Bidirectional ion-supply interface enables efficient active material utilization in wood-derived thick electrodes for ammonium-ion storage.

High-volumetric-energy thick electrodes are essential for compact energy storage. However, conventional free-standing carbon scaffolds possess solely macroporous channels, thereby restricting electrolyte access to a single side. Such surface-limited infiltration confines reactions to the superficial layer, resulting in sluggish ion kinetics and poor bulk utilization. To address this limitation, we designed a wood-derived carbon/NH4V4O10 composite featuring a bidirectional ion-supply interface. This unique configuration creates ion-enrichment zones on both sides, enabling cooperative NH4+ transport across the entire electrode thickness and rapid ion access to all active material surfaces. Consequently, the ion diffusion barrier is significantly reduced, increasing active-material utilization by 415% at 17.6 mg cm-2 and effectively eliminating "dead volume". The optimized electrode achieves a volumetric capacitance of 37.1 F cm-3 at 1 mA cm-2. Warburg analysis further reveals a 16-fold increase in the apparent NH4+ transport coefficient after activation, attributed to the activated carbon scaffold functioning as an electrolyte reservoir, enabling rapid ion supply to NVO and maximized accessibility of active sites for NH4+ storage. An assembled ammonium-ion hybrid capacitor delivers 4.1 mWh cm-3 at 10 mW cm-3, while a quasi-solid-state device reliably powers commercial electronics. This work redefines ion-transport pathways in thick electrodes and provides a design blueprint for high-loading, high-energy-density storage systems.