Current and future cathode materials for non-aqueous Li-air (O2) battery technology - A focused review

With an ever-increasing demand for replacing current lithium-ion batteries (LIBs) with low energy density, there has been a recent surge in interest and research on lithium-metal battery (LMB). Lithium-air batteries (LABs), in particular, have shown a compelling case for researchers due to their highest energy density (3600 Wh kg(-1)). However, despite decades of the tremendous amount of studies, LABs are still not commercialized as a practical energy storage system due to unsolved issues related to cathode materials. In this review, we present the most recent progress in cathode materials functioning as free-standing electrodes. Significantly, materials and processing to address the complicated problem are discussed in each section. Also, this review includes a discussion of the current controversy about the principles of useful cathode materials regarding ORR, OER and stability, and future perspectives of research related to them. Because the realization of current LAB to practical application is poorly understood, this review emphasizes on initiating a hasty search for practical LABs and their applications. A summary and outlooks on the current limitations and recommended future research directions of LABs are also presented.