The effect of Cu addition on Ge-based composite anode for Li-ion batteries

A Ge/Cu₃Ge/C composite, prepared by pyrolysis and a high energy mechanical milling process, was investigated as an anode material for Li-ion batteries. Electron probe micro-analyzer images showed that Ge and Cu₃Ge were well dispersed in the carbon matrix. Various analytical techniques were carried out to clarify the reaction mechanism of the Cu₃Ge single phase and the Ge/Cu₃Ge/C composite ex situ XRD and ex situ HRTEM analyses for Ge/Cu₃Ge/C composite electrode were carried out and the final phase formed was Li₁₅Ge₄. For the case of pure Cu₃Ge electrode, it reacted with Li at very low rate and the final product was probably a Li-Ge compound. Electrochemical tests showed that the Ge/Cu₃Ge/C composite exhibited better capacity retention than that of the Ge/C composite anode probably due to the presence of amorphous carbon which acted as a buffering matrix during volume expansion and Cu that formed during the first discharge increased the electrical conductivity locally.