The incorporation of inorganic fillers into poly(ethyleneoxide)(PEO)-based solid polymer electrolytes (SPEs) is well known as a low-cost and effective method to improve their mechanical and electrochemical properties.Porous zeolitic imidazolate framework-8 (ZIF-8) is firstly used as the filler for PEO-based SPEs in this work.Due to the introduction of ZIF-8,an ionic conductivity of 2.2 x 10-5 S/cm (30 ℃) is achieved for the composite SPE,which is one order of magnitude higher than that of the pure PEO.ZlF-8 also accounts for the broader electrochemical stability window and lithium ion transference number (0.36 at 60 ℃C) of the composite SPE.Moreover,the improved mechanism of ZIF-8 to the composite SPE is investigated by zeta potential and Fourier transform infrared spectrograph characterizations.The stability at the composite SPE/lithium interface is greatly enhanced.The LiFePO4‖Li cells using the composite SPE exhibit high capacity and excellent cycling performance at 60 ℃C,i.e.,85％ capacity retention with 111 mA·h/g capacity retained after 350 cycles at 0.5 C.In comparison,the cells using the pure PEO show fast capacity decay to 74 mA·h/g maintaining only 68％ capacity.These results indicate that the PEO-based SPEs with ZIF-8 are of great promise for the application in solid-state lithium metal batteries.