Hydrothermally Synthesized Calcium Tetragermanate Nanowires for Lithium-Ion Batteries

Germanium is an attractive anode material for Li-ion batteries (LIBs) due to its high theoretical specific capacity (1620 mAh g^–1), high intrinsic electronic conductivity (∼2.17 S m^–1), and Li diffusivity (∼1 × 10^–12 cm² s^–1). However, pure Ge is expensive, and germanium oxides and metal germanates represent cheaper and more easily synthesized alternatives, though they often suffer from low initial Coulombic efficiencies and poor capacity retention. In this study, we report a method to synthesize calcium tetragermanate nanowires (CaGe₄O₉ NWs) via a facile and scalable hydrothermal synthesis, using low-cost and environmentally friendly CaCO₃ and GeO₂ as precursors. The resulting CaGe₄O₉ NWs demonstrate a synergistic effect between conversion and alloying-type behavior and deliver reversible capacities of 780 mAh g^–1 after 150 cycles at 0.2 A g^–1 and 385 mAh g^–1 after 500 cycles at 1 A g^–1.