Nitrile-functionalized Poly(siloxane) as Electrolytes for High-Energy-Density Solid-State Li Batteries

In the quest to replace liquid Li-ion electrolytes with safer and non-toxic solid counterparts for Li-ion batteries, polysiloxane polymers have attracted considerable attention as they offer low glass transition temperatures, stability with metallic lithium, and versatility in chemical functionalization of the backbone. Herein, we present the synthesis of Li-ion conductive polysiloxane-based polymers functionalized with 60 % nitrile groups per chain unit. The synthesis procedure is based on the reaction of poly-(dimethylsiloxane-co-methylvinylsiloxane) polymer with 2-cyanoethanethiol, followed by the addition of lithium bis (trifluoromethanesulfonyl) imide. The presented polysiloxane-based polymers exhibit exceptionally high ionic conductivity up to 0.375 mS cm-1 at 60 degrees C and Li+ ion transfer number of 0.73, one of the highest reported for polymer Li-ion conducting electrolytes. Their electrochemical performance was evaluated in both symmetrical and full-cell configurations to test the utility of synthesized polymers as electrolytes in Li-ion batteries. Upper figure shows a schematics of the synthesized and crosslinked poly (siloxane) polymer electrolyte functionalized with nitrile groups. Bottom figure shows the voltage profile of a lithium symmetric cell prepared with the synthesized poly (siloxane) solid electrolyte, measured at a current density of 0.2 mA cm-2 with capacity limitation of 0.2 mAh cm-2 per half-cycle.image