Preparation And Properties Of Tin Dioxide And Molybdenum Carbide/Carbon Composites As Anode Materials For Lithium Ion Batteries

With the increasing demand of sustainable and clean energy,the development of advanced energy storage device has attracted much attention.Lithium ion batteries?LIBs?have become an important source of electrical energy for portable electronic devices and electric vehicles due to their high specific capacity and long cycle life.The progress of LIBs technology mainly depends on the innovative research and application progress of key battery materials,in which anode material is one of the main factors that affect the energy density of LIBs.However,the traditional low-capacity(372 mAhg^-1)graphite anode has been difficult to meet the increasing energy density of LIBs,so it is imperative to develop new high-capacity anode material.Tin dioxide and molybdenum carbide with high capacity are considered as ideal new anode material,and thus have attraced extensive attention from researchers.However,metal compound anode material generally have some defects such as large volume deformation and easy agglomeration during charging and discharging process,which results in poor cycle stability.Constructing effective composite electrodes of metal compounds and carbon materials,designing and preparing electrode materials with micro-nano structure in targeted manner is an effective strategy to improve the electrochemical performance of metal compound anode.This paper selects tin dioxide and molybdenum carbide as research objects,Sn O₂@C submicron box structure composites and Mo₂C/nitrogen-doped carbon?Mo₂C/N-C?nanotube composites were designed and prepared,the corresponding microstructure,composition and electrochemical performance were further studied.The results are as follows:?1?In this work,mesoporous carbon coated hollow tin dioxide?Sn O₂@C?submicron box composites was prepared through hydrothermal and carbonization methods using solid zinc metastannate precursors,phenolic resols and triblock copolymer F127 as starting materials,and followed treated with divalent cation chelating agent Na₂EDTA.Mesoporous carbon layer can not only promote conductivity of the electrode,but also relieve the large volume expansion of Sn O₂ and the agglomeration of Sn particles in the process of charging and discharging.In addition,the submicron size and mesoporous carbon layer of the composites can slow down the adverse reaction between the materials,and the hollow structure provides more buffer space for internal strain.The submicron box structure Sn O₂ and the surface mesoporous carbon layer are conducive to exert synergistic effect and exhibit excellent electrochemical performance.Electrochemical test results showed that the anode material can maintain discharege capacity of 891.7 mAhg^-1 after 100 cycles at100 mAg^-1,and the discharege capacity can still maintain 766.9 mAhg^-1 after 200cycles at 200 mAg^-1.?2?In this work,Mo₂C/nitrogen-doped carbon?Mo₂C/N-C?nanotube composites was prepared by hydrothermal and carbonization methods using molybdenum trioxide as molybdenum source,polydopamine as carbon source and nitrogen source.In this system,polydopamine formed mesoporous structure,and Mo₂C nanocrystals loaded in one-dimensional nitrogen-doped mesoporous carbon matrix to obtain mesoporous Mo₂C/N-C nanotube anode material.The nitrogen-doped mesoporous carbon nanotube framework can be used as protective layer to alleviate the agglomeration and volumetric deformation of Mo₂C particles and enhance the charge-discharge cycle stability of the electrode.The high-conductivity,interconnected network formed by nanotubes with larger aspect ratio is conducive to improve the migration efficiency of electron and Li⁺.In addition,this one-dimensional mesoporous structure is beneficial to make material large specific surface area,promote electrolyte infiltration and ion diffusion.Mo₂C nanocrystals and one-dimensional mesoporous nitrogen-doped carbon nanotubes are beneficial to synergistically improve the cycle stability of the electrode.Electrochemical test results showed that the anode material still keep discharege capacity of 578.2 mAhg^-1 after 100 cycles at 100 mAg^-1,and the discharege capacity can maintain 456.4 mAhg^-1 after 200 cycles at 200 mAg^-1.