3D nitrogen-doped framework carbon for high-performance potassium ion hybrid capacitor

Post-lithium ion hybrid capacitors have great potential to serve as mid-to large-scale energy storage applications because of their high energy/power densities, abundant resources and low cost. Here we report a high-performance dual-carbon potassium ion hybrid capacitor (PIHC) based on two carbon electrode materials derived from a single precursor-ethylene diamine tetraacetic acid tetrasodium (EDTA-4Na). By means of a simple calcination, the EDTA-4Na can be directly converted to a three-dimensional (3D) nitrogen-doped framework carbon (3DNFC) that exhibits high reversible capacity and good electrochemical kinetic property for potassium ion storage. Such 3DNFC can be further converted to a 3D nitrogen-doped framework activated carbon (3DNFAC) that shows ultrahigh specific surface area (3839 m(2) g(-1)) and excellent capacitance performance. Using the 3DNFC as battery-type anode and the 3DNFAC as capacitor-type cathode, a dual-carbon PIHC is fabricated, and it is able to normally work at 0-4.2 V, delivers high energy and power densities (163.5 Wh kg(-1) at 210 W kg(-1), and 76.4 Wh kg(-1) at 21 000 W kg(-1)), and exhibits outstanding cycling stability (91.7% capacity retention after 10 000 cycles at 2.0 A g(-1)), which are all the best values for the state-of-the-art PIHCs.