Conductivities and Electrochemical Stabilities of Lithium Salts of Polyfluoroalkoxyaluminate Superweak Anions

Abstract

Six lithium salts of tris-and tetrakis͑polyfluoroalkoxy͒aluminate superweak anions have been studied for their potential use as battery electrolytes. Four of the six are based on the formula LiAl͑OCR͑CF 3 ) 2 ) 4 (R ϭ H, Me, CF 3 , Ph); the other two are LiAl͑OCH 2 CF 3 ) 4 and LiAlF͑OCPh͑CF 3 ) 2 ) 3 . The thermally stable electrolytes LiAl͑OCH͑CF 3 ) 2 ) 4 and LiAl͑OCPh͑CF 3 ) 2 ) 4 were not oxidized at potentials less than or equal to 5.0 V vs. Li ϩ/0 in dimethoxyethane ͑DME͒ or in 50:50% ethylene carbonate:dimethylcarbonate ͑EC:DMC͒. The LiAl͑OCH͑CF 3 ) 2 ) 4 electrolyte was not reduced at 0 V vs. Li ϩ/0 in DME. Neither LiAl͑OCH͑CF 3 ) 2 ) 4 nor LiAl͑OCPh͑CF 3 ) 2 ) 4 promoted the corrosion of aluminum at 5.0 V vs. Li ϩ/0 . The electrolyte LiAl͑OCH͑CF 3 ) 2 ) 4 underwent efficient, reversible reductive intercalation of Li ϩ with MCMB carbon or LiCoO 2 electrodes over the potential ranges 0-2 and 2.4-4.8 V, respectively, vs. Li ϩ/0 , but did not react in any other way with these electrode materials. The conductivities of some of the LiAl͑OR F ) 4 electrolytes in DME or in EC:DMC were high enough for them to be considered as potential replacements for LiPF 6 in primary and secondary lithium batteries.

Tetraalkylammonium Salts of Weakly Coordinating Aluminates: Ionic Liquids, Materials for Electrochemical Applications and Useful Compounds for Anion Investigation

“…Quantum chemical calculations [15] as well as electrochemical measurements [16][17][18][19][20] of the lithium salts show the fluoroalkoxyaluminates Keywords: density functional calculations · electrochemistry · ionic liquids · tetraalkylammonium cations · weakly coordinating anions (WCAs) very redox stable [1] ; [7,15,17] their salts are usually soluble in media with low dielectric constants (stability vs Li/Li + in DME: > 5.0 V for [hfip] À and 5.5 V for [pftb] À ). Moreover we have shown that even very reactive cations like simple carbenium ions (CI 3 + ) [21,22] or reactive cations like PX 4 + , [23,24] AsBr 4 + , [25] [27] or P 7 S 6 I 2 + [28] (X = halogen) are compatible (i.e., could be stabilized) as salts of these aluminates.…”

Anodic oxidation of organometallic sandwich complexes using [Al(OC(CF3)3)4]− or [AsF6]− as the supporting electrolyte anion

“…The structure was solved with the Patterson method (SHELXS97), and then refined stepwise by full-matrix least squares refinement on F 2 with SHELXL97. 6 ] (Ozark Mahoning) in aqueous methanol, recrystallized from dichloromethane/ether, and vacuum dried. Ferrocene, ruthenocene and nickelocene (Strem) were vacuum sublimed.…”

“…The preparation of bis(fulvalene)dinickel, 1, has been previously described [17]. The sample used for this study was 1 [PF 6 ]. Since the concentration of this sample in electrolyte solution was about 100-fold less than that of the supporting electrolyte, the presence of the [PF 6 ] À should have minimal effect on the DE 1/2 values measured for 1.…”

“…Supporting electrolytes containing weakly-coordinating anions (WCAs) have proven to be superior to more traditional electrolyte anions such as [BF 4 ] À or [PF 6 ] À for the stabilization of reactive organometallic radical cations [1]. Among the WCAs used for organometallic electrochemistry, the fluoro-substituted aryl borates [B(C 6 F 5 ) 4 ] À (TFAB) and [B(C 6 H 3 (CF 3 ) 2 ) 4 ] À (BArF 24 ) have garnered the greatest attention [1][2][3].…”

“…Conductivities have been reported for their lithium [6] and tetraalkylammonium [7] salts, and it has been established that the anions are quite resistive to anodic oxidation [6,7]. A number of very reactive organic or inorganic cations have been stabilized and isolated as their [Al(OC(CF 3 ) 3 [9], electrophilic E-X cations (E = P, As, X = halogen) [10], and strong cationic Brønstead acids [11].…”