Decoupling Self‐Matching Effect Between Cathode and Anode in Hybrid Electrochemical Capacitors

Abstract Hybrid electrochemical capacitors (HECs) are advanced energy storage devices that offer high energy density, high power density, and long cycle life by integrating the energy storage mechanisms of both batteries and supercapacitors. The electrochemical coupling resulting from the cathode‐anode kinetic differences severely restricts the accuracy of predicting the performance of HECs based on electrode performance. However, no general method can decouple the effects of cathode‐anode kinetics matching on electrochemical performance by integrating electrochemical coupling from an electrochemical perspective. Here, using an integrated method that combines two distinct three‐electrode testing modes in the typical sodium‐ion hybrid capacitors, the self‐matching effect of cathode‐anode working potential ranges is first refined as the foundation for kinetic matching and electrochemical coupling. The discrepancies and interdependencies in cathode‐anode electrochemical coupling for an individual kinetic match are decoupled by examining the impact of the self‐matching effect on the electrochemical results. The critical matching current density is introduced as a key kinetic parameter for evaluating the degree of cathode‐anode matching in complex electrochemical systems. This advancement provides an innovative design principle for electrode matching and coupling in high‐performance HECs.