Preparation And Energy Band Change Analysis Of Cobalt Hydroxide-based Supercapacitor Electrode Material

With the rapid development of human society today,exploring green,economic and sustainable energy storage devices has become an indispensable necessary demand,and more and more research is devoted to the development of high-performance electrode materials.The energy storage characteristics of energy storage materials such as lithium ion batteries,sodium ion batteries,zion ion batteries,supercapacitors and so on are closely related to the crystal structure,morphology,specific surface area,valence/conduction band and physical and chemical properties of electrode materials.SEM,AFM,XPS,EPR and other test methods have been applied to the analysis and evaluation of electrode materials,but there is no study on valence/conduction band（VB and CB）.In this paper,the cobalt-based supercapacitor electrode materialα-Co（OH）₂ with low cost,environmental friendliness and high theoretical specific capacitance is selected as the research object.For the first time,the charge and discharge process of cobalt-based electrode material is systematically analyzed through the change of physical properties such as color,transmittance and energy band structure,and the influence of carrier intercalation/deintercalation on the band gap energy（E_g）,valence/conduction band（VB and CB）of electrode material is revealed.The main research contents are as follows:1.Through the changes of RGB value,optical spectroscopy（UV-Vis,XPS,UPS）and Mott-Schottky electrochemical test,the changes in color,band gap energy value and valence band values of Co（OH）₂ during the charge-discharge process were revealed.The variable band structure of Co（OH）₂ electrode material during the charge-discharge process was constructed,and the change law caused by the intercalation/deintercalation of charge carriers between layers during the charge-discharge process was explained.（1）The color of Co（OH）₂ electrode exhibits regular variations in Red-Green-Blue（RGB）value during the charge-discharge process.The RGB value of Co（OH）₂ when charged to 0.45 V is（79,79,76）,and that of Co（OH）₂ when discharged to 0 V is（78,78,76）.It is proved that the RGB value of Co（OH）₂ changes regularly during the charging and discharging process.（2）The intercalation of OH^–ions will reduce the valence/conduction bandand band gap energy values;The deintercalation of OH^–ions corresponds with the reversion of VB,CB and E_g to the initial values.（3）The reflectance of pristine Co（OH）₂ is much higher than that of discharged and charged Co（OH）₂,and the reflectance of discharged Co（OH）₂ is higher than that of charged Co（OH）₂.The band gap energy（E_g）values of Co（OH）₂ is greater than that of discharged and charged Co（OH）₂,and the band gap energy（E_g）values of discharged Co（OH）₂ is greater than that of charged Co（OH）₂.2.On the basis of work 1,in order to further improve the electrochemical energy storage performance of Co（OH）₂ supercapacitor electrode material,this work introduces Ni₃S₄ material with high specific capacity to prepare Ni₃S₄@Co（OH）₂composite electrode material with better electrochemical performance.Further,The electrochemical performance of a single Co（OH）₂material needs to be improved.In this work,Ni₃S₄@Co（OH）₂ electrode material with better electrochemical performance was prepared on nickel foam conductive substrate by the method of sulfide material composite.This kind of electrode material is constructed by the cross morphology of nanoneedles and nanosheets,and has a heterogeneous conductive network,exhibiting a larger specific area and active sites.Ni₃S₄@Co（OH）₂ shows excellent electrochemical properties as electrode materials for supercapacitors:（1）The area-specific capacity of Ni₃S₄@Co（OH）₂ reaches 2754.53 m F cm^-2 at 1 m A cm^-2.（2）The energy density of Ni₃S₄@Co（OH）₂//AC asymmetric supercapacitor reaches up to 0.1136 m Wh cm^-2 when the power density is 1.6 m W cm^-2,and the specific capacity remains at 82.6%of the initial capacity after 5000 charge/discharge cycles,performing the potential of practical application.