Electrochemical cyclability of orthorhombic LiMnO{sub 2}: Characterization of cycled materials
- I.M.N., Nantes (France). Lab. de Chimie des Solides
The electrochemical removal of lithium from orthorhombic LiMnO{sub 2} (o-LiMnO{sub 2}) leads to a phase transition with a first plateau at about 3.7 V. This corresponded to the formation of a spinel-like material; a possible transition to a rhombohedral Li{sub x}MnO{sub 2} phase was ruled out through structural and crystal-site energy considerations. Several electrochemical cycles were necessary to achieve a complete phase transformation; the smaller the crystallites/crystals the fewer the number of cycles needed. The capacity difference between large and small crystallite/crystal compounds was ascribed to kinetic reasons as shown by ex situ x-ray diffraction analyses and quasi-equilibrium electrochemical studies. Capacities as high as 200 Ah/kg were found for {approx}0.3 {micro}m crystal size materials. Contrary to the spinel prepared at high temperature, the electrochemically obtained spinel-like phase cycled very well in the 2.5 to 4.3 V range, suggesting structural differences between the two materials. An extended X-ray absorption fine structure study at the manganese K edge confirmed this observation through a marked difference between the manganese second neighbors for two compounds. This can be related to the orthorhombic-to-cubic phase transition itself and/or to the memory effect of the stacking faults originally present in o-LiMnO{sub 2}.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 562187
- Journal Information:
- Journal of the Electrochemical Society, Vol. 144, Issue 10; Other Information: PBD: Oct 1997
- Country of Publication:
- United States
- Language:
- English
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