Facile Design of Multiscale Cellulose‐Enhanced Hydrogel Electrolytes for Flexible Zn‐Ion Capacitors in Wearable Electronics

Abstract Flexible solid‐state supercapacitors show significant potential for wearable electronics; however, achieving simultaneous mechanical robustness and high ionic conductivity remains challenging. In this work, a polyacrylamide (PAM)/cellulose nanocrystal (CNC)‐based hydrogel electrolyte loading with carboxymethyl cellulose (CMC) is engineered to address this limitation (PAM/CNC‐CMC‐Zn 2+ ). Incorporating CNC improved the mechanical properties of hydrogels, while subsequently adding CMC‐Na enriched with hydrophilic groups (─OH and ─COO − ) into PAM/CNC hydrogels disrupted hydrogen‐bond networks within the ZnSO 4 electrolyte, thereby optimizing Zn 2+ solvation sheath structure. This modification suppressed corrosion currents and minimized side reactions. The hydrogel demonstrated outstanding mechanical properties, including a tensile strength of 0.22 MPa, high stretchability (1452.1%), and remarkable fracture toughness (0.98 MJ m −3 ). The zinc‐ion capacitors (Zn // PAM/CNC‐CMC‐Zn 2+ // AC) demonstrate exceptional electrochemical performance, achieving a significant specific capacitance of 151.4 F g⁻¹ at 0.5 A g⁻¹, coupled with a remarkable power density of 1150 W kg⁻¹ (at 10.9 Wh kg⁻¹). Notably, the device exhibits outstanding performance stability, maintaining its functionality under mechanical folding and retaining its efficiency after 10 000 long charge–discharge cycles. These multiscale cellulose‐based design highlights the hydrogel electrolyte's dual functionality in balancing mechanical adaptability and electrochemical efficiency, offering a potential solution for next‐generation wearable energy storage systems.