微型超级电容器的电化学阻抗谱分析

Analysis of the Electrochemical Impedance Spectroscopy of Miniature Supercapacitors

为了提高微型超级电容器的电化学性能,对其阻抗谱特性进行分析。通过三电极体系对微型超级电容器进行电化学阻抗谱(EIS)测试以及恒流充放电测试,分析复阻抗平面图及波特(Bode)图,获得内部体系的有用信息,并与传统的宏观超级电容器阻抗谱进行分析比较。在尼奎斯特(Nyquist)图中,高频区的半圆弧较长,等效串联电阻Rs约为5.5Ω,接触电阻Rct约为4Ω,低频区域直线与实轴的夹角θ约为65°,表明微型超级电容器的扩散阻抗较大。在Bode图中,当测试频率达到极限频率时,相角约为70°,说明其电容特性有待进一步提高。在1 A/g电流密度下,测得其比电容为471 F/g,功率密度为588 W/kg,能量密度为16.3 W·h/kg。在电容与频率关系图中,在高频区域,电容接近于0,当频率达到100 Hz(扩散阈值),电容趋于稳定,约为18μF。另外分析了充电电压、氧化石墨烯(GO)质量分数、电解质种类等因素,对微型超级电容器Nyquist图的影响。

To improve the electrochemical properties of miniature supercapacitors,the characteristics of the impedance spectra were analyzed.The electrochemical impedance spectroscopy（EIS）test and constant current charge and discharge test of the miniature supercapacitor were carried out by the three-electrode system.The complex impedance plane plot and Bode diagram were analyzed to obtain the useful information of the internal system,and compared with the traditional macro super capacitor impedance spectra.In the Nyquist diagram of the miniature supercapacitor,the semicircle is longer in the high frequency region,the equivalent series resistance（Rs）is about 5.5Ω,the contact resistance（Rct）is about 4Ω,and the straight line with the real axis angle（θ）is about 65°in the low frequency,all these show that the diffusion impedance of the miniature supercapacitors is larger.In the Bode plot,when the test frequency reaches the limit frequency,the phase angle is about 70°,which shows that the capacitance characteristics need to be further improved.Under the current density of 1 A/g,the test results are that the specific capacitance is 471 F/g,the power density is 588 W/kg,and the energy density is16.3 W·h/kg.In the diagram of the capacitance and frequency of the miniature supercapacitor,the capacitance is close to 0in the high frequency region,and when the frequency reaches 100 Hz（diffusion threshold）,the capacitance tends to be stable,about 18μF.In addition,the effects of the charging voltage,mass fraction of graphene oxide（GO）,electrolyte species and other factors on the Nyquist diagram of the miniature supercapacitors were analyzed.