Researchers at the Graz University of Technology (TU Graz) in Austria have identified the root cause of why lithium iron phosphate (LFP) consistently undercuts its theoretical capacity.
Using atomic-level microscopy and electron diffraction measurements, the researchers traced the movement of lithium ions and how they contribute to capacity loss.
LFP batteries are critical components of the energy transition humanity is aiming for as it looks to meet its energy demands from fewer fossil fuels and cleaner sources.
Whether in an electric vehicle (EV) or a battery energy storage system (BESS), an LFP battery is a reliable partner for storing energy since the technology is inexpensive and has a long service life.
LFP batteries have a lower energy density than their nickel, manganese, and cobalt (NMC) counterparts. However, scientists are also puzzled about why, in practice, LFP batteries consistently deliver up to 25 percent less storage capacity.
The research team at TU Graz decided to look at the problem at an atomic level to unlock a reserve capacity for the batteries.
Atomic-level analysis
Using transmission electron microscopes, the researchers tracked the movement of lithium ions as they passed through the battery material and how they were arranged in the crystal lattice structure of the iron phosphate cathode.
The team also prepared samples of fully charged and discharged battery electrodes and analyzed them using other techniques, such as electron energy loss spectroscopy and electron diffraction measurements.
“By combining different examination methods, we were able to determine where the lithium is positioned in the crystal channels and how it gets there,” said Nikola Šimić from the Institute of Electron Microscopy and Nanoanalysis at TU Graz in a statement.
TU Graz researchers with one of the electron microscopes used to investigate the LFP battery at the atomic level. Image credit: Lunghammer – TU Graz
What did they find?
To their surprise, the researchers found that some lithium ions remained in the cathode’s crystal lattice structure even when the battery was fully charged. This was the underlying underlying cause of the battery lower capacity battery’s lower capacity compared to its theoretical limit.
The researchers further found that these ions were distributed unevenly in the cathode and mapped them to a nanometer scale in their analysis. The uneven distribution was caused by distortions and deformations of the cathode’s crystal lattice structure.
High-resolution image of the sample material’s lithium-rich (bottom right) and lithium-poor (top left) areas. Image source: FELMI – TU Graz
“These details provide important information on physical effects that have so far counteracted battery efficiency and which we can take into account in the further development of the materials,” said Ilie Hanzu, a professor of advanced electrochemistry at the Institute of Chemistry and Technology of Materials, TU Graz, who was also involved with the research.
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The researchers now have a better understanding of ion diffusion occurring inside the batteries and their electrodes. The approach and lessons learned from the experiments can also be applied to other batteries in the future.
“The methods we have developed and the knowledge we have gained about ion diffusion can be transferred to other battery materials with only minor adjustments in order to characterise them even more precisely and develop them further,” added Simic in the press release.
Ameya Paleja Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.
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