Versatile potassium vanadium fluorophosphate (KVPO₄F) composites as Dual-Function cathode and anode materials for Potassium-Ion hybrid capacitors

Potassium-based energy storage has emerged as a promising alternative for advanced energy storage systems, driven by the abundance of potassium, fast ion migration, and low standard electrode potential. Hybrid capacitors, which combine the desirable characteristics of batteries and supercapacitors, offer a compelling solution for efficient energy storage. In this study, we present the development of versatile composite materials, specifically potassium vanadium fluorophosphate (KVPO₄F) composites, utilizing a sol–gel method. These composites enable tunable potassium storage and charge transport kinetics within regulated voltage windows, serving as both cathode and anode materials. The anode composite, composed of KVPO₄F and hierarchical porous carbon (HPC), exhibited exceptional stability over 400 cycles within a low-voltage window. On the other hand, the cathode composite, consisting of battery-like KVPO₄F and physisorption activated carbon (AC), demonstrated great potential as a cathode material, striking a balance between specific energy and cycle life within a regulated high-voltage window. By integrating KVPO₄F/C as the anode and KVPO₄F/AC as the cathode, we successfully created potassium-ion hybrid capacitors (PIHCs) that showcased an impressive capacity retention of 83% after 10,000 cycles within a high voltage window of 0.5–4.3 V. Furthermore, to explore the application of these materials in miniaturized energy storage, we fabricated potassium-ion micro hybrid capacitors (PIMHCs) with interdigitated electrodes. These devices exhibited a high areal energy density of 18.8 μWh cm⁻² at a power density of 111.6 μW cm⁻², indicating their potential for compact energy storage systems. The results of this study demonstrate the versatility and efficacy of the developed KVPO4F composite materials, highlighting their potential for future advancements in potassium-based energy storage technologies.