Preparation Of Manganese Dioxide Andinvestigation On The Performance Of Supercapacitor

Supercapacitors are new energy storage equipment and component between batteries and electrostatic capacitors, which have higher power density and longer cycle life than rechargeable batteries and larger specific capacitor than conventional capacitors. They can meet the high power need of electric vehicles when starting-up or accelerating. They can also be used as electric components, power sources for small apparatus and direct current switches. Supercapacitors have become a hotspot in research because of their wide potential application. According to the principle of energy-storage, there are two types of capacitors: electric double-layer capacitor and faradaic pseudocapacitor. Electrode material mainly contains carbon material, metal oxide and conducting polymer. Studies on supercapacitor are mainly focused on the preparation of high performance electrode material and electrode.The purposes of the thesis are to systemically research the inexpensive manganese as the electrode material which is from different material preparation and different crystal configuration. The thesis has investigated the material preparation, capacitive property and influencing factors, electrolyte optimization and so on. The main results are as follows:1. Nano- MnO₂ is prepared by sol-gel method. The influence of reaction temperature and other factor are investigated. It is fond that when the mass ratio of citric acid/Mn(Ac)2 is 0.4:1, pH=6,granding dry-gel for 10h,the content of MnO₂ is the highest. XRD and TEM characterization suggest the product containsα- MnO₂ andγ- MnO₂ with average diameter of 40nm. Electrochemical properties of the resultant are investigated by testing the charge/discharge curves and cyclic voltammetrys in different electrolyte, in which working electrode is made by the product. The results are follows: The electrode material has highest specific capacitors in NaCl solution and lowest specific capacitors in K2SO4 solution compared with other neutral solutions, the highest capacitors is 118.6 F/g and the least is 20.4 F/g; The capacitors performance of the electrode is test with in different KOH solution concentration, the capacitance arrives at the maximum in 7 mol/LKOH which has the specific capacitance of 121.2 F/g.2. A new electrode material of layer MnO₂ is synthesized by redox in liquid-phase. The influence of reaction temperature and alkali dosage for the structure of MnO₂ is investigated. It is fond that when the temperature is 25±3℃,n(OH^-):n(Mn²⁺)≧6,the product has the layered structure by XRD and the structure is steady by the analyzing of TGA. Cyclic voltammetrys curves in 7mol/LKOH solution has showed that electrochemical performance of capacitor is best when the potential range is -200⁶00mV. The specific capacitance of MnO₂ is 286 F/g at scan rate of 5mV/s.The more scan speed, the little specific capacitance. The specific capacitance become reduced after 150 cycles, but can retain above 200 F/g after 200 cycles, which show the material has better electrochemical performance.3. MnO₂ composite electrode material was synthesized by doping aluminium oxid with different ratio. XRD characterization suggests that the structure of MnO₂ is changeless and only the intensity of apex is lager. Cyclic voltammetrys curves shows that alumina-doped MnO₂ raise the electrochemistry performance of electrode, when the ratio of alumina is 1%, the maximum capacitance can reach 165 F/g ,but the capacitance of the pure MnO₂ is only 165 F/g. The specific capacitance can remain above 92% after 200cycles.