Exploring the impact of Al-based electrolytes on the charge storage behavior of vine shoots derived carbon

Abstract

A new concept for affordable supercapacitors based on Al aqueous electrolytes was proposed recently. This study provides a deeper insight into the cyclic performance of vine shoots-derived activated carbon using three different 1 M aqueous electrolytes: Al2(SO4)3, Al(NO3)3 and AlCl3. Cyclic voltammetry (CV), galvanostatic cycling and impedance measurements have shown that the type of anion causes the differences in the rate capability and long-term cyclability. Although CV deviation is provoked by aggravated sulphate penetration into pores upon switching at higher currents, Al2(SO4)3 emerged as the most promising electrolyte solution due to the best cycling stability of the 1.5 V full cell over 15,000 cycles. Intensive oxidation of the positive electrode during initial cycling, induced by nitrates reduction, is the main reason for the fastest capacitance drop observed in Al(NO3)3. Therefore, the capacitance values of the carbon cell measured after 5,000 cycles in Al(NO3)3 (75 F g-1) are two times lower than the corresponding values in Al2(SO4)3 and AlCl3 (131 and 127 F g-1, respectively). The oxidation becomes more pro­nounced only after 10,000 cycles in AlCl3, thus causing a notable capacitance drop, which is not evidenced in Al2(SO4)3. Al2(SO4)3-based cell can withstand 15,000 with good specific capacitance/energy retention.