The stability of Li4Ti5O12 spinet material in acidic solutions has been examined. Proton exchange with Li ions in Li4Ti5O12 is observed when in contact with acidic solutions. The spinet structure is retained up to 68% exchanged ions. This is associated with a 0.25% reduction of volume from the initial spinet. The protons reside on the 8a and 48f sites that form alternating planes with 16d Li and Ti sites in the spinel structure. Electrochemical results of the ion exchange material show a general decrease of capacity as more protons are present in the structure. Potential curves suggest that two solid solution phases are found above and below the 1.55 V two-phase plateau. In addition, electrochemical studies have shown that the initial material may react with water from the atmosphere under storage that slightly degrades the performance of this material. (c) 2006 Elsevier B.V. All rights reserved.