Electrochemical and Spectroscopic Analysis of the Ionogel-Electrode Interface

Ionogels, pseudo-solid-state electrolytes consisting of an ionic liquid electrolyte confined in a mesoporous inorganic matrix, have attracted interest recently due to their high ionic conductivity and physicochemical stability. These traits, coupled with their inherent solution processability, make them a viable solid electrolyte for solid-state battery systems. Despite the promising properties of ionogels, there have been very few investigations of the electrode-ionogel interface. In the present study, X-ray photoelectron spectroscopy, Raman spectroscopy, and electrochemical measurements were utilized to probe the surface reactions occurring at the electrode-ionogel interface for several electrode materials. Our results indicate that the sol acidity initiates breakdown of the organic constituents of the sol and reduction of the transition metals present in the electrode materials. This chemical attack forms an organic surface layer and affects the electrode composition, both of which can impede Li⁺ access. By modifying the silica sol-gel reaction via a two-step acid-base catalysis, these interfacial reactions can be avoided. Results are shown for a LiCoO₂ electrode in which a high Li-ion capacity and stable cycling were achieved.