Synergistically Boosted Na⁺ Migration and Deep Desodiation Stability of NASICON Cathode via High Entropy Regulation

Mn-containing sodium superionic conductor (NASICON) compounds have shown considerable potential as cathode for sodium-ion batteries (SIBs) owing to higher working voltage (V⁵⁺/V⁴⁺: 3.9 V), lower cost, and lower toxicity compared to full vanadium-based NASICON Na₃V₂(PO₄)₃. Taking Na_3.3V_1.7Mn_0.3(PO₄)₃ (NVMP) as an example, its practical application is still restricted by poor electronic conductivity, sluggish intrinsic Na⁺ diffusion, and poor high-voltage stability. In this work, a high entropy strategy is proposed to develop Na_3.3V_1.613Mn_0.3(Cr, Fe, Co, Ni, Zr)_0.1(PO₄)₃ (HE-NVMP) cathode for not only enabling more and rapid Na⁺ migration but also significantly improving deep desodiation stability. Based on theoretical calculations and experimental findings, such high entropy modification can efficiently alter the coordination environments of both V/Mn and Na sites for reducing Na⁺ diffusion energy barrier, increasing the occupancy of Na⁺ at Na(2) sites, and consolidating the structure stability. Thus, the obtained HE-NVMP delivers superior high-rate capability (91.7 mAh g^-1) up to 50 C and excellent cycling performance (capacity retention: 81.2%) after 10 000 cycles at 20 C at the cutoff voltage of 4.1 V. More importantly, such cathode also exhibits superior sodium storage properties at a higher cutoff voltage (4.5 V) with electrochemical polarization with 75% reduction at 1 C and higher capacity retention of 80.3% after 2000 cycles at 20 C compared to pristine counterpart, indicating a great potential for practical rechargeable batteries with excellent overcharge resistance capability.