Effect of CO2-induced side reactions on the deposition in the non-aqueous Li-air batteries

This paper presents a non-aqueous Li-air battery model that considers the side reactions of lithium carbonate (Li₂CO₃) formation from both electrolyte decomposition and carbon dioxide (CO₂) in the ambient air. The deposition and decomposition behaviors of discharge products, the voltage, and capacity evolutions during the cycling operation of the Li-air batteries are investigated. The deposition behavior analysis implies that the Li₂CO₃ generated by electrolyte decomposition is mainly distributed near the separator side, while it is dominantly generated by Li-O₂/CO₂ reaction near the air side. The formation of Li₂CO₃ by side reactions makes the Li-air batteries exhibit a peak discharge deposition inside the cathode. Moreover, Li₂CO₃ is difficult to decompose and gradually accumulates with cycles, especially near the air side. The severe accumulation of Li₂CO₃ near the air side significantly reduces the O₂ diffusion into the electrode, which induces severe cycling performance decay of the Li-air batteries. According to the distribution and evolution of the deposition, three simple hierarchical cathode structures with high porosities near the air side are finally studied. The simulation results indicate that the increase of the local porosity near the air side substantially improves the cycling performance of the Li-air batteries.