Construction And Electrochemical Properties Of Sulfur Cathode Materials With High Performance

Lithium-sulfur battery has been considered as one of the most promising candidates for next-generation rechargeable batteries because of its ultrahigh theoretical energy density,cost-effectiveness,and environmental friendliness.However,based on the sulfur redox reaction mechanism,the sulfur cathodes face several scientific issues,including highly soluble lithium polysulfides（Li PSs）in the electrolyte causing the“shuttle effect”and parasitic reaction to lithium anode,resulting in poor cycling stability of the sulfur cathode;and the low sulfur reaction kinetics due to heterogeneous precipitation of solid sulfur species（such as S8,Li2S,and Li2S2）on the cathode.In addition,the poor electrical conductivity of sulfur and the severe volume expansion during the cycle can easily lead to a decrease in the utilization of sulfur.Since the sulfur matrix is the core of the construction of sulfur cathode materials,the logical design of the sulfur matrix is a breakthrough in addressing the major issues with lithium-sulfur（Li-S）batteries.This work seeks to leverage the triple effects of physical adsorption,chemical adsorption,and catalytic activity by introducing metal carbides and sulfides with strong polarity and high catalytic activity into sulfur-based materials.（1）Nanosized tin sulfide embedded in carbon fibers（SnS@CF）was designed and synthesized from a electrospinning method.Through this method,the highly conductive carbon fibers and SnS with chemical adsorption and catalytic activity for lithium polysulfide are tightly connected,and SnS@CF composites with stable structure,high conductivity,and high catalytic activity are constructed.Well-dispersed SnS nanoparticles are expected to expose sufficient active sites for anchoring and transforming Li PSs.When the SnS content reaches 54%,SnS@CF-54-S exhibits the best electrochemical performance with a high initial capacity of 771m A h g^-1 at 1.0 C.A capacity of 399 m A h g^-1 is achieved after 400 cycles.Meanwhile,a high capacity of 622 m A h g^-1 at 3.0 C can still be maintained.Under a high sulfur loading of 4.0 mg cm^-2,SnS@CF-54-S exhibits an initial specific capacity of 649 m A h g^-1 at 0.2 C.（2）ZnS was used as a template and sulfur source to construct a 3D S@C/Mo2C composite.Sulfur is in-situ confined in a hollow thin-walled C/Mo2C reactor with a size smaller than 7 nm,in which these nanosized primary particles are connected to form secondary microsized particles.In such composites,the nanoscale sulfur core and continuous conductive network can facilitate lithium-ion and electron transport.Moreover,the microporous C/Mo2C shell can mitigate the outward diffusion of polysulfides via the physical/chemical obstruction and enhance redox kinetics by catalytic conversion of polysulfides.Stemmed from these merits,the S@C/Mo2C cathode materials can achieve a high reversible capacity of 1210 m A h g^-1 at0.5 C with a low capacity fading rate of 0.127%per cycle over 300 cycles and high rate performance(780 m A h g^-1 at 3.0 C).