Study On Preparation And Properties Of Electrode Materials For Electrochemical Capacitors

As the new energy storage devices, electrochemical capacitors possess high power density, high energy density, long cycle-life, et al, and have been applied widely in many fields. Electrode materials are one of the key factors for the electrochemical capacitive properties of the electrochemical capacitors. In this thesis, brinjaul and mushroom were used as the precursors and several activated carbons were synthesized. Also, multi-walled carbon nanotubes (CNTs) were used as the support of manganese oxide, manganese oxide/carbon nanotubes (MnOx/CNTs) composites were prepared. The electrochemical capacitive properties of these materials have been investigated in detail. The main works are summarized as follows:(1) With the help of pore-forming substances, such as ZnCl₂ and KOH, activated carbons were synthesized from brinjaul by pyrolysis and used as the electrode material for electrochemical capacitors. The specific surface area, pore diameter distribution and electrochemical properties have been characterized by surface area and porosity analyzer, cyclic voltammetry and galvanostatic charge-discharge method. The results demonstrate that the prepared activated carbons have good capacitive properties. The specific capacitance in 1 M Na2SO4 neutral electrolyte from 0 to 1V at a current density of 0.01 mA cm^-2 is 141.8 F·g^-1. The specific capacitance of the electrode can keep 87% of the initial value of the capacitance at a high current density of 0.1mA cm^-2 for 1000 cycles.(2) Two kinds of activated carbons were synthesized from mushroom by pyrolysis with pore-forming substances such as ZnCl₂ and KOH. The electrochemical properties, specific surface area and , pore diameter distribution and have been characterized by cyclic voltammetry, galvanostatic charge-discharge method, and surface area and porosity analyzer. The results demonstrate that two kinds of actived carbons exhibit typical double-layer capacitor characteristics and good electrochemical capacitive properties. The carbons activated by ZnCl₂ (ACZn) shows better capacitive properties than the carbons activated by KOH (ACK).(3) Manganese oxide/carbon nanotubes (MnOx/CNTs) composites were synthesized by the direct redox reaction between the CNTs and KMnO4. The capacitive behavior of MnOx/CNTs composites were evaluated by cyclic voltammetry and galvanostatic charge-discharge method in 1M Na2SO4 aqueous solutions. The results show that the MnOx/CNTs electrode exhibit good capacitive properties. When the mass ratio between KMnO4 and CNTs is 7:1, the specific capacitance of MnOx/CNTs electrode (based on MnO₂) at 0.01 mA cm^-2 equals 306.7 F·g^-1. On the other hand, only 14.5% decrease of the specific capacitance is observed after 1000 cycles at a discharge density of 0.1 mA·cm^-2.