NiCoAl Ternary Metal Hydroxides Prepared by Fluorine Ion Assisted Electrodeposition Process for Long Lifespan Supercapacitor Electrodes

Abstract

NiCo-based layered double hydroxides (NiCo-LDHs) have plenty of superior properties as electrode materials of supercapacitors, while the poor cycle performance heavily limits their application. An effective strategy to tackle this issue is to dope inactive Al that could stabilize the metallic layers to form ternary hydroxides. However, the desired ternary electrodes with appropriate content of Al3+ can hardly be prepared by conventional electrodeposition due to the great difference in solubility product constants (K sp) of corresponding hydroxides, where the non-electroactive Al(OH)3 (K sp = 1.3 × 10‒33) are preferentially deposited than the hydroxides of nickel and cobalt (K sp = 2.0 × 10‒15, 1.6 × 10‒15). Here, we propose a novel electrodeposition method assisted by F‒ to control Al3+ content in NiCoAl-LDHs. By adjusting the concentration of F‒ in the electrolyte, Al3+ content, as well as the morphology and electrochemical performance of the electrodes, could be manipulated. With the optimum ratio of F− to Al3+, the as-obtained electrode shows high specific capacitance along with a long lifespan (54.1%, 10000 cycles). An asymmetric supercapacitor is assembled using active carbon as the negative electrodes, which displays the maximal energy density of 35.5 Wh kg−1 at the power density of 477.3 W kg−1, with a long lifespan (75%, 10000 cycles).