High potassium ion storage capacity with long cycling stability of sustainable oxygen-rich carbon nanosheets

Abstract

The development of carbon materials for potassium storage is limited by their low specific capacity and poor cycling stability due to the sluggish kinetics of K ions. Herein, fucoidan-derived oxygen-rich carbon nanosheets are reported as a fantastic anode for potassium ion batteries. Attributed to its 2D porous sheet-like structure (morphology engineering), rich oxygen doping (defect engineering), and dilated graphitic layer in an amorphous structure (structure engineering), a competitive capacity of 392 mA h g⁻¹ at 0.05 A g⁻¹ and a long cycling span over 2500 cycles at 2 A g⁻¹ was achieved for the carbon anode, outperforming most of the reported carbons. The kinetic analyses reveal that rich active sites and a porous nanosheet structure account for the superb rate performance and cycling stability of the material. Ex situ X-ray photoelectron spectroscopy measurements demonstrate that the introduction of CO greatly promotes K⁺ adsorption, and that the improvement of the CO bonds during cycling contributes to enhancement in the capacity. The fabricated potassium ion hybrid capacitor displays an exceptional energy/power density of 193 W h kg⁻¹/22 324 W kg⁻¹, and a promising cycling stability with 99.3% capacity retention over 2000 cycles. This work provides a large-scale synthesis strategy for preparing oxygen-rich carbon nanosheets for advanced potassium ion storage.