Grafted Copolymer Electrolytes Based on the Poly(acrylic acid-co-oligo ethylene glycol acrylate) (P(AA-co-OEGA)) Ion-Conducting and Mechanically Robust Block

A series of completely amorphous polymer brushes composed of grafted copolymer electrolytes based on the ion-containing block of poly(acrylic acid-co-oligo ethylene glycol acrylate) (P(AA-co-OEGA)) doped with LiCF3SO3 (LiTf) or LiN(SO2CF3) (LiTFSI) and the glassy polystyrene (PS) block are synthesized and studied with respect to the structural, thermomechanical, and ion conduction properties. The incorporation of some AA units into the ion-conducting phase provides a trade-off between increased mechanical stability and anion/cation complexation. Consequently, the P(AA-co-OEGA) block can be engineered to simultaneously support ion conduction while exhibiting enhanced mechanical stability. Between the two anions ([Tf–] vs [TFSI–]), it is the latter that better supports the Li-ion transport. Diblock copolymer electrolytes doped with the larger anion ([TFSI–]) suppress ion complexation and give rise to superior ion conduction properties (by about 2 orders of magnitude), as compared to that of the smaller anion ([Tf–]). Overall, the PS-b-P(AA-co-OEGA)/LiTFSI diblock-random copolymer electrolyte with salt concentration, r = 0.08 (r is defined as the molar ratio of Li ions to EO units), best combines the required mechanical stability (storage modulus, G′ ∼ 108 Pa) with a relatively high dc-conductivity (σdc ∼ 10–6 S·cm–1) at an ambient temperature (for application as solid polymer electrolytes (SPEs) in Li-ion batteries). This work suggests routes toward further improving the mechanical stability via the random incorporation of acids into the ion-containing block of nanophase-separated electrolytes.