Onset mechanism of jahn-teller distortion in 4 V LiMn₂O ₄ and its suppression by LiM_0.05Mn_1.95O ₄(M = Co, Ni) coating

There have been several causes for the capacity fading of LiMn ₂O₄ 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, LiMn ₂O₄ 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.