Flexible All-solid Asymmetric Supercapacitors Based On Carbon Nanotubes/Manganese Dioxide And Carbon Nanotubes/Molybdenum Disulfide Composites

With the rapid development of portable electronics,wearable and other flexible electronic products,it is urgent to develop high-performance flexible energy storage devices.Among various kinds of energy storage devices,supercapacitor exhibit high power density,fast charging speed,long cycling life,excellent safety and stability,which plays an important role in the field of energy storage.However,the biggest challenge of supercapacitors is their relative low energy density,which greatly limits their practical applications in the market.To resolve the above problems,one promising strategy is to develop high flexible all-solid-state supercapacitors with light weight,high power and energy densities.Therefore,the aim of this dissertation is to construct flexible all-solid asymmetric supercapacitor with large working voltage window,high energy density and excellent mechanical flexibility.This thesis includs the following aspects:First,carbon nanotubes?CNTs?film was used as the conductive substrate for the design and fabrication of flexible electrodes.In order to overcome the hydrophobicity of CNTs,surface treatment on CNTs films was conducted,through which both of hydrophilicity and conductivity of CNTs films have been enhanced.After hydrophilic treatment,large mass loading of other active materials on CNTs films can be easily achieved.Then,two-dimensional manganese dioxide?MnO₂?sheets were directly grown on the surface of the CNTs films through an electrochemical deposition method,the formed CNTs/MnO₂ composites can be used as binder free positive electrode for supercapacitors.Next,simple hydrothermal synthesis method was employed to directly grow petaloid molybdenum disulfide?MoS₂?on carbon nanotubes surface as an efficient binder free negative electrode material.The obtained CNTs composites not only take full advantage of individual component,but also pocess excellent synergistic interaction between two components,resulting high-performance supercapacitors.Finally,asymmetric supercapacitor devices were assembled by using the CNTs/MnO₂ composite electrode and CNTs/MoS₂ composite as positive and negative electrodes,respectively,and polyvinyl alcohol/LiCl gel was used as electrolyte.The obtained asymmetric all-solid-state supercapacitors exhibited a maximum operating voltage of 1.8 V?much higher than that of symmetric supercapacitors?,which delivered a high power density of 1.95 mWh/cm²?at an energy density of 198?Wh/cm²,an area capacity of 440 mF/cm²and a current density of 1mA/cm²?.Their specific capacitance can maintain over 89.8%of their original value after 5000charge/discharge cycles at a current density of 5 mA/cm²,suggesting an excellent cycling stability.Additionally,the devices can well maintain 98%of the original specific capacitance even after being bent for 5000 times,and almost showed no obvious change under different bending and even twisting states at different angles,showing excellent flexibility.