Potassium storage behavior and low-temperature performance of typical carbon anodes in potassium-ion hybrid capacitors enabled by Co-intercalation graphite chemistry

Carbon materials are widely explored as anodes for potassium-ion storage, yet the slow K⁺ desolvation process in electrolyte at low temperatures presents a kinetic limitation that impedes reliable operation in specific conditions. In this work, we systematically investigate the potassium storage behavior of four typical carbon materials—graphite, hard carbon, activated carbon, and graphene—in a 1 M KFSI-Diglyme electrolyte, highlighting a co-intercalation approach that significantly reduces the desolvation energy barrier. The formation of ternary graphite intercalation compounds (t-GICs) through co-intercalation in graphite introduces weak interlayer interactions between the graphite layers and solvated K⁺, which accelerate K⁺ diffusion in the anode, thereby enhancing reaction kinetics. This unique mechanism enables the graphite anode to deliver remarkable rate performance (98 mAh g⁻¹ at 0.05 A g⁻¹ and 76 mAh g⁻¹ at 1 A g⁻¹) even at −20 °C. Furthermore, potassium-ion hybrid capacitors (PICs) using the graphite anode achieve impressive cycling stability, with 88 % capacity retention after 2000 cycles at 2 A g⁻¹ and a high power density of 11.1 kW kg⁻¹ (57 Wh kg⁻¹) at −20 °C. These findings provide key insights into the design of robust potassium-ion storage devices capable of sustaining high performance in low-temperature environments.