Low-cost and robust production of multi-doped 2D carbon nanosheets for high-performance lithium-ion capacitors

Consumer electric vehicles, portable electronic devices, future energy-storage systems, and large-scale grid storage are urgently demanding in the novel devices for bridging-the-gap between high energy density and power density. Carbon nanosheets (CNS)-based energy-storage systems are ideal candidates because of their exotic electronic properties, shortened ion transport paths, and large electrochemical active surfaces. Herein, we propose a facile approach to fabricate boron, oxygen and nitrogen multi-doped 2D CNS from viscous organic precursors (VOPs) and apply them as an anodic material of lithium-ion capacitors (LICs). Through rapid thermal expansion of the cellulose-rich VOPs at an intermediate temperature of 550 °C, the mass production of CNS with high specific surface area and abundant active sites are achieved. When the prelithiated CNS anode is coupled with an active carbon (AC) cathode using water-soluble carboxymethyl cellulose lithium (CMCLi) binder, the obtained 4.5 V green hybrid LIC device delivers a high energy density of 203.6 Wh kg⁻¹ at a power density of 225.0 W kg⁻¹, a high power density of 22.5 kW kg⁻¹ (achieved at 119.8 Wh kg⁻¹), and a reasonably good cycle performance (≈84.5% retention after 5000 cycles at 2 A g⁻¹). This work offers an opportunity to apply the CNS in green LICs, with predominant balance in energy and power density, high working voltage and long cycle life.