The First-Cycle Electrochemical Lithiation of Crystalline Ge: Dopant and Orientation Dependence and Comparison with Si

We use first principles Density Functional Theory (DFT), cyclic voltammetry (CV), and Raman spectroscopy to investigate the first-cycle electrochemical lithiation of Ge in comparison with Si - both high-capacity anode materials for Li ion batteries. DFT shows a significant difference in the dilute solubility of Li in Si and Ge, despite similarities in their chemical and physical properties. We attribute this difference to electronic, as opposed to elastic, effects. CV and Raman data reveal little dopant dependence in the lithiation onset voltages in Ge, unlike in Si, due to a smaller energy difference between dilute Li insertion in p-type Ge and bulk germanide formation than the corresponding difference in Si. Finally, we show that there is no orientation dependence in lithiation onset voltages in Ge. We conclude that approaches other than microstructuring are needed to fabricate effective electrodes able to take advantage of the higher rate capability of Ge compared to that of Si.