Researchers at TU Graz have shown that deliberately introducing defects into the crystal lattice of lithium titanate can activate a previously blocked transport pathway for lithium ions. The study focuses on lithium titanate, or LTO, a well-established battery material that in its pristine form is a relatively poor conductor of lithium ions. According to the researchers, the material develops high ionic conductivity only during charging, when additional lithium ions and electrons are incorporated into the structure.
Bernhard Gadermaier and Martin Wilkening from the Institute of Chemistry and Technology of Materials at TU Graz took a different approach by starting with pure, non-lithiated LTO in its original composition, Li4Ti5O12, and improving its ion transport properties through defect engineering. By removing individual oxygen atoms from the crystal lattice, they created oxygen vacancies that activated a migration pathway for lithium ions. Wilkening explained that this pathway is already present in the LTO structure but becomes active only through the defect structure.
To generate the defects, the team heated the lithium titanate to 300 degrees Celsius in an oxygen-poor atmosphere. They said this process gently removes individual oxygen atoms and changes the mobility of lithium cations, transforming the material from a poor ionic conductor into a significantly better one. The researchers emphasized that atomic-scale defect structures can have a major effect on the macroscopic properties of a material.
The enhanced ion transport was verified experimentally using conductivity spectroscopy and nuclear magnetic resonance spectroscopy. In particular, the NMR measurements provided direct evidence of the newly activated atomic-scale diffusion pathway.
The researchers also noted that their results show how the properties of a solid depend not only on chemical composition, but also on local defect structure and thermal history. They said the mobility of small lithium cations can be precisely controlled using concepts from anionic defect chemistry.
The team described the work as an example of how fundamental research can lead to new material functions. They said the targeted control of ionic conductivity through defect chemistry could have future relevance for iontronic, memristive, and neuromorphic devices in micro- and nanoelectronics.
