A design concept for halogen-free Mg2+/Li+-dual salt-containing gel-polymer-electrolytes for rechargeable magnesium batteries

Polymer-based electrolytes can greatly promote the development of rechargeable metal-sulfur batteries owing to the improved safety and high flexibility; however, liquid electrolytes, which are mostly investigated so far, often hinder practical application due to the severe shuttling effect and possible leakage of the electrolytes. Herein, a new cell design is presented, that bridges the gap between lab cells and application by a novel halogen-free gel-polymer-electrolyte (GPE) with outstanding electrochemical performance. The GPE was prepared via an in-situ crosslinking reaction between lithium/magnesium borohydrides and poly(tetrahydrofuran). This GPE displays outstanding ionic conductivities in a wide temperature range, superior polarization behavior, remarkable reversibility and more strikingly, excellent compatibility with different sulfur containing and intercalation cathodes: S8@activated carbon cloth (ACC/S), sulfur poly(acrylonitrile) (SPAN) composite, titanium disulfide, Chevrel phase Mo6S8 and lithium titanate. The effective suppression of the ‘polysulfide shuttle’ by the GPE allows for a stable cycling of Mg||SPAN and Mg||ACC/S cells at room temperature with high discharge capacities (600 and 420 mAh∙gs−1 after 140 and 50 cycles, respectively). Remarkably, the Mg||GPE||SPAN system features low self-discharge, excellent flexibility and safety characteristics, which significantly improve the possibility for practical applications.