Solid Electrolytes Make Batteries More Powerful

2023 Author : Hannah Pearcy | [email protected] . Last modified: 2023-05-24 11:12

For many future technologies, high-performance, long-lasting energy storage devices are of central importance: For example, for electromobility, for mobile devices such as tablets or smartphones or for the efficient use of renewable energies. Dr. Daniel Mutter from the Fraunhofer Institute for Mechanics of Materials IWM was able to clarify how solid electrolytes made of ceramic have to be chemically composed in order to perform well in lithium-ion batteries. He published this in the Journal of Applied Physics. Solid electrolytes of this type are said to be more environmentally friendly than conventional liquid electrolytes and could make lithium-ion batteries significantly more powerful and reliable

They pose a lower risk of explosion and if they are damaged, for example by a crash, no acid should escape, which can cause burns and poisoning in humans.

Battery electrolytes have to meet high requirements

The requirements for the material properties of battery electrolytes are considerable: The ionic conductivity should be high and the chemical elements used should be both non-toxic and rich in the earth's crust.

Using atomistic simulations, Dr. identified Mother now has several combinations of chemical elements for NZP ceramics that are particularly promising for these requirements.

Practically test predictions

"Under certain circumstances, we can combine these particularly advantageous ceramic solid - state electrolytes with very powerful lithium metal anodes - this is not possible with the liquid electrolytes currently in use, because they react strongly with metallic lithium and thereby damage the battery," explains Dr. Mother.

In the next step, the researcher wants to test with partners whether the predicted materials significantly increase the conductivity as expected. Specifically, this would mean: Shorter charging times with longer operating times , which would be particularly advantageous for electromobility.

In addition, this combination means less weight , since lithium metal anodes with the same capacity are significantly lighter than the graphite anodes previously used.

The chemical elements that Dr. Mother researches are said to be abundant in the earth's crust in Europe and are relatively easily degradable .

Batteries

Scientists are researching solid-state batteries for electric cars

Lithium ion batteries

30 percent more power possible with lithium-ion batteries

NZP ceramics have high ionic conductivity

In general, the ionic conductivity of ceramic materials is lower than that of liquid electrolytes. The class of so-called NZP ceramics, however, promises a high ionic conductivity: their structural structure enables the existence of " hiking trails" on which lithium ions can move easily . This makes them an interesting candidate for high-performance solid-state electrolytes for lithium-ion batteries.

However, it was previously unclear why certain connections are more powerful than others and which actually perform particularly well.

What are NZP ceramics?

The class of NZP ceramics has been known since the 1960s and is also called Nasicon. It got its name from the chemical structure NaZr2 (PO4) 3, for which particularly positive properties for the production of solid electrolytes were discovered.

The stability of NZP ceramics is made possible by a characteristic “lantern” structure of the polyhedra formed by the oxygen atoms around the other elements. This results in a three-dimensional network of migration paths for lithium ions, which leads to a high ionic conductivity of the ceramic. The chemical elements sodium, zirconium and phosphorus can be varied. As can be seen in the graphic above, sodium can be replaced by lithium and zirconium by titanium. The variability of the elements enables the material properties for a large number of elementary combinations to be analyzed with the aid of a computer.

Better understanding of NZP ceramics

In addition to predicting promising material compositions, the physicist's research aims to contribute to a better understanding of the atomic processes in NZP ceramics.

He found that the migration energy required for lithium-ion migration depends in a different way on the oxygen environment around the ion migration path than previously thought. Identified structure-property relationships enable significantly more well-founded predictions about the effects of the elementary populations on the structural framework and the ion conductivity of the NZP ceramics.

Dr. Mother's analyzes are part of a DFG-funded research project on the topic "Production and characterization of ceramic solid-state electrolytes with high lithium ion conductivity", which he carried out in cooperation with the Karlsruhe Institute of Technology (KIT) and the TU Munich.