Polyethylene glycol functionalized polyhedral cage silsesquioxane as all solid-state polymer electrolyte for lithium metal batteries

Abstract Polyethylene oxide (PEO) based solid polymer electrolyte is expected to be the safe and high energy density lithium-ion batteries owing to leakage-free and good flexibility, but high crystallinity results in low ionic conductivity at room temperature. In this paper, different molecular weights of the polyhedral oligomeric silsesquioxane-polyethylene glycol (POSS-(PEGw)8, w = 1 K g/mol and 2 K g/mol) is synthesized by click reaction between azido polyhedral oligomeric silsesquioxane (POSS-N3) and different weight of alkynyl methoxy polyethylene glycol (Alkynyl-PEG) are used as doped fillers to reduce the crystallinity of the PEO and enhance the ion conductivity of the electrolyte. The effect of the molecular weight of PEG in POSS-(PEGw)8 on the crystallinity and conductivity of composite solid polymer electrolytes (CSPEs) is analyzed and the result shows that PEO/POSS-(PEG1K)8 exhibits higher ionic conductivity (0.9 × 10−3 S·cm−1 at 50 °C) and Li+ transference number (0.47) than PEO/POSS-(PEG2K)8. Simultaneously, PEO/POSS-(PEG1K)8 presents a superior electrochemical window of 5.08 V. The LiFePO4‖PEO/POSS-(PEG1K)8–60%‖Li cell assembly reaches 133 mAh·g−1 after 100 cycles. The high capacity and good cycle performance prove the feasibility of applying POSS-(PEGw)8 to CSPEs, which contributes to the practical application of lithium metal batteries.