Mechanism of Accelerated Charge Transport in Doped Organic Ionic Plastic Crystals

Organic ionic plastic crystals (OIPCs) have attracted significant attention as potential candidates for solid-state electrolytes in electrochemical energy technologies due to their fast ionic diffusion. However, ionic conductivity in their solid phases appears significantly lower than expected from their fast ion diffusion. One of the reasons for conductivity suppression in OIPCs is related to strong ionic correlations, which decrease ionic conductivity by ∼100 times in solid phases. It was discovered that doping OIPCs with small amounts of salt can enhance ionic conductivity by several orders of magnitude. In this study, we employed a broad range of experimental techniques to unravel the ion dynamics in the OIPC 1-ethyl-1-methylpyrrolidinium-bis(trifluoromethyl sulfonyl)imide [P 12 ][TFSI] doped with 4.8 wt % of lithium bis(trifluoromethyl sulfonyl)imide [Li][TFSI] salt. Our results reveal that a significant increase of ionic conductivity in solid phases of this OIPC with the addition of small amounts of Li salt is caused by a disruption of its crystalline structure. We show that the disorder induced by small doping leads to a remarkable reduction in the ionic correlations. Thus, doped OIPCs with small weight fractions of salt hold considerable potential as new solid electrolytes for various electrochemical technologies.