Layered LixMoO2 Phases with Different Composition for Electrochemical Application: Structural Considerations

作者：Mikhailova D^*; Bramnik N N; Bramnik K G; Reichel P; Oswald S; Senyshyn A; Trots D M; Ehrenberg H

来源：Chemistry of Materials, 2011, 23(15): 3429-3441.

DOI：10.1021/cm2010715

• monoclinic LixMoO2
• rhombohedral LixMoO2
• Mo4O16-clusters
• in situ structural characterization
• lithium extraction/insertion
• thermal stability

Different modifications of LixMoO2 (1) without metallic Mo-Mo bonds (R-3m, a = 2.858(2) angstrom, c = 15.701(13) angstrom), (2) with endless Mo chains with metallic bonds (C2/m, a = 10.614(3) angstrom, b = 2.878(1) angstrom, c = 4.955(2) angstrom, beta = 99.37(3)degrees), and (3) with Mo4O16 clusters (C2/m, a = 9.905(6) angstrom, b = 5.739(3) angstrom, c = 5.472(4) angstrom, beta = 107.43(7)degrees) were synthesized by high-temperature solid-state reaction. Increasing lithium content supports the formation of the rhombohedral form. In situ structural investigations during electrochemical Li extraction and insertion between 2.4-3.5 V on Li1.0MoO2 material containing rhombohedral and monoclinic modifications with endless molybdenum chains revealed the instability of the monoclinic Li0.9MoO2 form with decreasing Li content against transformation into two rhombohedral phases LixMoO2 and Lix approximate to 0MoO2. In contrast, the rhombohedral Li-1.0(Mo0.9Li0.1)O-2 form showed a topotactical single-phase behavior during Li extraction and insertion. Further oxidation of LixMoO2 at voltages above 4.5 V led to insertion of large anions such as PF6- or BF4- into the crystal structure. The Li-free rhombohedral form is stable in Ar up to 570 K and transforms irreversibly at higher temperature into a rutile-like structure.

• 出版日期2011-8-9