Crown ether complex-incorporated Li-ion selective separators for high-performance Li–S batteries

The lithium-sulfur (Li–S) battery has emerged as one of the most promising candidates for next-generation energy storage systems due to its high specific capacity and potential low cost. However, the shuttle effect of lithium polysulfide (LiPS) is problematic because it results in the irreversible loss of active materials and rapid capacity decay. In this study, we developed a potent separator that overcomes the limitations posed by LiPS shuttling and improves the selectivity of Li-ions. The interior of a polypropylene separator was filled with self-assembled supramolecules comprising tetrabutyl ammonium, 18-Crown-6, and Ni(dmid)₂, which exhibited high selectivity for Li-ions and facilitates their rapid transmission. Utilizing the hard and soft acid-base effect between the supramolecule and LiPS, the proposed separator renders LiPS unstable upon contact with the separator. This promotes the transformation of LiPS and ensures smooth pathways for Li-ion migration, thereby inhibiting LiPS shuttling and enhancing Li-ion selectivity. As a result, experimental results demonstrated a Li–S battery with a remarkable lifetime of over 1000 cycles, an initial specific capacity of 1228 mAh/g at a current density of 0.5 C, and a cycle decay as low as 0.028% per cycle. Overall, by optimizing the sulfur redox kinetics, the separator presented in this work provides a rational design strategy for suppressing LiPS shuttling, enhancing Li-ion transport, and promoting highly efficient and durable Li–S batteries.