Hydrolysis of LiPF₆ in Carbonate-Based Electrolytes for Lithium-Ion Batteries and in Aqueous Media

The conducting salt in lithium-ion batteries, LiPF₆, can react with water contaminations in the battery electrolyte, releasing HF and further potentially harmful species, which decrease the battery performance and can become a health hazard in the case of a leakage. In order to quantify the hydrolysis products of LiPF₆ in a water-contaminated battery electrolyte (1 mol L^–1 LiPF₆ in EC/DEC) and in aqueous solution, ion chromatography (IC), coulometric Karl Fischer titration (cKFT), and acid–base titration were used on a time scale of several weeks. The results show that the nature of the hydrolysis products and the kinetics of the LiPF₆ hydrolysis strongly depend on the solvent, with the main reaction products in the battery electrolyte being HF and HPO₂F₂. From the concentration development of reactants and products, we could gain valuable insight into the mechanism of hydrolysis and its kinetics. Since the observed kinetics do not follow simple rate laws, we develop a kinetic model based on a simplified hydrolysis process, which is able to explain the experimentally observed kinetics.