Li+ extraction reactions with spinel-type LiM0.5Mn1.5O4 (M=Ti, Fe) and their electronic structures

Li+ extraction reactions with spinel-type LiM0.5Mn1.5O4 (M=Ti, Fe) in an aqueous phase were examined using chemical and X-ray diffraction (XRD) analysis. Their electronic structures and chemical bonding properties were also studied using a discrete variational (DV)-Xalpha molecular orbital method with a cluster model of (Li5M4Mn24O42)(19+). In the process of extraction reaction, the LiM0.5Mn1.5O4 showed a topotactic extraction of Li+ in the aqueous phase mainly through an ion exchange mechanism, and the extracted Li+ samples indicated a high selectivity and a large capacity for Li+ among 3d transition metal ions. In order to examine the net charge and magnitude of covalent bondings, Mulliken's population analysis was thoroughly conducted. Its results showed that the Mulliken's charge of Li in LiM0.5Mn1.5O4 was approximately 0.75, regardless of the M-species. The bond overlap population (BOP) of M-O was approximately the same as that of Mn-O in these compounds, and the BOP of Fe-O was smaller than that of the Ti-O bonds because the Fe-O anti-bonding interaction was greater than that of the Ti-O. (C) 2003 Elsevier Science B.V. All rights reserved.