Evidence of Two‐Phase Formation upon Lithium Insertion into the Li_1.33Ti_1.67 O ₄ Spinel

synthesized from and was electrochemically inserted with lithium at room temperature. The defect spinel and the fully lithiated with ordered rock‐salt‐type structure show nearly identical X‐ray diffractions. Due to similar lattice constants of both phases and the low scattering factor of the lithium ions, the identification of the insertion mechanism using X‐ray powder diffraction is possible only by using high angle X‐ray scans of several samples inserted with different amounts of lithium. Precise analysis of the obtained data supplies the evidence for the presence of two distinct phases which are mutually interconvertible upon lithium exchange. This result is in good agreement with electrochemical data postulating a two‐phase mechanism from the constant electrical potential found during cycling. © 1999 The Electrochemical Society. All rights reserved.