Hollow MoS₂ Spheres Confined in Carbon Fibers for Ultralong-life Potassium Storage

Potassium-ion energy storage systems are gradually showing their status due to abundant potassium resources and low cost. Unfortunately, K+ storage materials are still an exigent issue due to the large radius and sluggish kinetics of K+. Herein, a composite electrode (H-MoS2@CNFs) built by electrospun carbon fibers (CNFs) as the frame and the hollow MoS2 spherical shell as the inner core is designed. H-MoS2@CNFs is endowed with the following preponderance: the outside CNFs interlocked with the MoS2 nanosheets play a triple role in conducting electrons, buffering the volume expansion of MoS2, and maintaining the structural stability of the electrode; the exposed edges of the (002) plane of MoS2 nanosheets in direct contact with the electrolyte stored in the internal cavity facilitate the K+ reaction kinetics. As the anode of potassium- ion batteries, H-MoS2@CNFs delivers an excellent cyclic performance (187.7 mAh g(-1) at 2.0 A g(-1) after 5000 cycles with 0.0037% decay per cycle) and high rate capability (184.7 mAh g(-1) at 10.0 A g(-1)). Furthermore, owing to the superior potassium storage and freestanding characteristics without the binder and conductive additives, the potassium-ion capacitor (PIC) based on the anode exhibits a high energy density of 165 Wh kg(-1) at a power density of 378 W kg(-1), which furnishes a reliable basis for the development of two-dimensional materials for the PIC.