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.

A highly sensitive and selective fluorescence sensor using N,S-GQDs for the detection of Co²⁺within 3 minutes.

The growing demand for advanced lithium-ion batteries calls for the continued development of high-performance positive electrode materials. Polyoxyanion compounds are receiving considerable interest as alternative cathodes to conventional oxides due to their advantages in cost, safety and environmental friendliness. However, polyanionic cathodes reported so far rely heavily upon transition-metal redox reactions for lithium transfer. Here we show a polyanionic insertion material, Li₂Fe(C₂O₄)₂, in which in addition to iron redox activity, the oxalate group itself also shows redox behavior enabling reversible charge/discharge and high capacity without gas evolution. The current study gives oxalate a role as a family of cathode materials and suggests a direction for the identification and design of electrode materials with polyanionic frameworks.