Advanced in-situ characterizations of nanocomposite electrodes for sodium-ion batteries – A short review

Owing to low cost and natural abundance of sodium reserves, sodium-ion batteries (SIBs) are attracting increasing attention and become promising alternatives to lithium ion batteries (LIBs). Based on merits of high structure stability and superb conductivity, nanocomposites have been widely investigated for SIB electrodes. However, SIBs still face some significant issues like serious side reactions, low energy density, and poor cycling life. Further improvement of the electrochemical performance needs definitely a deep understanding of structural and kinetic process occurred in these nanocomposite electrodes during charging/discharging processes. Recently, a diversity of in-situ techniques has emerged to investigate the inner phenomena occurred. In this short review, we summarize the state-of-the-art in-situ techniques, including in-situ transmission electron microscopy (TEM), in-situ X-ray diffraction (XRD), in-situ X-ray absorption spectroscopy (XAS), and in-situ Raman spectroscopy, applied to the characterization of morphological evolutions, mechanical/chemical changes, and phase transitions of these nanocomposite electrodes during electrochemical sodiation/de-sodiation processes. Finally, we also discuss limitations and future opportunities of in-situ technologies in nanocomposite materials for SIBs. The review aims at better understanding of these in-situ techniques for researchers in the society of SIBs, and is expected to provide guidance of nanocomposites for other fields.