Formation and Structural Properties of Layered LiMnO[sub 2] Cathode Materials

and compounds (x ≤ 0.10) with an layer‐type crystal structure have been prepared by a high temperature solid‐state route. The compounds are well ordered with Al or Cr sharing the Mn sites and no detectable cation mixing between Mn and Li layers. Both Al‐ and Cr‐substituted materials cycled between 4.4 and 2.0 V in Li cells at 55°C show high stability of capacity. However the Al‐substituted materials undergo a structural transformation to a spinel‐type phase, accompanied by evolution of the discharge voltage curve to a two‐plateau profile. Materials modified with small amounts of Cr show a different evolution of the discharge voltage. X‐ray diffraction data for cycled cathodes show that these compounds do not undergo significant transformation to spinel on cycling, but retain a hexagonal structure established on first charge. © 2000 The Electrochemical Society. All rights reserved.