Preparation Of Freestanding Stannous Sulfide/Carbon Fiber Anode Materials And Its Properties For Lithium Storage

In the large background of highly advocating low-carbon environment protection,growing standard of life,the new energy cars,electronics products have been dramatically developed.It is urgent to exploit lithium-ion battery anode materials with high-capacity,fast charging,environmentally friendly.Stannous sulfide（SnS）has attracted much attention due to the large lattice spacing（4.04?）,high theoretical specific capacity(1138 m Ah g^-1)and safe potential（1.411 V）.However,the large volume expansion and low conductivity cause the SnS electrodes have poor cycling performance.Numerous studies indicating that the recombination of SnS with well conductive carbon fibers is an effective strategy to solve the above problems.Therefore,the paper aims to prepare self-supporting high-performance SnS/carbon fiber electrode materials.The effects of content of active materials,spinning process,metal compound and heteroatom doping modification on the performance of electrode materials were systematically investigated.The specific study contents are as follows:（1）The SnS/carbon fiber composites（SnS/MCFs-1,SnS/MCFs-2 and SnS/MCFs-3）with different ratios were prepared by electrospinning.Based on the optimal ratio,two composites with different structures were designed by coaxial electrospinning:SnS@hollow multichannel carbon fibers（SnS@HMCFs）and SnS@multichannel carbon fibers（SnS@MCFs）.As a result,the SnS@HMCFs electrode delivers a stable capacity of 379.3m Ah g^-1 at 0.5 A g^-1 after 500 cycles,exhibiting the best cycling performance.This is mainly attributed to that the designed hollow multichannel structure not only can effectively alleviate the volume change of SnS during intercalation/delithiation,but facilitate the penetration of electrolyte into the electrode materials and accelerate Li⁺transport.（2）Designing heterojunction structures to further raise the electrochemical performance of the SnS@HMCFs composites,the Ti O₂/SnS@HMCFs and MoS₂/SnS@HMCFs was prepared by electrospinning technique and hydrothermal method,respectively.Electrochemical investigations exhibit that the MoS₂/SnS@HMCFs owns better cycling stability:the discharging specific capacity is 610.1 m Ah g^-1 at 0.5 A g^-1 after 500 cycles,and the capacity retention is 53.79%.Mainly ascribed to the different lithium storage potentials of MoS₂versus SnS,which can reduce the internal stress of the electrode materials by alternating charging/discharging;in addition,MoS₂ and SnS can constitute p-n heterojunctions and accelerate the flow of electrons.（3）Boron and phosphorus atom were doped into carbon fibers to improve the physicochemical properties of carbon based materials.The MoS₂/SnS@B-HMCFs,MoS₂/SnS@P-HMCFs and MoS₂/SnS@BP-HMCFs were prepared by electrospinning and hydrothermal method.Among them,MoS₂/SnS@BP-HMCFs own better electrochemical performance:the reversible specific capacity is 854.4 m Ah g^-1 after 500 cycles at 0.5 A g^-1.At the current densities of 0.1 A g^-1,0.2 A g^-1,0.5 A g^-1,1.0 A g^-1 and 2.0 A g^-1,the reversible discharge specific capacities are 1261.8 m Ah g^-1,1013.6 m Ah g^-1,924.2 m Ah g^-1,709.4 m Ah g^-1 and 651.4 m Ah g^-1,respectively.This is benefited from the synergistic effect of B and P diatomic co-doping,which can endow electrode materials with higher conductivity and more Li⁺adsorption sites.