Ion Conductive Characteristics of Alkylborane Type and Boric Ester Type Polymer Electrolytes Derived from Mesitylborane

Abstract

Alkylborane type and boric ester type polymer electrolytes bearing mesitylboron units were prepared by hydroboration polymerization or dehydrocoupling polymerization using mesitylborane. The obtained well-defined organoboron polymer electrolytes showed ionic conductivities of 3.05 × 10-5−5.22 × 10-6 S/cm at 50 °C in the presence of various lithium salts. The maximum conductivity was observed when LiTFSI was doped to boric ester type polymers. The lithium ion transference number was calculated to be 0.35−0.50, indicating a significant anion trapping effect of the organoboron unit. The alkylborane type polymer exhibited a higher lithium ion transference number due to stronger Lewis acidity of the alkylborane unit. The organoboron polymer electrolytes were subjected to polymer reaction with organolithium reagents in aim of immobilizing the anion to the polymer chain as borate anion. After the reaction with phenyllithium, ionic conductivities of 9.45 × 10-7−8.22 × 10-7S/cm were observed with a lithium ion transference number of 0.78−0.82. When pentafluorophenyllithium or naphthyllithium was employed as an organolithium reagent, the conductivity increased by 1 order of magnitude due to the improved dissociation degree of the lithium borate unit in the presence of electron-withdrawing substituent.