Regensburg 2025 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 22: Materials for the Storage and Conversion of Energy

MM 22.1: Talk

Wednesday, March 19, 2025, 15:45–16:00, H23

Understanding Stability of Ni-rich NMC cathodes using beyond DFT many-body calculatations — •Hrishit Banerjee^1,2,3,4, Clare Grey^2,4, and Andrew Morris^3,4 — ¹University of Dundee — ²University of Cambridge — ³University of Birmingham — ⁴The Faraday Institution

High energy density Ni-rich LiNi_aMn_bCo_cO₂ (NMC) cathodes undergo degradation in the form of O loss from the surface of NMC particles. O loss increases with Ni content and higher voltages. Our first-principles study examines the redox behavior of transition metals and O in NMC cathodes as a function of (de)lithiation. Despite Ni, Mn, and Co K-edges calculated using GW Approximation showing an excellent match with experimentally obtained XANES, we demonstrate that the ionic model of ascribing shifts in the XANES to changes in metal oxidation states is inappropriate. In these cases, which are characterised by strong covalency between the strongly correlated transition metal and oxygen, Dynamical Mean-Field Theory calculations are essential to calculate charges and hence assign oxidation states accurately. Due to a charge transfer from O p to Ni d, a ligand hole forms on O in Ni-rich regions. The individual Ni charge remains fairly constant throughout the charging/discharging process. In contrast, O has dual redox behavior, showing greater involvement in redox in Ni-rich regions while showing negligible redox involvement in Ni-poor regions. The dual behaviour of O in terms of participation in the redox process explains the overall higher relative stability of lower Ni content NMCs compared to Ni-rich NMCs or LiNiO₂ in terms of O loss.

Keywords: Li-ion battery; Cathodes; First principles calculations; Energy storage materials; Theory