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

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 C[double bond, length as m-dash]O greatly promotes K+ adsorption, and that the improvement of the C[double bond, length as m-dash]O 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.