Researchers at the Dalian Institute of Chemical Physics have developed novel naphthalene-based organic redox-active molecules (ORAMs) for aqueous organic flow batteries. The newly developed ORAMs demonstrate that they can achieve stable cycling in normal ait-atmosphere condictions, a press release said.
A redox flow battery is a type of electrochemical cell in which electric current is generated by components dissolved in liquids stored on opposite sites of a membrane. Advantages of redox flow batteries include their ability to scale power and low cost of ownership. However, low cycle energy and the use of rare metals like vanadium have limited their use.
Research is therefore ongoing to develop organic redox flow batteries, in which organic materials are used, which are widely available and easier to produce. Depending on the solvent used for the electrolyte, organic redox batteries can be classified into two major categories: aqueous and non-aqueous.
An aqueous organic flow battery (AOFB) uses water as an electrolyte, whereas a non-aqueous organic flow battery (NAOFB) uses an organic solvent.
Challenge of ORAMs
Various types of AOFBs are in the works, classified based on the pH of the electrolyte, neutral, and acid, and offer cost and scale benefits. However, the organic redox-active molecules (ORAMs) used in the batteries are prone to deactivation due to side reactions if not used with an inert gas.
This can increase the cost of battery maintenance since the capacity loss is irreversible and severely degrades the battery’s lifespan as well.
A team led by Zhang Changkun and Li Xianfeng, both professors at the Dalian Institute of Chemical Physics, developed novel naphthalene-based derivatives with active hydroxyls and dimethylamine scaffolds that provide stability in air and can, therefore, be used in AOFBs.
Artistic representation of a redox flow battery and its advantages. Image credit: DICP.
How well did they perform?
The researchers used a combination of chemical and in situ electrochemical methods to synthesize the active naphthalene derivatives. This approach not only made it easier to purify the ORAMs but is also scalable and cost-effective.
The electrochemical step added another advantage since the researchers could now introduce hydrophilic alkylamine scaffolds into the naphthalene derivatives. This serves as protection from unintended side reactions while also improving the solubility of the molecules in the water-based electrolyte.
In their tests, the researchers found that the naphthalene flow battery, when used with a 1.5 mol/L electrolyte, has stable cycling performance for up to 850 cycles (approximately 40 days).
The capacity of the battery was recorded at 50 Ah per liter.
The researchers introduced a continuous air flow in the catholyte to test whether the AOFB could work with air exposure. They found that the battery performed well for 600 cycles (approximately 22 days) without a drop in performance or capacity.
In addition to the performance improvements, the researchers also worked on the scalability of naphthalene derivatives production and achieved outputs of 11 pounds (five kg) per pot, the press release added.
The researchers designed pilot-scale battery packs with their new synthesis and operation procedures. They tested them for stability and performance in the lab. With a capacity of 330 Ah, the pilot battery packs demonstrated cycling stability for 270 cycles (27 days) and capacity retention of 99.95 percent 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,” added Li in the press release.
Ameya Paleja Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.
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