▎ 摘　　要

Na2+2xFe2-x(SO4)(3) is considered a promising cathode material for advanced sodium ion batteries with higher energy density due to its advantage of high-voltage, earth-abundant elements material and low-cost. However, strongly impeded by its fatal environmental sensitivity and low electronic conductivity, the NFS usually shows unsatisfactory electrochemical performance. Herein, a facile synthesis of microspherical NES@reduced graphene oxide composites are synthesized through spray-drying method. The well-designed microspherical NES@rGO with confined NFS nanocrystal in the three-dimensional graphene framework exhibits superb electronic and ionic conductivity as well as structural stability. The NES@rGO composites show outstanding electrochemical properties: high sodium storage capacity (99 mAh g(-1) at 0.1 C), superior rate performance (78 mAh g(-1) at 60 C and even up to 72 mAh g(-1) at 80 C), ultralong cycling stability (80.8% capacity retention after 2000 cycles at 30 C). The excellent performance makes the NES@rGO material a prospective electrode candidate for large-scale SIBs. (C) 2018 Elsevier Ltd. All rights reserved.