Conductive Cellulose Nanofiber Enabled Thick Electrode for Compact and Flexible Energy Storage Devices

Abstract Thick electrodes are appealing for high energy density devices but succumb to sluggish charge transfer kinetics and poor mechanical stability. Nanomaterials with large aspect ratio, such as carbon nanotubes, can help improve the charge transfer and strength of thick electrodes but represent a costly solution which hinders their utility outside of “lab scale production.” Here, a conductive nanofiber network with decoupled electron and ion transfer pathways by the conformal electrostatic assembly of neutral carbon black particles on negatively charged cellulose nanofibers is reported. After integrating with lithium iron phosphate (LFP), the conductive nanofiber network enables a compact and high‐loaded (up to 60 mg cm −2 ) electrode with robust electrical networks and shortened ion transport paths. The interconnected nanopores inherited from the conductive network function as nanosized electrolyte reservoirs surrounding the electroactive materials and acting as ion‐conducting highways across the electrode. Based on the compact electrode structure and fast charge transfer kinetics, flexible Li‐LFP batteries with outstanding areal capacity and volumetric energy density (8.8 mAh cm −2 and 538 Wh L −1 ) are developed, substantially exceeding conventional LFP‐based batteries. Given the low cost raw materials together with the scale up processability, the conductive nanofiber design provides a promising strategy toward high‐performance energy storage devices.