Polymer electrolytes based on the doped comb-branched copolymers for Li-ion batteries

In this work, poly(4-vinylbenzeneboronic acid), PVBBA was synthesized via free-radical polymerization of 4-vinylbenzeneboronic acid (4-VBBA) and followed by modification with polyethylene glycol monomethy-lether (PEGME) with different molecular weights to produce boron containing comb-branched copolymers and abbreviated as PVBBAPEGMEX. Then copolymer electrolytes were successfully prepared by doping of the host matrix with CF3SO3Li at several stoichiometric ratios to get PVBBAPEGMEX-Y (X is the molecular weight of PEGME and Y is the EO/Li ratio). The materials were characterized by using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (H-1-NMR and B-11-NMR), thermogravimetry (TG) and differential scanning calorimeter (DSC). The ionic conductivity of these novel copolymer electrolytes was studied by dielectric-impedance spectroscopy. Li-ion conductivity of these copolymer electrolytes depends on the length of the side units as well as the doping ratio. Such electrolytes possess satisfactory ambient temperature ionic conductivity (exceeding 10(-4) S/cm) and good mechanical strength. At higher doping ratios, Vogel-Tamman-Fulcher (VTF) behavior of conductivity implies the coupling of the charge carriers with the segmental motion of the polymer chains. (C) 2010 Elsevier B.V. All rights reserved.