Rate Dependent Multi-Mechanism Discharge of Ag0.50VOPO4·1.8H2o: Insights from in-Situ Energy Dispersive X-Ray Diffraction

Thursday, 5 October 2017: 10:50
National Harbor 8 (Gaylord National Resort and Convention Center)
M. M. Huie (Stony Brook University), D. C. Bock (Brookhaven National Laboratory), A. Bruck, J. Yin, K. J. Takeuchi, E. S. Takeuchi, and A. C. Marschilok (Stony Brook University)
Ag0.50VOPO4·1.8H2O (silver vanadium phosphate, SVOP) demonstrates a counterintuitive higher initial loaded voltage under higher discharge current. Energy dispersive X-ray diffraction (EDXRD) from synchrotron radiation was used to create tomographic profiles of thick cathodes at various depths of discharge for two discharge rates. SVOP displays two reduction mechanisms, reduction of a vanadium center accompanied by lithiation of the structure, or reduction-displacement of a silver cation to form silver metal. In-situ EDXRD provides the opportunity to observe spatially resolved changes to the parent SVOP crystal and formation of Ag0 during reduction. Discharge rate can influence the preferred initial reaction either V5+ reduction or reduction of Ag+ with formation of conductive Ag0. Discharge rate also affects the spatial location of reduction products. This study highlights the importance of mesoscopic analysis and illuminates the roles of electronic and ionic conductivity limitations within a cathode and how they impact the course of reduction processes and loaded voltage.