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The growing demands for high-energy density electrical energy storage devices stimulate the coupling of conversion-type cathodes and lithium (Li) metal anodes. While promising, the use of these “Li-free” cathodes brings new challenges to the Li anode interface, as Li needs to be dissolved first during cell operation. In this study, we have achieved a direct visualization and comprehensive analysis of the dynamic evolution of the Li interface. The critical metrics of the interfacial resistance, Li growth, and solid electrolyte interface (SEI) distribution during the initial dissolution/deposition processes were systematically investigated by employing multidimensional analysis methods. They include three-electrode impedance tests, in situ atomic force microscopy, scanning electrochemical microscopy, and cryogenic scanning transmission electron microscopy. The high-resolution imaging and real-time observations show that a loose, diffuse, and unevenly distributed SEI is formed during the initial dissolution process. This leads to the dramatically fast growth of Li during the subsequent deposition, deviating from Fick’s law, which exacerbates the interfacial impedance. The compactness of the interfacial structure and enrichment of electrolyte species at the surface during the initial deposition play critical roles in the long-term stability of Li anodes, as revealed by operando confocal Raman spectroscopic mapping. Our observations relate to ion transfer, morphological and structural evolution, and Li (de)solvation at Li interfaces, revealing the underlying pathways influenced by the initial dissolution process, which promotes a reconsideration of anode investigations and effective protection strategies. 

Li–S batteries have attracted great attention for their combined advantages of potentially high energy density and low cost. To tackle the capacity fade from polysulfide dissolution, we have developed a confinement approach by in situ encapsulating sulfur with a MOF-derived CoS 2 in a carbon framework (S/Z-CoS 2 ), which in turn was derived from a sulfur/ZIF-67 composite (S/ZIF-67) via heat treatment. The formation of CoS 2 was confirmed by X-ray absorption spectroscopy (XAS) and its microstructure and chemical composition were examined through cryogenic scanning/transmission electron microscopy (Cryo-S/TEM) imaging with energy dispersive spectroscopy (EDX). Quantitative EDX suggests that sulfur resides inside the cages, rather than externally. S/hollow ZIF-67-derived CoS 2 (S/H-CoS 2 ) was rationally designed to serve as a control material to explore the efficiency of such hollow structures. Cryo-STEM-EDX mapping indicates that the majority of sulfur in S/H-CoS 2 stays outside of the host, despite its high void volumetric fraction of ∼85%. The S/Z-CoS 2 composite exhibited highly improved battery performance, when compared to both S/ZIF-67 and S/H-CoS 2 , due to both the efficient physical confinement of sulfur inside the host and strong chemical interactions between CoS 2 and sulfur/polysulfides. Electrochemical kinetics investigations revealed that the CoS 2 could serve as an electrocatalyst to accelerate the redox reactions. The composite could provide an areal capacity of 2.2 mA h cm −2 after 150 cycles at 0.2C and 1.5 mA h cm −2 at 1C. This novel material provides valuable insights for further development of high-energy, high-rate and long-life Li–S batteries.