Mechanistic Insights of Jahn–Teller Effect Suppression in High-Entropy Prussian Blue Analogue Cathodes

Abstract

The Jahn–Teller (J-T) effect, as discovered by Hermann Jahn and Edward Teller in 1937, often causes lattice distortion and structural instability in Mn-based battery materials. Recent studies suggest that high-entropy design may help suppress J-T distortion, yet the underlying mechanism remains largely elusive due to their compositional complexity and structural disorder. Herein, using a Mn-based Prussian blue analogue as a case study, we employed a machine learning interatomic potential combined with synchrotron extended X-ray absorption fine structure spectroscopy (EXAFS) to elucidate the fundamental mechanism of the J-T suppression in high-entropy materials. Unexpectedly, EXAFS spectra reveal the absence of the typical J-T Mn–N bond-length splitting in our high-entropy Prussian blue analogue sample, but instead a broader Mn–N bond-length distribution. Machine learning-assisted calculations demonstrate the [MnN6] octahedra exhibit randomly oriented distortions along x-, y-, and z-axes in high-entropy lattices, resulting in the local distortion averaging out at the macroscopic scale. Further analysis of the local Mn coordination environment reveals that the high-entropy configuration enhances d-electron delocalization and reduces the energy splitting between Mn dx2–y2 and dz2 orbitals. This allows two structurally and electronically distinct distortion modes to coexist within the lattice, which disrupts long-range cooperative J-T order. Strikingly, the ultralong cycling stability of high-entropy K0.46[Mn0.21Co0.19Ni0.21Cu0.20Zn0.19][Fe(CN)6]0.98·1.69H2O is experimentally demonstrated, achieving 91.0% capacity retention over 50,000 cycles for aqueous ammonium-ion storage, which surpasses all of the Mn-based rechargeable batteries to date. Our study uncovers the microscopic mechanism of J-T suppression in high-entropy materials and provides an effective strategy for designing durable high-entropy battery electrodes.