Dynamic Induction of Conversion−Based Anode Degradation by Valence State and Mechanical Cracks

Abstract Electrochemical energy storage through conversion reactions in crystalline electrode materials primarily depends on the size of guest ions. In this study, a combination of synchrotron−based transmission X−ray microscopy and X−ray absorption near edge spectroscopy is utilized to reveal the dynamic physicochemical changes in the micro−regions of spherical NiS ₂ active particles during the potassiation/depotassiation process. The findings show that, as the degree of potassiation increases, visible cracks and voids form within the bulk material, with significant differences in the chemical valence states of metal elements between the inner and outer regions. Furthermore, the voids induce the formation of new cracks, which propagate extensively into the bulk, serving as the root cause of electrode particle failure. Based on these observations, it is also demonstrated that this failure phenomenon in active materials can be mitigated through dimensional engineering strategies, paving the way for the development of high−capacity and highly stable potassium−ion batteries.