Linear-Sweep Thermammetry Study on Corrosion Behavior of Al Current Collector in Ionic Liquid Solvent

Abstract

The corrosion behavior of Al foil as the current collector for lithium-ion batteries is studied by linear-sweep thermammetry. The onset temperature for Al pitting corrosion depends on Li salt that is dissolved in an ionic liquid solvent; lithium bis͑trifluo-romethanesulfonyl͒imide ͑LiTFSI͒ Ͻ lithium bis͑perfluoroethanesulfonyl͒imide ͑LiBETI͒ Ͻ LiPF 6 Ͻ LiBF 4 . With LiBF 4 , no corrosion current is observed until 110°C. X-ray photoelectron spectroscopy study reveals that this Al surface is covered by Al-F compound ͑presumably AlF 3 ͒. Due to the formation of a highly passivating AlF 3 layer in this electrolyte, the high voltage LiNi 0.5 Mn 1.5 O 4 positive electrode coated on Al foil can be successfully cycled at 65°C without electrode failure.One of the recent issues in lithium-ion batteries ͑LIBs͒ is, among others, the cell life that is deeply associated with the thermal stability of the cell constituents. An occasional high temperature exposure causes a thermal degradation of electrode/electrolyte materials, leading to a shortened cell life. In this sense, the room-temperature ionic liquids ͑RTILs͒ that have a superior thermal stability to the organic solvents have been projected as the solvent for long-lived LIBs. [1][2][3][4] For RTILs to be used as the solvent for thermally stable ͑therefore, long-lived͒ LIBs, however, they should also be inert to the corrosion of Al foil that is used as the current collector for the positive electrodes of LIBs. That is, the breakdown of the native oxide ͑Al 2 O 3 ͒ upon high temperature exposure, which passivates the Al surface in a normal condition, can lead to cell failure. 5 The corrosion/passivation behavior of bis͑trifluoromethane-sulfonyl͒imide ͑TFSI͒ anion was reported. 6,7 When LiTFSI is dissolved in organic solvents, the anion attacks the native Al 2 O 3 to generate Al-TFSI compounds that is soluble in organic solvents to lead Al corrosion. In ionic liquid solvents, however, Al corrosion is greatly reduced because the Al-TFSI compounds are insoluble in ionic liquids. 8,9 The literatures on the corrosion behavior of RTILs at either ambient temperature or elevated temperatures are still quite limited. In this work, the RTIL ͓propylmethylpyrrolidinium ͑PMPyr͒-TFSI͔ effectively passivates an Al surface up to 5.0 V ͑vs Li/Li + ͒ at room temperature, but its protection becomes poorer at elevated temperatures. The selection of appropriate Li salt ͑LiBF 4 ͒, however, improves the passivation behavior even at elevated temperatures. ExperimentalThe used PMPyr-TFSI was prepared according to the previous report. 10 Coin-type cells ͑2032 size, Hohsen͒ were assembled with an Al foil electrode ͑Donghae, Ͼ99.85%, 20 m thick͒, a glass filter separator ͑Advantec, GA-55, 0.21 mm thick, 0.6 m pore͒, lithium metal foil ͑Cyprus͒, and an electrolyte. The Al working electrodes were prepared to be 1.1 cm in diameter and exposed to the electrolyte side in a cell. The electrolytes were prepared by dissolving 1.0 M lithium salts ͓LiTFSI ͑3M͒, LiBETI ͑Chemtall͒, LiPF 6 ͑Aldrich͒, and LiBF 4 ͑...

Reversible Intercalation of Bis(trifluoromethanesulfonyl)imide Anions from an Ionic Liquid Electrolyte into Graphite for High Performance Dual-Ion Cells

“…79 However, the corrosion of the aluminum current collector cannot be completely excluded and becomes even more serious at elevated temperatures. 80 The aim of the previously described investigations was to identify the optimal cut-off voltage for both dual-ion cell systems. The result is that a compromise between high discharge capacities and high efficiencies is necessary in order to minimize decomposition or degradation reactions of the electrolyte and the positive graphite electrode.…”

Physical and Electrochemical Properties of Some Phosphonium-Based Ionic Liquids and the Performance of Their Electrolytes in Lithium-Ion Batteries

“…7 In the last decade, a group of compounds called ionic liquids (ILs), has been of interest as an alternative to conventional battery electrolytes due to their excellent thermal and physiochemical properties such as non-flammability, negligible vapor pressure, good dissolution power, good electrochemical stability, wide liquid range and intrinsic ionic conductivity. [7][8][9][10][11][12][13] Despite these aforementioned properties, some ILs suffer from poor cathodic stability, very high viscosity, incompatibility with other active and inactive battery components, impurities and high cost which make their application as electrolytes a challenging task. 14 However, the right combination between a certain cation and anion (which can produce a huge number of possible ILs) can result in an IL that has the desired properties for an electrolyte for Li-ion batteries.…”

The Corrosion Study of Al Current Collector in Phosphonium Ionic Liquid as Solvent for Lithium Ion Battery

“…2 current at the 1st cycle is relative high, however it decreases along cycling processing. This phenomena is explained by passivation theory from previous papers 7,9) . FE-SEM analysis was conducted to visualize the surface of electrode to confirm absent of Al corrosion on the electrode.…”

“…Mostly RTILs were composed of TFSI anion to delocalize electron on anion to hinder coulombic interaction between ions, but TFSI anion is severely electrochemically-corrosive to Al substrate which is a conventionally requisite as current collector 6) . Although RTIL having TFSI is not corrosive to Al even at oxidative potential, however Al was corroded at elevated temperature 7) . From these, we studied Al corrosiveness of phosphonium along temperature to solve the problem of Al corrosion at elevated temperature.…”