Multiscale modeling of oxygen loss and phase transformation in Ni-rich cathode materials: Impact of electrode microstructure

Abstract

Ni-rich cathode materials have gained increasing importance in current Li-ion battery development due to their high capacity. However, the stability of these materials has been shown to be a severe limitation when cycling to high cutoff voltages [1]. A layered-to-rocksalt transformation, accompanied by the loss of lattice oxygen, has been observed at the particle surface [1,2]. Previous work on this mechanism mainly focusses on experimental investigation, while a simulative approach can help to bridge the gap between theoretical insights and practical applicability in electrode manufacturing. In this contribution, we present a novel P2D modeling approach to describe oxygen release and phase reconstruction in Ni-rich cathode materials [3]. The model is informed by atomistic simulation results and coupled to 3D microstructure-resolved simulations conducted in the framework BEST [4]. While an indirect coupling between the P2D and 3D models allows us to study degradation over several cycles, we also present a fully-coupled phase reconstruction model on a real 3D electrode microstructure and discuss implications for the phase reconstruction process. Our work unravels the effect of electrode microstructure and individual electrode parameters on phase reconstruction and oxygen loss. By applying our modeling approach to a high-resolution FIB-SEM tomography of a commercial Ni-rich cathode [5], we further demonstrate how transport processes cause inhomogeneous phase reconstruction across the electrode. This results in a thicker rock-salt layer at cathode regions close to the separator, while a thinner reconstructed layer is present near the current collector. We will further discuss the impact of rocksalt formation on the particle scale, namely the impact of particle cracking and preferential degradation of individual crystal facets. By combining an efficient P2D approach with both atomistic insights as well as 3D microstructureresolved simulations, we are able to comprehensively study the effect of electrode architecture on performance and aging of Ni-rich cathode materials to improve future electrode design.

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