Silicon-air batteries, invented by Profession Ein-Eli at the Technion - Israel Institute of Technology, utilise electrodes of oxygen and silicon, and are viewed as a promising, lightweight and cost-effective alternative to current energy storage technology. However, they have thus far achieved only relatively short running times. Now German researchers at the Jülich Research Centre have discovered why.
In theory, silicon-air batteries have a much higher energy density and are also smaller and lighter than current lithium-ion batteries. They are also environmentally friendly and have a high tolerance to hostile environmental influences such as extremely dry conditions and high humidity.
However, much of their promise lies in the material that goes into these batteries. Silicon and oxygen are the most abundant elements in the Earth's crust. Not only are they cheap and accessible, their reserves are practically inexhaustible.
But development of the silicon-air battery was held back because the flow of current stops after a relatively short period of time. Thus far, only assumptions have been made about why this happens. Some have theorised that a protective layer forms spontaneously on the silicon anode, stopping the reaction which causes current flow. Others assume issues with the electrolyte or the air electrode, but improving these components failed to rectify the problem.
One partial solution was to use a special, high-quality electrolyte based on an ionic liquid, which increased the battery's running time to several hundred hours, but failed to achieve the fundamental goal of the battery: to provide a cost-effective alternative to lithium-ion batteries.
Scientists at Jülich’s Institute of Energy and Climate Research theorised that there was another reason for the short running time: the consumption of the electrolyte, which is potassium hydroxide dissolved in water.
The researchers developed a pump system which periodically refilled the electrolyte fluid. As long as the silicon anode remains in contact with the electrolyte, the battery continues to run.
Using this system, the researchers were able to keep the battery running for over 1,100 hours, almost 46 days. The battery's running time was ultimately constricted by the dissolving of the silicon anode although simply exchanging the anode for a new one allowed the battery to be "recharged".
Having identified the problem, the scientists are now looking for a way to keep the silicon-air battery running without having the refill the electolyte. The answer could lie in additives in the electrolyte which prevent the fluid from being used up.
Energy will be a major topic of discussion at the Australian Engineering Conference 2016 in Brisbane on November 23-25.