Application of Noninvasive Imaging Techniques for High Energy Density Lithium Metal Rechargeable Batteries

Abstract Lithium metal batteries (LMBs) have the potential to exceed the energy density of current lithium‐ion batteries. Achieving this requires a thick positive electrode, a thin Li metal negative electrode, and minimal electrolyte‐loading. Despite their promise, high energy density LMBs with high‐loading positive electrodes, thin Li, and low electrolytes face significant challenges. A key issue is the high reactivity of Li metal with nonaqueous electrolytes, leading to the consumption of both during each cycle. This reaction causes insulating Li compounds to accumulate, increases electrode porosity and thickness, depletes the electrolyte, raises cell impedance, and reduces capacity. Therefore, understanding the interphase evolution of the Li metal electrode is crucial to addressing cell failure. While various ex situ and in situ techniques have been used to study these interphases, they often involve non‐practical cell configurations and sample‐damaging preparation processes. In this regard, noninvasive methods like X‐ray and neutron‐based imaging are beneficial as they do not damage samples, can be used both in situ and ex situ, employ practical cell configurations, and enable long‐term data collection. This review explores recent advancements in X‐ray and neutron‐based techniques for characterizing high‐energy LMBs, emphasizing their potential to improve understanding of interphasial dynamics and advance robust high‐energy‐density batteries.