Preparation Of Biomass-based Porous Carbon And Its Application In Modification Of Lithium-sulfur Battery Separator

Today,with the popularity of electronic equipment,people's requirements for various battery performances have become more and more stringent,such as battery life,service life,and safety performance.The higher specific capacity and energy density that people demand cannot be met by the currently widely used commercial lithium ion secondary batteries.Lithium-sulfur batteries have a very high theoretical specific capacity(1675 mAh g^-1)and energy density(2600 wh kg^-1).Moreover,sulfur has rich reserves,low toxicity and low price,making lithium-sulfur batteries a promising new high-performance energy storage system that can replace lithium-ion batteries.It can be said that the prospect of lithium-sulfur batteries is very broad and can be used as the research direction for the next few decades.However,the inherent weaknesses of sulfur in lithium-sulfur batteries have been restricting its practicality,including low electrical conductivity of sulfur,low utilization rate,volume expansion during discharge,especially the shuttle effect caused by polysulfide intermediates.In order to solve these problems,researchers have been trying to find a variety of materials combined with sulfur to prepare cathode materials with special structures and properties to suppress the shuttle effect,but their synthetic routes are often relatively complex and costly.Although the expensive investment has achieved certain results,it has clearly outweighed the gains and it is unrealistic to have large-scale production.Biochar materials have excellent performance in air purification and water pollution treatment due to their excellent adsorption properties.If it is used in a lithium-sulfur battery,it can effectively adsorb and block polysulfides,suppress the shuttle effect of polysulfides,and effectively reduce production costs.This paper uses different biomass carbon materials to modify the commercial separator.The main research contents of this paper are as follows:?1?Ricepaperplant Pith-based carbon?RPC?was prepared for separator modification to study their natural pore structure and polysulfide adsorption performance.Material characterization methods such as SEM,FTIR,XRD,Raman and electrochemical analysis were carried out.The electrochemical performance of batteries with RPC modified separator and commercial separator are compared.The results show that the initial capacity of the battery is 1168.5mAh g^-11 at 0.1C and905.6mAhg^-11 at 1C rate.The discharge specific capacity of the battery is 464.8 mAh g^-11 after 500 cycles,and the Coulombic efficiency remains 97%.?2?Puffied corn was used as the carbon source and activated with KOH to prepare a porous carbon material?APCC?with a large specific surface area for the modification of lithium-sulfur battery separators to study the physical adsorption performance of its artificial porous structure.The characterization process of the materials were similar to the RPC described above.The results showed that the initial discharge capacity of the battery with APCC coated separator showed 1169 mAhg^-11 at a rate of 0.1 C and 1045.5 mAhg^-11 at a rate of 1 C.At a rate of 1 C,its discharge capacity is also very high,and the specific capacity after 500 cycles can still reach471.6 mAhg^-1.?3?Bean sprouts are the carbon source.A double-doping experiment of nitrogen and sulfur was carried out,and the chemical adsorption performance of element-doped biochar on polysulfide was studied.The study creatively separated the bean sprout valves and bean sprout stems in the experiment for comparative experiments.The experimental characterization method is as described in?1?.The NS-BSVC obtained after carbonization of nitrogen and sulfur doped bean sprouts was used for the modification of lithium-sulfur battery separators.At 0.1C,the discharge specific capacity reached 1236.1 mAh g^-1.After 1000 cycles at a high rate of 1C,there are still 383mAhg^-11 specific capacity.