Synthesis And Characterization Of Manganese Oxides Cathode Materials For Zinc-ion Batteries

In the recent years,with the rapid development of grid energy storage systems and electric vehicles,the research of new high-performance energy storage devices has become quite a heated topic.The recently introduced zinc-ion battery has drawn much attention due to its safety,low-cost and high energy density.However,the research on zinc-ion battery is still in its infancy.Only a few cathode materials have been developed so far.Meanwhile,all these materials are not completely satisfactory in the respect of electrochemical properties,due to their poor electrical conductivity and/or other factors.On the other hand,the mechanism of zinc ion storage and the reason for the capacity fading in ZIB system have not been thoroughly clarified.In this dissertation,we focus on the research of both the electrode material and the reaction mechanism.Firstly,?-MnO₂ nanowire material was prepared through one kind of hydrothermal method.The material has high specific surface area,which can effectively improve the electrochemical performance.The material exhibited good cycling stability and excellent rate performance.The discharge specific capacity at current density of 100 mA g^-1 is 274 mAh g^-1 and the capacity retention after 50 cycles is 98.6%.The results showed that heat treatment would reduce the electrochemical performance of the samples.At the same time,cycling performance of the battery was effectively improved through one method of pre-adding Mn²⁺to the electrolyte.Secondly,?-Mn₂O₃ was reported to act as a new cathode material for zinc-ion battery.In addition,Zn/?-Mn₂O₃ battery was assembled.The specific capacity of this material is 148 mAh g^-1.The cathode also exhibited excellent cycling stability with a long cycle life up to 2000 times,which is far superior to that of previous reported MnO₂material.Lastly,the ion storage mechanism of?-Mn₂O₃ in zinc-ion battery and strcture changes during the charge/discharge process were also investigated.The results showed that?-Mn₂O₃ is capacble of decent zinc ion storage capability.The pristine?-Mn₂O₃undergoes a reversible phase transition from bixbyite structure to a layered-type zinc birnessite during the electrochemical zinc ion insertion and extraction.The results could not only benefit for the practical application of rechargeable zinc-ion battery,but also broaden the horizons of understanding the electrochemical behaviors and mechanism of the rechargeable zinc ion batteries.