Applications of Biomaterials in Separators for Secondary Batteries

ABSTRACT Conventional polyolefin battery separators suffer from poor thermal stability, limited ionic conductivity, and nonbiodegradability, creating an urgent need for safer, high‐performance, and sustainable alternatives. While all‐solid‐state batteries are considered an ideal solution, their practical realization remains distant, making high‐performance, eco‐friendly separators a viable near‐term alternative for improving battery safety. Biomaterials derived from a variety of natural sources offer promising solutions to these issues by delivering improved thermal stability, abundant functional groups, and benign end‑of‑life pathways. This review comprehensively examines biomaterial‐based separators spanning multiple biological kingdoms (Protista, Plantae, Animalia), analyzing how their structures and functional groups correlate with enhancements in electrolyte uptake, ionic transport, and mechanical stability. Rather than focusing on any single material, the review identifies universal design principles common to these biomaterial separators and features a data‐driven comparative performance analysis that compiles key metrics (e.g., electrolyte uptake, ionic conductivity, thermal stability) from numerous studies to quantitatively benchmark such separators against conventional polyolefin separators, with results visualized in a radar plot for easy comparison. Overall, the findings underscore the potential of biomaterial separators to simultaneously improve battery performance and environmental sustainability, providing valuable insights to guide future research and the development of next‐generation secondary batteries that are safer and more sustainable.