A synergistic Li/Zr co-doping: An effective lattice modulation strategy for stable O3-type sodium-ion battery...

O3-type NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) is an attractive cathode for sodium-ion batteries due to its high specific capacity and cost-effectiveness. But the sluggish kinetics and structural degradation limit its practical application. Herein, a synergistic strategy combining targeted lattice modulation with local electronic reconstruction is presented. By introducing Li⁺ and Zr⁴⁺ into the transition-metal layer, ionic LiO bonding helps maintain local charge environment, while ZrO bonding with strong covalent character reinforces the layered framework. This dual stabilization enhances lattice‑oxygen stability, which in turn broadens Na⁺ diffusion channels and suppresses Jahn-Teller distortion, yielding a stabilized O3-type Na(Ni_1/3Fe_1/3Mn_1/3)_0.985Li_0.005Zr_0.01O₂ (NFMLZ) layered structure. As a result, NFMLZ//Na cells (133.8 mAh g^-1, 0.1C) achieve 87.3% capacity retention after 300 cycles at 1C, far surpassing the 49.9% retention of the NFM//Na cell (140.6 mAh g^-1, 0.1C), and deliver 100.4 mAh g^-1 at 10C. NFMLZ//hard carbon full cells exhibit 81.9% capacity retention after 200 cycles at 1C. Combined experimental and computational analyses reveal that the LiZr synergy in NFMLZ effectively mitigates intergranular cracking, enhances Na⁺ diffusivity, reduces charge-transfer resistance, suppresses irreversible high-voltage phase transitions with diminished (003) peak shift, and ensures superior structural reversibility. This synergy also elevates the oxygen vacancy formation energy and Ni²⁺ migration barrier, thereby anchoring the lattice oxygen and stabilizing the structure, while simultaneously facilitating Na⁺ transport through a lowered diffusion barrier. This work elucidates a synergistic lattice modulation mechanism, providing a design pathway for high-performance layered oxide cathodes of sodium-ion batteries.