Lithium–Air Batteries: Performance Interplays with Instability Factors Luhan Ye, [a] Weiqiang Lv, [a] Junyi Cui, [a] Yachun Liang, [a] Peng Wu, [a] Xiaoning Wang, [a] Han He, [a] Senjun Lin, [b] Wei Wang, [c] James H. Dickerson, [d, e] and Weidong He* [a, f, g] 1. Introduction The fossil-fuel-based economy has become increasingly unsus- tainable over the past decades. The emerging energy crisis has affected various aspects of human society. To meet future social and industrial energy demands, scientists are facing un- precedented challenges. Much effort has been focused on the development of sustainable energy devices including solar cells, and those driven by biomass and hydrogen. [1–4] How to produce power efficiently has been a central theme through- out the industrial age. In addition, for better energy utilization, another strategy is to seek new methods for efficient energy storage. [5, 6] Until now, Li-ion batteries have dominated the bat- tery market. They have particularly long cycle lives and high operating voltages, and are thus suitable for certain practical applications such as powering laptops and cellphones. [7] Al- though the energy density of Li-ion batteries (  160 W h kg 1 ) is relatively high compared to traditional batteries, they are still far from being applied in electrical vehicles. Cost-effective and environmentally friendly storage devices with high energy densities are urgently needed. The lithium–air battery, due to its excellent energy density, can potentially meet this need. [8, 9] The first rechargeable nonaqueous lithium–air battery was in- troduced by Abraham and Jiang in 1996. [10] The theoretical energy density has been demonstrated to be up to 11 430 W h kg 1 , which is comparable to fossil fuels and is much higher compared with other widely used batteries (such as the Li-ion and Ni–Cd batteries), as shown in Figure 1. [9] The high energy density of lithium–air batteries is promising for powering electric vehicles and hybrid electric vehicles. Despite their high energy density, the applications of lithium–air bat- teries are still limited significantly by their instability. [11–16] Com- pared to the lead–acid battery widely used in industry, the per- formance of lithium–air batteries is affected directly by their in- stability. Conventional lithium–air batteries, including nonaqu- eous and aqueous types, are assembled as shown in Figure 2. [17] Much work has demonstrated their instability during charge–discharge processes between the application to internal structures; a subtle disturbance can lead to a large degradation in capacity and poor cyclic performance. [18–20] For instance, the main reaction product, Li 2 O 2 , is insoluble in organic solvents, and might consequently clog electrode pores. Furthermore, Bruce et al. [21] reported that carbon elec- trodes are unstable as the charge voltage increases beyond 3.5 V. Electrolytes also decompose during operation cycles. [19] In brief, overall physical transportation problems, decomposi- tion and parasitic reactions cause a sensitive instability in lithi- Lithium–air batteries are considered to be promising electro- chemical storage devices, due to their high specific energy density. However, instability limits their cyclic performance and rate capacity and also leads to a high overpotential; lithium– air batteries are typically characterized by capacity degradation and short cycle life. Such challenges prevent lithium–air batter- ies from entering and competing in the battery market. Elec- trodes, organic solvents, the interface between electrolyte and cathode, and ambient conditions have all been demonstrated to impact substantially the stability of the lithium–air battery. In this Minireview, we focus on electrode and electrolyte de- composition, side reactions, and physical mass transport in aprotic lithium–air batteries, as well as other types of lithium– air batteries, and aim to understand comprehensively their per- formance and association with instability factors. [a] L. Ye, W. Lv, J. Cui, Y.Liang, P. Wu, X. Wang,H. He, Prof. W. He School of Energy Science and Engineering University of Electronic Science and Technology Chengdu, Sichuan 611731 (P.R. China) [b] S. Lin Department of Industrial Design Zhejiang University of Technology Hangzhou, Zhejiang, 310014 (P.R. China) [c] W. Wang Department of Material Science and Engineering Shenzhen Graduate School, Harbin Institute of Technology Shenzhen 518055 (P.R. China) [d] J. H. Dickerson Center for Functional Nanomaterials Brookhaven National Laboratory Upton, NY 11973 (USA) [e] J. H. Dickerson Department of Physics, Brown University Providence, RI 02912 (USA) [f] Prof. W. He Interdisciplinary Program in Materials Science Vanderbilt University, Nashville, TN 37234-0106 (USA) [g] Prof. W. He Vanderbilt Institute of Nanoscale Science and Engineering Vanderbilt University, Nashville, TN 37234-0106 (USA) E-mail : weidong.he@uestc.edu.cn ChemElectroChem 2015, 2, 312 – 323  2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 312 Minireviews DOI: 10.1002/celc.201402315