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[摘要]：Different modifications of Li(x)MoO(2) (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 Mo(4)O(16) 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 Li(1.0)MoO(2) material containing rhombohedral and monoclinic modifications with endless molybdenum chains revealed the instability of the monoclinic Li(0.9)MoO(2) form with decreasing Li content against transformation into two rhombohedral phases Li(x)MoO(2) and Li(x approximate to 0)MoO(2). In contrast, the rhombohedral Li(1.0)(Mo(0.9)Li(0.1))O(2) form showed a topotactical single-phase behavior during Li extraction and insertion. Further oxidation of Li(x)MoO(2) at voltages above 4.5 V led to insertion of large anions such as PF(6)(-) or BF(4)(-) 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. |
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