Layered Na_2/3Ni_1/3Mn_2/3O₂ as electrode material with two redox active transition metals for high performance supercapacitor

In this work, simple solid state method was employed to synthesize Na_2/3Ni_1/3Mn_2/3O₂ which has two redox active transition metals. The electrochemical performance of the material was studied in a three electrode system with 1 M KOH aqueous solution as electrolyte, Hg/HgO as reference electrode and platinum wire as the counter electrode. Na_2/3Ni_1/5Mn_4/5O₂ and Na_2/3MnO₂ were also synthesized and used as control experiments to study the contribution of Ni in the complex. Our results confirmed that doping the base material (Na_2/3MnO₂) with an active mass of Ni increases the supercapacitive properties of the resulting material as a result of the multiple redox active sites offered by the two transition elements (Ni and Mn). Thus, the Na_2/3Ni_1/3Mn_2/3O₂ sample showed a specific capacitance of 532.121 F/g at a current density of 0.5 A/g while Na_2/3Ni_1/5Mn_4/5O₂ and Na_2/3MnO₂ samples showed specific capacitance of 283.50 F/g and 210.29 F/g respectively at a current density 0.5 A/g. Na_2/3Ni_1/3Mn_2/3O₂ also retained about 79% of its initial capacitance after 3000 cycles at 1.3 A/g.