Sulfur-Polypyrrole Composite Cathodes for Lithium-Sulfur Batteries

Sulfur-polypyrrole composite cathodes with sulfur contents of 77, 64, to 53 wt% have been synthesized by an in-situ deposition of sulfur with polypyrrole pre-synthesized by an oxidation method. The presence of polypyrrole in the form of nanoparticles prohibits the agglomeration of sulfur during the synthesis, resulting in small sulfur particles and well-mixed sulfur-polypyrrole composites. The sulfur-polypyrrole composite cathodes synthesized have been evaluated by cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The composite cathodes show better electrochemical stability, lower overpotential, and better cyclability compared to the pristine sulfur as the polypyrrole particles facilitate ion and charge transfer within the electrodes. The composites consisting of 64 and 53 wt% of sulfur exhibit higher discharge capacities and better cyclability than sulfur at C/2, 1 C, and 2 C rates, e. g., retaining capacities of > 500 mAh/g at 1 C and similar to 400 mAh/g at 2 C after 50 cycles. The polypyrrole in the composites improves the electrochemical contact within the electrodes as evidenced by the reduced charge transfer resistance and improved rate capability as well as the porosity of electrodes as revealed by scanning electron microscopy. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.027209jes] All rights reserved.