Lithium metal batteries have double the theoretical energy capacity of lithium-ion cells. Anyone that makes them work will immediately cut the mass in half or double the current range any electric car offers. The problem is getting there, but researchers from the University of Michigan may be getting close with an “anode-less” approach.
The video above shows what they have achieved, but that also deserves a written explanation.
Lithium metal batteries with liquid electrolytes face dendrite formation as its major problem, leading them quickly to thermal runaway. To solve that, Jeff Sakamoto and his team applied a solid electrolyte to their battery: Li7La3Zr2O12 (LLZO). But that is just part of what they accomplished.
One of the challenges to produce a lithium metal solid-state battery is integrating metallic lithium with the chosen solid electrolyte. What if that can happen after the battery is already assembled, through an electrochemical process? This is what the researchers managed to do.
Instead of getting a battery with the cathode, the electrolyte, and the anode, they have eliminated the anode, which was replaced by a metallic foil made of copper, but other metals would probably also work.
This metal foil helps create the anode, something that is performed through a charging process developed by the researchers that plates lithium there. Jeff Sakamoto told us more about that.
"Now that the ceramic technology has demonstrated the ability to stabilize Li metal, now it is time to develop better cathode technology. The cathode we used was not optimal and instead was used just to prove the concept of using Li from a state-of-the-art cathode material to form the Li anode. It is the polymer catholyte that is now the issue and alternatives need to be developed."
So far, the cells made through this process were stable after 50 cycles and presented “high Coulombic efficiencies,” meaning electrons move without signs of any parasitic reactions, such as lithium filaments' formation. With the proper cathode, Sakamoto believes the cell can resist many more cycles because it had a “capacity fade”, not efficiency fade.
Another issue the researcher and his team found relates to battery swelling – around 25 percent of volume change. Sakamoto is optimistic about solving it.
"I don't think this is an unsolvable problem. I am collaborating with three car manufacturers on a perspective article. They seem to agree that this points to the fact that Li-metal solid-state batteries are not a drop-in replacement for Li-ion: the pack design will likely require some modifications. Remember, thermal management could be dramatically reduced for lithium metal solid-state batteries. What's complicated by pressure could also be countered by less thermal management."
When it improves, they may have provided us with the recipe for cells with higher energy density and no thermal runaway risks which are simpler to produce. That's a bright perspective for drivers in search of lighter EVs or amazing ranges – or both.
Source: University of Michigan