Dual Role of Niobium(V) for Stabilizing High-Nickel Cathode Active Materials: Microstructural Control and Doping

High-nickel layered oxides are the leading commercial cathode candidates for lithium-ion batteries, yet their widespread deployment remains constrained by limited cycling stability. Niobium (Nb) coating/doping has emerged as an effective mitigation strategy, but current approaches typically rely on wet-chemical or gas-phase routes that are difficult to scale. Herein, we report a dry process that achieves homogeneous Nb⁵⁺ doping into Li₁Ni_0.83Mn_0.05Co_0.12O₂ by treating the precursor with ultrafine Nb₂O₅ nanoparticles synthesized via flame spray pyrolysis. With only 0.5 mol.% Nb⁵⁺, the doped material exhibits improved lattice ordering and refined particle architecture, delivering high capacity up to 211 mAh g^-1, exceptional capacity retention 97% after 100 cycles in half cell, and markedly improved rate capability (170 mAh g^-1 at 5C) and long-term cyclability (83% over 500 cycles at 1C) in full cells. Multiscale structural and chemical analyses reveal the crucial role of ultrafine Nb⁵⁺ addition at the precursor stage in modifying the grain morphology, which ends in homogeneous doping providing mitigation of intergranular cracking and suppression of surface rock-salt reconstruction, thereby preserving coherent grain boundaries under extended cycling. This work highlights the mechanistic effectiveness of homogeneous Nb⁵⁺ doping via dry process in microstructural control and stabilization of high-nickel cathodes.