The Regulation Of Cold Pressing Pressure On The Electrochemical Performance Of Nickel-based Transition Metal (hydrogen) Oxide Electrodes

The basic structure of supercapacitors is mainly composed of electrode,electrolyte,diaphragm and shell.Electrodes here are one of the most important components of supercapacitors,whose physical and chemical properties largely determine the electrochemical characteristics of supercapacitors.Powder pressing method is mainly used to prepare electrode of supercapacitors,where mechanical pressure and pressing time are two very important technological parameters.The optimization of these two parameters can control/improve the physical and chemical properties of the pressed powder pellet,and then affect the electrochemical properties of supercapacitor electrodes.Therefore,simple nickel-based transition metal（hydrogen）oxides（e.g.,Ni（OH）₂ and NiO）are regarded as the research object in our experiment.The electrodes containing Ni（OH）₂ and NiO are prepared by mechanical cold-pressing method in the pressure range of 2-10 MPa,using 1 M KOH aqueous solution as electrolyte.The effect of mechanical pressure on the electrochemical performance of electrodes containing Ni（OH）₂ and NiO was analyzed by the electrochemical workstation in order to know the role of pressure regulation.Firstly,the electrochemical performance of electrodes containing Ni（OH）₂ was measured under different pressures.The effect of mechanical pressure on the electrochemical performance of electrodes containing Ni（OH）₂ was analyzed.The results indicate that（1）Within the pressure range of 2-10 MPa,the specific capacitance,cycle stability,energy density and power density of electrodes containing Ni（OH）₂ increase with increasing cold pressure;（2）When the cold-pressing pressure is 10 MPa,the electrode containing Ni（OH）₂ has a smaller impedance（0.39Ω）in the high frequency region,and a better AC impedance characteristics in the middle and low frequency region.Secondly,the electrochemical performance of electrodes containing NiO was also measured under different pressures.The effect of mechanical pressure on the electrochemical performance of electrodes containing NiO was further analyzed.The results indicate that（1）the specific capacitance,energy density and power density of electrodes containing NiO increase with increasing cold pressure within the pressure range of 2-10 MPa;（2）When the cold-pressing pressure is 10 MPa,the NiO-containing electrode has a slightly larger impedance（0.83Ω）in the high-frequency region,and a general AC impedance characteristic in the medium and low-frequency region.Thirdly,the electrochemical properties of Ni（OH）₂ and NiO electrodes were compared under the same measurement conditions.The results indicate that（1）When the scanning rate is 50 mV/s or the current density is 2.5 mA/cm²,the specific capacitance of Ni（OH）₂ and NiO electrodes can be proportionally modulated by cold pressure.Moreover,the specific capacitances of NiO electrode are significantly higher or approximately equal to those of Ni（OH）₂ electrodes;（2）In the high frequency region,the solution impedances of Ni（OH）₂-containing electrodes are significantly lower than those of NiO-containing electrodes under different cold-pressing pressures.Moreover,the angle between the AC impedance curves of NiO-containing electrodes and Z’axis is slightly higher than those of Ni（OH）₂-containing electrodes in the middle and low frequency region.Therefore,the electrochemical properties of Ni（OH）₂ and NiO electrodes can be regulated by cold-pressing mechanical pressure in the range of 2-10 MPa.The experimental results indicate that optimizing the cold-pressing mechanical pressure is helpful to improve the electrochemical characteristics of supercapacitor electrodes.