Categorizing The Evolution Routes for Medium‐ and High‐Nickel Layered Oxide Cathodes

ABSTRACT The pursuit of high energy density in Ni‐based layered oxide lithium‐ion cathodes follows two primary routes: raising Ni content and elevating the upper cut‐off voltage. However, both routes can to some extent compromise bulk structural robustness and interfacial stability. Herein, we compare LiNi 0.6 Co 0.2 Mn 0.2 O 2 (N6, medium‐Ni) and LiNi 0.9 Co 0.05 Mn 0.05 O 2 (N9, high‐Ni) in a mechanism analysis at the same states of charge but with different cut‐off voltages. N9 cycled in a medium‐voltage window exhibits pronounced initial capacity loss, which is attributed to an intrinsic O3 to O1 phase transition that causes severe degradation of both the bulk structure and primary grain boundary. By contrast, N6 cycled in a high‐voltage window largely avoids severe slab gilding and phase evolution ascribed to the established zig‐zag arrangement of the transition‐metal (TM) layer, but suffers accelerated electrolyte oxidation, gaseous by‐products evolution, TM ions dissolution, and cathode electrolyte interphase (CEI) destabilization. After delineating these structural vs. interfacial tradeoffs for LiNi x Co y Mn (1‐x‐y) O 2 cathodes with different Ni contents, we find that lattice engineering (e.g., targeted doping and single‐crystallization) is most promising for high‐Ni cathode, while electrolyte engineering (e.g., LiDFOB and/or Si‐based additives) is an effective strategy for medium‐Ni candidates.