High Rate Performance of Aqueous Magnesium-iron-ion Batteries Based on Fe_(2)O_(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_(2)O_(3)is an anode material commonly used in Li-ion battery.However,the nano-cube Fe_(2)O_(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_(2)O_(3)/GH is used as anode in the dual MgSO_(4)+FeSO_(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 MgSO_(4)+FeSO_(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 MgO.The Fe_(2)O_(3)/GH demonstrates high rate properties and reversible capacities of 198,151,121,80,75 and 27 mAh g^(−1)at 50,100,200,300,500 and 1000 mA g^(−1)correspondingly.