Advanced cellulose-based materials for flexible energy storage systems

The rapid development of portable electronics, wearable technologies, and healthcare monitoring systems necessitates the innovation of flexible energy storage systems. Considering environmental pollution and the depletion of fossil resources, the utilization of renewable resources to engineer advanced flexible materials has become especially crucial. Cellulose, the most abundant natural polymer, has emerged as a promising precursor for advanced functional materials due to its unique structure and properties. Typically, the easy processability, tunable chemical structure, self-assembly behavior, mechanical strength, and reinforcing capability enable its utilization as binder, substrate, hybrid electrode, separator, and electrolyte reservoir for flexible energy storage devices. This review comprehensively summarizes the design, fabrication, and mechanical and electrochemical performances of cellulose-based materials. The structure and unique properties of cellulose are first briefly introduced. Then, the construction of cellulose-based materials in the forms of 1D fibers/filaments, 2D films/membranes, 3D hydrogels and aerogels is discussed, and the merits of cellulose in these materials are emphasized. After that, the various advanced applications in supercapacitors, lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, metal-air batteries, and Zn-ion batteries are presented in detail. Finally, an outlook of the potential challenges and future perspectives in advanced cellulose-based materials for flexible energy storage systems is discussed.