Assessing the Intrinsic Roles of Key Dopant Elements in High‐Nickel Layered Oxide Cathodes in Lithium‐Based Batteries

Abstract A rational compositional design is critical for utilizing LiNiO 2 ‐based cathodes with Ni contents > 90% as promising next‐generation cathode materials. Unfortunately, the lack of a fundamental understanding of the intrinsic roles of key elements, such as cobalt, manganese, and aluminum, makes the rational compositional design of high‐Ni cathodes with a limited range of dopants (<10%) particularly challenging. Here, with 5% single‐element doped cathodes, viz., LiNi 0.95 Co 0.05 O 2 , LiNi 0.95 Mn 0.05 O 2 , and LiNi 0.95 Al 0.05 O 2 , along with undoped LiNiO 2 (LNO), the influences of the dopants are systematically examined through a control of cutoff charge energy density and a common practice of cutoff charge voltage. Comprehensive investigations into the electrochemical properties, combined with in‐depth analyses of the structural and interfasial stabilities and electrolyte decomposition pathways through advanced characterizations, unveil the following: i) the intrinsic role of dopants regulates the cathode energy density or state‐of‐charge and, more critically, the occurrence of H2–H3 phase transition, which essentially dictates cyclability; ii) undoped LNO can be stabilized well with the avoidance of H2–H3 phase transition; and iii) Co provides more merits overall with an optimized electrochemical operating condition. This work provides guidance for the compositional design of high‐energy‐density high‐Ni cathodes and sheds light on the challenges of removing Co.