Li-ion battery (LIB) electrodes suffer from gradual performance loss during repeated electrochemical cycling. The battery community has identified a variety of mechanical and chemical degradation routes leading to capacity fade in LIBs, including fracture of the active electrode particles driven by cycling-induced chemomechanical stress. However, the detailed mechanisms by which this fracture due to electrochemical cycling – or electrochemomechanical fatigue – promotes capacity fade and impedance growth are not understood completely even in the most well studied positive electrode systems.

Here, we demonstrate this connection between fracture, capacity, and impedance growth in Li_XMn₂O₄ cathodes via complex cycling schedules designed to produce discrete fracture events. We implement variations in current and potential to control fracture by electrochemical means, confirmed with in situ acoustic emissions monitoring and post-mortem electron microscopy. We use electrochemical impedance spectroscopy and distribution of relaxation times analysis to identify the physical contributions to electrochemical impedance, and find that fracture causes an immediate increase in electronic contact resistance by creating insulating interfaces in the bulk of the electrode. We also observe an onset of severe capacity fade concurrent with electrochemically induced fracture, indicating that fracture plays a role in accelerating dissolution reactions that compromise battery cathode performance. Thus, we identify two distinct degradation mechanisms acting separately on capacity and impedance over two different time scales. The separation of these performance-reducing effects in a well-studied cathode material is critical to understanding the coupling between electrochemical and mechanical degradation in LIBs.