A cathode active surface includes a conductive framework of tangled nanofibers with lumps of amorphous carbon-sulfur distributed within them. The amorphous carbon-sulfur lumps are of carbon bonded to sulfur via carbon-sulfur chemical bonds and to the nanofibers via chemical bonds. The strength of the chemical bonds secures sulfur atoms within electrode to suppress the formation of undesirable polysulfides when in contact with an electrolyte. The tangled nanofibers bind the amorphous carbon-sulfur lumps and enhance thermal and electrical conductivities.