Hierarchically designed germanium microcubes with high initial coulombic efficiency toward highly reversible lithium storage

Germanium has been investigated intensively for its high specific capacity and tough nature, which make it a promising candidate anode for high energy lithium-ion batteries. However, the rational design of a germanium electrode with enhanced electrochemical performances is still a big challenge. Herein, we designed and synthesized germanium microcubes with a hierarchical structure directly on titanium foil via a simple hydrogen reduction method. An ultrahigh initial Coulombic efficiency of 91.8% was acquired due to the high crystallinity of germanium for reversible lithium insertion and extraction, less adverse side reaction for irreversible lithium loss, and unique hierarchical structure for easier electrolyte penetration. In addition, the Li₂CO₃-predominated solid electrolyte interface contributes significantly to the excellent cycling and rate performances of the anode. Both half and full cell performances demonstrate that germanium has potential applications in high-performance lithium-ion batteries.