Metal-air batteries can be used in a variety of applications ranging from range extenders for electric vehicles to emergency power systems. Metal-sea-water batteries are primarily used for underwater applications ranging from torpedoes to underwater unmanned vehicles. A team of researchers at the Department of Mechanical Engineering, MIT, has developed an oil displacement system to mitigate open-circuit corrosion in metal-air and metal-seawater batteries.

Metal-air/seawater batteries have high gravimetric energy densities; however, open-circuit (OC) anode corrosion causes severe capacity fade when the battery is shut off. Previous technologies focus on chemical mitigation methods (i.e., changing electrode or electrolyte composition), which provide insufficient corrosion mitigation and power density. Other mechanical corrosion mitigation methods require flushing the cell, which increases the volume of tanks required for the system. The proposed technology implements a system that displaces the electrolyte with oil when the battery is off to prevent OC corrosion.

The main elements of the system include a metal-air cell, a tank of mineral oil and electrolyte, and a separate tank of water. Pumps and pipes move liquids between these three parts. The device displaces corrosive electrolyte from the anode surface by pumping oil into the cell. In comparison to other mechanical corrosion mitigation methods, this oil displacement method increases volumetric energy density by 15 percent. Additionally, a liquid that has a different density than the electrolyte, is immiscible in the electrolyte, nonconducting, inviscid, and nonreactive with the other system components could replace the oil in this system.

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