In Situ Synthesis Of Core-shell Sulfur Cathode Material?the Study Of Their Electrochemical Performances And Activation Mechanism

Sulfur has a high specific capacity(1675 mAh g^-1),rather than low cost and environment friendly.It is a promising cathode material in future.However,the sulfur has low electrical conductivity,volume expansion during charge/discharge process,and dissolution of polysulfides in electrolyte.The shortcomings limit the commercial appication of sulfur.The presented paper used the good electrical conductivity material of carbon materials and oxide as the carrier and flexibe network structure of conductive polymers and metal organic frame material as coated material,designed a sandwich structure of the sulfur cathode materials.The paper clarified the potential mechanisms of performance optimization combined with electrochemical test and microstructure characterization.?1?.PANI/hS sulfur composite was prepared via template and in situ synthesis.The sulfur content in the composite was 71.69%.At 0.1 C rate,the composite had discharge capacity of 506.3 mAh g^-1 at the 150th cycle,which was better than pure sulfur.From SEM analysis,the particle size of PANI/hS composite was smaller than pure sulfur.Cyclic voltammetry?CV?results showed that the composite had lower cathodic reduction peaks and its discharge products had higher anodic peaks than pure sulfur,reflecting that the composite was easily reduced and its discharge product Li₂S₂?or Li₂S?was easily oxidized.Impedance data?EIS?showed that the composite had higher conductivity and its conductivity was improved with the increase of charge/discharge cycles.?2?.ZIF-8/S/ZIF-8 was prepared via hydrothermal process and fusion diffusion method.The sulfur concent in ZIF-8/S/ZIF-8 composite was 44.35%.At 0.1 C rate,the charge and discharge specific capacity of ZIF-8/S/ZIF-8 composite were 422.2?399.6 mAh g^-1 at the 100th cycle,which was higher than sulfur and ZIF-8/S.SEM results indicated that ZIF-8 had pore structure,which was beneficial for sulfur deposition.The results of CV and EIS indicated that ZIF-8/S/ZIF-8 composites had better electrical conductivity than ZIF-8/S composite.?3?.GO/SiOx/S/PPY composite was prepared via in situ deposition and polymerization method.The sulfur content in GO/SiO_x/S/PPY composite was 34.94%.The initial charge and discharge capacity of GO/SiOx/S/PPY composite were up to839.3 mAh g^-1,821.7 mAh g^-1.After 50 cycles,the charge and discharge performance tended to be stable,and the composite had a reversible capacity of 538.8 mAh g^-11 and525.5 mAh g^-1 at the 100th cycle.The SEM results indicated that GO and SiO_x had porous structure,which was good for small sulfur particle ranging in 1-5 um.PPY with a three-mesh network structure was observed to coat GO/S/SiO_x.The CV and EIS results showed the GO/SiOx/S/PPY composite was easily reduced,its discharge product Li₂S₂?or Li₂S?was easily oxidized and it had better electrical conductivity than GO/S,GO/SiOx/S composite.