The Cr-Substituted Spinel Mn Oxides LiCryMn2−yO4(0≤y≤1): Rietveld Analysis of the Structure Modifications Induced by the Electrochemical Lithium Deintercalation
✍ Scribed by C. Sigala; A. Verbaere; J.L. Mansot; D. Guyomard; Y. Piffard; M. Tournoux
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 371 KB
- Volume
- 132
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The electrochemical study of LiCr III y Mn III 1!y Mn IV O 4 compounds, 04y41, 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 y40.62, and that y"0.25 gives the best results. For y'0.62, the cyclability is worse than for LiMn 2 O 4 , and for y50.75 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 III -Mn IV oxidation. Further deintercalation between 4.3 and 5.1 V mainly corresponds to a Cr III -Cr IV oxidation with, however, the formation of a significant amount of Cr VI for the highest Cr content y ؍ 0.75. In the starting compounds LiM 2 O 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 (''Td defect'') or a 16c site (''16c defect''), instead of 16d. Both defects imply a lowering of the tetrahedral Li concentration which accounts for the experimental capacity loss upon cycling.