University of Michigan researchers assert their new lithium metal technology could double the output of today’s lithium ion cells, drastically extending electric vehicle ranges and time between cell phone charges without taking up any added space.

Note as you read along this technology is using the earlier lithium metal technology that predates the current lithium ion products.

By using a ceramic, solid-state electrolyte, engineers can harness the power of lithium metal batteries without the historic issues of poor durability and short-circuiting. The result is a roadmap to what could be the next generation of rechargeable batteries.

Jeff Sakamoto, a U-M associate professor of mechanical engineering who leads the work said, “This could be a game-changer – a paradigm shift in how a battery operates.”

In the 1980s, rechargeable lithium metal batteries that used liquid electrolytes were considered the next big thing, penetrating the market in early portable phones. But their propensity to combust when charged led engineers in different directions. The lithium atoms that shuttle between the electrodes tended to build tree-like filaments called dendrites on the electrode surfaces, eventually shorting the battery and igniting the flammable electrolyte.

The lithium ion battery, a more stable, but less energy-dense technology, was introduced in 1991 and quickly became the new standard. These batteries replaced lithium metal with graphite anodes, which absorb the lithium and prevent dendrites from forming, but also come with performance costs.

Graphite can hold only one lithium ion for every six carbon atoms, giving it a specific capacity of approximately 350 milliampere hours per gram (mAh/g.) The lithium metal in a solid state battery has a specific capacity of 3,800 mAh/g.

Current lithium ion batteries max out with a total energy density around 600 watt-hours per liter (Wh/L) at the cell level. In principal, solid-state batteries can reach 1,200 Wh/L.

To solve lithium metal’s combustion problem, the U-M engineers created a ceramic layer that stabilizes the surface – keeping dendrites from forming and preventing fires. This allows batteries to harness the benefits of lithium metal – energy density and high-conductivity – without the dangers of fires or degradation over time.

The research group’s findings have been published in the Journal of Power Sources.

A demonstration of a machine that uses heat to densify a ceramic known as LLZO at 1,225 degrees Celsius.  Image credit: Evan Dougherty, Michigan Engineering. Click image for the largest view.

“What we’ve come up with is a different approach – physically stabilizing the lithium metal surface with a ceramic,” Sakamoto said. “It’s not combustible. We make it at over 1,800 degrees Fahrenheit in air. And there’s no liquid, which is what typically fuels the battery fires you see. You get rid of that fuel, you get rid of the combustion.”

In earlier solid state electrolyte tests, lithium metal grew through the ceramic electrolyte at low charging rates, causing a short circuit, much like that in liquid cells. U-M researchers solved this problem with chemical and mechanical treatments that provide a pristine surface for lithium to plate evenly, effectively suppressing the formation of dendrites or filaments. Not only does this improve safety, it enables a dramatic improvement in charging rates, Sakamoto explained.

“Up until now, the rates at which you could plate lithium would mean you’d have to charge a lithium metal car battery over 20 to 50 hours (for full power),” Sakamoto said. “With this breakthrough, we demonstrated we can charge the battery in 3 hours or less. We’re talking a factor of 10 increase in charging speed compared to previous reports for solid state lithium metal batteries. We’re now on par with lithium ion cells in terms of charging rates, but with additional benefits.”

That charge/recharge process is what inevitably leads to the eventual death of a lithium ion battery. Repeatedly exchanging ions between the cathode and anode produces visible degradation right out of the box.

In testing the ceramic electrolyte, however, no visible degradation is observed after long term cycling, said Nathan Taylor, a U-M post-doctoral fellow in mechanical engineering.

Taylor noted, “We did the same test for 22 days. The battery was just the same at the start as it was at the end. We didn’t see any degradation. We aren’t aware of any other bulk solid state electrolyte performing this well for this long.”

Bulk solid state electrolytes enable cells that are a drop-in replacement for current lithium ion batteries and could leverage existing battery manufacturing technology. With the material performance verified, the research group has begun producing thin solid electrolyte layers required to meet solid state capacity targets.

Its a sure thing battery manufacturers are watching this closely. Yet in the back of every producer’s mind is the liability of those fires. This technology has to work every time without exceptions and still be price competitive.

Maybe this will launch the next surge in battery performance. Time and testing will tell. If the scale up to manufacturing works, we’re sure to see advertising trumpeting about the “new” lithium metal battery.


2 Comments so far

  1. B Cole on August 21, 2018 7:56 PM

    Great post.

    It is beginning to look like solid-state batteries are indeed the next big thing.

    In fact, we may be witnessing the end of the internal combustion engine as the vehicular propulsion system of choice.

    This is very big, dudes.

  2. Al Fin on August 25, 2018 9:25 AM

    Better batteries are very important for the future, although they have a long way to go if internal combustion engines are ever to be entirely replaced by electric motors. (I doubt it).

    High energy density will continue to carry the threat of explosion or combustion whether for liquid fuels or for batteries. What is surprising is how low the energy density is for lithium ion and yet they still find a way to combust or explode. If these new solid state batteries are safer and more energy dense at the same time, there are many applications where they will be welcome.

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