An overview of the unstable and irreversible lithium metal anode-related issues in nonaqueous Li–O2/air batteries

Abstract

Towards the practical application of nonaqueous Li–O₂/air batteries (LOBs/LABs) with high theoretical energy density (3500 W h kg⁻¹), they should work stably, effectively, and safely in an open-air environment and not be trapped in the closed-O₂ atmosphere. In these systems, Li-metal is the direct ion supply source, and thus the stability of Li-anode determines the lifetime and safety of LOBs/LABs. In this review, we firstly summarize the severe shuttle effect originating from a practical working environment (O₂, N₂, CO₂, H₂O, etc.) and operation process (electro-reduced oxygen species, redox mediators) towards Li-anode, which is fatal for inherently unhealthy Li-anode. Moreover, several concerns affecting the rechargeability of LOBs/LABs are also discussed, including factors affecting the mass transfer of O₂ (O₂ selective membrane, gas diffusion layer, and solubility of oxygen species), battery components controlling the transportation of Li ions (cathode, separator, liquid/solid/gel electrolytes, and Li-surface coating), reshaping of 3D structure/composition of the SEI of Li-surface, and irreversible electrolyte decomposition. Finally, four development directions (open gas environment, wide temperature range, evaluation standards, and practical pouch cell assembly) of LOBs/LABs on real applications are mentioned. This review emphasizes the importance of Li-metal anode-related issues in LOBs/LABs and also reveals development directions from scientific and engineering perspectives.