Topotactic Reactions, Structural Studies, and Lithium Intercalation in Cation-Deficient Spinels with Formula Close to Li2Mn4O9
✍ Scribed by A.Ibarra Palos; M. Anne; P. Strobel
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- English
- Weight
- 450 KB
- Volume
- 160
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The composition Li 2 Mn 4 O 9 , reported as a spinel oxide containing vacancies on both tetrahedral and octahedral sites [A. de Kock et al., Mater. Res. Bull. 25, 657 (1990)], was approached using three di4erent preparation routes: low-temperature solid state reaction (A), chemical delithiation (B), and electrochemical delithiation (C). Rietveld re5nements from neutron di4raction data con5rmed the double-vacancy scheme proposed previously for product A, but with more tetrahedral and fewer octahedral vacancies than in the ideal Li 2 Mn 4 O 9 formula. Low-temperature solid state reactions systematically result in broad re6ections. Sample B, which was obtained topotactically, exhibits much narrower re6ections. But chemical analyses, thermogravimetry, and neutron di4raction show that the acid treatment introduces signi5cant amounts of protons, resulting in a formula close to Li 0.92 HMn 4 O 9 . Samples A and B were cycled electrochemically in lithium cells at 3 V with better stability than LiMn 2 O 4 , probably due to their higher initial manganese oxidation state. No separate electrochemical step linked to the 5lling of vacancies is observed in A, whereas B gives an additional redox step ca. 200 mV above the main plateau. This feature is not observed on compounds A or C; it is reversible, and seems to be a speci5c property of this spinel with a low initial cell parameter (8.09 A > ). Sample A2 with double cation vacancies is especially stable on cycling at 3 V, and shows a very small volume variation on lithium intercalation.