Low-cost and high-power K4[Mn2Fe](PO4)2(P2O7) as a novel cathode with outstanding cyclability for K-ion batteries

De/intercalation of K+ ions results in more severe structural change and volume expansion/shrinkage than that of other monovalent ions such as Li+ and Na+ because of the larger K+-ion size. Thus, it is important to develop novel cathode materials with stable three-dimensional crystal structure and l...

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Published in:Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2021-01, Vol.9 (15), p.9898-9908
Main Authors: Kang, Jungmin, Park, Hyunyoung, Ko, Wonseok, Lee, Yongseok, Ahn, Jinho, Jung-Keun Yoo, Song, Seok Hyun, Kim, Hyungsub, Kim, Jongsoon
Format: Article
Language:English
Subjects:
Batteries
Cathodes
Crystal structure
Dimensional stability
Electrochemical analysis
Electrochemistry
Electrode materials
First principles
Intercalation
Ions
Manganese
Potassium
Reaction mechanisms
Specific capacity
Tetrahedra
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Summary:De/intercalation of K+ ions results in more severe structural change and volume expansion/shrinkage than that of other monovalent ions such as Li+ and Na+ because of the larger K+-ion size. Thus, it is important to develop novel cathode materials with stable three-dimensional crystal structure and large K+ diffusion pathways to prevent severe structural change during repeated K+ de/intercalation. Here, we introduce K4[Mn2Fe](PO4)2(P2O7) composed of three-dimensionally interconnected [Mn, Fe]O6 octahedra and PO4 tetrahedra as a promising cathode material for K-ion batteries. We demonstrate the outstanding electrochemical properties and reaction mechanism of K4[Mn2Fe](PO4)2(P2O7) in a K-ion battery system through combined studies using various experimental techniques and first-principles calculation. K4[Mn2Fe](PO4)2(P2O7) delivers ∼110 mA h g−1 with a high average operation voltage of 3.5 V (vs. K+/K) at C/20 (1C = 117 mA g−1). Even at 5C, its specific capacity is ∼85 mA h g−1, corresponding to ∼77% of the capacity measured at C/20. In addition, K4[Mn2Fe](PO4)2(P2O7) exhibits an outstanding capacity retention of ∼83% after 300 cycles at C/3 with a high coulombic efficiency of more than 99%. These findings confirm the importance of a stable three-dimensional crystal structure for high-performance K-ion batteries.
ISSN:2050-7488
2050-7496
DOI:10.1039/d1ta01602d