Synthesis And Electrochemical Performance Of Sulfide-based Cathode Material For Li-S Battery

With the rapid development of society and the growing demand for energy consumption,we urgently need to search the requiements of intelligent communications and electric vehicles in the field of high specific energy,long cycle life of the battery system.Lithium-sulfur batteries are considered to be the most promising next-generation batteries due to their high specific capacity and high energy density.However,the practical production and application of lithium-sulfur batteries is still facing many challenges.The modification of sulfur-based cathode materials is one of the main methods to improve the electrochemical performance of lithium-sulfur batteries.In this paper,ultrathin SnS2 nanosheets were synthesized by hydrothermal method,and the S/C-SnS2 composites were prepared by melting method.The electrochemical performances of the S/C-SnS2 composites were studied systematically.It was found that SnS2 nanosheets could improve the cycle performance and the rate performance of lithium-sulfur batteries because of its strong binding energy towards polysulfides,high conductivity and large specific surface which can provide multiple active sites.Moreover,we investigated the effect of different content of ultrathin SnS2 nanosheets on the performance of the batteries.It is found that the mass ratio of ultrathin SnS2 nanosheets was optimized,and the electrochemical properties of the composites were further improved.Secondly,we encapsulated CuxS into graphene to synthesize graphene-coated CuxS nanoparticles(CuxS@GO)composite.The composite was followed by infultrating sulfur to design CuS modified sulfur-based cathode materials(S/CuS@GO).The electrochemical properties of the composites at different C-rates could obtain good cycle stability.The main contents of this paper are summarized as follows:1.The ultrathin SnS2 nanosheets and SnS2 microspheres were prepared by hydrothermal method,respectively.The average sizes of SnS2 nanosheets and SnS2 microspheres were?30 nm and-5 ?m,respectively.The S/C-SnS2 composites were prepared by mixing commercial sulfur,Ketjen black and SnS2 uniformly in a vacuum tube at 155 ?.Compared with SnS2 microspheres,the ultrathin SnS2 nanosheets have small size,large specific area and strong chemical adsorption towards polysulfides which can effectively improve the cycle stability and rate performance of lithium-sulfur batteries.In addition,the mass ratio of ultrathin SnS2 nanosheets was designed as 5 wt%,10 wt%and 15 wt%in S/C-SnS2 composites,and the electrochemical performances of the composites were systematically studied.The results showed that the 10 wt%SnS2-modified composites display the best electrochemical activity.It could maintained a high reversible capacity of 800 mAh g-1 for 300 cycles at 0.5 C and 540 mAh g-1 for 700 cycles at high rate of 2 C.This can be attributed to the optimal synergistic effect of ultrathin SnS2 nanosheets and porous carbon material.2.First,the CuxS nanocrystals were prepared by hydrothermal method,followed by coating with graphene.Then,the composites,served as matrix,were mixed with commercial sulfur in vaccum and heated to synthesize S/CuS@GO composites with sulfur loading of 80 wt%.Morphology characterization showed that the CuS nanocrystals were uniformly encapsuled in graphene and electrochemical properties indicated the good cyclic stability and rate performance of S/CuS@GO composites with a high reversible capacity of 650 mAh g-1 after 350 cycles at current density of 0.5 C and 600 mAh g-1 after 500 cycles at 1 C.The supior electrochemical performances can be ascribed to the high conductivity and large specific area of CuS nanocrystals which is conducive to the redox reaction during charging/discharging process and enhance the utilization of active materials.