The method for preparing an electrolyte capacitor includes: providing an oxidant dopant agent for preparing the conductive polymer including: ferric naphthalenesulfonate; and at least one compound selected from the group consisting of phosphate, phosphite, borate, thiophosphate, and dithiophosphate. The method also includes preparing a conductive polymer by using the oxidant dopant agent to obtain an electrolyte comprising the conductive polymer.