Comprehensive Review of Li-Oxygen Batteries: Electrolytes, Electrodes, Redox Mediators, and Thermodynamics

A Li-oxygen (Li–O2) battery is a next-generation Li-battery with extremely high theoretical energy density, reaching up to that of a gasoline engine. Unfortunately, practical Li–O2 batteries have limited energy density and discharge capacity due to several issues. The recent decade has witnessed intense research in defining and understanding the working mechanism of Li–O2 batteries. All components of a Li–O2 battery are crucial for its effective working, but they have limitations and face specific issues during service life, such as the electrolyte defines the working potential window of the battery and solvents used in making these electrolytes control the thermodynamics and reaction pathways of the Li–O2 battery’s electrochemistry. Solvent variation has serious implications for the Li–O2 battery’s electrochemistry. Similarly, the cathode limits the energy storability and dictates the morphologies and growth mechanisms of the reaction products. On the other hand, the anode critically affects the stability and cyclic life of the Li–O2 battery. In addition, the major reaction products of Li–O2 batteries are insulators with wide energy band gaps, which results in low reaction kinetics and limited capacity. To boost the efficient reversibility of the reaction products, redox mediators are required which mainly facilitate the decomposition of these reaction products. All of the aforementioned components of the Li–O2 battery are vital and face certain issues that require considerable attention to build a practical Li–O2 battery. To comprehensively discuss all these components and their implications on the Li–O2 battery’s performance, this review summarizes recent trends and challenges these components face during service life.