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.