Carbon confined GeO₂ hollow spheres for stable rechargeable Na ion batteries

Germanium (Ge) based nanomaterials are regarded as promising high-capacity anode materials for Na ion batteries, but suffer fast capacity fading problems caused by the alloying/de-alloying reactions of Na-Ge. Herein, we report a new method for preparing highly dispersed GeO₂ by using molecular-level ionic liquids (ILs) as carbon sources. In the obtained GeO₂@C composite material, GeO₂ exhibits hollow spherical morphology and is uniformly distributed in the carbon matrix. The as-prepared GeO₂@C exhibits improved Na ion storage performances including high reversible capacity (577 mA h g^-1 at 0.1C), rate property (270 mA h g^-1 at 3C), and high capacity retention (82.3% after 500 cycles). The improved electrochemical performance could be attributed to the unique nanostructure of GeO₂@C, the synergistic effect between GeO₂ hollow spheres and the carbon matrix ensures the anode material effectively alleviates the volume expansion and the particle agglomeration problems.