Abstract
Electrochemical energy storage is essential in everyday life and is crucial for energy transition requiring sustainable energy sources and clean transportation. Li-ion batteries are widely used due to their high energy density while other technologies are now emerging, as Na-ion batteries, to offer a variety of energy storage systems. The electrode materials are one of the key components that should be improved for better battery performance. This requires the investigation of the electrochemical reactions that take place within the batteries. Mössbauer spectroscopy is a powerful tool to probe the local environment at the atomic scale in electrode materials. This technique can be used for ex situ analyses or to follow in situ the electrochemical reactions. In this chapter, some general aspects of currently commercialized Li-ion batteries are briefly described to introduce electrode materials, electrochemical mechanisms and their characterizations. The basic concepts of the Mössbauer effect and hyperfine interactions are presented to define the Mössbauer parameters that provide information about structural, electronic and magnetic properties, with a special attention to in situ measurements. Then, some selected examples of insertion, alloying and conversion materials are considered to illustrate the application of 57Fe and 119Sn Mössbauer spectroscopies to elucidate reaction mechanisms in Li-ion and Na-ion batteries.