Synthesis and properties of Sn₃₀Co₃₀C₄₀ ternary alloy anode material for lithium ion battery

With the development of advanced lithium ion batteries, electrode materials with higher capacity are urgently in demand. With respect to the anode materials, Sn-based alloy materials with high theoretical capacity (990 mAh/g) have the potential to replace the traditional, low capacity carbon-based materials. However, the practical application of Sn-based anode materials is severely retarded due to the poor cycling stability of electrode, which is believed to be caused by the pulverization of active particles resulting from the large volume of Sn during lithiation/delithiation process. The Sn-Co-C ternary alloy with amorphous or nano microstructure can overcome this problem and therefore display attractive electrochemical performance, including high capacity and good cycle stability. In the present work, amorphous Sn₃₀Co₃₀C₄₀ alloy material was synthesized through a simple and scalable two-step method (carbothermal reduction-high energy ball milling method). CoSn₂ alloy was firstly prepared by the carbothermal reduction route from low cost metal oxide and activated carbon. Then the prepared CoSn₂ were mixed with metal cobalt and graphite in a molar ratio of 3:3:8 via a high energy ball milling process to synthesize the final Sn₃₀Co₃₀C₄₀ material. The preferential synthesis of CoSn₂ alloy was important to get Sn₃₀Co₃₀C₄₀ material with much smaller CoSn grain dispersed in carbon matrix and thus critical to the better electrochemical performance. XRD, SEM, TEM, HR-TEM, S-TEM and electrochemical tests were used to evaluate the structure and electrochemical performance of the CoSn₂ and Sn₃₀Co₃₀C₄₀ materials. The synthesized Sn₃₀Co₃₀C₄₀ material displayed micro-sized particle morphology, which in fact was composed of 10 nm CoSn grains distributed well in amorphous carbon matrix. The Sn₃₀Co₃₀C₄₀ material showed high specific capacity of 550 mAh/g with an initial coulombic efficiency of 80%, good cycling stability and excellent rate-capability. The specific capacity of 430, 380, 280 mAh/g could be achieved at the rate of 1 C, 2 C and 5 C, respectively.