Vanadium-doped Prussian blue analogues as advanced cathode for sodium-ion batteries

Prussian blue analogues (PBAs) have broad application prospects in the field of cathode electrode for sodium ion batteries (SIBs) because they can promote the insertion and extraction process of sodium ions. Unfortunately, PBAs exhibits poor cycling performance and low coulombic efficiency because of their large vacancy flaws and inadequate structural stability during the insertion/extraction of Na+. Herein, we have developed a series of vanadium-doped PBAs with different transition metal (Fe, Co, Ni) via chemical co-precipitation method combined with water bath process. Through rigorous regulation of transition metals, the designed sodium vanadium ferrohexacyanate (VFeHCF) exhibits optimal electrochemical properties, including an initial specific capacity of 110 mAh g_ 1 at 20 mA g_ 1 with a coulombic efficiency of 93.7 %, and a reversible capacity of 80 mAh g_ 1 after 100 cycles with a capacity retention of 72.7 %, outperforming VCoHCF and VNiHCF. The enhancement in sodium storage can be attributed to the establishment of a stable Na+ interspersion potential between V4+ and Fe2+, as well as the extensive coordination environment of the iron ions, which promotes both electron transfer and Na+ transport.