This water-based battery won’t catch fire and is powerful enough to charge household appliances
The battery, invented by researchers at the US Army Research Laboratory, uses a water-salt solution as its electrolyte. It is similar to a battery developed in 2015, but, crucially, this one can reach the required voltage for household electronics.
“In the past, if you wanted high energy, you would choose a non-aqueous lithium-ion battery, but you would have to compromise on safety. If you preferred safety, you could use an aqueous battery such as nickel/metal hydride, but you would have to settle for lower energy,” says co-senior author Kang Xu. “Now, we are showing that you can simultaneously have access to both high energy and high safety.”
In 2015, a paper in Science produced a three-volt battery, but it was unable to produce the higher voltages required to power everyday electronics like laptops. Each time the voltage was upped one end of the battery, the anode, which is made of lithium or graphite, was degraded by the water-salt electrolyte.
The study’s lead author Chongyin Yang, from the University of Maryland, designed a new gel polymer electrolyte coating that can be used on the anode.
The gel is hydrophobic, or water repelling, meaning it creates a layer that separates the anode from the electrolyte. This meant the battery would be able to make the leap from three volts to four.
“The key innovation here is making the right gel that can block water contact with the anode so that the water doesn’t decompose and can also form the right interphase to support high battery performance,” said co-author Chunsheng Wang, Professor of Chemical and Biomolecular Engineering at Maryland.
The gel also makes the batteries safer because if the battery case were damaged, the layer would interact slowly with the anode, preventing the metal from directly contacting the electrolyte and causing a fire.
Before the battery becomes competitive with those in use currently, some improvements need to be made. For instance, the number of full cycles the battery can complete is low. “Right now, we are talking about 50-100 cycles, but to compare with organic electrolyte batteries, we want to get to 500 or more,” Wang said.
The hydrophobic gel might come in useful in other ways too. “This is the first time that we are able to stabilise really reactive anodes like graphite and lithium in aqueous media,” says Xu.
“This opens a broad window into many different topics in electrochemistry, including sodium-ion batteries, lithium-sulfur batteries, multiple ion chemistries involving zinc and magnesium, or even electroplating and electrochemical synthesis; we just have not fully explored them yet.”
The research is published in the journal Joule.