In-Situ Raman Spectroscopy of Li+ and Na+ Storage in Anodic Nanotubes

Abstract

Anodizing is a high-voltage electrochemical conversion process that forms barrier-type oxide layers or self-organized nanoporous/nanotubular structures. So far, the Al2O3-like nanopores and TiO2-like nanotubes could be successfully synthesized on many valve metals and alloys.Recently, it become possible to form nanotubular structures on iron and consequently control the ratio of hematite (Fe2O3) to magnetite (Fe3O4) by subsequent thermal treatment.1 Electrochemically active nanotubes, such as self-organized TiO2 are of high interest in the battery field due to a unique one-dimensional (1D) geometry offering high volume expansion tolerance and applications without binders and conductive additives. Herein, we report an in - situ Raman spectroscopy study under current control for a better fundamental understanding of Li+/Na+ storage in nanotubes and correlate the structural fingerprints with the electrochemical data on differential capacity plots of d(Q–Q 0) dE –1.2 Real-time measurements revealed that the nanotubes had undergone two major phase transformations with increasing lithium content, disclosing the sequential steps of a lithium intercalation type of storage. In contrast, sodium-ion insertion induced no significant crystal structure modification but instead a slight crystallinity rupture, signifying a dominant nondiffusion-limited capacitive type of storage. The insight into the charge storage in a 1D material in relation to other nanostructures such as nanoparticles3 will be discussed.1. L. Fadillah, D. Kowalski, M. Vincent, C. Zhu, S. Kitano, Y. Aoki and H. Habazaki, ACS Applied Materials & Interfaces , 2023, 15, 52563-52570.2. M. Vincent and D. Kowalski, ACS Applied Nano Materials , 2023, 6, 6528-6537.3. M. Vincent, S. S. Kumar and D. Kowalski, Electrochimica Acta , 2023, 469, 143161. Figure 1