Tunable anionic ratio synthesis of tantalum oxyfluoride nanoparticles as high-rate performance anode materials for lithium-ion battery

Transition metal oxyfluorides have elicited considerable interest as potential anode materials for LIBs owing to their distinctive chemical properties and crystal structures. Herein, two unique types of crystalline tantalum oxyfluoride (TaO2F) nanoparticles were synthesized through the annealing of mesocrystalline (NH4)2Ta2O3F6 precursor in both air and argon atmospheres. Specifically, the heat-treatment process in oxygen-deficient (argon) atmosphere facilitated the substitution of O2– with smaller F- within anion sites of the TaO2F lattice, culminating in a decreased band-gap energy and thereby enhancing conductivity. Notably, nonstoichiometric TaO2F nanoparticles characterized by higher F/O ratio (denoted as TA), when utilized as anode materials in LIBs, showcased remarkable rate capability, achieving 166.5 mAh/g at high current density of 1250 mA g−1, and exemplary cyclic stability with average coulombic efficiency of approximately 99.8 % over 900 cycles. This enhanced electrochemical performance, surpassing that of sample TO, can be primarily ascribed to the rapid kinetics of surface capacitive process.