Researchers develop lithium metal battery cells that are much more stable
Scientists at Stanford University have developed a coating for the anodes of lithium metal batteries that makes these batteries more stable. Due to the lightness of the metal and the capacity, these batteries could in theory be very beneficial for electric cars.
A joint research team from Stanford and the US government agency SLAC National Accelerator Laboratory have tested their coating in the laboratory on the anode of the battery cells. This was combined with commercially available components to create a fully operational battery. After 160 charge cycles, the lithium metal cells still have 85 percent of their capacity from the first charge cycle. Regular lithium metal cells have about 30 percent after 160 cycles, making them nearly useless.
The scientists’ invention is a special coating that prevents the formation of dendrites. These are finger or tree-like structures formed by accumulating lithium atoms. As soon as these structures penetrate the dividing wall in a cell and form a bridge between the anode and the cathode, a short circuit can occur. With lithium-ion batteries, this is prevented by a protective layer of graphite at the anode. This has the disadvantage that the capacity is also somewhat less high.
Lithium metal batteries do not use graphite and the energy capacity is higher, but then the problem of the dendrites has to be solved in a different way. In addition, lithium tends to react quickly with anything, such as the partially lithium electrolyte. The anode can therefore easily overheat, resulting in fire or explosion. That is why lithium metal batteries have been eclipsed by lithium ion batteries.
In order to make use of the higher energy capacity of lithium metal batteries, the lithium still has to be kept in check. Since no graphite is used, something else had to be invented. The scientists have come up with a coating that forms a network of molecules that uniformly transfers the charged lithium ions. According to the researchers, this prevents unwanted chemical reactions and limits chemical deposition on the anode.
According to the researchers, lithium metal batteries can deliver at least a third more energy per unit weight than lithium-ion batteries. This is related to the fact that the anodes of lithium metal batteries have a higher density of lithium and therefore more energy carriers. In addition, lithium is a light element. An anode consisting almost entirely of lithium makes the cell lighter; this can translate into lighter batteries and thus a greater range for electric cars. This is in addition to the already higher energy capacity.
The researchers see the use of stable lithium metal batteries in electric cars as the ultimate goal, but think that commercialization will probably start with consumer electronics. In this way, the safety of the battery can be demonstrated. The scientists are now refining their coating design and are testing their cells on even more charge cycles.
The research is published in the journal Joule, under the title A Dynamic, Electrolyte-Blocking, and Single-Ion-Conductive Network for Stable Lithium-Metal Anodes.