| The intensification of energy crisis and environmental pollution has greatly promoted the exploration and research of new energy and energy storage systems.Over the past few decades,lithium-ion batteries?LIBs?have become the first choice due to its high energy density and superior cycling performance.However,with the rapid development of society and the continuous improvement of requirements for energy storage systems,the large-scale application of LIBs has been continuously restricted.Therefore,there is a common concern in the world to seek electrical energy storage system with higher energy density and better cycle stability.A lighter sulfur elements gradually enters researcher's perspective due to its advantages of abundant storage,environmentally friendly and low-cost.However,due to poor conductivity,shuttle effect and low utilization of active materials during the application process,it shows that there is still a long way to go for the research of lithium-sulfur batteries?LSBs?.In order to improve the electrochemical performance of LSBs,this paper mainly focuses on carbon materials and conductive polymers on modification of cathode material.?1?In this paper,nano-scale elemental sulfur particles were prepared by in-situ deposition method,which showed good dispersibility in composite materials.At the same time,commercialized acetylene black?AB?was chosen as carbon source and sulfur-storing substrate,and AB/S binary composite was obtained by in-situ precipitation method.The electrochemical tests demonstrate that the addition of acetylene black can improve the electrochemical performance of pure sulfur electrode.In order to further enhance the cycle stability of electrode material,conductive polymer polypyrrole?PPy?coating layer was introduced into the AB/S/PPy ternary composite by chemical oxidation polymerization.The electrochemical tests show that the AB/S/PPy composite exhibits the best performance with an initial discharge capacity of 1090.3 mAh g–1 at the current density of 200 mA g–1,and retains 577.4 mAh g–1 after100 cycles.?2?The conductive polymer PPy was selected as the main research object,and the PPy with tubular and granular morphology was synthesized successfully.Firstly,PPy with a tubular morphology was synthesized by a self-degrading template method,subsequently calcined at 900?to obtain tubular amorphous carbon?TAC?.The TAC was used as the attachment of nano-sulfur particles.TAC@S composite can be prepared with evenly dispersed sulfur.Secondly,the granular PPy as coating layer for above material,the TAC@S@PPy composite was sythesized by in-situ chemical oxidative polymerization.Finally,a one-step heat treatment was carried out at 155?to provide a better dispersion of sulfur in conductive substrate and coating layer.Therefore,the TAC@S@PPy composite cathode for LSBs exhibits excel ent electrochemical cyclin g performance(initial discharge specific capacity of 1111 mAh g-1 at 335 mA g-1),stability(731 mAh g-1 after 100 cycles)and good rate performance(620 mAh g-1 at2000 mA g-1).?3?In addition,we performed UV-Vis spectroscopy and adsorption experime nts on the as-prepared different cathode composites.The main purpose of this study was to simulate the adsorption of above cathodes for polysulfides in charge-discharge process,and further determine their electrochemical performance.The obtained experimen ta l results show that:?i?compared with pure phase,the addition of carbon materials in binary materials?AB,TAC?can provide many attachment sites for sulfur and further play a certain inhibition effect on the dissolution of polysulfides;?i?compared with binary composite,the presence of PPy coating in ternary composite provides a stronger adsorption and storage space for polysulfides,and inhibiting the dissolution of polysulfides in a greater extent. |
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