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We report a comprehensive in-situ phase-change study on polycrystalline Sn0.98Se via high-temperature X-ray diffraction and in-situ high-voltage transmission electron microscopy from room temperature to 843 K. The results clearly demonstrate a continuous phase transition from Pnma to Cmcm starting from 573 to 843 K, rather than a sudden transition at 800 K. We also find that the thermal-conductivity rise at high temperature after the phase transition, as commonly seen in pristine SnSe, does not occur in Sn0.98Se, leading to a high thermoelectric figure of merit. Density functional theory calculations reveal the origin to be the suppression of bipolar thermal conduction in the Cmcm phase of Sn0.98Se due to the enlarged bandgap. This work fills the gap of in-situ characterization on polycrystalline Sn0.98Se and provides new insights into the outstanding thermoelectric performance of polycrystalline Sn0.98Se.

Rechargeable lithium–sulfur batteries (LSBs) are of great interest in the field of energy storage due to their favorable operational characteristics, for example, high theoretical energy density and low cost. However, LSBs are limited by long‐term degradation, caused by the dissolution of intermediate lithium polysulfide phases. Further improvement of LSBs requires an in‐depth understanding of the underlying redox reactions and active‐material degradation mechanisms. Advanced characterization techniques, especially in situ/in operando characterization tools, are used and developed in the field of LSBs to probe the rate‐limiting performance and design characteristics of functional materials. Here, common in situ/in operando techniques are reviewed with regard to recent research significance and practical limitations, with the aim of providing a comprehensive treatise on in situ characterization technique selection for LSBs, thereby allowing their future development and improvement.

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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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