Antisite-Driven Self-Pillaring as a Design Strategy for High-Voltage P2-Type Na-Ion Cathodes: Zr-Doped P2-Na0.84Zr x Ni0.37– x Mn0.63O2

Sodium-ion batteries are very promising for sustainable large-scale energy storage. Among various cathode materials, Mn-based P2-type layered oxides emerged for their high theoretical capacity and fast sodium-ion diffusion pathways, but the detrimental P2-O2 phase transition at high voltage limits their cycle life and energy density. Here, we address this challenge with a design strategy based on Zr substitution in P2-Na0.84Ni0.37Mn0.63O2. To this end, we exploit an integrated experimental and theoretical approach with electrochemical measurements, ex situ X-ray diffraction, and first-principles DFT+U calculations. Zr substitution delays the experimentally observed onset of the P2-O2 transition from approximately 3.7 V in the undoped material to 4.0 and 4.1 V for the 3 and 6% Zr compositions, respectively. At deep desodiation, calculations identify a strong thermodynamic preference for Zr/Na-vacancy antisite formation relative to Ni and Mn antisites. In the resulting tetrahedral coordination, Zr bridges adjacent transition-metal slabs, providing an atomic-scale self-pillaring motif that can hinder layer gliding. Overall, the 3% Zr cathode exhibits the best capacity retention among the investigated compositions during cycling between 2.0 and 4.1 V. These findings connect dopant-dependent defect energetics with electrochemical and structural signatures and provide a mechanistic framework for controlling high-voltage phase transformations in layered sodium-ion cathodes.