Rechargeable lithium batteries (RLBs) have revolutionized energy storage technology. However, short lifetime and safety issues have hampered their further commercialization, which is mainly attributable to the unstable solid‐electrolyte interphase (SEI) and uncontrolled lithium dendrite growth. In recent years, research on SEI has been pursued with determination worldwide. However, the structure and composition of the SEI have long been debated. Especially, the role of the main component, LiF, remains elusive. In this review, the structure and composition of SEIs are focused upon and the role of LiF in SEI is further analyzed. To this end, first, the development history of the SEI model is recounted. Second, the fundamental understanding of SEI is recalled. Third, the anode materials that can generate LiF in the SEI are categorized and discussed. Fourth, the characterization techniques of SEI layers are introduced. Fifth, the transport mechanism of Li+ ions within the SEI is discussed. Sixth, the physical properties of LiF are revisited. Seventh, the source of LiF is deeply analyzed. Finally, general conclusions and a perspective on the future research directions for SEI that may promote the large‐scale applications of lithium metal batteries is discussed.

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Isotherms have been determined for the adsorption of polyvinylpyrrolidone (PVP) samples of various molecular mass (104 to 2.5 × 106) onto anionic polystyrene (PS) latices from both water and 0.5 M NaCl. The adsorption capacity, Γads, was found to be about 0.7 mg m-2 from water and was independent of the PVP molecular mass. These results were consistent with gel permeation chromatography experiments which indicated that there was no preferential adsorption of high or low molecular mass material. In the presence of 0.5 M NaCl, however, the amount adsorbed was between two and four times greater than that in water, depending on the molecular mass, and high molecular mass material was found to adsorb preferentially. The adsorbed layer thicknesses, δ, were also very different for adsorption from the two solvents. In water, thicknesses of 1−3 nm were obtained, indicating that the molecules were lying flat on the surface in the form of trains. In 0.5 M NaCl, the values of δ increased with increasing molecular mass and were between 4 and 29 nm, indicating a more extended configuration with loops and tails protruding away from the surface into solution. In order to explain the different behavior in the two solvents, it was concluded that, in water, interaction with the PS occurred through the PVP hydrophobic methylene/methine groups and the positive dipole of the amide nitrogen of the pyrrolidone ring. The negative dipole associated with the amide oxygen is directed away from the surface into the solution. In 0.5 M NaCl, interaction occurred predominantly through the hydrophobic groups, since the polar interactions would be screened by the electrolyte present. The effect of PVP on the stability of PS was monitored by turbidity measurements. In the absence of electrolyte, stability was achieved due to electrostatic repulsions between the PS particles whereas in 0.5 M NaCl stability was achieved through steric repulsions for the higher molecular mass PVP samples (i.e. >4 × 104).

Polymer-based conductive nanocomposites are promising for electromagnetic interference (EMI) shielding to ensure stable operations of electronic devices and protect humans from electromagnetic radiation. Although MXenes have shown high EMI shielding performances, it remains a great challenge to construct highly efficient EMI shielding polymer/MXene composite films with minimal MXene content and high durability to harsh conditions. Here, hierarchically porous polyimide (PI)/Ti 3 C 2 T x films with consecutively conductive pathways have been constructed via a unidirectional PI aerogel-assisted immersion and hot-pressing strategy. Contributed by special architectures and high conductivities, PI/Ti 3 C 2 T x films with 2.0 volume % Ti 3 C 2 T x have high absolute EMI shielding effectiveness up to 15,527 dB cm 2 g −1 at the thickness of 90 μm. Superior EMI shielding performance can be retained even after being subjected to hygrothermal or combustion environments, cryogenic (−196°C) or high (250°C) temperatures, and rapid thermal shock (∆T = 446°C), demonstrating high potential as high-performance EMI shielding materials resisting harsh conditions.