In the realm of battery innovation, traditional metals have long been employed as active materials for negative electrodes. However, a notable shift is underway, focusing on the utilization of redox-active organic molecules like quinone- and amine-based compounds as negative electrodes in rechargeable metal-air batteries. These batteries, featuring oxygen-reducing positive electrodes, harness the participation of protons and hydroxide ions in redox reactions. Notably, they exhibit remarkable performance nearing the theoretical maximum capacity. Importantly, this departure from metals addresses issues such as dendrite formation, which compromises battery efficiency and has adverse environmental effects. Yet, these advanced batteries still employ liquid electrolytes akin to metal-based counterparts, posing significant safety challenges due to electrical resistance, leaching risks, and flammability.

Recent strides in battery research have yielded promising results. A group of Japanese researchers, led by Professor Kenji Miyatake from Waseda University and the University of Yamanashi, has unveiled an all-solid-state rechargeable air battery (SSAB) and examined its capacity and endurance. Their study, featured in Angewandte Chemie International Edition, introduces the use of 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and its polymer poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM) as active materials for the negative electrode due to their stable and reversible redox reactions under acidic conditions. Additionally, they adopted a proton-conductive polymer called Nafion as the solid electrolyte, replacing conventional liquid counterparts.

A significant achievement of the study lies in the successful creation of an SSAB incorporating redox-active organic molecules as the negative electrode, a proton-conductive polymer as the solid electrolyte, and an oxygen-reducing, diffusion-type positive electrode. The SSAB displayed notable improvements over conventional counterparts. Notably, the SSAB did not deteriorate in the presence of water and oxygen, a challenge commonly encountered by typical air batteries with metallic negative electrodes and organic liquid electrolytes.

Furthermore, the researchers made strides in enhancing the performance of the SSAB. By substituting the redox-active molecule DHBQ with its polymeric counterpart PDBM, they achieved a superior negative electrode, exhibiting a discharge capacity of 176.1 mAh, a substantial improvement compared to traditional designs. The study also explored the coulombic efficiency and cyclability of the SSAB, revealing significant potential for sustained use.

Electron microscopic images confirmed that augmenting the negative electrode with Nafion had a positive impact on both performance and durability, underscoring the potential of this novel approach.

Professor Miyatake envisions far-reaching applications for this technology, particularly in extending the battery life of small electronic devices like smartphones. Ultimately, these advancements hold the potential to contribute to the realization of a carbon-free society, marking a pivotal step towards sustainable energy solutions.

By Impact Lab