Towards Germanium Layered Materials as Superior Negative Electrodes for Li-, Na-, and K-Ion Batteries

The germanium high theoretical capacity renders it as a promising anode material with 1384 mAh/g for Li (Li15Ge4) and 369 mAh/g for Na (NaGe) and K (KGe). Nevertheless, Ge suffers from volume variations due to alkali insertion, to mitigate this issue several strategies have been proposed. Among them the use of layered Ge-based phases, obtained from the CaGe2 Zintl phase by topotactic deintercalation of Ca2+ to form the germanane (GeH)(n.) This last one has a particular morphology of Ge-6 rings interconnected to form planes that buffers the volume changes and shortens the diffusion pathways. Here, we have studied the germanane alkali storage properties and 2150, 495 and 205 mAh/g of reversible capacity were obtained for Li, Na and K, respectively. These results indicate that germanane can store more alkali ions than the predicted phases, perform well at high rates and maintain a good capacity retention.