Fabrication Of Super Capacitor By De-alloying Al-based Metallic Glasses

Electrochemical capacitances(also called super-capacitors or ultra-capacitors)have become one of the promising energy storage devices for next-generation power devices because of their high power density,fast charge/discharge rates,long cycle life,and better cycling stability compared with secondary batteries.The rapid development of nanostructured materials is also accelerating the development of super-capacitors.In recent years,the pseudo capacitor has attract more attentions due to its several times or even hundreds of times of the capacitance than the electric double layer capacitor.The electrode material of the pseudo capacitor is mainly transition metal oxides,such as RuO2,NiO,CoO,MnO2,etc.However,the band gap of transition metal oxides between the conduction band and valence band is relatively narrow,which result in poor electrical conductivity leading to their low capacitance.In current years,scientists have developed on method to overcome this deficiency.The method is the external conductive reinforcements by compositing with conductive materials,such as carbon,conducting polymers,and conductive metal oxides.Unfortunately,these reinforcements are often limited by weak oxide/conductor interfaces.In order to improve the conductivity of materials,the design,synthesis and properties of electrode materials are studied in this thesis.The concentration of the electrolyte,the time of the de-alloying,the composition and the state of the precursor were adjusted,and this is the first time to systematically study the amorphous alloy was used as the electrode material of super-capacitor.This paper introduces the amorphous alloy as precursor in a new structure materials is expected to be applied in super capacitor,at the same time,we hope that the materials and methods in this paper can be applied to other areas and guiding to structure control of other materials.The main contents of this paper are as follows:(1)Effect of de-alloying process of the amorphous precursor on the capacitance properties.We prepared porous electrode materials by de-alloying aluminum based metal glass and applied it to super capacitors.We investigate the effects of the de-alloying time and the concentration of the de-alloying solution on the morphology and electrochemical properties of the prepared electrode.The experimental results show that:(a)We prepared electrode material is three dimensional continuous porous structure of the pore size is about 50 nm.(b)De-alloy time has a great influence on the capacitance performance of electrode.With the increase of de-alloy time,the specific capacitance increased first and then decreased,and 50 min is the best time to de-alloy process.(c)The concentration of the de-alloying solution has a great influence on capacitance performance.With the increase of the concentration of the de-alloying solution,the speed of the elemental dissolution is faster,resulting in the ligaments are more fine,so the electrode material has a high specific surface area and more active position lead to larger capacity(the electrode material corrode in 4 M KOH for 50 min can reach the maximum specific capacitance of 1.22 F cm-2).(2)Effect of composition of the amorphous precursor on the capacitance properties.We fabricate the electrode materials for super-capacitor by de-alloying the Al85-XNi6Y6Co3CuX(x=1,3,5)amorphous alloys of three different compositions,and we study the content of copper doping how to affect the electrochemical on the electrode materials.The experimental results show that:(a)In the same de-alloying process,Al82Ni6Y6Co3Cu3 in those three component(Al85-XNi6Y6Co3CuX(x=1,3,5))has the best electrochemical performance.(b)It is found that suitable alloying of Cu can increase the capacitance by decreasing the equivalent series resistance.The Al82Ni6Y6Co3Cu3 in Al85-XNi6Y6Co3CuX(x=1,3,5)three components has minimal value in equivalent series resistance,so it has the maximum specific capacitance.(3)Effect of annealing temperature of amorphous precursor on the capacitance properties.We fabricate the electrode materials for super-capacitor by de-alloying Al82Ni6Y6Co3Cu3 amorphous alloy annealed at different temperature.We study the effect of annealing temperature of amorphous precursor on the capacitance properties.The experimental results show that:(a)With the increase of annealing temperature,the porous size of electrode material is increasing.(b)In the annealing temperature at 421 ?,the electrode material we prepared has the best capacitance performance,the specific capacitance as high as 2.05 F cm-2.