Li insertion into Li-Ti-O spinels: Voltammetric and electrochemical impedance spectroscopy study

The insertion of Li into nanocrystalline Li-Ti-O spinel electrodes was stud ied using cyclic voltammetry combined with electrochemical quartz crystal m icrobalance, open circuit potential measurements, and electrochemical imped ance spectroscopy studies. Insertion characteristics of spinel were compare d with those of titania polymorphs. The insertion into spinet occurs at pot ential 300 mV more negative to that of insertion into anatase, and about 40 mV positive to that into rutile. The specific capacity (160 mAh/g) is comp arable with that of TiO2 polymorphs. Due to the relatively negative potenti al of the insertion and significantly lower tendency to self-discharge, Li- Ti-O spinel is more convenient for use in a 2 V lithium-ion battery than ar e other active phases in the Li-Ti-O system. The behavior of the spinel ele ctrodes in equilibrium can be described by the Frumkin insertion isotherm m odel. The value of interaction parameter, g, below -4 indicates that the in sertion process leads to a first-order phase transition. Diffusion coeffici ent of Li in spinel ranges between 10(-15) and 10(-16) cm(2) s(-1); the cha rge transfer kinetics depends on the redox composition. Heterogeneous rate constant ranges between 1 x 10(-8) and 4 x 10(-10) cm s(-1) that is ca. two orders of magnitude higher than that reported for anatase. (C) 2001 The El ectrochemical Society.