Neutron-based characterization: A rising star in illuminating rechargeable lithium metal batteries

Lithium metals are considered to be the proverbial "holy grail" for lithium batteries. The integration of high-energy cathodes, such as sulfur or oxygen cathodes, enables the fabrication of high-energy storage devices. Nevertheless, energy storage systems based on lithium metals face a number of complex challenges, including matrix and interface concerns. State-of-the-art characterization techniques are prerequisites for solving present-day challenges. In contrast to electrons, protons or X-rays, neutrons exhibit a unique advantage of high penetration due to their electrical neutrality. This characteristic will have irreplaceable advantages in the operando characterization of high-energy storage devices that undergo gradual increases in volume or mass. More importantly, the nuclear scattering characteristics of neutrons interacting with matter make them more sensitive to lithium elements compared to X-rays. Therefore, neutron-based characterization may be a powerful tool in resolving current problems associated with lithium metal batteries. In this review, neutron techniques (including neutron diffraction, quasi-elastic neutron scattering, small angle neutron scattering, neutron reflectometry, neutron imaging and neutron depth profiling) are categorized and their applications in anodes, cathodes, electrolytes and electrochemical interfaces of lithium metal batteries are summarized, respectively. The potential application of neutron techniques in lithium metal battery components is prospected. The perspectives elucidated in this article may serve as a methodical manual for resolving the present challenges associated with lithium metal-based batteries and as inspiration for applying them to other high energy storage devices.