Theoretical And Experimental Investigations On Hybrid Super-capacitors

Super-capacitor has large capacitance and high energy density as a new-type of energy storage element, which has great potential for applications on electric vehicles, UPS and electromagnetism arms. On pushing forward the application of supercapacitor on pulse power technology we need to solve some urgent problems such as large inner resistance and low work voltage of the super-capacitor. So the goal of this work is to investigate a new-type hybrid super-capacitor. We deal with electrode materials and structures of super-capacitor, and try to solve its theoretical and technology problems.In order to raise the work voltage of super-capacitor, we combine the anodes of electrolytic capacitor with the cathodes of electrochemical capacitor to form a new structure of hybrid super-capacitor. By the optimized combination, the hybrid super-capacitor unit is fabricated, and its electricity performances are studied. The results show that the work voltage of hybrid super-capacitor gets rising greatly. Moreover, we analyse the influence of improving the inner structure of hybrid super-capacitor and physical dimension of electrodes on the performance of the super-capacitor in the work, so that optimizes the structure design and enhances its electric performance. The optimized structure of the hybrid super-capacitor is paralleled with several units, the work voltage of the unit is 40V, the capacitance is 18.4mF, the resistance is 0.46 Ω, and the energy density is 1.13J/ cm~3. The equivalent circuit model of the hybrid super-capacitor is proposed, and it is used to analyze the impedance performances of the hybrid super-capacitor, the methode is meaningful for the comprehension of electrochemical process and the decisition of electrochemical parameters.One of the key technologies for super-capacitors is electrode preparation. In this work, we preparated amorphous hydrous ruthenium oxide powder by a Sol-gel process, then prepared ruthenium oxide/active carbon composite electrodes for super-capacitors, tested their electrochemical performances and physical characteristics for different ratios of ruthenium oxide/active carbon composite electrodes, try to find out the best ratio in them. The results indicate that it can improve impedance characteristics to add active carbon into ruthenium oxide, but decrease the capacitance of composite electrodes simultaneously. When the content of ruthenium oxide is 60%, the composite electrode is ideal for super-capacitor, its specific capacitance and inner resistance are 457.3F/g and 1.291Ω, respectively. Another technology isdeveloped to improve impedance performance of electrodes; the membrane of Ruq -dip is grown on tantalum foil by heat decomposing rU(CO 2H5 )3 at proper temperature. The specificcapacitance of the electrode is 362F/g and the inner resistance is 1.08Q. It can be suitable for the requirement of charging and discharging rapidly as the electrodes of super-capacitor.Based on the charge transition theory, electrode process kinetics and electromagnetics field theory, the mechanism that stores and releases the charges is explained. Through discribing electrochemical reaction rate, reaction current density and electric field distribution, it can be concluded that changing the electrode potential can influence the reaction current density, the distribution of electric fields are related with the characteristics of electrode materials and physical dimension of the electrodes. Adjusting the parameters such as the dielectric constant of separator membrane, the thickness of electrode, can resolve the problem that local field is too high. The descriptions play an important role in interpreting the mechanism and optimizing the structure of super-capacitors.Packaging structures of the hybrid super-capacitor are also studied in the work. The temperature distribution inside the hybrid super-capacitor is simulated by finite element method. The effects of different packaging structures on the heat transfer process of the hybrid super-capacitors are examined by the model: It shows that, as the ratios of the heat transfer are balance in axial and radial directions, the temperature field inside the hybrid super-capacitors is uniform, and the effect of heat transfer is the best under these conditions. Based on the results and the electric performance, the best packaging structure of the hybrid super-capacitors is three units in parellel. At the last, the design of the structure was optimized.As an example of the application for super-capacitors, we design a battery-supercapacitor hybrid power sources so as to achieve optimal power performance of the power source, it is necessary to explore the application of supercapacitor on electric vehicle.