Single-ion block copolymer electrolytes based on poly(ethylene oxide) and methacrylic sulphonamide for lithium batteries

Polymer electrolytes are expected to replace flammable liquid electrolyte in next-generation lithium metal batteries. In addition to intrinsic enhanced safety, their chemical structure can be tailored in order to display unique properties such as lithium-ion transference number (t+) approaching unity, not otherwise achievable with conventional electrolytes. This new class of materials, namely Single-Ion Conductors, has attracted increasing interest in recent years. Nevertheless, practical applications of polymer electrolytes are still limited by low ionic conductivities (σ), typically far below 10-5 S cm-1 at 25 °C. In this work, new families of single-ion conducting copolymers based on the specifically designed lithium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethylsulfonyl)imide (LiMTFSI) anionic monomer will be introduced. RAFT polymerization techniques were employed to prepare well-defined anionic di- and tri-block copolymers comprising poly(LiMTFSI) and poly(ethylene oxide) blocks. The effect of the macromolecular architecture and molecular weight on thermal and conduction properties will be discussed. Block copolymers were semicrystalline, showing a single glass transition temperature (Tg) due to the miscibility of the amorphous regions of both blocks. Both Tg and degree of crystallinity (Xc) were composition dependent and ranged from –55 to 7 ºC for Tg, and from 51 to 0% for Xc, respectively. Block copolymers showed very high σ as compared to previous examples (up to ≈ 10-4 S cm-1 at 70 ºC) combined with t+ ≈ 0.91. In addition to these promising features, solid polymer electrolytes were successfully tested in lithium metal cells at 70 ºC providing long lifetime up to 300 cycles, and outstanding rate performance up to C/2 (≈100 mAh g-1).