Regulation of polysulfide adsorption and LiF-rich interface chemistry to achieve high-performance PEO-based lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries configured with solid-state electrolytes (such as poly(ethylene oxide), PEO), featuring high energy density and safety, seem to have become one of the promising next-generation storage devices. Polysulfide shuttle and lithium dendrite formation still need to be tackled in PEO-based lithium sulfur batteries. In this work, we have developed a functional electrolyte additive, viz. MgF2 (or AlF3) with strong Lewis acidity, to resolve the above dilemma. The introduction of MgF2 restricts the migration of polysulfide species by Lewis acid-base interaction and thus, significantly enhances the coulombic efficiency (more than 98.5% @0.05C, 1C = 1675 mA g-1). Also, a robust SEI composed of LiF-rich and LixMg alloy layer is constructed on the anode, inhibiting the brutal growth of lithium dendrites. The MgF2-functional solid-state electrolyte achieves stable lithium plating/stripping cycles up to 500 h at 0.2 mA cm-2 in a Li//Li symmetric battery. A Li-S battery using such a modified PEO-based electrolyte delivers a high capacity of 982 mA h g-1 and enhanced cyclability (90% capacity retention ratio for 40 days' cycles) at 0.05C. This work provides a guideline for the design of high-performance, long-life PEO-based all solid-state Li-S batteries. The MgF2 functional additive achieves the regulation of polysulfide adsorption and in situ construction of the LiF-rich/LixMg interface, enabling a stable PEO-based Li-S battery, with high coulombic efficiency.