Star-shaped polyethylene glycol methyl ether methacrylate-co-polyhedral oligomeric silsesquioxane modified poly(ethylene oxide)-based solid polymer electrolyte for lithium secondary battery

Abstract

Poly(ethylene oxide) (PEO)-based solid polymer electrolyte (SPE), as a key component connecting the internal channels, can improve the safety performance for lithium secondary battery, but it is still challenged by limited ionic conductance due to high polymer crystallinity at room temperature. Here, we develop a SPE by blending PEO with star-shaped polymer of polyethylene glycol methyl ether methacrylate-co-polyhedral oligomeric silsesquioxane (POSS-(PPEGMEM)8), which is synthesized by atom transfer radical polymerization (ATRP) under octa (2-bromoisobutyryloxyethyl sulfide) octasilsesquioxane (POSS-Br8) as initiator and poly(ethylene glycol) methyl ether methacrylate (PEGMEM) as polymerization monomer. The unique star-shaped structure of POSS-(PPEGMEM)8 is helpful to increasing the segmental motion by reducing the crystallinity of PEO polymer and supporting more ion transport channels to obtain higher ion conductivity. The mixed electrolyte containing 40% POSS-(PPEGMEM)8 exhibits the highest ionic conductivity (1.4 × 10−4 S cm−1, 50 °C) with a Li+ transference number of 0.51 and a wide electrochemical window (5.0 V vs. Li/Li+) and a high mechanical strength. The LiFePO4||Li battery, assembled with PEO/POSS-(PPEGMEM)8–40%, carries out 100 cycles at a current density of 0.1C, provides a stable reversible capacity of 129.4 mAh g−1 and a high capacity retention rate due to the high ratio of free volume of polymer electrolyte formed by the star-shaped POSS-(PPEGMEM)8, which indicates that PEO/POSS-(PPEGMEM)8 has good application prospects in high-performance all-solid-state lithium secondary battery.