| Autor: |
Horne, C. R., Bergmann, U., Grush, M. M., Perera, R. C. C., Ederer, D. L., Callcott, T. A., Cairns, E. J., Cramer, S. P. |
| Zdroj: |
The Journal of Physical Chemistry - Part B; October 2000, Vol. 104 Issue: 41 p9587-9596, 10p |
| Abstrakt: |
We have performed Mn K-edge X-ray Absorption and Mn L-edge emission spectroscopies on LiMn2O4, its chemically delithiated and lithiated derivatives (λ-MnO2 and Li2Mn2O4, respectively), and two Mn3+ spinel model compounds. These experiments were undertaken to understand the associated changes in atomic and electronic structure occurring when LiMn2O4 is used in a rechargeable lithium cell. Subtle changes in the Mn K-edge X-ray absorption near edge structure (XANES) occur upon delithiation that are consistent with literature reports of the oxidation of Mn3+ to Mn4+, retention of the cubic phase, and contraction of the spinel lattice. Conversely, when LiMn2O4 is lithiated, the XANES changes dramatically due to the concurrent transformation from a cubic to a tetragonal spinel. The spectrum is different from XANES of tetragonal Mn3+ spinels possessing approximately the same degree of tetragonal distortion as Li2Mn2O4. This spectral difference is attributed to the inserted Li+ imparting an increased degree of covalency within the Li2Mn2O4 structure resulting in a 1s → 4p + LMCT (ligand to metal charge transfer) shakedown. This increase in covalency was confirmed through Mn L-edge X-ray Emission Spectroscopy measurements. The increased degree of covalency provides insight into the lower Li+ diffusion coefficients reported in the literature and the electronic conduction mechanism for LixMn2O4 when x > 1. |
| Databáze: |
Supplemental Index |
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