High-Power Na-Ion and K-Ion Hybrid Capacitors Exploiting Cointercalation in Graphite Negative Electrodes

Enhanced solid-state ionic diffusion for high-power Na-ion and K-ion hybrid capacitors (SIHCs and PIHCs) is usually attained via tailoring anode materials to the nanoscale, which inevitably requires costly preactivation processes for practical applications. As an alternative to nanoscaling, herein, we propose SIHC and PIHC prototypes exploiting microsized graphite as the host anode material for cointercalation of diglyme-solvated Na+ or K+ and activated carbon as the capacitor-type cathode material. Despite the large grain size, the cointercalation of solvent–cation complexes in graphite is highly reversible and fast, endowing the devices with good cyclability (above 88% capacity retention after 5000 cycles) and power density (17 127 and 15 887 W kg–1 based on electrode materials for SIHCs and PIHCs, respectively) without any preactivation process. Furthermore, a calculation of the energy and power densities representative of the practical system was also performed, demonstrating the influence of the active electrolyte and emphasizing the importance of electrolytes and activated carbon in performance optimization.