Research Of Synthesis And Modification In Metal Sulfides As Anodes For Sodium Ion Batteries

As one of the most promising candidate anodes for sodium ion batteries（SIBs）,metal sulfides possess high theoretical specific capacity.Compared to metal oxides,metal sulfides as SIBs anodes show kinetically more advantageous to sodiation/desodiation processes,resulting from their relatively weaker M-S bonds,thus yielding better cycling reversibility and initial coulombic efficiency.However,there are two disadvantages in metal sulfides anodes.First,the electronic conductivity of metal sulfide is inherently poor.Second,the large volume expansion during cycling will result in the pulverization of anode materials.Third,polysulfides as possible intermediate will react with carbon-ester-based electrolyte and dissolve into ether-based or carbon-ester-based electrolyte,leading to irreversible capacity loss.In order to increase the electronic conductivity,SnS_x with unique layered structure and large interlayer spacing were mixed with carbon matrix.Additionally,the rational synthesis strategy and architecture design for SnS_x-based anodes devotes to improve the cycling stability.As a novel bimetallic sulfide,FeSb₂S₄ is rationally designed and synthesized for sodium ion storage.Furthermore,graphene after chemical modification is used to enhance the reversible capacity and long-term cycling stability of FeSb₂S₄.Here,SnS_x nanoparticles were encapsulated within hollow carbon spheres to enhance electrochemical performances.Sn₂S₃ was for the first time studied as a sodium ion battery anode.To leverage the structural advantage of Sn₂S₃ and make it a workable SIB anode,Sn₂S₃@CS was prepared and was further investigated its electrochemical properties systematically.To realize the cycling stability at high rate,nano TiO₂ as hard particle was introduced into SnS₂@CS anode to fabricate pomegranate-like SnS₂ NP/TiO₂@C,and its physical properties and electrochemcial performances were studied via many measurement strategies.The experimental results demonstrate that SnS₂ NP/TiO₂@C showed enhanced capacity retention rate and cycling stability enven at high rate due to the role of the unique anode construction.SnS₂ NP/TiO₂@C composite can achieve a reversible capacity of 338.2 mAh g^-1 after 600 cycles with an excellent cycling retention rate of 82.4%.In order to improve the cycling stability and rate performance of FeSb₂S₄,mixing ethylenediamine chemically modified graphene with FeSb₂S₄ to construct FeSb₂S₄/EN-rGO can be a promising strategy.The experimental results reveal that FeSb₂S₄/EN-rGO exhibited high reversible capacity,long-term cycling stability and excellent rate performance.FeSb₂S₄/EN-rGO delivered a high capacity of 782.5 mAh g^-1 at 0.1 A g^-11 for 100 cycles with an ultra-high initial coulombic efficiency（ICE）of83.4%.Even at 5 A g^-1 for 500 cycles,this anode shows a low capacity loss rate of0.04%per cycle with a high capacity of 515.7 mAh g^-1.And the rate capability of FeSb₂S₄/EN-rGO is much superior to that of other reported bimetallic sulfide anodes.