Analysis of the Local Physicochemical Properties of the Electrolyte at the Dynamic Electrochemical Interface Using the Quartz Crystal Resonator Technique

Abstract

The mass change of the electrode and the local physicochemical properties of the electrolyte at the dynamic electrochemical interface during electrode reactions in non-aqueous electrolytes were analyzed in situ using an impedance-type electrochemical quartz crystal microbalance (EQCM). The changes in the local properties of the electrolyte (viscosity and density), reflecting the concentration distribution of the dissolved species formed near the electrode, were observed during the electrochemical deposition and dissolution of metals in an ionic liquid and the insertion/extraction of Li⁺ in an organic electrolyte used in commercial lithium-ion secondary batteries. It is necessary to subtract the contribution of the changes in the local viscosity and density of the electrolyte from the observed change in the resonant frequency to evaluate the mass change of the quartz crystal electrode, especially when the local properties of the electrolyte change significantly during the electrode reaction. The dissolved species of metals in solvate ionic liquids and chlorocuprate ionic liquids depend on the composition. The observed changes in the local properties of the electrolyte during the electrode reactions in these electrolytes were considered to reflect the transient changes in the liquid structure at the dynamic electrochemical interface in addition to the concentration distribution of the metal complexes.