Studies On The Preparation And Supercapacitive Performances Of Nano Porous Mixed-metal Oxides

Supercapacitors?SCs?,with high power density,long cycle life,environmental protection and so on,are becoming continuously an ideal candidate for large energy storage system and electric vehicle power system.However,the practical application of SCs is seriously limited by its lower energy density(typically < 6 Wh kg^-1).It is well known that the electrochemical properties of electrode materials are the main factors that determine the energy storage properties.Therefore,novel electrode materials with high specific capacity,high rate performance and long cycle life are essential to realize the high performance of supercapacitors.The AB2O4 type double metal oxide with spinel structure,based on the principle of faradic pseudocapacitance,is a kind of electrode material with higher theoretical specific capacity.However,the redox reaction can only be carried out on the surface or near surface of the material,and thus the specific surface area is important to enhance the electrochemical performance of AB2O4 type double metal oxides.In this paper,we mainly fouce on designing nano porous mixed-metal oxides with large specific surface area,which can improve the electron/ion conductivity as well as the performance of supercapacitors.The study includes the following sections.?1?Studies on the preparation and supercapacitive performances of porous ZnCo₂O₄ and NiCo₂O₄ nanoparticles.The uniform ZnCo₂O₄ and NiCo₂O₄ nanoparticles?< 20 nm?have been successfully prepared via a facile ball-milling method followed by a thermal treatment.It all show excellent electrochemical performance.The uniform ZnCo₂O₄ nanoparticles exhibit high specific capacitance of 1193.4 F·g^-1 at 1 A g^-1and 816.3 F g^-1 at 10 A g^-1,demonstrating its excellent cycling stability.Moreover,the ultrasmall nanosize of the electrode material may provides more active sites for the redox reactions and increases the electrode/electrolyte contact area,which is favorable to improve the utilization of active materials.On the other hand,the superior electrochemical performance is also attributed to the electrons and ions transportation during the redox process.The simple synthesis process can also be applied to prepare other mixed metal oxides.?2?Studies on the preparation and supercapacitive performances of mesoporous ZnCo₂O₄ microspheres.We report a simple template-free solvothermal route followed by a thermal treatment for the synthesis of uniform mesoporous ZnCo₂O₄ microspheres.The uniform sphere-like ZnCo₂O₄ microsphere is composed of numerous primary nanoparticles?NPs?in size tens nanometers,generating some small mesopores among these NPs.The unique porous nanostructures and large specific surface area have contributed to the superior electrochemical performance of the ZnCo₂O₄ electrode.The ZnCo₂O₄ electrode shows a high specific capacitance of 953.2 F g^-1and 768.5 F g^-1 at discharge current densities of 4 A g^-1 and 30 A g^-1,desirable rate specific capacitance(768.5 F g^-1 at 30 A g^-1)and excellent cycling stability?maintain 97.8% after 3000 cycles?.The energy density can be estimated to be 26.68 Wh kg^-1 at a power density of 8 kW kg^-1.?3?Studies on the preparation and supercapacitive performances of porous mixed metal oxide?MMO?hollow spheres.To further improve the electrochemical performance of ZnCo₂O₄ materials,we report a general and facile “ion adsorption-annealing” approach for preparating mixed metal oxides hollow spheres.The ZnCo₂O₄ spheres possess an ultrathin shell?about 20 nm in thickness?composed of nanoparticles several nanometers in size,among which numerous mesopores have been generated.The unique structure could provide large areas of electrode/electrolyte contact interface,abundant electrochemically active sites,and fast electron and electrolyte ion transportation/diffusion,as well as superior structural stability for electrode materials.The capacitances are calculated to be 1158 F g^-1 and 915 F g^-1 at discharge current densities of 1 A g^-1 and 10 A g^-1,respectively.The highest specific capacitance reaches 1191 F g^-1,and after 2300 cycles,1109 F g^-1 is still retained,with a capacitance retention rate of 93.11%.In addition,the “ion adsorption-annealing” technique is very effective for the synthesis of other porous mixed metal oxide hollow spheres?ZnSnO3 and NiFe2O4 for example?with ultrathin shells and high porosity.