In one aspect, a method of producing a sulfur-infused carbonaceous material as a cathode material for use in a Li—S battery is described, including providing a carbonaceous material; mixing elemental sulfur with the carbonaceous material; and heating the mixed sulfur and the carbonaceous material at a temperature from about 445° C. to about 1000° C. for a period of time and under a pressure greater than 1 atm to generate a sulfur vapor to infuse the carbonaceous material to result in a sulfur-infused carbonaceous material. In another aspect, a reactor for producing a sulfur-infused carbonaceous material as a cathode material for use in a Li—S battery is described, including a reactor body capable of withstanding a pressure from about 1 atm to about 150 atm; and an inner sulfur-resistant layer at the inner surface of the reactor, wherein the inner layer is inert to sulfur vapor at a temperature from about 450° C. to about 1000° C.