Potassium Regulation at Na1 Sites for Enhanced Redox Utilization and Structural Reversibility in Multimetal NASICON Cathodes

NASICON polyanionic cathodes are widely studied because they combine structural stability, low cost, and superior rate capability for sodium‐ion batteries (SIBs). However, local lattice strain and sluggish multielectron redox kinetics during deep (de)sodiation limit the energy density and lifespan of NASICON cathodes. Here, we regulate Na1 sites with potassium in the multimetal NASICON cathode Na 3 K 0.6 V 1.4 Mn 0.3 Fe 0.3 (PO 4 ) 3 (NKVMFP). Calculations and experiments indicate that K occupation at Na1 sites regulates the alkali ion environment, which in turn modifies the MnO 6 crystal field, improves Mn/V redox utilization, and suppresses Na + /vacancy ordering. NKVMFP delivers an energy density of 381 Wh kg −1 , sustains 12,000 cycles at 4 A g −1 , and shows a volume variation of 4.13%; its stable operation in a 320 mAh pouch cell further supports its practical potential. These results show that Na1 site alkali ion regulation can improve redox utilization and structural reversibility in multimetal NASICON cathodes.