The Construction And Electrochemical Performance Of Carbon Composited Tin Dioxide-based Electrode Material

The concept of environmental protection and low-carbon economy has been generalized globally.The environmental protection and low-carbon economy eagerly requires the development of new energy and electric vehicles,and the corresponding construction of smart grids and establishment of charging infrastructures for electric vehicles are also indispensable.The storage of new-type renewable energy and the electric power transmission both need lithium-ion batteries?LIBs?.In addition,with the popularization of various electronic products such as mobile phones and laptop computers,the use of LIBs is also increasing,and its performance have a direct impact on product quality and user experience.The rapid growth of various portable electronic products,the energy storage of renewable energy and the development of environmentally friendly electric vehicles all have a strong demand for high capacity,long life,high rate performance and low price of batteries.The electrode material in the battery is an important part of the battery,and determines the theoretical capacity of the battery that can be achieved.It also has an important influence on the cycling performance,the rate performance and the safety of the battery.At present,most of LIBs on the market use graphite as the anode material,and the theoretical capacity of graphite is only 372 mAh g^-1,which can no longer meet the needs of social development.Therefore,it is necessary to develop LIBs anode materials with high-capacity.SnO₂-based anode material with a high theoretical capacity of 871 mAh g^-1 has been highly concerned for a long time and viewed as a potential new-generation high-performance LIB anode material.However,the SnO₂ anode material suffers the problems of low initial Coulombic efficiency and poor cycling stability,mainly due to the irreversible reduction of SnO₂ to Sn and the huge volume change during the alloying of Sn and Li.This project aims to solve the existing problems of SnO₂ anode material by introducing the MOF material for an assistance.We designed and constructed Co/SnO2@C nanocubes and CNTs@SnO2/C nanowires.The main research results are as follows:?1?A simple and universal thermal solid-phase reaction was adopted to obtain the MOF shell-coated intermediate product,following by a further carbonization to obtain Co/SnO₂@C nanocubes,which gathers structural characteristics of nano-size and a large number of internal voids,metal doping and porous uniform carbon coating.Based on existing battery assembly and electrochemical testing techniques,the electrochemical performance of Co/SnO₂@C nanocubes was tested as the anode material in LIBs by cyclic voltammetry test,galvanostatic charge/discharge cycling test,and so on.Co/SnO₂@C Nanocubes show the capacity of⁸00 mAh g^-1 after cycling for 100 times at the current density of 200 mA g^-1,400 mAh g^-11 after 1800cycles at 5 A g^-1.There are some reasons for the excellent electrochemical performance of the Co/SnO₂@C nanocubes:the porous carbon coating not only enhances the conductivity but also inhibits the diffusion of the active material and stabilizes the structure of electrode.The doping of the Co metal promotes the reversible conversion of SnO₂ and contributes to the total capacity.Nano-scale sizes and rich internal voids effectively relieve volumetric expansion.?2?Ultrafine SnO₂ particles is successfully composited on the surface of CNTs to fabricate CNTs@SnO₂/C nanowires.When CNTs@SnO₂/C nanowires were tested as the anode material in LIBs,they were able to release a high capacity of⁹00 mAh g^-1after cycling for 70 times at a current density of 100 mA g^-1.CNTs@SnO₂/C nanowires in the presence of CNTs significantly improve the electrode conductivity,and the ultra-small size of SnO₂ and the composite carbon also greatly promoted the electrochemical reaction kinetics,ease the interior stress of the material.