WHY THIS MATTERS IN BRIEF
- Renewable energy sources are still, by their very nature, unreliable which is why we need cheap, grid scale energy storage solutions if we’re ever going to wean ourselves off of fossil fuels and nuclear power, and MIT’s latest breakthrough could move the dial
The cost of Renewable energy is coming down, and it’s now the cheapest form of energy in over 58 countries, but while it might be clean and increasingly popular, as more cities in the US, such as Las Vegas, hit their 100 percent renewable energy goals, it’s not always reliable. For example, when the Sun vanishes behind clouds or the wind dies down this is why all of a sudden you’ll see the amount of energy coming into your home, or onto the grid, decline, and that’s why today whether it’s your home, or the grid, we’re increasingly reliant on being able to store energy cheaply and reliably for long periods of time – all just so you can turn your lights and power your electric cars on when the clouds roll over.
In order to counter some of this variability today energy companies are forced to combine a range of different sources, such as solar, wind, hydro, tidal, and biomass, with large grid scale energy storage systems, but, while these systems are getting better and cheaper they’re still expensive – especially if you plan on using them in anger.
Now though a team from MIT has developed a new type of battery that could make grid scale energy storage cheaper, by about 80 percent, and it does it by breathing air.
The new design is what the team call a “rechargeable flow battery,” meaning its Cathode and Anode components are liquids, called Catholyte and Anolyte, that can pass ions back and forth to store or release energy. In this case, the Anolyte is made up of sulfur dissolved in water, and the hunt for an equally abundant material for the Catholyte led the team to an oxygenated liquid salt solution.
“We went on a search for a positive electrode that would also have exceptionally low cost that we could use with sulfur as the negative electrode,” says Yet-Ming Chiang, co-author of the study, “and thanks to an accidental laboratory discovery, we figured out that it could actually be oxygen, and therefore air. We needed to add one other component, which was a charge carrier to go back and forth between the sulfur and air electrode, and that turned out to be sodium.”
The clever part of the battery is the fact that the Catholyte “breathes” in air in from outside while discharging, and exhales while recharging. Using this mechanism, the battery creates negatively-charged hydroxide ions in the Catholyte while inhaling, and while recharging that oxygen is released, creating hydrogen ions which then send electrons back into the Anolyte.
“This battery literally inhales and exhales air, but it doesn’t exhale carbon dioxide, like humans — it exhales oxygen,” says Chiang, “what this does is create a charge balance by taking oxygen in and out of the system.”
Lithium-air batteries use the same mechanism, but sulfur, water and salt are far cheaper materials than Lithium, and, if we want renewable energy to be our future then we’ve got to cut down the cost of these grid scale storage systems, like the one Elon Musk is famous for deploying across a variety of islands, as much as possible.
The team also say their battery would cost far less to make and run than today’s ubiquitous Lithium-ion batteries, while retaining almost the same energy density, and once in use they estimate a scaled-up version of their flow battery would cost between US$20 and $30 per kWh stored to run, compared to about $100 per kWh for other storage systems.
The current prototype is about the size of a coffee cup but they’re confident the design can be scaled up for use in larger applications, and next they plan on making it more efficient, less expensive, and expand its working life from its current 1,500 hours.
The research was published in the journal Joule.
