Morphology memory but reconstructing crystal structure: porous hexagonal GeO₂ nanorods for rechargeable lithium-ion...

Hexagonal GeO₂, with high theoretical reversible capacity and low operating voltage, is regarded as a promising anode material for Li ion batteries. Being similar to other alloy type anode materials, the practical application of GeO₂ is confronted with large volume change and fast capacity fading during lithiation/delithiation cycles. Constructing unique GeO₂ nanostructures is proposed as an effective strategy to address this issue of fast capacity degradation. However, the controllable synthesis of GeO₂ nanomaterials is challenged due to the fast hydrolysis of Ge precursors in aqueous solution. In this work, we report a simple strategy to synthesize GeO₂ nanorods by using orthorhombic Ca₂Ge₇O₁₆ nanorods as the sacrificial template with HNO₃ as the etching agent. With the morphology memory of orthorhombic Ca₂Ge₇O₁₆ nanorods, the as-prepared porous hexagonal GeO₂ nanorods exhibit excellent electrochemical performance with a high capacity of 747 mA h g^-1 after 50 cycles, which should be attributed to the porous and one dimensional nanostructure of GeO₂ nanorods. This facile 'morphology memory but restructuring crystal structure' method could be extended to the controllable preparation of other GeO₂ nanostructures, and achieve more efficient anode materials.