Study On The Preparation And Electrochemical Performance Of Zinc-manganese Spinel Transition Metal Oxide

The spinel-type transition oxide material has become the focus of lithium-ion anodes due to its simple preparation process,high theoretical specific capacity,abundant content,low price,and easy control of morphology and structure.ZnMn₂O₄,stands out due to advantages of high theoretical specific capacity（1008mAh/g）,low cost,safety and nontoxic properties.However,the material has the disadvantages of large volume change in the circulation,easy particle agglomeration and poor conductivity,which greatly limits its application.In order to improve these problems,this dissertation begins with the preparation method and explores the influence of different methods on morphology and properties.ZnMn₂O₄ composites were successfully prepared by a simple one-step hydrothermal method.The effects of the kinds of compounds and their additions on the ZnMn₂O₄ composites were investigated.The results show that the composite of ZnMn₂O₄ with reduced graphene oxide（rGO）and carbon nanotubes（CNTs）is better than one of them alone.The study on the amount of graphene oxide（GO）found that the prepared ZnMn₂O₄/rGO composites had the best comprehensive performance when the addition amount of GO was 0.1 g.After 226 cycles at a current density of 200 mA/g,the specific capacity of charge and discharge can be as high as 1134 mAh/g and 1161 mAh/g,and the trend of rising is still maintained.At a current density of 500 mA/g,the specific discharge capacity remained at 587.8mAh/g after 500 cycles.The results of CNTs and GO addition showed that the sample prepared by adding CNTs with GO were 0.06 g and 0.1 g have good electrochemical properties.After 200 cycles at a current density of 500 mA/g,The discharge capacities and the capacity retention rates of the sample are 886 mAh/g and 104.4%,respectively.ZnMn₂O₄ micro-nanospheres with porous structure were successfully prepared by simple coprecipitation method.In the experiment,the effects of the stirring speed and the heating rate during sintering were analyzed in detail.The results show that too high stirring speed will make the prepared ZnMn₂O₄ micro-nanospheres agglomerate,while the excessive heating rate will lead to the breakup of ZnMn₂O₄micro-nano spheres.When the stirring rate was 200 r/min and the sintering temperature was increased by 2℃/min,the samples prepared had a loose porous micro-nanospheres structure.The shortest time to complete all the morphological changes in the cycle and the best electrochemical performance were obtained.The discharge specific capacity is 723 mAh/g after 500 cycles at a current density of1000 mA/g,with a capacity retention of 102.7%compared to the second cycle.In this work,starting from·the preparation of zinc-manganese spinel and its complex species,the morphologies and properties were studied.Excellent performance makes this material be expected to be applied to high energy batteries.This work provided a simple and effective method to improve the conductivity,agglomeration and large volume changes of spinel-type transition metal oxides.