Recent advances in understanding the chemistry and electrochemistry of lithium-air (Li-air) batteries are reviewed. Li-air batteries have the highest theoretical specific energy of any rechargeable battery, but their practical implementation is hindered by a lack of fundamental understanding of the reactions and processes involved. The review focuses on the mechanisms of oxygen reduction to Li₂O₂ during discharge and the reverse process during charge, as well as the consequences for battery rate and capacity. It also considers parasitic reactions involving the cathode and electrolyte, and examines design principles for better Li-air batteries. The Li-air battery uses oxygen from the air as the positive electrode, and the reaction at the cathode is the reduction of O₂ to Li₂O₂. The mechanism of this reaction depends on the solvation of Li⁺ in the electrolyte. In solutions with high donor numbers, LiO₂ is soluble and forms particles in solution, while in solutions with low donor numbers, LiO₂ is insoluble and forms a film on the electrode surface. The solubility of LiO₂ is influenced by the solvent and the anions in the electrolyte. Additives to the electrolyte can also influence the solubility of LiO₂. Recent studies have shown that the reaction pathway for O₂ reduction to Li₂O₂ can be altered to avoid the formation of LiO₂, which is reactive and can lead to side reactions. A mediator such as DBBQ can be used to facilitate the reaction, allowing Li₂O₂ to form in solution and leading to higher discharge rates and capacities. The oxidation of Li₂O₂ during charge is also discussed, with the challenge being the oxidation of large particles of insulating Li₂O₂. The use of oxidation mediators can help overcome this challenge by facilitating the oxidation of Li₂O₂ in solution. The electrolyte is a critical component of the Li-air battery, as it must be stable in the presence of reduced oxygen species. The review discusses the reactivity of various solvents and electrolytes with reduced oxygen species, and the importance of choosing a stable electrolyte. The design of the cathode is also discussed, with the need for materials that provide sufficient electronic conductivity and Li⁺/O₂ transport, while being resilient to Li₂O₂-induced oxidation and not promoting parasitic reactions. Overall, the review highlights the importance of understanding the fundamental chemistry and electrochemistry of Li-air batteries to develop practical devices that can meet the energy storage needs of future generations.Recent advances in understanding the chemistry and electrochemistry of lithium-air (Li-air) batteries are reviewed. Li-air batteries have the highest theoretical specific energy of any rechargeable battery, but their practical implementation is hindered by a lack of fundamental understanding of the reactions and processes involved. The review focuses on the mechanisms of oxygen reduction to Li₂O₂ during discharge and the reverse process during charge, as well as the consequences for battery rate and capacity. It also considers parasitic reactions involving the cathode and electrolyte, and examines design principles for better Li-air batteries. The Li-air battery uses oxygen from the air as the positive electrode, and the reaction at the cathode is the reduction of O₂ to Li₂O₂. The mechanism of this reaction depends on the solvation of Li⁺ in the electrolyte. In solutions with high donor numbers, LiO₂ is soluble and forms particles in solution, while in solutions with low donor numbers, LiO₂ is insoluble and forms a film on the electrode surface. The solubility of LiO₂ is influenced by the solvent and the anions in the electrolyte. Additives to the electrolyte can also influence the solubility of LiO₂. Recent studies have shown that the reaction pathway for O₂ reduction to Li₂O₂ can be altered to avoid the formation of LiO₂, which is reactive and can lead to side reactions. A mediator such as DBBQ can be used to facilitate the reaction, allowing Li₂O₂ to form in solution and leading to higher discharge rates and capacities. The oxidation of Li₂O₂ during charge is also discussed, with the challenge being the oxidation of large particles of insulating Li₂O₂. The use of oxidation mediators can help overcome this challenge by facilitating the oxidation of Li₂O₂ in solution. The electrolyte is a critical component of the Li-air battery, as it must be stable in the presence of reduced oxygen species. The review discusses the reactivity of various solvents and electrolytes with reduced oxygen species, and the importance of choosing a stable electrolyte. The design of the cathode is also discussed, with the need for materials that provide sufficient electronic conductivity and Li⁺/O₂ transport, while being resilient to Li₂O₂-induced oxidation and not promoting parasitic reactions. Overall, the review highlights the importance of understanding the fundamental chemistry and electrochemistry of Li-air batteries to develop practical devices that can meet the energy storage needs of future generations.