In Situ Electrochemical Transmission Electron Microscopy for Sodium-Ion Batteries

Sodium-ion batteries(SIBs)possess promising application prospects for large-scale energy storage systems due to the abundance of sodium ions as a resource and their low cost.Development of advanced SIBs requires a clear understanding of the structures and kinetic/dynamic processes occurring in the cells during the charging/discharging process.In situ transmission electron microscopy(TEM)is a powerful tool for direct visualization of the phase transitions as well as morphological and structural evolutions of the electrodes during the electrochemical reaction process.Herein,we summarize the state-of-the-art in situ TEM studies on SIBs with a specific focus on real-time observations of the electrochemical behavior of battery materials.This review emphasizes the necessity of in situ TEM to elucidate fundamental issues regarding the reaction mechanism,phase transformation,structural evolution,and performance degradation of SIBs.Finally,critical challenges and emerging opportunities for in situ TEM research about SIBs are discussed.