Structural properties and electrochemical performance of different polymorphs of Nb2O5 in magnesium-based batteries

The selection of the most suitable crystal structure for ions storage and the investigation of the corresponding reaction mechanism is still an ongoing challenge for the development of Mg-based batteries. In this article, high flexible graphene network supporting different crystal structures of Nb2O5 (TT-Nb2O5@rGO and T-Nb2O5@rGO) are successfully synthesized by a spray-drying-assisted approach. The three-dimensional graphene framework provides high conductivity and avoids the aggregation of Nb2O5 nanoparticles. When employed as electrode materials for energy storage applications, TT-Nb2O5 delivers a higher discharge capacity of 129.5 mAh g−1, about twice that of T-Nb2O5 for Mg-storage, whereas, T-Nb2O5 delivers a much higher capacity (162 mAh g−1) compared with TT-Nb2O5 (129 mAh g−1) for Li-storage. Detailed investigations reveal the Mg intercalation mechanism and lower Mg2+ migration barriers, faster Mg2+ diffusion kinetics of TT-Nb2O5 as cathode material for Mg-storage, and the faster Li+ diffusion kinetics, shorter diffusion distance of T-Nb2O5 as cathode material for Li-storage. Our work demonstrates that exploring the proper crystal structure of Nb2O5 for different ions storage is necessary.