Zinc Complex Based Multifunctional Reactive Lithium Polysulfide Trapper Approaching Its Theoretical Efficiency

Abstract

The “shuttle effect” of soluble lithium polysulfides (LPS), which causes rapid capacity fading, remains a lingering issue for lithium-sulfur batteries (LSBs). Herein, we report a new type of reactive molecule-based (or molecular) LPS trapper, zinc acetate-diethanolamine (Zn(OAc)2·DEA), which demonstrated a molecular efficiency of 1.8 for LPS trapping, approaching its theoretical limit of 2. This is the highest trapping capability among all reported LPS trappers. During discharge the trapped polysulfides are much more thermodynamically favored for reduction compared to the non-trapped ones, while during charge the complex Zn(SLi)2·DEA formed in the previous discharging process can be more easily oxidized due to its lower energy barrier in comparison to Li2S, indicating the catalytic effects of Zn2+·DEA on the redox of sulfur species. Zn(OAc)2·DEA is also an excellent binder owing to its multiple intermolecular hydrogen bonds. LSBs using Zn(OAc)2·DEA as a LPS trapper, a binder, and a redox catalyst exhibited excellent long-term cycling stability (with a capacity retention of 85% after 1000 cycles at a rate of 0.5 C) and enhanced rate performance. The work demonstrated the potential of this novel type of multifunctional metal complex-based reactive molecular LPS trappers for high capacity and stable LSBs.