MECHANISM OF IONIC-CONDUCTION AND ELECTROCHEMICAL INTERCALATION OF LITHIUM INTO THE PEROVSKITE LANTHANUM LITHIUM TITANATE

The ionic conductivity and electrochemical intercalation properties of La2/3-xLi3xTiO3 solid solutions (for 0.07 less than or equal to x les s than or equal to 0.13) have been studied. These compounds present a perovskite-type structure (ABO(3)) with cation deficiency at the A-sit es. The purely ionic conductivity was confirmed and the mechanism of i onic conduction investigated using impedance spectroscopy techniques. We find that the temperature dependence of conductivity can be modeliz ed by a Vogel-Tamman-Fulcher (VTF)-type relationship. In these materia ls, where the high ionic conductivity may originate from the presence of vacancies in the A-sites of the perovskite structure, the VTF behav ior would suggest a mechanism of conduction involving the tilting of t he TiO6 octahedra. The lithium intercalation was also investigated in LiClO4(M)-PC electrolyte using galvanostatic discharge and charge at v ery low rates (one Li/250 and /1500 h) in order to approach the equili brium. It was shown that the lithium intercalation leads to the presen ce of a plateau around 1.5 V/Li in the discharge curve, it is partly r eversible and the capacity of the electrode is not very high. A maximu m lithium uptake of 0.15 was found. The diffusion coefficient of lithi um in the intercalated material was determined by impedance spectrosco py at room temperature and found to range from 10(-8) cm(2) s(-1) to 1 0(-9) cm(2) s(-1) as intercalation proceeds. Since the experimental im pedance spectroscopy data performed at room temperature follow a Warbu rg behavior at low frequency, the intercalation seems to proceed in a single-phase process although a plateau is observable in the discharge curve.