Preparation And Composite Modified Study Of Cathode Material MgMn₂O₄ For Aqueous Magnesium Ion Battery

MgMn₂O₄has a high theoretical capacity of 270 m Ah/g as the cathode material of magnesium ion batteries,which value is about 1.8 times that of Li Mn₂O_4.However,magnesium ion has strong polarization,high diffusion energy barrier and fast capacity fading,which limits its practical application and is worthy of further study.In this paper,MgMn₂O₄compounds with spinel structure have been prepared successfully by glucose-assisted hydrothermal method.As well known,carbon nanotubes（CNTs）and Reduced graphene oxide（r GO）possess an excellent electrical conductivity and large surface area,compared to Mg Mn₂O₄,the composites of Mg Mn₂O₄/CNTs and Mg Mn₂O₄/r GO exhibit higher specific capacity and better cycle stability.Electrochemical performance was effectively improved and enhanced.First,the precursors were prepared by glucose assisted hydrothermal method and fully calcined in air at 450℃～750℃.The effects of calcination temperature on the phase evolution,surface morphology and electrochemical cycling performances of the products have been studied systematically.It was found that a nearly single-phase Mg Mn₂O₄has been obtained at 550℃and 650℃for 5h,respectively.By comparison,the sample calcined at 650℃for 5h showed a maximum discharge specific capacity of 170.6 m Ah/g at a current density of 100 m A/g,and the discharge specific capacity remained 147.5 m Ah/g after 50 cycles.The capacity retention is about 86%.MgMn₂O₄/CNTs composites were prepared by annealing the well dispersed mixtures after ultrasoinc treatment in the liquid phase.The effects of the annealing temperature of 200℃～400℃and the amount of CNTs on the structure and electrochemical properties have been investigated systematically.The results show that the maximum discharge capacity of the composite sample annealed at 300℃with 5 wt.%CNTs at a current density of 100 m A/g is up to the theoretical capacity of269.5 m Ah/g,which is close to the theoretical capacity and about 1.6 times of Mg Mn₂O₄.And the cycle capacity remains at 168.8m Ah/g after 50 cycles.MgMn₂O₄/r GO composites were prepared by hydrothermal method.The effects of hydrothermal temperature from 160℃to 180℃and duration time from 6 h to 12h on the structure and electrochemical properties have been investigated systematically.The results show that the Mg Mn₂O₄/5%r GO samples obtained at 160℃for 12h have spherical pore morphology and a specific surface area of 41.4 m²/g.The maximudischarge specific capacity is as high as 259.8 m Ah/g at the current density of100 m A/g.The discharge specific capacity remained 151.6 m Ah/g after 100 cycles,and the capacity retention was 58.4%compared with the maximum discharge specific capacity.