DOI: 10.1002/ijch.201400089 A Review of the Design Strategies for Tailored Cathode Catalyst Materials in Rechargeable Li-O 2 Batteries Kyeongse Song, DanielAdjei Agyeman, Jaepyeong Jung, MiRu Jo, Junghoon Yang, and Yong- Mook Kang* [a] 1. Introduction High-energy and high-power rechargeable batteries are crucial for next-generation portable electronic appliances, electric vehicles (EVs), and large-scale energy storage systems (ESSs). In particular, because EVs based on re- chargeable batteries do not emit any combustion gases, their effective application is regarded as a promising energy solution to environmental concerns, such as global warming and diminishing fossil fuel supplies. Moreover, these batteries facilitate the economical consumption of energy obtained from renewable energy sources that depend on climate, and thus, the development of ad- vanced ESSs is indeed an urgent global task. [1] The energy density of state-of-the-art lithium-ion bat- teries (LIBs) cannot meet the strict requirements of these applications. In current LIB technology, the operating voltage and capacities are mainly determined by cathode or anode materials, which have already been confronted with the theoretical limitation in capacity. Consequently, to deliver higher energy and power density (to meet in- dustry requirements), many researchers have dedicated themselves to developing new energy storage/conversion systems. [2,3] The aprotic (nonaqueous) rechargeable lithium-oxygen (Li-O 2 ) battery was first introduced by Abraham et al. [3] It consisted of an Li metal anode, a porous carbon compo- site cathode, a conductive organic polymer electrolyte, and oxygen, the electroactive material that could be ac- cessed from the outside, through the porous carbon. During the discharge process (oxygen reduction reaction, ORR), O 2 is reduced in the porous air cathode, with a re- lease of electrical power. The reduced O 2 species (O 2  ) then reacts with dissolved Li ions, ideally yielding an in- soluble Li 2 O 2 and/or Li 2 O product. Meanwhile, the charge process (oxygen evolution reaction, OER) accom- panies the electrochemical dissociation of these dis- charged products. Such Li-O 2 electrochemical cells are considered as the most promising metal-air batteries ever developed, since their theoretical specific energies (11,140 W h kg 1 (Li) and 5200 W h kg 1 (Li 2 O)) are comparable to the energy density of gasoline fuel (13,000 W h kg 1 ). [4] Through Abstract : For the purpose of reducing not only the con- sumption of natural resources, but also the environmental pollution from internal combustion engines, much effort has been dedicated to developing new energy storage sys- tems (ESSs) and electric vehicles (EVs) powered by batter- ies. There are several stringent requirements, such as high power/energy density, good safety, and high reliability against external environmental abuse. For next-generation batteries to meet these requirements, the development of a new energy conversion system is crucial. Therefore, lithi- um-oxygen (lithium-O 2 ) batteries have attracted intensive at- tention, due to their high theoretical energy density, com- pared with those of gasoline engines. However, present lithi- um-O 2 batteries exhibit low round-trip efficiency and cyclic degradation, thus preventing their commercialization as next-generation power sources. This drawback may be at- tributed to the high thermodynamic stability of discharge products and their intrinsic insulating character, leading to the surge of polarization in oxygen reduction reactions/ oxygen evolution reactions (ORRs/OERs). To alleviate cyclic degradation and improve round-trip efficiency, it has been reported that the polarization can be reduced by adopting adequate cathode catalysts, based on their surface struc- tures regulating oxygen adsorption. Here we provide and discuss several design strategies for tailoring catalytic mate- rials from a structural and morphological viewpoint, as well as their effect on discharge products. Keywords: catalysts · electrochemistry · lithium · metal oxides · nanomaterials [a] K. Song, D.A. Agyeman, J. Jung, M. R. Jo, J. Yang, Y.-M. Kang Department of Energy and Materials Engineering Dongguk University-Seoul Seoul 100-715 (Republic of Korea) Tel.: (+ 82) 2-2260-8674 e-mail: dake1234@dongguk.edu Isr. J. Chem. 2015, 55, 458 – 471 # 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 458 Review