Conductivity enhancement of poly(vinylimidazoline)-based electrolytes by addition of cascade nitrile

Abstract

Polyvinylimidazoline (PVI)-based electrolytes containing lithium perchlorate (LiClO4) were prepared and their characterizations were performed. Conductivities of PVI-based electrolytes, (PVI150)a(LiClO 4)b(EtOH)d complexes, were 1.93 × 10-5 S cm -1 (a = 3.7, b = 1.0, d = 3.0), and 3.49 × 10-4 S cm-4 (a = 1.5, b = 1.0, d = 1.2) at 70°C. However, their conductivities at 30°C were ca. 10-6-10-7 S cm -1. Addition of cascade nitrite compound, [-CH2-N(CH 2CH2CN)2]2, ED4 CN, to the PVI-based electrolytes enhanced their conductivities about one order. Conductivity of (PVI150)1.5(LiClO4) 1(ED4CN)1(EtOH) 6.11 complex was 5.00 × 10-5 S cm-1 at 30°C and it was about one order higher than that of the ED4CN-free PVI-based electrolyte. Conductivity enhancement mechanism by addition of ED4CN was investigated with X-ray diffraction, DSC, and solid state NMR measurements. Predominant coordination of ED4CN to lithium ions separated the strong coupling between lithium ion and imine-nitrogen in vinylimidazoline ring, and then increased mobility of lithium ions in the matrix. Therefore, conductivities of the PVI-based electrolytes were enhanced by addition of ED4CN to their matrix.