The Preparation Of Manganese Dioxide Electrode Materials And Their Capacitance Performances Study

Supercapacitors?SCs?are a promising energy storage divices,which have drawn increasing attention because of their unique feartures of high power density,fast charge/discharge rate,long-term stability and so on.Manganese dioxide is an attractive supercapacitors materials with high theoretical specific capacitance(up to 1370 F g^-1),low cost,naturally abundant,and environmentally friendly.However,the poor conductivity(10-5 10-6 S cm^-1)of manganese oxide has limited development of MnO₂-based supercapacitors with high capacity performance.In the thesis,we focus on the nanostructured MnO₂ electrode materials and the MnO₂-based composite electrode materials with highly external conductive materials toimprove electrochemical performance of MnO₂-based supercapacitors.We prepared nanostructured MnO₂ electrode materials and MnO₂/AgNW composite electrode materials through electrochemical deposition technology.We systematically investigated their electrochemical performance using cyclic viltammetry?CV?,galvanostatic charge/discharge?GCD?,and electrochemical impedance spectroscopy testing.Furthermore,the MnO₂/AgNW composite electrode materials assemble intoflexible asymmetric paper-based MnO₂/AgNW supercapacitor devices,and their manufacture process and performances were optimized.The main research contents and results as follows:1.A birnessite-MnO₂/ramsdellite-MnO₂/F-SnO₂?FTO?composite planar electrode with 3D peony-like micro-structure for micro-supercapacitors?m-SCs?was prepared via an original seriesresistor electrochemical deposition?SRED?of MnO₂ and subsequent secondary-growth.The composite electrode achieves an excellent specific capacitance of 1261 F g^-1 at 10 A g^-1 and extraordinary cycling stability with a significant 304% capacity retention after 10000 GCD cycles.Different from conventional cases,the MnO₂ prepared by the seriesresistor electrochemical deposition would undergo a surely happened secondary-growth with phase transition process during the GCD cycling,which could dramatically improve the pseudocapacitance performance by surface/inner-surface and bulk capacity aspects.The mechanism is discovered by EIS,CV,GCD,and first principle calculation based on density functional theory?DFT?.The secondary-growth process also offers a fabulous self-repairing feature of the SC electrode materials,which caters the maintenance-free and long-life requirement of the m-SCs applications.2.AgNW network act as a highly conductive current,and the MnO₂ nanorods are direct grown on the AgNW network by electrochemical deposition method to fabricate 3D three-dimensions MnO₂/AgNW composite materials,and its electrochemical performance systematically investigated.The AgNWs can beweldedeach other well at 300 oC to prevent the AgNW networkfrom peeling off,which dramatically improves the conductivity and lifetime of the electrode.The 3D MN/w-ANN electrode also shows an ever-increasing specific capacitance from 423.5 F g^-1 to 663.4 F g^-1 due to the gradual morphology changes from flower-like to honeycomb-like MnO₂ with the increasing cycle number,revealing 156.6% retention after 7000 cycles of GCD.3.Based on the MnO₂/AgNW composite electrode materials with excellent electrochemical behavior,a flexible asymmetric paper-based MnO₂/AgNW supercapacitor devices with excellent electrochemical performance are prepared using MnO₂/AgNW composite electrode materials.To prevent the AgNW network from peeling off,the AgNW films was pressure treatment.The flexible supercapacitor device showed a specific capacitance of 166.6 F g^-1 at scan rate of 10 mVs^-1,and the capacitance performance is well maintained after 10000 cycles of GCD.When the flexible device was folded,its specific capacitance is up to 101.4 F g^-1.