Graft-to/Graft-From Synthesis of Janus Graft Copolymers for Bottlebrush Polymer Electrolytes

Janus graft copolymers, which combine the characteristics of block and graft copolymers, have been used in the fields of reaction catalysis, surface modification, and drug delivery, but their applications in lithium batteries have rarely been reported. Herein, Janus graft copolymers with polyethylene glycol (PEG) and polystyrene (PS) side chains are synthesized by combining reversible addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) methods and doped with lithium salts to fabricate Janus bottlebrush polymer electrolytes (PEG-J-PS). The PEG side chains of the brush polymers impart good ion-conducting properties to the electrolytes, while the PS side chains improve the mechanical strength and thermal and chemical stability of the electrolytes. Notably, the PEG-J-PS can effectively improve the motility of the polymer chain segments compared to the conventional block copolymer electrolytes (PEG-b-PS). The prepared PEG-J-PS exhibits a considerable ionic conductivity of 2.06 × 10^-5 S cm^-1 at 30 °C and high tensile stress (2.39 MPa) and tensile strain (143%) of the PEG₄₅-J-PS₂₀ owing to its Janus graft structure.