Study On CuSn Alloy Anode Materials For Lithium-ion Batteries

CuSn alloy anode materials for lithium-ion batteries have been widely studied due to its relatively large theoretical capacity and high safety. In this work, CuSn alloy anode materials were synthesized by carbothermal reduction and reductive precipitation methods, respectively. The phase compositions, particle morphology and electrochemical properties of the final materials were characterized by XRD, SEM, TEM and electrochemical techniques such as galvanostatical cycling, cycle voltammogram and AC Impedance. The effects of the particle morphology, the synthesizing method and preparing technique on the electrochemical performance of CuSn alloy materials were studied. In order to improve the cycling performance of the electrode, nanometer CuSn alloy particles were encapsulated by amorphous carbon layer through carbonization of polymer at high temperature. Reasons of fast capacity fading of alloy electrode were also discussed in this study.The CuSn alloy anode materials synthesized by carbothermal reduction exhibit lower first irreversible capacities and better cycling stability. Carbon black, mesocarbon microbeads, graphite, acetylene black were used as reductant respectively, morphology and electrochemical performance of samples were affected by reductants. Micro-scaled spherical CuSn alloy powders were synthesized using mesocarbon microbeads as reducing agent and showed best cycling performance. Nano-fiber CuSn alloy powders were synthesized using vapor grown carbon fiber as reducing agent and showed worst cycling performance. The electrode containing 10 wt% Conductive agents (vapor grown carbon fiber) displays a good cycling stability.PH values of NaBH4 solution and heat treatment exert great impact on morphology, phase compositions or electrochemical performance of nanometer CuSn alloy materials synthesized by reductive precipitation method. When the the PH values of NaBH4 solution are Greater than 12 and the materials are heat-treated, the so-prepared electrode exhibits a preferable electrochemical property. Nanometer CuSn alloy particles were encapsulated by amorphous carbon layer through carbonization of polymer at high temperature. Compared with the non-carbon coated nanometer CuSn alloy, the carbon coated materials showed lower coulomb efficiency at the first cycle, but better cycling performance. The first discharge and charge capacities of the carbon-coated CuSn alloy electrode are 1015mAhg-1 and 600mAhg-1, respectively. And after 40 cycles, there is 460mAh retention. When the carbon coating temperature is above 800℃and the rate of the alloy and polymer is 5:1, the carbon-coated CuSn alloy materials shows best electrochemical performance.The SEM, TEM photos and XRD, AC impedance test of different cycle numbers indicate that the face of electrode gradually deteriorate, emerge flaw and hole, alloy particle loose contact, volume expand, and electrode crack finally. Hence, the specific capacity decreased.