Etching Asymmetric Germanium Membranes with Hydrogen Peroxide for High-Capacity Lithium-Ion Battery Anodes

Germanium (Ge) is deemed as one of the most promising alloying anodes for rechargeable lithium-ion batteries (LIBs) due to its large theoretical capacity, high electrical conductivity, fast lithium-ion diffusivity, and mechanical robustness. However, Ge-based anodes suffer from large volume changes during lithiation and delithiation, which can deteriorate their electrochemical performance rapidly. Herein, the large volume change issue is effectively addressed using an asymmetric membrane structure that is prepared using a phase-inversion method in combination with hydrogen peroxide etching and surface coating. The asymmetric Ge membrane etched by ≈30 wt% H₂O₂ at 90 °C for 30 s demonstrates a capacity retention higher than 80% in 50 cycles at 160 mA g⁻¹. Coating the H₂O₂-etched Ge membrane with carbonaceous membranes can further improve the retention up to 95% in 50 cycles at 160 mA g⁻¹, whereas ≈100% capacity of 700 mAh g⁻¹ can be maintained in 170 cycles at 400 mA g⁻¹. A combination of electron microscopy, spectrophotometry, and X-ray analyses confirms the electrochemical performance of asymmetric Ge membranes as the LIB anode can be significantly affected by membrane geometry, the duration of hydrogen peroxide etching, carbonaceous membrane coating, and Ge concentration.