TU Graz researchers boost lithium titanate conductivity through ‘hole punching’ crystal lattice
Researchers at TU Graz have found a way to significantly increase the ionic conductivity of lithium titanate, potentially opening up new possibilities for the battery anode material. By deliberately introducing defects into the material's crystal lattice structure, they "activated a previously block pathway" for lithium ions.
Alongside graphite, lithium titanate (LTO) is a widely used anode material in batteries. However, in its untreated state, it conducts lithium ions poorly. Its high ionic conductivity only develops during battery charging, when additional lithium ions and electrons are intercalated into the material.
Researchers Bernhard Gadermaier and Martin Wilkening from the Institute of Chemical Technology of Materials at TU Graz have now succeeded in transforming pure (‘non-lithiated’) LTO with its original composition Li4Ti5O12 into a significantly better ionic conductor using an entirely new approach. The duo achieved this by deliberately creating ‘holes’ in the crystal lattice, known as oxygen vacancies. “When individual oxygen atoms are removed from the crystal lattice, these vacancies unlock a migration pathway for ions that was previously blocked. This diffusion path is already predefined by the LTO structure but is only activated by the defect structure,” explains Wilkening. The results of the experimental study were published in the journal Science Advances.
To create the vacancies in LTO, the researchers heated the lithium titanate in a low-oxygen atmosphere to 300 degrees Celsius. “This gentle heating removes individual oxygen atoms from the crystal lattice,” Wilkening continues. “The resulting anionic vacancies in the crystal lattice directly influence the mobility of lithium cations and transform the originally poor ionic conductor into a significantly better one. The example of LTO clearly demonstrates the enormous impact of atomic defect structures on the macroscopic function of a material.”
Complex experimental validation
The researchers experimentally demonstrated the rapid ion conduction using a combination of conductivity spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The NMR measurements provided direct experimental evidence of the newly activated atomic diffusion pathway.
“Our experimental study impressively shows that the properties of a solid are not solely determined by its chemical composition but are also significantly influenced by its local defect structure and thermal history,” summarises Martin Wilkening. “We demonstrate how the mobility of small lithium cations can be precisely controlled using classical concepts of anionic defect chemistry.”
The work also serves as a prime example of how curiosity-driven fundamental research can lead to new material functionalities,” the researchers note. “The targeted control of ionic conductivity through defect chemistry opens up long-term perspectives for ionotronic, memristive, and neuromorphic components in micro- and nanoelectronics.”