Polyanion Lattice Engineering of Na₄MnV(PO₄)₃ Cathode for High‐Performance Sodium‐Ion Batteries

The Na + superionic conductor (NASICON)‐type Na 4 MnV(PO 4 ) 3 (NMVP) has been considered as one of the most promising cathode materials for sodium‐ion batteries because of its higher operating voltage and low cost compared to Na 3 V 2 (PO 4 ) 3 . However, the Jahn‐Teller effect of Mn 3+ during (de)sodiation processes and the sluggish electrode reaction kinetics strongly restrict its cycling stability and rate‐capability. Herein, polyanion lattice engineering is developed by SiO 4 4− substitution on PO 4 3− to strengthen the adjacent local environment of the active coordination octahedron and improve the structural stability. The relieved lattice local distortions induce an enhanced Na + diffusion simultaneously. Moreover, the SiO 4 4− substitution leads to an improved intrinsic electronic conductivity. With these synergetic effects, the as‐synthesized Na 4 MnV(PO 4 ) 2.9 (SiO 4 ) 0.1 /C composite delivers a reversible specific capacity of 98.7 mAh g −1 at 0.5C and an excellent cycle stability, with 91.4% capacity retention after 200 cycles at 0.5C and 76.4% capacity retention after 1000 cycles under a high rate of 5C. Besides, significantly improved rate performance of a capacity retention (C 10C /C 0.5C ) at 10C (77.4%) that far exceeds that of the pristine Na 4 MnV(PO 4 ) 3 /C electrode (45.3%) is realized. This structural regulation strategy offers new insights for developing high‐performance Mn‐based polyanionic cathodes with superior cycling stability.