Nitrogen-Doped Carbon-Confined Ni_0.6Fe_0.4Se₂ Nanoboxes Bridged by Carbon Nanotube Networks for Efficient Sodium-Ion Batteries

The reasonable design of effective anode materials while simultaneously achieving rapid rate capacity and satisfied long lifespan is urgently required yet still challenging for sodium-ion batteries (SIBs). Herein, we design and build Ni0.6Fe0.4Se2 nanoboxes confined by a nitrogen-doped carbon layer and bridged by carbon nanotube networks (Ni0.6Fe0.4Se2@NC/CNTs) via a precipitation method combined with a carbonization and selenylation process to suitable anode materials toward efficient SIBs. The obtained Ni0.6Fe0.4Se2@NC/CNTs combines multiple merits of ample ion/electron active sites of hierarchical structure, enhanced ability to mitigate substantial volume expansion of nitrogen-doped carbon sheet layers, and fast electron- and Na+-transfer kinetics induced by high conductivity of the interconnected carbon nanotube networks. As expected, the optimized Ni0.6Fe0.4Se2@NC/CNTs render a prominent sodium storage performance with an exceptional reversible capacity (564.3 mAh g–1 after 100 cycles at 0.1 A g–1) and a superior prolonged cycle lifespan (401.1 mAh g–1 at 5.0 A g–1 over 1000 long-term cycles), surpassing most previously reported NiFe-based electrodes to our knowledge. This work hereby highlights a practical strategy for engineering advanced anode materials for high-efficiency SIBs.