New Insights into Decoupled Cation and Anion Transport and Dynamic Heterogeneity in a Diethyl(methyl)(isobutyl)phosphonium Hexafluorophosphate Organic Ionic Plastic Crystal

Abstract

Organic ionic plastic crystals (OIPCs) are an emerging family of materials with demonstrated applications in electrochemical devices such as lithium/sodium ion batteries, dye-sensitized solar cells, and hydrogen fuel cells. Herein, we present direct evidence of anion diffusion through a relatively static background of a cation lattice in an ionic plastic crystal compound, [P 122i4 ][PF 6 ], in an elevated temperature solid phase. We found all anions are diffusive, whereas only a small population of cations is diffusive. Two anion populations were identified with diffusion coefficients differing by 2 orders of magnitude. The slow-diffusing anion is attributed to the plastic crystal region where the cation forms a relative static background, allowing anions to diffuse possibly through a defect-assisted hopping mechanism.

Aromatic heterocyclic anion based ionic liquids and electrolytes

“…The latter can arguably be due to stronger interionic interactions as well as the comparatively more symmetric (4-PyrA) À and (Pyr-2,6-diA) À anions, as symmetry is known to facilitate crystallinity. [40][41][42]…”

Lithium-Ion and Chloride-Ion Transfer in Chiral and Racemic 3-Hydroxyquinuclidinium Perchlorate: Influence of Defects and a Mixed Plastic Crystal Matrix

“…The higher effective activation energy for chloride-ion conduction than that for lithium ions demonstrates a relatively more difficult process for chloride ions. Defects of the system (see the next section) and dynamics of the constituent ions of the OIPCs may help the understanding of the present ion conduction behaviors. , Moreover, the ion conduction of the doped mixtures should be consistent with the dynamics of the constituent ions, as suggested in the NMR analysis, where only the ion mobility (e.g., rotating) could facilitate the transfer of the target ions (Li + and Cl – ). In other words, if the conductivity is truly enhanced, ion movements of the constituent ions of the host material in the plastic phases should be expected. − …”

Thermal, structural and dynamic properties of ionic liquids and organic ionic plastic crystals with a small ether-functionalised cation

“…Two different diffusive anion species in an OIPC have previously been observed by Zhu et al in 1-methyl-1,1- diethyl-1-isobutylphosphonium hexafluorophosphate ([P 122 i 4 ][PF 6 ]), where the two anion populations have diffusion coefficients differing by approximately two orders of magnitude at 100 °C in phase II. 99 Future work, including molecular dynamics simulations, will further investigate the complex diffusion behaviour observed in [N 111,1O1 ][FSI] to more fully understand the nature of the different mechanisms of ion transport through these regions.…”

“…The [OTf] − salt displays good conductivity even in phase II (1.5 × 10 −6 at 30 °C) and can be further explored by pairing the anion with other cations such as [C (i3) mpyr] + and [P 122 i 4 ] + . 62,99…”

“…The [OTf] À salt displays good conductivity even in phase II (1.5 Â 10 À6 at 30 1C) and can be further explored by pairing the anion with other cations such as [C (i3) mpyr] + and [P 122i4 ] + . 62,99 To exploit the benefits of oxygen to a greater extent, the [N 111,1O1 ] + cation and other ether-functionalised cations such as [C 1 moxa] + and [C 2 moxa] +27 should be paired with other oxygen containing anions such as fluorosulfate ([SO 3 F] À ), difluorophosphate ([PO 2 F 2 ] À ), 109 difluoro(oxalato)borate ([DFOB] À ) 110 or cyanate ([OCN] À ), 111 to further understand the benefits of oxygen atoms on the cation and anion in OIPC/IL systems.…”