Electrolytes superacids

Like LiAsFe, LiBF4 is a salt based on an inorganic superacid anion and has moderate ion conductivity in nonaqueous solvents (Table 3). It was out of favor in the early days of lithium battery research because the ether-based electrolytes containing it were found to result in poor lithium cycling efficiencies, which decayed rapidly with cycle number. ° The reactivity of LiBF4 with lithium was suspected as discoloration occurred with time or heating. 

The most important use of /3-sultones is for the preparation of fluorinated polymers such as Nafion 64. These solid acid catalysts containing perfluorinated sulfonic acid groups have been known for many years and the presence of the electron-withdrawing F atoms increases the acid strength of the terminal sulfonic acid groups, which become comparable to that of pure sulfuric acid. Prior to the last decade, Nafion had been in use as a superacid, a fuel cell electrolyte and as a membrane-ion separator <1996CHEC-II(1B)1083>. 

Many/most of the anions used for electrolyte lithium salts were initially developed in efforts to generate stronger superacids. The term superacid generally refers to acids which are more acidic than mineral Brpnsted acids [20-27]. In particular, a widely used definition for superacids was given by Gillespie who defined this term to be applicable to acids which are more acidic than sulfuric acid [28-30]. The stronger the acidity, the weaker the coordination of the anions is with the associated protons (H cations). The gas-phase acidity is given by ... 

In fact, two-phase electrolytic media do not constitute practical systems for electrochemistry, and homogeneous benzene-acid solutions appeared preferable. These were achieved by using various mixtures of strong acids and superacids. 

On the basis of the model described above, one would expect that the enhancement of the transport properties should depend upon the degree of acidity of the ceramic s surface states. This is indeed the case as demonstrated by the behaviour of PEO-based polymer electrolytes using ceramic fillers with a high surface acidity, e.g. the sulfate-promoted superacid zirconia, S-ZrOi. The results show that this ceramic filler considerably enhances the transport properties of the electrolyte. 

CROCE, F., SETTiMi, L. and scROSATi, B.,2006. Superacid Zr02-added, composite polymer electrolytes with improved transport properties. Electrochemistry Communications, 8(2), 364-368. 

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