Revisiting high-valence dopant mechanisms in Ni-rich cathodes: cation ordering dominates over morphological alignment for enhanced stability

Abstract

Layered ultra-high-nickel oxides are promising cathodes for high-energy-density lithium-ion batteries but suffer from severe structural degradation. Although high-valence doping is widely employed to enhance stability, the underlying mechanism—whether dominated by morphological alignment or cation ordering—remains contested. Through systematic investigation of W⁶⁺-doped LiNi_0.92Co_0.04Mn_0.04O₂ across varied doping concentrations and sintering temperatures, this work demonstrates that cation ordering, rather than morphological alignment, plays the decisive role in electrochemical enhancement. Although W-doping refines primary particles and sustains a radial microstructure even under extreme sintering conditions (up to 850 °C), correlation analysis reveals that cycling stability and specific capacity depend strongly on the suppression of Li⁺/Ni²⁺ cation mixing, while showing only weak correlation with grain morphology. The 0.75 mol% W doped cathode calcined at 800 °C delivered a high specific capacity of 244.3 mAh g⁻¹ and exceptional long-term cyclability, retaining 91.53% capacity after 1000 cycles in full cells. These findings clarify that high-valence dopants enhance performance primarily via lattice stabilization through cation ordering and highlight the necessity of co-optimizing doping content with synthesis temperature. This work revises the conventional understanding of high-valence doping mechanisms by establishing cation ordering as the primary factor for stability, providing a generalizable principle for designing next-generation ultra-high-nickel cathodes.