Preparation Of Zinc Sulfide/carbon Cloth Composites And Their Application In Lithium-sulfur Batteries

In advanced energy storage systems,the capacity of commercial lithium-ion batteries is close to its theoretical limit,which cannot meet the higher energy density demand of electric vehicles and smart grids.Lithium-sulfur batteries have obtained significant attention due to their high theoretical specific capacity and theoretical specific energy,which are considered to be one of the most promising candidate for the next generation rechargeable battery system.However,several bottlenecks hinder the further development of Li-S batteries,in which,one of the most serious problems is the“shuttle effect”of polysulfides.Researchers have proposed various strategies aimed at this problem,which are categorized into three types based on the chemical nature of interaction with polysulfide:（a）physical limit;（b）chemical adsorption;（c）catalytic conversion.In this research,from the point of the strategy“catalytic conversion”,ZnS was selected as the catalyst for promoting the conversion of lithium polysulfides.From reported researches,ZnS has great affinity with sulfur/polysulfides and promotion to the kinetic conversion of polysulfides.In addition,ZnS is inexpensive and non-toxic,which is conducive to the large-scale application.Therefore,a conductive carbon cloth was picked as a substrate to load ZnS to form a composite material,which was further applied to Li-S batteries for the electrochemical performance research.The composite materials achieved a balance between the conductivity and the catalytic performance in the material,and effectively reduced the amount of catalyst.The research contents mainly include the following two aspects:（1）The ZnS nano-layer was coated on the surface of carbon cloth.Through characterization of its structure and morphology,the surface of the carbon cloth was coated with the layer of ZnS nanoparticles with a thickness of 50 nm-70 nm.Matched with the sulfur/super P cathode,carbon cloth coated with ZnS was used as an interlayer on the cathode side in Li-S batteries.Compared to those batteries with the carbon cloth interlayer or without any interlayer,the Li-S battery with the ZnS-coated carbon cloth interlayer exhibited greater cycling stability and rate performance.The battery displayed 754.2 m Ah g^-1 after 70 cycles at 0.1C and 590.2 m Ah g^-1 after 100 cycles at 0.5C with capacity decay of 0.096%per cycle.The results of lithium polysulfides adsorption and electrochemical analysis showed:the introduction of the ZnS-coated interlayer enhanced the kinetic activity of Li-S battery system,effectively inhibited the diffusion of lithium polysulfides to the negative electrode side,and enhanced the electrochemical performance of Li-S batteries.（2）The flake-shaped ZnS was composited with carbon cloth,benefitted from TiO₂coating outside ZnS to fix the morphology.Through characterization of its structure and morphology,the results showed that ZnS flakes coated with TiO₂ were uniformly distributed on the surface of carbon fibers.Composited with sulfur,it was used as the cathode of Li-S batteries.In the cathode,the capacity reached 1165.3 m Ah g^-1 in the first cycle.However,with the cycle number increasing,the capacity rapidly decayed.Therefore,the thickness of TiO₂ coating is supposed to be further optimized.