Li/Ti Dual-Doping Synergy Enabling Stable High-Voltage O3-Type Layered Oxide Sodium-Ion Batteries Cathode

O3-type layered oxides are key materials for achieving high-energy-density sodium-ion batteries (SIBs). However, their irreversible phase transitions, oxygen loss, and interface degradation at high voltages (>4.0 V) lead to rapid capacity fading. In this work, using O3-Na_0.9Ni_0.22Fe_0.3Mn_0.48O₂ (NFM) as the base material, a stable structural framework and efficient ion channels were constructed through a Li⁺/Ti⁴⁺ dual-doping strategy. The dual-doped Na_0.9Ni_0.22Li_0.1Fe_0.2Ti_0.1Mn_0.38O₂ (NLFTM) material exhibited significantly improved specific capacity and rate performance in the voltage range of 2.0-4.3 V. It delivered a reversible capacity of 180.7 mAh/g at 0.1 C and maintained a capacity of 91.1 mAh/g even at a high rate of 10 C. Furthermore, after 100 cycles at 1 C, NLFTM retained 83% of its capacity, markedly outperforming the pristine NFM (56.6%). Ex situ XRD results confirmed that dual-doping enhanced the reversibility of the O3↔P3 phase transition during charge/discharge, thereby ensuring structural stability during high-voltage cycling. XPS analysis revealed that the dual-doping strategy successfully inhibited irreversible oxygen loss, breaking the detrimental cycle of "oxygen release-structural collapse-capacity decay" at high voltage. The EIS, GITT, and CV test results demonstrated that the synergistic effect of dual-doping effectively enhanced charge transfer and improved Na⁺ diffusion kinetics.