Full Parametrisation and Newman Modelling of the Mixed Niobium Oxide - NMC System: Unveiling the Limiting Factor and Tackling Problems with Solid State Diffusion Parametrisation

Abstract

Over the last decade, Mixed Niobium Oxide (MNO) materials have been widely researched as new lithium-ion battery anode material[1]. Their MO3-x perovskite-like host structure enables faster lithium-ion transport than graphite with higher specific capacities than LTO, while it also has excellent cycle life and voltage window respectively. Recent DFT modelling and in-situ material studies have greatly improved understanding at the material level[2]. However, for full scale implementation, more holistic parametrisation and modelling is needed to further interpret MNO behaviour in full cells, to perform sensitivity analysis for increased life and rate performance, and to design NMC/MNO battery systems. Here, we present one of the first full parametrisations and physics-based Newman models of the NMC/MNO system based on experimental data. The main governing mechanisms in the model are illustrated in Fig. 1.In particular we focus on parametrisation and modelling of the particle size and solid-state lithium-ion diffusion coefficient. While these are shown to be crucial controlling factors in performance, there is considerable disagreement on definitions and measurement methods of the solid-state lithium-ion diffusion coefficient in literature. Values attained through DFT, PFG-NMR, GITT, EIS and Cyclic Voltammetry differ by orders of magnitude[3,4,5], and there is a knowledge gap between diffusion coefficients determined at the crystal level and at the cell level[6]. Literature on solid-state lithium-ion diffusion theory and measurement techniques is reviewed, and a better approach to parametrisation of solid-state lithium-ion diffusion is presented to improve cell modelling.The resulting model helps in a more complete understanding of the NMC/MNO system and provides insights in why the NMC/MNO cell has superior properties compared to other cell configurations. It reveals what processes control NMC/MNO cell performance parameters such as polarisation, and therefore directs further research. Finally, it is shown how the model can be used to design new battery applications.