Exploring the Solvation Sphere and Spatial Accumulation of Dissolved Transition-Metal Ions in Batteries: A Case Study of Vanadyl Ions Released from V2O5 Cathodes

Dissolution of transition-metal ions from Li-ion battery cathodes is a well-known degradation phenomenon. In addition to capacity decrease due to metal loss in the bulk cathode, dissolved transition-metal ions might migrate through the electrolyte and participate in redox reactions resulting in electrolyte decomposition. Aside from the oxidation state and concentration of the transition metal, its ligand sphere and spatial accumulation have to be determined for complete characterization and prediction of possible detrimental impact. Here, pulse electron paramagnetic resonance and density functional theory are exploited to investigate the coordination and location of vanadyl ions, which are a dissolution product of V2O5 cathodes. The solvation sphere is found to be dominated by electrolyte degradation products and also contains contributions from nonelectrolytic sources. Additionally, adjacent lithium and hexafluorophosphate ions are observed.