(2kl) Multi-Phase Ge(GeOx)/T-Nb2O5-X/C Composite with Synergistically Improved Electrochemical Performance Toward Lithium Storage

In recent years, germanium-based materials have emerged as one of the most potential anode materials for lithium ion batteries, exhibiting exceptional lithium-ion storage capacity (approximately four times that of commercial carbon anodes). However, the inferior capacity retention resulting from severe volume swings during lithium cycling impedes their widespread application. Herein, we report a multi-phase Ge(GeO_x)/T-Nb₂O_5-x/C composite that is synthesized via a simple and scalable high energy ball milling (HEBM) approach and thoroughly studied by combining first-principles calculations and experimental characterization techniques. Electrochemical evaluation shows that Ge(GeO_x)/T-Nb₂O_5−x/C has much improved Li-storage properties in terms of reversible specific capacity, cyclic stability, and initial coulombic efficiency (ICE), which can be ascribed to the synergistic effects of (i) the construction and multiphase compositional merit and (ii) suppression of Ge volume expansion by a rigid Li₂O barrier. The as-synthesized composite delivers a reversible capacity of 960 mAh g−1 at 0.1 C along with an initial coulombic efficiency of 87.3% and still maintains a capacity of 745 mAh g−1 after 150 cycles at 0.5 C, with a capacity retention of up to 86.6%. The lithium accommodation mechanism in the composite electrode is revealed through ex-situ XRD, Raman and XPS investigations, suggesting good reversibility of the material during lithiation/delithiation. Density functional theory calculation combined with cross-section SEM characterization was performed to reveal the alleviation of Ge volume expansion owing to the suppression from Li₂O as an obstacle during the electrochemical process, providing novel insight into the design of alloy-type based anode materials synergizing high reversible capacity and good cycling stability. To further evaluate its viability in practical applications, the Ge(GeO_x)/T-Nb₂O_5−x/C anode without prelithiation was coupled with LiFePO₄ (LFP) or LiCoO₂ cathodes to form full cells, resulting in an ICE of 82.3% with the LFP cathode and excellent cycling performance.