Electrolyte salts trifluoromethanesulfonates

The metallic salts of trifluoromethanesulfonic acid can be prepared by reaction of the acid with the corresponding hydroxide or carbonate or by reaction of sulfonyl fluoride with the corresponding hydroxide. The salts are hydroscopic but can be dehydrated at 100°C under vacuum. The sodium salt has a melting point of 248°C and decomposes at 425°C. The lithium salt of trifluoromethanesulfonic acid [33454-82-9] CF SO Li, commonly called lithium triflate, is used as a battery electrolyte in primary lithium batteries because solutions of it exhibit high electrical conductivity, and because of the compound s low toxicity and excellent chemical stabiUty. It melts at 423°C and decomposes at 430°C. It is quite soluble in polar organic solvents and water. Table 2 shows the electrical conductivities of lithium triflate in comparison with other lithium electrolytes which are much more toxic (24). 

Recently, there has been considerable interest in developing molten salts that are less air and moisture sensitive. Melts such as l-methyl-3-butylimidazolium hexa-fluorophosphate [211], l-ethyl-3-methylimidazolium trifluoromethanesulfonate [212], and l-ethyl-3-methylimidazolium tetrafluoroborate [213] are reported to be hydro-phobic and stable under environmental conditions. In some cases, metal deposition from these electrolytes has been explored [214]. They possess a wide potential window and sufficient ionic conductivity to be considered for many electrochemical applications. Of course if one wishes to take advantage of their potential air stability, one loses the opportunity to work with the alkali and reactive metals. Further, since these ionic liquids are neutral and lack the adjustable Lewis acidity common to the chloroaluminates, the solubility of transition metal salts into these electrolytes may be limited. On a positive note, these electrolytes are significantly different from the chloroaluminates in that the supporting electrolyte is not intended to be electroactive. 

All these electrolytes are neutral in Bronsted acid-base properties. Although rather exceptional, an acid, a base, or a pH buffer may be added to the supporting electrolyte of neutral salts. The acid-base system to be selected depends on the purpose of the measurement. We often use trifluoromethanesulfonic acid (CF3S03F1) as a strong acid acetic acid, benzoic acid, or phenol as a weak acid an amine or pyridine as a weak base and tetraalkylammonium hydroxide (ILtNOH) as a strong base. Examples of buffer systems are the mixtures of picric acid and its R4N-salt and amines and their PlCl04-salts. Here, we should note that the acid-base reactions in aprotic solvents considerably differ from those in water, as discussed in Chapter 3. 

Tetraalkylammonium tosylates [74] and trifluoromethanesulfonates [72] are also excellent electrolytes. Although tetraalkylammonium ions are favored as the cations for supporting electrolytes because of their wide potential range, other cations are sometimes used for special applications—for example, methyltri-phenyl phosphonium, whose tosylate is freely soluble in methylene chloride, and other fairly nonpolar solvents [74] or metal ions (lithium salts tend to have the best solubility in organic solvents) where undesirable reactions of the tetraalkylammonium ion might occur [13,75]. The properties of many electrolytes suitable for nonaqueous use have been surveyed [76]. 

Aromatic sulfonic acid and perfluoroalkanesulfonic acids resins are widely used as ion-exchange resins in water treatment and multiple other industrial applications. In the form of membranes, they are routinely used in electrochemical cells, particularly in electroplating of metals and in battery applications. The lithium salts of trifluoromethanesulfonic acid and N-trifluoromethanesulfonyl trifluoromethanesulfonamide are both employed as electrolytes in secondary battery applications. 

LiSOjCFs. Lithium trifluoromethanesulfonate (triflate— most commonly abbreviated as CF3SO3" in the scientific literature) was at one time widely used for electrolytes, especially for polymer electrolytes [97-107], This salt has a high thermal stability [56] and is not susceptible to hydrolysis due to the stability of the C-F bond. Electrolytes with this salt, however, are found to be notably less conductive than those with LiPFg [5,108-110], and LiSOsCFj-based electrolytes corrode the A1 current collector at high potential [59, 65-67], Thns, while this salt has been extensively nsed for research purposes, it is not used in commercial Li-ion batteries. 

The electrical conductivity of the salt-in-polymer-type polymer electrolyte prepared by dissolving an alkaline salt such as lithium trifluoromethanesulfonic acid lithium into polymethoxy ethyleneglycol methacrylate. The electrical conductivity of the polymerized salt-in-polymer-type polymer electrolyte is a function of the combination of temperature and salt. The Arrhenius plot becomes linear. 

Obtain polymer by isobisisobutyronitrile as an initiator to polymerize it in benzene at 65°C for 48 h. After refining, evaporate the solvent slowly from the mixed solution that dissolved the alkaline salt along with the lithium trifluoromethanesulfonic acid in the anhydride methanol solvent. Solid-state auxiliary battery using a gel electrolyte... 

Kumutha and Alias performed a Fourier transform infrared (FTIR) study of the samples of NR grafted with 30% of PMMA plasticized with EC and containing lithium trifluoromethanesulfonate (LiCFjSOj). The aim of this study was to investigate the interactions between the polymer and salt and also the influence of the plasticizer (EC), on the salted polymer electrolyte. From this study the authors observed the complex formations in NR-LiCFsSOs and EC-LiCF3S03 systems, but no interaction between NR-EC. It was also concluded that the plasticizer molecules had penetrated the salted polymer matrix in NR-LiCF3S03-EC complex. 

Table 11.3 Lithium salts as electrolyte solutes [1] with L1BF4 lithium tetrafluoroborate, LiBF lithium hexafluorophosphate, LiAsFs lithium hexafluoroarsenate, UCIOa lithium perchlorate, Li-triflate lithium trifluoromethanesulfonate Li itnide (LiTFSI) BIS (trifluoromethane) suifonimide lithium...

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