上海科技大学知识管理系统

Lithium (Li) and sodium (Na) intercalation into molybdenum disulfide (MoS2) flakes with layer thicknesses of 2.2 nm (3 layers) and 51 nm (ca. 82 layers) was investigated in situ under potential control via a combination of Raman spectroscopy and optical microscopy. A Raman frequency shift indicative of reduced strain along the MoS2 sheet during Na intercalation compared with Li intercalation is observed, despite the atomic radii of Na being larger than Li, r(Na+) 1.02 Å > r(Li+) 0.76 Å. Overall, the shift of Raman bands exhibited similar trends in trilayer and multilayer flakes during lithiation. A combination of strain and electron doping was used to explain the observed Raman frequency shifts. The differences between lithiation and sodiation in MoS2 flake were also observed visually by optical microscopy, whereby Li inserted into MoS2 via a pushed-atom-by-atom behaviour and Na via a layer-by-layer behaviour. Variation of the insertion behaviour between lithiation and sodiation in MoS2 was further investigated via galvanostatic intermittent titration technique, in which the diffusion coefficient as a function of x in MxMoS2 (M = Li or Na) suggested a stable intermediate phase existed in NaxMoS2 during sodiation, whereas this stable intermediate phase was absent in LixMoS2.
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