High Rate Performance of Aqueous Magnesium-iron-ion Batteries Based on Fe_2O_3@GH as the Anode

Aqueous Mg-ion batteries (MIBs) are safe,non-toxic and low-cost.Magnesium has a high theoretical specific capacity with its ion radius close to that of lithium.Therefore,aqueous magnesium ion batteries have great research advantages in green energy.To acquire the best electrode materials for aqueous magnesium ion batteries,it is necessary for the structural design in material.Fe_2O_3 is an anode material commonly used in Li-ion battery.However,the nano-cube Fe_2O_3 combined with graphene hydrogels (GH) can be successfully prepared and employed as an anode,which is seldom researched in the aqueous batteries system.The Fe_2O_3/GH is used as anode in the dual Mg SO_4+Fe SO_4 aqueous electrolyte,avoiding the irreversible deintercalation of magnesium ions.In addition,the Fe element in anode material can form the Fe~(3+)/Fe~(2+)and Fe~(2+)/Fe~(3+)redox pairs in the Mg SO_4+Fe SO_4 electrolyte.Thus,the reversible insertion/(de)insertion of magnesium and iron ions into/from the host anode material can be simultaneously achieved.After the initial charge,the anodic structure is changed to be more stable,avoiding the formation of Mg O.The Fe_2O_3/GH demonstrates high rate properties and reversible capacities of 198,151,121,80,75 and 27 m Ah g~(-1) at 50,100,200,300,500 and1000 m A g~(-1) correspondingly.