Fabrication And Property Research Of Tin Oxide Based Anode Materials For Lithium-ion Batteries

As a new generation of energy storage devices,lithium-ion batteries（LIBs）have become the mainstream choice for energy storage in many spheres,such as portable electronic devices,electric vehicles and aerospace.Tin and its oxides are quite promising anode materials for high-performance LIBs owing to their high theoretical capacities,abundant resource,and environmental benignity.The main problems of Sn O_x-based anodes are volume expansion and the aggregation of tin particles during cycling,which will greatly damage the capacity performance of LIBs.Considering environmental pollution and cost,we explored a facile and environmentally friendly route to synthesize Sn O_x-based composites.We systematically studied their microstructures,composition,chemical states and properties,and analyzed the effects of different preparation conditions（such as annealing temperature and graphene content）on the electrochemical properties of the composites.（1）Preparation and properties of Sn O_x with multiple oxidation statesIn our work,we adopted a simple Galvanic replacement method to quickly obtain abundant foamed tin as raw material.This method is easy to operate,energy-saving and environmentally friendly,avoiding the use of toxic chemical reagents.The foamed tin has dendritic microstructures and high purity,which was annealed in air at different temperatures to obtain Sn O_x with multiple oxidation states.With the increase of annealing temperature,the oxidation degree of foamed tin enhances.The annealed product at 300℃contains Sn,Sn O and Sn₃O₄ components;the products annealed at 400 and 500℃contain Sn₃O₄,Sn O and Sn O₂;however,the product annealed at 600℃is almost Sn O₂.Commonly,the product synthesized by hydrothermal methods or solvothermal methods is a single composition of Sn O₂.Therefore,our work provides a new way for the preparation of multi-oxidation state Sn O_x.（2）Preparation and lithium storage performance of Sn O_x/G compositesSnO_x/G composites were prepared by using a simple ball milling method to combine Sn O_x with graphene.Compared with other complex chemical preparation methods,the ball-milling method is easier to realize large-scale production.We studied the compositions and microstructures of the products and analyzed the effects of ball milling and different graphene content on the Sn O_x/G composites.After ball milling,the oxidation degree of the composites increased,the size of the crystal grains decreased and a part of the crystal changed into an amorphous state.Besides,graphene defects increased in the composites.Then,the electrochemical performance and the reaction mechanism of the assembled cells were studied by cyclic voltammetry,electrochemical impedance spectroscopy and galvanostatic discharge/charge tests.The research shows that the content of graphene has a significant impact on the cycling performance of the cells.Although graphene can reduce the charge transfer resistance and alleviate the volume expansion of the active materials,adding too much graphene will reduce the capacity of the battery.The composite obtained by ball milling the oxidized product of the foamed tin at 300℃and graphene（Sn O_x-300/G）exhibited a quite high initial Coulombic efficiency（84.03%）and great cycling stability(786 m A h g^-1 at 0.1A g^-1 after 150 cycles),which can be attributed to its unique components（Sn and Sn O_x）and the synergistic effect of graphene.Therefore,this facile synthesis method provides a new route to realize green and large-scale preparation for high-performance energy storage materials.