Cobalt-based bimetallic Prussian blue analogues modified with Selenization and carbon coating as high-performance anodes for sodium-ion batteries

Prussian blue analogues (PBAs) are widely recognized as versatile precursors for designing high-performance anode materials in sodium-ion batteries (SIBs), but their application is restricted by poor conductivity and severe volume variation. Selenization generates metal selenides with superior electrical conductivity and richer redox chemistry, while polydopamine (PDA)-derived carbon coating provides nitrogen-doped carbon frameworks that stabilize the structure and facilitate charge transport. In this work, cobalt-based PBAs with secondary metals including Mn, Zn, Fe, and Ni are synthesized and systematically compared as the anode materials of SIBs. Among them, cobalt–iron PBA (CoFe PBA) exhibits the highest initial capacity of 1054.4 mAh/g at 0.05 A/g but suffers from rapid fading. Post-synthetic modification through combined selenization and carbon coating (CoFe/Se/NC) markedly improves electrochemical behavior, delivering reversible capacities of 782.1 and 514.1 mAh/g respectively at the first and second cycles, and retaining 421.5 and 323.9 mAh/g respectively at 0.1 and 1.0 A/g after 100 cycles. The enhanced sodium ion diffusion coefficient of CoFe/Se/NC confirms accelerated ion transport and favorable reaction kinetics. This study establishes clear correlations between composition, surface modification, and sodium-storage performance, demonstrating the effectiveness of compositional engineering and hybrid structural design in developing PBAs as competitive anode materials for next-generation SIBs.