Pulverization Strategy for Graphite-CoOx Composite Cathode of Lithium-Air Batteries

Abstract

The lithium-air battery has been attracted around the world owing to very high energy density, which could well satisfy the increased energy requirement from electronic devices, especially the electric vehicle.1-3 However, despite large R&D efforts devoted to its implementation, several issues have so far limited the performance of the lithium oxygen battery because of few discharge-charge cycles, large polarization and low rate capability.4, 5 Some researchers used many materials for cathode in lithium air batteries because inherent activation effect and morphology of each material had an effect to decrease polarization and increase capacity. Although carbon has been talked making by-product like Li2CO3, it is the mostly used material because of the advantage in the way that amount and cost. Some paper told that not only carbon but also electrolyte co-makes this side reaction problem in lithium oxygen battery system. In this study, a new physical pulverization strategy has been developed to prepare a highly active composite of CoOx and crushed graphite (CG) for the cathode in lithium–air batteries. The effect of CoOx loading on the charge potential in the oxygen evolution reaction was investigated in coin cell tests. The CoOx (38.9 wt%)/CG composite showed a low charge potential of 3.92 V with a delivered capacity of 2 mAh/cm2 under a current density of 0.2 mA/cm2. The charge potential was 4.10 and 4.15 V at a capacity of 5 and 10 mAh/cm2, respectively, with a current density of 0.5 mA/cm2. The stability of the electrolyte and discharge product on the gas-diffusion layer after the cycling were preliminarily characterized by 1H nuclear magnetic resonance spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The high activity of the composite was further analyzed by electrochemical impedance spectroscopy, cyclic voltammetry, and potential-step chronoamperometry. The results indicate that our near-dry milling method is an effective and green approach to preparing a nanocomposite cathode with high surface area and porosity, while using less solvent. Its relative simplicity compared with the traditional solution method could facilitate its widespread application in catalysis, energy storage, and materials science.