Inhibiting the shuttle effect in lithium–sulfur batteries using a layer-by-layer assembled ion-permselective separator

A novel strategy for introducing ion-permselective properties in a conventional polyethylene (PE) separator to inhibit the shuttle effect of polysulfides in high-performance lithium–sulfur batteries is reported. This was accomplished by taking advantage of the pH-responsive multilayers of weak polyelectrolytes such as poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) assembled on the PE separator using layer-by-layer (LbL) assembly. It was found that the cationic permselectivity (permeability of cation/anion) of an ultrathin multilayer coated separator is highly tunable with respect to the number of bilayers and external pH, benefiting from fine tuning of the internal charge density of the multilayered films. The movement of polysulfide anions was significantly inhibited by five bilayers of PAH/PAA (ca. 98% with multilayers assembled at pH 3/3), while the movement of Li cations was preserved. As a result, the ion-permselective separator demonstrated a high initial reversible capacity of ca. 1418 mA h g−1 with multilayers assembled at pH 3/3 because of the good permselectivity and the enhanced wetting properties of the LbL treated separator for electrolytes, leading to a significantly improved Coulombic efficiency as compared to a conventional PE separator, i.e., almost 100% over 50 cycles. We anticipate that the permselectivity controllable coating method will be applied for various other membrane technologies.