We have synthesized highly conducting and electrochemically stable solidlike ionogels based on poly(vinylidene fluoride-co-hexafluoropropylene) P(VdF− HFP) copolymer matrix, succinonitrile (SN) plastic crystal plasticizer, lithium trifluromethanesulfonate (LiOTf) salt, and 1-butyl-1-methylpyrrolidinium trifluromethanesulfonate (BMPyrrOTf) ionic liquid. It is observed that the presence of SN in the ionogels enhances their ionic conductivity. The composition SN/BMPyrrOTf/ P(VdF−HFP) with a ratio 40:40:20 (w/w/w) containing 0.5 M LiOTf (ionogel-3) exhibits the highest ionic conductivity (∼12.18 mS cm −1 ) and Li + -ion transference number (∼31%). Ionogel-3 has shown long-term stability performance in lithium plating and stripping experiments at several current densities and improved electrochemical compatibility with electrodes at 30 °C. The Li-ion battery fabricated with ionogel-3 has delivered high specific discharge capacities of 86, 120, 139, 144, and 150 mAh g −1 at current densities of C/3, C/5, C/8, C/10, and C/12, respectively, at 30 °C. The fabricated Li−graphite dual-ion battery has also delivered high specific discharge capacities of 126, 89, and 51 mAh g −1 at 100, 300, and 500 mA g −1 current densities, respectively, maintaining a high average discharge voltage of ≥4.5 V.
Ionic conduction and relaxation for the cubic phase of three-dimensional CsPbCl3 perovskite with a mean crystal size of 500 nm, synthesized via a facile solution based method, have been investigated in wide temperature and frequency ranges by dielectric spectroscopic measurements. Dielectric data have been analyzed in terms of the complex impedance spectroscopy, AC conductivity and the complex electric modulus by using Maxwell–Wagner equivalent circuit model, universal power law, Havrilliak–Negami, and Kohlrausch–Williams–Watts models to explore the fundamental aspects of the ionic transport and relaxation mechanism in CsPbCl3 perovskite. Nyquist plots indicate the individual grain and grain boundary contributions to the total impedance. The temperature dependence of the DC conductivity and the relaxation time obtained from the analysis was observed to follow the Arrhenius behavior. The activation energy for the DC conductivity was found to be ∼0.25 eV, which was very close to that for the relaxation time. The scaling of the AC conductivity and the electric modulus spectra at different temperatures indicates the validity of the time-temperature superposition principle, i.e., common ionic conduction and relaxation mechanisms at different temperatures in CsPbCl3 perovskite.
The impact of physicochemical properties of imidazolium based different ionic liquids such as BDMIMBF4, BMIMBF, and EMIMBF4 on the ion conduction and relaxation mechanisms in ionogels is investigated using broadband dielectric spectroscopy. The complex conductivity isotherms of these ionogels are analyzed using a universal power law coupled with a modified Poisson-Nernst-Planck model for the contribution of electrode polarization dominated in the low frequency region. The effect of electrode polarization is analyzed by using the Macdonald-Coelho model to determine free-ion diffusivity and number density in these ionogels. The relaxation process of ions is also systematically studied using electric modulus spectroscopy over wide frequency and temperature ranges. The temperature dependence of the ionic conductivity, free-ion diffusivity, and relaxation times follows the Vogel-Tammann-Fulcher relationship, indicating existence of coupling between the ion transport and segmental dynamics in these ionogels. The EMIMBF4 ionic liquid doped ionogel shows the highest ionic conductivity, lowest relaxation time, highest free-ion diffusivity and highest number density due to the smallest size of cations, highest static dielectric constant, and lowest viscosity of the EMIMBF4 ionic liquid. It is observed that the stretched exponents for different ionogels obtained from Havriliak-Negami and Kohlrausch-Williams-Watts fits of electric modulus are lower than unity, indicating highly nonexponential relaxation in the investigated ionogels.
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