Studies On Supercapacitor Electrode Materials Of MnO₂

Supercapacitors is a new energy storage component. Nowadays supercapacitors have become a researching hotspot for its high specific capacitance, excellent reversibility and long cyclic performance. When work with secondary batteries, it can be used as electromotion automobile power system, enhance power density and energy density of rechargeable batteries. Moreover, it can be used as start-up power for fuel batteries, mobile communication and sustain computer system. In our works, electrode materials is studied which is synthesized and modificated, selection of electrolytes and other related techniques. The structure is analyzed by X-rays diffraction(XRD) and transmission electronic microscope measurements(TEM). The electrochemistry performance is tested by cyclic voltammetric measurements (CV), constant charge/discharge measurements and so on.Fibreforms nano-MnO2 is synthesized by liquid-phase between KMnO4 and different Mn2+ solution, such as MnCl2, MnSO4, Mn(Ac)2 and Mn(NO3)2. The results of the cyclic voltammograms and the constant current charge/discharge curves show that MnO2 synthesized by MnSO4 can provide ideal specific capacitance and good electrochemical performance. The results of calcined show that MnO2 provide better charge/discharge performance and specific capacitance than that of uncalined. The maximum capacitance can reached 86.7F·g-1 before calcined and 110.0 F·g-1 after calcined. Nano-MnO2 likes whiskers is synthesized by low temperature solid redox reaction using KMnO4 and MnCl2. Charactrization of samples are studied by XRD, the results show that the product is the multicrystal of α-MnO2 and γ-MnO2 and its length is 300~500nm, its diameter is 5~10nm. The capacitor characteristics of nano-MnO2 likes whiskers show better capactive performance than that of the capacitor characteristics of liquid-phase reaction. The more scan speed, the little specific capacitance. The results of the cyclic voltammograms and the constant current charge/discharge curves show that MnO2 electrode can provide excellent capacitance characterization in 2.0 mol·L-1(NH4)2SO4 solution,the maximum capacitance can reached 183.7F·g-1.A new electrode material of nmMnO2-μmMnO2 composite is synthesized by mechanism commingle. The results of the cyclic voltammograms and the constant current charge/discharge curves show that the electrochemistry performance is better than that of pure MnO2. When the weight ratio of nm to μm was 9:1, the maximum capacitance can reached 242.4F·g-1, the discharge capacity of MnO2 electrodes raise to 32%. Cr-doped MnO2 obtain by low temperature solid redox reaction using KMnO4, MnCl2 and K2Cr2O7. The results show that Cr-doped MnO2 raised the electrochemistry performance of electrode, when the mole ratio of Mn to Cr was 100:1, the maximum capacitance can reached 248.8F·g-1, the discharge capacity of MnO2 electrodes raise to 35%. Doped metal oxide in MnO2 by ratio of 100:1 is synthesized by solid redox reaction preparation electrode. The results show that specific capacitance and recurrence performance of MnO2 eletrode doped Fe2O3, TiO2 are better than that of pure MnO2 electrode, furthermore, electrode resistance is reduce. But the result is opposition when it doped PbO2, Bi2O3 and Al2O3.