Since the development of batteries for energy storage, the search for new materials that allow high energy densities and fast intercalation kinetics is more important than ever. With a high specific capacity of 372 mAh g−1 graphite is a well-established anode material used for lithium-ion batteries[1]. However, batteries with graphite anodes undergo irreversible capacity loss during their first cycles. TiO2-based anode materials could be a promising alternative, especially due to their comparably high theoretical specific capacity of 335 mAh g−1 combined with their high cycling stability[2]. Core-shell particles consisting of titanium oxide coated with carbon are expected to show further improved cycling stability together with enhanced lithium absorption. It is proposed, that expanding the interlayer spacing of graphitic carbon will have further advantages, such as better intercalation kinetics, and widen the application scenario to sodium-ion batteries[3]. In the presented work, core-shell C-TiO2 nanoparticles with controlled layer spacing have been synthesized using acetylene/nitrogen decomposition. We focused on the correlation between process parameters and material properties. The C-TiO2 core-shell nanoparticles were characterized by TEM, XPS and Raman spectroscopy.

We found an alteration of the interlayer distance from 0.42 ±0.05 nm for the lowest treatment temperature to an interlayer spacing of 0.38 ±0.03 nm for the highest treatment temperature. During depth profiling in XPS measurements, we observed Ti3+/Ti2+ species in all investigated samples because of the transition of Ti4+ to reduced species during Ar+ ion bombardment. However, it is noteworthy to mention that XPS measurements comparing pure TiO2 and C-TiO2 have revealed an influence of the carbon shell on the conversion of Ti4+ to reduced Ti3+/Ti2+ species. Furthermore, TEM images have shown a graphitic shell constructed from structural building blocks rather than continuous graphene layers. This observation was supported by Raman spectroscopy as well as by the presence of a defective non-sp2 carbon peak as part of the C 1s XPS spectra. The results provide a deeper understanding of C-TiO2 core-shell particles fabricated via a comparably simple method and open an effective path for controlling the interlayer spacing of graphitic carbon.

References

[1] D. Deng, Energy Science & Engineering 2015, 3, 385.

[2] S. Paul, Md. A. Rahman, S. B. Sharif, J.-H. Kim, S.-E.-T. Siddiqui, Md. A. M. Hossain, Nanomaterials 2022, 12, 2034.

[3] Y. Wen, K. He, Y. Zhu, F. Han, Y. Xu, I. Matsuda, Y. Ishii, J. Cumings, C. Wang, Nat Commun 2014, 5, 4033.