Unraveling the Lithium Storage Mechanism at Low Potentials in Niobium Pentoxide Anodes for Lithium-Ion Batteries

Abstract

State-of-the-art lithium-ion anodes based on graphite exhibits high specific capacity and a low de-/lithiation potential, thus, enabling very high energy densities at full-cell level. However, the rather sluggish lithiation kinetics render them less suitable for fast-charging batteries[1]. A potential alternative that has gathered increasing interest in recent years is Nb2O5, but the commonly employed lower cut-off voltage of 1.0 V vs. Li+/Li in combination with the lower capacity compared to graphite limit the achievable energy density[2,3].Herein, the extended lithiation to lower cut-off voltages is reported, resulting in increased capacities while maintaining a very stable cycle life. Remarkably, this behavior is generally independent from the initial polymorph, and both monoclinic and orthorhombic Nb2O5 show a substantial increase in capacity for several hundred cycles. To elucidate the underlying storage mechanism, comprehensive characterization via operando/ex-situ X-ray diffraction (XRD), operando Raman spectroscopy, operando isothermal microcalorimetry (IMC), ex-situ X-ray absorption spectroscopy (XAS), and ex-situ X-ray photoelectron spectroscopy (XPS) was conducted. It appears that the occurrence of an additional phase transition at low potentials plays a decisive role for the enhanced capacity and superior cycling stability. Reference [1] J. Asenbauer, T. Eisenmann, M. Kuenzel, A. Kazzazi, Z. Chen, D. Bresser, Sustain. Energy Fuels 2020, 4, 5387–5416.[2] P. Jing, K. Liu, L. Soule, J. Wang, T. Li, B. Zhao, M. Liu, Nano Energy 2021, 89, 106398.[3] T. Li, G. Nam, K. Liu, J. H. Wang, B. Zhao, Y. Ding, L. Soule, M. Avdeev, Z. Luo, W. Zhang, T. Yuan, P. Jing, M. G. Kim, Y. Song, M. Liu, Energy Environ. Sci. 2022, 15, 254–264.