Synthesis And Electrochemical Performance Of Manganese Based Aqueous Zinc Ion Battery Cathode Materials

The development and utilization of renewable energy has solved the problems of energy and environment pollution to a certain extent.Nevertheless,renewable green energy has the serious problem of discontinuity caused by geography and time.Lithium-ion batteries（LIBs）already dominate commercial rechargeable batteries,which has been widely used in electronic equipment,electric vehicles and other fields.Its developed rapidly because of its long cycling life and high energy density.However,the use of toxic organic electrolytes poses serious safety risks,and the shortage of lithium resources and the strict requirements of LIBs assembly environment have caused a big cost problem,which severely limits its future development in the field of energy storage.Aqueous zinc-ion batteries（ZIBs）are safe,non-flammability,and low-cost because of the advantages of using a salt solution containing large amounts of water as an electrolyte.It can be assembled without oxygen.In ZIBs,cathode materials such as manganese-based materials,vanadium-based materials,prussian blue derivatives and organic compounds have been widely studied.Manganese-based compounds have attracted much attention due to their rich valence states and crystal structures.However,manganese-based materials have the problem of manganese dissolution,which leads to the instability of the material structure,with poor cycle life.In this paper,the cathode materials of aqueous ZIBs were modified and its zinc storage performance was studied.The main research work is as follows:Na_2/3Ni_1/3Mn_2/3O₂micorods with single crystal structure were successfully prepared by a simple high-temperature calcination method.The successful doping of Ni plays a supporting role in stabilizing the structure of the material and effectively inhibiting the dissolution of manganese.The Ni-doping increases interlayer spacing of Na_0.7Mn O₂,which is more conducive to the storage of Zn²⁺and rapid reaction kinetics.As a cathode material of aqueous ZIBs,it maintains the specific capacity of 130 m Ah g^-1at a high current density of 5 A g^-1in a long-term cycle of up to 2500 cycles and the capacity retention rate is as high as 93%.Single crystal structure of MnMoO₄was synthesized by a simple co-precipitation method which was dopamine coated to MnMoO₄@NC.It shows an excellent electrochemical performance as cathode material of aqueous ZIBs.The carbon layer covering its surface not only improves the electrical conductivity,inhibits the dissolution of Mn,avoid direct contact between electrode material and electrolyte,but also providing more ion storage sites.Specifically,it presents a high specific capacity of 249.5 m Ah g^-1at 1 A g^-1after 400 cycles,and demonstrates excellent rate capability.