Functional batteries that incorporate lithium metal into the anode could herald a huge breakthrough in energy research, with the material promising incredibly high energy density compared to the copper and graphite used today. Scientists at Pennsylvania State University are putting forward a new solution to one of the key problems plaguing the technology so far, demonstrating a self-assembling layer that helps to keep a lithium-metal battery in working order.
Swapping out the copper and graphite anodes for ones made from pure lithium could not only make for batteries with as much as 10 times the capacity, but ones that charge a lot faster, too. Standing in the way, however, are small tentacle-like growths called dendrites, which can form on the anode as the battery is charged rapidly or in cold conditions and can cause it to short-circuit, catch fire and ultimately give it a very short lifecycle.
"The lithium metal battery is the next generation of battery after the lithium ion battery," says Donghai Wang, professor of mechanical engineering at Penn State. "It uses a lithium anode and has higher energy density, but has problems with dendritic growth, low efficiency and low cycle life."
We've seen a range of promising possibilities when it comes to overcoming this dendrite problem with lithium metal batteries, including designs that use nanotube films and sound waves to drown them out. Wang and his team have taken a different approach, in developing a protective layer that can be incorporated into the battery to safeguard the longevity of the lithium metal.
This layer consists of electrochemically active molecules which are deposited on a thin film of copper. As the battery is charged, lithium comes into contact with the layer, which kicks off a process that sees part of it decompose and reform on top of the lithium, protecting it against dendrite formation.
"The key is to tune the molecular chemistry to self-assemble on the surface," says Wang. "The monolayer will provide a good solid electrolyte interface when charging, and protect the lithium anode."
In testing, the researchers demonstrated that the battery could maintain its function across a few hundred charging cycles, and believe that with further work it could come to power things like electric vehicles and unmanned aircraft.
"The key is that this technology shows an ability to form a layer when needed on time and decompose and spontaneously reform so it will stay on the copper and also cover the surface of the lithium," says Wang. "Eventually it could be used for drones, cars, or some very small batteries used for underwater applications at low temperatures."
The research was published in the journal Nature Energy.
Source: Pennsylvania State University