Facile One Pot Polycondensation Method to Synthesize the Crosslinked Polyethylene glycol‐Based Copolymer Electrolytes

Abstract

Comb‐like polyethylene glycol (PEG)‐based copolymer electrolytes with given crosslinking density are synthesized using PEG as the main chain segments (denoted as MC‐PEG), methoxy polyethylene glycol (MPEG) as side chain segments (denoted as SC‐PEG), and hexamethylene‐1,6‐diisocyanate homopolymer (HDI trimer) as bridging and/or crosslinking agent. In this study, the effects of molecular weight of MC‐PEG and SC‐PEG on Li ion conductivities of the copolymer have been examined. If MC‐PEG and/or SC‐PEG do not crystallize, the ion conductivities of graft copolymer electrolyte increase with either decreasing MC‐PEG or increasing SC‐PEG segment length. The highest ion conductivity of the copolymer electrolyte at room temperature reaches up to 7.7 × 10−4 S cm−1 when the molecular weight of MC‐PEG is 400 g mol−1 and SC‐PEG is 1000 g mol−1 (denoted as GC400‐1000). However, when the MC‐PEG and/or SC‐PEG segments begin to crystallize (i.e., GC400‐2000), where the flexibility of the related PEG molecular chains is largely reduced, the ion conductivity drops by almost two orders comparing to that of GC400‐1000 copolymer electrolyte. Meanwhile, crosslinked GC400‐1000 electrolyte has good thermal and electrochemical stability as well as high mechanical properties, making it suitable for commercial applications in Li ion secondary batteries. image