Towards practically accessible aprotic Li-air batteries: Progress and challenges related to oxygen-permeable membranes and cathodes

Aprotic Li-air (O 2 ) batteries (ALBs), with theoretical energy density 3∼5 times higher than that of state-of-the-art Li-ion batteries, could potentially power an electric vehicle to be comparable to gasoline vehicles. However, the practical application of ALBs is hindered by O 2 -breathing and O 2 (electro)-chemistry issues in Earth's atmosphere. Recent investigations revealed that the oxygen permeable membranes (OPMs) and oxygen permeable cathodes (OPCs) could significantly improve the cycling life and energy efficiency of ALBs. Although great efforts have been made for the OPMs and OPCs, many scientific and technical challenges still need to be overcome to achieve ALBs that reach industrial standards. In addition, there is a degree of commonality in some of the challenges facing OPMs and OPCs, especially concerning O 2 transport. In this review, we summarize the recent process related to the challenges, preparation, and application of OPMs and OPCs in practical ALB systems. We first discuss the O 2 -breathing issues of ALBs and then summarize the application of advanced OPMs, which are frequently invoked as a protective strategy to resist the invasion of undesired gas species (CO 2 , H 2 O, etc.) from external air. Specifically, the O 2 (electro)-chemistry issues involving the kinetics of the oxygen evolution reaction (OER)/oxygen reduction reaction (ORR), and tri-phase transfer channels for electrons, lithium ions, and oxygen gas on OPCs are equally important for ALBs. Following these insights, main challenges and perspectives are given in the end on how to design high-performance OPMs and OPCs for practically accessible ALBs in Earth's atmosphere. Towards Practically Accessible Aprotic Li-Air Batteries: Progress and Challenges Related to Oxygen-Permeable Membranes and Cathodes