Mechanism of ionic conduction and electrochemical intercalation of lithium into the perovskite lanthanum lithium titanate
Abstract The ionic conductivity and electrochemical intercalation properties of La 2 3−x Li 3 x TiO 3 solid solutions (for 0.07 ≤ x ≤0.13) have been studied. These compounds present a perovskite-type structure (ABO 3 ) with cation deficiency at the A-sites. The purely ionic conductivity was confirmed and the mechanism of ionic conduction investigated using impedance spectroscopy techniques. We find that the temperature dependence of conductivity can be modelized by a Vogel-Tamman-Fulcher (VTF)-type relationship. In these materials, where the high ionic conductivity may originate from the presence of vacancies in the A-sites of the perovskite structure, the VTF behavior would suggest a mechanism of conduction involving the tilting of the TiO 6 octahedra. The lithium intercalation was also investigated in LiClO 4 (M)-PC electrolyte using galvanostatic discharge and charge at very low rates (one Li/250 and /1500 h) in order to approach the equilibrium. It was shown that the lithium intercalation leads to the presence of a plateau around 1.5 V/Li in the discharge curve, it is partly reversible and the capacity of the electrode is not very high. A maximum lithium uptake of 0.15 was found. The diffusion coefficient of lithium in the intercalated material was determined by impedance spectroscopy at room temperature and found to range from 10 −8 cm 2 s −1 to 10 −9 cm 2 s −1 as intercalation proceeds. Since the experimental impedance spectroscopy data performed at room temperature follow a Warburg behavior at low frequency, the intercalation seems to proceed in a single-phase process although a plateau is observable in the discharge curve.