Zr Incorporation Into Lithium Nickel Oxides: Bulk or Surface Substitution?

ABSTRACT

High‐capacity lithium nickel oxides (LNO) are promising cathode active materials for next‐generation batteries. However, their practical application is limited by poor cycling stability. Doping the LNO cathode with high‐valence elements is an effective strategy to enhance structural stability. In this study, we investigate the mechanism of Zr ⁴⁺ incorporation into LNO using experimental and theoretical techniques. Our findings reveal that under oxygen‐rich conditions, Zr‐doped LNO can be realized as a single phase, but most Zr cations localize at the surface of primary particles. In contrast, under oxygen‐deficient or non‐equilibrium conditions a secondary layered Li _1‐x Ni _1+x O ₂ phase, characterized by Ni migration into the Li layers (cation ordering), is stabilized coexisting with Zr‐doped LNO. This promotes elongation of primary particles at the aggregation surface. The Zr enrichment at the microparticle surface, Zr‐induced cation‐ordered superstructure, and the formation of elongated grains enhance the chemical stability as well as the structural integrity at atomistic‐ and micro‐scale of the LNO cathode, improving its cycling performance. However, only 1–3% Zr is necessary to maintain the initial capacity and enhance cyclability through surface coating and low bulk doping with Zr. With increasing Zr concentration, an electronically insulating impurity (Li ₂ ZrO ₃ ) forms, leading to a decrease in the initial capacity.