Associate Professor Wang Qing, Department of Materials Science and Engineering, National University of Singapore (NUS) Faculty of Engineering and his group focus their attention on understanding everything from “charge propagations in mesoscopic energy conversion and storage systems, to the development of new approaches for advanced electrochemical/photoelectrochemical energy conversion and storage.” That places them in the perfect position to take a stab at developing new forms of batteries. And that’s just what they’re doing. Professor Wang is currently working on a new technology called redox flow X-batteries. He was nice enough to set aside the time to answer a few questions.

What is the biggest question facing your field today?

In my view, it will be the low energy density and the associated high capital cost of flow battery systems. Taking the most mature vanadium redox flow battery (VRFB) as an example, its energy density is only 10-20% while its cost is 1.5-2.0 times higher than state-of-the-art lithium-ion batteries.

Why is it significant?

Unlike conventional batteries, flow battery systems store energy in separate tanks instead of the battery’s interior. They are highly scalable – bigger tanks can store more energy – and are much safer as energy is not stored within the battery. Flow batteries also provide greater operational flexibility in terms of installation and maintenance. Such batteries work on a unique principle in which energy storage and power generation are separated, making them especially promising for large-scale stationary energy storage, including smart grids, solar and wind farms, as well as distributed energy storage for households. These applications generally require the deployment of energy storage in extremely large scale, for which the cost and safety is of utmost importance.

Where will the answer likely come from?

To address the current limitations of conventional redox flow batteries, we devised a novel redox targeting concept, where energy is stored in solid materials kept in tanks, while power is generated using the same way as conventional flow batteries. In this way, the energy density is considerably enhanced – making it comparable to solid enclosed batteries such as lithium ion battery – without sacrificing the advantages of flow batteries. We have demonstrated the concept of redox targeting-based flow batteries in various battery chemistries.

For instance, based on lithium ion battery chemistry, the energy density of our Redox Flow Lithium Battery (RFLB) is 10 times higher than the VRFB when commercial lithium ion battery materials are used as energy storage media. This greatly reduces the footprint of the battery system and validates our redox targeting concept for large-scale, high-density energy storage.

Based on lithium-air battery chemistry, the depth of discharge and power of the cell can be significantly improved as the surface passivation and pore clogging issues are eliminated in our Redox Flow Lithium-oxygen Battery (RFLOB). By mitigating these critical limitations of conventional lithium-air batteries, our RFLOB provides an important approach and will be a big leap towards practical application.

For the near term applications, the redox targeting concept has been applied to aqueous systems for enhanced power density. Our research team has developed a water-based, non-flammable Condensed-phase Aqueous Redox-flow Battery (CARB) based on VRFB battery chemistry. The CARB utilises significantly less vanadium and is thus cheaper than conventional redox flow batteries. Its energy and power densities are also considerably better than the VRFB. The CARB is suitable for grid-scale energy applications, such as peak shavings, at wider operating temperatures of up to 80 degrees Celsius.

For more information about Prof. Wang’s research, visit his lab page.


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