Abstract
Multivalent batteries, e.g., those based on magnesium (Mg), are promising candidates for next-generation energy storage due to their high volumetric energy densities and low cost. However, the corresponding ion migration and structural transition mechanisms are often linked and difficult to observe directly. Here, we report the direct investigation of atomic transport pathways of cations in spinel magnesium chromate (MgCr2O4) by using aberration-corrected scanning transmission electron microscopy (STEM). Cr atoms are directly observed to reversibly occupy the otherwise vacant octahedrally coordinated interstitial sites, passing through tetrahedral sites normally occupied by Mg. Furthermore, imaging and electron energy loss spectroscopy show that electron irradiation induces the formation of Mg and O vacancies, facilitating the migration of Cr and leading to an irreversible phase transition. These results demonstrate the ability of STEM to capture the pathway of deleterious point defects that can result in undesirable phase transitions.
| Original language | English |
|---|---|
| Pages (from-to) | 8455-8463 |
| Number of pages | 9 |
| Journal | Chemistry of Materials |
| Volume | 35 |
| Issue number | 20 |
| DOIs | |
| State | Published - Oct 24 2023 |
Funding
This work was supported as part of the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. This work was performed in part using MIT.nano’s Characterization facilities. Use of the Advanced Photon Source (APS) was supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357. This research used resources at the Nanoscale-Ordered Materials Diffractometer (NOMAD) instrument at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.