Orthorhombic Bipyramidal Sulfur Coated with Polypyrrole Nanolayers As a Cathode Material for Lithium-Sulfur Batteries

A sulfur-polypyrrole composite consisting of orthorhombic bipyramidal sulfur particles (63.3 wt %) coated with a polypyrrole nanolayer has been synthesized by a low-cost, scalable, environmentally benign process and investigated as a cathode material for Li-ion batteries. Cathodes containing the sulfur-polypyrrole composite have been evaluated in half cells by cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The sulfur-polypyrrole composite cathode shows better electrochemical stability, cyclability, and rate capability than pristine sulfur as the polypyrrole coating acts as a conductive matrix for electron transfer while prohibiting lithium polysulfide dissolution. At C/5 rate, the sulfur-polypyrrole composite cathode exhibits similar to 200 mAh/g higher capacity than the pristine sulfur after 50 cycles. At C/2 and 1C rates, the composite shows significantly better capacity retention than the pristine sulfur over 100 cycles.