Improving the Durability and Minimizing the Polysulfide Shuttle in the Li/S Battery

Abstract

The effect of surfactants and protective interlayers (commercial carbon paper and homemade mixed-conduction composites) on the electrochemical performance of sulfur batteries has been studied. Modification of cell configuration by the insertion of Toray-carbon paper between the cathode and separator improved the utilization of the active material and increased the initial discharge capacity from 800 to 1400 mAh/gS. The latter is about 84% of the theoretical value. The use of a few-micron-thick PEO-PVP-XC72 or SWCNT-PVP interlayer composites, cast on the cathode or separator, resulted in a similar positive effect on the initial sulfur utilization. The cells that were assembled in the discharge state and contained carbon interlayers exhibited a faradaic efficiency (FE) of above 99%, while the FE of the cells with the unprotected cathode is 95–96%. High faradaic efficiencies confirm the functionality of protective interlayers, which minimizes the polysulfide shuttle. Analysis of the impedance spectra of the conventional and modified cells shows that the SEI resistance decreases by about 50% and the apparent thickness of the SEI becomes smaller in the interlayer-protected cells. The cells with ultrathin composite layers hold the 30% capacity gain induced by the barrier for at least 400 cycles.