Unraveling Hydride-Driven Multiphasic Reduction Toward Tunable Germanium Structures for Lithium-Ion Batteries.

Germanium (Ge) stands out as a promising anode due to its high theoretical capacity combined with intrinsically superior ionic and electronic conductivities. Nevertheless, the high cost and pronounced volume expansion upon lithiation pose significant challenges for its practical implementation. Herein, sodium hydride (NaH)-driven multiphasic reduction is introduced to synthesize micrometre Ge with a tailored porous and hybrid nanocrystalline-amorphous structure, which uniquely emerges under off-stoichiometric reduction conditions. By elucidating the underlying multiphase reaction pathways, this structural evolution can be attributed to the dual role of NaH decomposition, where hydrogen regulates porosity and crystallinity while metallic Na acts as the primary reductant for germanium dioxide. This synthesized Ge exhibits outstanding reversibility and an exceptionally cycling stability even at high current density compared to commercial Ge microparticles, while also preserving the electrode integrity throughout cycling. This study offers mechanistic insights into extending NaH-driven reduction beyond GeO