Polymerized ionic liquids (PolyILs) are promising candidates for energy storage and electrochemical devices applications. Understanding their ionic transport mechanism is the key for designing highly conductive PolyILs. By using broadband dielectric spectroscopy (BDS), rheology, and differential scanning calorimetry (DSC), a systematic study has been carried out to provide a better understanding of the ionic transport mechanism in PolyILs with different pendant groups. The variation of pendant groups results in different dielectric, mechanical, and thermal properties of these PolyILs. The Walden plot analysis shows that the data points for all these PolyILs fall above the ideal Walden line, and the deviation from the ideal line increases upon approaching the glass transition temperature (T g ). The conductivity for these PolyILs at their T g s are much higher than the usually reported value ∼10 −15 S/cm for polymer electrolytes, in which the ionic transport is closely coupled to the segmental dynamics. These results indicate a decoupling of ionic conductivity from the segmental relaxation in these materials. The degree of decoupling increases with the increase of the fragility of polymer segmental relaxation. We relate this observation to a decrease in polymer packing efficiency with an increase in fragility.

Many-body effects produce deviations from the predictions of conventional band theory in quantum materials, leading to strongly correlated phases with insulating or bad metallic behavior. One example is the rare-earth nickelates RNiO3, which undergo metal-to-insulator transitions (MITs) whose origin is debated. Here, we combine total neutron scattering and broadband dielectric spectroscopy experiments to study and compare carrier dynamics and local crystal structure in LaNiO3 and NdNiO3. We find that the local crystal structure of both materials is distorted in the metallic phase, with slow, thermally activated carrier dynamics at high temperature. We further observe a sharp change in conductivity across the MIT in NdNiO3, accompanied by slight differences in the carrier hopping time. These results suggest that changes in carrier concentration drive the MIT through a polaronic mechanism, where the (bi)polaron liquid freezes into the insulating phase across the MIT temperature.

Continuous progress in energy storage and conversion technologies necessitates novel experimental approaches that can provide fundamental insights regarding the impact of reduced dimensions on the functional properties of materials. Here, we demonstrate a nondestructive experimental approach to probe nanoscale ion dynamics in ultrathin films of polymerized 1-vinyl-3-ethylimidazolium bis­(trifluoromethylsulfonyl)­imide over a broad frequency range spanning over 6 orders of magnitude by broadband dielectric spectroscopy. The approach involves using an electrode configuration with lithographically patterned silica nanostructures, which allow for an air gap between the confined ion conductor and one of the electrodes. We observe that the characteristic rate of ion dynamics significantly slows down with decreasing film thicknesses above the calorimetric glass transition of the bulk polymer. However, the mean rates remain bulk-like at lower temperatures. These results highlight the increasing influence of the polymer/substrate interactions with decreasing film thickness on ion dynamics.

A series of diblock copolymers bearing a polymerized ionic liquid (polyIL) block (poly(N-(methacryloyloxy)ethyl-N,N-dimethyl-N-ethylammonium bis-(trifluoromethylsulfonyl)imide)) and a noncharged block (poly(methyl methacrylate) (PMMA)) or poly(n-butyl methacrylate) (PBuMA)) were studied using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), wideangle X-ray scattering (WAXS), and broadband dielectric spectroscopy (BDS) to probe the effect of ion concentration on the morphology and ion transport in these polyelectrolytes. Two majority PMMA block copolymers, having mole ratios of the polyIL of 0.19 and 0.22, exhibited evidence of aggregation indicated by interfacial polarization in the dielectric spectra. The 0.19 mole ratio sample also displayed two distinct glass transitions by DSC. The SAXS measurements showed that no long-range order was present in these samples. The ionic conductivity of these samples were lower than the polyIL homopolymer due to hindered ion transport at the aggregate boundaries. Copolymers with majority polyIL blocks were found to exhibit disorder based on SAXS and DSC measurements. Furthermore, at a mole fraction of 0.91 of the polyIL the ionic conductivity was enhanced by a factor of ca. 1.5 with respect to the polyIL homopolymer, with a similar increase observed for the static dielectric permittivity. The effective number density and mobility of the ions were calculated for these systems from BDS and WAXS data, indicating that the enhancement of the ionic conductivity corresponds to an increase in the density of mobile charge carriers. The higher effective number density of charge carriers correlates with increased static dielectric permittivity, suggesting that ion pair dissociation is the likely mechanism behind the observed enhancement of ion transport. This study showcases the wealth of information that can be obtained from a combination of complementary experimental techniques.

The impact of molecular structure on ion dynamics and morphology in ammonium-and imidazolium-based glassy polymerized ionic liquids (polyILs) is investigated using broadband dielectric spectroscopy (BDS), wide-angle X-ray scattering (WAXS), and classical molecular dynamics (MD) simulations. It is shown that ammonium-based polyILs exhibit higher dc ionic conductivity at their respective glass transition temperatures (T g ) compared to imidazolium systems. In addition, the length of the alkyl spacer has a more drastic impact on ionic conductivity at comparable time scales of segmental dynamics for ammonium than imidazolium polyILs. Agreement between the characteristic ion diffusion lengths estimated from the dielectric data and the ion-to-ion correlation lengths from the WAXS and all-atom MD simulations is observed. A recently proposed approach is employed to determine ionic mobility in a broad frequency range spanning 5 orders of magnitude below the T g of polyILs studied, providing access to a regime of diffusivities that is inaccessible to many current experimental techniques. The ion mobility is found to be more sensitive to variation of the molecular structure than to the effective number density of the mobile ions. These results showcase the subtle interplay between molecular structure, morphology, and ion dynamics in polymerized ionic liquids.