Passivation behaviour of aluminium current collector in ionic liquid alkyl carbonate (hybrid) electrolytes

• Published in: Npj Materials degradation Vol. 2; no. 1
• Main Authors: Theivaprakasam, Sowmiya, Girard, Gaetan, Howlett, Patrick, Forsyth, Maria, Mitra, Sagar, MacFarlane, Douglas
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 29.03.2018; Nature Publishing Group
• Subjects: 639/4077/4079/891; 639/638/161/891; Accumulators; Aluminum; Chemistry and Materials Science; Cobalt compounds; Collectors; Composition; Corrosion; Corrosion and Coatings; Corrosion inhibitors; Corrosion tests; Electrochemical analysis; Electrochemistry; Electrolytes; Flux density; Ionic liquids; Ions; Lithium; Lithium batteries; Lithium-ion batteries; Manganese; Materials Science; Oxidation; Passivity; Rechargeable batteries; Solvents; Storage batteries; Storage capacity; Structural Materials; Surface properties; Tribology; X ray photoelectron spectroscopy
• ISSN: 2397-2106; 2397-2106
• DOI: 10.1038/s41529-018-0033-6

The compatibility of current collectors with the electrolyte plays a major role in the overall performance of lithium batteries, critical to obtain high storage capacity as well as excellent capacity retention. In lithium-ion batteries, in particular with cathodes that operate at high voltage such as lithium nickel cobalt manganese oxide, the cathodic current collector is aluminium and it is subjected to high oxidation potentials (>4 V vs. Li/Li + ). As a result, the composition of the electrolyte needs to be carefully designed in order to stabilise the battery performance as well as to protect the current collectors against corrosion. This study examines the role of a hybrid electrolyte composed of an ionic liquid ( N -methyl- N -propyl pyrrolidinium bis(trifluoromethanesulfonyl)imide or N -methyl- N -propyl pyrrolidinium bis(fluorosulfonyl)imide) and a conventional electrolyte mixture (LiPF 6 salt and alkyl carbonate solvents) with correlation to their electrochemical behaviour and corrosion inhibition efficiency. The hybrid electrolyte was tested against battery grade aluminium current collectors electrochemically in a three-electrode cell configuration and the treated aluminium surface was characterised by SEM/EDXS, optical profilometry, FTIR, and XPS analysis. Based on the experimental results, the hybrid electrolytes allow an effective and improved passivation of aluminium and lower the extent of aluminium dissolution in comparison with the conventional lithium battery electrolytes and the neat ionic liquids at high anodic potentials (4.7 V vs. Li/Li + ). The mechanism of passivation behaviour is also further investigated. These observations provide a potential direction for developing improved hybrid electrolytes, based on ionic liquids, for higher energy density devices. Battery electrolytes: helping with hybrids The use of ionic liquids in hybrid electrolytes has reduced the corrosion of an important Li-ion battery component. Aluminium current collectors in Li-ion batteries are susceptible to corrosion when subjected to high oxidation potentials and thus the composition of the electrolyte is critical to both battery performance and stability. The addition of ionic liquids to conventional carbonate-based solvents has previously demonstrated corrosion inhibition. Now, Sowmiya Theivaprakasam and colleagues, as part of an international collaboration between researchers at Deakin University and Monash University in Australia and the Indian Institute of Technology Bombay in India, have confirmed the corrosion inhibition properties of hybrid electrolytes, specifically those featuring a pyrrolidinium ionic liquid. Using surface characterisation techniques they show that bis(fluorosulfonyl)imide and bis(trifluoromethanesulfonyl)imide anions enable improved passivation at the aluminium surface.