Lithium-ion batteries (LIBs) are one of the promising power sources for mobile electronics, electric vehicles and energy storage systems. Recently, the safety issues of the LIBs have become a considerable concern for utilization of batteries in large capacity applications. Although liquid electrolytes currently used in LIBs show the high ionic conductivity and good electrochemical properties, they have drawbacks such as flammability, solvent leakage and growth of lithium dendrite in case of lithium metal anode. Accordingly, the development of non-flammable solid electrolytes can give a solution in consideration of safety issue of LIBs.¹ Solid polymer electrolytes based on poly(ethylene oxide) have received great attention so far owing to their flexibility in the shape of battery design, an absence of leakage and enhanced safety. However, their low ionic conductivities at ambient temperatures, which range from 10^-8 to 10^-5 S cm^-1 due to their high degree of crystallinity, preclude their practical applications at room temperature. Moreover, their poor mechanical properties resulting from their melting transition may cause short circuits between two electrodes if unexpected heat is generated.² In our study, poly(ε-caprolactone) (PCL)-based solid polymer electrolytes supported by porous membrane were prepared and their electrochemical properties were investigated. The PCL-based solid polymer electrolyte was applied to the all-solid-state lithium cells composed of a lithium anode and a layered LiNi_0.6Co_0.2Mn_0.2O₂ cathode, and their electrochemical performance was evaluated.

1. J. Janek and W.G. Zerier, Nature Energy, 1, 16141 (2016).
2. Y. Tominaga, K. Yamazaki, and V. Nanthana, Journal of The Electrochemical Society, 162, A3133 (2017).