Polar interaction of polymer host–solvent enables stable solid electrolyte interphase in composite lithium metal anodes

The lithium (Li) metal anode is an integral component in an emerging high-energy-density rechargeable battery. A composite Li anode with a three-dimensional (3D) host exhibits unique advantages in suppressing Li dendrites and maintaining dimensional stability. However, the fundamental understanding and regulation of solid electrolyte interphase (SEI), which directly dictates the behavior of Li plating/stripping, are rarely researched in composite Li metal anodes. Herein, the interaction between a polar polymer host and solvent molecules was proposed as an emerging but effective strategy to enable a stable SEI and a uniform Li deposition in a working battery. Fluoroethylene carbonate molecules in electrolytes are enriched in the vicinity of a polar polyacrylonitrile (PAN) host due to a strong dipole–dipole interaction, resulting in a LiF-rich SEI on Li metal to improve the uniformity of Li deposition. A composite Li anode with a PAN host delivers 145 cycles compared with 90 cycles when a non-polar host is employed. Moreover, 60 cycles are demonstrated in a 1.0 Ah pouch cell without external pressure. This work provides a fresh guidance for designing practical composite Li anodes by unraveling the vital role of the synergy between a 3D host and solvent molecules for regulating a robust SEI.