Silicon-air batteries are one of the more promising candidates for the succession of lithium-ion batteries for cars. They feature a much higher energy density and thus are smaller and lighter. Plus, they are environmentally friendly and resilient against external influences. What’s more: The material they are made of is not a rare earth material but instead silicon, and thus cheap and in unlimited supply. But if this looks too promising to be true, you are right: This type of battery has also a drawback, and a massive one. Silicon-air batteries so far had a lifetime of just a few minutes, already after a short time, the electric current from the battery stops flowing.
The reason for the early death of these batteries has been widely unknown. Expert assumed that an isolating layer developed at the silicon anode, or that there are problems with the air electrode. Attempts to attack the problem through improved electrodes had little success. The best results were achieved with specific electrolytes on the basis of an ionic liquid. This measure boosted the lifetime to several hundred hours. However, it proved detrimental to the idea to develop a cost-effective alternative to lithium-ion batteries.
The scientists from Forschungszentrum Jülich suspected another reason for the problem: The expenditure of the electrolytes, an aqueous solution of potassium hydroxide. They developed a pump system that refills the electrolyte from time to time. “As long as the silicon anode is in contact with the electrolytes, the battery generates electricity”, explains researcher Hermann Tempel. With this method, the battery remained active until the silicon was used up – in the case of the Jülich researcher more than 1100 hours. Once the electrode is used up, it can be reactivated by replacing the anode.