Asbjørn Ulvestad, Institute for Energy Technology (Norway)

Amorphous and substoichiometric silicon nitride (SiNx) has been demonstrated to exhibit convertible alloy anode behaviour in Li-ion batteries, i.e., that it irreversibly converts into a mixture of active silicon and an inactive matrix during the initial lithiation of the material. In the subsequent cycles the active silicon component is reversibly lithiated and delithiated, contributing significant reversible capacity, while the inactive matrix component mitigates the severe degradation silicon usually undergoes during such treatment. The result is a material that can maintain a high capacity over a large number of charge and discharge cycles. The properties of the material have been found to be strongly dependent on its nitrogen content; however, the mechanisms that govern this dependency, in particular the specifics of the conversion reaction, have yet to be conclusively determined. Gaining this understanding would allow targeted tuning of the material properties to fit different sets of requirements and applications. Some has been deduced from electrochemical analyses, but further characterization is needed to better elucidate the process. This is the basis for the SAIL project, where we will employ advanced characterization methods, like TEM and synchrotron-based techniques, both in and ex-situ, to further our understanding of this promising material.