Understanding of the degradation and aging mechanisms in Ni-rich NMC cathode material at the nanoscale

Abstract text (incl. figure legends and references)

Ni-rich NMC (Ni_xMn_yCo_1-x-yO₂ with x > 0.8) has been a promising candidate for cathode active materials (CAMs) in Li-ion batteries (LIBs) [1,2]. Reducing the Cobalt content in NMC cathodes leads to a more environment-friendly and affordable material. Also, the specific capacity of Ni-rich NMC is significantly increased compared to conventional NMC material. However, the cycle stability is reduced. To improve the lifetime of Ni-rich NMCs, it is important to gain a deeper understanding of the degradation and aging mechanisms appearing during material synthesis and cycling. Therefore, studies of the micro- and nanostructure are key for tailoring material properties specifically, for instance through doping or coating.

Modern focused-ion-beam (FIB) preparation allows cutting of extremely thin samples, enabling high-resolution imaging. Figure 1 shows a lamella of a polycrystalline Ni-rich NMC particle, which was prepared by FIB and a corresponding HRSTEM image of a layered structure. In addition to ex-situ experiments at the atomic scale, in-situ experiments play a key role in understanding degradation and aging mechanisms in LIBs [3,4]. By applying voltage or temperature more realistic scenarios can be represented. Therefore, we focus both on ex-situ and on in-situ setups (Figure 2).

Figure 1: Polycrystalline NMC particle prepared by FIB (a) and ex-situ study of the layered structure at the atomic scale (b).

Figure 2: Setup of a biasing in-situ experiment using NMC prepared using FIB.

[1] Chao Xu et al., Adv. Energy Mater. 2021, 11, 2003404.

[2] Yu Xia et al., Nano Energy, Volume 49, 2018, 434-452.

[3] Shibabrata Basak et al., ACS Appl. Energy Mater. 2020, 3, 6, 5101-5106.

[4] Shibabrata Basak et al., Chem. Commun., 2022, 58, 3130-3133.