Researchers from the Scherman and Grey research groups demonstrate a path to batteries that do not contain rare metals and are stable in the air. The researchers show how a ‘custom-built’ class of metal-free pyridinium molecules can act effectively as charge-carrying electrolytes in redox-flow batteries, even when exposed to air, which has potential for more stable and lower-cost batteries.
PhD student and co-first author Mark Carrington said: “The air stability would give us a new capability to create grid-scale energy storage which can be used under harsh conditions or in remote locations. It could be used to power cities and to help mitigate the intermittent nature of renewable energy.”
Grid-scale energy
“One of the biggest challenges we face now is how to create the large-scale storage of energy from intermittent energy sources like wind and solar,” said Grey, who is a co-corresponding author. “We need batteries that are large enough and last long enough for the grid, say 20 to 40 years.”
Redox flow batteries (RFBs) are one of the most promising solutions for this challenge. RFBs are typically used for grid energy storage, for example attached to power plants or electrical grids, because they offer larger capacity in comparison to conventional solid-state batteries.
Stable in air
Most RFBs are based on liquid electrolytes that are pumped through the system on separate sides of a membrane and degrade when exposed to air. One of the major advantages of the pyridinium-based molecules reported by the researchers is that they have potential to work in the air.
“The molecules exist as a powder which is air stable and can be stored under ambient conditions, so preparation of the electrolyte solution is as simple as dissolving the molecules in a saline solution,”Kamil Sokolowski, Yusuf Hamied Department of Chemistry, University of Cambridge,
Capacity fade
A major barrier to extending battery life that we are all familiar with is ‘capacity fade,’ which is when the amount of charge stored begins to decrease with repeated cycling. The researchers used an array of characterisation techniques such as nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and mass spectrometry to study the pyridinium molecules in flow battery conditions over thousands of cycles.
“We found the molecules were able to carry a substantial amount of charge,” said Scherman. “Over hundreds of cycles they don’t fall apart, they don’t decompose, and what’s unique is that they can form looser, non-covalent dimers, so they can still transport the electrons.”
Grey said: “Normally the charge-carrying molecules react with trace oxygen and form ROS, which leads to degradation. However, these pyridinium molecules form non-covalent dimers which can encapsulate carried electrons. They do not interact with dissolved oxygen and they don’t degrade.”
Further research
The Grey group has recently been awarded a Faraday Institution Industry Sprint grant for £240 thousand to continue investigating high voltage redox flow batteries for demanding applications and to scale the concept from lab scale to kilowatt hour scale.
Continued development of the core electrolyte and electron mediator technology is ongoing in the Scherman lab from both fundamental and commercial perspectives.
Grey said: “This work takes us one step closer to designing commercial redox systems.”
Read the full Yusuf Hamied Department of Chemistry article
Associative pyridinium electrolytes for air-tolerant redox flow batteries, M. E. Carrington, K. Sokolowski, E. Jónsson, E. W. Zhao, A. M. Graf, I. Temprano, J. A. McCune, C. P. Grey and O. A. Scherman, Nature, (Nov 2023), 623, 949-955.