CPM Seminar

Understanding advanced materials:
from Li-ion batteries to magnetic phase competition in Heusler alloys

Eric McCalla

Department of Chemistry
McGill University

The research performed in my group looks at synthesizing and understanding advanced functional materials for various applications. Here, two such applications will be discussed, the first being materials for Li-ion batteries. Advanced Li-ion battery positive electrodes designed to meet targets for widespread use of electric vehicles currently show a number of challenges including oxygen gas released during cycling, migration of cations, voltage fading with cycling and a large irreversible capacity during the first formation cycle. In this talk a survey of model systems will be presented in order to better understand the mechanisms behind each of these processes. With the use of in-situ XRD, STEM, Mössbauer spectroscopy and XPS, a picture emerges where reversible oxygen redox must take place below 4.3 V at which point oxygen gas begins being evolved. The second area of interest is with respect to materials of interest for their magnetic properties. Ru₂Mn_1-xFe_xSn Heusler alloys show ferromagnetic/antiferromagnetic phase separation over remarkably long lengths scales despite the fact that no structural phase separation is apparent. Detailed neutron powder diffraction and small angle neutron scattering will be presented in order to better understand the nature of the phase separation and possible impact of a coherently structured contaminant hcp phase.