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.