Researchers at the Chinese Academy of Sciences (CAS) claimed to have built a stable kilowatt-scale aqueous redox flow battery (AOFB) with high-performance organic redox-active molecules for renewable storage.

The battery is a promising candidate for large-scale energy storage due to its high security and effectiveness.

Further, aqueous organic flow batteries utilize structurally tunable and eco-friendly redox-active molecules and are getting increasing attention.

The researchers assembled ten units of AOFBs stacks, which exhibited a stable capacity for over 500 cycles. Moreover, the stack based on MB electrolyte achieved a stable long-life cycle performance for roughly 32 days.

Aqueous organic flow batteries (AOFBs) possess unique advantages, including elemental abundance, and are adaptive compared to traditional flow batteries (FBs).

However, achieving air stability and high-performance electrolytes is still one of the main challenges for their practical applications. Most organic molecules in AOFBs are prone to oxidization, resulting in irreversible capacity decay and hindering further applications.

A team of researchers led by Li Xianfeng and Zhang Changkun from the Dalian Institute of Chemical Physics (DICP), CAS, sought to address this by using an electrolyte based on methylthioninium chloride, also known as MB.

The researchers demonstrated that the stabilizations of MB, in both the intermediate free radical and reduced states, played a vital role in improving redox reversibility and air stability.

With the help of nuclear magnetic resonance and electron paramagnetic resonance (EPR) techniques, both the oxygen-resistant MB radicals and the reduced MB states in acidic electrolyte displayed more stable molecular structure. It played a vital role in the high reversibility of MB molecules under ambient air conditions.

“We optimized electrolyte composition by tuning the interaction between different components in the electrolyte, thereby increasing the battery capacity,” Li said.

Recently, researchers at the University of Sydney claimed to have developed a new, low-cost sodium-sulfur battery with four times the energy capacity of lithium-ion batteries. The success of the technology could significantly reduce the cost of transitioning to a decarbonized economy.

In October, researchers at the Technical University of Munich claimed that certain crystalline materials could convert solar energy into electrical energy and store it long enough to have practical applications in off-grid energy distribution.