Cr-substituted spinel Mn oxides LiCr{sub y}Mn{sub 2-y}O{sub 4} (0 {le} Y {le} 1): Rietveld analysis of the structure modifications induced by the electrochemical lithium deintercalation
- Laboratoire de Chimie des Solides, Nantes (France); and others
The electrochemical study of LiCr{sub y}{sup III}Mn{sub 1-y}{sup III}Mn{sup IV}O{sub 4} compounds, 0 {le} y {le} 1, between 3.5 and 5.4 V vs Li metal, shows that the Cr substitution is beneficial to the overall performances (capacity, specific energy, and cyclability) for y {le} 0.62, and that Y = 0.25 gives the best results. For y > 0.62, the cyclability is worse than for LiMn{sub 2}O{sub 4}, and for y {ge} 0.75 the capacity fading becomes very fast. The electron energy loss spectroscopy study confirms that the deintercalation in the range 3.5-4.3 V corresponds to a Mn{sup III}-Mn{sup IV} oxidation. Further deintercalation between 4.3 and 5.1 V mainly corresponds to a Cr{sup III}-Cr{sup VI} oxidation with, however, the formation of a significant amount of Cr{sup VI} for the highest Cr content y = 0.75. In the starting compounds LiM{sub 2}O{sub 4}, M = Cr, Mn, Rietveld refinements show that the 8a and 16d sites of the spinel structure are occupied by Li and M, respectively. The Li deintercalation up to 5.1 V induces structural defects which do not disappear completely upon the subsequent intercalation down to 3.5 V; their concentration increases upon cycling. Such defects consist of M cations occupying an 8a site ({open_quotes}Td defect{close_quotes}) or a 16c site ({open_quotes}16c defect{close_quotes}), instead of 16d. Both defects imply a lowering of the tetrahedral Li concentration which accounts for the experimental capacity loss upon cycling.
- OSTI ID:
- 569696
- Journal Information:
- Journal of Solid State Chemistry, Vol. 132, Issue 2; Other Information: PBD: Sep 1997
- Country of Publication:
- United States
- Language:
- English
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