(Invited) High Rate Cycling in ε-VOPO4 with Niobium Substitution for Lithium-Ion Batteries

Abstract

In order to push the energy density of current commercialized lithium-ion batteries, a second lithium must be incorporated into the cathode host without causing any structural damage during intercalation. ε-VOPO4 is a promising high energy density cathode material for lithium-ion batteries due to its ability to fully reversibly intercalate two Li+ from the two redox transitions of V3+/V4+ and V4+/V5+. As a result, ε-VOPO4 displays a high discharge capacity of 305 mAh/g at C/50 (C = 2 Li) for over 50 cycles. However, this vanadyl phosphate material experiences poor Li+ kinetics which impedes its high rate capability at the high voltage plateau. In this work, we determine if niobium substitution can improve the electrochemistry of ε-VOPO4. Through X-ray diffraction and scanning electron microscopy, we investigate the incorporation of niobium in the structure and the effect on morphology. The analysis of substitution on the electrochemical performance will also be discussed alongside with X-ray absorption spectroscopy to confirm the oxidation states of the transition metals during cycling. This research is supported as part of the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0012583. CS gratefully acknowledges the financial support from Graduate Assistance in Areas of National Need (GAANN) Fellowship and Binghamton University Provost's Doctoral Summer Fellowship.