Electrochemical intercalation of lithium into the perovskite-type NbO2F: influence of the NbO2F particle size

Niobium(V) oxyfluoride, NbO2F, has a perovskite structure and presents the property of lithium intercalation by topotactic chemical reaction either wi th n-butyllithium dissolved in n-hexane or by electrochemical reaction. The intercalation leads to the reduction of the transition metal from the oxid ation state Nb(V) to the oxidation state Nb(III). This allows a theoretical Li/NbO2F intercalation ratio of 2. In this paper we will show that this th eoretical value can be approached by using micron the sized active material particles. Moreover, the electrical properties of the cathode studied by t he galvanostatic intermittent titration technique and a.c. impedance spectr oscopy are explained in terms of structural and grain size considerations. Results of cycling experiments are also described.