Chemically etched CeO2-x nanorods with abundant surface defects as effective cathode additive for trapping lithium polysulfides in Li-S batteries

Abstract

The commercialization of Li-S batteries has been seriously hindered by the notorious polysulfides shuttling and sluggish redox kinetics. To effectively address these technical issues, in this work, oxygen-deficient CeO2-x nanorods (NR) decorated on free-standing carbon cloth (CeO2-x NR@CC) were used as a promising dual-functional cathode host material to enhance the electrochemical and cycling performance of Li-S batteries. The oxygen-deficient CeO2-x NR were prepared in a facile processing route by tuning the surface structures of pristine CeO2 NR in strong reducing NaBH4 solution. In contrast to the pristine CeO2NR@CC control sample, chemically etched CeO2-x NR@CC with abundant implanted oxygen vacancies effectively trapped the polysulfides and dramatically accelerated electron charge transfer, leading to faster redox kinetics. The main working mechanism of CeO2-x NR@CC on the improved electrochemical performance was attributed to chemical binding effect on trapping lithium polysulfides and even promoting the conversion of polysulfides, thanks to reversible Ce3+/Ce4+ transformation, oxygen vacancies, and other surface defects. Hence, the CeO2-x NR@CC electrode delivered an outstanding initial capacity of 1358 mAh g−1 at 0.2C for the 1st cycle and a superb sulfur utilization of 81%, compared to an initial capacity of 1176 mAh g−1 at 0.2C and a sulfur utilization of 70% for the CeO2 NR@CC electrode. The improved electrochemical performances of the CeO2-x NR@CC electrode can be mainly attributed to the successful adsorption of more dissolvable polysulfides by the dual-functional cathode host materials that combine the physical confinement of conductive CC and the chemical binding of CeO2-x NR with ample surface defects.