The recent tendency in the battery field toward the use of aqueous electrolytes stimulated several studies searching for compatible electrode materials and charge carriers. Still, another aspect to forge ahead is the fundamental understanding of interfacial processes occurring at electrode/electrolyte interface. To this end, we investigated interfacial properties of a model LiCoO2 composite electrode in Li2SO4 aqueous electrolyte through extensively exploiting operando electrochemical quartz crystal microbalance (EQCM) and its coupling with electrochemical impedance spectroscopy (ac-electrogravimetry). EQCM revealed a global cation-exchange behavior, which is decoded by ac-electrogravimetry into multispecies contribution with different proportions/kinetics, benefiting from the capacity of the latter to study interfacial dynamics. Li+ plays the major role in the charge-compensation mechanism, but a strong interaction with H2O has been revealed with close interfacial transfer kinetics, which provides experimental evidence on the essential character of H2O assisting the Li+ insertion in layered materials due to the weakened charge density by screening the electrostatic interactions between the Li+ ions and the host lattice of cathode materials.