Cathode Materials for Mg batteries – Mg-garnets
Research Associate: Benjamin Zimmermann
Besides sustainable energy production there is also the important matter of how to store it efficiently to balance out production spikes from renewable sources. The go-to day-to-day storage method is via lithium-ion batteries. They provide a high energy density, solid operating voltage, and long lifetime. However, there are also impactful drawbacks such as high cost, safety issues due to flammable electrolytes and the declining supply of available lithium. Lithium-ion batteries are also said to be at the end of their maximum potential.[1] Alternatives which moved into the center of attention are, among others, magnesium batteries. They alleviate the problems of lithium-based batteries by offering higher safety, low cost, and less environmental hazard. In contrast to the lithium-based batteries, here the bare metal can be used as an anode which provides excellent energy density (3833 mAh cm-3 vs. 2046 mAh cm-3 for Li).[2] Current limitations are compatibility problems with electrolyte and cathode materials. The small radius of Mg2+ and high charge lead to problems with the reversibility of intercalation due to the strong coulomb interactions.
In this context, embedded into a project from the POLiS cluster of excellence (KIT, JLU, ZSW, Ulm University), new cathode materials are being researched to overcome the problems. Promising candidates are magnesium garnets in the class of nesosilicates. They offer high structural stability with low volume changes during the redox reactions and low cation migration barriers.[3] Their highly symmetrical space group la3d allows for isotropic properties which boosts migration processes. The garnet structure also allows for a wide variety of constituent elements. This allows for deliberate tuning of the desired properties.[4]
Focus on this project lies on testing the feasibility of synthesis approaches via solid-state sintering, wet chemical methods, and hot pressing. Afterwards the characterization will be done through x-ray diffraction, electron microscopy and x-ray photoelectron spectroscopy.
References:
[1] T. L. Kulova et al., Int. J. Electrochem. Sci., 2020, 15, 7242 – 7259.
[2] M. Walter et al., New J. Chem., 2020, 44, 1677-1683.
[3] E. G. Ahn et al., ACS Appl. Mater. Interfaces, 2021, 13, 47749-47755.
[4] C. A. Geiger, Elements, 2013, 9, 447-452.
This project is funded by the German Research Foundation (DFG) through the POLiS Cluster of Excellence (EXC 2154).
