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X-ray diffraction studies on lithium intercalated MoS[2]

University of British Columbia

Li[sub x]MoS₂. samples were prepared by cathodically intercalating a MoS₂ powder cathode with lithium. X-ray diffraction patterns of these samples were taken using the Debye-Scherrer method. From these patterns, the crystal structure of the lithium intercalated M0S₂ was determined as a function of cell voltage. There is no apparent change in the powder patterns until a phase transition occurs in the sample at ≃1.1 V. This transition appears to involve a slipping of lattice planes in the M0S₂ crystal. Straining of the lattice is evident after this phase transition takes place. Non-uniform straining blurred the X-ray pictures with the result that the structure of the new phase could not be unambiguously determined. It does seem certain though, that an aligning of the Mo atoms takes place in this transition. The new phase could be fit to a hexagonal unit cell. The lattice parameters were measured over a charge-discharge cycle in the new phase. The unit cell parameters reversibly change throughout a cycle, implying that intercalation takes place. The c axis exhibits a maximum with increasing lithium content, while the a axis increases monotonically. The volume of the unit cell increases smoothly however, reaching a maximum value some 15% larger than the original. Another phase transition may take place at ≃ 0.55 V. Samples discharged below this voltage appear almost amorphous in the powder patterns, possibly due to extreme non-uniform straining of the lattice. Some decomposition products of the Li-MoS₂ cells have also been discovered.

Text

2010-03-04

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http://hdl.handle.net/2429/21483

Physics

University of British Columbia

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