Charge redistribution at active carbon electrodes

U ovome radu uspoređene su karakteristike komercijalnog PowerStor® superkondenzatora te superkondenzatora sastavljenog u laboratoriju te je praćena redistribucija naboja na elektrodama oba superkondenzatora. Metode kojima su se određivale karakteristike su: ciklička voltametrija, elektrokemijska impedancijska spektroskopija (EIS) i metoda punjenja i pražnjenja konstantnom strujom. Ovim metodama određen je utjecaj struje punjenja na redistribuciju naboja, kapacitet i promjena kapaciteta s vremenom, određena je impedancija i unutarnji otpor te su dobivene krivulje punjenja/pražnjenja za navedene superkondenzatore. Određene karakteristike komercijalnog superkondenzatora su gotovo u svim segmentima bolje od karakteristika sastavljenog superkondenzatora što ukazuje na precizniju izvedbu pri proizvodnji PowerStor® superkondenzatora. Proces samopražnjenja superkondenzatora određen je parametrima kao što su početni napon i trajanje punjenja. Utvrđen je složeni električni model koji uzima u obzir učinke redistribucije iona koji se javljaju u superkondenzatorima, a istraživanja su pokazala da je utjecaj redistribucije naboja djelomično posljedica pada napona superkondenzatora na otvorenom krugu. Produljeno punjenje ili punjenje manjim strujama omogućuje ionima da se homogenije raspodjele kroz pore zbog čega je smanjen pad napona nakon procesa punjenja superkondenzatora.In this work the comparison of the electric characteristics was carried out for two supercapacitors, the commercial PowerStor® supercapacitor and the laboratory assembled supercapacitor. The effect of the charge redistribution for both supercapacitors was determined. The methods used for determination of the characteristics were: cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and the constant current charge/discharge method. Such methods enabled to reveal the influence of the charging currents on the charge redistribution, the capacitance values and their changes in time. Also, the impedance and the internal resistance for both supercapacitors were determined, and the charge/discharge curves were obtained. The electric characteristics of the commercial supercapacitor are almost in each segment better in comparison to the laboratory assembled supercapacitor which indicates the more precise techniques of commercial PowerStor® supercapacitors production. A self-discharge process of supercapacitors is determined by the initial voltage value and by charging time of supercapacitor. A complex electrical model has been established to consider the redistribution of ions occurring in the supercapacitors. However, experimental studies suggest that the redistribution effects are in part responsible for measured potential decay. Extended charging or charging with lower current values allows ions to allocate themselves more homogenously throughout the pores so the voltage decay is reduced after charging process of supercapacitor