Organic redox-active molecules (ORAMs) hold immense promise for affordable and sustainable energy storage, especially in aqueous organic flow batteries (AOFBs). However, the challenge lies in ensuring the stability of these molecules during charging and discharging to prevent deactivation due to side reactions, particularly in air.
Recently, Prof. LI Xianfeng and Prof. ZHANG Changkun’s team at the Dalian Institute of Chemical Physics (DlCP) of the Chinese Academy of Sciences (CAS) made a groundbreaking advancement. They developed air-stable naphthalene derivatives with active hydroxyls and dimethylamine scaffolds that exhibit remarkable stability and serve as highly effective catholytes for AOFBs.
Their study, published in Nature Sustainability, showcases these novel ORAMs as capable of achieving long-term stable cycling even in air-atmosphere conditions.
ORAMs face serious challenges, such as instability and high costs, especially when used without inert gas protection. This can result in irreversible capacity loss and a shortened battery lifespan.
In this groundbreaking study, the researchers devised a method to synthesize active naphthalene derivatives using a scalable approach that merges chemical and in situ electrochemical methods. This innovative technique not only streamlines the purification process but also dramatically cuts down the cost of molecular synthesis.
Furthermore, the researchers showcased specific structural transformations in the naphthalene derivatives during the electrochemical process. The resulting naphthalene derivatives boast a multisubstituted framework with hydrophilic alkylamine scaffolds, offering protection against potential side reactions while enhancing their solubility in aqueous electrolytes.
The performance of the 1.5 mol/L naphthalene-based Aqueous Organic Flow Battery (AOFB) is truly remarkable. It displayed stable cycling performance for an impressive 850 cycles (equivalent to about 40 days) with a capacity of 50 Ah L-1.
Even with continuous air flow in the catholyte, the naphthalene-based AOFB demonstrated exceptional resilience, running smoothly for approximately 600 cycles (about 22 days) without any capacity and efficiency decay. This clearly underscores the outstanding air stability of the naphthalene-based catholyte.
In addition, the researchers successfully scaled up the production of naphthalene derivatives to the kilogram scale, achieving 5 kg per pot. The pilot-scale battery stacks containing these naphthalene derivatives showcased an average system capacity of an impressive 330 Ah. Furthermore, they exhibited remarkable cycling stability over 270 cycles (approximately 27 days) with a phenomenal capacity retention of 99.95% per cycle.
“This study is expected to open a new field in the design of air-stable molecular for sustainable and air-stable electrochemical energy storage,” said Prof. LI.
Journal reference:
- Ziming Zhao, Tianyu Li, Changkun Zhang, Mengqi Zhang, Shenghai Li & Xianfeng Li. Air-stable naphthalene derivative-based electrolytes for sustainable aqueous flow batteries. Nature Sustainability, 2024; DOI: 10.1038/s41893-024-01415-6