Synthesis of MnO Nano-Particle@Flourine Doped Carbon and Its Application in Hybrid Supercapacitor

Abstract

In order to meet the increasing demand for the high energy and high power in the same time, while neither secondary batteries nor double-layer supercapacitors cannot satisfy, a new energy storage device, hybrid supercapacitor, attracked lots of attentions in recent days. The new device hybrid the double layer capacitor electrode, which provides the high power density, with the secondary battery electrode, which supplys the high energy density. Various of lithium ion batteries(LIBs) electrodes are introduced into this hybrid system. As the alternative materials to the carbonaceous anode in commercial LIBs, numerous of transition metals have been studied as the anode of LIBs due to their high theoretical capacity, high safety and environmental benignity. Here, a transition metal MnO, a promising material used as anode in LIBs, worked with porous carbon materials to form a new lithium ion hybrid supercapacitor. In this device, MnO is used as negative electrode. Meantime the porous active carbon electrode serves as positive electrode. Similar with other transition metal materials, the intrinsic high resistance, large volume variation during the charge and discharge will still impede the MnO involving into the hybrid system. Especially the late one will cause the pulverization of the MnO materials and then the loosing contact between active materials and current collector. This will cause a significantly capacity fading and bad cycling stability. Since the high energy capacity, excellent cycle-ability and good rate performance are the major merits of hybrid supercapacitor, therefore those problems of MnO should be solved first. To solve those problems, covering nano-sized MnO materials with conductive carbon layer is a proper approach. Furthermore, It is widely recognized that doping hetero-atom onto the carbon can change their electronic configuration and then improve the electrochemical performances of the carbon materials. Therefore, in this study, a fluorine-doped carbon encapsulated MnO nano-particle (MnONP@FC) was fabricated through a novel process. In this synthesis process, Nafion ionomers was used as the fluorine doped carbon precursor. As shown in Scheme 1, Mn ions are first self-assembly trapped within the Nafion matrix through the electrostatic interaction between positive charged Mn ion and negative charged sulfonate end groups in Nafion ionomer. Then after pyrolysis under nitrogen atmosphere, the Nafion ionomers was transformed into carbon frameworks and MnO nano-particles was formed and highly dispersed within them. The formed MnONP@FC was characterized through SEM, TEM and XPS and the electrochemical performances of the hybrid device, which composited MnONP@FC with the porous carbon materials, were also investigated. The results exhibited that this new hybrid supercapacitor showed a high energy density up to 40 mAh g-1, long cycle stability and good rate performance. Figure 1