Studying Electrochemical Performance Of Three Dimensional Porous Si@C Composite Coatings

Development of new energy automobiles,electronic products and energy storage devices call for high performance lithium ion batteries(LIBs).Nowadays,scientists pay much attention to the next generation LIBs with high specific capacity,excellent cyclic and rate performance.Si was considered as the most promise anode materials for LIBs due to its highest theoretic specific capacity(4200 mAh/g).however its commercial application still encounter some challenges such as,poor electrical conductivity,dramatic volume change during discharge-charge processes and unstable solid electrolyze interface(SEI)film in LiPF₆ electrolyze,etc.Synthesis of Si-C composites is one of the most effective strategies to deal these issues.In this paper,Cu-supported carbon based composite coatings containing Si and metal oxides(SnO₂ and ZnO)nano-particles were successfully synthesized by techniques combining merits of carbonization of mixed polymers and pyrolysis of precursor of metal oxides.Si-SnO₂-C composite coatings produced by tin dichloride pore forming agent have three dimensional(3D)network structure which was constructed by continuous carbon based branches with width of 0.1-1?m.The carbon based branches contain Si and SnO₂nano-particles with size of 30-50 nm and micro-pores with size of 1-5 nm.Si-ZnO-C composite coatings with 3D network structure were constructed by continuous carbon based branches with width of 0.1-1?m.The formation of carbon based composite coatings containing Si and metal oxides(SnO₂and ZnO)nano-particles is related to volatilization of PMMA and pyrolysis of metal oxide precursors at high temperature.The volatilization of PMMA will cause big size void in carbon matrices,which leads to network structure of the composite coatings.The pyrolysis of metal oxide precursors will cause a lot of micro-pores with nanometer scale in carbon matrices.The obtained Si-SnO₂-C composite coatings have high specific capacity,excellent cyclic and rate performance.After 200 cycles at a current density of 0.5A/g,they deliver specific capacity of 1358.59mAh/g without apparent capacity fading during cycling.At current densities of 2,4,8 and 20,their specific capacities are 1290.11,1114.62,847.31 and512.16 mAh/g.The obtained Si-ZnO-C composite coatings deliver specific capacities of 1740.015,1540.951,1170.649 and 688.333 mAh/g at current densities of 0.5,1,2 and 5 A/g.The addition of zinc nitrate has significant effects on their electrochemical performance.The optimal addition of zinc nitrate is 0.18 g.The addition of zinc nitrate will enhance their cyclic and rate performance and decrease their surface resistance and diffusion resistance.On the contrary,excessive zinc nitrate addition will decrease their cyclic and rate performance and increase their surface resistance and diffusion resistance.The carbon based composite coatings containing Si and metal oxides(SnO₂ and ZnO)nano-particles exhibit excellent electrochemical performance,their synthesis techniques are simple and suitable for a large scale producing,which makes them promise anode materials for next generation LIBs.