The lithium-rich limit of the electrolyte stability window of the fast-ion-conducting defect perovskite Li029La057TiO3 was found to be about 1.7 V vs. Li at 24°C.The coulometric titration curve was determined, indicating that reversible insertion/extraction of 0.14 additional Li, corresponding to the complete occupation of the vacant A-sites, is possible.The galvanostatic intermittent titration technique was used to evaluate the chemical diffusion coefficient as a function of composition. It was very high, and varies less than a half-order of magnitude over this stoichiometry range. Values of 0> 1 0 cm2/s were found both for lithium insertion and for lithium extraction. To our knowledge this is one of the highest diffusion coefficients observed in a lithium-conducting insertion-reaction oxide.
Evidence of Two-Phase Formation Upon Lithium Insertion into the Li 1.33 Ti 1.67 O 4 Spinel.-The title compound is prepared from Li 2 CO 3 and TiO 2 and Li is electrochemically inserted at room temperature. The defect spinel compound Li 1.33 Ti 1.67 O 4 and the fully lithiated compound Li 2.33 Ti 1.67 O 4 with ordered rock salt type structure show nearly identical X-ray patterns. Precise analysis of the obtained data supplies evidence for the presence of two distinct phases which are mutually interconvertible upon Li exchange. -(SCHARNER, S.; WEPPNER, W.; SCHMID-BEURMANN, P.; J.
The high oxygen and lithium ion conductivity in LiNbO3 was investigated and interpreted in terms of lithium and oxygen vacancies being intrinsically present in congruently grown single crystals. As a result of this, it was found that the stoichiometry of lithium niobate crystals may be changed with respect to lithium and oxygen. The optical and electrical properties of electrically colored LiNbO3 crystals were studied and it was shown that the absorption spectra of thermally reduced and electrocolored samples are identical. Therefore, the origin of the absorption processes is considered to be the same in both cases. The formation of regions with different stoichiometry due to the injection of additional lithium or oxygen into the LiNbO3 crystals was also observed and investigated. The motion of these stoichiometric domains through a LiNbO3 crystal from one electrode to the other was studied and described in terms of electrodiffusion of the ions and electrons. A model is proposed which considers the injection of oxygen and lithium vacancies for the generation of concentration profiles in the originally homogeneous material. The numerical calculation of the concentration profiles shows good agreement with the experimental results.
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