Solvent effect on the kinetics of lithium ion intercalation into LiCoO2

Solvent effect on the kinetics of lithium ion intercalation into LiCoO2 cathode material is addressed by contrasting the reaction in aqueous and carbonate-based electrolytes. Combination of cyclic voltammetry, potentiostatic intermittent titration and electrochemical impedance spectroscopy electroanalytical methods allowed for an accurate determination of the key kinetic parameters of the insertion/deinsertion reaction: diffusion coefficient and apparent heterogeneous rate constant values. XRD investigation of the lithiated sample in aqueous electrolyte points to the strong changes in the electrode material structure, induced by the intercalation of solvated lithium ions. Both rate constant and diffusion coefficient values were found to be substantially higher in aqueous medium, as compared to commercial ethylene carbonate/dimethyl carbonate electrolyte, which was attributed to the dominating effect of the adsorbate CEI layer elimination in aqueous electrolyte. The observed potential dependence of the apparent rate constant in aqueous electrolyte points to the difference in limiting reaction steps in water and carbonate electrolyte. The obtained results provide new information on the mechanism and the role of solvent in ion intercalation reactions.