Effect of Lithium Ion Concentration on Thermal Properties in Novel Single-Ion Polymer Electrolyte

Abstract

Polymer electrolytes consist of heptadecane functionalized poly(ethylene oxide) (PEO) methacrylate and lithium methacrylate were prepared by radical copolymerization and neutralization. The polymer electrolyte was designed to have lithium ion conducting and crystalline domains into an inner-outer double cylinder like array by a macromonomer structure which results in interesting thermal behaviors. In fact, crystalline melting temperature of the heptadecane domain was found at 40 °C but decreased gradually after introduction of lithium ions into the polymer electrolyte. The more the lithium ion concentration, the lower the melting temperature was observed in DSC study. This result suggests that the crystalline domain size of heptadecane became smaller and broader in their size and size distribution by increasing the lithium ion concentration. The polymer electrolytes reveal 2×10−7 S cm−1 of room temperature ionic conductivity due to the single-ion nature and quite low content (∼38 wt %) of the conducting PEO domains. However it was found that there was no active migration of counter anion from the DC-polarization test which indicates a high lithium ion transference number of the polymer electrolyte.