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

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 (MGO ǁDME ǁPG), is proposed. It exhibits a high energy density of 150 Wh kg-1cathode at a high power density of 21443 W kg-1cathode (calculation based on total mass: 60 Wh kg-1 at 8577 W kg-1). In ester-based electrolyte, the interactions between the cations and anions are stronger, displaying a crowded solvated-ion environment, which results in a slow ion-storage kinetics. On the contrary, the ether solvents can isolate the cations and anions efficiently, endowing weaker interactions between the cations and anions, which further benefits the fast ion-storage kinetics in ether-based electrolyte.image