Effect of Anion Solvation on the Passivation Chemistry of Lithium Ion Electrodes

Ion solvation in electrolytes is a key issue in the understanding of interfacial behavior in lithium ion batteries. It has been shown experimentally that the solvation of Li⁺ in binary electrolyte solutions directly influences the formation of the solid electrolyte interphase (SEI) layer at the surface of graphitic anodes, and likely other types of anodes as well. Anions in lithium salt systems, especially the important anion PF₆^-, exhibit specific solvent preferences as well, though PF₆^- and comparable anions (BF₄^-, TFSI^-, FSI^-, ClO₄^-) do not form strong or long-lasting interactions with solvent molecules. This talk will explore new evidence of anion-solvent interactions, and will summarize efforts to link anion solvation to cathode SEI formation. Passivation of cathode interfaces with SEI is an important topic, as cathodes are increasingly reaching higher oxidation potentials that cause degradation of electrolytes. New, higher-voltage lithium ion batteries will be limited by development and understanding of oxidation behavior at the cathode-electrolyte interface.