(CN) – A team of scientists has developed a battery that could solve one of the biggest challenges facing renewable energy: storage.
Powered by sulfur, salt, air and water, the prototype is nearly 100 times cheaper than options currently on the market and can store twice as much energy as current lead-acid batteries.
The team’s findings, published Wednesday in the journal Joule, suggest the battery could be used to store enough power to provide an uninterrupted energy flow even in areas that have limited exposure to the sun and generally calm winds – issues that continue to undermine the viability of renewable energy systems.
“It has become increasingly clear that in order for renewable energy to become the main part, if not all, of our electricity generation system, it needs to match the output of the demand that we have as a society,” said senior author Yet-Ming Chiang, a scientist at the Massachusetts Institute of Technology.
Currently, the pairing of energy storage and renewable generation is in its infancy. Of the total volume of solar and wind power generated, only a very small portion is stored – with the cost of storage being one of the largest hurdles.
The team set out to drastically reduce the cost of storing renewable energy in response to a “5-5-5” objective for grid storage set by the U.S. Department of Energy under former Secretary Steven Chu. The objective calls for a five-fold reduction in cost and five times more energy density within five years.
Led by Chiang, the team focused on the first part of the objective and analyzed how to create a storage unit with a low cost-per-stored-energy metric, defined as U.S. dollars per kilowatt hour, or $/kWh. Cost is based on the price of the anode, cathode and electrolytes of a battery. Current chemical costs range from $10 to $100/kWh since battery materials often have to be mined and shipped from around the world.
The group was especially interested in the potential of sulfur – an abundant nonmetal that is a product of natural gas use – as a key component of an inexpensive and lightweight storage battery. All batteries contain a positive anode, a negative cathode and an electrolyte, which carries the charge. The researchers were eager to explore how sulfur could be the cathode and water could be the electrolyte in their battery prototype.
“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,” Chiang said.
“Through 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 total chemical cost of the team’s battery is roughly $1/kWh.
After deciding on the components, the group then had to determine how to construct the rest of the battery. As all of its chemical components are dissolved in water, the team chose a flow battery architecture in which, through a set-up of pumps and tubes, electrical charges trigger components of the battery to flow past each other, producing chemical reactions that help it capture electrons.
One limitation to this approach is that the volume of electrical charge that can be stored depends on the amount of liquid in the anode and cathode. Due to this complication, the battery has to take up more space than what is traditionally used. However, the cost of the materials neutralizes that drawback.
“We hope to get the community thinking more about long-duration storage, which we’ll need more of as we reach higher penetration of renewables onto the energy grid,” Chiang said. “For example, there are seasonal variations, and we’ll have to figure out how to deal with that. Up until now, electrochemical storage is not the first thing that people think about to accommodate that seasonal variation, just because the cost of it is so high.”
The group now wants to make their prototype even more efficient, in addition to driving down the costs of the battery’s architecture and increasing its lifespan. Their battery can currently operate for up to 1,500 hours, or about 62.5 days – a far cry from the 5 to 20-year lifespan it would require in practice.
“We think that this work helps move us in the right direction and creates more hope that this is possible, but we need to push it ahead very quickly because we don’t have a lot of time,” Chiang said.