Carbon coated and oxygen vacancies incorporated Wadsley-Roth phase molybdenum niobium oxide for high-performance lithium-ion storage

Abstract

Nb-based oxides with Wadsley-Roth shear structure have been aroused extensive research interest as promising anode for Li-ion batteries, due to the multi-electron redox, safe working voltage and open structural framework. However, the low intrinsic electronic conductivity limits their further practical applications. Herein, the lithium storage performances of MoNb6O18 with Wadsley-Roth shear structure are optimized by carbon coating and oxygen vacancies (VO-MNO@C), which synthesized with freeze-drying and subsequently heat treatment. As expected, the VO-MNO@C electrode demonstrates a high initial reversible capacity of 259.6 mAh/g at 0.2C and the capacity retention rate of 85.7 % after 200 cycles at 1C. Moreover, the reversible of Mo6+/Mo5+ and Mo5+/Mo4+ redox reaction can be effectively improved. In situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopy (XPS) characterization indicate that VO-MNO@C undergoes a solid-solution structural evolution disclosing the stepwise reaction of Mo5+/Mo6+, Mo4+/Mo5+, Nb4+/Nb5+ and Nb3+/Nb4+ redox couples with a small volume variation of 5.7 %. Also, the full cell based on commercial LiMn2O4 cathode and VO-MNO@C anode displays an operating voltage about 2.4 V with the high energy density of 681.4 Wh/kg (calculated with the mass of anode). This work will offer more insights for the development of Wadsley-Roth shear structure anode materials with excellent Li-ion storage properties.