Revisiting doping strategies: The critical role of dopant-host interplay in cobalt-free, high-nickel cathode materials

Abstract

Cobalt-free, high-nickel (Ni-rich) layered oxides are promising cathode materials for next-generation lithium-ion batteries, offering high specific capacity while circumventing the economic and ethical issues associated with cobalt. However, the inherent structural and interfacial instabilities of Ni-rich compositions present significant challenges. While doping is a widely adopted strategy to enhance cathode stability, previous studies have predominantly focused on the intrinsic physicochemical properties of the dopants themselves. In contrast, this study reveals that the efficacy of a dopant is critically dependent on the specific composition of the host cathode materials, a factor that becomes particularly pronounced in Co-free, Ni-rich systems. To systematically investigate this compositional dependence, we introduced four common dopants-Al, B, Mg, and Ti-into a Co-free, Nirich layered oxide. Our findings indicate that the stabilizing effects of Al, B, and Mg were diminished due to a functional overlap with the role of manganese (Mn) already present in the host material. Conversely, titanium (Ti) provided a complementary stabilizing function that Mn could not, leading to a significant enhancement in overall performance. Specifically, the Ti-doped cathode material demonstrated superior capacity retention over long-term cycling and effectively suppressed detrimental phenomena such as impedance growth and microcrack formation. This work highlights that the interplay between the dopant and the host material's existing elements is a key design parameter, providing a new, more holistic perspective for developing next-generation, highperformance cathodes.