Abstract
Potassium-ion batteries are a compelling technology for large scale energy storage due to their low-cost and good rate performance. However, the development of potassium-ion batteries remains in its infancy, mainly hindered by the lack of suitable cathode materials. Here we show that a previously known frustrated magnet, KFeC2O4F, could serve as a stable cathode for potassium ion storage, delivering a discharge capacity of ~112 mAh g−1 at 0.2 A g−1 and 94% capacity retention after 2000 cycles. The unprecedented cycling stability is attributed to the rigid framework and the presence of three channels that allow for minimized volume fluctuation when Fe2+/Fe3+ redox reaction occurs. Further, pairing this KFeC2O4F cathode with a soft carbon anode yields a potassium-ion full cell with an energy density of ~235 Wh kg−1, impressive rate performance and negligible capacity decay within 200 cycles. This work sheds light on the development of low-cost and high-performance K-based energy storage devices.
Highlights
Potassium-ion batteries are a compelling technology for large scale energy storage due to their low-cost and good rate performance
Rechargeable energy storage devices based on other alkali elements, such as sodium-ion batteries (SIBs)[7,8,9,10,11,12] and potassium-ion batteries (KIBs)[13,14,15,16], have attracted extensive attention because of their obvious advantage in abundant resources
Upon close inspection of a magnetic material, KFeC2O4F, we notice that its 3D open structure is similar to PBAs51,52, which is very promising for K ion storage
Summary
Typical cyclic voltammogram (CV) curves of the KFeC2O4F electrode in 10th, 20th, and 30th cycles in the range of 1.5–4.6 V were recorded at a scan rate of 0.1 mV s−1 (Fig. 2a) The overlapping of these curves indicated the good cyclic stability of the cathode. To reveal the distinctive nature of the long-term reaction kinetics of KFeC2O4F cathode, electrochemical impedance spectroscopy (EIS) tests in different cycles were performed, with the Nyquist plots shown in Supplementary Fig. 10. It can be seen that the profiles of XRD patterns were almost unchanged within the cycle, indicating the good structural stability of the framework upon K ion extraction and insertion. In the fullcharging [FeC2O4F], Fe3+ exhibits a half-filled electron configuration t2g3eg[2] in the highest spin state (S = 5/2), obeying the Hund’s rule The GCD curves at 200th, 100th, 50th, and 10th cycles almost overlap with each other (Fig. 6e), manifesting the considerable cycling stability of our full battery
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