Phase Behavior of the [N(C₂H₅)₄][BF₄]-[N(C₃H₇)₄][BF₄] Binary System

Abstract

Phase behavior of the [N 2222 ] [BF 4 ]- [N 3333 ] [BF 4 ] (N 2222 + = tetraethylammonium, and N 3333 + = tetrapropylammonium,) binary system has been investigated by differential scanning calorimetry and powder X-ray diffraction.

Investigation of the Physicochemical Properties of Pyrrolidinium-Based Mixed Plastic Crystal Electrolytes

“…In a study by Wang et al, it was reported that when [N 3333 ]­[BF 4 ] with a larger ammonium cation is introduced to [N 2222 ]­[BF 4 ], the melting transition for compositions x [N 3333 ]­[BF 4 ], x = 0.1–0.7, remained at 202 °C, while, for x [N 3333 ]­[BF 4 ], x = 0.8–1, the onset of melt increased (213–241 °C) . Interestingly, the entropy of fusion for the melt gradually increased as the composition of [N 3333 ]­[BF 4 ] was increased from 0.1–1 (1.2–16 J K –1 mol –1 ) .…”

“…In a study by Wang et al, it was reported that when [N 3333 ]­[BF 4 ] with a larger ammonium cation is introduced to [N 2222 ]­[BF 4 ], the melting transition for compositions x [N 3333 ]­[BF 4 ], x = 0.1–0.7, remained at 202 °C, while, for x [N 3333 ]­[BF 4 ], x = 0.8–1, the onset of melt increased (213–241 °C) . Interestingly, the entropy of fusion for the melt gradually increased as the composition of [N 3333 ]­[BF 4 ] was increased from 0.1–1 (1.2–16 J K –1 mol –1 ) . Interestingly, our pyrrolidinium-based mixed OIPC systems show a trend where as the composition of the secondary OIPC is increased, the melting transition increased, while the entropy of melt remained within the range of 7–11 J K –1 mol –1 for all compositions.…”

“…Contrary to the mixed anion system, Wang et al reported a mixed cationic system with [N 2222 ]­[BF 4 ] 1– x [N 3333 ]­[BF 4 ] x ( x = 0–1) where only a few compositions formed solid solutions . Based on XRD analysis of compositions of [N 2222 ]­[BF 4 ] 1– x [N 3333 ]­[BF 4 ] x , it was concluded that x = 0.1 and x = 0.9 at 210 °C showed diffraction patterns that were similar to neat [N 2222 ]­[BF 4 ] and neat [N 3333 ]­[BF 4 ], respectively.…”

“…Refinement analysis revealed [N 2222 ]­[BF 4 ] 1– x [N 3333 ]­[BF 4 ] x , x = 0.1, undergoes a 5.7% lattice expansion compared to pure [N 2222 ]­[BF 4 ], while [N 2222 ]­[BF 4 ] 1– x [N 3333 ]­[BF 4 ] x , x = 0.9, undergoes a 1.3% volume contraction compared to pure [N 3333 ]­[PF 6 ]. It was determined that substitution of a larger cation [N 3333 ] + , in place of [N 2222 ] + , is more difficult compared to substitution of anions ([BF 4 ] − / [PF 6 ] − ), as the ammonium-based cations are considered to be closely packed, and their substitution has a significant effect on the volume change of the plastic crystal lattice compared to substituting the anions . Studies of transport properties of pure [N 2222 ]­[BF 4 ] in phase I showed a low ionic conductivity of 2.4 × 10 –9 S cm –1 at 150 °C.…”

“…However, after the addition of 10 mol % [N 3333 ]­[BF 4 ] to [N 2222 ]­[BF 4 ], an increased ionic conductivity of 3.5 × 10 –7 S cm –1 at 150 °C was reported. It was concluded that the increase in ionic conductivity was due to the lattice expansion formed by the addition of 10 mol % [N 3333 ]­[BF 4 ] to [N 2222 ]­[BF 4 ] . Reports correlate lattice expansion in plastic crystals to increases in vacancies and defect volume, which as a result increase rotational disorder in the system. , Thus, the combined effect of increased rotational freedom and increased defect volume in the lattice may facilitate improvements in ionic conductivity. , …”