Super stable garnet ceramics may be ideal for high-energy lithium batteries

Super stable garnet ceramics may be ideal for high-energy lithium batteries
ORNL researchers used scanning transmission electron microscopy to take an atomic-level look at a cubic garnet material called LLZO that could help enable higher-energy battery designs. Credit: ORNL

Scientists at the Department of Energy's Oak Ridge National Laboratory have discovered exceptional properties in a garnet material that could enable development of higher-energy battery designs.

The ORNL-led team used scanning transmission electron microscopy to take an atomic-level look at a cubic garnet material called LLZO. The researchers found the material to be highly stable in a range of , making the compound a promising component in new configurations.

Researchers frequently seek to improve a battery's energy density by using a pure lithium anode, which offers the highest known theoretical capacity, and an aqueous electrolyte that can speedily transport lithium. The ORNL scientists believe the LLZO would be an ideal separator material, which is crucial.

"Many novel batteries adopt these two features [lithium anode and aqueous electrolyte], but if you integrate both into a single battery, a problem arises because the water is very reactive when in direct contact with ," said ORNL postdoctoral associate Cheng Ma, first author on the team's study published in Angewandte Chemie. "The reaction is very violent, which is why you need a protective layer around the lithium."

Battery designers can use a solid electrolyte separator to shield the lithium, but their options are limited. Even the primary separator of choice, known as LAPT or LISICON, tends to break down under normal battery operating conditions.

"Researchers have searched for a suitable solid electrolyte separator material for years," said ORNL's Miaofang Chi, the study's lead author. "The requirements for this type of material are very strict. It must be compatible with the lithium anode because lithium is reactive, and it also has to be stable over a wide pH range, because you can have an alkaline environment—especially with ."

The researchers used atomic resolution imaging to monitor structural changes in LLZO after the samples' immersion in a range of aqueous solutions. The team's observations showed that the compound remained structurally stable over time across neutral and extremely alkaline environments.

"This solid electrolyte separator remains stable even for a pH value higher than 14," Ma said. "It gives battery designers more options for the selection of aqueous solutions and the catholyte." Catholyte is the portion of the electrolyte close to the cathode.

In lithium-air batteries, for instance, researchers have previously tried to avoid the degradation of the separator by diluting the aqueous solutions, which only makes the battery heavier and bulkier. With this new type of solid electrolyte separator, there is no need to dilute the aqueous electrolyte, so it indirectly increases the battery's energy density.

Higher-energy batteries are in demand for electrified transportation and electric grid energy storage applications, leading researchers to explore battery designs beyond the limits of -ion technologies.

The researchers intend to continue their research by evaluating the LLZO garnet's performance in an operating battery. Coauthors are ORNL's Chengdu Liang, Karren More, Ezhiylmurugan Rangasamy, and Michigan State University's Jeffrey Sakamoto. The study is published as "Excellent Stability of a Li-Ion-Conducting Solid Electrolyte upon Reversible Li+/H+ Exchange in Aqueous Solutions."


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More information: Angewandte Chemie, onlinelibrary.wiley.com/doi/10 … e.201408124/abstract
Journal information: Angewandte Chemie

Citation: Super stable garnet ceramics may be ideal for high-energy lithium batteries (2014, October 21) retrieved 27 May 2019 from https://phys.org/news/2014-10-super-stable-garnet-ceramics-ideal.html
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Oct 21, 2014
I don't think it would be a good idea to use this technology in electric car batteries. If this garnet solid electrolyte were to be broken in a collision, the battery could become a bomb.

Oct 21, 2014
I don't think it would be a good idea to use gasoline-powered cars. If the fuel tank were to be ruptured in a collision, the car could become a bomb.


Oct 21, 2014
I don't think it would be a good idea to use gasoline-powered cars. If the fuel tank were to be ruptured in a collision, the car could become a bomb.
Except it doesn't. It has the fuel but lacks the oxygen to explode until it is dispersed at the correct ratio within the surrounding air.

A battery that contains lithium and H2O has both the fuel and the oxygen, because lithium "burns" in water, generating heat, hydrogen, and lithium hydroxide which is caustic. The heat will cause the hydrogen to build up pressure, which ruptures the battery and disperses it rapidly into the surrounding air, and also ignites it.

If the ignition happens within the battery, the result is a large blowtorch-like jet shooting out of the casing. If the battery isn't yet hot enough to ignite when the hydrogen is vented out, the result can easily be an air-fuel explosion because hydrogen has a very wide explosive ratio, unlike gasoline that only explodes in a narrow range of concentration in air.

Oct 21, 2014
Remind me to tell all those folks who got burned up in Pintos.

Oct 21, 2014
What makes gasoline dangerous and problematic in a crash is the fact that a regular 10 gallon tank contains 300 kWh worth of chemical energy, whereas a small EV battery currently contains about 24 kWh.

The Tesla fires made it pretty clear that having a large amount of energy in an unstable lithium battery results in nice fireworks. They have a pretty high fires per crashes ratio compared to ordinary cars.

Remind me to tell all those folks who got burned up in Pintos.


Shifting goalposts there mate.

Oct 21, 2014
Remind me to tell all those folks who got burned up in Pintos.


Besides, the car behind the Pinto was in a more immediate danger because they rolled over the pool of gasoline left behind in the collision.

The fact that actually made the Pinto dangerous in a crash was not the gas tank rupturing and catching flame on rear-end collision, but the fact that the same collision also caused the doors to jam due to the frame bending. It was just an engineering blunder all over.

Oct 23, 2014
Except it doesn't. It has the fuel but lacks the oxygen to explode until it is dispersed at the correct ratio within the surrounding air.

A battery that contains lithium and H2O has both the fuel and the oxygen, because lithium "burns" in water, generating heat, hydrogen, and lithium hydroxide which is caustic. The heat will cause the hydrogen to build up pressure, which ruptures the battery and disperses it rapidly into the surrounding air, and also ignites it.

If the ignition happens within the battery, the result is a large blowtorch-like jet shooting out of the casing. If the battery isn't yet hot enough to ignite when the hydrogen is vented out, the result can easily be an air-fuel explosion because hydrogen has a very wide explosive ratio, unlike gasoline that only explodes in a narrow range of concentration in air.


pretty much the same thing you have in conventional engine with internal combustion. high pressure + heat..

Oct 23, 2014
pretty much the same thing you have in conventional engine with internal combustion. high pressure + heat..


Except that heat and pressure isn't in the gasoline tank.

It's in the engine, and the engine contains only a small amount of fuel at a time, which is not enough to instantly cause anything dramatic to happen. In case of ignition starting from the engine, it's more likely that all the plastic parts in the interior of the car will burn before the flame reaches the gasoline in the tank.

The point is that the gasoline tank burns from the outside in. The lithium battery burns from the inside out.

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