Broadband dielectric and conductivity spectroscopy of Li-ion conducting three-dimensional hybrid inorganic–organic networks as polymer electrolytes based on poly(ethylene glycol) 400, Zr and Al nodes

The dielectric and conductivity study of two series of five three-dimensional hybrid inorganic–organic networks as polymer electrolytes (3D-HION-APEs), with formula {Al[O(CH2CH2O)8.7]ρ/(LiClO4)z}n (1.86 ≤ ρ ≤ 2.24, 0 ≤ z ≤ 1.06) and {Zr[O(CH2CH2O)8.7]ρ/(LiClO4)z}n (1.81 ≤ ρ ≤ 1.99, 0 ≤ z ≤ 0.91) is presented. The real and imaginary components of the complex dielectric permittivity spectra ɛ* and conductivity spectra σ* are measured between −60 °C and 80 °C. Spectral analysis points out that the conductivity mechanism is determined by two dielectric relaxation events, α and β. The relaxation β occurs at higher frequencies than α, and is attributed to the segmental motion with characteristic frequency fseg. The relaxation α is attributed to the ionic motion with characteristic frequency fion. The profiles of the direct conductivity σdc and the frequencies fion and fsegvs. the reciprocal temperature exhibit a Vögel–Tamman–Fülcher (VTF) behavior. The study of the activation energies of the dielectric relaxations α and β allows to determine their relative contribution to the direct conductivity σdc at lower and higher temperatures. The dependence of the VTF parameters vs. the mole-to-mole ratios nLi/nO and nLi/nM (M = Zr, Al) in combination with previous equivalent conductivity studies, allows to identify the role of the ionic species and the metal nodes present in the polymer structure at various salt concentrations. The correlation between the diffusion coefficient D and the relaxation frequencies fseg and fion of the 3D-HION-APEs is investigated.

► The electric properties and ion conduction mechanism of two families of lithium hybrid inorganic-organic networks are investigated.
► The networks are doped with LiClO4 and include either Zr or Al nodes, bridged by PEG 400 molecules.
► The correlation between relaxation phenomena and the long-range charge migration is studied.