Double-shell and hierarchical porous nitrogen-doped carbon nanocages as superior anode material for advanced sodium-ion batteries

Carbon-based materials are the most advantageous candidates for anode in sodium-ion batteries (SIBs). Nevertheless, their practical utilization has been hampered by their low reversible capacity and poor cyclic performance. In this study, novel double-shell and hierarchical porous N-doped carbon nanocages (DHNCNs) were prepared by a soft template-assisted strategy in the presence of ZIF-8 as the matrix, dopamine hydrochloride as the nitrogen and carbon source, and F127/TMB as the soft template. The study found that the carbonization temperature has a significant impact on the surface area, pore volume, interlayer distance, defect concentration, and N content of DHNCNs, thereby altering their electrochemical performance. The DHNCNs-900 synthesized at 900 degrees C exhibit the best sodium-ion storage performance, including high discharge capacity of 235.5 mAh g-1 after 100 cycles at 50 mA g-1, outstanding rate performance of 209.4 mAh g-1 at 2.0 A g-1, and excellent longterm cycling stability of 171.3 mAh g-1 after 900 cycles at 500 mA g-1. The exceptional electrochemical performance of the DHNCNs-900 electrode is induced by synergistic effects of the double-shell, hierarchical porous, N-doped, and hollow structure. Additionally, the electrochemical kinetic analysis indicates that DHNCNs-900 electrode possesses a reinforced sodium-ion storage mechanism by the pseudo-capacitive-control behavior. In conclusion, this study presents a superior anode material for SIBs and exhibits a simple method for synthesizing N-doped carbon nanocage materials, holding promise for advanced energy storage systems.