The Structural Design Of High Performance Transition Metal Composite And Its Application In Aqueous Supercapacitor

Supercapacitors（SCs）are new type of energy storage devices between secondary batteries and traditional capacitors,which have the advantages of highly power density,fast charging/discharging time and environmental friendliness thus received widespread attentions.However,the large-scale application of SCs was limited by the restrained energy density and poor stability.By matching the cathode and anode,the assembled asymmetric supercapacitors（ASCs）can widen the voltage window of the devices and break through the energy storage limitations of symmetric devices.Aqueous electrolytes are the most cost-effective option due to their high ionic conductivity,safety and low preparation costs.Therefore,it is extremely important to prepare highly efficient wide voltage aqueous ASCs by modifying the electrode materials while maintaining the inherent advantages of SCs.This thesis focuses on the key scientific issues of aqueous ASCs,preparation of highly efficient aqueous ASCs through the construction of electrode materials and the matching of positive with negative electrodes.The main research includes:（1）Although metal oxides possess high theoretical specific capacitance and voltage window,their poor conductivity and structural stability make it difficult to meet the demands of efficient SCs during long-term redox reactions.In this paper,PEDOT was electrodeposited on the surface of manganese dioxide（Mn O₂）nanospheres to prepare Mn O₂@PEDOT nanocomposite electrodes.Thanks to the synergistic effect of the nanocomposites,the Mn O₂@PEDOT cathode exhibits excellent specific capacitance and conductivity.In order to widen the voltage window of the device,V₂O₅with comparable voltage and capacitance was prepared as the anode by a similar electrodeposition method.The assembled aqueous planar ASCs possess a voltage window of 1.8 V,an energy density of 15.1μWh cm^-2,excellent long-term cycling stability and integration performance.（2）The matching properties of positive and negative materials significantly affects the overall performance of aqueous ASCs.Vanadium dioxide（VO₂）has received significant attention from researchers due to its wide operating voltage window at both cathode and anode,thus improving matching performance effectively.However,VO₂suffers from poor specific capacitance,inferior structural stability and low conductivity as electrode materials.Therefore,VO₂@Mn O₂ cathode and VO₂@C anode were prepared by hydrothermal method to improve the overall performance of VO₂.Ultimately,the assembled VO₂@C//VO₂@Mn O₂ aqueous ASCs can operate a stably voltage window of 0～2.2 V,achieving an energy density of 77.1 Wh kg^-1,at the same time,the quasi-solid ASCs have good stability and mechanical flexibility.（3）The structural of most flexible electrodes are prone to damage during long-term service and unable to meet the demands of highly stable ASCs applications.Therefore,we designed chemical crosslinking PVA/citral free-standing electrode with pretty stability and flexibility.This 3D spatial network structure with a porous structure offers higher stability and bending resistance than pure hydrogels.The assembled asymmetric devices possess a wide voltage window of 2.6 V,high specific capacitance of 61.2 F g^-1 and outstanding energy density of 57.5 Wh kg^-1 in high concentration electrolyte.Meanwhile,the quasi-solid ASCs exhibit superior temperature resistance and excellent mechanical flexibility.