| Supercapacitor(SC)is regarded as one of the most potential products for next-generation energy storage devices due to its high power density,fast charge-discharge rate,environmental friendliness and long lifespan.Unfortunately,the low energy density of SC limits its large-scale application.In this paper,asymmetric supercapacitors(ASC)were assembled by combining activated carbon(AC)electrodes with capacitive energy storage mechanism and transition metal oxide electrodes with faradic charge storage mechanism to widen the operating voltage window of conventional SCs,while a variety of electrode materials with excellent redox activity were designed and synthesized.The main content and the results obtained of this paper are as follows:1.In chapter 3,two groups of bimetallic cationic molybdates(CoxNi1-xMoO4 and CoxCa1-xMoO4,0?x?1)with multiple redox-active species were efficiently synthesized by microwave-assisted method.The effects of the relative contents of different metal acetates in the reactants on the phase composition,morphology,pore distribution and specific surface area of the products were investigated and the specific capacity of the conventional transition metal molybdates was improved.A comprehensive evaluation of the nine active materials in the two groups of synthesized bimetallic cationic molybdates by electrochemical property tests revealed that the improved performance of the hybrid electrodes was derived from their more diverse redox active species and larger specific surface area.The best overall performance of the hybrid electrodes was achieved when n(Co(CH3COO)2·4H2O):n(Ni(CH3COO)2·4H2O)or n(Co(CH3COO)2·4H2O):n(Ca(CH3COO)2·H2O)=8:2(molar ratio)in the reactants.The optimal electrode in each group was used as the positive electrode,AC was used as the negative electrode to assemble the alkaline aqueous ASC device,respectively.And the two assembled ASC devices could achieve the highest energy density of 11.1Wh kg-1 and 8.4 Wh kg-1,respectively.2.In chapter 4,ZnCo2O4/MnO2 hybrid nanosheets were synthesized directly on nickel foam current collectors using a two-step hydrothermal method and a subsequent calcination treatment.The outstandng cycling stability of the hybrid materials is attributed to the excellent structural foundation of the ZnCo2O4 nanosheets substrate-the nanosheets support each other to form a three-dimensional network with highly-open space;the further coating of the MnO2 layer can endows the composite electrodes a better cycling life.The ZnCo2O4/MnO2 hybrid electrode with excellent specific capacity and stability was assembled with the AC electrode to form an all-solid-state ASC device with a stable operating voltage of 1.55 V,which could reach a maximum energy density of 29.41 Wh kg-1 at the power density of 628.42 W kg-1.3.In Chapter 5,CuO@NiMoO4 composites with core-shell nanostructures were firstly synthesized via in situ oxidation of copper foam substrates through a simple chemical bath deposition strategy,followed by a mild hydrothermal and calcination treatment.The electrochemical tests show that the construction of the core-shell nanowire arrays not only allows the synergistic effect between the CuO core and NiMoO4 shell,but also reduces the capacity loss of the electrode during high-current cyclic charge-discharge;The duration of hydrothermal reactions has a significant effect on the thickness of the NiMoO4 shell.When the thickness of NiMoO4 shell is about 50nm,the electrode material obtains a higher electrochemical surface area and exposes more abundant electrochemical active sites,which is the most favorable condition for electrolyte migration in the nanostructure and at the same time,the composite electrode exhibits optimal conductivity.An all-solid ASC device composed of CuO@NiMoO4 positive electrode and AC negative electrode could deliver a stable operating voltage of 1.6 V and the maxium energy density of 42.3Wh kg-1.In this paper,the author used various strategies to modify electrode materials for SC devices from different perspectives,and provided new ideas for the design and development of next-generation high-performance SCs. |
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