An iron-based polyanionic cathode for potassium storage with high capacity and excellent cycling stability

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2020-05, Vol.8 (18), p.9128-9136
• Main Authors: He, Haiyan, Yao, Wenjiao, Tunmee, Sarayut, Zhou, Xiaolong, Ji, Bifa, Wu, Nanzhong, Song, Tianyi, Kidkhunthod, Pinit, Tang, Yongbing
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; Attenuation; Cathodes; Energy storage; Ion migration; Ion storage; Iron; Life span; Lithium; Oxalic acid; Potassium; Retention; Storage systems; Synchrotron radiation; X ray absorption; X-ray absorption spectroscopy
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d0ta01239d

Potassium storage systems are attracting more and more attention for large scale energy storage owing to the great abundance of potassium in the earth. The development of potassium-based devices has so far been hindered by the lack of appropriate potassium-host materials since the large radius of potassium has put forward the requirement of more rigid frameworks and larger channels for K ion migration, in comparison with lithium and sodium-based devices. In this study, we report an iron-based oxalate as a positive electrode for K-ion storage. KLi 3 Fe(C 2 O 4 ) 3 @C delivered a stable capacity of 140 mA h g −1 at 120 mA g −1 , and showed a 91% capacity retention after 200 cycles. By combining cyclic voltammetry analysis and synchrotron X-ray absorption spectroscopy, the K storage mechanism is demonstrated to be a combined Fe 2+ /Fe 3+ redox reaction and pseudocapacitive process. Remarkably, it displays a stable capacity of ∼130 mA h g −1 and little attenuation over 5000 cycles at 240 mA g −1 in the lifespan test. A K-based full cell was successfully constructed via pairing this cathode with a soft carbon anode and exhibited good rate capability together with a capacity retention of ∼90% for 200 cycles, indicating its promising prospect as an environment friendly and stable K-storage cathode. KLi 3 Fe(C 2 O 4 ) 3 @C is developed as a positive electrode for potassium-ion storage with high stability and long cyclability.