High Energy and High Power Lithium-Ion Capacitors Based on Boron and Nitrogen Dual-Doped 3D Carbon Nanofibers as Both Cathode and Anode

High energy density at high power density is still a challenge for the current Li-ion capacitors (LICs) due to the mismatch of charge-storage capacity and electrode kinetics between capacitor-type cathode and battery-type anode. In this work, B and N dual-doped 3D porous carbon nanofibers are prepared through a facile method as both capacitor-type cathode and battery-type anode for LICs. The B and N dual doping has profound effect in tuning the porosity, functional groups, and electrical conductivity for the porous carbon nanofibers. With rational design, the developed B and N dual-doped carbon nanofibers (BNC) exhibit greatly improved electrochemical performance as both cathode and anode for LICs, which greatly alleviates the mismatch between the two electrodes. For the first time, a 4.5 V "dual carbon" BNC// BNC LIC device is constructed and demonstrated, exhibiting outstanding energy density and power capability compared to previously reported LICs with other configurations. In specific, the present BNC//BNC LIC device can deliver a large energy density of 220 W h kg(-1) and a high power density of 22.5 kW kg(-1) (at 104 W h kg(-1)) with reasonably good cycling stability (similar to 81% retention after 5000 cycles).