3D display of EPR data for a deeper investigation of bulk manganese compounds

Abstract

Numerous families of battery technologies have been developed in the scope of electrochemical energy storage, many of which include cathode active materials based on manganese. These materials or their precursors are strongly paramagnetic and often partially amorphous, which impedes the characterization of their bulk by means of XRD and NMR. Rightfully, electron paramagnetic resonance (EPR) stood for us as great ally when it came to lab's scale analysis as part of our work on the synthesis of bulk (lithium) manganese (oxy)fluorides. In this article, we share on our experience and methods regarding the practical application of EPR to materials chemistry. Accordingly, we provide a 3D display of EPR data to co-represent EPR key parameters {g-factor, ΔH_pp and absorption signal area}. Within the frame of bulk (lithium) manganese (oxy)fluorides, we found out that coupled analysis of these parameters empirically enables qualitative chemistry identification and quantitative titration of the identified phases provided pure references. We define the boundaries of validity of this display procedure both through theory description and extensive experimental control experiments. In addition, we provide a well-stocked database of EPR spectra and data for bulk (lithium) manganese oxides, fluorides and oxyfluorides including among others MnO, Mn₃O₄, Mn₂O₃, MnO₂, MnOOH, MnF₂, Mn₂F₅, MnF₃, MnF₄, MnOF, Li₂MnO₃ and Li₂MnF₆. We also provide practical application cases of the 3D display. By elaborating on the potency and limits of this method when applied to practical cases, we wish to extend the scope of EPR within the community of bulk materials chemistry.