Ionic semi-interpenetrating networks as a new approach for highly conductive and stretchable polymer materials

The synthesis and characterization of ionically conductive polymer films with high stretchability and good elasticity based on ionic semi-interpenetrating polymer networks (semi-IPNs) are discussed. Such innovative semi-IPN materials were prepared by radical copolymerization of an ionic monomer, namely, (N-[2-(2-(2-(methacryloyloxy)ethoxy)ethoxy)ethyl]-N-methylpyrrolidinium bis(fluorosulfonyl)imide) with poly(ethylene glycol)(di)methacrylates in the presence of the dissolved nitrile butadiene rubber, ionic liquid and lithium salt, using a simple one-step process. The suggested approach allows for simultaneous imparting of high ionic conductivity (1.3 × 10−4 S cm−1 at 25 °C) and excellent mechanical properties (tensile strength up to 80 kPa, elongation up to 60%) to a single polymer material. Ionic semi-IPNs, possessing unusual “Emmentaler cheese” like structure, exhibit a wide electrochemical stability window (4.9 V) and acceptable time-stable interfacial properties in contact with metallic lithium. Preliminary battery tests have shown that Li/LiFePO4 solid-state cells are capable to deliver a 77 mA h g−1 average specific capacity at 40 °C during 75 charge/discharge cycles.