Honeycomb-like micro-/nano-hierarchical porous germanium for high-performance lithium-ion battery anodes

Germanium (Ge) is a promising anode material for lithium-ion batteries due to its large theoretical specific capacity, good electrical conductivity, and fast lithium-ion diffusivity. However, Ge still suffers from huge volume expansion during the delithiation/lithiation process. Herein, using "Mg" as a soft template, a honeycomb-like porous Ge (hp-Ge) anode was successfully synthesized via a facile thermal nitridation of Mg2Ge in N2, followed by an acid-etching process. The obtained hp-Ge presents a typical void-containing micro-/nano-hierarchical porous architecture, which can effectively alleviate the volume expansion of the host Ge. The formation of uniformly distributed voids in hp-Ge is closely related to the etching of Mg3N2, which is the by-product of the reaction between Mg2Ge and N2. Benefiting from the fascinating micro-/nano-hierarchical porous structure, the resulting hp-Ge anode without employing any complex surface modification techniques demonstrated a high specific capacity of 1534.70 mAh g-1 at 0.2 A g-1 with a high initial Coulombic efficiency of 85.0%, and a high capacity of 483.9 mAh g-1 at 8 A g-1. The hp-Ge anode also possesses excellent cyclability and can deliver a satisfying reversible specific capacity of 1375.40 mA h g-1 at 0.5 A g-1 after 200 cycles with a high capacity retention of 96.8%. The proposed facile and scalable void-introducing strategy in this study also provides an alternative route for designing advanced micro-/nano-hierarchical porous materials, especially for anodes with large volume expansion during the lithiation process. The synthesized honeycomb-like micro-/nano-hierarchical porous Ge (hp-Ge) anode demonstrates comparable capacity to that of pristine solid Ge microparticles but with an enhanced ICE, better rate capability and more excellent cyclability.