New Families of Single-Ion Block Copolymer Electrolytes based on Poly(Ethylene Oxide) and Methacrylic Sulfonamide for Lithium Batteries

Polymer electrolytes have been proposed as a replacement for conventional liquid electrolytes in next-generation lithium-based batteries, mainly because of their intrinsic enhanced safety and peculiar chemical structure that can be tailored as desired to display unique properties such as lithium-ion transference number (t+) approaching unity. This new class of materials, namely Single-Ion Conductors, has attracted increasing interest in recent years. Nevertheless, practical application of polymer electrolytes is still limited mainly by low ionic conductivity (σ), which is far below 10-5 S cm-1 at 25 °C.Herein, the preparation and characterization of new families of single-ion conducting copolymers based on the specifically designed lithium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethylsulfonyl)imide (LiMTFSI) anionic monomer is described. RAFT polymerization was employed to prepare well-defined anionic di- and tri-block copolymers comprising poly(LiMTFSI) and poly(ethylene oxide) blocks.1 The effect of the macromolecular architecture and molecular weight on thermal and ionic conduction properties is thoroughly discussed. Block copolymers were semi crystalline, with a single glass transition temperature (Tg) due to the miscibility of the amorphous regions of both the blocks. Tg, ranging from –55 to 7 ºC, as well as degree of crystallinity (Xc, ranging from 51 to 0%) were both composition dependent. Block copolymers showed very high σ as compared to previous examples (up to ≈ 10-4 S cm-1 at 70 ºC) combined with and impressive t+ ≈ 0.91, and wide 4.5 V electrochemical stability. In addition to these promising features, solid polymer electrolytes were successfully tested in LiFePO4/Li cell prototypes at different temperatures providing long lifetime up to 300 cycles, and outstanding rate performance up to C/2 (≈100 mAh g-1).