Researchers at ETH Zurich have made significant progress in developing cheap, efficient, durable, safe and environmentally friendly zinc metal batteries that could be used as an alternative to lithium-ion batteries. Most batteries that power smartphones and electric cars are lithium-ion batteries, which are expensive and highly flammable. In contrast, zinc is abundant and has mature recycling infrastructure, making zinc batteries a promising alternative.
However, the engineers have faced some challenges in developing these batteries. For example, when zinc batteries are charged at high voltage, the water in the electrolyte fluid reacts on one of the electrodes to form hydrogen gas. This causes the electrolyte fluid to dwindle and battery performance to decrease. Additionally, the reaction causes excess pressure to build up in the battery that can be dangerous. Another issue is the formation of spikey deposits of Zinc during charging of the battery, known as dendrites, that can pierce through the battery and even cause short circuits, rendering the battery unusable.
To address these issues, the researchers have enriched the aqueous liquid electrolyte with salts, which has made the electrolyte fluid viscous and slowed down the charging and discharging processes considerably. Moreover, many of the salts used contain fluorine, making them toxic and harmful to the environment.
The researchers have now devised a strategy that brings key advances to the development of such zinc batteries, making them more powerful, safer and more environmentally friendly. The ideal salt concentration for water-based zinc-ion batteries is not, as was previously assumed, the highest one possible, but a relatively low one: five to ten water molecules per salt's positive ion. Moreover, the researchers didn't use any environmentally harmful salts for their improvements, opting instead for environmentally friendly salts of acetic acid, called acetates. With an ideal concentration of acetates, the batteries can be charged and discharged much faster.
So far, the ETH researchers have tested their new battery strategy on a relatively small laboratory scale. The next step will be to scale up the approach and see if it can also be translated for large batteries. Ideally, these might one day be used as storage units in the power grid to compensate for fluctuations, say, or in the basements of single-family homes to allow solar power produced during the day to be used in the evening.
Source: ethz.ch