Composite polymer electrolytes (CPE) based on triethylene glycol diacetate-2-propenoic acid butyl ester (TEGDA-BA) incorporating Al2O3 nanoparticles have been fabricated via in situ polymerization. The CPE have exhibited highly uniform morphology, excellent mechanical property (maximum stress up to ~1.3MPa), high ionic conductivity up to 3.92×10-3Scm-1 at 25°C, coupled with very high electrochemical stability (>5.0V vs. Li/Li+). The Li|CPE|Li[Li1/6Ni1/4Mn7/12]O7/4F1/4 cells have demonstrated remarkably stable charge/discharge performance and great capacity retention in the potential range of 2.0-4.8V. The unexpected growth of interface resistance has been retarded with the presence of Al2O3, indicating the enhancement of the interface stability. The results suggest that the CPE have demonstrated tremendous application potential in high-voltage lithium ion batteries.