Non-invasive current density imaging of lithium-ion batteries

The rapid pace of replacing fossil fuel propelled transport by electric vehicles is critically dependent on high-performing, high energy density batteries. Optimal and safe use of existing battery cells and development of much-needed novel battery chemistries and geometries require a multitude of diagnostic and monitoring tools. While structural and chemical information is readily extracted through a host of imaging techniques, non-invasive functional detection of interior battery processes remains limited. Here we introduce sensitive magnetometry performed outside the battery, revealing internal current distribution. As a key application, we use a sensor array to image the internal current flow of a pouch cell cycling between charge states. We find good agreement between measured and modelled fields with sufficient resolution to detect percent-level deviations around high current density areas. This opens the path towards rapid and reliable assessment throughout the battery life cycle, from battery development and manufacturing quality assurance to optimised use.