The chemistry and design principles of cellulose-based materials toward eco-friendly flexible supercapacitors

The demand for sustainable energy storage has accelerated the development of cellulose-based materials (CBMs) for flexible supercapacitors (FSCs). However, widespread commercialization of FSCs remains challenged by their low gravimetric energy density (approximately 35 Wh kg -1 ), far below lithium-ion batteries (exceeding 200 Wh kg -1 ), and a limited operational temperature range (from -20 °C to 60 °C), restricting their use in extreme environments. To date, no comprehensive review has elucidated the crucial role of the chemistry and structure-property relationships of CBMs in advancing FSC technology. This review fills this gap by examining the chemical attributes and versatility of cellulose and its derivatives, including their physicochemical characteristics, assembly methodologies, and functional modifications such as oxidation, esterification, etherification, grafting polymerization, nucleophilic substitution, and crosslinking reactions. We further provide an overview of the chemistry and structure-function correlations of various cellulose forms used in advanced electrodes, solid electrolytes, separators, binders, current collectors, and substrate/encapsulation materials, alongside relevant microelectrode processing technologies. Given that large-scale application of FSCs is still in its early stages, we offer insightful design principles for guiding future development of cellulose-based FSCs. By proposing a “chemistry-performance-sustainability” design framework, this review not only addresses existing limitations but also outlines a roadmap for next-generation eco-friendly FSCs. This review focuses on the chemistry-structure-performance relationships of cellulose-based materials (CBMs) in flexible supercapacitors (FSCs), covering modification strategies and applications across all FSC components (electrodes to substrates), while proposing a pioneering "chemistry-performance-sustainability" design framework for next-generation eco-friendly energy storage.