Researchers at MIT have discovered a way to significantly reduce corrosion and provide longer shelf life to metal-air batteries, as reported in journal Science.
Metal-air batteries such as aluminum-air batteries are considered to be one of the most compact and lightest types of batteries, but when not in use, degrade easily as the metal electrodes are highly susceptible to corrosion. They can lose about 805 of their charge in a month, despite the cost effectiveness and compact model.
As electrolyte or fluid between two battery electrodes eats away the metal when the battery is on standby, the researchers introduced an oil barrier between the electrolyte and aluminum electrodes to counteract corrosion. When the battery is in use, the oil is quickly pumped away and replaced with electrolyte. This has resulted into loss of energy to just 0.02% a month, according to the researchers, which has improved over thousand folds.
Former MIT graduate student Brandon J. Hopkins said that although there have been several methods to extend the shelf life of metal-air batteries, they compromise the performance of the batteries. Further, approaches to replace the electrolyte with less corrosive chemicals led to reduction of battery power, he added.
In the new system, a thin membrane is introduced between the battery electrodes. Liquid electrolyte is filled in both sides of the membrane when the battery is in use and on standby, oil is filled into the side nearest to the metal electrodes. The oil then protects the metal surface from the corrosive electrolyte on the other side of the membrane.
Aluminum, when immersed in water, repels oil from the surface; this property is known as ‘underwater oleophobicity’. Due to this property, when the battery is reactivated, the electrolyte quickly displaces the oil from the aluminum surface in the new system, which efficiently restores power capacity of the battery. On the contrary, this system exploits similar property of aluminum that stimulates corrosion in conventional systems.
As compared to conventional aluminum-air batteries, the MIT design showed much longer shelf life. After repetitive use, when the batteries was put on standby for one to two days, the conventional design lasted only for three days while the new design retained its power capacity for 24 days. The researchers reported that the new battery design is still five times lighter than and twice as compact as lithium-ion batteries even after introducing oil and pumping system.
The research team, who have filed patent on the process, believe that the longer shelf life that could be afforded by the MIT design will boost the applications of aluminum-air batteries to greater extent.