The Preparation And Electrochemical Properties Of Carbon Coated Manganese And Nickel Nanoparticles

Supercapacitor, because of its high energy density, high power density and good cycle life, is a new type of energy storage device that has become a focus in the recent years. Electrode materials are the key part of a supercapacitor, they have a decisive role to the application of supercapacitor, and affectted the power density of the output of the capacitor directly, therefore is very important the search for a type of material that can bring high power density, high energy density, good cycle life, which can also be cheap and pollution-free.This paper uses the method of dc electric arc, uses Ar (0.02 MPa) as the protective gas, CH4 (0.01 MPa) as carbon source, tungsten as cathode, mixture of manganese nickel as anode, preparation core-shell (Mn7C3,Ni)@C nanoparticles. Subsequently, the nanoparticles were oxidized in a vacuum tube furnace at 300℃,2 h, producing core-shell (Mn3O4,NiO)@C nanoparticles. XRD, Raman, XPS, TEM were used as characterization techniques of the nanoparticles. The study of the influence of different percentage of nickel and manganese on nanoparticle electrochemical performance was carried out.The results showed that:(1) The prepared (Mn7C3,Ni)@C nanoparticles own a well-defined core-shell structure with an average diameter of 50 nm. The shell is a graphitic carbon layer and the core is a mixture of Mn7C3 and Ni. Nickel has a catalytic effect, promoting the formation of a carbon source and affecting the thickness of the carbon shell. Manganese and carbon react into Mn7C3 which is able to provide pseudo-capacitance. Hence, the variation of Ni-Mn ratio had a dominant influence on the electrochemical performance. The specific capacitance of the composite material increased with the proportion of Mn (when the scanning rate is 2 mV/s, the specific capacitance is 485.12 F/g). In contrast, the sample with higher proportion of Ni has better cycle stability, i.e., the nanocomposite showed a good cycle stability of retaining 70% of the specific capacitance after 1000 cycles (the scanning rate is 2 mV/s; the specific capacitance is 303.57 F/g). (2) (Mn3O4,NiO)@C nanoparticles were still a clear core-shell structure. The shell was a graphitic carbon layer and the core was a mixture of Mn3O4 and NiO. Hence, the variation of Ni-Mn ratio had a dominant influence on the electrochemical performance. It was found that with the increase of the proportion of nickel, the specific capacitance and cycle life were increased, i.e., for a low content of nickel, the specific capacitance was 92.91 F/g at scanning rate of 2 mV/s. However, for high proportion of nickel, the specific capacitance reached 285.09 F/g (at 2 mV/s), and retained 73.9% of the specific capacitance after 1000 cycles.