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

A rational compositional design is critical for utilizing LiNiO2-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., LiNi0.95Co0.05O2, LiNi0.95Mn0.05O2, and LiNi0.95Al0.05O2, along with undoped LiNiO2 (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.