Lithium storage in conductive sulfur-containing polymers

Conductive sulfur-containing cathode materials for high-capacity lithium secondary batteries have been synthesized by heating a mixture of polyacrylonitrile and elemental sulfur. The structures and electrochemical properties of the materials depend on the reaction conditions, particularly synthesis temperatures. FTIR, Raman and XPS measurements show that the fundamental chemical structure of the materials is composed of a dehydropyridine type matrix with S-S bonds in the side-chain. The cycle performances of the materials synthesized at different temperatures have been examined as active cathode materials in lithium cells. Due to the existence of π-conjugation and the C-S-S-C covalent bond, significantly improved redox rates and cycleability at room temperature are achieved. A stable discharge capacity for the material synthesized at 450°C is maintained at about 480 mAh/g and the capacity retention remains at ca. 92% (referred to the second cycle) after about 240 cycles. The excellent cycle characteristics supply a good foundation for practical application of this material in rechargeable lithium batteries.