Fluorine-Doped GeO₂@C Composite with Abundant Oxygen Vacancies for High-Capacity Lithium-Ion Batteries

Rational engineering of nanostructured anode materials is important to develop lithium-ion batteries (LIBs). In this study, hierarchical composites of fluoridated carbonaceous GeO2 (F-GeO2@C) with rich oxygen vacancies were prepared by a simple annealing method. It is found that F– ions not only exist in the carbon matrix but also replace O2– of metallic oxides. The abundant introduced oxygen vacancies can provide more active sites and contribute to better electronic conductivity. Moreover, density functional theory (DFT) calculations confirm that F-doping greatly changes the electronic structure of the GeO2 composite, exhibiting interesting metallic behavior. Consequently, the F-GeO2@C anode shows an enhanced initial Coulombic efficiency (ICE) value of 71.6% and delivers excellent rate capability, much higher than most reported GeO2-based anodes. The enhancement of the electrochemical performance for F-GeO2@C is attributed to the hierarchical nanostructure and F-doping by increased reaction kinetics, reversibility, and cycling stability. Thus, such rational fabrication of the composite can motivate other high-performance germanium-based materials in LIBs.