Determining Performance-Limiting Mechanisms in Fluorophosphate Sodium-Ion Battery Cathodes Via Transition-Metal Mixing
This work reports on our efforts to determine the mechanism by which fluorophosphate cathodes appear to be limited to their single-electron capacity. Our method is to examine systems that decouple previously observed Na+extraction limits from redox limits. We will discuss the electrochemical characterization of novel mixed-transition metal fluorophosphate systems, from which we can conclude that fluorophosphate cathodes’ capacities are not redox-limited. We demonstrate reversible capacity exceeding the single-electron theoretical capacity during a single charge/discharge. In addition, computational examination of limiting behaviors will be elaborated on. Specifically, possible site-limiting and diffusion-limiting mechanisms in fluorophosphate cathodes will be presented.
 R. A. Shakoor, D. H. Seo, H Kim, Y. Park, J. Kim, S. Kim, H. Gwon, S. Lee, and K. Kang. J. Mater. Chem., 22, 20535–20541 (2012).
 K. Chihara, A. Kitajou, I. Gocheva, S. Okada, and J. Yamaki. J. Power Soources., 227, 80 – 85 (2013).