°C at a rate of 4°C / min for high temperature carbonization treatment for 120 min. The furnace was cooled to room temperature, and the material was discharged to obtain the biomass carbon for lithium-sulfur battery cathode.

[0087] Example 4

[0088] Compared with Example 1, the difference is that:

[0089] The process of high temperature carbonization is different, specifically:

[0090] The composite material treated in step S3 was heated to 500°C at a rate of 8°C / min under an argon atmosphere, and after holding for carbonization for 40 min, the temperature was continued to be increased to 800°C at a rate of 8°C / min for high temperature carbonization treatment for 80 min. The furnace was cooled to room temperature, and the material was discharged to obtain the biomass carbon for lithium-sulfur battery cathode.

[0091] Example 5

[0092] Compared with Example 1, the difference is that:

[0093] The process of high temperature carbonization is different, specifically:

[0094] The composite material treated in step S3 was heated to 800-1000°C at a rate of 2°C / min under an argon atmosphere for high temperature carbonization treatment for 80 min. The furnace was cooled to room temperature, and the material was discharged to obtain the biomass carbon for lithium-sulfur battery cathode.

[0095] Comparative Example 1

[0096] The difference between the present comparative example and Example 1 is that no isopropyl alcohol aluminum vapor is passed, i.e., no aluminum oxide is deposited in the pores inside the ellipsoidal carbon particles, and the rest of the conditions remain unchanged.

[0097] Comparative Example 2

[0098] The difference between the present comparative example and Example 1 is that the process of low-speed shearing is adjusted to obtain ellipsoidal carbon particles with a sphericity of 0.4 and a Dv50 of 8 μm; specifically:

[0099] By increasing the shearing rate of low-speed shearing and simultaneously prolonging the shearing time, the higher impact force makes the particles more likely to produce sharp edges, flakes or rod-shaped fragments, thereby reducing the sphericity to 0.4; specifically: the shearing rate is 150 r / min, and the shearing time is 17 min.

[0100] Comparative Example 3

[0101] The difference between the present comparative example and Example 1 is that the process of low-speed shearing is adjusted to obtain ellipsoidal carbon particles with a sphericity of 0.7 and a Dv50 of 8 μm; specifically:

[0102] The shearing rate is 90 r / min, and the shearing time is 16 min.

[0103] The products obtained in the examples and comparative examples are subjected to performance tests, and the specific test methods and test results are as follows:

[0104] The biomass carbon obtained in different examples and comparative examples is first loaded with sulfur to obtain positive active materials:

[0105] The raw materials are prepared according to a mass ratio of biomass carbon to sulfur of 3:7;

[0106] The two are placed in a ball mill tank, a small amount of ethanol is added to improve the mixing uniformity; zirconium oxide balls are added according to a ball-to-material mass ratio of 10:1, and ball milling is carried out at 120 rpm for 3 hours;

[0107] The uniformly mixed slurry is dried in a vacuum drying oven at 60°C for 12 hours to completely remove the solvent, and a carbon-sulfur physical mixture powder is obtained;

[0108] Subsequently, in an argon atmosphere, the material is heated to 165°C in a sealed container, and sulfurization is carried out for 12 h; after the heat preservation is completed, the material is naturally cooled to room temperature, and the material is dispersed to obtain a positive material for lithium-sulfur batteries.

[0109] The positive material, conductive agent Super P, and binder LA133 are mixed in a mass ratio of 8:1:1 in a blender, deionized water is added as a solvent, and stirring is carried out at a speed of 2000 rpm for 2 h to form a uniform slurry;

[0110] The slurry is blade coated on the surface of an aluminum foil, dried to remove water, and then rolled and sliced to obtain a positive electrode tab with a loading amount of 2.5 mg / cm 2 ;

[0111] In an inert atmosphere, battery assembly is performed in a glove box to obtain a CR2032 type button cell;

[0112] In the above process, lithium metal sheets are used as the negative electrode, and Celgard 2325 type separators are used.

[0113] In the electrolyte, the concentration of LiTFSI is 1 mol / L, the mass fraction of lithium nitrate is 2%, and the solvent is obtained in a volume ratio of DOL:DME of 1:1, and the injection amount is 40 μL.

[0114] The following tests are performed at a temperature of 25°C using a blue light test system:

[0115] First coulombic efficiency:

[0116] First, the battery is placed at room temperature for 4 h, then charged to 2.8 V at a rate of 0.1 C, and after 10 min of standing, discharged to 1.7 V at a rate of 0.1 C to evaluate the first coulombic efficiency during the first cycle, and the detailed evaluation results are shown in Table 1.

[0117] Cycle performance test:

[0118] First, the battery is placed at room temperature for 4 h, and then cycled 2 times at a rate of 0.1 C to activate.

