Exploration of materials electrochemistry in rechargeable batteries using advanced in situ/operando x-ray absorption spectroscopy

Rechargeable batteries (Li-ion batteries and beyond) have received extensive attention as powerful boosters for the development of human society. The rapid progress achieved in this research area largely relies on the in-depth efforts on the improvement of battery electrode materials and decrease of the cost. However, the application of rechargeable batteries is still hindered by low energy density, serious voltage hysteresis, and long-term degradation. Therefore, it is of great importance for understanding the underlying redox reaction and capacity fading mechanisms to circumvent these problems and improve the overall battery performance. Advanced characterization techniques, especially synchrotron-based x-ray absorption spectroscopy (XAS), have been widely applied to the mechanistic understanding of rechargeable batteries. Particularly, in situ/operando XAS allows the characterization of practical working mechanisms by measuring the electronic structure evolution of the electrode materials under real operation conditions, which is an imperative prerequisite for the further optimization of the battery performance. Herein, the recent progress in the understanding of the operating principles of several common rechargeable batteries (including lithium-ion batteries, sodium-ion batteries, and lithium-sulfur batteries) based on in situ/operando XAS technique is reviewed and summarized. We aim to provide a comprehensive treatise on in situ/operando characterization of rechargeable batteries using XAS, which could provide guidance for further improvement of battery performance.