Cobalt-free LiNiO₂ (LNO) is considered a promising cathode for its high energy density and cost-effectiveness. However, its structural instability under deep delithiation severely limits practical application in next-generation batteries. Herein, we propose a high-valence Mo⁶⁺ doping strategy to simultaneously improve mechanical robustness and electrochemical stability. By stabilizing intergranular interfaces, this method effectively suppresses mechanical degradation induced by lattice strain under deep delithiation. The modified cathode exhibits exceptional electrochemical performance, achieving a specific capacity of 234 mAh·g⁻¹ at 0.1 C with 83.4% retention over 100 cycles at 45 °C in lithium-ion batteries (LIBs). Notably, it maintains comparable efficacy in all-solid-state batteries (ASSBs), delivering 239 mAh·g⁻¹ at 0.05 C and 82.8% retention after 300 cycles. Density functional theory (DFT) calculations demonstrate a pronounced rise in oxygen vacancy formation energy, increasing from 1.42 to 3.27 eV. These findings offer valuable insights into overcoming the kinetic performance limitations of cobalt-free LNO under deep delithiation conditions.