<p>Ultra-high Ni layered cathodes are considered leading candidates for next-generation lithium-ion batteries due to their high energy density. However, their practical application is hindered by structural instability, rapid capacity degradation, and sluggish lithium-ion kinetics. To overcome these challenges, a synergistic modification strategy combining gradient Nb doping with <i>in situ</i> formation of a LiNbO₃ surface layer is proposed. The radially distributed Nb dopant effectively mitigates internal lattice strain and suppresses the formation of microcracks, while the LiNbO₃ coating enhances interfacial stability and facilitates Li-ion transport. As a result, the optimized sample (0.5%Nb-NCM) delivers a high specific capacity of 222.2 mAh·g⁻¹ at 0.1C, retains 94.7% of its capacity after 200 cycles at 1C, and achieves 147.7 mAh·g⁻¹ at an ultra-high rate of 20C. This work highlights the effectiveness of combining compositional and interfacial engineering to develop structurally robust and electrochemically stable ultrahigh-Ni cathodes for advanced Li-ion battery applications.</p> Graphical abstract <p></p>