The Preparation And Electrochemical Properties Of SnO₂/Carbon Composites For Lithium Ion Batteries

The development of environmentally friendly and efficient alternative energy sources has become the focus of current research to meet the mounting necessities of environmental and energy needs.In this regard,lithium-ion batteries are particularly important as A?green energy source.It is urgent to develop the next generation of rechargeable batteries with high energy density,long life,high safety and reasonable price.As a promising tin-based lithium storage material,SnO₂ has attracted wide attention for a long time.However,the lithium storage mechanism of SnO₂ indicates that the development of SnO₂ as an anode material is severely limited due to the irreversibility of conversion steps,high irreversible capacity and poor cyclic stability caused by volume expansion/contraction during charging and discharging.Hence,how to overcome the shortcomings of SnO₂ and prepare a novel anode material for lithium ion batteries with high energy density,high safety and reasonable price has become the research emphases on tin-based materials.In this paper,based on three main optimization methods of SnO₂,three types of carbon materials including hollow carbon microspheres,mesoporous carbon and carbon microtubes were designed to load SnO₂,which can improve the reversible capacity and cyclic stability of SnO₂ composites.The effects of carbon matrices with different sizes and structures on the electrochemical properties of the composites were also investigated.1.SnO₂/porous carbon hollow composite microspheres were prepared by sulfonation and high temperature calcination using PS-co-PMAA hollow microspheres prepared by seed emulsion polymerization（two step soap free emulsion polymerization）as templates.The prepared composite materials are mainly in spherical shape with particle size of 120-150 nm and SnO₂ nanoparticles are homogeneously distributed on the surface of carbon microspheres with 3.94 nm mesopores.The composites consisting64.8 wt%of SnO₂ deliver the best electrochemical performance with a charge capacity of 476 mAh?g^-1 retained after 120 cycles at 100 mA?g^-1 and the rate capability is better.2.SnO₂/mesoporous carbon composites were prepared by self-assembly and high temperature calcination using resorcinol and hexamethylenetetramine as precursors,F127 as structure-directing agent and SnCl₂·2H₂O as tin source.The results show that regular and ordered mesoporous channels are beneficial to improve the electrochemical properties of the composites.It was found that the composites consisting 65.9 wt%of SnO₂ have regular and ordered channels which lead to the good electrochemical properties.After 120 cycles,the capacity can achieve 285 mAh?g^-1 and the rate capability performs well.3.Carbon microtubes and SnO₂/carbon microtubes composites were prepared by impregnation and carbonization of the poplar catkin.The synthesized composites have an open-ended tubular structure with size of 10μm and a large number of micropores（1.34 nm）on the surface.The composites consisting 51.9 wt%of SnO₂ have good cycling performance,but its reversible capacity is relatively low(205 mAh?g^-1 after 120cycles).This is probably resulted from the low space utilization and small pore size of carbon microtubes,which is not conducive to ion transport in electrolyte.Thus,the performance of the material needs further exploration and optimization.