Solid-State Nuclear Magnetic Resonance Studies of Lithium and Sodium Metal Batteries

Lithium/sodium metal batteries have become a pivotal focus in the field of rechargeable batteries due to their potential to offer the highest specific capacity and lowest operating voltage. However, this high energy density brings significant instability between the lithium/sodium metal anode and the electrolyte. This instability can lead to uneven lithium/sodium deposits, known as dendrites or mossy type deposits, and uncontrolled formation of solid electrolyte interphases (SEIs), which further impede the ionic transport of working ions at the interface. Understanding the origins of morphological evolution, side reactions, and ion transport at the alkali metal/electrolyte interface is crucial for improving the cycle life of lithium/sodium metal batteries. Solid-state NMR, with its ability to provide detailed information about the chemistry, morphology, and ionic dynamics, is becoming an indispensable technique for studying metal anodes. In this review, we first introduce the basics of NMR in studying metal anodes and then select specific examples to illustrate how various NMR methods, including multinuclear magic angle spinning (MAS) NMR, electrochemical in situ NMR, and NMR dynamics methods, provide unique insights into the chemical composition of SEIs, deposit morphological evolution, and ionic dynamics at the lithium metal/electrolyte interface.