N-Doped Porous Carbon Cubes Exhibit Excellent Low-Temperature Performance in Symmetric Li-Ion Capacitors

Fabricating high gravimetric/volumetric energy power densities along with ultralong cycle performance of carbon-based lithium-ion capacitors (LICs) in a low-temperature environment is still a huge challenge due to the sluggish Li+ diffusion rate and intrinsic unmatched kinetics between the anode and cathode. Herein, a N-doped porous carbon cube (NPCC) has been obtained through combining a facile hydrothermal and N-doping method. The NPCC owing to its unique cubic morphology, abundant hierarchical pore structures, large interlayer spacing, and high N-doped content is capable of improving the solid-phase diffusion rate of Li+, thereby improving the low-temperature performance of LICs. As a result, the as-assembled symmetric LIC of NPCC//NPCC shows the maximum gravimetric and volumetric energy densities (216.3 W h/kg and 147.8 W h/L, respectively) as well as 93.3% capacity retention ratio for 10,000 cycles at 25 °C. At a lower temperature of −30 °C, NPCC//NPCC still exhibits high capacities of 180.3 and 88.7 F/g at 1 and 10 A/g, respectively. Additionally, the symmetric LIC exhibits high gravimetric and volumetric energy densities (181.9 W h/kg and 124.2 W h/L, respectively) accompanied by 88.4% capacity retention for 10,000 cycles. To further verify the resulting outstanding electrochemical performance, the molecular dynamics simulation) models in which various N-doped atoms adsorb Li+ and PF6– have been rationally constructed. The results demonstrate that various N-doped types have a strong binding energy with Li+ and PF6–, thereby improving the solid-phase diffusion kinetics of Li+. This study will provide strong guidance for applying the porous carbon materials to low-temperature energy storage devices.