Review—Understanding and Mitigating Some of the Key Factors that Limit Non-Aqueous Lithium-Air Battery Performance

Abstract

In this article, we have reviewed our work on understanding and mitigating some of the key factors that limit non-aqueous Li-air battery performance. Advances in Li-air battery technology require fundamental understanding of the discharge and charge processes. We first summarize an investigation of Li-air batteries based on a well-defined cathode surfaces having size-selected silver clusters. This work provided key insight into the nucleation and growth mechanism of the discharge product and its relationship to lowering charge potentials. We then describe the development of new cathode materials including ones based on Pd and Mo 2 C nanoparticles that give very low charge potentials. This work has shown that it is possible to achieve very good round-trip efficiencies as well as up to 100 cycles in a Li-air cell. Finally, we discuss investigations of likely sources of electrolyte decomposition at the cathode and anode, which need to be resolved in order to achieve the long cycle life that is necessary to enable Li-air batteries.Lithium air batteries have recently been of much interest as a revolutionary new technology for energy storage because their theoretical energy densities far exceed that can be obtained from lithium ion batteries. 1-8 A reversible non-aqueous Li-air battery uses a lithium metal anode, a liquid organic electrolyte, and a carbon-supported metal-based catalyst air cathode. Li-air cells differ from conventional battery systems such as lithium-ion or nickel-metal hydride in that oxygen is supplied as a reactant to the cell during discharge through a porous carbon cathode. The cell has a lithium anode for release of electrons to the external circuit resulting in addition of lithium cations to the electrolyte. At the cathode, the oxygen molecule can be reduced in a one-, two-, or possibly four-electron process to form lithium superoxide (LiO 2 ), lithium peroxide (Li 2 O 2 ), or lithium oxide (Li 2 O), respectively, which then have to be decomposed during the charging process. A breakthrough in Li-air battery technology would enable long range electric vehicles including advantages of significantly reducing battery cost and weight.A host of scientific and engineering challenges need to be overcome in order to approach the potential theoretical capacities of the lithium air battery and also to be able to achieve the long cycle life required before any commercial development is possible. The key challenges include are efficiency, cycle life, and capacity. These challenges can in turn be related to specific scientific issues that require fundamental understanding in order to enable design and development of advanced electrode and electrolyte materials for improved efficiency, longer cycle life, and increased capacity. One key aspect that is poorly understood is what controls the microstructure/morphology (e.g. toroid and film growth) and composition of the discharge product. The morphology and composition of the product plays an important role in determining the charging behavior of the Li-air batter...

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