[0119] Subsequently, after 200 consecutive cycles at a rate of 0.2 C and a voltage window of 1.7-2.8 V, the capacity retention rate is evaluated, and the detailed evaluation results are shown in Table 1.

[0120] Table 1: Product performance evaluation results

[0121]

[0122] As can be seen from the test results in Table 1, the product obtained by the present application can have good first coulombic efficiency and good cycle performance based on good inhibition of the polysulfide shuttle effect in the lithium-sulfur battery reaction process.

[0123] The above examples are preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A method for producing biomass carbon for a lithium-sulfur battery positive electrode, characterized by, The specific preparation steps include: S1. Low-temperature carbonization: rice husks are heated to 200-300℃ at a rate of 1-2℃ / min under an inert atmosphere for low-temperature pyrolysis treatment, to obtain primary carbonized products; S2. Morphology screening: the primary carbonized products obtained in step S1 are crushed and screened to screen ellipsoidal carbon particles with a sphericity of 0.5-0.6; The crushing is carried out at a shearing rotation speed of 100-140 r / min for 15-20 min; The ellipsoidal carbon particles have a particle size Dv50 of 8-12 μm; S3. Gas-phase impregnation and hydrolysis: the ellipsoidal carbon particles obtained in step S2 are contacted with aluminum organic source vapor in a reaction device, and then water vapor is introduced for hydrolysis reaction, so that the generated aluminum oxide is deposited in the pores of the ellipsoidal carbon particles in situ, to obtain a composite material; S4. High-temperature carbonization: the composite material treated in step S3 is heated to 500-600℃ at a rate of 8-10℃ / min under an argon atmosphere, and after holding for carbonization for 40-60 min, it is continuously heated to 800-1000℃ at a rate of 2-4℃ / min for high-temperature carbonization treatment for 80-120 min, and then cooled to room temperature in the furnace, discharged, to obtain the biomass carbon for lithium-sulfur battery cathodes.

2. The method for preparing biomass carbon for a lithium-sulfur battery cathode according to claim 1, characterized in that, The rice husks are subjected to acid pickling before the low-temperature carbonization: The rice husks are soaked in an acid solution, continuously stirred at a temperature of 60-90℃ and a stirring rotation speed of 200-300 r / min for 8-12 h of acid pickling, filtered, the filter cake is collected, washed with water until neutral, and then dried, to complete the acid pickling of the rice husks; The concentration of the acid solution is 0.5-0.8 mol / L; The acid solution is selected from any one of hydrochloric acid, sulfuric acid or nitric acid.

3. The method for preparing biomass carbon for a lithium-sulfur battery cathode according to claim 2, characterized in that, The low-temperature carbonization further includes: The rice husks after acid pickling are heated to 200-300℃ at a rate of 1-2℃ / min under an argon atmosphere for low-temperature pyrolysis treatment for 6-8 h, and then cooled to room temperature in the furnace, discharged, to obtain the primary carbonized products.

4. The method for preparing biomass carbon for a lithium-sulfur battery cathode according to claim 1, characterized in that, The gas-phase impregnation and hydrolysis further include: The ellipsoidal carbon particles obtained in step S2 are transferred to a reaction device, preheated to 140-160℃, the system pressure is adjusted to 0.4-0.5 atm, and then under the condition of keeping the system pressure constant, isopropyl alcohol aluminum vapor is introduced into the reaction device by taking nitrogen gas with a flow rate of 40-60 sccm as the carrier, so that the isopropyl alcohol aluminum vapor is contacted in the reaction device for 2-3 h, and then cooled to 100-105℃, and deionized water vapor with a temperature of 95℃ is bubbled into the reaction device by taking nitrogen gas with a flow rate of 40-60 sccm as the carrier, to introduce water vapor for hydrolysis reaction for 3-5 h, so that the generated aluminum oxide is deposited in the pores of the ellipsoidal carbon particles in situ, after the reaction is completed, the water vapor is stopped, and nitrogen gas is continuously blown for 1 h, to obtain the composite material.

5. The method for preparing biomass carbon for a lithium-sulfur battery cathode according to claim 1, characterized in that, The screening in step S2 includes: The crushed particles are placed on a 400-mesh screen for screening, and the fine powder passing through the 400-mesh screen is collected; The fine powder is sieved on a 800 mesh screen, and the particles remaining on the 800 mesh screen are collected.

6. A biomass carbon for a lithium-sulfur battery positive electrode, characterized by, The preparation method according to any one of claims 1-5.

7. A method for applying biomass char to a lithium-sulfur battery, characterized by, The biomass charcoal prepared by the preparation method according to any one of claims 1-5 is used as a carrier for a lithium-sulfur battery, and after loading sulfur, it is used as a positive electrode material for a lithium-sulfur battery.

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