A K₂Fe₄O₇ superionic conductor for all-solid-state potassium metal batteries

Abstract

Potassium ferrite exhibits super-high ionic conductivity for all-solid-state potassium metal batteries.

Oxo‐Hydroxoferrate K2−xFe4O7−x(OH)x: Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures

“…This might be due to partial hydrolysis/decomposition and surface impurities like KOH and/or K 2 CO 3 ⋅ H 2 O (see below). A reasonably good ion conductivity was recently reported for K 2 Fe 4 O 7 , which – based on the published structural data – seems to be the same compound without addressing the potassium non‐stoichiometry …”

“…The potassium off‐stoichiometry was not reported for materials in references although obtained under similar reaction conditions and described with analogous structural data.…”

“…After this steady state, two minor steps of mass loss are recorded, associated with a steady increase in the MS signal for m / z =18. It should be noted, that the thermal behavior of K 2− x Fe 4 O 7− x (OH) x is markedly different from that of “K 2 Fe 4 O 7 ”, where neither DTA nor TG signals were found upon heating up to 800 °C.…”

“…The high usability of iron results from its unique combination of properties, such as strong magnetism in almost all of its oxidation states, the adoptable coordination, and last but not least, the overwhelming availability on earth . Iron oxides were studied extensively over many decades, however, there are still new discoveries in the field of alkali and alkaline earth metal ferrates, such as the potassium ferrate K 2 Fe 4 O 7 , which is a superionic conductor, e. g …”

Appraisal of calcium ferrites as cathodes for calcium rechargeable batteries: DFT, synthesis, characterization and electrochemistry of Ca4Fe9O17

“…3,35,42,43 Interestingly, a related compound, K 2 Fe 4 O 7 , has been recently reported and suggested as a K-superionic conductor. 44 The framework of K 2 Fe 4 O 7 consists of planes of edge-sharing FeO 6 octahedra sandwiched between planes of FeO 4 tetrahedra and octahedrally coordinated K ions. The K octahedra form rings around FeO 4 tetrahedra, thus providing a 2D conduction plane similar to that in Ca 4 Fe 9 O 17 (Fig.…”