Faisal Alamgir: Soft and Hard X-ray Operando and In/Ex-situ XAFS: Towards a Unified View of Local Structure and Magnetic Properties in LiMO2 Delafossite Batteries

We will look at how electrochemically active materials such as batteries can be studied in a concerted way by tuning to relevant resonant x-ray absorption at both the soft and the hard x-ray energy regimes. We will specifically examine the role of oxygen in the charge compensation of LiMO2 delafossite compounds, that serve as cathodes for an important class of rechargeable batteries, and the consequences of such for battery safety and for unprecedented changes to magnetic properties. As a case study of the reactions in LiCoO2, the electronic and atomic structure local to oxygen was first examined indirectly using hard x-rays by operando resonant Co K-level measurements and was later complemented by operando measurements at the O K-level using soft x-rays. A charge compensation roadmap was established for the LiCoO2 cathodes where we find tandem charge compensation reactions, first involving oxygen and later by cobalt. The generation of electron holes at oxygen sites explains the transitions in magnetic moment observed in LiCoO2 as a function of de-lithiation. A similar case was found in in the de-lithiation of Li[Ni1/3Co1/3Mn1/3]O2 cathodes. We hope to make the case that a detailed electrochemical roadmap for the reaction mechanisms in LiMO2 cathodes could only be revealed by a combination of soft and hard x-ray based experiments.

References:
F. M. Alamgir et al., LiCoO2 Thin-Film Batteries: Structural Changes and Charge Compensation, Journal of The Electrochemical Society},152, 5, (2005) A845. doi: 10.1149/1.1872672 ;
C. F. Petersburg, et al, Oxygen and transition metal involvement in the charge compensation mechanism of LiNi1/3Mn1/3Co1/3O2 cathodes, J. Mater. Chem., 22, 37, (2012) 19993-20000;
C. F. Petersburg, et al, Soft X-ray characterization technique for Li batteries under operating conditions, J. Synchrotron Rad., 16, (2009) 610-615.