Weak Interaction Between Cations and Anions in Electrolyte Enabling Fast Dual‐Ion Storage for Potassium‐Ion Hybrid Capacitors

Abstract Identifying an effective electrolyte is a primary challenge for hybrid ion capacitors, due to the intricacy of dual‐ion storage. Here, this study demonstrates that the electrochemical behavior of graphite oxide in ether‐solvent electrolyte outperforms those in ester‐solvent electrolytes for the cathode of potassium‐ion hybrid capacitor. The experimental and theoretical assessments verify that the anion and cation are isolated effectively in dimethyl ether, endowing a weaker interaction between cations and anions compared to that of ester‐solvent electrolytes, which facilitates the dual‐ion diffusion and thus enhances the electrochemical performance. This result provides a rational strategy to realize high‐rate cations and anions storage on the carbon cathode. Furthermore, a new low‐cost and high‐performance capacitor prototype, modified graphite oxide (MGO) cathode versus pristine graphite (PG) in ether‐solvent electrolyte (MGOǁDMEǁPG), is proposed. It exhibits a high energy density of 150 Wh kg⁻¹_cathode at a high power density of 21443 W kg⁻¹_cathode (calculation based on total mass: 60 Wh kg⁻¹ at 8577 W kg⁻¹).