Fast and durable anodes for sodium-/potassium-ion hybrid capacitors: tailoring self-adaptive nanocages inside hybrid fibers with high alignment

Abstract

Metal-ion hybrid capacitors (MIHCs) have received growing interest because they combine the merits of both batteries and capacitors. However, their applications are impeded by the sluggish kinetics and poor structure stability of the battery-type anode. To address these issues, an ultrafast and highly durable anode is fabricated via tailoring self-adaptive nanocages into central hollow and highly aligned fibers. The prepared SAAF aligned fiber with ultrafast electronic pathways and a highly porous structure are beneficial to fast kinetics and high-rate capability. Meanwhile, the buffer cushions inside the nanocages accommodate the volume variations during repeated charge/discharge cycling. For the first time, FeSe2@C SAAF fibers are constructed, and moreover, the general application of the SAAF structure to other kinds of iron-based composites, such as FeP, FeS2, FeOxetc., is also demonstrated. The fast kinetics, superior rate capability and good cycling stability are achieved for the FeSe2 SAAF fibers in both sodium-ion and potassium-ion systems. Moreover, sandwich-type Na-/K-ion hybrid capacitors (SIHCs/PIHCs) are assembled based on the FeSe2@C SAAF anodes. They not only achieve high energy/power densities and good pliability, but also have superior high-rate long-term properties under outside deformations. Therefore, this work provides a general and efficient strategy to build highly durable and superior performance anodes for advanced hybrid capacitors towards diverse electronics.