Insights into the pseudocapacitive behavior of sulfurized polymer electrodes for Li-S batteries
Practical applications of sulfurized polymer (SP) materials in Li-S batteries are often written off due to their low S content (~35 wt. %) by placing them on the same footing as S8/C composite cathodes. Here, we show that some SP materials function as pseudocapacitors with an active carbon backbone using a comprehensive array of tools including in-situ Raman and electrochemical impedance spectroscopy. We calculated the critical metrics for 35 wt. % S containing SP cathodes by including pseudocapcitive contributions from the carbon backbone. We found that SP cathodes with an active carbon backbone are suitable for 350 Wh/kg target at the cell level if S loading >5 mg/cm 2 , E/S ratio < 2 µL/mg, and N/P ratio < 5 can be achieved. Although 3D current collectors can enable such high loadings, they often add excess mass that decreases the total capacity at the cell level. To overcome this, we developed an "active" carbon nanotube bucky sandwich (BS) current collector (amenable for roll-to-roll processing) that contributes to the total capacity offsetting its excess weight. We prepared SP cathode with ~5.5 mg/cm 2 of S loading (~15.8 mg/cm 2 of SP loading), which yielded a sulfur-level gravimetric capacity ~1360 mAh/gs (~690 mAh/gs), electrode level capacity 200 mAh/gelectrode (100 mAh/gelectrode), areal capacity ~7.8 mAh/cm 2 (~4.0 mAh/cm 2) at 0.1C (1C) rate for ~100 cycles at E/S ratio = 7 µL/mg. We also succeeded in preparing pouch cells using BS SP cathodes containing ~5 mg/cm 2 S with a capacity ~1300 mAh/gs (~190 mAh/gelectrode) at 0.1C rate.