Regulating Hybrid Na + /Zn 2+ ‐Ion Acetonitrile‐Water Electrolyte Enables High Rate and Long‐Life Na 3 V 2 (PO 4 ) 3 Cathode for Zn‐Ion Batteries

ABSTRACT Na 3 V 2 (PO 4 ) 3 (Na 3 VP) is an attractive cathode for rechargeable aqueous zinc‐ion batteries (RAZBs). Yet it suffers from inferior cycling stability and rate performance in aqueous electrolytes due to structural degradation, dissolution and sluggish transport of guest cations. To tackle these issues, we tailor high concentration hybrid electrolytes (HCHEs) containing Zn‐ and Na‐ions as charge carriers and water‐acetonitrile co‐solvents to enhance the electrochemical performance of Na 3 VP cathode. By tuning the chemical compositions of hybrid electrolytes, we unequivocally prove that Na + ‐ions are the primary charge carriers in the intercalation of Na 3 VP, whereas the charged state of cathode remains intrinsically unstable in aqueous electrolyte, leading to rapid capacity fading. To address this limitation, we introduce acetonitrile co‐solvent which gets adsorbed at the cathode/electrolyte interface over water molecules and alleviates the dissolution. Increasing sodium salt concentration in HCHE further improves the structural, morphological and cycling stability through the formation of anion‐rich solvation structure, which in turn produces inorganic‐rich cathode/electrolyte interface (CEI). Consequently, the Na 3 VP cathode exhibits extraordinary cycling stability and rate performance (97% capacity retention after 3000 cycles at 5C and 95 mAh g −1 at 4C). This work opens new platform for developing HCHEs to enable high‐voltage cathodes for RAZBs.