NaV6O15: A promising cathode material for insertion/extraction of Mg2+ with excellent cycling performance

The rechargeable magnesium batteries (RMBs) are getting more and more attention because of their high-energy density, high-security and low-cost. Nevertheless, the high charge density of Mg2+ makes the diffusion of Mg2+ in the conventional cathodes very slow, resulting in a lack of appropriate electrode materials for RMBs. In this work, we enlarge the layer spacing of V2O5 by introducing Na+ in the crystal structure to promote the diffusion kinetics of Mg2+. The NaV6O15 (NVO) synthesized by a facile method is studied as a cathode material for RMBs with the anhydrous pure Mg2+ electrolyte. As a result, the NVO not only exhibits high discharge capacity (119.2 mAh center dot g(-1) after 100 cycles at the current density of 20 mA center dot g(-1)) and working voltage (above 1.6 V vs. Mg2+/Mg), but also expresses good rate capability. Besides, the ex-situ characterizations results reveal that the Mg2+ storage mechanism in NVO is based on the intercalation and de-intercalation. The density functional theory (DFT) calculation results further indicate that Mg2+ tends to occupy the semi-occupied sites of Na+ in the NVO. Moreover, the galvanostatic intermittent titration technique (GITT) demonstrates that NVO electrode has the fast diffusion kinetics of Mg2+ during discharge process ranging from 7.55 x 10-(13) to 2.41 x 10-(11) cm(2)center dot s(-1). Our work proves that the NVO is a potential cathode material for RMBs.