Intermetallics such as Cu6Sn5, NiSi2, and CuGa2 etc., are promising candidate materials to replace carbon-based lithium-ion battery anodes. However, the lithiation reactions of these anodes often involve the separation of the inactive phases, a slow process that retards the lithiation kinetics and deactivates their role as a stress buffer. This research visualizes the separated Cu in a lithiated Cu6Sn5 anode by advanced transmission electron microscopy techniques. Cu nanospheres of 3–4 nm are found homogeneously distributed in both Li(13+y)Sn5 and Li13Cu6Sn5 phases, suggesting that Cu is transported by long-range diffusion from the reaction site at the Li(13+y)Sn5/Li13Cu6Sn5 phase boundaries.

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Phase engineering through chemical modification can significantly alter the properties of transition-metal dichalcogenides, and allow the design of many novel electronic, photonic, and optoelectronics devices. The atomic-scale mechanism underlying such phase engineering is still intensively investigated but elusive. Here, advanced electron microscopy, combined with density functional theory calculations, is used to understand the phase evolution (hexagonal 2H→monoclinic T'→orthorhombic T ) in chemical vapor deposition grown Mo W Te nanostructures. Atomic-resolution imaging and electron diffraction indicate that Mo W Te nanostructures have two phases: the pure monoclinic phase in low W-concentrated (0 < x ≤ 10 at.%) samples, and the dual phase of the monoclinic and orthorhombic in high W-concentrated (10 < x < 90 at.%) samples. Such phase coexistence exists with coherent interfaces, mediated by a newly uncovered orthorhombic phase T '. T ', preserves the centrosymmetry of T' and provides the possible phase transition path for T'→T with low energy state. This work enriches the atomic-scale understanding of phase evolution and coexistence in multinary compounds, and paves the way for device applications of new transition-metal dichalcogenides phases and heterostructures.

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