MXene-enabled chemomechanical interface toward stable high-voltage O3-type cathodes for sodium-ion batteries

The increasing demand for grid-scale energy storage has intensified the pursuit of cost-effective sodium-ion batteries. O3-type layered sodium cathode materials, such as NaNi_1/3Fe_1/3Mn_1/3O₂, offer high theoretical capacities but suffer from severe structural degradation during deep sodiation/desodiation at high-voltage. This degradation stems from anisotropic volume changes and continuous cathode-electrolyte interphase deterioration. Here, we show that a conformal MXene buffering layer constructed on the cathode surface simultaneously mitigates lattice strain accumulation and passivates the interphase. In situ XRD reveals that the MXene layer promotes highly reversible lattice restoration during cycling, while distribution of relaxation times analysis shows effective suppression of the solid-phase diffusion resistance surge at deep discharge states. Density functional theory calculations further demonstrate that the MXene layer weakens the adsorption of reactive PF₅ byproducts from -0.46 eV to -0.26 eV, thereby suppressing electrolyte decomposition. Consequently, the cathode delivers remarkable high-voltage cyclability, retaining 60% capacity after 300 cycles at 1C with a 4.2 V cutoff, far exceeding the 13% retention of the bare counterpart. This work provides an effective chemomechanical interface to enhance the structural and interfacial stability of high-voltage O3-type cathodes for advanced sodium-ion batteries.