Comment on “A K2Fe4O7 superionic conductor for all-solid-state potassium metal batteries”, by H. Yuan et al., J. Mater. Chem. A, 2018, 6, 8413–8418

Abstract

We comment on the article J. Mater. Chem. A, 2018, 6, 8413–8418 by Yuan et al., which describes the synthesis of a novel ionic conductor for potassium with excellent performance. We tried to replicate the synthesis, but unfortunately we obtained hematite instead, which is not a conductor of ions. We suggest that the material analyzed by the authors of the article is not a novel material but rather a mixture of hematite and potassium hydroxide, a residue of the synthesis. The observed conductivity is explained with the presence of an aqueous solution of potassium hydroxide, which forms due to air moisture.