The Preparation And The Electrochemical Performance Of Tin-based Negative Materials For Lithium Ion Batteries

Lithium ion batteries(LIB) have been widely used as a power supply for portable electronic devices because of their some advantages such as high energy density,long cycle life and environmental safety.As a new anode material for lithium ion battery, tin-based materials are attracting growing attention owing to their high theoretical capacity.In this dissertation,the pure tin and SnO₂ materials were prepared,and their properties were investigated by scanning electron microscopy(SEM),energy dispersive analysis of X-ray(EDAX),X-ray diffraction(XRD) analysis,cyclic voltammetry(CV) and galvanostatic charge-discharge tests.The Sn coatings as the electrode material for lithium-ion batteries were prepared by electroplating using copper foil as current collector.It was found that the morphologies of the tin coatings might be effectively changed by adjusting electroplating time.The Sn coating with porous network structure,obtained by electroplating for 5 min,showed large irreversible capacity and good electrochemical-cycling stability.The dense granular tin coatings obtained by electroplating for longer time displayed larger reversible lithium storage capacity,but the capacity decay occurred during the electrochemical cycling.For the dense granular tin coatings,smaller tin grain size facilitates the improvement of electrochemical performances.The dense granular tin coating with smaller grain size,obtained by electroplating for 15 min,presented the reversible capacity of 400 mAh·g^-1 after 30 cycles.A B₂O₃-doped SnO₂ thin film was prepared by a novel experimental procedure combining the eletrodeposition and the hydrothermal treatment.The effects of hydrothermal temperature and NaBH₄ contents on the properties of SnO₂ were studied.It was found that the synthesis conditions have large influences on the morphology and electrochemical performance of the as-prepared SnO₂ films.The SnO₂ thin film prepared by the hydrothermal treatment in 0.01 mol·L^-1 NaBH₄ aqueous solution at 180℃showed a porous network structure with large specific surface area and high crystallinity.The results of electrochemical tests showed that the modified SnO₂ electrode presents the largest reversible capacity of 676 mAh g^-1 at the fourth cycle,close to the theoretical capacity of SnO₂(790 mAh g^-1);and it still delivers a reversible Li storage capacity of 524 mAh g^-1 after 50 cycles.In addition, the SnO₂ film prepared by the hydrothermal treatment in pure water at 180℃exhibited relatively poor electrochemical performance.