An energy storage device, such as a battery or supercapacitor, that includes at least two electrodes, at least one of the electrodes includes an electrically conducting substrate having a layer of energy accumulating redox polymer complex compound of transition metal having at least two different degrees of oxidation, which polymer complex compound is formed of stacked transition metal complex monomers. The stacked transition metal complex monomers have a planar structure with the deviation from the plane of no greater than 0.1 nm and a branched system of conjugated &pgr;-bonds. The polymer complex compound of transition metal can be formed as a polymer metal complex with substituted tetra-dentate Schiff's base. The layer thickness of redox polymer is within the range 1 nm-20 &mgr;m.