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 (V/V: 3.9 V), lower cost, and lower toxicity compared to full vanadium-based NASICON NaV(PO). Taking NaVMn(PO) (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 NaVMn(Cr, Fe, Co, Ni, Zr)(PO) (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) 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.