Stability challenges in non-aqueous Li–O2 batteries and their protective strategies: a comprehensive review on electrode and electrolyte engineering

Abstract

Non-aqueous Li–O₂ batteries are at the forefront of next-generation energy storage research due to their exceptionally high theoretical energy density, which could surpass that of conventional Li-ion batteries. However, despite their potential, practical implementation is hindered by several critical challenges including poor cycle life and high overpotentials due to the instability of the lithium metal anode, air cathode, and electrolyte. The ineffectiveness of electrocatalysts in non-aqueous Li–O₂ systems is critically examined. Although catalysts such as noble metals and transition metal oxides have been explored to enhance the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), their performance in non-aqueous environments remains suboptimal due to side reactions and catalyst degradation. To provide a detailed understanding of the ORR and OER kinetics, the rotating ring-disk electrode (RRDE) technique is discussed as a valuable tool for evaluating the catalytic activity, identifying reaction intermediates, and probing the role of superoxide species in battery degradation. More detailed discussions of the challenges/strategies with regard to the anode, cathode, electrolyte, redox mediator (RM), and oxygen selective membrane and the recent advances are presented. This review focuses on threefold strategies for protecting the lithium metal anode, air cathode, and electrolyte, which are highly susceptible to attack by reactive oxygen species (ROS) and their intermediates (O₂⁻, LiO₂, ¹O₂, and O₂²⁻), lithium metal corrosion, parasitic reactions, electrolyte degradation/volatilization, electrode passivation, and sluggish kinetics. Special emphasis is placed on advanced protective approaches including the design of artificial solid–electrolyte interfaces (SEIs), inducing solution-mediated growth of lithium peroxide (Li₂O₂), and electrolyte stabilization by a threefold strategy using electrolyte additives, which shows promise in extending the battery cyclability. This review aims to provide a comprehensive understanding of the key issues limiting the performance of non-aqueous Li–O₂ batteries and explores potential pathways to overcome these challenges through advanced electrolyte additive engineering and electrochemical techniques.