Fig. 3: Electrochemical performance of the KMF-EDTA | K metal cells within 2.7–4.4 V (vs. K⁺/K).

a, b Galvanostatic charge–discharge voltage profiles (a) and cycling performance at 15 mA g⁻¹ (~0.1 C) (b). The inset in a shows the differential capacity (dQ dV⁻¹) curve of the 2^nd cycle. The inset in b shows the enlarged view of efficiency, including the coulombic efficiency and round-trip efficiency. c, d Rate capability (c) and voltage profiles (d) cycled at different specific currents from 30 mA g⁻¹ to 500 mA g⁻¹. e–g Long-term cycling performance at e 30 mA g⁻¹, f 100 mA g⁻¹, and g 500 mA g⁻¹, respectively. The inset in e shows the enlarged view of Coulombic efficiency. h Average discharge voltage and specific energy versus specific capacity of some reported cathodes for LIBs, NIBs, and KIBs. The capacity and specific energy are calculated based on the mass of cathode materials in the corresponding metallic Li/Na/K cells. The data used for plotting (h) are listed in Supplementary Table 5.