Next-Generation Bio-Based Battery Separators: Current Status and Future Research Opportunities.

Conventional polyolefin battery separators are limited by inherent deficiencies in thermal stability, electrolyte wettability, and environmental sustainability, which collectively hinder the advancement of high-energy-density energy storage systems. In this context, biomass macromolecular materials, including cellulose, chitin/chitosan, and lignin, have emerged as promising candidates for next-generation separators owing to their environmental benefits, exceptional hydrophilicity, and superior thermal resistance. This review systematically evaluates the molecular characteristics of these three biomass systems, alongside core gel-state processing and network-forming processes such as electrospinning, solution casting, nonwoven technology, and hydrogel-assisted film formation. It further highlights their cutting-edge applications in lithium-ion, lithium-sulfur, zinc-ion, and solid-state batteries, emphasizing their behavior as polymer gel electrolytes and gel-derived structural matrices. To overcome key challenges associated with mechanical robustness, interfacial compatibility, and network uniformity, advanced modification strategies are critically discussed, including surface chemical functionalization, multicomponent hybrid composite formulation, and rational three-dimensional structural engineering. Overall, current research evidence demonstrates that rationally designed biomass-based gel networks and membranes can effectively suppress metal dendrite growth, immobilize soluble polysulfide intermediates via supramolecular interactions, and reduce interfacial impedance in solid-state systems, thereby offering a viable pathway toward safer, more sustainable, and commercially competitive high-energy-density batteries.