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.