An electronegative biomimetic separator suppresses side effects of iodine species in Li-O₂ batteries

LiI in Li-O₂ batteries has shown promise in reducing charge overpotential. However, the shuttle effect of oxidated iodine species (OISs) can lead to lithium metal corrosion and loss of OISs. During the discharging process, these iodine species can undergo side reactions, resulting in the accumulation of LiOH and other parasitic products, which in turn accelerates battery failure. In this work, we have drawn inspiration from mussel protein and utilized a simple co-deposition method to form a robust biomimetic functionalized coating on the surface of the glass fiber separator. This was achieved by grafting catechol/polyamine (CA/PA) with 11-mercaptoundecanoic acid (MUA). This separator exhibits strong electrostatic repulsion towards negatively charged OISs and, conversely, electrostatic attraction towards Li⁺, this dual action effectively suppresses the shuttle effect and facilitates Li⁺ transport. When equipped with this modified separator, the Li-O₂ battery effectively reduces the accumulation of LiOH and demonstrates significantly enhanced rate performance and cycle stability. Our findings provide a versatile approach for the design of modified separators for Li-O₂ batteries with redox mediators (RMs).