Electrochemical and interfacial behavior of a FeSi2.7 thin film electrode in an ionic liquid electrolyte

A FeSi2.7 thin film is deposited on a copper substrate by RF magnetron sputtering of a Fe-Si alloy target. The electrochemical behavior of the FeSi2.7 electrode in ionic liquid electrolyte based on 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide is investigated and compared with that of a FeSi2.7 electrode in conventional liquid electrolyte. The FeSi2.7 electrode in the ionic liquid electrolyte delivers an initial discharge capacity of 756 mAh g(-1) at room temperature, and its discharge capacity is maintained to be 92% of the initial discharge capacity after the 100th cycle. AC impedance and FTIR analysis reveal that the formation of a stable solid electrolyte interphase (SEI) layer on the FeSi2.7 electrode in the ionic liquid electrolyte leads to a good capacity retention. This study demonstrates that the FeSi2.7 electrode exhibits stable cycling behavior and good interfacial characteristics in the ionic liquid electrolyte without any solvents and additives. (C) 2011 Elsevier Ltd. All rights reserved.