Preparation And Electrochemical Properties Of Nickel/Cobalt/Aluminum Ternary Hydrotalcite For Supercapacitors

Hydrotalcite-like materials which are used as supercapacitor electrode materials havebeen widely studied and have got great achievements in recent years. In this article, weprepared nickel-cobalt-aluminum ternary hydrotalcite by hydrothermal method, sol-gelmethod, calcination recovery method and in situ growth method, and then we studied theirelectrochemical performances for supercapacitor.We prepared hydrotalcite with four different molar ratio of metal ions by hydrothermalmethod, using urea as precipitation. The XRD analysis shows that the molar ratio of metalions has little effect on polymorphs of these products. When Ni:Co:Al=2:1:1, the preparedhydrotalcite obtains the largest single electrode capacitance of594F/g. After500cycles ofcharge-discharge，the specific capacitance is71.9%of the initial capacitance.In the sol-gel method, we used two different kinds of aluminum salts, aluminumisopropoxide and aluminum sec-butoxide, and the as-prepared materials show differentspecific capacitances. When using aluminum isopropoxide, the product’s specific capacitancecould reach210F/g, but attenuates seriously with increasing of the discharge current density.While using aluminum sec-butoxide, the product’s specific capacitance could reach164.9F/g.And after400cycles of charge-discharge, the capacity retention of the electrod is92%,showing a good cycle performance.Calcination recovery method is based on the structure memory effect of the hydrotalcite.The sample (Ni:Co:Al=2:1:1) which was calcined at300℃could recover the structure ofhydrotalcite, and shows a maximum capacitance of489.5F/g. But when the calcinetemperature increases to400℃or500℃, the calcined samples could not recover thestructure of hydrotalcite. After calcined hydrotalcite with different molar ratio of metal ions at400℃, the layered structures were destroyed and their specific capacitances were decreased.When Ni:Co:Al=1.5:1.5:1, the hydrotalcite sample after calcined-recovery experiment showsa larger specific capacitance(550.2F/g) when compared to that of the prescursorhydrotalcite(451.6F/g).Hydrotalcite prepared by in situ growth method have special morphologies. WhenNi:Co:Al=2:1:1, the as prepared hydrotalcite shows a structure of nano-needle. WhileNi:Co:Al=1:2:1, the as prepared hydrotalcite shows a micron-scale banded structure. Themaximum specific capacitances of these two materials are704F/g and523F/g, respectively. The specific capacitance retention of the former is93%after500cycles of charge-discharge.In situ method can not only simplify the traditional electrode fabrication process, but alsoincrease the specific capacitance of the product when compared to the other three methods.This exhibits the advantages of the in situ method.