Preparation And Electrochemical Performance Of Bamboo Charcoal/Sulfur/Aluminum Fluoride Composites

Lithium sulfur batteries have high theoretical mass energy density(2600 Wh/Kg)and volume energy density,which has become a hot topic of research.However,there are still many limitations in the commercialization of lithium-sulfur batteries.First,the conductivity of elemental sulfur is poor,which limits the increase in battery rate performance.Second,the intermediate product of sulfur in the charge-discharge process of active material sulfur is susceptible to polysulfide.Dissolved in the electrolyte,causing a serious "shuttle effect",resulting in rapid capacity decay and lower Coulomb efficiency.In view of the above problems,we prepared the aluminum fluoride/sulfur composite by melting and tested the adsorption of polysulfide by aluminum fluoride.Then bamboo charcoal-sulfur composites were prepared by the liquid-phase method using bamboo charcoal with good conductivity as the substrate material for carrying sulfur.Finally,the composite aluminum fluoride polysulfide adsorption and bamboo charcoal has good conductivity,the preparation of bamboo charcoal/sulfur/aluminum fluoride composite materials,and its structure,morphology and electrochemical performance were analyzed and tested.The research content of this paper is mainly divided into the following three parts:(1)For the lithium-sulfur battery in the process of reaction polysulfide easily dissolved in the electrolyte,the use of aluminum fluoride on the polysulfide has strong adsorption characteristics,the use of the fusion synthesis of sulfur content of 70%aluminum fluoride The initial discharge specific capacity of the aluminum fluoride/sulfur composite was 999 mAh/g at 0.2 C rate,and the discharge specific capacity was 602 mAh/g after 100 cycles.The capacity retention rate was 60.2%.Shows good electrochemical performance.It shows that the adsorption characteristics of aluminum fluoride can effectively inhibit the dissolution of polysulfide and reduce the shuttle effect.(2)For the poor conductivity of sulfur and aluminum fluoride,we use bamboo charcoal with good conductivity and large specific surface area as the substrate for sulfur loading.However,there are certain impurities in bamboo charcoal materials.We used ball milling,pickling,and water washing pretreatment processes to obtain bamboo charcoal materials.Then a bamboo charcoal/sulfur composite material with a sulfur content of 70%was prepared by the liquid phase method..Under the condition of 0.5 C rate,the initial discharge specific capacity was as high as 932 mAh/g.After 100 cycles,the discharge specific capacity was 723.6 mAh/g,and the cycle holding rate was 77.6%,showing good electrochemical performance.It shows that the charcoal material has good conductivity,and the adsorption characteristics can reduce the shuttle effect.(3)In order to further improve the electrochemical performance of composite materials,we synthesized bamboo charcoal/sulfur using the liquid phase method with the advantages of low cost,good conductivity,strong adsorption,and strong adsorption of polyaluminum fluoride with aluminum fluoride./Aluminum fluoride composites.At 1 C rate,the discharge capacity of bamboo charcoal/sulfur/aluminum fluoride composites was 763 mAh/g,the discharge capacity after 500 cycles was 526 mAh/g,the capacity holding rate was 68.9%,single discharge.The specific capacity attenuation is 0.062%,and the Coulomb efficiency is always maintained at about 98.5%,showing excellent electrochemical performance.It showed that the structure of composites was stable,bamboo charcoal and aluminum fluoride double adsorbed polysulfide,inhibited the shuttle effect,and still had good electrochemical performance under the condition of 1 C large rate discharge.