Preparation And Electrochemical Performance Of Opal Shale/S-Based Cathode Composites

With the development of science and technology,the performance requirement for battery is improved.Lithium-sulfur battery is one of the research hotspots in recent years owing to its high theoretical energy density(2600 Wh/kg)and high theoretical specific capacity(1675 mAh/g).However,the commercial application of lithium-sulfur battery is limited by some challenges,such as the poor conductivity of elemental sulfur and the high solubility of the reaction intermediates polysulfide.To improve the electrochemical performance of the lithium-sulfur battery,oxides,conductive polymers or carbon nanomaterials are usually used to combining sulfur.Opal shale is a kind of natural mineral with excellent ion exchange capacity and good affinity for sulfur,whose content of SiO2 is more than 80%,and the Si-O bond in SiO2 nanoparticles can adsorb the polysulfide effectively.Besides,polyaniline(PANI)is one of the most common conductive polymers,which has good electrical conductivity,high environmental stability,insolubility in electrolytes,and a unique proton doping mechanism.Meanwhile,special functional groups on the surface and unique chain structures of polyaniline can react with sulfur or polysulfide,and restrict sulfur simultaneously.In this work,the morphology,structures and electrochemical performance of the opal shale/S and opal shale/S-PANI composites were investigated.The research content includes the following three parts:(1)The raw material of opal shale was pretreated by washing,and the opal shale/S composites with sulfur contents of 40%,50% and 60% were prepared via thermal fusion method.The electrochemical results show that opal shale/S composites with 50% sulfur exhibited the best electrochemical performance,the initial discharge specific capacity was 980.7 mAh/g at the current rate of 0.2 C,and the discharge specific capacity remained at 462.0 mAh/g after 100 cycles,which was 47.1% of the initial cycle.(2)For enhancing the porosity of opal shale and synthesis composites with small size of sulfur,opal shale/S composites with sulfur content of 40%,50% and 60% were prepared by chemical deposition method,which revealed better electrochemical performance than thermal fusion method.The electrochemical results show that opal shale/S composites with 50% sulfur have the best electrochemical performance.It revealed a high initial discharge specific capacity of 1161.1 mAh/g at the current rate of 0.2 C,with 599.4 mAh/g remained after 100 cycles,which was 51.6% of the first cycle.Meanwhile,an initial discharge specific capacity of 832.4 mAh/g obtained for the composites at the current rate of 0.5 C,keeping 373.5 mAh/g after 300 cycles,with the capacity retention rate of 44.9%.(3)In order to further improve the electrochemical performance of the lithium-sulfur battery,the opal shale/S composite with 50% sulfur was prepared by chemical deposition method,which was coated with different content of polyaniline through chemical oxidation polymerization method.The electrochemical performance of the opal shale/S-PANI composites was improved.When the amount of the aniline monomer added to the composites was 0.5 mL/g,the thickness of the polyaniline coating in the opal shale/S-PANI composites was about 400 nm,which expressed the best electrochemical performance.The maximum discharge specific capacity of 1164.9 mAh/g was obtained after activation and retained a discharge specific capacity of 539.3 mAh/g after 300 cycles at the current rate of 0.5 C,the capacity retention rate was 46.3%.