TFSI— anion

Holbrey, J.D., Reichert, W.M., and Rogers, R.D., Crystal structures of imidazo-lium bis(trifluoromethanesulfonyl)imide ionic liquid salts The first organic salt with a ds-TFSI anion conformation, Dalton Trans., 2267-2271,2004. 

From this table, it is clear that refractive index of ILs increases with increase in the alkyl chain length of the imidazolium cation. Moreover, the refractive index is strongly afFected by the anion the refractive index of ILs with larger anions, such as [(CF3S02)2N]- (TFSI anion) is lower than that of ILs having smaller anions such as acetate or halide anions. 

Welton reported the effect of cations and anions on the Kamlet-Taft Parameters [78]. The Kamlet-Taft parameters for some ILs are summarized in Table 3.9. As seen, n values for these ILs are high, 0.9-1.3, in comparison with those for protic molecular solvents as shown in the same table. Both cation and anion affect the n value. For anions, the n value for ILs having TFSI anion is low due to weakened coulombic interaction caused by delocalized anionic charge. 

Figure 14.3 Linear sweep voltammograms of Glassy Carbon in various ionic Liquids with a TFSI anion at 25° C. Sweep rate 50 mv/s. (Adapted from Matsumoto et at. [ 18]).

Bipyridinium cation 9 [58], phosphonium [59-62], guanidinium [63], and vina-midinium [64] cations were used to form thermotropic ionic liquid crystals. For example, the mixture of diheptyl and dioctyl viologens 9 (20 80 by wt%) with TFSI anion forms a smectic A phase between 22° and 132°C. It was reported that the viologens show fluorescence in both non-polar and polar organic solvents, which can be useful for the development of biological and chemical sensors [65]. 

Monomer II is also a polymerizable IL composed of quatemized imidazoliimi salt, as shown in Figure 29.1. This monomer is liquid at room temperature and shows a Tg only at —70°C. Its high ionic conductivity of about 10 S cm at room temperature reflects a low Tg. Although the ionic conductivity of this monomer decreased after polymerization as in the case of monomer I, it was considerably improved by the addition of a small amount of LiTFSI. Figure 29.3 shows the effect of LiTFSI concentration on the ionic conductivity and lithium transference number ( Li ) for polymer II. The bulk ionic conductivity of polymer II was 10 S cm at 50°C. When LiTFSI was added to polymer 11, the ionic conductivity increased up to 10 S cm After that, the ionic conductivity of polymer II decreased gradually with the increasing LiTFSI concentration. On the other hand, when the LiTFSI concentration was 100 mol%, the of this system exceeded 0.5. Because of the fixed imidazolium cations on the polymer chain, mobile anion species exist more than cation species in the polymer matrix at this concentration. Since the TFSI anions form the IL domain with the imidazolium cation, the anion can supply a successive ion conduction path for the lithium caiton. Such behavior is not observed in monomeric IL systems, and is understood to be due to the concentrated charge domains created by the polymerization. 

Zhang Z, Yang L, Luo S, et al. Ionic hquids based on aliphatic tetra-alkylammonium dications and tfsi anion as potential electrolytes. /. Power Sources. 2007. 167, 217-222. 

TFSI anions. The electrodeposit containing Ti without TFSI anions was obtained by the potentiostatic cathodic reduction below -3.0 V. Andriyko et al. studied the electrochemical behavior of titanium tetrachloride solutions in l-butyl-2,3-dimethylimi-dazolium azide ([BMMImlNj) at 65°C [183]. It was found that Ti (IV) formed a hexaazidotitanate complex which can only be irreversibly reducted to Ti(ni) species. 

