Towards the development of economic, high specific energy metal-air batteries in vehicle propulsion applications

Abstract

Since the advent of the automobile, earth’s petroleum supply has been undergoing increasingly rapid depletion as private vehicles become more commonplace. Since the majority of petroleum is used for vehicle propulsion, the scientific community recognizes the imminent need to obtain the widespread implementation of an alternative energy carrier for transportation. The most obvious alternative would be the electric vehicle (EV). However, the range of EVs is still far from adequate, and this is a result of the low specific energy inherent to current lithium-ion systems. Many other caveats exist, including the high cost of lithium and in particular the large number of safety concerns associated with the system. One solution to the lithium-ion system’s problems — the lithium-air system — was first proposed in the 1970s and is regaining its popularity as can be seen by the rise of relevant publications in the last few years. The cathode in the lithium-air battery is just air from the atmosphere (i.e. there is essentially an infinite supply of the cathode material), and the support can be porous carbon with a high surface area, leading to a tremendous reduction in the weight of battery. The anode is pure bulk metal instead of intercalated metal atoms, which again reduces the weight of the battery. Moreover, since one of the reactive species is not stored in the battery but instead uptaken when necessary, there is much less concern over its safety. Taking it a step further, other metals could in principle be substituted for lithium in order to reduce the costs of production. For example, aqueous magnesium- and aluminum-air batteries theoretically possess nearly as high specific energies as lithium-air and are much more abundant, but have not been well researched or developed yet. Most studies in current technical literature are simply trying to build batteries without conducting fundamental research that probe the basic mechanisms and performance-limiting parasitic reactions. It would be greatly beneficial to obtain a clear picture of the basic reactions in such systems, and this is exactly what this project aims to achieve. Specifically, this project will initially focus on understanding the oxidation mechanism of magnesium with Quantum Espresso, an ab initio software package for electronic structure calculations of solids and is based on density functional theory. Adsorption studies are currently being carried out to study the surface behaviour as a function of hydroxide coverage on the magnesium close-packed surface. Similar calculations will be carried on a kink surface as well to establish a mechanism for dissolution of magnesium hydroxide to simulate a discharge cycle in the battery. The broader goal of this project is to develop a methodology to discern a trend in the behaviour of different metals in the same environment and summarize the results with a rationale on how better systems can be achieved.