Ultralong Lifespan Zero‐Cobalt/Nickel Prussian Blue Analogs Cathode Realized by Solid Solution Reaction Sodium Storage Mechanism

Abstract Despite their low cost and high specific capacity, the practical use of monoclinic Mn‐based Prussian blue analogs (Mn‐PBAs) is limited by poor cycling stability, primarily due to the structural degradation caused by the multiple phase transitions and Jahn–Teller effect associated with Mn ³⁺ ions throughout the entire cycle. Herein, by synergistic incorporation of low‐cost Cu and Fe into the manganese sites of Mn‐PBAs, the ternary PBAs (T‐PBAs) achieve solid solution reaction of Na ⁺ extraction and insertion, successfully eliminating the inherent multi‐phase transition from the sodium storage mechanism of T‐PBAs. Ex situ analysis and density functional theory calculations are employed to confirm that T‐PBAs consistently maintain a cubic phase with smaller lattice distortion rather than occur in conventional three‐phase transition during the charging and discharging processes, forcefully inhibiting the structural degradation of T‐PBAs. Therefore, the T‐PBAs showcase unprecedented cycling stability at both room temperature (10 000 cycles at 1 A g ⁻¹ ) and −20 °C (over 3000 h, 4200 cycles at 0.2 A g ⁻¹ without distinct capacity degradation), More importantly, when paired with commercial hard carbon, the T‐PBAs based sodium‐ion batteries exhibit excellent capacity retention (2000 cycles 76.8%), showcasing their immense potential in practical applications.