Effects of the oxygen transport properties of electrolytes on the reaction mechanisms in lithium-oxygen batteries

Lithium-oxygen batteries attract considerable attention due to exceptionally high theoretical energy density, while the development remains in its early stage. As is widely suggested, the solution mechanism induces greater discharge capacity, while the surface mechanism induces greater cycle stability. Therefore, battery performance can be improved by adjusting the reaction mechanism. Previous studies predominantly focus on extremely thin or flat electrodes. In contrast, this work utilizes thick electrodes, emphasizing the importance of mass transport. Given that the electrolyte solvent is the main site of mass transport, the effects of two typical solvents on mass transport and battery performance are investigated: dimethyl sulfoxide with low viscosity and a high O₂ diffusion rate and tetraethylene glycol dimethyl ether with high O₂ solubility and high Li⁺ transport capability. The results reveal a novel pathway for reaction mechanism induction where the mechanism varies with the spatial position of the electrode. As the spatial distribution of the electrode progresses, a layered appearance of solution mechanism products, transition state products, and surface mechanism products emerges, which is attributed to the increase in the mass transfer resistance. This work presents a distinct perspective on the way solvents influence reaction pathways and offers a new approach to regulating reaction pathways.