Unique Octupolar 2D-Polymer Frameworks as Mixed Conductors and Metal-Free Catalysts for Dual-Promoted Li and S Electrochemistry: Multi-regulation Role of Ethoxylation Chemistry

Here, we for the first time introduce ethoxylation chemistry to develop a new octupolar cyano-vinylene-linked 2D polymer framework (Cyano-OCF-EO) capable of acting as efficient mixed electron/ion conductors and metal-free sulfur evolution catalysts for dual-promoted Li and S electrochemistry. Our strategy creates a unique interconnected network of strongly-coupled donor 3-(acceptor-core) octupoles in Cyano-OCF-EO, affording enhanced intramolecular charge transfer, substantial active sites and crowded open channels. This enables Cyano-OCF-EO as a new versatile separator modifier, which endows the modified separator with superior catalytic activity for sulfur conversion and rapid Li ion conduction with the high Li+ transference number up to 0.94. Thus, the incorporation of Cyano-OCF-EO can concurrently regulate sulfur redox reactions and Li-ion flux in Li-S cells, attaining boosted bidirectional redox kinetics, inhibited polysulfide shuttle and dendrite-free Li anodes. The Cyano-OCF-EO-involved Li-S cell is endowed with excellent overall electrochemical performance especially large areal capacity of 7.5 mAh cm-2 at high sulfur loading of 8.7 mg cm-2. Mechanistic studies unveil the dominant multi-promoting effect of the triethoxylation on electron and ion conduction, polysulfide adsorption and catalytic conversion as well as previously-unexplored -CN/C-O dual-site synergistic effect for enhanced polysulfide adsorption and reduced energy barrier toward Li2S conversion. A new class of versatile cyano-vinylene-linked octupolar 2D-polymer framework (Cyano-OCF-EO) has been explored as both efficient mixed ionic/electronic conductors and metal-free sulfur evolution catalysts via ethoxylation chemistry, which enables a novelmultifunctional separator interlayer to simultaneously tune bidirectional sulfur redox kinetics and Li ion flux for advanced Li-S cells.+image

Automated summary

A new octupolar cyano-vinylene-linked 2D polymer framework has been developed using ethoxylation chemistry, exhibiting efficient electron/ion conductance and catalytic activity for sulfur evolution. This new material can be used as a separator modifier in Li-S cells, improving the overall electrochemical performance.