Abstract
Potassium-ion batteries (KIBs) are promising electrochemical energy storage systems because of their low cost and high energy density. However, practical exploitation of KIBs is hampered by the lack of high-performance cathode materials. Here we report a potassium manganese hexacyanoferrate (K2Mn[Fe(CN)6]) material, with a negligible content of defects and water, for efficient high-voltage K-ion storage. When tested in combination with a K metal anode, the K2Mn[Fe(CN)6]-based electrode enables a cell specific energy of 609.7 Wh kg−1 and 80% capacity retention after 7800 cycles. Moreover, a K-ion full-cell consisting of graphite and K2Mn[Fe(CN)6] as anode and cathode active materials, respectively, demonstrates a specific energy of 331.5 Wh kg−1, remarkable rate capability, and negligible capacity decay for 300 cycles. The remarkable electrochemical energy storage performances of the K2Mn[Fe(CN)6] material are attributed to its stable frameworks that benefit from the defect-free structure.
Highlights
Potassium-ion batteries (KIBs) are promising electrochemical energy storage systems because of their low cost and high energy density
The general composition of Prussian blue analogues (PBAs) can be expressed as AxM[M′(CN)6]1−y□ynH2O (0 ≤ x ≤ 2, y < 1), where A represents alkaline metal ions, M/M′ represent the transition metals (Fe, Mn, Co, Ni, etc.), and x, y, and n represent the contents of alkaline metal ions, [M′(CN)6] vacancies, and crystal water (including ligand water which occupies the [M′(CN)6] vacancy sites and is chemically bonded with the unsaturated M ions and zeolite water which is located in the interstitial sites), respectively
Equivalent to a calculated chemical formula of K1.72Mn[Fe (CN)6]0.92□0.081.43H2O, consistent with the results reported in the literature[11,12]
Summary
Potassium-ion batteries (KIBs) are promising electrochemical energy storage systems because of their low cost and high energy density. Decomposition of H2O occurs at high potentials in KMF-C, leading to side reactions;[10] (3) the severe dissolution of Mn-ion in KMF-C, causing the poor cycling stability;[39] (4) other reasons, such as the [Fe(CN)6] vacancies induced the unevenly varied MnN bond length during Jahn–Teller distortion (see Supplementary Fig. 24 and the corresponding text)[37], may contribute to the capacity degradation of KMF-C.
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