Electrochemical Activities in Li[sub 2]MnO[sub 3]

is shown to be electrochemically active, with a maximum charge capacity of and a discharge capacity of at . A total of of Li can be extracted from , and the first cycle efficiency is regardless of state of charge. Larger charge-discharge capacity is obtained from materials with smaller particle size and larger amount of stacking faults. Composition and structural analyses indicate that Li are removed from both the Li and transitional metal layers of the material during charging. Results from X-ray-absorption fine-structure measurements suggest that the valence of Mn remains at during charging but is reduced during discharging. Charging is accompanied by gas generation: at , oxygen is the main gas detected, and the total amount accounts for of generation from . At an elevated temperature, amount of increases due to electrolyte decomposition. shows poor cycle performance, which is attributed to phase transformation and low charge-discharge efficiency during cycling. Low first-cycle efficiency, gas generation, and poor cycle performance limit the usage of in practical batteries.