Sulfur-air flow battery reduces grid costs

October 12, 2017 // By Rich Pell
Researchers at MIT (Cambridge, MA) have developed a sulfur-based flow battery that could store electricity for very long durations for about a fifth of the cost of current grid energy storage technologies.

Compared to current grid energy storage solutions that cost about $100 per kilowatt hour and function only in certain locations, the researchers' battery would cost only about $20 to $30 per kilowatt hour.

A rechargeable flow battery, the device uses cheap, readily available sulfur dissolved in water for its anode. The battery's cathode has an aerated liquid salt solution that continuously takes in and releases oxygen - i.e., "breathes" - which balances charge as ions move between the electrodes.

The oxygen flowing into the cathode causes the anode to discharge electrons to an external circuit. The oxygen flowing out sends electrons back to the anode, recharging the battery.

"This battery literally inhales and exhales air, but it doesn't exhale carbon dioxide, like humans — it exhales oxygen," says Yet-Ming Chiang, the Kyocera Professor of Materials Science and Engineering at MIT and co-author of a paper describing the battery.

Because the battery uses ultra-low-cost materials, say the researchers, its chemical cost is one of the lowest — if not the lowest — of any rechargeable battery to enable cost-effective long-duration discharge. Its energy density is slightly lower than current lithium-ion batteries.

The battery prototype is about the size of a coffee cup, but flow batteries are highly scalable, says Chiang, and cells can be combined into larger systems. Since the battery can discharge over months, it may be best suited for storing electricity from intermittent wind and solar power sources.

"The intermittency for solar is daily, but for wind it's longer-scale intermittency and not so predictable," says Chiang. "When it’s not so predictable you need more reserve — the capability to discharge a battery over a longer period of time — because you don’t know when the wind is going to come back next."

According to the researchers, this technology may be the first to compete - in cost and energy density - with pumped hydroelectric storage systems. These currently