Manganese hexacyanoferrate (MnHCF) with an open framework is suitable for accommodating sodium ions. However, it suffers from severe capacity decay caused by the large structural deformation resulting from the Jahn−Teller (J−T) distortion of Mn−N 6 octahedra. By taking advantage of the strong chelation between EDTA and Mn ions, a strategy employing Mn vacancies (V Mn ) in combination with the introduction of Ni is proposed to suppress the J−T distortion of MnHCF. A Ni-doped MnHCF with V Mn and a low crystal water content (K 1.95 Na 0.05 Ni 0.02 Mn 0.93 [Fe(CN) 6 ] □ 0.05 •0.41H 2 O) is prepared, which delivered an improved capacity retention of 80% at 0.5C after 100 cycles. This work provides a combined vacancy and composition engineering strategy for effective suppression of J−T distortion in the MnHCF framework toward high-performance sodium-ion batteries.

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