We firstly observed that activated carbon (AC) deposited by atomic-layer vanadium pentoxide (V2O5) was used as CDI electrodes to utilize the high dielectric constant for enhancing the capacitance equipped with atomic layer deposition (ALD). It was demonstrated that the vanadium pentoxide (V2O5) with sub-nanometer layer was effectively deposited onto activated carbon, and the electric double-layer capacitance of the AC was improved due to an increase in the surface charge density originated from polarization, leading to high ion removal in CDI operation. It was confirmed that the performance of modified-AC increases more than 200%, comparable to that of pristine-AC under 1.5 V at 20 mL min-1 in CDI measurements.