Li-ion and Li-S batteries find enormous applications in different fields, such as electric vehicles and portable electronics. A separator is an indispensable part of the battery design, which functions as a physical barrier for the electrode as well as an electrolyte reservoir for ionic transport. The properties of the separators directly influence the performance of the batteries. Traditional polyolefin separators showed low thermal stability, poor wettability toward the electrolyte, and inadequate barrier properties to polysulfides. To improve the performance and durability of Li-ion and Li-S batteries, development of advanced separators is required. In this review, we summarize recent progress on the fabrication and application of novel separators, including the functionalized polyolefin separator, polymeric separator, and ceramic separator, for Li-ion and Li-S batteries. The characteristics, advantages, and limitations of these separators are discussed. A brief outlook for the future directions of the research in the separators is also provided.

This study reports an ambient-air-tolerant approach for negative electrode prelithiation by using 1 M lithium-biphenyl (Li-Bp)/tetrahydrofuran (THF) solution as the prelithiation reagent. Key to this strategy are the relatively stable nature of 1 M Li-Bp/THF in ambient air and the unique electrochemical behavior of Bp in ether and carbonate solvents. With its low redox potential of 0.41 V vs Li/Li + , Li-Bp can prelithiate various active materials with high efficacy. The successful prelithiation of a phosphrous/carbon composite electrode and the notable improvement in its initial Coulombic efficiency (CE) demonstrates the practicality of this strategy.

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Composite polymer electrolytes (CPEs) are very promising for high-energy lithium-metal batteries as they combine the advantages of polymeric and ceramic electrolytes. The dimensions and morphologies of active ceramic fillers play critical roles in determining the electrochemical and mechanical performances of CPEs. Herein, a coral-like LLZO (Li6.4La3Zr2Al0.2O12) is designed and used as a 3D active nanofiller in a poly­(vinylidene difluoride) polymer matrix. Building 3D interconnected frameworks endows the as-made CPE membranes with an enhanced ionic conductivity (1.51 × 10–4 S cm–1) at room temperature and an enlarged tensile strength up to 5.9 MPa. As a consequence, the flexible 3D-architectured CPE enables a steady lithium plating/stripping cycling over 200 h without a short circuit. Moreover, the assembled solid-state Li|LiFePO4 cells using the electrolyte exhibit decent cycling performance (95.2% capacity retention after 200 cycles at 1 C) and excellent rate capability (120 mA h g–1 at 3 C). These results demonstrate the superiority of 3D interconnected garnet frameworks in developing CPEs with excellent electrochemical and mechanical properties.