Air-stable naphthalene derivative-based electrolytes for sustainable aqueous flow batteries

The growing global capacity for renewable energy generation necessitates the deployment of energy storage technologies with a combination of low cost, good performance and scalability. With these advantages, aqueous organic flow batteries have the potential to be the system of choice because they could store energy from organic redox-active molecules. Here we report naphthalene derivatives as organic redox-active molecules that exhibit high solubility (~1.5 M) and a stable redox-active framework with no obvious capacity decay over 40 days (50 Ah l⁻¹) in an air atmosphere in flow batteries. We report a battery that runs smoothly even under continuous airflow without obvious capacity decay for ~22 days (more than 600 cycles). A series of spectral analyses and theoretical calculations reveal that the dimethylamine scaffolds improve the water solubility and protect the active centre, ensuring the stability of the molecules during the charge and discharge process. Owing to the success in kilogramme-scale molecular synthesis, pilot-scale stack expansion with notable cycling stability over 270 cycles (~27 days) is attained. The cost benefit evidenced by technoeconomic analysis together with the stability even under open-air conditions indicates the practical value of the present molecular system in grid-scale energy storage.