Selenium vacancies enable efficient immobilization and bidirectional conversion acceleration of lithium polysulfides for advanced Li-S batteries

Heterostructures composed of oxides and sulfides (nitrides or carbides) show great potential as sulfur host additives because of the strong adoptability of oxides and catalytic capability of sulfides towards the notorious lithium polysulfides (LiPSs). However, the migration and conversion pathway of LiPSs is seriously confined at a localized interface with inadequate active sites. In this work, the introduction of selenium vacancies into VSe2−x has been demonstrated to successfully synergize the adsorbability and catalytic reactions of LiPSs at an integrated functional surface. The N-doped carbon nanosheets-assembled flower architectures embedded with selenium vacancy-rich VSe2−x and partial vanadium oxides have been controllably synthesized and employed as the cathode additives for lithium-sulfur (Li-S) batteries. Both the experiments and first-principle calculations reveal their strong adsorption to LiPSs and their bidirectional catalytic functionality towards the conversion between S8 and Li2S. As expected, the charge and discharge kinetics of VSe2−x containing sulfur cathodes is fundamentally improved (an outstanding rate capabilitiy with 693.7 mAh·g−1 at 2 C, a remarkable long-term cyclability within 1,000 cycles at 2 C with S loading 2.27 mg·cm−2, and an excellent areal capacity with 3.44 mAh·cm−2 within 100 cycles at 0.5 C). This work presents an effective resolution to couple the adsorbability and catalytic reactions of LiPSs at the material design perspective, and the insights on bidirectional catalytic functionality are of vital to develop functional materials for advanced Li-S batteries.