Solvent-to-Material Engineering of Cellulose-Based Electrolytes toward Stable Aqueous Zinc Batteries

ConspectusAqueous zinc batteries (AZBs) are emerging as promising candidates for grid-scale energy storage due to their inherent safety, low cost, and environmental compatibility. However, their practical commercialization is hindered by three critical challenges: uncontrollable Zn dendrite growth, notorious parasitic side reactions, and sluggish Zn2+ transport kinetics. Electrolyte engineering has been demonstrated as an effective strategy to overcome these obstacles, such as hydrogel electrolytes and electrolyte additives. Among these, cellulose-based electrolytes exhibit unique advantages, including abundant hydroxyl (−OH) groups, hierarchical structures, and excellent sustainability. These characteristics enable strong affinity for solvated Zn2+ and good wettability toward Zn metal. Additionally, the nanoporous architecture in cellulosic materials can precisely regulate the flux of Zn2+, thereby promoting uniform Zn deposition. Moreover, cellulose-based electrolytes are easily accessible and biodegradable, making AZBs attractive in terms of scalability and sustainability. However, cellulose can only be dissolved in specific solvent systems owing to the intrinsic intra- and interhydrogen-bonding network within its molecular chains. To enable cellulose-derived materials to meet the requirements for both mechanical properties and electrochemical performance in AZBs, the efficient and mild dissolution/activation along with the controllable derivatization and functionalization of cellulose remain challenging.In this Account, we present recent advances from our collaborative research on cellulose-based electrolyte design for AZBs, focusing on network architecture, functional groups, and their fundamental electrochemical mechanisms. To establish a foundation, we first outline prominent solvent systems by comparing their dissolution mechanisms and advantages. Among these, the alkali/urea and CO2-based solvent platforms pioneered in our laboratories serve dual functions: as efficient cellulose dissolution media and as reactive environments for modifying −OH groups via diverse reactions, including Williamson ether synthesis, transesterification, acylation, and Michael addition.Leveraging these solvents, we have fabricated cellulosic hydrogels through advanced cross-linking strategies such as surface engineering, double-network architectures, and dual cross-linking. These methods effectively homogenize network structures while enhancing mechanical properties, enabling uniform electric field distribution and suppressing parasitic reactions. Furthermore, to strengthen Zn2+–cellulose binding affinity, we synthesized tailored cellulose derivatives as electrolyte additives, including nanocellulose, cellulose levulinate ester, cellulosic poly(ionic liquid)s, and amphoteric cellulose, by functionalizing the abundant modifiable −OH groups along cellulose chains. The introduced functional groups regulate the ion transport/diffusion kinetics, accelerating hydrated Zn2+ desolvation to achieve stable Zn anodes. The principles and strategies discussed herein provide design guidelines to accelerate the development of sustainable cellulose-based electrolytes for next-generation green energy storage.