Lithium Air Batteries; Challenges and Opportunities

Abstract

Metal-air batteries are greatly considered as an advanced solution for future energy requirements due to their remarkably high-energy density. For instance, the theoretical energy density of Li-air batteries (3500 Wh/kg) is about one order of magnitude higher than that of commonly used Li-ion batteries (~400 Wh/kg). In terms of cruising-speed range on passenger cars, the performance of Li-air batteries is comparable to that of internal combustion engines. Thus far, the research on the Li-air battery has been limited to the short life study of lithium oxygen (Li-O2) batteries where the O2, as the oxidant in Li–air cells, needs to be extracted from air to eliminate the side reactions of N2, CO2 and water with lithium or cell components. Hence although oxygen is an abundant and freely available element, its use will require on-site purification, which is energetically expensive and reduce the energy density of practical cells. In this presentation, I will overview our recently developed Li-air battery system that operates with the actual air components (N2, O2, CO2 and H2O) with a superior cycle life and energy efficiency that can operate up to 700 continuous cycles with the capacity of 500 mAh/g [1]. This Li-air battery benefits from a novel protected Li-anode, an air cathode based on MoS2 catalyst and a mixture electrolyte including DMSO and EMIM-BF4 ionic liquid. Various characterizations including differential electrochemical mass spectroscopy (DEMS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy on the cathode reveal that the only discharge product in our system is lithium peroxide (Li2O2) with no evidence of side products such as lithium hydroxide (LiOH) and lithium carbonate (Li2CO3). Nuclear magnetic resonance (NMR) results also show the stability of the electrolyte. Density functional theory calculations suggest that the combination of MoS2 cathode and ionic liquid in the electrolyte provides a kinetically favorable system for Li2O2 formation. The study of this Li-air system is a key step toward the development of next generation lithium batteries with higher energy density and cycle life for transportation and grid scale applications. [1] A. Salehi-Khojin et al., A lithium–oxygen battery with a long cycle life in an air-like atmosphere, Nature, 555 (7697), 502, 2018.