Figure 15.10 SEM images PPy films doped with TFSI anions and prepared on (A) a glassy carbon electrode and (B) on a Pt electrode. The electrode side (with a macroporous morphology on Pt) is shown on the left in each case, and the solution side on the right. (Reprinted with permission from Synthetic Metals, Tris(trifluoromethylsulfonyl)methide-doped polypyrrole as a conducting polymer actuator with large electrochemical strain by S. Hara, T. Zama, W. Takashima and K. Kaneto 156, 2-4, 351-355. Copyright (2006) Elsevier Ltd)...

Ionic liquids (ILs) also face the same purification problem. The traditional trace impurities are water, oxygen, and halide ions [25]. The less common impurities include the by-products of the hydrolysis of water-sensitive ions and also even the hydrogen fiuoride [26]. The water in various ILs based on the bis(trifluoromethylsulfonyl) imide (TFSI) anion can be removed by high-temperature evaporation (e.g., 24 h at 130°C) [25]. Otherwise, special attention should be paid to ILs with hydrophobic anions, in which a small amount of water in the ILs may benefit the long-term durability of the electrolyte [1]. 

FIGURE 4.19 In operando infrared spectroelectrochemical results initialized time-resolved concentration (concentration units g/g corresponds to gpMiMiiTFsi/geiectrode) of the EMIM cation and TFSI anion in NCNFs during three CV at 20 mV s from (a) 0-1 V, (b) 0-1.5 V, and (c) 0-2 V. (d) Illustration showing ion adsorption within nanopores of NCNFs. (Reprinted with permission from Richey, F. W. et al., Ionic liquid dynamics in nanoporous carbon nanofibers in supercapacitors measured with in operando infrared spectroelectrochemistry. The Journal of Physical Chemistry C 118, 21846-21855. Copyright 2014 American Chemical Society.)... 

Similarly, the TFSI" anion can be viewed as the SO3CF3" anion with a =NS02Cp3 group replacing an =0 ... 

In fact it is hard to measure the intrinsic anodic behavior of LLMOj, cathode materials in standard electrolyte solutions because at too high potentials the anodic reactions of solution species may dominate the potentio-dynamic response. However, ionic liquid solutions based on quaternary ammonium cations, TFSI anion, and LiTFSI salt demonstrate very high anodic stability. The passivation of Al current collector is excellent in these solutions. So, the anodic stability of Al... 

The most thermally stable PILs reported were those with the TFSI anion, as shown in Table 2 with alkylammonium cations,the imidazolium cation, and a variety of heterocyclic cations. These PILs all had decomposition temperatures stated as >200 °C, with most >300 °C. In contrast, PILs containing a carboxylate anion, particularly formate, may have lower thermal stability due to undergoing a condensation reaction to form amides. " ... 

More recently, this reaction was trialed using protic imidazolium ILs with lactate, salicylate, BF4, or TFSI anions.The selectivities of endo/exo were mostly in the range of 3.2-3.8, with excellent yields of 90-97%. The selectivity was significantly increased to 5.2—6.0 through using the TFSI anion in the IL. 

The use of pyridinium PILs for the esterification of cyclic olefines with acetic acid is summarized in entries 2—4 in Table 7, where it is evident that the choice of anion was significant. The TFSI anion promoted excellent conversions and selectivities, while the TFA anion led to excellent selectivity but poor conversion, and the HSO4 anion produced no reaction at all. ... 

More recently, Tigelaar et al. have developed an alternative polymer membrane to Nafion that contains rigid sulfonated aromatic backbones linked with diamine-terminated poly-(ethylene oxide) (PEO) oligomers. This polymer was developed to increase the amount of ionic liquid in the membrane, where in Nafion, the perfiuorinated nature was thought to be reducing the uptake. The polymer membranes were soaked with a 1 1 mixture of a PIL and water, where the PILs trialed contained the imidazolium cation with either sulfate, triflate, or TFSI anions. The highest conductivity obtained with these polymer membranes was 50 mS/cm at 150 °C with imidazolium—CF3SO3H. ... 

