| As a new type of energy storage device,supercapacitors play an important role in many fields of modern society due to their high power density and long cycle life.However,because of the limitation of the electrode material,the supercapacitor can not be available for the large-scale application.Manganese-based oxides are potential candidate materials due to its high theoretical specific capacity,abundant reserves,low-cost and environment-friendly.However,the conventional manganese-based oxides can not show ideal performance due to poor cycling stability and low electrical conductivity.In this paper,a series of manganese-based oxides with excellent cycling stability and high electrical conductivity were designed and synthesized.The main contributions of this dissertation are described as follows:(1)The synthesis and electrochemical performance study of graphene/manganese-based oxide compositeThe graphene/manganese-based oxide composite with different morphology were synthesized by a sample hydrothermal treatment,then various characterization and electrochemical performance tests were carried out.The results showed that the electrochemical performance of electrode materials is concerned with the dispersion degree and conductive properties.MnOOH nanorods/graphene composite materials revealed higher specific capacitance(198.2 F g-1 at 1 A g-1)and superior cycling stablility(86.2%after 5000 cycles),the better electrochemical performance is due to the graphene substrate,which can improve the electrical conductivity,and increase the specific surface area as well as prevent the agglomeration of the material,which can improve the electron transfer rate and enhance the mechanical properties of the materials.(2)The synthesis and electrochemical performance study of yolk-shell-structured MnO2 microspheres.The MnCO3 microspheres were first synthesized by a simple precipitin reaction.Then,the as-obtained MnCO3 microspheres served as templates and underwent continuous redox reactions to form yolk-shell MnO2@MnO2/MnCO3 microspheres in KMnO4 solution by controlling the treatment time.Next,the unreacted MnCO3 templates were removed by dilute hydrochloric acid,resulting in the yolk-shell porous MnO2@MnO2 microspheres.The yolk-shell porous MnO2@MnO2 microspheres exhibited a specific surface area of 171.66 m2 g-1,which can provide a large number of electrochemical active sites and diffusion channels for electrolyte ion.In addition,the special structure can suppress the powdering and agglomeration effect.Thus the specific capacitance was 226.4 F g-1 and 191.5 F g-1 at 1 A g-1 and 10 A g-1 of yolk-shell porous MnO2@MnO2 microspheres.The MnO2/MnO2@MnO2 microspheres obtained by hydrothermal treatment revealed better rate capability(241.1 F g-1 at 1 A g-1 and 212.1 F g-1 at 10 A g-1)and cycle performance(91.9%after 10000 cycles)due to its more stable structure.(3)The synthesis and electrochemical performance study of yolk-shell-structured Mno2 microspheres with oxygen vacanciesYolk-shell-structured Mno2@Mno2 microspheres showed the ideal morphology,but the conductivity is still poor.In order to improve the conductivity of the material,oxygen vacancies were introduced to Mno2@MnO2 microspheres via a facile heat treatment method under a hydrogen/argon gas atmosphere,the yolk-shell-structured MnO2 microspheres with oxygen vacancies(ov-MnO2@MnO2)were successfully obtained.The yolk-shell-structured ov-MnO2@MnO2 microsphere electrode exhibited a large specific surface area(259.83 m2 g-1)and good conductivity,thus achieved a high specific capacitance(452.4 F g-1 at 1 A g-1 and 316.1 F g-1 at 50 A g-1),excellent cycling stability(92.2%after 10000 cycles)and superior rate capability(～79.2%and 69.9%of the initial capacity at 20 A g-1 and 50 A g-1,respectively).The superior electrochemical performance of ov-MnO2@MnO2 is mainly ascribed to the unique yolk@void@shell nanostructure,the presence of oxygen vacancies in the crystal lattice and the synergistic effect of individual components of the hybrid. |
PDF Full Text Request