May 13 2021
Quick-charging and long-lasting batteries are crucial to expand the electric vehicle sector but despite this fact, the current generation of lithium-ion batteries does not meet this requirement because they are extremely costly, quite bulky, and take a considerable amount of time to charge.
The first electrolyte (green) is more stable with lithium but prone to dendrite penetration. The second electrolyte, (brown) 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. Image Credit: Second Bay Studios/Harvard SEAS.
For many years, scientists have attempted to harness the ability of solid-state, lithium-metal batteries that hold significantly more energy in the same charge and volume in a fraction of the time compared to conventional lithium-ion batteries.
A lithium-metal battery is considered the holy grail for battery chemistry because of its high capacity and energy density. But the stability of these batteries has always been poor.
Xin Li, Associate Professor of Materials Science, Harvard John A. Paulson School of Engineering and Applied Science
Li and his research team have now developed a stable, lithium-metal solid-state battery that can be charged and discharged for a minimum of 10,000 times—cycles that are substantially more than have been demonstrated before—at a high current density. The team combined the novel design with a commercially available high-energy-density cathode material.
The new battery technology can boost the lifetime of electric vehicles equivalent to that of gasoline cars, that is, 10 to 15 years, without having to substitute the battery. This battery, with its high current density, could result in electric vehicles that can completely charge in less than 10 to 20 minutes.
The study has been published in the Nature journal.
Our research shows that the solid-state battery could be fundamentally different from the commercial liquid electrolyte lithium-ion battery. By studying their fundamental thermodynamics, we can unlock superior performance and harness their abundant opportunities.
Xin Li, Associate Professor of Materials Science, Harvard John A. Paulson School of Engineering and Applied Science
Chemistry has always posed a major challenge when it comes to lithium-metal batteries. At the time of charging, lithium batteries tend to shift lithium ions from the cathode to the anode. When the anode is composed of lithium metal, needle-like structures known as dendrites, tend to develop on the surface. Such structures grow just like roots into the electrolyte and penetrate the barrier that separates the cathode and anode, causing a shortage in the battery or even allowing it to catch fire.
To address this problem, Li and his research team fabricated a multilayer battery that closely packs different materials of different stabilities between the cathode and the anode. Through this multilayer, multi-material battery, the penetration of lithium dendrites is prevented by regulating and containing them instead of stopping them altogether.
Imagine a battery similar to a BLT sandwich. First comes a piece of bread—the lithium metal anode—and then the lettuce—a graphite coating. This is followed by a layer of tomatoes—the first electrolyte—and then a layer of bacon—the second electrolyte. This is finally completed with another layer of tomatoes and a final piece of bread—the cathode.
The first electrolyte (chemical name LPSCI or Li5.5PS4.5Cl1.5) was found to be more stable with lithium but it is prone to the penetration of dendrites. The second electrolyte, (LGPS or Li10Ge1P2S12) is less stable with lithium but seems to be resistant to dendrites.
In the new design, dendrites are permitted to grow through the first electrolyte and graphite but are stopped as soon as they reach the second electrolyte. To put this in simple terms, the dendrites grow through the tomato and lettuce but cease at the bacon. The barrier of bacon prevents the dendrites from forcing through and causing a shortage in the battery.
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.
Luhan Ye, Study Co-Author and Graduate Student, Harvard John A. Paulson School of Engineering and Applied Science
Li added, “The difference is that our anchor quickly becomes too tight for the dendrite to drill through, so the dendrite growth is stopped.”
The new battery also heals on its own. Its chemistry enables it to backfill holes produced by the dendrites.
“This proof-of-concept design shows that lithium-metal solid-state batteries could be competitive with commercial lithium-ion batteries. 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,” Li concluded.
The study was funded by Dean’s Competitive Fund for Promising Scholarship at Harvard University and Harvard Data Science Initiative Competitive Research Fund. Additional developments of this project will be funded by Harvard Physical Sciences and Engineering Accelerator Award and Harvard Climate Change Solutions Fund.
Journal Reference:
Ye, L & Li, X (2021) A dynamic stability design strategy for lithium metal solid state batteries. Nature. doi.org/10.1038/s41586-021-03486-3.