Neutron imaging of lithium batteries

Advanced batteries are critical to achieving net zero and are proposed within decarbonization strategies for transport and grid-scale applications, alongside their ubiquitous application in consumer devices. Immense progress has been made in lithium battery technology in recent years, but significant challenges remain and new development strategies are required to improve performance, fully exploit power density capacities, utilize sustainable resources, and lower production costs. Suitable characterization techniques are crucial for understanding, inter alia, three-dimensional (3D) diffusion processes and formation of passivation layers or dendrites, which can lead to drastic capacity reduction and potentially to hazardous short circuiting. Studies of such phenomena typically utilize 2D or 3D imaging techniques, providing locally resolved information. 3D X-ray imaging is a widely used standard method, while time-lapse (4D) tomography is increasingly required for understanding the processes and transformations in an operational battery. Neutron imaging overcomes some of the limitations of X-ray tomography for battery studies. Notably, the high visibility of neutrons for light-Z elements, in particular hydrogen and lithium, enables the direct observation of lithium diffusion, electrolyte consumption, and gas formation in lithium batteries. Neutron imaging as a non-destructive analytical tool has been steadily growing in many disciplines as a result of improvements to neutron detectors and imaging facilities, providing increasingly higher spatial and temporal resolutions. Further, ongoing developments in diffraction imaging for mapping the structural and microstructural properties of battery components make the use of neutrons increasingly attractive. Here, we provide an overview of neutron imaging techniques, generally outlining advances and limitations for studies on batteries and reviewing imaging studies of lithium batteries. We conclude with an outlook on development methods in the field and discuss their potential and significance for future battery research