Preparation Of Tin-based Anode Materials And Their Electrochemical Performance

Due to the non-renewable nature of fossil energy,the search for new sustainable alternative energy sources has become a research hotspot.As a key link in energy storage,the development of secondary batteries such as lithium-ion batteries and sodium-ion batteries has attracted more and more attention.However anode materials of secondary with low theoretical capacity will not satisfy the requirement of energy storage in large scale.It is crucial to find high capacity and structural stability anode materials to assemble high energy density and cycle stability batteries.The large volume expansion and poor conductivity of high specific capacity anodes limit their application in energy storage,especially for tin-based anode.In the present thesis,the electrical conductivity of Sn-based anodes was enhanced by carbon coating,and the large volume expansion was suppressed by special microstructure.The relationship between morphology and electrochemical performance was revealed and the related electrochemical mechanism during charge/discharge process was investigated.The main contents are summarized as following.(1)A special core-shell structured SnO2@SnS wrapping with amorphous carbon anode,synthesized via a co-precipitation reaction,etching processes and solvothermal method,was designed for high performance sodium-ion battery.The unique ball-cactus-like microsphere structured SnO2@SnS/C consists of hollow SnO2 cubic with 2?3 ?m in size and-350 nm in thickness,elongated SnS nanosheets with?1 ?m in thickness and amorphous carbon shell with a few nanometers in thickness.The SnO2@SnS/C anode exhibits excellent electrochemical performance with outstanding cycling stability and high rate capability,delivering a specific capacity of 189 mAhg-1 at a current density of 1 Ag-1 after 500 cycles.The remarkable properties can be attributed to the synergistic effects on the stable hollow SnO2 cubic core,protection of the SnS nanosheets shell and carbon shell.The core-shell structured SnO2@SnS not only can offer enough space to buffer the volume expansion during charge/discharge process,as well as increase electrode/electrolyte contact area and reduce the diffusion distance of Na+.while the carbon layer shell can further improve structural stability and electronic conductivity.The present strategy for special structured tin-based anode materials can be extended to other novel electrodes for high-performance energy storage devices.(2)Sn-based metal-organic framework was formed via water bath reaction from SnSO4 and 1,4-BDC.After calcined under nitrogen atmosphere,Sn/C composites were successfully synthesized.At last,SnS/C and Sn4P3/C anode materials were obtained after sulfidation and phosphorization processes,respectively.The Sn-MOF derived SnS/C and Sn4P3/C composites show similar microstructure in which SnS or Sn4P3 particles are wrapped with porous carbon.Both SnS/C and Sn4P3/C anodes exhibit outstanding electrochemical performance with excellent cycling stability and high rate capability.The SnS/C anode exhibits reversible capacities of 413.4 mAhg-1 after 500 cycles at 2 Ag-1 and the Sn4P3/C anode shows reversible capacities of 422.5 mAhg-1 after 500 cycles at 2 Ag-1.The remarkable properties are attributed to the uniform distribution of SnS or Sn4P3 in porous carbon and the highly-conductive porous carbon matrix.Firstly,the porous carbon matrix can not only work as protection to improve structural stability,but also increase contact area between active material and electrolyte with high specific surface area,facilitate lithium ion/electron diffusion with rich pore structure.Secondly,the uniform distribution of SnS or Sn4P3 in carbon matrix can release mechanical stress of anode materials during lithium ion intercalation/deintercalation process.Lastly,the high-conductive carbon will improve conductivity of SnS/C and Sn4P3/C anodes to accelerate the transmission speed of lithium ions and electrons.