Study On Energy Storage And Electrochemical Performances Of Tin-based Sulfides@rGO Composites

Recently,potassium resources are very abundant and widely distributed around the world,more and more researchers pay close attention to the application of potassium ion batteries（PIBs）in large scale energy storage.At present,the development of PIBs is just at the infancy stage,the specific capacity of carbon materials is relative low,for example,the theoretical capacity of graphite is only 279 mAh g^-1.Even though some reported conversion and/or alloying materials show high capacity,but their inferior cycle stability and relative high diachage operating voltage limited their further study.At the same time,some materials’energy storage mechanisms are still unclear.Therefore,the purpose of this thesis is to develop tin-based sulfides@rGO composities through one-pot low temperature solvothermal method,we also used a series of measurements to study electrochemical performances and energy storage mechanism,this is of great significance for the develop anode materials for PIBs.The main contents of this paper are as fellows:（1）In this paper,pure SnS₂ and SnS₂@rGO-x composites were prepared by a facile low temperature solvothermal method,we analyzed the effct of the content of graphene on the morphology and electrochemical performances of the SnS₂@rGO-x electrodes,at the same time,using ex-situ XRD,ex-situ TEM and ex-situ XPS studied the energy storage mechanism of SnS₂.The experimental result shows,the number of atomic layer of SnS₂ can be controlled by regulation of the content of graphene,the SnS₂@rGO-2 as PIBs anode material delivered high reversible capacity,superior rate performance and good cycle stability.The reversible discharge specific capacity of this material was 448 mAh g^-1 at the current density of 50 mA g^-1,after 100cycles the capacity still as high as 400 mAh g^-1.Even at high current density of 1 A g^-1,it still delivered a specific capacity of 574.4 mAh g^-1 with capacity retention over 70%after 300 cycles.The electrochemical analysis results show that the fastest K⁺diffusion rate and high surface capacity can be achieved in the SnS₂@rGO-2 electrode.Energy storage mechanism study indicates that SnS₂ going through conversion and two steps alloying reactions during charge process,the final discharge products are KSn and Na₂S.More importantly,the conversion reaction is partly reversible.（2）In this paper,amorphous Sn_xMo_（1-x）/2S@rGO-x were fabricated by a facile low temperature solvothermal method,and the electrochemical performance in organic electrolyte was tested.This work provides a new perspective for the systhesis amorphous materials and optimize tin-based materials.The isoropy property of amorphous materials result in higher ion conductivity than corresponding crystalline materials,this beneficial for relieve huge volume change during long cycles.The physical property of the Sn_xMo_（1-x）/2S@rGO-2 is elucidated by XRD、TEM、XPS etc.The Sn_xMo_（1-x）/2S@rGO-2 as PIBs anode material delivered high reversible capacity,superior rate performance and good cycle stability.The reversible discharge specific capacity of this material was 342 mAh g^-1 at the current density of 50 mA g^-1,after 50cycles the capacity still as high as 310 mAh g^-1 with capacity retention over 90.6%.