In a method for making sulfurized polyacrylonitrile, polyacrylonitrile, a first solvent, a catalyst, and sulfur or sodium thiosulfate are provided. The polyacrylonitrile is dissolved in the first solvent to form a polyacrylonitrile solution. The catalyst is uniformly dispersed in the polyacrylonitrile solution. The polyacrylonitrile solution with the catalyst is heated to induce a cyclizing reaction of the polyacrylonitrile, thereby forming a first conjugated polymer solution with a conjugated polymer. The sulfur or sodium thiosulfate is uniformly mixed with the conjugated polymer to form a mixture. The mixture is heated to form sulfurized polyacrylonitrile.