̽��ֱ�� of Cambridge - Evan Wenbo Zhao

New approach topples major barrier to commercialisation of organic flow batteries

sc604 — Thu, 16 Jun 2022 15:00:00 +0000

̽��ֱ��process works a bit like a pacemaker, periodically providing a shock to the system that revives decomposed molecules inside the batteries. Their results, reported in the journal Nature Chemistry, demonstrated a net lifetime 17-times longer than previous research.

“Organic aqueous redox flow batteries promise to significantly lower the costs of electricity storage from intermittent energy sources, but the instability of the organic molecules has hindered their commercialisation,” said co-author Michael Aziz from Harvard. “Now, we have a truly practical solution to extend the lifetime of these molecules, which is an enormous step to making these batteries competitive.”

Over the past decade researchers have been developing organic aqueous flow batteries using molecules known as anthraquinones – composed of naturally abundant elements such as carbon, hydrogen, and oxygen – to store and release energy.

Over the course of their research, the team discovered that these anthraquinones decompose slowly over time, regardless of how many times the battery has been used.

In previous work, the researchers found that they could extend the lifetime of one of these molecules, named DHAQ but dubbed the ‘zombie quinone’ in the lab, by exposing the molecule to air. ̽��ֱ��team found that if the molecule is exposed to air at just the right part of its charge-discharge cycle, it grabs oxygen from the air and turns back into the original anthraquinone molecule — as if returning from the dead.

But regularly exposing a battery’s electrolyte to air isn’t exactly practical, as it drives the two sides of the battery out of balance — both sides of the battery can no longer be fully charged at the same time.

To find a more practical approach, the researchers developed a better understanding of how the molecules decompose and invented an electrical method of reversing the process.

Researchers from Professor Clare Grey’s group in Cambridge’s Yusuf Hamied Department of Chemistry, carried out in situ nuclear magnetic resonance (NMR) – essentially ‘MRI for batteries’ – measurements and discovered the recomposition of active materials by an electric method, the so-called deep discharge.

̽��ֱ��team found that if they performed a deep discharge, in which the positive and negative terminals of the battery get drained so that the voltage difference between the two becomes zero, and then flipped the polarity of battery, forcing the positive side negative and the negative side positive, it created a voltage pulse that could reset the decomposing molecules back to their original form.

“Usually, in running batteries, you want to avoid draining the battery completely because it tends to degrade its components,” said co-first author Yan Jing from Harvard. “But we’ve found that this extreme discharge where we actually reverse the polarity can recompose these molecules — which was a surprise.”

“Getting to a single-digit percentage of loss per year is really enabling for widespread commercialisation because it’s not a major financial burden to top off your tanks by a few percent each year,” said Aziz.

̽��ֱ��research team also demonstrated that this approach works for a range of organic molecules. Next, they aim to explore how much further they can extend the lifetime of DHAQ and other inexpensive anthraquinones that have been used in these systems.

“ ̽��ֱ��most surprising and beautiful thing to me is that this organic molecule can transform in such a complex way, with multiple chemical and electrochemical reactions occurring simultaneously or sequentially,” said co-first author Dr Evan Wenbo Zhao, who carried out the work while he was based at Cambridge, and is now based at Radboud ̽��ֱ�� Nijmegen in the Netherlands. “Yet, we are able to unpick many of these reactions and let them happen in a controlled fashion that favours the operation of a redox flow battery.”

̽��ֱ��research was supported in part by the US National Science Foundation, the Centre of Advanced Materials for Integrated Energy Systems (CAM-IES); the Engineering and Physical Sciences Research Council (EPSRC) and the Science and Technology Facilities Council (STFC), both of which are part of UK Research and Innovation (UKRI).

Reference:
Yan Jing et al. ‘Electrochemical Regeneration of Anthraquinones for Lifetime Extension in Flow Batteries.’ Nature Chemistry (2022). DOI: 10.1038/s41557-022-00967-4

Adapted from a Harvard ̽��ֱ�� press release.

Researchers from the ̽��ֱ�� of Cambridge and Harvard ̽��ֱ�� have developed a method to dramatically extend the lifetime of organic aqueous flow batteries, improving the commercial viability of a technology that has the potential to safely and cheaply store energy from renewable sources such as wind and solar.

̽��ֱ��most surprising and beautiful thing to me is that this organic molecule can transform in such a complex way

Evan Wenbo Zhao

Andriy Onufriyenko via Getty Images

Solar panel close up

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

New tools show a way forward for large-scale storage of renewable energy

sc604 — Mon, 02 Mar 2020 15:57:02 +0000

̽��ֱ��new tools, developed by researchers at the ̽��ֱ�� of Cambridge, will help scientists design more efficient and safer battery systems for grid-scale energy storage. In addition, the technique may be applied to other types of batteries and electrochemical cells to untangle the complex reaction mechanisms that occur in these systems, and to detect and diagnose faults.

