The lithium-rich limit of the electrolyte stability window of the fast-ion-conducting defect perovskite Li0.29La0.57TiO3 was found to be about 1.7 V vs. Li at 24 degrees 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 (D) over tilde > 10(-7) cm(2)/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.