Wisdom from the Human Eye: A Synthetic Melanin Radical Scavenger for Improved Cycle Life of Li-O2 Battery

Li-O-2 batteries are attractive systems because they can deliver much higher energy densities than those of conventional lithium-ion batteries by engaging light gas-phase oxygen as a cathode active material. However, the inevitable generation of residual superoxide radicals gives rise to irreversible side reactions and consequently causes severe capacity degradation over cycling. To address this chronic issue, herein, we have taken a lesson from the human eye. Analogous to Li-O-2 batteries, the human eye is liable to attack by reactive oxygen species (ROS), from its lifetime exposure to sunlight. However, it protects itself from the ROS attack by using melanin as a radical scavenger. To mimic such a defense mechanism against radical attack, we included polydopamine (pD), which is one of the most common synthetic melanins, in the ether-based electrolyte. As an outcome of the superoxide radical scavenging by the pD additive, the irreversible side reaction products were alleviated significantly, resulting in superior cycling performance. The present investigation provides a message that simple treatments inspired by the human body or nature could be effective solutions to the problems in various energy devices.