Defect-rich and N-doped hard carbon as a sustainable anode for high-energy lithium-ion capacitors.

Lithium-ion capacitors (LICs) are regarded as the most potential devices in the energy storage systems. Unfortunately, the mismatched in the intrinsic kinetics and specific capacities between anode and cathode lead to a depressed electrochemical performance. Thus, designing an advanced electrode material that combines high performance with low-cost is one of the main challenges for LICs, especially in a sustainable anode material until now. Here, a high-energy LIC has been successfully developed using the defect-rich and N-doped hard carbon (DNC) as anode, which is prepared through the carbonization process of the low-cost biowaste sepia without additional template or catalyst. The DNC shows nanospherical structure with a diameter of about 100 nm. Owing to the two-pronged strategy of N-doping and defect engineering, it delivers a high specific capacity (580.3 mAh g at 0.05 A g), excellent rate capability, and long cycle stability (1000 cycles). The electrochemical kinetic analysis and density functional theory (DFT) calculations have confirmed its prominent pseudocapacitive behaviors and excellent Li storage capability. As expected, the as-fabricated LIC delivers a remarkable energy density (101.7 Wh kg), an outstanding rate capability (56.3 Wh kg at 12.5 kW kg), and a superior cycle lifespan (3000 cycles), demonstrating the tremendous potential for the next-generation energy storage systems.