Cobalt substitution in lithium manganate spinels: examination of local structure and lithium extraction by XAFS

Abstract

Lithium manganate spinel LiMn₂O₄ was partially substituted with Co and chemically delithiated and relithiated. Variations in the local structure surrounding the substitutional ion, which are probed by EXAFS and XANES, are related to the long range (average) structure and performance as battery cathode materials. The substituent ion is randomly distributed in the spinel and present as trivalent ions replacing Mn³⁺. The substituent ion stabilises the lattice through a reduction in Jahn–Teller distortion of the lattice at the local level, but can limit the quantity of lithium that may be extracted due to its redox inactivity at potentials up to ca. 4 V. The 5 V plateau reported during the electrochemical extraction of Li from LiCo_xMn_{2 – x}O₄ appears to be due to oxidation of Co³⁺ to Co⁴⁺.