Lithium iron phosphate is one of the most important materials for batteries used in electric vehicles, stationary energy storage systems, and tools. It is durable, relatively inexpensive, and does not pose a risk of self-ignition. Its energy density is also making steady progress. However, the scientific community still puzzles over why lithium iron phosphate batteries fall up to 25% short of their theoretical energy storage capacity in practical applications. To unlock this untapped capacity reserve, it is crucial to understand precisely where and how lithium ions are stored and released within the battery material during charge and discharge cycles. Researchers at TU Graz have now taken a significant step forward: using transmission electron microscopes, they systematically tracked lithium ions through the battery material, visualized their arrangement in the crystal lattice of an iron phosphate cathode with unprecedented resolution, and quantified their distribution within the crystal.
Key Insight for Further Increasing Battery Capacity
“Our investigations have shown that even when the test battery cells are fully charged, lithium ions remain trapped in the cathode’s crystal lattice instead of migrating to the anode. These immobile ions reduce capacity,” explains Daniel Knez from the Institute of Electron Microscopy and Nanoanalysis at TU Graz. The immobile lithium ions are unevenly distributed within the cathode. The researchers succeeded in pinpointing the areas with varying lithium enrichment down to a few nanometers. In the transition regions, distortions and deformations in the cathode’s crystal lattice were observed. “These details provide crucial insights into physical effects that currently hinder battery efficiency and that we can address in future material developments,” says Ilie Hanzu from the Institute of Chemistry and Technology of Materials, who closely collaborated on the study.
Methods Transferable to Other Battery Materials
For their investigation, the researchers extracted material samples from electrodes of charged and discharged batteries and analyzed them using the atomic-resolution ASTEM microscope at TU Graz. They combined electron energy loss spectroscopy with electron diffraction measurements and atomic-scale imaging. “By combining multiple analytical methods, we were able to determine where lithium is positioned within the crystal channels and the pathways it takes to get there,” explains Nikola Šimić from the Institute of Electron Microscopy and Nanoanalysis, first author of the paper detailing the results recently published in the journal Advanced Energy Materials. “The methods we developed, along with our findings on ion diffusion, can be transferred with minimal adjustments to other battery materials to characterize and optimize them even more precisely.”
This research is embedded in the Field of Expertise “Advanced Materials Science,” one of five strategic focus areas at TU Graz.
Publication:
Phase Transitions and Ion Transport in Lithium Iron Phosphate by Atomic-Scale Analysis to Elucidate Insertion and Extraction Processes in Li-Ion Batteries
Published in: Advanced Energy Materials, 2024, 2304381
Authors: Nikola Šimić, Anna Jodlbauer, Michael Oberaigner, Manfred Nachtnebel, Stefan Mitsche, H. Martin R. Wilkening, Gerald Kothleitner, Werner Grogger, Daniel Knez, Ilie Hanzu
DOI: https://doi.org/10.1002/aenm.202304381
Contact Information:
Daniel KNEZ
Dipl.-Ing. Dr.techn. BSc
TU Graz | Institute of Electron Microscopy and Nanoanalysis
Tel.: +43 316 873 8831
knez@tugraz.at
Nikola ŠIMIĆ
TU Graz | Institute of Electron Microscopy and Nanoanalysis
Tel.: +43 660 258 9406
nikola.simic@tugraz.at
Ilie HANZU
Ass. Prof. Priv.-Doz. Dr.
TU Graz | Institute of Chemistry and Technology of Materials
Tel.: +43 316 873 32329
hanzu@tugraz.at
