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 ∼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.