Nanolignin Functional Separators for Flexible Lithium–Sulfur Batteries With Enhanced Performance

In this study, a nanolignin functionalized separator has been designed to maximize the thermo‐mechanical response of commercial separators while blocking polysulfide shuttling in lithium–sulfur batteries. A uniform, thin, and mechanically robust biobased nanocomposite functional coating, exhibiting reduced porosity compared to the commercial polypropylene separators, was produced. The nano‐composite coating, based on poly(ethylene glycol) diacrylate embedding kraft lignin nanoparticles through a waterborne, dual‐curing process, afforded excellent resistance to thermo‐oxidative and thermolytic degradation and yielded a wide temperature operating window for the separator. Furthermore, flame resistance was also markedly improved versus benchmark non‐coated polypropylene, with the modified separator exhibiting slower combustion kinetics and char formation under direct flame exposure. Such a functionalized biobased system was employed as a functional/structural component in flexible lithium–sulfur batteries pouch cells, which were shown to achieve an initial discharge capacity as high as 1128.7 mAh g −1 at 0.1 C, maintaining 541 mAh g −1 after 250 cycles. This work presents a scalable and environmentally friendly approach to separator design, offering important advances toward safer, high‐performance lithium–sulfur batteries devices for applications in portable electronics and electric vehicles.