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HIU researchers develop extremely high energy density lithium-metal cell with good stability

Researchers at the Helmholtz Institute Ulm (HIU), founded by the Karlsruhe Institute of Technology (KIT) in cooperation with the University of Ulm, have developed a new lithium-metal battery that offers extremely high energy density of 560 Wh/kg—based on the total weight of the active materials—with remarkably good stability.

The team used a a promising combination of cathode and electrolyte: the nickel-rich cathode allows a large amount of energy per mass to be stored, while the ionic liquid electrolyte ensures that the capacity is largely retained over many charging cycles. The team reports on the lithium metal battery in an open-access paper in Joule.

Although lithium-metal batteries are attractive as a higher-capacity energy storage solution than current Li-ion batteries, their stability poses a challenge because the electrode materials react with common electrolyte systems, affecting stability.

The HIU researchers used a low-cobalt, nickel-rich layered cathode (NCM88), which offers high energy density. With the commonly used commercially available organic electrolyte (LP30), however, the stability is unacceptable.

In the LP30 electrolyte, particle cracks occur on the cathode. The electrolyte reacts within these cracks and destroys the structure. In addition, a thick, moss-like lithium-containing layer forms on the anode.

—Professor Stefano Passerini, Director of the HIU and head of the battery electrochemistry research group

The researchers therefore used a non-volatile, non-flammable ionic liquid electrolyte with two anions (ILE) instead.

With the help of the ILE, the structural changes in the nickel-rich cathode can be significantly reduced, said Dr. Guk-Tae Kim from the Battery Electrochemistry Research Group at HIU.

2021_075_Rekordverdaechtige Lithium-Metall-Batterie_2_72dpi

With the ionic liquid electrolyte ILE (right), structural changes in the nickel-rich cathode NCM88 can be largely avoided; 88% of the battery’s capacity is retained over 1,000 charging cycles. (Image: Fanglin Wu and Dr. Matthias Künzel, KIT / HIU) Illustration: Fanglin Wu and Dr. Matthias Künzel, KIT / HIU

With the cathode NCM88 and the electrolyte ILE, the lithium-metal battery initially has a storage capacity of 214 mAh/g); 88% of the capacity is retained over 1,000 charging cycles. The Coulombic efficiency, which indicates the ratio between the withdrawn and supplied capacity, averages 99.94%.


  • Fanglin Wu, Shan Fang, Matthias Kuenzel, Angelo Mullaliu, Jae-Kwang Kim, Xinpei Gao, Thomas Diemant, Guk-Tae Kim, and Stefano Passerini (2021) “Dual-anion ionic liquid electrolyte enables stable Ni-rich cathodes in lithium metal batteries.” Joule doi: 10.1016/j.joule.2021.06.014



That is one heck of an improvement from a relatively simple change!


based on the total weight of the active materials
That is a different matter



It was the upgrade in stability for NMC that I was cheering.

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The question is . . . How close is this to commercial production?
The research is about improving the long-term cycling performance of a Li-metal battery employing a dual-anion ionic liquid electrolyte (ILE) using a NCM88 cathode.
Guess who has a Li-metal battery using an ILE? Cuberg.
Except Cuberg was acquired by Northvolt (who is working with VW) and is focused on Li-metal batteries. Who has a NCM88 Cathode - SK Innovation (they call it a NCM 9½½ type) and they are a partner with VW, too.
From the Northvolt website: "The path ahead for Northvolt now envisions the commercialization of a breakthrough lithium metal cell boasting energy density of 1000 Wh/l by 2025, alongside Northvolt’s entry into the electric aviation market.".


The promise of Li metal batteries looks to be within reach if they can solve the stability problems; many believe dry electrolytes should be used instead of liquid to remove the safety issue of runaway cells.

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Check the Cuberg Nail Puncture test on CleanTechnica (


I've tracked down the Northvolt article gryf got his quote from, and it is well worth a read:

I thought this was particularly interesting in view of some of our previous discussions here, where what battery technology would be electric aviation companies were hypothesising they did not make clear:

' Lithium metal technology provides the key to unlock a new market for Northvolt: aviation. Cuberg has focused much of its development objectives to date around serving the electric aviation market’s needs for high energy density cell technology, and has already attracted customers in this segment, including Boeing, BETA Technologies, Ampaire, and VoltAero along the way.'

As Northvolt say though:

' Still, the work is far from over. What remains to be done is in many ways the most difficult part of the innovation process – to take the technology into larger format cells with increased capacity to meet the range of applications Northvolt intends to serve, and scale production on Northvolt manufacturing lines.'

I like what Northvolt have to say on recycling, too, and their cradle to grave approach.


active materials
That metric is not commonly used


The ratios in SK Innovation's NCM88 batteries are 8:1:1

I'm pretty happy with that together with Northvolt's strong sourcing and recycling:

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The reference:high energy density of 560 Wh/kg—based on the total weight of the active materials, means that this does not include the inactive and polymeric binder mass. Even if they quoted the Lithium full cell energy density, it is still only a lab specimen. Until a fully developed pouch or cylindrical cell is produced, you can only estimate battery energy density.
Cuberg does have a product with a 369 Wh/kg energy density (though poor cycle life). Depending on the configuration (pouch, 2170, 4680, etc) energy density would be in this range. The HIU research extended the cycle life by using a dual-anion ionic liquid electrolyte.


Lab coin cell data is normalized to a real energy density
This is a bit misleading

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