Structural and silver/vanadium ratio effects on silver vanadium phosphorous oxide solution formation kinetics: Impact on battery electrochemistry

The detailed understanding of non-faradaic parasitic reactions which diminish battery calendar life is essential to the development of effective batteries for use in long life applications. The dissolution of cathode materials including manganese, cobalt and vanadium oxides in battery systems has been identified as a battery failure mechanism, yet detailed dissolution studies including kinetic analysis are absent from the literature. The results presented here provide a framework for the quantitative and kinetic analyses of the dissolution of cathode materials which will aid the broader community in more fully understanding this battery failure mechanism. In this study, the dissolution of silver vanadium oxide, representing the primary battery powering implantable cardioverter defibrillators (ICD), is compared with the dissolution of silver vanadium phosphorous oxide (Ag_wV_xP_yO_z) materials which were targeted as alternatives to minimize solubility. This study contains the first kinetic analyses of silver and vanadium solution formation from Ag_0.48VOPO₄·1.9H₂O and Ag₂VP₂O₈, in a non-aqueous battery electrolyte. The kinetic results are compared with those of Ag₂VO₂PO₄ and Ag₂V₄O₁₁ to probe the relationships among crystal structure, stoichiometry, and solubility. For vanadium, significant dissolution was observed for Ag₂V₄O₁₁ as well as for the phosphate oxide Ag_0.49VOPO₄·1.9H₂O, which may involve structural water or the existence of multiple vanadium oxidation states. Notably, the materials from the SVPO family with the lowest vanadium solubility are Ag₂VO₂PO₄ and Ag₂VP₂O₈. The low concentrations and solution rates coupled with their electrochemical performance make these materials interesting alternatives to Ag₂V₄O₁₁ for the ICD application.