The growing demand for energy storage necessitates significant improvements in current battery electrode materials, as well as the development of advanced electrode materials. To achieve this, it is essential to have a comprehensive understanding of the reaction processes, degradation mechanisms, and thermal decomposition mechanisms that occur under realistic operating conditions. This knowledge can be acquired through in situ and operando characterization techniques, which provide valuable insights into structural evolution, redox mechanisms, the formation of the solid-electrolyte interphase (SEI), side reactions, and lithium-ion transport properties during operation.