There is provided a composite comprising a) a short chain sulfur; and b) a carbon-supported conductive polymer such as polyacrylonitrile, wherein sulfur atoms of said short chain sulfur are covalently linked to the conductive polymer of said carbon-supported conductive polymer via a C—S bond. A method of preparing said composite comprising polymerizing a plurality of monomers in the presence of a carbon scaffold, mixing elemental sulfur and heating the mixture to obtain said composite is also disclosed. An electrochemical cell comprising said composite as cathode, a sodium anode and a liquid electrolyte such as sodium trifluoromethanesulfonate dissolved in a mixture of solvents is disclosed.