Electrochemical deposition and dissolution of metallic lithium in various phosphonium ionic liquids with bis(trifluoromethylsulfonyl)imide anion were evaluated by cyclic voltammetry using a Ni electrode. In the voltammograms measured in phosphonium ionic liquids containing 0.8 mol dm(-3) lithium cation, cathodic and anodic peaks attributed to the deposition and dissolution of metallic lithium were observed at approximately -3.1 V vs Fc/Fc(+). It was also found that phosphonium ionic liquids tended to give larger redox responses for the lithium deposition/dissolution than those of the corresponding ammonium ionic liquids. (c) 2007 The Electrochemical Society.