Studies On Synthesis And Electrochemical Energy Storage Properties Of NiMoO₄ And CuO@MnO₂ Nanostructure

With the development of the world economy,the demand for energy is increasing.Using of the traditional energy sources,such as coal,oil,has brought the serious environmental problem.The solar energy may be the most reliable approach to take the road of sustainable development.However,it is not stable and facile to generate power from solar energy.Hence,it is worth to study how to store and utilize solar energy.Among the field of energy storage,electrochemical energy storage has take a significant place with its facile,efficient property.Among electrochemical energy-storage devices,supercapacitors and lithium-ion batteries have been widely used for our modern society.Supercapacitors have attracted a great deal of attention due to their fast recharge ability,high energy storage capability,good rate performance and long cycle stability.At the same time,its energy density is much lower than lithium-ion batteries,which limits its further application.Meanwhile,lithium-ion battery has been world-widely used in area of electronics and electric devices due to their high energy density and output voltage,safety and low self-discharge rate.The lithium-ion batteries is beginning to penetrate the transportation sector with plug-in hybrid electric vehicles and with small all-electric vehicles.For both the supercapacitors and lithium-ion batteries,the electrode materials are the key components.As for the electrode materials,its morphology,structure,electron conductivity,porosity and specific surface area have played the crucial role to the final performance.In this thesis,several electrode materials with unique structure and novel morphology have been successfully synthesized and its relevant property were potimized to improve the performance.The main content is as follow:1.NiMoO4·H2O nanoflake(H-NF)and NiMoO4·H2O nanowire arrays(H-NW)were directly fabricated on Ni foam.The effect of crystalline water in NiMoO4 on electrochemical perfornance was aslo investigated.The morphology of NiMoO4·H2O could be facilely controlled to be nanoflake or nanowire by adding NH4F or not in the process of hydrothermal syntiesis.The electrochemical test indicated that the NiMoO4 ·H2O show better electromical properties than that of the NiMoO4 which lost its crystal water.The crystal water in NiMoO4 has provided the ions and proton transport channel which enhanced the electrochemical ability.In addition,the structure of nanoflake arrays with higher specific surface and higher conductivity show more advantages than nanowire arrays.Furthermore,asymmetric supercapacitor(ASC)device was assembled using the H-NF as positive electrode and activated carbon(AC)as the negative electrode,which delivered a high energy density of 53.824 Wh Kg-1 at a power density of 239.37 W Kg-1(56.389 mAh g-1 at 1 A g-1).2.Oxygen-deficient NiMoO4 NF arrays and NW arrays were successfully synthesized on Ni foam by hydrogenation process for assembling an all-solid-state ASC device.The XPS and TGA have been investigated to demonstrate its molecular formula of nanoflake and nanowire as NiMoO3 63 and NiMoO3 358.The introduction of oxygen vacancies in NiMoO4 significantly increased the conductivity and accelerated the kinetics of the surface redox reactions,which improved electrochemical performance.The Oxygen-dificient NiMoO4//AC all-solid-state ASC device achieved a maximum energy density of 49.11 Wh Kg-1 at a current density of 800 W Kg-1.3.CuO@MnO2 core-shell nanosheet arrays were synthesiszed on Cu foil by water bath and hydrothermal process.In this unique core-shell structure,the primary single-crystalline CuO nanosheet arrays directly grown on Cu substrates allowed for efficient electrical and ionic transport.The MnO2 shell enhanced surface area and high theoretical Li+ storage capacity,and can also serve as volume spacers between neighboring CuO nanosheet arrays and maintain electrolyte penetration as well as reduce the aggregation during Li+ intercalation,thus leading to the improvement of electrochemical energy storage performance.The CuO@MnO2 nanosheet arrays were assembled with LiCoO2 as a full cell,which exhibited high spcific capacity(120 mA h g-1 at a rate of 150 mA g-1)and an excellent cycle stablity(81.37%retention after 100 cycles).