Development of conversion coatings on iron via corrosion in LiPF6 solution

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. (C) 2019 Elsevier Ltd. All rights reserved.