Conductivity, DSC, and solid-state NMR studies 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 has been characterized by differential scanning calorimetry (DSC), AC impedance, 13C and 7Li solid-state nuclear magnetic resonance (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). 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. Moreover, the 13C solid-state NMR spectra for the carbons attached to the ether oxygen atoms exhibited significant line broadening and a slight upfield chemical shift and short TCH when the dopant was added to the polymer. These findings indicate coordination between the Li cation and the ether oxygens in the PEG segment. Tg 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.