Dielectric Barrier Discharge (DBD) Plasma Coating of Sulfur for Mitigation of Capacity Fade in Lithium–Sulfur Batteries
Ahmed Shafique, Vijay Shankar Rangasamy, Annick Vanhulsel, Mohammadhosein Safari, Silvia Gross, Peter Adriaensens, Marlies K. Van Bael, An Hardy, Sébastien Sallard
Abstract
Sulfur particles with a conductive polymer coating of poly(3,4-ethylene dioxythiophene) “PEDOT” were prepared by dielectric barrier discharge (DBD) plasma technology under atmospheric conditions (low temperature, ambient pressure). We report a solvent-free, low-cost, low-energy-consumption, safe, and low-risk process to make the material development and production compatible for sustainable technologies. Different coating protocols were developed to produce PEDOT-coated sulfur powders with electrical conductivity in the range of 10–8–10–5 S/cm. The raw sulfur powder (used as the reference) and (low-, optimum-, high-) PEDOT-coated sulfur powders were used to assemble lithium–sulfur (Li–S) cells with a high sulfur loading of ∼4.5 mg/cm2. Long-term galvanostatic cycling at C/10 for 100 cycles showed that the capacity fade was mitigated by ∼30% for the cells containing the optimum-PEDOT-coated sulfur in comparison to the reference Li–S cells with raw sulfur. Rate capability, cyclic voltammetry, and electrochemical impedance analyzes confirmed the improved behavior of the PEDOT-coated sulfur as an active material for lithium–sulfur batteries. The Li–S cells containing optimum-PEDOT-coated sulfur showed the highest reproducibility of their electrochemical properties. A wide variety of bulk and surface characterization methods including conductivity analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and NMR spectroscopy were used to explain the chemical features and the superior behavior of Li–S cells using the optimum-PEDOT-coated sulfur material. Moreover, postmortem [SEM and Brunauer–Emmett–Teller (BET)] analyzes of uncoated and coated samples allowed us to exclude any significant effect at the electrode scale even after 70 cycles.