Geminal Nickel Atom Boosting the Electrochemical Performance of Cobalt Single Atom/Nanoparticle Synergistic Catalysts for Rapid Polysulfide Conversion in Li–S Batteries

Single atom catalysts (SACs) are an effective approach to improving conversion kinetics of lithium polysulfide (LiPSs) and confining their shuttle effect in a lithium–sulfur (Li–S) battery. The catalytic performance of SACs can be further improved by regulating their local electronic states. The regulating techniques currently include coordinatively engineering the central single atom (SA) or integrating iso-elemental metal/metal oxide nanoparticles as adjacent auxiliary cocatalysts. Both approaches substantially improve the electrochemical activity of the SACs, but even better catalytic performance is expected for practical applications of the Li–S batteries. Elevating the number of regulation dimensions facilitates enhancing the degrees of freedom of the local electronic state changes of the SACs and hence affords more possibilities for further optimization of their performance. Keeping this in mind, adopting Co SACs supported on nitrogen-doped carbon as a conceptual model, with Co nanoparticle as one modulator and Ni atom intercalated into the Co SA site as another modulator, we achieve two-dimensional regulation on their local electronic states. Theoretical calculations reveal that introduction of a Ni atom will further rectify the charge distribution of the nanoparticle-modulated Co site and increase its total density of states near the Fermi level; consequently, the optimized adsorption affinity and the increased electrical conductivity are favorable for enhancing the conversion kinetics and confining effects of LiPSs. Therefore, the Li–S battery based on the obtained materials demonstrates impressive energy storage performances: an initial specific capacity of 1216 mAh g–1 at 0.1C; a rate capability of 602 mAh g–1 at 2C; and a cyclability of 633 mAh g–1 after 300 cycles at 0.2C. This work sheds light on maximizing the electrocatalytic performance of SACs via increasing the dimension number of regulating their local electronic state.