Electrochemical characterization of a Ge-based composite film fabricated as an anode material using magnetron sputtering for lithium ion batteries

Amorphous germanium and germanium-based films are sputter-deposited as anodes for lithium ion batteries. The structures of Ge and Ge-Mo composites are investigated using an X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The surface morphologies of the electrodes are observed using a field emission scanning electron microscope (FESEM). In order to determine the influence of inactive material in the anode, cell tests are carried out on half cells (Ge/Li metal and GexMo1-x/Li metal) and full cells (Ge/LiCoO2 and GexMo1-x/LiCoO2). The Ge film electrodes prepared on rough copper foil substrates showed stable capacities of 1000 mA h g-1 over 50 cycles. The Ge0.88Mo0.12 composite film electrode showed reversible gravimetric capacities of up to 1000 mA h g-1 with 77.9% capacity retention rates of the half-cell test after 100 cycles. Therefore, it may be possible to fabricate Ge-based anode materials with high capacity and improved capacity retention. The results of this study suggest that sputtered Ge-based electrodes are promising anode materials for next generation lithium ion batteries.