Study On Aluminum Ferrocyanide As Cathode Material For Aqueous Ion Batteries

Rechargeable aqueous metal-ion batteries（RAMBs）,which have the advantages of safety,non-toxic,environmental friendiness and inexpensive,have great application prospects in the field of large-scale energy storage.However,aqueous metal-ion batteries generally suffer from low operating voltage and low energy density,which limit their large-scale applications.So suitable cathode materials have become the keys to constructing high-performance aqueous batteries.In this paper,a novel cathode material,aluminum ferrocyanide,was synthesized by incorporating aluminum ions with high ionization potential into the Prussian blue framework and systematically studies its electrochemical properties,with a view to improving battery energy density and cycling stability.The main research contents and results are as follows:Firstly,a new Prussian blue analogue named aluminum ferrocyanide（Al HCF）was prepared by high temperature coprecipitation method.Samples with different morphologies were obtained by adjusting the ingredient ratio.The results showed that when Al³⁺:Fe（CN）₆^4-=2:1,the electrochemical performance of the material was the best.By adding graphene to improve its cycle stability and rate performance.When the amount of graphene is 5 wt%,the cycle stability is improved by 48.9%,and the rate performance is improved by nearly 10%.The electrochemical behavior of Al HCF/Gr cathode in monovalent ion battery was tested by three-electrode system.It was found that the smaller the intercalated ion radius,the higher the battery capacity.Secondly,the Al HCF/Gr cathode was investigated in detail in the three-electrode system,and it was found that Al HCF had an obvious activation process in the zinc ion electrolyte,the capacity increased and the polarization voltage decreased after activation.A high-voltage and high energy density aqueous zinc-ion battery was well-established.It has a high operating voltage of 1.79 V,which is the highest value among the reported aqueous zinc-ion batteries,and can deliver an energy density of 120.56 Wh kg^-1.The refinement data found that the voltage increase was achieved through the elongation of Fe-C bonds in the Fe-C≡N-Al covalent structure.The working mechanism of the battery is discussed by Ex-situ XRD,XPS.With the migration of zinc ions,the valence of Fe atoms changes,and Al HCF has an obvious phase transition process.Finally,the electrochemical performance of the Al HCF/Gr cathode in aqueous aluminum-ion batteries was preliminarily investigated.The sample has different properties in different solutions,and the capacity is low and decays rapidly.Among them,Al HCF in the Al₂（SO₄）₃solution has the highest capacity of 24.9 m Ah g^-1,while it has no electrochemical activity in the Al Cl₃ solution.In addition,the Al（OTF）₃ solution has the highest stability and coulombic efficiency,which may be the most suitable electrolyte for aqueous aluminum-ion batteries based on Al HCF cathode.The reason for the low capacity of the material in aluminum-ion batteries was analyzed by SEM and XPS,which may caused by the collapse of graphene,the crystallization of aluminum salt and only a small amount of Al³⁺intercalation involved in the reaction.