In Situ Generation of a Gel Polymer Electrolyte via the Controlled Formation of Ethylene Carbonate in a Poly(ethylene carbonate)‐Hydrogenated Nitrile Butadiene Rubber Solid Polymer Electrolyte

Abstract Electrolytes play an essential role in electrochemical energy storage devices. Liquid electrolytes have good ionic conductivity but tend to be flammable, prompting some of the safety concerns that are associated with these devices. Solid polymer electrolytes (SPEs) are presented as a potential solution to this problem. These materials have higher mechanical stability and can be formulated to be non‐flammable. However, ionic conductivity in solid polymer electrolytes tends to be several orders of magnitude lower than that of liquid electrolytes, significantly limiting device performance making electrolyte safety and performance difficult to optimize simultaneously. However, gel electrolytes which combine lower flammability, higher mechanical strength, and adequate ionic conductivity may present a solution to this challenge. To this end, the melt processing of hydrogenated nitrile rubber (HNBR) with poly(ethylene carbonate) (PEC) followed by the in situ formation of ethylene carbonate (EC) is reported. Conversion of PEC to EC is confirmed via NMR spectroscopy. Electrochemical testing reveals improved ionic conductivity following the conversion of the solid polymer electrolyte to the gel polymer electrolyte. Improvements in ionic conductivity, relative to the initial SPE, are attributed to decreased salt‐polymer interactions in favor of salt‐EC interactions as observed via differential scanning calorimetry, Fourier transform infrared, and nuclear magnetic resonance spectroscopy.