Preparation And Properties Of Tin-based Anodes For Lithium/Sodium-ion Batteries

Lithium/sodium-ion batteries（LIBs/SIBs）have high energy density,and have great development prospects in the field of large-scale energy storage.However,the commercial graphite anode with a low lithium/sodium storage capacity,which restricts the development of high-capacity and high-power LIBs/SIBs.SnS₂ has a high lithium/sodium storage capacity,so it is a potential anode for LIBs/SIBs.However,in the energy storage process,the large volume change and the poor conductivity limit the large-scale application of SnS₂.Therefore,aiming at the inherent defects of SnS₂ materials in the process of lithium/sodium storage,SnS₂/rGO composites with different structures were designed to improve the electrochemical performance.（1）A one-step hydrothermal method was used to synthesize nano-sheet SnS₂-rGO composite materials.The diameter of SnS₂ nanosheets is 100-200 nm,and the thickness is about 10 nm,graphene is uniformly distributed in the composite material.Graphene can be closely combined with SnS₂ nanosheets via chemical bonds,limiting the aggregation of SnS₂ nanosheets during cycling,so that the material has a stable structure.In addition,S-doped graphene can provide a part of storage sites for lithium/sodium ions,so that SnS₂-rGO has a higher capacity.When it is applied for LIBs/SIBs,the cycle performance is characterized at 0.1 A g^-1.After 100 cycles,the lithium/sodium storage capacity can reach 1641.9 mAh g^-1/610.5 mAh g^-1,showing excellent cycling stability.（2）In order to solve the problem of SnS₂ volume expansion,the SnS₂-rGO microspheres with the hierarchical structure were synthesized.The diameter of SnS₂-rGO microspheres is about 1 μm,the length of a single SnS₂ nanosheet is 400-600 nm,and the thickness is about 20 nm.The hierarchical structure allows the electrolyte to fully infiltrate the electrode materials and increase the transmission rate of lithium/sodium ions,it can also reserve space for the volume change of SnS₂,so that the SnS₂-rGO microspheres have outstanding cycle stability.The graphene sheets are evenly distributed in the SnS₂-rGO microspheres,which can act as a conductive network to accelerate the transfer of electrons.The SnS₂-rGO microspheres are applied to LIBs/SIBs,and its cycle performance is characterized at 0.1 A g^-1.After 100 cycles,the lithium/sodium storage capacity can reach 1647.8 mAh g^-1/776.2 mAh g^-1.（3）By constructing a heterostructure to improve the conductivity of SnS₂ and the diffusion rate of lithium/sodium ions.The CoSn（OH）₆@GO composite material was synthesized by the co-precipitation method.The diameter of the CoSn（OH）₆ with a hollow structure is about 200 nm.The graphene oxide is uniformly distributed in the composite material,preventing the accumulation of CoSn（OH）₆.In the hydrothermal process,CoSn（OH）₆@GO was transformed into SnS₂/CoS₂@rGO,and the morphology and structure of the material did not change.The graphene in the composite material can limit the agglomeration and the volume change of the SnS₂/CoS₂ during cycling,which improves the reversibility of the composite material.The hollow structure can reserve space for the volume change of SnS₂/CoS₂ during cycling and increase the cycle stability of the composite material.In addition,the heterostructure existing in the SnS₂/CoS₂@rGO can accelerate the migration of electrons and increase the diffusion rate of lithium/sodium ions,so that the SnS₂/CoS₂@rGO can exhibit a higher capacity.When it is used as an anode material for LIBs/SIBs,its cycle performance is characterized at 0.1 A g^-1.After 100 cycles,the lithium/sodium storage capacity can maintain 1226.7 mAh g^-1/561.2 mAh g^-1.