Sustainable Biomass‐Based Fiber Materials as Structural and Functional Scaffolds for Advanced Metal Batteries

Biomass‐based fiber materials, including cellulose, chitosan, bacterial cellulose, and their derivatives, have emerged as a distinctive class of structural and functional scaffolds, effectively bridging renewable materials chemistry with advanced energy storage technologies. This review systematically elucidates their hierarchical structural characteristics, classifications, and the intrinsic structural‐function‐application relationships that underpin their versatility. Furthermore, the critical roles of these materials as key components‐including solid‐state/liquid electrolytes, separators, electrodes, and binders‐in various metal battery systems, particularly lithium‐ and zinc‐based batteries, are comprehensively summarized. The discussion further highlights how the rational architectural design of biomass‐derived fibrous materials can significantly enhance ionic conductivity, interfacial stability, and mechanical integrity. By improving these fundamental properties, such materials provide effective strategies for addressing major challenges, including dendrite formation and cycling instability. Finally, the current challenges and future research perspectives are discussed, with particular emphasis on precise molecular‐level design, scalable fabrication technologies, and standardized evaluation protocols, all of which are essential for advancing the development of next‐generation green and sustainable energy storage devices.