Denis O. Ponkratov

Design and synthesis of new anionic “polymeric ionic liquids” with high charge delocalization

Three novel ionic monomers having highly delocalized anions and electrochemically stable mobile cations, namely, 1-butyl-1-methylpyrrolidinium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethane-sulfonyl)imide, 1-butyl-1-methylpyrrolidinium 1,1-dicyano-1-[(3-(methacryloyloxy)propylsulfonyl)]methanide and 1-butyl-1-methylpyrrolidinium 1-cyano-1-[(3-(methacryloyloxy)propylsulfonyl)]imide were synthesized and characterized. The structure of these monomers was designed to be a mimic of the most highly conductive bis(trifluoromethylsulfonyl)imide, tricyanomethanide and dicyanamide anions. By radical polymerization procedure a series of new anionic “polymeric ionic liquids” (PILs) were prepared. The solubility of these linear PILs, thermal stability, glass transition temperatures, molar masses and ionic conductivities were estimated. An advantage of the novel PILs was demonstrated by the comparison of their ionic conductivity at 25 °C (2.0 × 10−8 ÷ 1.6 × 10−7 S cm−1) with the unmodified poly(1-ethyl-1-methylpyrrolidinium 3-(methacryloyloxy)propane-1-sulfonate) analog. The increase in ionic conductivity is as high as three orders of magnitude and was found to depend on the size of the attached anion. The new ionic monomers were subsequently copolymerized with poly(ethylene glycol) dimethacrylate and poly(ethylene glycol) methyl ether methacrylate. The investigation of the copolymers properties revealed further improvement of the conductivity in approximately two orders of magnitude and the achievement of σ = 4.8 ÷ 6.8 × 10−6 S cm−1) at 40 °C.

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.