Enhanced Sodium-Ion Battery Performance via Carbon Nanotube-Confined Prussian Blue Crystallites

Sodium-ion batteries are promising candidates for large-scale energy storage due to their low cost and resource abundance. However, their cathode materials suffer from poor conductivity and limited cycling stability. Here, we report a Prussian blue (PB)-based cathode hybridized with carboxyl-functionalized carbon nanotubes (CNTs) via a glutamic acid-assisted in situ coordination route. This approach enables directional nucleation of PB crystallites onto CNT surfaces, forming a compact, three-dimensional conductive network. The resulting PB@CNT composites exhibit enhanced crystallinity and strengthened interfacial bonding through the formation of Fe-O-C covalent linkages, as confirmed by XPS. Among the variants, PB@CNT-1.0 shows the smallest particle size and most uniform CNT coverage. It delivers a high discharge capacity of 160.2 mAh g^-1 at 100 mA g^-1, and retains 90.0 mAh g^-1 at 2000 mA g^-1, with full recovery at lower rates. Long-term cycling shows 82.1% capacity retention after 450 cycles, outperforming the undoped PB electrode (75.7%). Kinetic analysis reveals a dominant diffusion-controlled mechanism (76.5% contribution), with the lowest charge-transfer resistance and highest sodium-ion diffusion slope among all samples. These results highlight the synergistic role of CNT-induced electronic connectivity and lattice regulation, offering an efficient design pathway for next-generation PB-based cathodes in sodium-ion batteries.