Ion transport dynamics in ionic liquid incorporated CuBTC–metal-organic framework based composite polymer electrolyte

Abstract

Cu based metal-organic framework (MOF), copper 1,3,5-benzenetricarboxylate (CuBTC) has been incorporated with ionic liquid (IL) 1-butyl-3 methylimidazolium bromide at different wt% to be used as composite nanofiller in poly (ethylene oxide) polymer electrolyte system. Shifting of carboxylate vibrational modes is observed from FTIR and significant changes of binding energies of Cu spin–orbit peaks are obtained from XPS spectra suggesting strong interaction between Cu metal cluster of MOF and Br− anions of the IL. Oscillation periodicity and local coordination structure of Cu K-edge are investigated in k-space and R-space from the scanning XANES and EXAFS spectra. Dielectric modulus spectra show non-Debye relaxation dynamics and optimum ionic conductivity of 5 × 10−3 S cm−1 is obtained for the nanocomposite containing 50 wt% IL at 380 K. The frequency dependent AC conductivity curves depict ion concentration and temperature independent scaling behavior by collapsing to a single curve. The electrochemical stability and cycling performance increases with increasing IL concentration and attains electrochemical stability of 6.1 V with discharge capacity of 152.5 mAh/g after 500 cycles at 50 wt% of IL.