B/N/O-Codoped 2D Porous Carbon Nanosheets for High-Performance Dual-Carbon Lithium-Ion Capacitors

The development of dual-carbon lithium-ion capacitors (DC-LICs) with high energy at high power density is still a challenge due to the mismatch of capacity and dynamics of battery-type anodes/capacitor-type cathodes. Two-dimensional porous carbon nanosheets (2D-PCS) possess a large open flat layer with nanoscale thickness, exposing more active sites and shortening the ion diffusion route, which can effectively resolve the mismatch issue in DC-LICs. However, developing an easy-to-manipulate and widely available method to prepare 2D-PCS is still a challenge. Herein, using borax as the pore-forming agent and heteroatom dopants, an electrode with a 2D-PCS structure is obtained (noted as C-B-2). Benefiting from the open structure and doping effect, C-B-2 shows a satisfactory rate ability and high capacity both as a cathode and an anode. Besides, a symmetric “dual-carbon” device C-B-2//C-B-2 LIC working in the 0.01–4.5 V range was successfully fabricated, demonstrating a high energy density of 173.1 Wh kg–1 at a power density of 225.5 W kg–1 and a superior cycling stability of 10,000 cycles at 2 A g–1. Furthermore, the C-B-2//C-B-2 LICs demonstrate their practical application potential in successfully powering color LEDs. This work provides an efficient method for developing highly efficient DC-LIC devices.