文摘
Thanks to the advantages of low cost and good safety, magnesium metal batteries get the limelight as substituent for lithium ion batteries. However, the energy density of state-of-the-art magnesium batteries is not high enough because of their low operating potential; thus, it is necessary to improve the energy density by developing new high-voltage cathode materials. In this study, nanosized Berlin green Fe2(CN)6 and Prussian blue Na0.69Fe2(CN)6 are compared as high-voltage cathode materials for magnesium batteries. Interestingly, while Mg2+ ions cannot be intercalated in Fe2(CN)6, Na0.69Fe2(CN)6 shows reversible intercalation and deintercalation of Mg2+ ions, although they have the same crystal structure except for the presence of Na+ ions. This phenomenon is attributed to the fact that Mg2+ ions are more stable in Na+-containing Na0.69Fe2(CN)6 than in Na+-free Fe2(CN)6, indicating Na+ ions in Na0.69Fe2(CN)6 plays a crucial role in stabilizing Mg2+ ions. Na0.69Fe2(CN)6 delivers reversible capacity of approximately 70 mA h g–1 at 3.0 V vs Mg/Mg2+ and shows stable cycle performance over 35 cycles. Therefore, Prussian blue analogues are promising structures for high-voltage cathode materials in Mg batteries. Furthermore, this co-intercalation effect suggests new avenues for the development of cathode materials in hybrid magnesium batteries that use both Mg2+ and Na+ ions as charge carriers.