W.A., Phase behavior of ionic liquid-LiX mixtures Pyrrolidinium cations and TFSI anions -linking structure to transport properties, Chem. Mater. 23 (19), 4331 337 (2011). 

B, 109, 22814 (2005). NMR Investigation of Ionic Liquid-LiX Mixtures Pyrrolidinium Cations and TFSI Anions. 

Fig. 10 Crystal structure of PE06 (LiAsF6)i-x(LiTFSI)x. Blue spheres Li ions Pink structures a AsFe anion mixed colors structure b TFSI anion. Taken from Ref. [68] with the permission of the publisher (Color figure online)...

Recently, a series of IL electrolytes were tested for their applications in Li-S cells. Traditionally, the TFSI anion dominates the anion part of the ILs for the Li-S electrolytes, while typical cation examples are including the l-butyl-3- methyl-imidazolium (BMIM), l-ethyl-3-methylimidazolium (EMIM), 1-butyl-1-methy Ipyrrolidinium (PYR14), and 1-butyl-1-methylpiperidinium (PiP14) in Fig. 11 [18]. As in the traditional liquid electrolyte systems, the physical properties determine the solubility power charge distribution, polarity, viscosity and so forth. In the IL systems, however, the permittivity is largely independent of the combination of cations and anions, while variation in cations and anions affects the molecular level interactions, type/strengtii, and solvation. Due to unique properties, the ILs were studied as effective liquid electrolytes for the Li-S cells. 

As stated in Sect. 7.2.1 of this chapter, for electrodes of the first kind, the metal ions should not react with the ILs. Basile et al. have noted that the presence of water results in the formation of silver nanoparticles for solutions of Ag" ions dissolved into [Cqmpyr] [TFSI] [31]. These authors postulate that this occurs via chelation of Ag" by the [TFSI] anion and a subsequent disproportionation reaction in the presence of water to form a Ag -[TFSI] complex and Ag° [31]. Thus, the choice of a reference electrode based on AglAgOTfl[C4mpyr][TFSI] may be problematic. The authors did note that over a short period of time, when chemical reaction rates were low, the FcIFc" reversible potential was close to that reported by Snook et al. [27, 31]. According to Snook et al. [27] the AglAgOTfl[C4mpyr][TFSI] reference electrode is only stable for 3 weeks before the solution needs to be replaced and the electrode remade. Therefore, if the AglAg" couple is to be used in other ILs, then any potential chemical reactions of Ag irais within this IL should be explored prior to use, as well as the stability of the reference electrode over time. 

Holbrey JD, Reichert WM, Rogers RD (2004) Crystal stmctures of imidazolium bis(trifluor-omethanesulfonyl)imide ionic liquid salts the first organic salt with a cs-TFSI anion conformation. Dalton Trans 2267-2271... 

Generally, small sized aliphatic quaternary ammonium cations cannot easily form an ionic liquid, however, by attaching a methoxyethyl group to the nitrogen atom, many aliphatic quaternary ammonium salts can form ionic liquids with BF4 and TFSI anions. For instance, DEME-BF4 and DEME-TFSI are novel ionic liquids whose liquid state covers a wide temperature range (Fig. 2) (Maruo et al.,2002). 

Fig. 8. The discharge capacitance of EDLCs containing various electrolytes. The test cell was discharged at a constant current I = 0.2 A from V = 3.0 to 0 V at 25 °C. Cell capacitance is plotted against the molecular weight of salts, cations and anions for (a), (b) and (c), respectively. The electrolyte concentration was IM in PG ( ) DEME-cation sp>ecies ( ) MEMP-cation species (A) DEMM-cation sp>ecies (x) MMTM-cation species ( ) MMMP-cation species ( ) EMI-cation species in figure (a) and (c). In figure (b) ( ) BFfanion species ( ), PFe-anion species (A) TFSI-anion species. The ptrepared EDLC with IM DEME-BF4 in PC had 44 F g-i of the sp>ecific cap>acitance p>er electrode weight.

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