Graphene-like nitrogen-doped porous carbon nanosheets as both cathode and anode for high energy density lithium-ion capacitor

Abstract Carbon materials have unique stability and controllable structure for all-carbon lithium-ion capacitors (LICs) electrode materials. In this paper, we used chitosan as a carbon source and self-doped nitrogen source, zinc nitrate as a templating agent. Hierarchical porous carbon nanosheets (PCNS) materials with graphene-like structure and abundant nitrogen doping were prepared through a one-step carbonization process. The PCNS materials were used as both capacitor-type cathode and battery-type anode for LICs. Due to the multi-mesoporous and ultrathin nanosheets structure, a large specific surface area (1321.3 m2 g−1) was obtained of PCNS materials, which ensures a high specific discharge capacity of 65.8 mAh g−1 at 3 A g−1 for the capacitor-type cathode. The interconnected graphene-like structure not only provides a large adsorbable area but also reduces the diffusion distannce of ions between the surface of the electrode and electrolyte. When the PCNS materials used as an anode for LIC, it also appeared a high specific discharge capacity of 285.0 mAh g−1 at a big current density of 20 A g−1. Finally, all-carbon symmetric LIC with a broad voltage window of 0.01–4.5 V was constructed successfully. The symmetric LIC shows a high energy density of 146 Wh kg−1 (at a power density of 1125 W kg−1) and an excellent capacity retention rate of 84.5% (10,000 cycles at 5 A g−1).