Insertion of lithium into mesoscopic anatase electrodes – an electrochemical and in-situ EQCM study

Abstract

The insertion of Li⁺ into mesoscopic TiO₂ (anatase) electrodes was studied using cyclic voltammetry combined with the in situ gravimetric monitoring of the electrode mass in LiClO₄ and Li(CF₃SO₂)₂ N/propylene carbonate (PC)-based solutions. The insertion of Li⁺ takes place at potentials less than 2.0 V vs Li/Li⁺. The cathodic process is associated with a mass uptake; the subsequent oxidation process is associated with a mass decrease. The apparent molar mass of the inserted/extracted material is, however, remarkably different from that expected for the simple insertion/extraction of unsolvated Li⁺ ions. For a more accurate description of the behaviour of the mesoscopic anatase electrodes, we consider them as gold electrodes modified with a porous film. Thus, the mesoscopic anatase electrode behaves similarly to a polymer-modified electrode, i.e. the overall process includes coupled electron/ion transfer (insertion of Li⁺) and a transfer of neutral species. Analysing the EQCM (electrochemical quartz crystal microbalance) data, one can conclude that the controlling step of the insertion/extraction of Li⁺ into/from anatase electrodes is a coupled electron/ion transfer or the transfer of neutral species in solutions containing ClO₄ ⁻ and (CF₃SO₂)₂N⁻ respectively.