StructuralpropertiesandelectrochemicalperformanceofdifferentpolymorphsofNb2O5inmagnesium-basedbatteries

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 Nb2 O5（TTNb2 O5@rGO and T-Nb2 O5@rGO） are successfully synthesized by a spray-drying-assisted approach.The three-dimensional graphene framework provides high conductivity and avoids the aggregation of Nb2 O5 nanoparticles.When employed as electrode materials for energy storage applications,TT-Nb2 O5 delivers a higher discharge capacity of 129.5 mAh g-1, about twice that of T-Nb2 O5 for Mg-storage,whereas,T-Nb2 O5 delivers a much higher capacity(162 mAh g-1) compared with TT-Nb2 O5(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-Nb2 O5 as cathode material for Mg-storage,and the faster Li+ diffusion kinetics,shorter diffusion distance of T-Nb2 O5 as cathode material for Li-storage.Our work demonstrates that exploring the proper crystal structure of Nb2 O5 for different ions storage is necessary.