Preparation of encapsulated Sn-Cu@graphite composite anode materials for lithium-ion batteries

Electroless encapsulation of graphite particles with copper-tin alloy (Sn-Cu@graphite) is demonstrated as a feasible anode preparation method that is cost effective and provides both high cyclability and reversible capacity. Heat treatment of the electroless composites at 200 oC yielded Sn-Cu@graphite anode composites with a 20 wt.% Sn loading, specific surface area of 22.5 m²/g and a 1^st discharge capacity of 1074 mAh/g at 0.2C rate. In contrast, the graphite substrate particles used for the encapsulation has a surface area of 2.34 m²/g) and a 1^st cycle discharge capacity of 327 mAh/g at 0.2 C rate. At the 300^th cycle, these capacities decreased to ~400 mAh/g and 208 mAh/g for the Sn-Cu@graphite and graphite substrate, respectively. Above 300 cycles, the electroless encapsulated Sn-Cu@graphite anode maintained a capacity higher than that determined experimentally and theoretically for graphite. The electrochemical impedance and cyclic voltammetric results demonstrate that the electroless encapsulated Sn-Cu@graphite anode has very low resistance and high reversible redox reactions. The higher capacity and long term cycling (> 300 cycles) achieved with the electroless composite anodes are attributed to the buffering effect of the electroless Cu in the Sn-Cu alloy encapsulating graphite particles, Sn-Cu@graphite's higher surface area (22.5 m²/g), and curvature of the graphite particles. The electroless encapsulated Sn-Cu graphite composite anode materials with extended cycling have potential application for the anode of Li-ion battery.