October 2020

Due to their high theoretical storage capacity, lithium-oxygen batteries are regarded as possible energy storage systems of the future, both for mobile and stationary applications. In them, metallic lithium (anodic reaction) is converted with oxygen (cathode reaction) to lithium peroxide. The lithium peroxide formed is stored in the battery and converted back into oxygen and metallic lithium when charged. Despite intensive research in recent years, this type of battery is not yet able to achieve high cycle numbers for electrical recharging. This is due to various side reactions during the charging and discharging process, the origin of which has not yet been fully understood. A possible source of the unintentionally generated by-products is singlet oxygen (¹O₂) formed during operation. ¹O₂ is an excited, short-lived variant of molecular oxygen. It is a strong oxidant and reacts with the other components of the battery such as the electrolyte and the electrode materials. However, since ¹O₂ is not long-term stable and reacts after only a few milliseconds, detection is difficult. One possibility for detection is the so-called trapping in which ¹O₂ is reacted with other molecules, which can then be detected later. At the AG Schröder, the molecule 9,10-dimethylanthracene (DMA) shown in the figure is currently being investigated as an agent for detecting 1O2 in lithium-oxygen batteries, since it reacts specifically with singlet oxygen to form 9,10-dimethyl-9,10-epidioxyanthracene (DMA-O₂). Little is known about its stability and its influence on the chemistry of lithium-oxygen batteries. The DMA-O₂ required for this is produced photochemically in the AG Schröder (see picture) and then purified before it is further investigated. (Image by: Adrian Schürmann)