Conjugated Microporous Polycarbazole-Sulfur Cathode Used in a Lithium-Sulfur Battery

Abstract

The electropolymerization of Conjugated Microporous Poly-1,3,5-tris (N-carbazolyl) benzene (CMPTCBz) was investigated using a range of techniques. After the potential window was optimized for the electropolymerization process, a fixed potential was found to generate a CMPTCBz with minimal overoxidation and a high BET surface area. The CMPTCBz was mixed with sulfur and used in the optimized preparation of CMPTCBz-S cathodes. Coin cells were assembled with lithium metal used as the anode and electrochemically evaluated. Results showed that the CMPTCBz-S cathodes with different sulfur loadings have excellent charge/discharge cycling performance with initial discharge capacities ranging from 800 to 1400 mAh·g−1S and a capacity retention greater than 80% after 100 cycles. This is due to both the enhanced electrical conductivity of the cathode and physical confinement of the generated lithium-polysulfides inside the pores of the CMPTCBz. In a further experiment, a high sulfur loaded CMPTCBz-S cathode produced an initial discharge capacity of 548 mAh·g−1S and a capacity retention of 95% after 100 cycles using an organic electrolyte. Analysis using XPS showed that the sulfur to polysulfide conversion coupled with the dual functionality of the CMPTCBz in retaining the generated polysulfide are the key parameters for this superior performance.