Scientists from Stanford University have developed a coating for the anodes of lithium metal batteries that make these batteries more stable. Due to the lightness of the metal and the capacity, these batteries can, in theory, be very beneficial for electric cars.
A joint research team from Stanford and the US government agency SLAC National Accelerator Laboratory have tried their coating in the laboratory at the anode of the battery cells. This was combined with commercially available components to achieve a fully operational battery. After 160 charge cycles, the lithium metal cells still have 85 percent of their capacity compared to the first charge cycle. Regular lithium metal cells have around 30 percent after 160 cycles, making them almost useless.
The scientists’ finding is a special coating that prevents the formation of dendrites. These are finger or tree-like structures that are formed by accumulating lithium atoms. As soon as these structures pierce the dividing wall in a cell and, as it were, 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 the problem of dendrites must be solved in a different way. In addition, lithium tends to react quickly with anything, such as the partial electrolyte. The anode can therefore easily overheat, resulting in a fire or explosion. That is the reason that lithium metal batteries have been overrun by lithium-ion batteries.
To be able to use the higher energy capacity of lithium metal batteries, the lithium must still be contained. Because 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 undesired chemical reactions and limits chemical deposition on the anode.
According to the researchers, lithium metal batteries can provide at least a third more energy per unit weight than lithium-ion batteries. This is due 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 that consists almost entirely of lithium makes the cell lighter; that can translate into lighter batteries and therefore a greater range for electric cars. That comes on top of 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 is likely to start with consumer electronics. In this way, the safety of the battery can be demonstrated. The scientists are now working on refining their coating design and are testing their cells for even more loading 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.