▎ 摘　　要

Sulfate-based (SO42-) polyanionic materials with low cost and ionic-conduction break fresh ground for "rocking-chair" systems. But the high moisture sensitivity and limited conductivity led to their poor crystal stability and inferior alkaline-ion intercalation chemistry. Here we report the design of graphene-based sandwich-type nanoarchitecture for sulfate. The three-dimensional graphene-based network not only provides continuous electron/ion pathways for fast intercalation kinetics, but also effectively protects the crystal structure from deterioration to depress moisture sensitivity. As a case study, the hydrated sulfate (Na2Fe(SO4)(2)center dot 2H(2)O)-graphene composite with a sandwich-type structure is prepared by a facile low-temperature synthesis. The depressed moisture sensitivity of hierarchical graphene-Na2Fe(SO4)(2)center dot 2H(2)O compared to the pristine one is demonstrated by comparing their hydration process, and moreover, a shell-core hydration mechanism is disclosed. The hierarchical composite exhibits improved electronic conductivity and better sodium-lithium insertion capability than the pristine one. It delivers a reversible capacity of 72 and 69 mA h g(-1) with redox potentials of 3.415/3.234 V (vs. Na+/Na) and 3.579/3.483 V (vs. Li+/Li) in sodium and lithium intercalation systems, respectively. Moreover, it also exhibits superior high rate capabilities and good cycling stability, which delivers 81% (for sodium) and 70% (for lithium) of the capacity at a 5 C rate. Therefore, the hierarchical sandwich-type architecture is favorable to realizing superior electrochemical performance for the sulfate, which presents a significant step forward in the development of low-cost large-scale batteries.