Cellulosic Composites in Lithium Metal Batteries

ABSTRACT Lithium metal batteries (LMBs) hold great promise for next‐generation high‐energy‐density energy storage, yet their practical deployment is severely hindered by lithium dendrite growth, unstable solid electrolyte interphase (SEI), infinite volume expansion of lithium anodes, and poor thermal safety. As an abundant, renewable, biodegradable, and low‐cost biomass polymer, cellulose and its derivatives feature outstanding mechanical robustness, tunable flexibility, rich surface hydroxyl groups, and designable hierarchical micro/nanostructures, which endow them with unique advantages in addressing critical bottlenecks of LMBs. This review focuses on the multifunctional roles and underlying mechanisms of cellulose‐based composites in boosting the electrochemical and safety performance of LMBs. By virtue of polar functional groups and rigid‐flexible integrated structures, cellulose can effectively homogenize Li + flux, guide uniform lithium deposition, suppress dendrite nucleation and propagation, and alleviate volume fluctuation during cycling. Meanwhile, cellulose‐based matrices significantly enhance the mechanical strength, thermal stability, flame retardancy, and ionic conductivity of polymer electrolytes and separators. Seven types of functional cellulose composites are highlighted regarding their applications in electrolytes, separators, 3D anode hosts, artificial interphase layers, and interface regulators. Finally, the future development of cellulose materials toward high‐performance LMBs is prospected from the aspects of precise molecular modification, biomimetic ordered ion transport, and scalable green fabrication. This review provides systematic insights into the performance enhancement mechanisms and application strategies of cellulose for high‐safety and long‐lifespan lithium metal batteries.