The phase behaviour, ionic conductivity, electrochemical stability and diffusion coefficients of mobile components in three organic ionic plastic crystals (OIPCs): triisobutylmethylphosphonium bis(fluorosulphonyl)amide (PFSI), triisobutylmethylphosphonium bis(trifluromethanesulphonyl)amide (PNTf) and trimethylisobutylphosphonium bis(trifluoromethanesulphonyl)amide (PNTf) are compared to study the effect of the anions and cations on phase behaviour and dynamics. The FSI-based OIPC shows lower melting point and higher conductivity values most likely because of the higher degree of charge distributions and weaker ion-ion interactions compared to NTf anion-based OIPCs. Cyclic voltammetry of electrolytes consisting of these OIPCs with 70 mol% sodium salt incorporated indicates stable sodium plating/stripping behaviour at 70 and 50 °C for all samples. The magnitude of the peak currents, however, are much higher for the FSI-based electrolyte.

Thermoelectric (TE) materials have drawn enormous research interest for decades as the TE effect facilitates direct conversion of heat into electrical energy or vice versa, thereby providing an alternative for power generation/refrigeration. However, the lack of TE materials that are simultaneously inexpensive, nontoxic, and efficient limits their industrial utilization. A new approach to address this challenge could be the electrical functionalization of commercially usednontoxic, sustainable, lightweight, and low-costthermal superinsulating materials, e.g., Aerosil200, by doping. In the present work, as a first step toward this approach, we employ density functional theory calculations through the Vienna ab initio simulation package to create and validate a numerical model of pure Aerosil200. This was followed by the calculation of its electronic structure as well as TE properties using the BoltzTrap code. The calculated Seebeck coefficient and electrical conductivity, and thereby the power factor, showed excellent agreement with the experimentally determined values. Our numerical model, therefore, paves the way for further improvement of the power factor, hence ZT, through doping of Aerosil200 while retaining its low thermal conductivity.