Understanding Challenges of Cathode Materials for Sodium‐Ion Batteries using Synchrotron‐Based X‐Ray Absorption Spectroscopy

Abstract An in‐depth understanding of the electrochemical behavior of cathode materials in a complex chemical environment is critical for the development of state‐of‐the‐art sodium‐ion batteries. Advanced synchrotron‐based characterization is a powerful tool for collecting valuable information on complicated reaction mechanisms. X‐ray absorption spectroscopy can be used to precisely monitor the valence state and corresponding changes during cycling of various elements. Information on the local structure, such as coordination number and bond information can also be extracted from the fitting data in Fourier transform extended X‐ray absorption fine structure. In this review, we summarize findings on state‐of‐the‐art cathode materials using ex‐situ/in‐situ X‐ray absorption spectroscopy to probe fundamental discoveries on sodium‐ion battery systems and what important and valuable results have been obtained. Further possible improvements and practical operating advice are also discussed in detail.