KIT – Record-breaking lithium metal cell, extremely high energy density with good stability.
An extremely high energy density of 560 watt hours per kilogram – based on the total weight of the active materials – with remarkably good stability is offered by a novel lithium-metal battery.
For this purpose, researchers at the Helmholtz Institute Ulm (HIU), founded by Karlsruhe Institute of Technology (KIT) in cooperation with Ulm University, have used a promising combination of cathode and electrolyte: The nickel-rich cathode allows a lot of energy per mass to be stored, the ionic liquid electrolyte ensures that the capacitance is largely maintained over many charging cycles.
The team reports on the record-breaking lithium-metal battery in Joule magazine (DOI: 10.1016/j.joule.2021.06.014)
Currently, lithium-ion batteries are the most common solution for mobile power supply. However, the technology reaches its limits in some requirements. This is especially true for electromobility, where lightweight, compact vehicles with long ranges are in demand.
Lithium metal batteries offer an alternative: they are characterized by a high energy density, which means that they store a lot of energy per mass or volume. However, their stability is a challenge – because the electrode materials react with ordinary electrolyte systems.
Researchers at Karlsruhe Institute of Technology (KIT) and Helmholtz Institute Ulm – Electrochemical Energy Storage (HIU) have now found a solution. As they report in joule magazine, they are using a promising new combination of materials. They use a low-cobalt, nickel-rich layered cathode (NCM88).
This offers a high energy density. With the commonly used commercially available organic electrolyte (LP30), however, the stability leaves much to be desired. The storage capacity decreases with increasing number of charging cycles.
Professor Stefano Passerini, Director of the HIU and head of the Research Group Electrochemistry of Batteries, explains why this is the case:
In the electrolyte LP30, particle cracks occur at the cathode.
“Within these cracks, the electrolyte reacts and destroys the structure. In addition, a thick moss-like lithium-containing layer forms on the anode.”
The researchers therefore used a low-volatile, non-flammable ionic liquid electrolyte with two anions (ILE) instead.
Dr. Guk-Tae Kim from the Electrochemistry of Batteries research group at HIU.
With the help of the ILE, the structural changes at the nickel-rich cathode can be significantly contained.
Capacity over 1,000 charging cycles maintained to 88 percent
The results: With the NCM88 cathode and the electrolyte ILE, the lithium metal battery achieves an energy density of 560 watt hours per kilogram (Wh/kg) – based on the total weight of the active materials. It initially has a storage capacity of 214 milliampere-hours per gram (mAh/g); over 1,000 charging cycles, 88 percent of the capacity is retained.
The Coulomb efficiency, which indicates the ratio between extracted and supplied capacity, averages 99.94 percent. Since the battery presented is also characterized by a high level of safety, the researchers from Karlsruhe and Ulm have thus succeeded in taking a significant step on the way to carbon-neutral mobility.
About the Helmholtz Institute Ulm
The Helmholtz Institute Ulm (HIU) was founded in January 2011 by Karlsruhe Institute of Technology (KIT) as a member of the Helmholtz Association in cooperation with Ulm University. With the German Aerospace Center (DLR) and the Center for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW), two other renowned institutions are integrated into the HIU as associated partners.
The international team of around 130 scientists at the HIU is researching the further development of the foundations of sustainable energy storage systems for stationary and mobile use.
Highlights:
- Nickel-rich cathode and ionic liquid electrolyte enable extremely high energy density with good stability – researchers report in the magazine Joule.
- READ the latest Batteries News shaping the battery market
Record-breaking lithium metal cell, Augusto 23, 2021
