Suppressing the Jahn–Teller effect in Mn-based Prussian blue analogues by linear (N[dbnd]O) anions

Manganese-based Prussian blue analogues (PBAs) have been touted as a promising cathode material for sodium-ion batteries (SIBs) due to their low cost, long cycle life and high energy density. However, manganese-based PBAs perform poorly during cycling due to the Jahn-Teller effect. In this study, highly stable manganese nitrosylpentacyanoferrate (Mn[Fe(CN)₅NO]) particles were synthesized using a simple hydrothermal method. The presence of nitroso group breaks the symmetry of the crystals to some extent, which is favorable to reduce the Jahn-Teller effect. Through experiments and DFT calculations, we confirm that the presence of linear (N[dbnd]O) anions reduces the lattice volume fluctuations of the samples during charging and discharging, thus contributing to the mitigation of the Jahn-Teller effect. The electrochemical properties of Mn[Fe(CN)₅NO] were significantly improved compared to manganese hexacyanoferrate (MnFe[CN]₆). Mn[Fe(CN)₅NO] exhibited excellent sodium storage performance with an initial discharge capacity as high as 144.5 mAh/g at 20 mA g⁻¹ and capacity retention as high as 82.1 % after 400 cycles at 100 mA g⁻¹. This Mn[Fe(CN)₅NO] sample provides a promising cathode for sodium-ion batteries in large-scale energy storage systems.