Correlating Electronic Structure with Cycling Performance of Substituted LiMn₂O₄ Electrode Materials:  A Study Using the Techniques of Soft X-ray Absorption and Emission

Rechargeable batteries using LiMn₂O₄ cathodes are commercially attractive, if the problem of excessive capacity fading can be overcome. The cycling properties of these systems can be improved by partial metal substitution for the Mn. To understand the correlation between electrode performance and composition, Mn, Co, and Ni L-edge XAS and XES spectra of a series of LiMn_2-yMe_yO₄ samples (Me = Co, Ni, Li) were recorded. Cobalt is shown to substitute into the spinel system as Co(III) and nickel as Ni(II). A positive correlation between the cycling stability of the electrode and the covalency of the Mn is observed.