Mitigating Jahn-Teller Effects by Fast Electrode Kinetics Inducing Charge Redistribution

Manganese hexacyanomanganates have attracted significant attention as promising cathode materials for sodium-ion batteries owing to the high theoretical capacity and low cost of Mn resources. Because of the strong Jahn-Teller effect, causing unstable local phase transition and distortion, the redox reactions of the high-spin state of Mn(III) are considered to be a conundrum. Herein, it is reported that the charge-redistribution mechanism of low-spin Mn-III + high-spin Mn-III -> low-spin Mn-II + high-spin Mn-IV in manganese hexacyanomanganates can decrease unstable high-spin Mn-III, leading to the mitigation of Jahn-Teller distortion. X-ray absorption near-edge spectroscopy and X-ray photoelectron spectroscopy suggest that the fast reaction rate activates charge redistribution. Moreover, different crystal structures, reported using post-mortem synchrotron X-ray diffraction analysis, confirm a large orthorhombic structure, thus verifying the presence of charge redistribution based on the superexchange rule. These results demonstrate that manganese hexacyanomanganate in an aqueous electrolyte can achieve long-term cyclability, thus paving the way for high-performance batteries.