Investigating PEDOT:PSS Binder as an Energy Extender in Sulfur Cathodes for Li-S Batteries.

ABSTRACT

Although lithium-sulfur (Li-S) batteries offer a high theoretical energy density, shuttling of dissolved sulfur and polysulfides is a major factor limiting the specific capacity, energy density, and cyclability of Li-S batteries with a liquid electrolyte. Cathode host materials with a microstructure to restrict the migration of active material may not totally eliminate the shuttling effect or may create additional problems that limit the full dissolution and redox conversion of all active cathode materials. Selecting a cathode coating binder with a multifunctional role offers a universal solution suitable for various cathode hosts. PEDOTPSS is investigated as such a binder in this study via experimental testing and material characterization as well as multiscale modeling. The study is based on Li-S cells with a sulfur cathode in hollow porous particles as the cathode host and the 10 wt % PEDOTPSS binder and electrolyte 1 M LiTFSI in 11 DOLDME 11 v/v. A reference supercapacitor cell with the same electrolyte and electrodes comprising a coating of the same hollow porous particles and 10 wt % PEDOTPSS revealed the pseudocapacitive effect of PEDOTPSS following a surface redox mechanism that dominates the charge phase, which is equivalent to the discharge phase of the Li-S battery cell. A multipore continuum model for supercapacitors and Li-S cells is extended to incorporate the pseudocapacitive effects of PEDOTPSS with the Li+ ions and the adsorption effects of PEDOTPSS with respect to sulfur and lithium sulfides in Li-S cells, with the adsorption energies determined via molecular and ab initio simulations in this study. Experimental data and predictions of multiscale simulations concluded a 7-9% extension of the specific capacity of Li-S battery cells due to the surface redox effect of PEDOTPSS and elimination of lithium sulfides from the anode by slowing down their migration and shuttling via their adsorption by the PEDOTPSS binder.