Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 32, Issue 19, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.202111901
Keywords
charge redistribution; Jahn-Teller effect; Prussian Blue analogs; sodium-ion batteries; superexchange rule; water-in-salt electrolyte
Categories
Funding
- UNIST [1.210033.01]
- Individual Basic Science AMP
- Engineering Research Program [2019R1C1C1009324]
- Technology Development Program to Solve Climate Changes through the National Research Foundation of Korea - Ministry of Science and ICT (MSIT) [2021M1A2A2038148]
- Ministry of Trade, Industry AMP
- Energy/Korea Institute of Energy Technology Evaluation and Planning (MOTIE/KETEP) [20194010000100]
- Academic Research Fund Tier 2 from Ministry of Education, Singapore [MOE2019-T2-1-122]
- MSIT at UNIST
- POSTECH at UNIST
- UCRF at UNIST
- National Research Foundation of Korea [2021M1A2A2038148] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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In this study, the mechanism of manganese hexacyanomanganates as cathode materials for sodium-ion batteries is investigated. The charge-redistribution mechanism in the material is found to decrease the instability of the high-spin state of Mn(III), leading to improved battery performance.
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.
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