Fabrication And Application Of Metal Sulfide Nanostructured Electrodes In Electrochemical Encergy Storage Devices

With the demand for energy storage devices and flexible electronics,it is urgent to develop and design energy materials and devices efficiently.Metal sulfides are often selected as the electrode active materials for electronic devices due to their high Faraday activities,excellent capacitity performance,abundant raw materials and environmental friendliness properties.These compounds have different oxidation states and nanostructures,which can effectively improve the performance of various devices.In this dissertation,supercapacitors were taken as target devices,and metal sulfides with different structure and morphological characteristics were synthesized on different substrates by various methods and their energy storage performance in supercapacitors were well investigated.The main conclusions and innovations of the dissertation are as follows:(1)Different methods were used to prepare Cu2S nanorod films with two crystal phases and structural characteristics on copper plates,and the growth process and mechanism were carefully investigated.When they served as electrodes in supercapacitors,hexagonal Cu2S nanorod delivered better electrochemical properties with a specific capacitance of 346 mF cm-2 at the current density of 5 mA cm-2,and a retention rate of over 90%after 2000 cycles.In addition,hierarchical Cu2S nanorods exhibited good photocatalytic degradation ability for methylene blue(MB)and RhB dyes under visible light and with the assistance of H2O2,which verified the versatility of the prepared materials.(2)Hierarchical structured Co9S8-NiCo2O4 films were prepared on carbon cloth substrates by a multi-step method,where the structure of Co9S8 was hollow nanoneedles while NiCo2O4 was ordered nanosheets.Co9S8-NiCo2O4 processed high specific surface area and showed superior electrochemical characteristics to each single stage structure.At the current density of 1 A g-1,its capacity was as high as 221.11 mAh g-1 and the retention rate was about 92.9%after 5,000 cycles.A flexible solid-state hybrid supercapacitor based on the Co9S8-NiCo2O4 electrode provided a high energy density of 86 Wh kg-1.In addition,after 10,000 cycles,the retention rate of the hybrid supercapacitor remained 84.2%at 10 A g-1,indicating its excellent stability.(3)A series of metal sulfide composite nanofilms(Co9S8-MoS2/NiS2/NiCo2S4,NiCo2S4-CuS/NiS2/MoS2)were prepared on the carbon cloth substrates by a universal method.Among them,the Co9S8-NiCo2S4 electrode delivered best energy storage ability with a capacity of 337.78 mAh g-1 at 1 A g-1,and it also yielded excellent stability with a retention rate of 93%after 5,000 cycles.The Co9S8-NiCo2S4 electrode was then assembled into a flexible all-solid-state hybrid supercapacitor with a maximum energy density of 104 Wh kg-1.Finally,the hybrid capacitor device could be turned into a wearable charger that drove low-power electronics.