A Convenient Method to Estimate Ion Size for Electrolyte Materials Design

Abstract

Ion size is an important parameter in interpreting the electrochemical properties of the electrolyte materials. There is difficulty in selecting a representative value for ionic radius when the ion has a shape far from spherical. Since the van der Waals volume becomes a good parameter for ion size, it was calculated by numerical integral based on a simple overlapped spherical model using the optimized structures by ab initio molecular orbital calculation. We have examined the extent of errors affected by the coordinates, and given the van der Waals radii of each atom, and the integral grid size, and give the van der Waals volumes of various ions applied for the electrolyte materials of lithium batteries and double-layer capacitors. © 2002 The Electrochemical Society. All rights reserved.

Contrast structure and EDLC performances of activated spherical carbons with medium and large surface areas

“…According to ab initio molecular orbital calculation by Ue et al [16], the cation (Et 4 N + ) and the anion (BF 4 − ) of the electrolyte in the present study have respective solvated sizes of 0.68 and 0.44 nm in propylene carbonate. The simple sum of both ions corresponding to the size of their ion pair is estimated to be 1.12 nm, which is certainly larger than the average pore diameter of M500.…”

High performance electrochemical and electrothermal artificial muscles from twist-spun carbon nanotube yarn

“…Figure 2c and d shows that torsional actuation and yarn tensile actuation are correlated and both depend on the size of the electrolyte ion used to compensate electronic charge. When a 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (BMP.TFSI) electrolyte was used (Figure 2c), which has similar van der Waals volumes [18] of the anion (147 Å 3 ) and cation (167 Å 3 ), similar torsional and tensile actuation was shown at both positive and negative potentials. Likewise, the much large actuation during reduction than for oxidation in Figure 2d for the TBA.PF 6 electrolyte reflects the larger unsolvated van der Waals volume [18] for the TBA cation (293 Å 3 ) than for the PF 6 anion (69 Å 3 ).…”

“…When a 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (BMP.TFSI) electrolyte was used (Figure 2c), which has similar van der Waals volumes [18] of the anion (147 Å 3 ) and cation (167 Å 3 ), similar torsional and tensile actuation was shown at both positive and negative potentials. Likewise, the much large actuation during reduction than for oxidation in Figure 2d for the TBA.PF 6 electrolyte reflects the larger unsolvated van der Waals volume [18] for the TBA cation (293 Å 3 ) than for the PF 6 anion (69 Å 3 ). While these advances using liquid electrolytes are fundamentally important (and use of the torsional muscles in a microfluidic circuit was demonstrated) [1], more general practical utilization is restricted by the use of a liquid electrolyte bath and the associated need for a containment system, which dramatically degrades the gravimetric and volumetric performance of the overall actuator device.…”

Application of Ionic Liquids to Double‐Layer Capacitors

“…This behavior can be explained by the thinner double-layer being due to the higher ionic concentration than that of nonaqueous solutions. However, the correlation between the doublelayer capacitance and anion size [41] observed in PC solutions [8] is not clear. It was further shown that the double-layer capacitance of the ionic liquid was not dependent on the choice of electrode from among DME, GC, and activated carbon fiber [31].…”

“…This observation is attributed to the ''ionsieving effect'' of the activated carbons because EMI þ (V c ¼ 116 Å 3 ) is smaller than Et 4 N þ (159) [41]. The smaller anion also affords higher capacitance in the following order [51]: EMIBF Figure 17.7 shows the change of the capacitances of the double-layer capacitors using various electrolytes, when operating temperature was varied from 25 to À25 C. The capacitance of all ionic liquids decreased rapidly compared with the 1 M Et 3 MeNBF 4 /PC due to the increase of internal resistance reflecting the temperature dependence of electrolytic conductivity in Figure 17.4.…”