Structure and Electrochemistry of Chromium Substituted Lithium Vanadyl Phosphate for Lithium-Ion Batteries

Abstract

Lithium vanadyl phosphate (LiVOPO4) is an attractive cathode material for next-generation lithium ion batteries, having the ability to reversibly extract and insert two lithium ions to reach a theoretical capacity of 318 mAh/g. LiVOPO4 also has very high energy density over two voltage plateaus of about 2.5 and 4 V. However, the transition between the two voltage plateaus goes differently upon lithiation and delithiation, causing poor energy efficiency and cycling stability. Here we explore experimentally and by the first-principle calculations, if there is room to improve the efficiency and cyclability of this material with the use of chromium substitution. A series of lithium vanadyl phosphates with varying percentages of chromium from two different chromium sources, chromium oxide and chromium acetate, are synthesized by hydrothermal method. The structure and composition of the products are determined by x-ray diffraction and inductively coupled plasma atomic emission spectroscopy. The effect of chromium substitution on the reaction voltages is compared to the first-principle calculation results and the electrochemical performance as a function of chromium substitution is discussed. 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