̽��ֱ��researchers tested their techniques on organic redox flow batteries, promising candidates to store enough renewable energy to power towns and cities, but which degrade too quickly for commercial applications. ̽��ֱ��researchers found that by charging the batteries at a lower voltage, they were able to significantly slow the rate of degradation, extending the batteries’ lifespan. ̽��ֱ��results are reported in the journal Nature.

Batteries are a vital piece of the transition away from fossil fuel-based sources of energy. Without batteries capable of grid-scale storage, it will be impossible to power the economy using solely renewable energy. And lithium-ion batteries, while suitable for consumer electronics, don’t easily scale up to a sufficient size to store enough energy to power an entire city, for instance. Flammable materials in lithium-ion batteries also pose potential safety hazards. ̽��ֱ��bigger the battery, the more potential damage it could cause if it catches fire.

Redox flow batteries are one possible solution to this technological puzzle. They consist of two tanks of electrolyte liquid, one positive and one negative, and can be scaled up just by increasing the size of the tanks, making them highly suitable for renewable energy storage. These room-sized, or even building-sized, non-flammable batteries may play a key role in future green energy grids.

Several companies are currently developing redox flow batteries for commercial applications, most of which use vanadium as the electrolyte. However, vanadium is expensive and toxic, so battery researchers are working to develop a redox flow battery based on organic materials which are cheaper and more sustainable. However, these molecules tend to degrade quickly.

“Since the organic molecules tend to break down quickly, it means that most batteries using them as electrolytes won’t last very long, making them unsuitable for commercial applications,” said Dr Evan Wenbo Zhao from Cambridge’s Department of Chemistry, and the paper’s first author. “While we’ve known this for a while, what we haven’t always understood is why this is happening.”

Now, Zhao and his colleagues in Professor Clare Grey’s research group in Cambridge, along with collaborators from the UK, Sweden and Spain, have developed two new techniques to peer inside organic redox flow batteries in order to understand why the electrolyte breaks down and improve their performance.

Using ‘real time’ nuclear magnetic resonance (NMR) studies, a sort of functional ‘MRI for batteries’, and methods developed by Professor Grey’s group, the researchers were able to read resonance signals from the organic molecules, both in their original states and as they degraded into other molecules. These ‘operando’ NMR studies of the degradation and self-discharge in redox flow batteries provide insights into the internal underlying mechanisms of the reactions, such as radical formation and electron transfers between the different redox-active species in the solutions.

“There are few in situ mechanistic studies of organic redox flow batteries, systems that are currently limited by degradation issues,” said Grey. “We need to understand both how these systems function and also how they fail if we are going to make progress in this field.”

̽��ֱ��researchers found that under certain conditions, the organic molecules tended to degrade more quickly. “If we change the charge conditions by charging at a lower voltage, the electrolyte lasts longer,” said Zhao. “We can also change the structure of the organic molecules so that they degrade more slowly. We now understand better why the charge conditions and molecular structures matter.”

̽��ֱ��researchers now want to apply their NMR setup on other types of organic redox flow batteries, as well as on other types of next-generation batteries, such as lithium-air batteries.

“We are excited by the wide range of potential applications of this method to monitor a variety of electrochemical systems while they are being operated,” said Grey.

For example, the NMR technique will be used to develop a portable battery ‘health check’ device to diagnose its condition.

“Using such a device, it could be possible to check the condition of the electrolyte in a functioning organic redox flow battery and replace it if necessary,” said Zhao. “Since the electrolyte for these batteries is inexpensive and non-toxic, this would be a relatively straightforward process, prolonging the life of these batteries.”

̽��ֱ��research was funded in part by the Engineering and Physical Sciences Research Council (EPSRC) and Shell.

Reference:
Evan Wenbo Zhao et al. ‘In situ NMR metrology reveals reaction mechanisms in redox flow batteries.’ Nature (2020). DOI: 10.1038/s41586-020-2081-7

A technique based on the principles of MRI and NMR has allowed researchers to observe not only how next-generation batteries for large-scale energy storage work, but also how they fail, which will assist in the development of strategies to extend battery lifetimes in support of the transition to a zero-carbon future.

We need to understand both how these systems function and also how they fail if we are going to make progress in this field

Clare Grey

Nicholas Doherty on Unsplash

Wind farm

Yes