Mitigating Jahn–Teller Effect in Layered Cathode Material Via Interstitial Doping for High-Performance Sodium-Ion Batteries

Layered transition metal oxides are promising cathode materials for sodium-ion batteries due to their high energy density and appropriate operating potential. However, the poor structural stability is a major drawback to their widespread application. To address this issue, B³⁺ is successfully introduced into the tetrahedral site of Na_0.67Fe_0.5Mn_0.5O₂, demonstrating the effectiveness of small-radius ion doping in improving electrochemical performance. The obtained Na_0.67Fe_0.5Mn_0.5B_0.04O₂ exhibits excellent cycling performance with 88.8% capacity retention after 100 cycles at 1 C and prominent rate performance. The structure-property relationship is constructed subsequently by neutron powder diffraction, in situ X-ray diffraction and X-ray absorption spectroscopy, which reveal that the Jahn–Teller distortion and the consequent P2-P2' phase transformation are effectively mitigated because of the occupancy of B³⁺ at the interstitial site. Furthermore, it is found that the transition metal layers are stabilized and the transition metal dissolution are suppressed, resulting in excellent cycling performance. Besides, the prominent rate performance is attributed to the enhanced diffusion kinetics associated with the rearrangement of Na⁺. This work provides novel insight into the action mechanism of interstitial site doping and demonstrates a universal approach to improve the electrochemical properties of P2-type manganese-based sodium cathode materials.