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

The synthesis of the perovskite Li 0.3 La 0.566 TiO 3 by a Pechini-type polymerizable precursor method is described. TGA-DTA analysis was carried out on the precursors, and powder XRD analysis was performed on the final products obtained by heating the precursors over a temperature range from 600 to 900 °C during 2 h. Highly pure and crystalline powders were obtained by this method. The morphology of the powder after heating at 900 °C was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The determination of the grain size by an optical method shows the formation of small grains around 100 nm in size that aggregate. This chemical method allowed us to obtain well crystallized lithium lanthanum titanate (LLTO) at a much lower temperature and with a shorter synthesis time in comparison to the conventional solid-state reaction method.

The layered perovskite compound LiLaNb2O7 is a lithium-deficient material. This product is obtained by ion exchange in molten salt from KLaNb2O7. Electrochemical intercalation of lithium ions is possible and leads to the formation of Li,+a,LaNboO7.The intercalation is investigated in LiC1O4(M)-PC electrolyte using galvanostatic discharge, the galvanostatic intermittent titration technique, and impedance spectroscopy. A maximum lithium uptake of x = 1 was found without any structural change. The discharge curve clearly shows the existence of interactions between the host material and the intercalated lithium ions as intercalation proceeds. The energy of these interactions remains small for x <0.5 and increases drastically to 1 eV for x> 0.5. A detailed study of the discharge curve shows that superlattice orderings of Li ions appear at x = 0.25 and 0.5 leading to a small but sudden change of the electrode potential. Complex impedance spectroscopy, performed during the discharge, shows that for x < 0.5 the charge-transfer reaction occurs with the adsorption of intermediate species. This adsorption reaction disappears for x> 0.5. An equivalent electrical model which includes charge-transfer, adsorption, constant-phase elements, and diffusional impedance is proposed. The fit between the experimental data and this model is good and leads to the determination of the kinetics parameters as a function of x. The mechanism of the intercalation is discussed on the basis of the crystallographic structure of the layered perovskite.