Controlled Fabrication And Electrochemical Properties Of Micro/nano-structured Electrode Materials For New-concept High-energy Supercapacitors

At present,the structure of energy storage devices evloved with the growing demand of small,thin,light and flexible electronic devices.Recent developments in device construction have facilitated the further application of supercapacitors.However,the practical application of supercapacitors still faces challenges,such as low energy density and poor cycling performance etc.Researches now focus on developing high-capacity supercapacitor electrode materials and assembling high-energy density new-concept supercapacitor devices.This thesis is focused on the fabrication of new-type micro/nano-structured electrode materials for high-performance supercapacitors,and the construction of new-concept supercapacitor devices with high energy densities The main contents and results are as follows:（1）NiO/Ni（OH）₂ nanoflowers encapsulated in three-dimensional interconnected poly（3,4-ethylenedioxythiophene）（PEDOT）have been fabricated on contra wires through a mild electrochemical route.The as-formed hybrid electrode made of NiO/Ni（OH）₂/PEDOT delivered a high specific capacitance of 404.1 mF cm^–2(or 80.8 F cm^–3)at a current density of 4 mA cm^–2 and a long cycle life with 82.2%capacitance retention after 1000 cycles.Furthermore,a fiber-shaped flexible all-solid-state asymmetric supercapacitor based on the resulting hybrid electrode was assembled.The energy density of 0.011 mWh cm^–2 at a power density of 0.33 mW cm^–2 was achieved under an operating voltage window of 1.45 V.This work provides an effective strategy to fabricate high-performance electrodes for fiber-shaped flexible asymmetric supercapacitors through a facile and low-cost route.（2）A flexible asymmetric supercapacitor with high electrochemical performance is designed and fabricated using WS₂/rGO aerogel and Fe₂O₃/C cloth as the positive and negative electrodes,respectively.Self-supporting WS₂/rGO aerogel composite electrode was prepared by a one-step exfoliation and functionalization method,which showed a high specific capacitance of 38.9 mF cm^–2 at a current density of 1 mA cm^–2.Benefiting from the large surface area of the few layer nanosheets,the flexible asymmetric supercapacitor based on the WS₂/rGO aerogel composite electrode exhibited a high specific capacitance of 89.7 mF cm^–2 and a high energy density of 0.19 mW h cm^–3 at a voltage window of 1.5 V,as long as a good cycling stability.These results indicate that the WS₂/rGO aerogel composites are quite suitable and promising as high-performance electrode materials for flexible supercapacitors.（3）A unique hybrid supercapacitor is designed and fabricated using self-assembled orthorhombic-phase niobium oxide@carbon（T-Nb₂O₅@C）nanowires as an anode and commercially available activated carbon as a cathode.The 3D-interconnected T-Nb₂O₅@Cnanowireshavebeensynthesizedviaahighlyefficient microwave-solvothermal method combined with subsequent thermal treatment.The experimental parameters（e.g.,time and temperature）can be easily programmed,and the synthesis time can be significantly shortened,thus enabling to build up abundant recipes for engineering scale-up production.The Li-ion intercalation pseudocapacitance electrode made of the as-formed self-assembled T-Nb₂O₅@C nanowires shows excellent charge storage and transfer capability.When assembled into a hybrid supercapacitor with a cathode of activated carbon,a high energy density of 60.6 W h kg^–1 and a high power density of 8.5 kW kg^–1 with outstanding stability are achieved.In virtue of easy optimization and programmability of the synthetic strategy and the remarkable electrochemical performance,the self-assembled T-Nb₂O₅@C nanowires offer a promising anode for asymmetric hybrid supercapacitors.