Ultrathin Na4Mn3(PO4)2P2O7 and Na4Fe3(PO4)2P2O7 nanoplates with multivacancies defects and short pathway for high rate and long-life Na+ storage

Mn- and Fe-based mixed-phosphates have gained significant attention as low-cost and eco-friendly Na-storage cathodes. However, traditional mixed phosphates are hindered by low intrinsic conductivity, a large particle size, and limited ion-transport kinetics, restricting the improvement of their rate capabilities and cycling performances. Herein, ultrathin Mn- and Fe-based mixed-phosphate nanoplates (Na 4 Mn 3 (PO 4 ) 2 P 2 O 7 -NP and Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 -NP, NMPP/NFPP-NP) were prepared by a modified liquid-phase mechanical thinning technique. High-index crystal facets of both materials were more easily sheared, realizing preferential exposure and providing rich active sites in high-polarity ethanol solvent. The difference between two materials could focus on the distinct coordination environments of atoms on the exposed high-index facets. The exposed high-index facets of NMPP-NP mainly contained the high-coordination Mn(3)-O 6 and Na(3)-O 7 sites, while the exposed high-index facets of NFPP-NP were dominated by the low-coordination Fe(3)-O 5 and Na(3)-O 5 sites. Further characterization revealed that numerous cationic and anionic vacancy defects and reduced internal resistance of grain boundaries, resulted in a 4–6-fold increase in conductivity of NMPP/NFPP-NP. Sodium-ion diffusion coefficients improved significantly, especially in the high-voltage region, enhancing kinetic performances based on the size effect of ultrathin nanoplates. Consequently, NMPP-NP and NFPP-NP cathodes exhibited a breakthrough in enhanced cycling stabilities and rate performance compared to bulk counterparts. This work highlights collaborative advantages of multivacancies and ultrashort ion/electron pathways for high-rate, long-life polyanion-type cathodes in sodium-ion batteries.