Development of conversion coatings on iron via corrosion in LiPF6 solution

• Published in: Electrochimica acta 2019-05, Vol.304, p.428-436
• Main Authors: Guitián, B., Nóvoa, X.R., Pintos, A.
• Format: Article
• Language: English
• Subjects: Conversion coatings; Conversion electrodes; Corrosion; Corrosion rate; Electrochemical impedance spectroscopy; Gravimetry; Iron; Li-ion batteries; LiPF6; Photoelectrons; Spectrum analysis; Transmission lines; X ray photoelectron spectroscopy
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2019.03.011

The corrosion process of iron in 1M LiPF6 solution using an ethylene carbonate/diethyl carbonate (EC/DEC) mixture solvent is studied using gravimetric and electrochemical methods. The electrochemical technique employed is electrochemical impedance spectroscopy, EIS, and a special electrode arrangement is used in a pouch cell. The electrochemical and gravimetrical data match reasonably well, indicating a decreasing corrosion rate with time of exposure. The EIS data are analysed using a transmission line model that accounts for the shifts observed in the high frequency limit of the impedance. The data presented suggest that PF6− corrodes Fe to Fe2+ that further evolves to Fe3+, forming porous structures based on FeF3. The formation of Fe3+ has also been confirmed by X-ray photoelectron spectroscopy, XPS analysis. In the presence of non-oxidising salts (e.g., LiBOB, LiBF4), the Fe corrosion rate decreases. [Display omitted] •Iron as an active material and current collector for LiBs.•LiPF6 in typical LiBs electrolyte is corrosive to iron.•The corrosion products layer is porous and reducible to Fe.•EIS allows following the film-forming process.