Local built-in electric field of oxygen vacancy generated in fluorine-doped Nb2O5 structure modified by sulfur/fluorine co-doped carbon improves lithium storage performance

Abstract

Monoclinic Nb2O5 (H–Nb2O5) as an prospect anode material for lithium ion batteries due to its high theoretical specific capacity of 250 mAh g-1 and a safe working voltage in the range of 1–3 V, but the inherent low electron conductance greatly limits its high-rate performance. In this paper, we synthesized F-doped Nb2O5 with S/F co-doped carbon composites (F–Nb2O5@SFC) by simple high-temperature annealing method, XPS and EPR analysis results show that the composites has abundant of oxygen vacancies. Under the dual effects of F− doping and oxygen vacancy, the free electron concentration of Nb2O5 structure is greatly increased, and the conductive network provided by SFC accelerates the electron transport process, thus, the obtained F–Nb2O5@SFC material achieves excellent conductivity. In addition, the charge density difference results indicate that the unbalanced charge distribution around oxygen vacancies provides additional Li+ active sites, and the constructed electric field accelerates the transmission of Li+. The fast Li+/electron transfer kinetics of the F–Nb2O5@SFC electrode has achieved excellent storage performance, with a reversible specific capacity of 165 mAh g-1 at 1A g-1 after 600 cycles and a high-rate capacity of 130 mAh g-1 at 10A g-1.