Identification of LiPF6 Decomposition Products in Li-Ion Batteries with Endogenous Vanadyl Sensors Using Pulse Electron Paramagnetic Resonance and Density Functional Theory

Abstract

The evaluation and enhancement of Li-ion battery chemistries relies on detailed knowledge of the chemical processes occurring. Undesired side reactions have to be identified and correlated with used materials and operation/storage conditions, which requires suitable analytical tools, especially for minor and reactive species. Herein, a complementing experimental and theoretical method based on pulse electron paramagnetic resonance and density functional theory is presented using vanadyl ions as sensors for the chemical battery environment. The sensor is endogenously formed via cathode dissolution during battery operation. Probing the ligand sphere of the sensor, decomposition products of the electrolyte salt LiPF6 are identified, which are proposed to comprise P(+V) and P(+III) constituents. Extensive conformational flexibility of the ligands is observed, which is investigated in terms of structural parameters and holistically with molecular dynamics simulations.