Modulating molecular orbital energy level of lithium polysulfide for high-rate and long-life lithium-sulfur batteries

Abstract

Despite high energy density, lithium-sulfur (Li-S) battery suffers from severe capacity fading due to the dissolution and the slow reaction kinetics of lithium polysulfides (LiPSs). Novel strategies to limit LiPSs are greatly desired by high-performance lithium-sulfur batteries towards practical applications. Here, modulating molecular orbital energy level of LiPSs by adding 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) into organic electrolyte is reported to improve the electrochemical performance of Li-S batteries. The soluble catalyst DBBQ is able to form complexes with LiPSs via medium-strength Li-O bonding. Compared with LiPSs, the complexes have higher HOMO energies and lower LUMO energies, and therefore shows the stronger redox activity, indicating that DBBQ can facilitate the electrochemical reactions of LiPSs. This strategy leads to a long cycling stability and excellent rate performance of sulfur-based electrodes. The Li-S battery with DBBQ not only delivers the capacity of 745 mA h g−1 at 10C rate, but also retains the capacity of 850 mA h g −1 after 500 cycle at 1C rate. Moreover, the DBBQ additive enables the cathode to achieve steadily cyclable at high sulfur content (78 wt%) and sulfur loading (7 mg cm−2).