Design a multiphase interfaced Ge(GeOx)/T-Nb2O5-x/C anode with synergistic high capacity and durability for Li-ion batteries

Germanium-based anodes for lithium-ion batteries have attracted strong focus due to an exceptional storage capacity as high as four times of commercial carbon. Inferior capacity retention, however, caused by large volume changes during cycling impedes their widespread application. Herein, we report a multi-phase Ge (GeOx)/T-Nb2O5-x/C composite synthesized using a simple and scalable high-energy ball milling approach. During ball milling, Nb2O5 substrate would react with Ge to produce amorphous GeOx on the interface of them to realize a unique construction. The Ge(GeOx)/T-Nb2O5-x/C demonstrated far longer durable and reversible ca-pacity for Li storage (960 mAh g-1 at 0.1C and 745 mAh g-1 after 150 cycles at 0.5C, with a capacity retention of up to 86.6%) and much higher initial coulombic efficiency (87.3%) than milled Ge and Ge-T-Nb2O5-C mixture samples. The underlying mechanism is unveiled using thorough experimental characterization and density functional theory calculations. Both clearly and consistently decoupled key factors: the synergistic effects of (i) formation of multiphase structure and (ii) suppression of Ge volume expansion by forming a rigid Li2O from the GeOx on the interface of Ge and T-Nb2O5 over the cycling process. To evaluate the feasibility for practical applications the Ge(GeOx)/T-Nb2O5-x/C without prelithiation is coupled with LiFePO4 or LiCoO2 cathodes for the full-cell test. The initial coulombic efficiency is measured as high as 82.3%. Our study provides a clue to the design of highly reversible capacitive and durable anodes for Li-ion batteries.