Atomic Editing of the First-Shell to Modulate the d-Electron State of Transition Metal Sites for Accelerated Redox Kinetics in Lithium-Sulfur Batteries.

Abstract

Organometallic macrocyclic molecules have shown great potential to accelerate the reaction kinetics in Li-S batteries. However, it is still challenging to precisely tailor the microenvironment of metal sites and enhance its intrinsic reactivity. Herein, inspired by single-atom editing in organic chemistry, we prepared a series of isolobal nickel-based organometallic macrocyclic molecules (denoted as Ni-N_xC_y) to optimize the steric configuration and d-orbital states of Ni sites by tuning the first coordination shell at atom-level. In situ x-ray absorption spectroscopy revealed the dynamic evolution of nickel sites, while in situ Raman spectra demonstrated the accelerated sulfur conversion kinetics for Ni-N₂C₂ in Li-S batteries. Theoretical calculations confirmed that the geometric configuration of Ni-N_xC_y can be modulated by first-shell atoms, when the d_xy and d_x ²-_y ² orbitals of nickel can be activated for N₂C₂-coordinated Ni site. In addition, the up-shift of d-band center for Ni-N₂C₂ further facilitates its hybridization with sulfur species. Consequently, cells with Ni-N₂C₂ deliver 1277 mA h g^-1 at 0.5 C, while showing a decay rate of 0.04% at 2 C. Furthermore, an Ah-level pouch cell with energy density of 393 W h kg^-1 can be achieved based on the total mass of cell. This work provides mechanistic insights into the microenvironment regulation of single-metal-site and structure-activity relationships in Li-S batteries.