Activated carbons have been mechanochemically modified by bromine incorporation through high-energy milling route. Varying the milling duration and bromine content, carbon-bromine nanocomposites of different compositions were fabricated. The highly reactive and electronegative bromine reacts with host carbon, which can modify its characteristic properties. We have examined the effect of bromination on the structure, chemistry, morphology and electrochemical properties of a mesoporous activated carbon. Bromination leads to possible charge transfer reaction, structural disordering with polybromide formation. Consequently, the non-faradaic capacitance improves and a faradaic pseudocapacitive reaction occurs at 3.1 V and a more traditional bromine reduction at 3.5V. The formation of carbon-bromine nanocomposites was found to deliver improved gravimetric and volumetric capacity. The effect of bromination on physical and electrochemical properties of activated carbons have been presented and contrasted to that of iodine incorporation.