An electrochromic energy storage device disclosed herein comprises a first electrode and a second electrode disposed in an electrolyte, wherein the first electrode comprises a coordination polymer, wherein the coordination polymer comprises a transition metal and a tetradentate ligand conjugated to the transition metal, wherein the transition metal and the tetradentate ligand render the first electrode operable to (i) store electrical energy and at the same time change its optical state upon electrical charging of the electrochromic energy storage device, and (ii) release electrical energy stored therein and at the same time change its optical state upon electrical discharge of the electrochromic energy storage device. A method of forming the electrochromic energy storage device and a method of forming an electrochromic energy storage film are disclosed herein. In a preferred embodiment, the first electrode is prepared by growing one dimensional π-d conjugated coordination polymer nanowires film comprising metallic nickel nodes and organic linkers of 1,2,4,5-benzenetetramine (BTA) on a transparent fluorine-doped tin oxide (FTO) conducting substrate.