Exploring functionalized nanocrystalline cellulose binders for potassium-ion batteries

• Cellulose nanocrystals were tested as green binders for K-ion battery anodes. • Enzymatic CNCs showed highest capacity and 97 % retention after 100 cycles. • CNCs enabled improved electrode morphology and reduced impedance. • Binders were electrochemically stable within 0.01–3 V vs. K⁺/K. • CNCs outperformed CMC in capacity, reversibility and cycling stability. The development of sustainable and efficient binder materials is crucial to improve the performance and environmental compatibility of potassium-ion batteries (KIBs). In this study, we investigate the use of cellulose nanocrystals (CNCs) as eco-friendly binders for carbon-based anodes for KIBs. Three types of CNCs are synthesized from microcrystalline cellulose via enzymatic, hydrochloric acid, and sulfuric acid hydrolysis, and fully characterized by spectroscopic, elemental, crystallographic, and morphological analyses. Their electrochemical stability is confirmed by cyclic voltammetry on binder-only electrodes, which shows negligible activity in the 0.01–3 V vs. K⁺/K window. When incorporated as binders into anode electrodes based on commercial Super C45 carbon, CNCs enable excellent electrochemical performance, outperforming conventional carboxymethyl cellulose-based counterparts. Among them, CNCs synthesized from enzymatic hydrolysis provide the best results in terms of specific capacity, capacity retention (97 % after 100 cycles), rate capability, and electrode morphology. These improvements are attributed to the neutral surface chemistry and enhanced structural homogeneity. Our findings highlight CNCs as promising, low-cost, and sustainable binder materials for next-generation KIB systems.