Bifunctional Fluorinated Anthraquinone Additive for Improving Kinetics and Interfacial Chemistry in Rechargeable Li-S Batteries

The uncontrollable Li deposition and severe lithium polysulfide (LiPS) shuttling hinder the commercial application in lithium-sulfur (Li-S) batteries. Here, we propose a bifunctional electrolyte additive, 1,4-difluoroanthraquinone (DFAQ), to be used for lithium regulation and acceleration of sulfur redox kinetics. DFAQ is conducive to form a rigid and smooth LiF-rich organic- inorganic hybrid solid electrolyte interphase (SEI), realizing reversible Li plating/stripping, restraining dendrite growth, and shielding Li anode from the detrimental side reaction with LiPSs. More importantly, DFAQ can be used as a redox mediator to enable an oxygen radical-mediated catalytic cycle to dramatically promote the conversion of LiPSs. Accordingly, the Li-S battery with DFAQ demonstrates ultrahigh discharge capacities, enhanced high-rate performance, and outstanding long-cycle stability (1693.4 mAh g-1 at 0.5C over 700 cycles). Even under harsh conditions including high sulfur loading (5.8 mgS cm-2), ultrathin Li anode (50 mu m), and low E/S ratio (5.0 mu L mgS-1), the Li-S battery with DFAQ shows 80 cycles in comparison to just 30 cycles for control battery. This work demonstrates a facile additive strategy originated from bond chemistry to build applicable Li-S batteries.

Automated summary

In this study, a bifunctional electrolyte additive, 1,4-difluoroanthraquinone (DFAQ), is proposed to control lithium deposition and accelerate sulfur redox kinetics in lithium-sulfur (Li-S) batteries. DFAQ forms a solid electrolyte interphase (SEI) rich in LiF, allowing reversible lithium plating/stripping, suppressing dendrite growth, and protecting the lithium anode from side reactions with lithium polysulfides (LiPSs). Additionally, DFAQ acts as a redox mediator, promoting the conversion of LiPSs and enhancing the performance of Li-S batteries.