Synthesis of MnO{sub 2} phases from LiMn{sub 2}O{sub 4} in aqueous acidic media. Mechanisms of phase transformations, reactivity, and effect of Bi species

Journal Article · Thu Oct 01 04:00:00 EDT 1998 · Journal of the Electrochemical Society

DOI:https://doi.org/10.1149/1.1838818· OSTI ID:659169

Larcher, D; Courjal, P; Gerand, B; Blyr, A; Pasquier, A du; Tarascon, J M ^[1]; Urbina, R H ^[2]

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1. Univ. de Picardie Jules Verne, Amiens (France). Lab. de Reactivite et Chimie des Solides
2. Univ. of Sonora, Hermosillo (Mexico). Dept. of Chemical Engineering and Metallurgy

The nature of the phases obtained by acid digestion of LiMn{sub 2}O{sub 4} phases prepared at 800 C from a mixture of MnO{sub 2} (EMD) and Li{sub 2}CO{sub 3} was investigated. The authors found that the complete transformation toward {alpha}-MnO{sub 2} and then {gamma}-MnO{sub 2} observed for LiMn{sub 2}O{sub 4} treated in 2.5 M H{sub 2}SO{sub 4} for 24 h at 95 C is highly dependent on the amount of water in the reaction medium. The {lambda} {yields} {alpha}/{gamma} transformation was found to be the result of a dissolution-crystallization mechanism that can be completely avoided by adding a soluble Bi, Pb, or Tl salt to the reaction medium. By coupling energy dispersive spectroscopy analysis, infrared spectroscopy, and potentiometric titration, the authors demonstrated the presence of Bi species adsorbed at the surface of the {lambda}-MnO{sub 2} oxide thus modifying its reactivity. In addition, the kinetics of the {lambda} {yields} {alpha}/{gamma} phase transformation was found to depend on the amount of added Bi salt, suggesting the complexing role of Bi toward Mn (Bi-Mn complexes), thereby affecting the crystallization step of the reaction. The same treatment was applied to LiMn{sub 2}O{sub 4} in the presence of a Bi salt in anhydrous electrolyte (LiPF{sub 6}/ethylene carbonate/dimethyl carbonate). In this case, the spinel oxide dissolution slows down and BiF{sub 3} precipitates. With respect to recent findings about the mechanisms involved in the electrochemical capacity failure at elevated temperature in Li-ion LiMn{sub 2}O{sub 4} cells, these results open new alternatives to solve this recurrent problem.

• Sponsoring Organization: USDOE
• OSTI ID: 659169
• Journal Information: Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 10 Vol. 145; ISSN 0013-4651; ISSN JESOAN
• Country of Publication: United States
• Language: English

Related Subjects

25 ENERGY STORAGE
36 MATERIALS SCIENCE
ACTIVATION ENERGY
BISMUTH
CATHODES
CRYSTALLIZATION
DISSOLUTION
LITHIUM COMPOUNDS
MANGANATES
MANGANESE OXIDES
METAL-NONMETAL BATTERIES
PHASE TRANSFORMATIONS