A novel eutectic solvent precursor for efficiently preparing N-doped hierarchically porous carbon nanosheets with unique surface functional groups and micropores towards dual-carbon lithium-ion capacitors

High performance carbon-based materials are ideal electrode materials for Li-ion capacitors (LICs) but there are still many challenges such as the complicated preparation processes, high cost, and low yield. Also, the intrinsic structure and surface functionalities need to be optimized. This paper designs a novel route for the facile, low cost, and high efficiency fabrication of N-doped hierarchically porous carbon nanosheets (NPCSs). The NPCSs are achieved from the direct pyrolysis of a homogeneous low temperature eutectic solvent containing sugar as the carbon source and a eutectic salt with ferric chloride as the activation agent and the nitrogen source. It is indicated that the application of moderate ferric chloride additive during the activation process plays key roles, which not only facilitates the formation of a highly distributed layered structure but also optimizes the proportion of the micropores and surface functional groups of the final NPCSs. Specifically, the as-obtained NPCS-1 sample, with appropriate proportion of N- and O-containing surface groups as well as micropores, exhibits an excellent electrochemical performance as both cathode and anode materials for an LIC, with specific discharge capacities of ∼62.1 and 331 mA h g⁻¹at a current density of 5 A g⁻¹, respectively. Furthermore, the resultant NPCS-1//NPCS-1 LIC device can deliver a high energy density of 135.6 W h kg⁻¹at 500 W kg⁻¹, with a capacity retention of 82% after 10 000 cycles at 2 A g⁻¹