Composite electrolyte with polyethylene oxide and metal–organic framework for lithium‐ion conduction

Polyethylene oxide based solid polymer electrolytes (SPEs) are safer alternatives to the current flammable liquid electrolytes used in lithium‐ion batteries. Lithium ions are typically thought to conduct through the amorphous regions of SPEs with the aid of polymer segmental motion, which is correlated with the glass transition temperature (Tg). The ionic conductivity is generally increased by making the polymer more flexible (decreasing Tg) and/or by increasing the amorphous regions of the SPE, at the cost of compromising its stiffness. This trade‐off makes it impossible to optimize both ionic conductivity and stiffness of SPEs. By incorporating a metal–organic framework (MOF) nanowhisker with the composition EO:Li = 6:1 [EO = ether oxygen, Li = lithium], we synthesized a unique composite electrolyte. We observed an atypical conductivity mechanism in this composite electrolyte, where lithium ions conduct through the crystalline regions without decreasing Tg or increasing amorphous fraction. The room‐temperature ionic conductivity of the 6:1 polymer electrolyte increased by almost 400% when 2 wt% MOF nanowhisker was added. Our results supported the potential of a composite electrolyte, which enables simultaneous improvement in both conductivity and stiffness.