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Multiple polytypes of MoTe2with distinct structures and intriguing electronic properties can be accessed by various physical and chemical approaches. Here, we report electrochemical lithium (Li) intercalation into 1T′-MoTe2nanoflakes, leading to the discovery of two previously unreported lithiated phases. Distinguished by their structural differences from the pristine 1T′ phase, these distinct phases were characterized using in situpolarization Raman spectroscopy and in situsingle-crystal X-ray diffraction. The lithiated phases exhibit increasing resistivity with decreasing temperature, and their carrier densities are two to 4 orders of magnitude smaller than the metallic 1T′ phase, as probed through in situHall measurements. The discovery of these gapped phases in initially metallic 1T′-MoTe2underscores electrochemical intercalation as a potent tool for tuning the phase stability and electron density in two-dimensional (2D) materials.

Renewable energy sources such as solar and wind are critical to combatting global warming. Nevertheless, their intermittent energy generation requires the development of large-scale grid energy storage, in contrast to the on-demand generation of coal-based power plants. Sodium-ion batteries offer a promising potential technology, yet because sodium ions are larger than lithium ions, sodium-ion intercalation results in more drastic structural rearrangements. An improved understanding of structural dynamics and ionic diffusion pathways is crucial to developing more durable sodium-ion batteries. Here, we synthesize epitaxial NaxCoO2by using molecular-beam epitaxy and topotactic transformation. In the synthesized epitaxial films, the CoO2layers are canted with respect to the film surface, allowing electrochemical extraction of sodium ions, which we confirm via ex situX-ray diffraction. We anticipate the epitaxial thin films reported here to enable future operando studies of interfaces, subtle lattice distortions, and microstructure during electrochemical cycling.