Lithium ion batteries (LIBs) have been widely used in many fields as power suppliers for mobile equipments. Recently, ε-LiVOPO₄ has been regarded as a promising multi-electron cathode material that is capable to intercalate two Li per vanadium to achieve a very high theoretical capacity of 318 mAh/g, which exceeds any cathode material in the market today. However, the experimental capacity at useful current densities currently falls short of the theoretical one, and there is no data on long-term cycling behavior. In this study, pure ε-LiVOPO₄ was successfully synthesized by an optimized solid-state reaction. This material demonstrates capacities close to the theoretical at moderate current densities. The long-term cycling data was obtained over various voltage windows. The electrochemical results demonstrate that this material suffers capacity loss upon long-term cycling. It is found the phase transformation from LiVOPO₄ to VOPO₄ is not completely reversible after several cycles, which is likely driven by low electronic and Li ionic conductivity. In this work, different carbon additives were applied to increase electronic conductivity; and surface modification was conducted to improve ionic conductivity. The results demonstrate that the optimized ε-LiVOPO₄ has achieved great improvements of electrochemical performance in terms of capacity, rate capability, reversibility and cyclibilty.

This project is supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) program under Award No. DE-EE0006852.