Effect of alumina on triethylene glycol diacetate-2-propenoic acid butyl ester composite polymer electrolytes for flexible lithium ion batteries

Triethylene glycol diacetate-2-propenoic acid butyl ester (TEGDA-BA) based composite polymer electrolytes (CPE) are fabricated by incorporating alumina (Al₂O₃) nanoparticles (average particle size 10-20 nm) as inorganic filler via in situ polymerization. Effects of Al₂O₃ concentration on ionic conductivities, Li⁺ transfer numbers and charge/discharge properties are studied in details. Due to the uniformly dispersed Al₂O₃ nanoparticles, significant improvements in the mechanical flexibility and bendability are presented in the resulting polymer electrolytes. The CPE with 5 wt% Al₂O₃ nanoparticles exhibits the highest ionic conductivity up to 6.02 × 10^-3 S cm^-1 at 25 °C and the highest Li⁺ transference number (0.675), coupled with the most stable electrochemical window (>4.5 V vs. Li/Li⁺). With the presence of Al₂O₃, the growth of interface resistance is retarded, which increases the interface stability. The Li|CPE|Li₄Ti₅O₁₂ and Li|CPE|LiFePO₄ cells demonstrate remarkably stable charge/discharge performance and excellent capacity retention during cycling test. The results suggest that the CPE holds great application potential in flexible lithium ion batteries.