3D\nHierarchically Structured CoS Nanosheets: Li⁺ Storage Mechanism\nand Application of the High-Performance\nLithium-Ion Capacitors

Abstract

Lithium-ion\ncapacitors possess excellent power and energy densities,\nand they can combine both of those advantages from supercapacitors\nand lithium-ion batteries, leading to novel generation hybrid devices\nfor storing energy. This study synthesized one three-dimensional (3D)\nhierarchical structure, self-assembled from CoS nanosheets, according\nto a simple and efficient manner, and can be used as an anode for\nlithium ion capacitors. This CoS anode, based on a conversion-type\nLi⁺ storage mechanism dominated by diffusion control, showed\na large reversible capacity, together with excellent stability for\ncycling. The CoS shows a discharge capacity ≈434 mA h/g at\n0.1 A/g. The hybrid lithium-ion capacitor, which had the CoS anode\nas well as the biochar cathode, exhibits excellent electrochemical\nperformance with ultrahigh energy and power densities of 125.2 Wh/kg\nand 6400 W/kg, respectively, and an extended cycling life of 81.75%\nretention after 40 000 cycles. The CoS with self-assembled\n3D hierarchical structure in combination with a carbon cathode offers\na versatile device for future applications in energy storage.