Synthesis And Lithium Storage Properties Of Tin-based Nanocomposites

With the advent of electric vehicles and large-scale electrical energy storage systems,advanced lithium-ion batteries(LIBs)technology with high energy density and cycle stability has attracted increasing attention.In the recent decade,there has been an increasing demand for advanced LIBs with higher energy density and longer lifespan.However,the theoretical specific capacity of commercial graphite anodes is too low to fulfill the requirements of high-performance LIBs.Thus,the exploitation of excellent novel anode materials with high energy and power density for LIBs is crucially demand.Tin(Sn)anodes have been extensively studied due to its high lithium storage capacity(994 m Ah g^-1),low lithium storage potential,and abundant reserves.In addition,tin disulfide(Sn S₂),as a sulfide of Sn,has a unique two-dimensional layered structure that allows Li⁺to be reversibly inserted and a higher theoretical specific capacity(1232 m Ah g^-1)than Sn anodes.It is expected to replace graphite materials as next generation anodes for LIBs.Unfortunately,the severe volume expansion of Sn and Sn S₂ anodes during cycling causes the cycling performance to decline rapidly.Besides,as a semiconductor,a relatively low intrinsic conductivity of Sn S₂deteriorates its rate capability.At present,there are a variety of effective methods to improve the electrochemical performance of tin-based materials,including nanocrystallization,modification by compounding with buffer materials,and microstructure regulation.In this paper,the Sn and Sn S₂ anodes were modified by introducing hard TiC nanoparticles with high conductivity to improve their electrochemical performance.Sn/TiC nanoparticles and Sn S₂/TiC nanocomposites were prepared by combining a DC-arc plasma evaporation and a subsequent solid-phase sulfurization process.The TiC contents in the sample was controlled by adjusting the atomic ratio of Sn and Ti in the raw materials,and the effect of TiC contents on the phase morphology and lithium storage performance of Sn/TiC nanoparticles and Sn S₂/TiC nanocomposites was explored.The main work and conclusions are as follows:(1)Sn/TiC nanoparticles were synthesized through a DC-arc plasma evaporation method.XRD and TEM measuremental results show that Sn/TiC nanoparticles are composed of spherical Sn nanoparticles and polygonal TiC nanoparticles with a particle size of about 20-70nm.The uniformly dispersed TiC can prevent the aggregation of Sn nanoparticles and buffer the volume expansion of the electrode.As an anode material for LIBs,Sn/TiC nanoparticles show better electrochemical performance than Sn nanoparticles.When the TiC content reaches 36%,the electrochemical performance of the electrode is the best.It exhibits the discharge capacities of 380 m Ah g^-1 and the capacity retentions of 73.0%after 100 cycles,respectively.(2)Sn S₂/TiC nanocomposites were prepared by using Sn/TiC nanoparticles as precursors,combined with the subsequent solid-phase sulfurization reaction.SEM observation results show that pure Sn S₂ possesses a morphology of hexagonal nanosheets with a thickness of about 50 nm and the nanosheets become irregular after modifing by TiC.As the TiC contents increase,the nanosheets become thinner and thinner.TEM results of Sn S₂/TiC(35%)sample show that ultrathin Sn S₂ nanosheets have an average thickness of 5.8 nm and TiC is evenly dispersed on Sn S₂ nanosheets.The electrochemical test results showed that the Sn S₂/TiC electrodes have better electrochemical performance than pure Sn S₂ electrode,and the electrochemical performance progressively improves with the increase of TiC contents.Among them,the Sn S₂/TiC(35%)electrode exhibits the higher electrochemical performance.It delivers a high reversible capacity of 631 m Ah g^-1 at 0.3 A g^-1 after 100 cycles,corresponding to a capacity retention of 87.0%.In particular,at a high current density of 1 A g^-1,Sn S₂/TiC(35%)electrode can still possess a high specific capacity of 597 m Ah g^-1 after350 cycles,showing outstanding rate capability and long-cycle performance.The excellent electrochemical performance of Sn S₂/TiC(35%)electrode is attributed to the strong synergistic effect of ultrathin Sn S₂ nanosheets and highly conductive TiC nanoparticles.