Enhanced catalytic activity of Co-CoO via VC0.75 heterostructure enables fast redox kinetics of polysulfides in Lithium-Sulfur batteries

Abstract

The shuttle effect and sluggish redox kinetics of lithium polysulfides lead to a short lifespan and poor rate capability of lithium-sulfur (Li-S) batteries. Introducing electrocatalysts into sulfur host materials has been deemed a promising strategy to overcome these issues in Li-S batteries. Herein, an efficient catalytic sulfur host material (i.e., VC0.75/Co-CoO) has been fabricated by simply pyrolyzing the electrospun vanadium and cobalt salt-based polymer fibers. Electrochemical measurements demonstrated that the as-formed heterostructure of Co-CoO with VC0.75 evidently strengthens the redox kinetics of polysulfides due to the enhanced adsorption ability to polysulfides and adjusts the electronic structure of heterostructure via the introduction of VC0.75. Further theoretical computation discloses that Co-CoO mainly plays the role in stretching the SS bond in polysulfides to facilitate the reduction of polysulfide, extending the Li-S bond in Li2S and reducing energy barriers of Li2S decomposition to promote the oxidation process of Li2S. Accordingly, the collaboration of Co-CoO and VC0.75 synergetically facilitates the redox kinetics of polysulfides, prolonging the lifespan of Li-S batteries. Impressively, VC0.75/Co-CoO composites endow Li-S batteries with a discharge capacity decay rate as low as 0.02 % per cycle at the current density of 0.2 C. The specific capacity reaches 626 mAh/g at the high current density of 1.0 C even after 450 cycles. This work sheds light on a facile methodology for improving the catalytic activity of sulfur host materials in Li-S batteries.