Nano-scale uniform distribution of Ge/Cu3Ge phase and its electrochemical performance for lithium-ion batteries

A germanium/copper germanide/carbon (Ge/Cu3Ge/C) composite is prepared by the Pechini method using GeO2, CuSO4, and citric acid/ethylene glycol as the Ge, Cu and carbon sources, respectively. The microstructure and electrochemical properties of this nano-composite are compared to those of germanium/carbon (Ge/C) that is prepared without the copper precursor. In the latter composite, irregular-shaped submicron-sized (0.4–0.5 μm) Ge particles are dispersed inside a carbon matrix. In the former, however, sphere-shaped nano-sized (<100 nm) Ge particles are produced, inside of which a Cu3Ge phase is uniformly dispersed in nano-scale. The pure Ge component in both electrodes is lithiated up to Li15Ge4 after a lithiation down to 0.0 V at a current density of 100 mA g−1. The Cu3Ge-containing electrode gives a superior cycle and rate performance to that of the Cu3Ge-free counterpart. This difference has been ascribed to the favorable roles provided by the nano-sized Cu3Ge phase that is intimately contacted with the nano-sized Ge particles within a sphere. The electrochemical dilatometry study reveals that the electrode swelling is much smaller for the Cu3Ge-containing electrode, illustrating that the electrochemically inactive Cu3Ge phase serves as a buffer against a massive volume change encountered in the Ge component.