Study On Preparation And Electrochemical Performance Of Nano Titania/Titanate Electrode Material

Supercapacitors have received more and more attention for developing new efficient and practical electrochemical energy storage devices.Electrode materials are the key to the performance of supercapacitors.TiO₂is widely used in electrode materials due to good cycle stability,low cost and no harm to the environment.However,the specific capacitance of TiO₂differs greatly from its theoretical specific capacitance in practical application,which limits its application in supercapacitors.Therefore,it is particularly urgent to improve the capacitance performance of TiO₂electrode materials.The TiO₂is modified through two aspects in this thesis.On the one hand,TiO₂nanostructures are designed to increase specific surface area and specific capacitance;on the other hand,active materials are compounded with nanostructured TiO₂to obtain materials with stable structure,long cycle life and high specific capacitance.The specific research contents are as follows:?1?The TiO₂nanostructures were designed by hydrothermal method in order to improve the specific surface area and specific capacitance.With K doping,the morphology,phase composition and electrochemical performance were investigated by changing the solution concentration and reaction time.Finally,at 250?,KOH concentration of 0.25 M and reaction time of 5 h,the obtained sample was K-doped mixed phase?anatase and rutile?TiO₂nanowire structures.The nanowire structure was interconnected to form a porous network structure,which effectively increased the specific surface area and electrochemical performance of the material.The specific capacitance was 6.26 m F·cm^-2at current density of 0.1 m A·cm^-2.?2?In order to improve the specific capacitance of TiO₂,the nanostructured TiO₂was modified with Mo S₂to obtain the K-TNW@MNs electrode with a core-shell structure.Chitosan was a soft template to control the growth of Mo S₂so that it could grow uniformly on TiO₂nanowire structures.The TiO₂nanostructure increased surface area and provided better support for Mo S₂nanosheets.As a result,The K-TNW@MNs exhibited a high specific capacitance of123.53 m F·cm^-2at 0.4 m A·cm^-2and outstanding cycling stability of 84.49%capacitance retention over 6000 cycles.K-TNW@MNs was assembled into a new all-solid symmetric supercapacitor,exhibited a good capacitance retention rate of 78.44%after 6000 cycles.?3?In order to obtain more excellent electrochemical performance,TiO₂was modified by surface graphitization and in-situ growth of MnO₂to prepare K-TNW/C@MnO₂electrode.The graphitized carbon improved conductivity of TiO₂and provided reducing agents for in-situ synthesis of MnO₂.The K-TNW/C@MnO₂effectively improved surface conductivity of TiO₂and full exerted electrochemical advantages of MnO₂.As a result,K-TNW/C@MnO₂obtained specific capacitance of 281.88 m F·cm^-2at 0.3 m A·cm^-2.The capacitance retention rate of K-TNW/C@MnO₂was 70.65%in the cycle life.?4?The undesirable combination between MnO₂and TiO₂leaded to decline of cycle performance although the capacitance performance of TiO₂was obviously improved by MnO₂.Therefore,in order to improve the capacitance performance and maintain good cycle stability,PANI nanoparticles were successfully grown in-situ on large-area TiO₂nanowires by hydrothermal reaction and graft polymerization?PANI-APTEs-TNW?.The grafted functional groups effectively improved bonding strength of materials and surface.As a result,the specific capacitance of PANI-APTEs-TNW could reach 315.16 m F·cm^-2at 0.2 m A·cm^-2and capacitance retention of 86.81%after 1000 cycles.Compared to PANI-TNW,the obtained better capacitive behavior was attributed to PANI and TiO₂shown better bonding performance due to strong intermolecular force by introduction of APTEs,resulting in excellent specific capacitance and good cycle stability during charge-discharge process.Three kinds of TiO₂modified composite electrode materials were successfully prepared using TiO₂nanowires as the skeleton,and electrochemical properties of composite electrode materials were discussed.The results are:it is necessary to consider the full utilization of active materials for matrix nanostructures while increasing specific surface area through nanostructures.It is necessary to consider the damage of active materials to nanostructures and the connecting strength of nanomaterials with matrix nanoskeletons while introducing active substances to improve the surface capacitance performance.This will have a good reference value for rational design of TiO₂electrode material structures,improving the electrochemical performance of supercapacitor electrodes,and provide a new design idea for the preparation of supercapacitor materials.