Aluminum Electrodeposition from Chloride-Rich and Chloride-Free Organic Electrolytes

Abstract

The corrosivity of chloride-based electrolytes is a major shortcoming in the practical realization of rechargeable aluminum batteries. Herein, the effect of Cl − on Al speciation and electrochemistry in tetrahydrofuran (THF) was measured by employing theoretical and experimental approaches for three systems: Al(OTF) 3 /THF, Al(OTF) 3 plus LiCl in THF, and AlCl 3 /THF. The high consistency between measured and computed spectroscopic aspects associated with Al(OTF) 3 /THF electrolyte provided both a rationale for understanding Al complex-ion formation in a Cl − -free environment and an approach for examining the effect of Cl − on Al speciation. Room-temperature Al plating was achieved from dilute solutions ([Al] = 0.1 M) at potentials ≥ 0 V (vs Al/Al 3+ ). Cl − is found to enable facile Al plating and SEM reveals that Al is electrochemically deposited as nanocrystalline grains.

Hydride-Enhanced Plating and Stripping of Aluminum from Tri-flate -Based Organic Electrolytes

“…Motivated by the exceptional work conducted by Frech et al [45][46][47][48] on the spectroscopic attributes of the OTF -, in our previous work on Al(OTF)3/THF we described a new method that allows for the determination of the reaction progress between Al(OTF)3 and Li-based salts by exploiting the computed and measured spectroscopic features of the OTF -. 34 Indeed, these results are well represented by the FTIR measurements shown in Figure 1G. Upon the addition of LiAlH4 to the Al(OTF)3/THF electrolyte at 1:3 mole ratio's, a shift in frequency from 1238 to 1253 cm -1 , corresponding to the transfer of the OTFfrom Al to Li ions, is observed.…”

“…FTIR spectra for the Cl --based electrolytes shown in Figure 1H,I reveals that the bands associated with AlCl3(THF), cis-and trans-AlCl3(THF)2, those previously identified in an AlCl3/THF solution, 34,49 remain intact. However, peaks attributable to a new species are observed at 501 and 667 cm -1 .…”

“…27 Unlike the Al(OTF)3/diglyme electrolyte, however, non-reversible Al electrodeposition can be carried out from Al(OTF)3 in tetrahydrofuran (THF) electrolytes, as we have revealed in our previous reports. 32,34 To highlight the role of hydrides (H -) in the Al plating/stripping process, in this report, we demonstrate reversible Al plating/stripping from an active-halide-free organic electrolyte based on Al(OTF)3/THF facilitated by a lithium aluminum hydride (LiAlH4) additive. The spectroscopic and electrochemical aspects of the trifluoromethanesulfonate (OTF -)-based electrolyte were evaluated and compared to the well-known chloride (Cl -)-based system.…”

“…Moreover, the νas(Al-Cl) band for AlCl3(THF)2 was measured at 490 cm -1 in the AlCl3/THF electrolyte. 34,49 The shift in frequency for the νas(Al-Cl) mode from 490 to 501 cm -1 suggest that strong ionic association is taking place. It is important to note that the presence of AlCl3Hin a Hrich environment was confirmed by the detailed NMR studies conducted by Lefebvre and Conway, 42 however, computational and experimental evidence for the ionic association of AlCl3Hwith AlH3 is presented here for the first time.…”

“…26 Thus far, only a handful of active-halide-free organic electrolytes have been reported. [27][28][29][30][31][32][33][34] A timeline showing the progress in organic electrolyte development for rechargeable Al battery is shown in Figure S1. Early work on active-halidefree electrolytes involved aluminum trifluoromethanulfonate (Al(OTF)3) and urea in N-methyl acetamide (NMA), 29 and Al(OTF)3 in 2-methoxy ethyl ether (diglyme).…”