Fabrication of SulfurCarbonClay mineral cathode material and its electrical performance

Lithium–oxygen (Li-O2) batteries have been developed as the next generation in energy storage due to their high theoretical energy densities (11,140 Wh/kg) [1]. Therefore, Li-O2 batteries have got attention as one of the most promising electrochemical energy storage technologies in recent years. Although, there remain challenges, including low round-trip efficiency and charge/discharge rate, also short cycle life as well as poor stabilities of electrolytes [2]. Development of materials and components of Li-O2 batteries are highly desired. Designing the cathode material has gained much attention, in terms of catalyst systems and unique properties (such as porous structure, electronic conductivity, high surface area and high catalytic activity) to promote both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the non-aqueous electrolyte, therefore improving electrochemical performance of the battery. Here, we have designed a cathode air electrode to improve electrochemical performance of current lithium-oxygen batteries by utilizing high-efficiency nanocatalysts of Ruthenium oxide (RuO2) and manganese oxide (MnO2) supported on reduced graphene oxide (rGO). rGO with noble metals such as RuO2 have been explored as oxygen evolution reduction (OER) electrocatalysts in Li−air cells to lower the charge overpotentials and exhibited stable cycling performance [3]. We are expected rGO@RuO2@α-MnO2 nanocomposite cathode emerges their unique properties to obtain high discharge specific capacity and good cyclability of Li–O2 cells. In the first step, Graphene oxide (GO) was prepared by modified hummers method. Next, rGO@RuO2 was synthesized via reduction of GO and RuCl3 with 1M NaOH to form rGO@RuOH. In the next step, rGO@RuOH was annealed at 150ºC to obtain rGO@RuO2. We believed deposition of RuO2 on the surface of rGO, due to the strong interactions between cationic Ru+2 and the oxygen functional groups (hydroxyl, epoxy and carboxyl groups) on the surface and the edge of the GO sheets, increase the surface area, avoid aggregation of rGO and lead to enhance electrochemical performance. Afterward, α-MnO2 nanowires, which synthesized through hydrothermal method, was anchored between as-prepared rGO@ RuO2 sheets by mechanical milling. The prepared samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, Field emission scanning microscopy (FESEM) and Energy dispersive X-ray spectroscopy (EDS). Moreover, Galvanostatic discharge/charge experiments were performed in the potential range of 2–4.3 V (vs. Li/Li+) at a current density of 100 mAg−1 using ECC-Air test cell. Cyclic voltammetry (CV) tests were measured at a scanning rate of 0.3 mVs−1 between 2.0 and 4.5 V (vs. Li/Li+) to study lithium peroxide formation and decomposition reactions on the rGO@RuO2@α-MnO2 cathode. Electrochemical impedance spectroscopy (EIS) were analyzed in the working frequency ranging from 100 kHz to 0.01 Hz.