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Dynamic high-resolution transmission electron microscopy (DHRTEM) has been used to provide the first detailed dynamic atomic-level observations of lamellar deintercalation reaction processes. HgxTiS2 (1.25 > x > 0.00) was chosen as a model low-valent (very little ionic guest-host charge transfer) intercalation system for detailed investigation. Complete deintercalation of stage-1 Hgi.25TiS2 was induced in situ by resistive and electron-beam heating (-170 °C to above ambient temperature). Deintercalation onset was most often observed at the externalmost guest layers, consistent with greater external host-layer flexibility. Onset also frequently occurred at internal guest layers, which can be associated with the strain induced by defects reducing the deintercalation activation energy of internal guest layers locally. Deintercalation generally progresses away from the onset layer(s) forming primarily randomly staged regions, with occasional short-range order. Guest and host-layer behavior during deintercalation provide strong support for the applicability of the Daumas-Herold guest-island model of staging to intercalation/deintercalation reaction processes. These observations include guest-island formation and deintercalation, frequent formation of stable staggered domain-wall boundaries, and guest-layer separation. The symmetry (or asymmetry) of guest-edge dislocation terminations is directly associated with the minimization of local host-layer strain energy and host-layer restacking.

We have prepared the first known lithium manganese oxynitride, Li 7.9 MnN 3.2 O 1.6 , and characterized both its structure and electrochemistry. Powder diffraction experiments show that it adopts a cubic antifluorite lattice, while electron microscopy studies reveal the existence of an incommensurate modulated superstructure due to partial Li/Mn and/or O/N ordering. This is consistent with the 6 Li magic angle spinning-nuclear magnetic resonance spectra, which show only a limited number of Li local environments. Li 7.9 MnN 3.2 O 1.6 is electrochemically active when tested as an electrode in a lithium battery and can be reversibly oxidized up to 1.9 V. Additional reversible capacity is obtained on reduction down to 0 V due to the insertion of Li onto the existing lithium-ion vacancies. In situ X-ray diffraction experiments indicate that the redox mechanism is single-phase and involves the formation of a solid solution Li 7.9±x MnN 3.2 O 1.6 . This compound exhibits an overall specific capacity of 310 mAh/g, with only a 4% loss after the 40th cycle. The higher capacity retention of Li 7.9 MnN 3.2 O 1.6 when compared to that of Li 7 MnN 4 is due to both the easier diffusion of the lithium within the structure caused by the additional cationic vacancies, and the fact that its lithium exchange mechanism goes through the formation of a solid solution, with no biphasic regions.

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