O3-type NaNi_1/3Fe_1/3Mn_1/3O₂ layered oxide is a low-cost, high-capacity cathode material for sodium-ion batteries, yet its practical deployment is hindered by sluggish sodium-ion transport and irreversible structural transformation during cycling. Herein, trace Ti⁴⁺ ions are introduced into transition-metal sites through solid-state sintering to enhance structural robustness. Possessing an ionic radius close to those of Ni²⁺, Fe³⁺ and Mn³⁺, Ti⁴⁺ readily occupies transition-metal lattice positions. Strong Ti–O covalent bonds rigidify the transition-metal layer framework and subtly alter local crystal geometry, which in turn widens interlayer channels for sodium-ion diffusion. Such structural modification accelerates Na⁺ insertion/extraction kinetics and alleviates electrochemical polarization. At a doping level of 7500 ppm, the NaNi_1/3Fe_1/3Mn_1/3O₂ material delivers a reversible specific capacity of 155.68 mAh g⁻¹ at 0.1 C, and retains 111.43 mAh g⁻¹ at 2 C. The capacity retention reaches 80.5% after 100 cycles at 0.5 C, and remains at 65.1% after 300 cycles at 2 C. This work clarifies how Ti⁴⁺ doping stabilizes layered lattices and offers a straightforward route to improve the electrochemical performance of layered oxide cathodes.