Extra tomato stabilizes solid-state battery
Tomato is metaphoric, lithium-metal battery results are real Metal Tech News – May 13, 2021
Last updated 5/13/2021 at 2:48pm
Second Bay Studios-Harvard SEAS
Adding an extra layer of tomato on a metaphoric BLT could be the solution to a decades-long problem that has prevented scientists from developing the solid-state lithium batteries that would significantly increase the range and lessen the charging time of electric vehicles.
For roughly 40 years, researchers have tried to harness the potential of solid-state, lithium-metal batteries, which hold substantially more energy in the same volume and charge in a fraction of the time compared to traditional lithium-ion batteries.
"A lithium-metal battery is considered the holy grail for battery chemistry because of its high capacity and energy density," said Xin Li, associate professor of materials science at the Harvard John A. Paulson School of Engineering and Applied Science (SEAS). "But the stability of these batteries has always been poor."
This poor stability of solid-state batteries has to do with dendrites, stalagmite-like structures that grow from the lithium metal anode as lithium ions flow from the cathode during charging. These dendrites continue to grow through the electrolyte until they pierce a barrier that separates the anode from the cathode, shorting the battery.
Over the past four decades, scientists have been attempting to overcome this problem by preventing or at least minimizing the growth of the troublesome dendrites.
Li and his team at Harvard, however, have taken a different approach. Instead of preventing dendrite growth, the researchers added an extra layer to the battery sandwich. This multilayer, multi-material battery prevents the penetration of lithium dendrites not by stopping them but by controlling and containing them.
Li likens this new solid-state, lithium-metal battery design to a BLT sandwich. First comes a slice of lithium-metal anode bread, then a coating of graphite lettuce, a layer of tomato electrolyte, a bacon electrolyte, then another layer of tomato electrolyte, finished off with a slice of cathode bread.
The first (tomato) electrolyte is more stable with lithium but prone to dendrite penetration. The second (bacon) electrolyte is less stable with lithium but appears immune to dendrites. In this design, dendrites are allowed to grow through the graphite and first electrolyte but are stopped when they reach the second. In sandwich terms, the dendrites grow through the lettuce and tomato but stop at the bacon.
"Our strategy of incorporating instability in order to stabilize the battery feels counterintuitive but just like an anchor can guide and control a screw going into a wall, so too can our multilayer design guide and control the growth of dendrites," said Luhan Ye, co-author of a research paper on the findings published in Nature and graduate student at SEAS.
"The difference is that our anchor quickly becomes too tight for the dendrite to drill through, so the dendrite growth is stopped," Li added.
The team says the battery is also self-healing – its chemistry allows the holes created by the dendrites to be backfilled.
The Harvard researchers have paired the new design with a commercial high-energy-density cathode material and say the new design can be charged and discharged at least 10,000 times.
"This proof-of-concept design shows that lithium-metal solid-state batteries could be competitive with commercial lithium-ion batteries," said Li. "And the flexibility and versatility of our multilayer design makes it potentially compatible with mass production procedures in the battery industry. Scaling it up to the commercial battery won't be easy and there are still some practical challenges, but we believe they will be overcome."
Overcoming these challenges could result in a battery that increases the lifetime of electric vehicles to 10 to 15 years without the need to replace the battery. And, with its high current density, the battery could pave the way for EVs that can fully charge within 10 to 20 minutes.
"Our research shows that the solid-state battery could be fundamentally different from the commercial liquid electrolyte lithium-ion battery," said Li. "By studying their fundamental thermodynamics, we can unlock superior performance and harness their abundant opportunities."