The application of synchrotron X-ray techniques to the study of rechargeable batteries

The increased use of rechargeable batteries in portable electronic devices and the continuous development of novel applications (e.g. transportation and large scale energy storage), have raised a strong demand for high performance batteries with increased energy density, cycle and calendar life, safety and lower costs. This triggers significant efforts to reveal the fundamental mechanism determining battery performance with the use of advanced analytical techniques. However, the inherently complex characteristics of battery systems make the mechanism analysis sophisticated and difficult. Synchrotron radiation is an advanced collimated light source with high intensity and tunable energies. It has particular advantages in electronic structure and geometric structure (both the short-range and long-range structure) analysis of materials on different length and time scales. In the past decades, synchrotron X-ray techniques have been widely used to understand the fundamental mechanism and guide the technological optimization of batteries. In particular, in situ and operando techniques with high spatial and temporal resolution, enable the nondestructive, real time dynamic investigation of the electrochemical reaction, and lead to significant deep insights into the battery operation mechanism. This review gives a brief introduction of the application of synchrotron X-ray techniques to the investigation of battery systems. The five widely implicated techniques, including X-ray diffraction (XRD), Pair Distribution Function (PDF), Hard and Soft X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) will be reviewed, with the emphasis on their in situ studies of battery systems during cycling.