Lattice strengthening of Na4MnV(PO4)3 by dual doping as advanced cathode materials for sodium-ion batteries

Na 4 MnV(PO 4 ) 3 is a typical Na-super-ionic-conductor (NASICON), which shows great promise as cathode material for high-performance cost-effective sodium ion batteries. However, sluggish Na + diffusion kinetics coupling with Jahn-Teller effect severely deteriorate its high-rate capability and long-term stability. In this work, we report a regulation strategy of jointly doping dual heteroatoms (Fe and Ni) to realize structural stability of Na 4 MnV(PO 4 ) 3 by shortening bond length and fast ion diffusion. The FMVN electrode delivers a highly reversible capacity of 98 and 79 mAh g −1 at 0.1C and 10C, respectively, while maintaining a stable cycling life over 2000 cycles at 10C. Theoretical calculations and kinetic analysis unveil that the regulation of crystal structure by Fe and Ni joint substitution effectively reduces the Na + migration barrier and simultaneously increases the reversible capacity. Additionally, in-situ x-ray diffraction investigation verifies reversible structure evolution and minor volumetric change (∼4.91 %) in the sodiation/desodiation process. An assembled full cell (FMVN||HC) demonstrates an energy density of 353.9 Wh kg −1 at 0.1C and outstanding cycling durability with 89 % capacity retention after 100 cycles at 2C. This dual substitution strategy in this work holds great promise to develop high-performance NASICON-type cathodes for practical applications.