<i>In Situ</i>/<i>Operando</i> Spectroscopic Techniques for Nonaqueous Lithium-Based Batteries

Nonaqueous lithium-based batteries have become a dominating stream of modern energy storage systems. Understanding the physicochemical processes and mechanisms of the electrode evolution and interfacial reactions in lithium batteries is highly desired to further improve their capabilities. Compared with ex situ testing techniques, in situ/operando spectroscopic techniques are of significant importance in battery research because they can provide more dynamic and transient information under working conditions. Herein, in this review we systematically introduce various in situ/operando spectroscopic techniques for the research and development of nonaqueous Li batteries, including infrared (IR) spectroscopy, Raman scattering (Raman) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, sum frequency generation vibrational spectroscopy (SFG-VS) and X-ray absorption spectroscopy (XAS). The recent advances of these techniques, especially their applications in studying electrode materials and electrode–electrolyte interphases, have been comprehensively summarized. Finally, we propose future potential applications of these spectroscopic techniques for battery research.