Fe³⁺ intercalated hierarchical structured hydrated vanadate cathode for flexible iron ion hybrid supercapacitor

Energy storage devices are the core hub in constructing the modern energy system and have become an indispensable factor in driving the development of new electronic devices. In this work, we synthesized a flexible cathode of Fe³⁺ intercalated V₂O₅·3H₂O (VOH) on carbon cloth (FeVOH@CC) and explored an advanced iron ion hybrid supercapacitor (IIHS). The presence of V⁴⁺/V⁵⁺ electrons in FeVOH@CC enhances the material's conductivity, while Fe³⁺ acts as a stabilizing pillar to accommodate structural expansion and contraction, thereby ensuring improved ion diffusion dynamics and cycling stability. Additionally, the growth of the material directly on the carbon cloth, eliminates the negative effects of conductive agents, binders, and other additives, and the prepared FeVOH@CC maintains structural flexibility, which is crucial for the effective insertion/extraction of Fe²⁺. As a result, the aqueous IIHS exhibits excellent areal capacitance (882.4 mF cm^-2 at 1 mA cm^-2) and energy density (176.5 μWh·cm^-2 at 606.4 μW·cm^-2). After 20,000 cycles, it retains 85.7 % of its capacity, significantly outperforming VOH. Meanwhile, we have developed a polyacrylamide/sodium alginate/glycerol-Fe²⁺ gel electrolyte for flexible IIHS, and the device exhibits outstanding performance by retaining 85.9 % of its capacity after 5,000 cycles. Therefore, FeVOH@CC cathode based flexible IIHS opens up new exploratory possibilities for next-generation energy storage devices.