Effect of Chemical Extraction of Lithium on the Local Structure of Spinel Lithium Manganese Oxides Determined by X-ray Absorption Spectroscopy

Abstract

The local structural modifications resulting from chemical extraction and reinsertion of lithium in spinels of composition LiMn2O4 and Li4/3Mn5/3O4 have been investigated by X-ray absorption spectroscopy (XAS) at the manganese K-edge. For LiMn2O4, Mn−O and Mn−Mn distances determined from the extended X-ray absorption fine structure (EXAFS) decrease significantly when lithium is extracted in 0.1 M HCl, but are restored to their original values when ∼90% of the lithium content is reconstituted by sorption in LiOH solution. The Mn−O and Mn−Mn distances for Li4/3Mn5/3O4 are shorter than for LiMn2O4, consistent with a higher manganese oxidation state and lower unit cell parameter for this compound, and show much smaller variations on lithium extraction and reinsertion. In addition lithium extraction from LiMn2O4 results in an increase in local structural order, followed by a return to the lower symmetry state of the parent material when lithium is reinserted. These changes are not observed in the spectra of Li...