Real-time in situ spectroelectrochemical studies have been carried out in N,NЈ-dimethyl formamide containing lithium trifluoromethane sulfonate as an electrolyte and the results are reported. The results indicate that the primary reduction product of the cyclic form of sulfur, S 8c 2Ϫ , undergoes an equilibrium reaction to its linear chain counterpart, S 8l 2Ϫ , which then dissociates into various products. These two dianions and S 3 Ϫ• were produced along with a minor product, S 4 2Ϫ , at the potential corresponding to the first electron transfer. These products were further reduced or dissociated to species including S 7 2Ϫ , S 6 2Ϫ , S 5 2Ϫ , S 4 2Ϫ , S 3 2Ϫ , S 2 2Ϫ , and S 2Ϫ at the second electron-transfer step as evidenced by the spectral shifts observed during electrolysis. The reduction reactions are generally chemically reversible, making it possible to use sulfur reduction as a cathode reaction for Li/S batteries.

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Although the exceptional theoretical specific capacity (1672 mAh g−1) of elemental sulfur makes lithium–sulfur (Li–S) batteries attractive for upcoming rechargeable battery applications (e.g., electrical vehicles, drones, unmanned aerial vehicles, etc.), insufficient cycle lives of Li–S cells leave a substantial gap before their wide penetration into commercial markets. Among the key features that affect the cyclability, the shuttling process involving polysulfides (PS) dissolution is most fatal. In an effort to suppress this chronic PS shuttling, herein, a separator coated with poled BaTiO3 or BTO particles is introduced. Permanent dipoles that are formed in the BTO particles upon the application of an electric field can effectively reject PS from passing through the separator via electrostatic repulsion, resulting in significantly improved cyclability, even when a simple mixture of elemental sulfur and conductive carbon is used as a sulfur cathode. The coating of BTO particles also considerably suppresses thermal shrinkage of the poly(ethylene) separator at high temperatures and thus enhances the safety of the cell adopting the given separator. The incorporation of poled particles can be universally applied to a wide range of rechargeable batteries (i.e., metal‐air batteries) that suffer from cross‐contamination of charged species between both electrodes.

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