A Zn8 Double-Cavity Metallacalix[8]arene as Molecular Sieve to Realize Self-Cleaning Intramolecular Tandem Transformation of Li-S Chemistry.

Abstract

Toward the well-explored lithium-sulfur (Li-S) catalytic chemistry, the slow adsorption-migration-conversion kinetics of lithium polysulfides on catalytic materials and Li₂ S deposition-induced passivation of active sites limit the rapid and complete conversion of sulfur. Conceptively, molecular architectures can provide atom-precise models to understand the underlying active sites responsible for selective adsorption and conversion of LiPSs and Li₂ S₂ /Li₂ S species. Here, an octanuclear Zn(II) (Zn₈ ) cluster is presented, which features a metallacalix[8]arene with double cavities up and down the Zn₈ ring. The central Zn₈ ring and the specific double cavities with organic ligands of different electronegativity and bonding environments render active sites with variable steric hindrance and interaction toward the sulfur-borne species. An intramolecular tandem transformation mechanism is realized exclusively by Zn₈ cluster, which promotes the self-cleaning of active sites and continuous electrochemical reaction. Notably, the external azo groups and internal Zn/O sites of Zn₈ cluster in sequence stimulate the adsorption and conversion of long chain Li₂ S_x (x ≥ 4) and short chain Li₂ S/Li₂ S₂ , contributing to remarkable rate performance and cycling stability. This work pioneers the application of metallacalix[n]arene clusters with atom-precise structure in Li-S batteries, and the proposed mechanism advances the molecule-level understanding of Li-S catalytic chemistry.