Rechargeable battery with molten salt freezes energy on site for long-term storage

In the spring in the northwestern Pacific Ocean, the melted water from the thawing snow rushes down the rivers and the wind often blows strongly. These forces run many energy turbines in the region and generate an abundance of electricity during mild temperatures and relatively low energy consumption. But much of this seasonal surplus of electricity that can power air conditioners in the summer is lost because the batteries can’t store it long enough.

Researchers at the Pacific Northwest National Laboratory (PNNL), a national laboratory of the Department of Energy in Richland, Washington, are developing a battery that could solve this problem. In a recent paper published in Cell Reports Physical Sciencethey demonstrated how freezing and thawing molten saline creates a rechargeable battery which can store energy cheaply and efficiently for weeks or months at a time. Such capability is crucial in shifting the US grid from fossil fuels that emit greenhouse gases to renewable energy. President Joe Biden has set a goal of halving carbon emissions in the United States by 2030, which will require a significant increase in wind, solar and other clean energy sources, as well as ways to store the energy they produce.

Most conventional batteries store energy as chemical reactions waiting to happen. When the battery is connected to an external circuit, electrons travel from one side of the battery to the other through that circuit, generating electricity. To compensate for the change, charged particles, called ions, move through the liquid, paste or solid material that separates the two sides of the battery. But even when the battery is not in use, the ions gradually diffuse into this material, which is called the electrolyte. As this happens for weeks or months, the battery loses energy. Some rechargeable batteries can lose almost a third of their stored charge in a month.

“In our battery, we really tried to stop this state of self-discharge,” said PNNL researcher Guoshen Li, who is leading the project. The electrolyte is made from a saline solution that is solid at ambient temperature but becomes liquid when heated to 180 degrees Celsius – the approximate temperature at which cookies are baked. When the electrolyte is solid, the ions lock in place, preventing self-discharge. Only when the electrolyte liquefies can the ions pass through the battery, allowing it to charge or discharge.

Creating a battery that can withstand multiple cycles of heating and cooling is no small feat. Temperature fluctuations cause the battery to expand and contract, and researchers had to identify resistant materials that could withstand these changes. “What we’ve seen before is very active research to make sure you don’t have to go through this thermal cycle,” said Vince Sprenkel, PNNL’s strategic energy conservation adviser and co-author of the new article. We say, “We want to get through this, and we want to be able to survive and use that as a key feature.”

The result is a rechargeable battery made of relatively inexpensive materials that can store energy for long periods. “This is a great example of promising long-term energy storage technology,” said Aurora Eddington, political director of the GridWise Alliance, which did not participate in the study. “I think we need to support these efforts and see how far we can take them to commercialization.

The technology can be particularly useful in a place like Alaska, where near-constant summer sunlight coincides with relatively low levels of energy use. A battery that can store energy for months can allow plenty of summer solar energy to meet electricity needs in the winter. “What’s so appealing about the freeze-thaw battery is this seasonal switching capability,” said Rob Royce, chief innovation officer at Launch Alaska, a nonprofit that works to accelerate the state’s climate change. . Royce hopes to pilot a PNNL battery in a remote part of his state.

Warming up the battery can be a challenge, especially in cold places. Even under mild conditions, the heating process requires energy equivalent to about 10 to 15 percent of the battery’s capacity, Lee said. Later phases of the project will explore ways to reduce temperature requirements and include a heating system in the battery itself. Such a feature would simplify the battery for the user and could potentially make it suitable for home or small use.

Right now, experimental technology is focused on business and industrial purposes. Sprinkle envisages something like containers for trucks with tractors with huge batteries inside, parked next to wind farms or solar blocks. The batteries will be charged on site, allowed to cool and transported to facilities called substations, where energy can be distributed through power lines if needed.

The PNNL team plans to continue to develop the technology, but ultimately the industry will depend on developing a commercial product. “Our job at DOE is really to reject new technologies,” Sprenkel said. “The industry will decide if it thinks it has been underestimated enough, and they will take that and work with it.”

DOE is working to reduce the backlog that typically occurs between initial research demonstrations and the commercialization of energy technologies. Although scientists began developing lithium-ion batteries in the 1970s, for example, batteries did not end up in consumer products until about 1991 and were not plugged in until the late 2000s. Artificial intelligence and machine learning can help speed up the process of validating and testing new technologies, Sprenkel said, allowing researchers to model and predict a decade of battery life without the need for 10 years to collect data.

It is unclear whether the adoption will take place quickly enough to achieve the decarbonisation targets. “If we are really trying to achieve the decarbonisation targets for 2030, 2035, all of these technologies need to be accelerated by about five times,” Sprenkel said. “You’re looking at developments that need to go online, be validated and ready for submission over the next four to five years to have a real, real impact.”