Modulating the structure of O3-type NaNi1/3Fe1/3Mn1/3O2 for high-performance sodium-ion batteries via Na2MoO4 reactive wetting coating combined with Mo doping and interface reconstruction.

Abstract

O3-type NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) is considered as a promising cathode material for sodium-ion batteries (SIBs) due to its high theoretical energy density and low production cost. However, the applications of NFM are restricted owing to detrimental interfacial side reactions and phase evolution during cycling. Herein, a three-in-one modification strategy, including Na₂MoO₄ coating, surface reconstruction from layered to spinel phase, and Mo⁶⁺ doping, is proposed to design NFM. A uniform and tight Na₂MoO₄ coating layer formed via reactive wetting mechanism can effectively inhibit the unfavorable side reactions between cathode and electrolyte. The formation of nanoscale spinel layer can anchor the interior layered structure, leading to a decrease in volume change during the sodiation/desodiation process. The incorporation of Mo⁶⁺ with a high valence state and strong MoO bonds into the O3 phase promotes the expansion of transition-metal layer spacing and enhances the structural stability. As a result, tri-modified NFM exhibits superior cycling stability with a capacity retention of 85.20 % after 300 cycles at 100 mA g^-1 and rate performance with a discharge capacity of 56.9 mAh/g at 2000 mA g^-1, outperforming those of pristine NFM (61.76 % and 39.4 mAh/g). This synergistic modification approach provides a new avenue to improve the performance of layered-oxide cathode materials for SIBs.