High-Capacity Aqueous Potassium-Ion Batteries for Large-Scale Energy Storage

The synthesis of high-potassium-ion-content potassium iron (II) hexacyanoferrate dehydrate nanocubes and their performance as electrodes in aqueous electrolyte potassium-ion batteries were reported. To maintain a uniform size distribution, surfactants such as poly(vinylpyrrolidone) have been used. Here, we found that changing the solvent from water to ethylene glycol, which is also a mild reducing agent, gave uniform particle size and maintained the iron in the divalent state. Uniform potassium iron hexacyanoferrate dehydrate nanocubes with an edge length of =200 nm were obtained using a solvothermal method at 80°C. For comparison, when water was used as a solvent, potassium iron hexacyanoferrate dihydrate with a large particle size distribution was obtained. Rietveld-refined XRD was used to identify the crystal structure of the as-prepared potassium iron hexacyanoferrate. The results show that the particles have an orthorhombic symmetry structure with the Pmn21 space group