Hierarchical Flux Competition Governs Electrochemical‐Chemical Coupling in Redox‐Mediated Batteries

Redox‐mediated processes offer an effective strategy to accelerate sluggish kinetics and improve active‐material utilization across diverse battery chemistries. However, rational optimization remains challenging due to the lack of a quantitative framework describing the interplay among competing kinetic processes. Here, we establish a kinetic framework for electrochemical (EC)‐chemical coupling by defining three flux descriptors for interfacial electron transfer, solid‐state ion transport, and mediator diffusion. Integrated with EC parameters, these descriptors reveal the hierarchy of competing fluxes and enable analytical determination of current‐matching boundaries. The framework identifies and regulates rate‐limiting steps to achieve flux‐balanced operation with enhanced utilization and reduced polarization. Guided by this framework, a redox‐targeting flow battery based on a [Fe(CN) 6 ] 3‐/4− /Prussian blue catholyte delivers a volumetric capacity of 48.6 Ah/L at 100 mA/cm 2 over 6500 h in a symmetric‐cell configuration and achieves 27.6 Wh/L in a full‐cell configuration. A ferrocene/LiFePO 4 redox system also achieves 93.91% capacity retention at a practical areal capacity of 3 mAh/cm 2 over 2800 h. This work establishes a general framework for flux‐balanced battery design, enabling simultaneous enhancement of energy density and rate capability.