Investigation of the Electrochemical Behaviour of Al Current Collector Material Polarised Highly Anodically and Located in Butyltrimethylammonium Bis(trifluoromethylsulfonyl)imide Room-Temperature Ionic Liquid

The electrochemical behaviour of Al, used as a current collector in supercapacitors and in Li-ion and Na-ion electrochemical power sources, was investigated for the first time using the in situ soft X-ray photoelectron spectroscopy (XPS) method, collecting the information directly at the electrolyte-covered Al current collector polarised electrochemically at high anodic potentials. Cyclic voltammetry, electrochemical impedance spectroscopy, and synchrotron in situ soft XPS methods were applied to collect physical and electrochemical information characterising the electrochemically polarised Al-current-collector RTIL interface soaked into the butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N4111(TFSI)) room-temperature ionic liquid. The obtained data show the start of intensive oxidation processes, including aluminium oxidation and the formation of an insoluble Al(TFSI)3 surface layer in N4111(TFSI) at E ≥ 3.0 V (vs. Ag-QRE). Very intensive electro-oxidation of TFSI− anions at E ≥ 6.5 V (vs. Ag-QRE) has been observed. CV data indicate that the electrochemical oxidation of once-activated Al is possible in N4111(TFSI) at 1.1 V < E < 1.6 V (vs. Ag-QRE). Therefore, the oxidation of Al starts at E ≥ 2.05 V (vs. Ag-QRE) if the Al surface is modified with electro-oxidation products of TFSI− anions.