3D Hierarchically Structured CoS Nanosheets: Li+ Storage Mechanism and Application of the High-Performance Lithium-ion Capacitors

Abstract

Lithium-ion capacitors, which possess excellent power and energy densities, can combine both those advantages from supercapacitors and lithium-ion batteries, leading to the novel generation hybrid devices for storing energy. This study synthesized one three-dimensional (3D) hierarchical structure self-assembled from CoS nanosheets, according to a simple and efficient manner, have been used as anode for lithium ion capacitors. This CoS anode, based on a conversion-type Li+ storage mechanism dominated by diffusion controlled, showed a large reversible capacity, together with excellent stability for cycling. The CoS shows a discharge capacity ≈ 434 mA h/g at 0.1 A/g. The hybrid lithium-ion capacitor, which had the CoS anode as well as the biochar cathode, exhibits excellent electrochemical performance with ultra-high energy and power densities of 125.2 Wh/kg and 6400 W/kg, respectively, and an extended cycling life of 81.75% retention after 40000 cycles. The CoS with self-assembled 3D hierarchical structure in combination with a carbon cathode offers a versatile device for future applications in energy storage.