Pseudocapacitance Behavior in Battery Materials: Phase Transitions and Charge Compensation Governed by Ionic Spatial Equilibrium

Pseudocapacitance behavior in conventional battery electrodes is widely attributed to the reduction of material dimensions and the increase in current density, where bulk and interfacial contributions are conventionally separated through electrochemical techniques. However, the underlying chemical mechanisms governing this phenomenon have remained elusive. By designing size-controlled Prussian blue analogue electrodes, we isolate these two critical factors: the current density and particle dimension. To elucidate the universal origin of pseudocapacitance responses, we employ a time-resolved synchrotron-radiation-based multitechnique approach, revealing its phase transition suppression and accelerated charge-transfer kinetics. Experimental findings demonstrate that the homogeneity of ion diffusion serves as the primary determinant governing the progressive transition from battery-type to pseudocapacitance behavior. These results establish a fundamental correlation between ion diffusion characteristics and the pseudocapacitance response in electrode materials, offering critical insights for designing cathode architectures that simultaneously achieve a high energy density and high power density.