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. (C) 2010 Elsevier Ltd. All rights reserved.