Thermodynamics and Kinetics of Alkali Insertion in VOPO4 Polymorphs

Abstract

Multi-electron polyanion cathodes offer the potential for achieving both high voltage and high capacity in rechargeable alkali-ion batteries. Among the few materials known to exhibit multi-electron cycling, the polymorphs of VOPO4 , which operate on the V3+«V4+«V5+ redox couples, are particularly promising due to the high gravimetric capacities that have been achieved and the high voltage of the V4+/ 5+ couple. In this talk, we will provide an integrated computational and experimental study of the thermodynamics and kinetics of alkali (Li/Na) insertion into the α-I, β and ε polymorphs of VOPO4. We show that differences in voltage and rate capability of these different polymorphs for Li and Na insertion can be traced back to their fundamentally different VO6-PO4 frameworks. We will also provide an overview of the different contributions to the thermodynamic stability of the different polymorphs. This work was 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, Basic Energy Sciences under Award # DE-SC0012583.