The Role of Niobium Substitution in Lithium Vanadyl Phosphate for Lithium-Ion Batteries

Abstract

Li-ion intercalation compound enlisting multi-electron redox is a promising strategy to maximize the storage capacity of LIBs. Lithium vanadyl phosphate, LiVOPO4, is one such material that can intercalate up to two Li+ ions per vanadium ion through the change in vanadium valence from V5+ to V3+, which translates to a theoretical capacity of 305 mAh/g and an energy density above 900 Wh/kg. However, Li-ion intercalation in the high voltage region (V5+/V4+) is kinetically limited by the sluggish Li-ion diffusion, and thus impedes the use of LiVOPO4 in practical applications. The goal of this work is to explore experimentally if niobium substitution can enhance the electrochemical performance of LiVOPO4. Lab X-ray diffraction, electron microscopy-energy-dispersive X-ray analysis, and inductively coupled plasma atomic emission spectroscopy indicate niobium is substituted into the LiVOPO4 crystal structure. A qualitative difference in the charge-discharge voltage profile is observed between the pristine and the niobium-substituted samples, suggesting a more complex substitution mechanism than the direct V substitution with Nb. The effects of niobium substitution on the crystal structure and the electrochemical performance of LiVOPO4 will be discussed.