Decoupling Substitution Effects from Point Defects in Layered Ni‐Rich Oxide Cathode Materials for Lithium‐Ion Batteries

• Published in: Advanced functional materials 2024-10, Vol.34 (41), p.n/a
• Main Authors: Karger, Leonhard, Korneychuk, Svetlana, Sicolo, Sabrina, Li, Hang, van den Bergh, Wessel, Zhang, Ruizhuo, Indris, Sylvio, Kondrakov, Aleksandr, Janek, Jürgen, Brezesinski, Torsten
• Format: Article
• Language: English
• Subjects: Cathodes; Charge materials; Cobalt; Decoupling; Density functional theory; Electrode materials; first‐cycle capacity loss; Ion exchange; Lithium; Lithium-ion batteries; Manganese; Materials substitution; Nickel; Ni‐rich cathode; Point defects
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202402444

Ni‐rich LiNixCoyMnzO2 cathode materials offer high practical capacities and good rate capability, but are notorious for being unstable at high state of charge. Here, a series of such layered oxides with nickel contents ranging from 88 to 100 mol% is fabricated by sodium‐to‐lithium ion exchange, yielding materials devoid of NiLi•${\mathrm{Ni}}_{{\mathrm{Li}}}^ \bullet $ substitutional defects. Examining the initial charge/discharge cycle reveals effects that are specifically caused by transition‐metal substitution, which would otherwise be obscured by changes in lithium‐site defect concentration. Lowering the nickel content helps to stabilize the high‐voltage regime, while simultaneously negatively affecting lithium diffusion. Operando X‐ray diffraction indicates mitigation of volume variation during cycling and transition toward solid‐solution behavior with sufficiently high cobalt and manganese contents, thus providing an explanation for the increased stability. The interplay between transition‐metal substitution, kinetic hindrance, and solid‐solution behavior may be a result of local inhomogeneities due to lithium‐vacancy pinning, which is further elucidated through density functional theory calculations. Overall, this work sheds new light on the effects of manganese and cobalt incorporation into the transition‐metal layer and their conjunction with NiLi•${\mathrm{Ni}}_{{\mathrm{Li}}}^ \bullet $ defects. Nickel substitution strongly impacts the electrochemistry of layered Ni‐rich oxide cathode materials. In particular, changes in composition alter the defect concentration, rendering substitution‐based structure‐property relationships ambiguous. In this work, the nickel content is varied while maintaining defect‐free character, thus allowing for selective study of substitution effects.