Ion clustering in electrolytes: impact on correlated transport and voltage stability

The study of ionic transport is an important tool for the optimization of the performance of Lithium ion batteries. The diffusion of Lithium ions across the electrolyte system often exhibits complex correlated motion, which remain relatively poorly understood. Building on previous studies showing the existence of cluster motion in different electrolytes (solid polymers, ionic salts …) we study the fundamentals of the clustering behavior, to provide insights into cluster formation. In particular, we develop algorithms to describe conditions for clustering to appear, the nature and composition of these clusters, the distribution in size, composition and diffusion coefficient of clusters during transport. We also investigate the lifetime of cluster and relate it to the transport properties of the electrolyte, particularly with regard to the recently reported negative transference number in a variety of systems. This study is also linked back to our work on the voltage stability of organic electrolytes, that shows how the stability of anions in these systems is weakened by the presence of the solvent, and increased by the presence of cations. Therefore, clustering behavior would impact not only the diffusion properties but also the voltage window of the electrolyte.