A supercapacitor includes a first electrode, a second electrode, and a solid-state polymer electrolyte. The first electrode and the second electrode are spaced from each other and immersed in the solid-state polymer electrolyte. The first and second electrode includes a carbon nanotube structure and an electrically conductive polymer layer. The carbon nanotube structure includes a number of carbon nanotubes and a number of micropores defined between adjacent two carbon nanotubes. The electrically conductive polymer layer coats surfaces of the number of carbon nanotubes.