Tuning Graphene oxide and Manganese oxide composites to improve the capacity and stability for lithium ion battery via heat-treatments

Abstract

Electric vehicles (EVs) and energy storage system (ESSs) require the electrode materials with low cost and high mass-production efficiency via easy synthesis method as well as high capacity and stability. In the perspective, manganese oxides (MnOx) is one of the attractive materials because manganese is abundant, non-toxic, and has low cost. The MnOx as electrode materials for lithium ion battery (LiB) has attracted much attention. However, during LiB cycling, the crystalline MnOx is easily pulverized and covered with insulating solid electrolyte interphase (SEI), which causes a fast capacity fading. In this study, graphene oxide (GO) and manganese oxide composite (MnOx), that is GO@MnOx, is prepared with a facile and one-pot chemical synthesis method. In the synthesis, not only GO increases electrical conductivity, but also provides a template where MnOx is anchored, which alleviates pulverization of MnOx during lithiation/delithiation. The GO@MnOx was heat-treated at 0, 200, 400, and 600℃, respectively. The crystalline structure of GO@MnOx heat-treated at 0℃ and 200℃ was Mn3O4, that is, Hausmannite, and that heat-treated at 400℃ was composed of Mn3O4 and MnO simultaneously, and that heat-treated at 600℃ was MnO, that is, Manganosite. According to the crystalline structure, specific capacity of GO@MnOx was different. In particular, the GO@MnO heat-treated at 600oC showed the highest specific capacity of 850 mAh g-1and the most stable cycling performance. Contrary to the GO@MnO, the GO@Mn3O4 showed 480 mAh g-1. In addition, it is very notable that the specific capacities of all kinds of GO@MnOx increase with initial cycling between 50 and 150 cycles. The behavior is probably due to pulverization of active materials and structure change from crystalline to amorphous. The strain induced between amorphous and crystal active materials forces MnOx to be pulverized, which results in the exposure of active materials leading to a capacity increase. It seems to be partially attributed to the formation of new solid electrolyte interface (SEI). Those are clarified through X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and High resolution Transmission electron microscopy (HR-TEM) analysis.