Synthesis and capacitance performances of Ni–Mn-Oxides as electrode materials for high-performance supercapacitors

Ni–Mn-Oxides were prepared by adsorption with MnCO3 microspheres followed by calcination. It was found that the Ni–Mn-Oxides synthesized under different temperature and transition metal element ratios were all the mixture of three or two transition metal oxides, and the morphologies of the samples are from microspheres turning to nanoparticles with increasing temperature but maintaining microsphere at the lower Ni and Mn ratios and agglomerating seriously at the higher nickel content. Moreover, the capacitance performances of the synthesizes Ni–Mn-Oxides were further surveyed in supercapacitor systems. The electrode material with a Ni/Mn ratio of 1: 3 calcined at 500 °C exhibited excellent electrochemical performances in comparison to the other temperatures and ratios. The discharge specific capacitance of the spherical oxide (Ni: Mn = 1:3) is 1128.53 F/g at the scan rate of 1 A/g and the capacity retention rate is 71.7% after 5000 cycles at 20 A/g with the initial capacitance of 316 F/g, respectively. The excellent capacitance performances were attributed to not only the synergistic effect between chemical compositions, the microspheres providing more reactive sites due to its large specific surface area, but also the stable structure withstanding the continuous charge-discharge cycles.