The environment of lithium ions and conductivity of comb-like polymer electrolyte with a chelating functional group

The behavior of lithium ions in a comb-like polymer electrolyte with a chelating functional group have been characterized by differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR) spectroscopy, ac impedance and ⁷Li solid-state NMR measurements. The comb-like copolymer is synthesized by poly(ethylene glycol-methyl ether methacrylate) (PEGMEM) and (2-methylacrylic acid 3-(bis-carboxymethylamino) -2-hydroxy-propyl ester) (GMA-IDA). FTIR and ⁷Li solid-state NMR spectra demonstrate the interactions of Li⁺ ions with both the ether oxygen of the PEGMEM and the nitrogen atom of the GMA-IDA segments. Moreover, ⁷Li solid-state NMR shows that the lithium ions are preferentially coordinated to the GMA-IDA segment. The T_g increases for the copolymers doped with LiClO₄. These results indicate the interactions of Li⁺ with both PEGMEM and GMA-IDA segments form transient cross-links. The Vogel-Tamman-Fulcher (VTF)-like behavior of conductivity implies the coupling of the charge carriers with the segmental motion of the polymer chains. The dependence of the maximum conductivity on the composition of the copolymers and the doping lithium ion concentration was determined. The GMA-IDA unit in the copolymer improves the dissociation of the lithium salt, the mechanical strength and the conductivity.