Energy Storage Systems Eat CO2 For Breakfast, Lunch, Dinner

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All-day energy storage is the avenue through which more wind and solar power will stroll, but getting there has been a tough row to hoe. Lithium-ion battery backs only last a few hours. The only long duration option in widespread use today is pumped hydropower, which is geographically limited. On the plus side, new technologies are beginning to emerge, and some of them have the added benefit of deploying carbon dioxide to store clean kilowatts from wind and solar resources.

Where Will All The Carbon Dioxide Come From?

If you’re thinking direct air capture systems are in the works, that’s a thought. However, the new CO2 batteries spotted by CleanTechnica rely on CO2 harvested from power plants and other industrial sources, not from the ambient air.

In an ideal world these point source emissions would not exist in the first place, but they do, and they will continue to circulate carbon dioxide into the global economy for years to come. Capturing CO2 emissions and locking them away in systems and products is the next best thing.

The question is how to make carbon capture from point sources more efficient and economical for commercial development. Researchers at the US Department of Energy’s Oak Ridge National Laboratory have come up with one solution, a new gas-based membrane.

“Unlike existing chemical methods to capture CO₂ from industrial processes, membranes are easy to install and can operate unattended for long periods with no additional steps or added energy costs,” ORNL noted back in 2022. Reducing costs, figuring out the supply chain, and scaling up the technology to market-readiness are the next steps, so stay tuned for more on that.

CO2 Energy Storage In The Lab, Ceramic Brain Edition

Meanwhile, the US Department of Energy showcased two new CO2-based energy storage projects last week under the ORNL wing. Both projects aim to capture and deploy CO2 from industrial sources, using low-cost and abundant energy storage formulas, and convert it to a solid form.

One project deploys sodium from saltwater and an iron-nickel catalyst. Whether or not this battery can ever be deployed commercially remains to be seen. The challenge is that CO2-based batteries have not expressed much durability, at least not so far. ORNL’s saltwater Na-CO2 battery, for example, is still a work in progress. Its ability to function is limited by a buildup of film on the electrode.

On the bright side, the ORNL research team has found that pulsing the charge/discharge cycle can help prevent film from accumulating, so that’s area of further improvement. The team will also concentrate its next steps on focus on developing a “very fine, dense, mechanically stable ceramic membrane,” to separate the battery chambers.

The ceramic “brain” of the new battery is no simple pot off the throwing wheel. High tech ceramic electrolytes are a feature of new solid state battery technology. Last year a research group in China reviewed the literature, noting that Na-CO2 solid-state batteries “are a kind of promising energy storage system, which can use excess CO2 for electrochemical energy storage.”

“They not only have high theoretical energy densities, but also feature a high safety level of solid-state batteries and low cost owing to abundant sodium metal resources,” they added, though they also noted a laundry list of challenges to be resolved including “short cycle life, high charging potential, poor rate performance and lower specific full discharge capacity.”

Ouch! That doesn’t sound too promising, but the ORNL team, for one, seems up for the challenge.

Aluminum Takes The Energy Storage Spotlight

The other project under way at ORNL is an aluminum-CO2 formula. It is also a work in progress, but the research team notes that previous iterations of an Al-CO2 battery have only been tested for eight hours of cycling. In contrast, the ORNL team was able to test their new battery for 600 hours without losing capacity.

“The cherry on top is that this battery captures almost twice as much carbon dioxide as the Na-CO2 [saltwater] battery. It can be designed for the system to operate in a single chamber, with both electrodes in the same liquid solution, so there is no barrier to ion movement,” ORNL explains.

That’s not the only cherry on top. The new Al-CO2 battery can also store electricity for 10 hours or more, meeting the Energy Department’s definition of long duration energy storage.

“That’s huge for long-duration storage. This is the first Al-CO2 battery that could run with stability for a long time, which is the goal,” said ORNL lead researcher Ruhul Amin. “Holding just a few hours of stored energy doesn’t help.”

The next steps for the Al-CO2 battery include scaling it up, extending its lifetime, and improving its CO2-capturing skills.

CO2 For A More Sustainable Supply Chain

Instead of releasing CO2 to the atmosphere, the ORNL batteries convert bubbles of CO2 gas into a solid powder.

“The byproduct either continuously enriches the liquid to enhance battery performance, or it can be filtered from the bottom of the container without interrupting battery operation,” ORNL explains of the Al-CO2 battery.

The lab anticipates that the pharmaceutical and cement industries are two leading markets for battery-generated carbon products. They also note that the batteries produce oxygen and hydrogen, both of which can be captured for re-use.

If research interest in carbon-converting CO2-based batteries appears to be picking up elsewhere around the world, too. In February, for example, a team of scientists in Korea reported on a carbon-converting battery that deploys zinc instead of aluminum.

The potential for removing hazardous and rare substances from battery supply chains could also motivate additional research. In 2022, for example, a research team at the University of Cambridge reported on a seawater-based carbon-capturing battery composed with electrodes made of carbon sourced from discarded coconut shells.

Many Roads To Long Duration Energy Storage

Electrochemical systems are not the only kind of CO2 battery under development in the long duration energy storage field. On interesting example is a liquid CO2 battery that draws inspiration from the field of compressed air energy storage. (see more long duration projects here).

Another avenue for deploying CO2 in an energy storage system is represented by the US firm EarthEn, which has received Energy Department funding to develop a closed loop, long duration system based on supercritical CO2, a liquid form of CO2 that acts like a gas.

Don’t give up on lithium just yet, though. Researchers at the University of Surrey have been working to address the electrolyte leakage and evaporation issues that bedevil lithium-CO2 energy storage systems. Researchers at the school also participated in a multinational project, published earlier this week, aimed at identifying efficient catalysts for lithium-CO2 batteries.

Whether or not an energy storage system is involved, carbon-capturing technology is also being deployed to provide a more sustainable source for the graphite used in lithium-ion batteries.

In 2022 the EU launched a consortium aimed at capturing carbon from industrial emissions and converting it into graphite. Aside from sustainability, the aim is to release the EU supply chain from dependence on graphite from China.

The effort was organized in support of the Estonian startup UP Catalyst, and has progressed to the pilot phase with the help of a €4 million seed investment round.

UP Catalyst closed the round last December “amidst China’s announcement of graphite export curbs that has added urgency to the quest for local battery raw material alternatives,” the company noted in a press release dated December 6, 2023.

“This is particularly crucial given that Europe currently depends on graphite imports for 99% of its supply,” UP Catalyst added.

The new funds will enable UP Catalyst to increase production 10 times over it previous rate, with the next step being a pilot-scale reactor with the aim of processing 100 tons of CO₂ from industrial emissions per year, to produce 27 tons of carbon materials.

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Image (cropped): “Researchers at Oak Ridge National Laboratory and the University of Tennessee, Knoxville, demonstrated a novel fabrication method for affordable gas membranes that can remove carbon dioxide from industrial emissions (by Zhenzhen Yang/UT via ORNL).