Regulating Phase Transition and Restraining Fe Distortion at High Potential Window via Rare Earth Metal Incorporation on O3-Type Layered Cathodes

Rapid capacity fading and structural collapse, along with other deep-rooted challenges in the high-voltage region, are insufficient to meet the requirements for commercial applications of O3-type layered cathodes. Hereby, rare earth metal (RE) within the IIIB group are utilized as the robust dopants for O3-NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) to achieve the purpose of reconstructing the crystal lattice and regulating the interlayer structure. The inactive RE³⁺ acts as a pillar, reinforces the TMO₆ octahedron, and broadens the Na⁺ diffusion layer in the configuration of O-Na-O-TM (RE)-O-Na-O, giving rise to the enhanced crystal stability and accelerating the transmission of sodium ions. More impressively, the scandium incorporation is working as a “vitamin” that improves Ni/Fe redox reversibility, alleviating the irreversible P3-O3’-P3’ phase transformation and further restraining the disordered Fe migration into the neighboring Na layer, which is firmly validated by in situ X-ray diffraction coupled with the synchrotron X-ray absorption spectroscopy. Consequently, the as-designed NFM-Sc exhibits impressive rate capability (82.5 mAh g⁻¹ at 10 C) and excellent cycle stability with 80.2% capacity retention after 500 cycles at the high voltage of 4.2 V. Given this, the elaborate work may shed new insight into the operational mechanism of rare metal through strategically regulating the structure for sodium-ion batteries.