| Aqueous zinc-ion batteries/hybrid capacitors（ZIBs/ZICs）are considered to be one of the most promising energy storage devices because of their eco-friendliness,low cost,and high safety.Recently,a great number of meterials such as vanadium-based oxides and manganese-based oxides,have been extensively investigated to find high-performance cathodes.Among them,Mn O2 materials have received extensive concern owing to their multiple crystal structures,environmental friendliness,and great theoretical capacity.However,its low ion conductivity and structural instability endow it with poor rate capability and cycle performance as an electrode material.Thesis has solved the above problems as the starting point.High-performance electrode materials were prepared by nano-and composite modification of Mn O2 materials,and their zinc storage properties and mechanism were studied.The specific research works and results are as follows:（1）Firstly,α-Mn O2 nanoneedles were successfully prepared by one-step hydrothermal method,and the preparation processes of ZIBs and ZICs were explored by using this material as cathode.As a result,the ZIBs and ZICs are successfully constructed withα-Mn O2 nanoneedles as the cathode,zinc foil and porous carbon（PC）as the anode,and Zn SO4/Mn SO4 mixed solution as the electrolyte,showing good electrochemical performance.（2）On the basis of the device process in the previous chapter,δ-Mn O2 nanodots（δ-Mn O2 NDs）were prepared through one-step redox reaction route to solve the problems of poor rate performance and structural instability of manganese-based oxides during charge and discharge,and it was used for the first time as a cathode in ZIBs/ZICs.Compared with the controlδ-Mn O2（C-Mn O2）,theδ-Mn O2 NDs with ultra-small size can significantly enlarge the specific surface area of electrode materials,shorten the diffusion pathways of the ions/electrons,and alleviate the stress caused by the structural change of electrode materials during charging and discharging processes,thereby resulting in improved specific capacity,rate capability and cycling stability.The ZIBs constructed withδ-Mn O2 NDs as cathode and Zn as anode have a large specific capacity(335 m Ah g-1 at 0.1 A g-1),a superior rate performance(125 m Ah g-1 at 2.0 A g-1),a large specific energy(466.7 Wh kg-1 at 139W kg-1),and a satisfactory cyclability(86.2%of initial capacity retention over 1000 cycles at 1.0 A g-1).Meanwhile,the electrochemical kinetics analyses（CV,GITT and EIS）results verify that the ultra-small particle size can significantly improve the dynamic performance of Mn O2 cathode,and further explore the energy storage mechanism of H+/Zn2+co-insertion during the charging and discharging process by ex-situ tests（XRD,FESEM and XPS）.In addition,the ZICs were constructed by usingδ-Mn O2 NDs as cathode and Zn as anode,which shows a high energy density of 68.7 Wh kg-1 at a power density of 100 W kg-1 and a good cycle stability with 86.9%of capacitance retention over 5000 cycles at 1A g-1.（3）Finally,to improve the electrical conductivity of the Mn O2 and reduce the agglomeration of nanodots,the Mn O2 NDs/r GO composite was prepared by using reduced graphene oxide（r GO）as conductive substrate.As a cathode for ZIBs,the Mn O2 NDs/r GO composite electrode exhibits enhanced specific capacity(294 m Ah g-1 at 0.1 A g-1),rate property(124 m Ah-1 at 2.0 A g-1),energy density(403.6 Wh kg-1 at 139W kg-1),and cyclic stability(90.1%capacity retention after 1000 cycles at 1.0 A g-1)compared to the Mn O2.Meanwhile,the enhanced kinetic performance was verified by kinetic analysis（CV,GITT and EIS）,and the energy storage mechanism of the H+/Zn2+co-insertion process for the Mn O2 NDs/r GO composite electrode was further explored by ex-situ testes（XRD,FESEM and XPS）.In addition,the assembled ZICs were designed based on the Mn O2 NDs/r GO composite cathode and porous carbon anode,demonstrating a high energy density(67.2 Wh kg-1 at 100W kg-1)and satisfactory cycle life(90.9%capacity retention after 5000cycles at 1.0 A g-1). |
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