Alloying Strategy Balances the Adsorption-Reduction-Oxidation Process of Sulfur Species Across Wide Temperature Ranges

Abstract

Transition metal-based catalysts have been demonstrated to effectively anchor and utilize lithium polysulfides (LiPSs), thereby enhancing the capacity of lithium-sulfur batteries (LSBs). However, the immobilized d-band electronic structure of a single transition metal is inadequate for achieving satisfactory adsorption and catalytic conversion. In this study, an alloying strategy is employed to modulate the d-band structure with the aim of achieving the optimal adsorption capacity for LiPSs. For this purpose, cobalt (Co)-nickel (Ni) encapsulated in nitrogen-doped carbon nanotubes as bimetallic catalysts (CoNi/NCNT) are synthesized. The theory calculations and experimental analysis demonstrate that by hybridizing the d-orbitals of Co and Ni, the d-band structure of the CoNi bimetallic is modulated to be at the optimal central position. This configuration leads to the moderate adsorption and detachment of LiPSs on the surface of the catalysts, thereby balancing the “adsorption-reduction-oxidation” process of sulfur (S) species. Therefore, the LSBs with CoNi/NCNT separator are able to achieve good cycling at room temperature (capacity decay rate of 0.086% after 500 cycles at 0.5 C). The modified batteries can achieve excellent cycling performance across a wide temperature range (capacity decay rate of 0.057% after 100 cycles at 0 °C, and 0.34% after 100 cycles at 60 °C).