Sorption of Li+ ions from diluted aqueous medium has been investigated on activated carbons. The pure chemical sorption is controlled by pH of the solution as well as by the nature and concentration of surface groups, showing cation-exchanger properties of the carbon substrate. Lithium sorption is enhanced by applying a cathodic polarization to the activated carbon, and reversing voltage allows a full desorption of trapped lithium. In the selected conditions of investigation, the electrostatic attraction is not responsible of ions sorption as demonstrated by the low values of capacitance measured at constant potential or current. Our experiments proved that local high pH values at the carbon cathode, due to reduction of water, are the cause for increasing the dissociation of surface groups and consequently the amount of adsorbed lithium ions. On the other hand, with positive polarization, water is oxidized at the carbon surface, and proton exchange favors the release of lithium ions to the solution.