Multi‐Element Doping Regulation of the Disordered Phase Transition and Multi‐Step Phase Transition Suppression Effect in O3‐Type Sodium‐Ion Batteries

O3-type layered sodium-ion battery (SIB) cathode materials have attracted significant attention due to their high reversible capacity and abundant sodium storage sites. However, their complex phase transitions and significant volume changes during charge/discharge processes lead to unsatisfactory cycling performance. Herein, a Ti⁴⁺, Fe³⁺, and Al³⁺ co-doped O3-type NaNi_0.5Mn_0.5O₂ cathode (NaNi_0.40Mn_0.40Ti_0.13Fe_0.06Al_0.01O₂, NaNMTFA) is reported that effectively suppresses complex multi-step phase transitions and enables solid-solution reactions over a wide voltage range. Theoretical and experimental results confirm that the Ti⁴⁺-Fe³⁺-Al³⁺ ternary doping enhances structural stability of the NaNMTFA cathode by mitigating lattice distortions to inhibit phase transitions, compensating shielding effect attenuation during sodium de/intercalation, and strengthening electrostatic interactions within transition metal layers. Consequently, the NaNMTFA cathode delivers 125.1 mAh g^-1 at 0.1C and maintains 103.4 mAh g^-1 at 1C with 82.2% capacity retention over 200 cycles. Notably, the 3D-printed NaNMTFA||HC full-cell with a cathode areal loading of 5.42 mg cm^-2 delivers 118.7 mAh g^-1 at 1C with 88.9% capacity retention after 100 cycles, outperforming conventional coated electrodes. This study elucidates the modulation mechanism of elemental doping on interlayer forces and phase transitions, and establishes 3D printing as a novel method for optimizing high-performance O3-type SIB cathodes.