Onset mechanism of Jahn-Teller distortion in 4 v LiMn2O4 and its suppression by LiM0.05Mn1.95O4 (M = Co, Ni) coating

There have been several causes for the capacity fading of LiMn2O4 reported by many authors, which include Mn dissolution into the electrolyte, and the onset of a Jahn-Teller distortion. One of the main remedies suggested to combat those causes has been doping with other transition-metal ions. However, most of the deterioration reactions take place on the LiMn2O4 surface. In this study, LiMn2O4 was coated with a doped-spinel oxide to combat the causes of capacity fading in LiMn2O4, which modifies only the surface of the electrodes, and its effect was diagnosed using the bending beam method (BBM). The doped-spinel coated LiMn2O4 showed an excellent cycle performance. From the BBM data, it was confirmed that this excellent performance was largely due to the suppression of the Jahn-Teller distortion, which takes place at the end of the cathodic sweep in the 4 V range. Furthermore, the mechanism for the onset and suppression of Jahn-Teller distortion in 4 V LiMn2O4 is proposed based on the strain variations of the stoichiometric, doped, and doped-spinel coated spinel electrodes. (c) 2005 The Electrochemical Society.