Stoichiometric Layered Potassium Transition Metal Oxide for Rechargeable Potassium Batteries

• Published in: Chemistry of materials Vol. 30; no. 18; pp. 6532 - 6539
• Main Authors: Kim, Haegyeom, Seo, Dong-Hwa, Urban, Alexander, Lee, Jinhyuk, Kwon, Deok-Hwang, Bo, Shou-Hang, Shi, Tan, Papp, Joseph K, McCloskey, Bryan D, Ceder, Gerbrand
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 25.09.2018; American Chemical Society (ACS)
• Subjects: ENERGY STORAGE; MATERIALS SCIENCE
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.8b03228

K-ion batteries are promising alternative energy storage systems for large-scale applications because of the globally abundant K reserves. K-ion batteries benefit from the lower standard redox potential of K/K+ than that of Na/Na+ and even Li/Li+, which can translate into a higher working voltage. Stable KC8 can also be formed via K intercalation into a graphite anode, which contrasts with the thermodynamically unfavorable Na intercalation into graphite, making graphite a readily available anode for K-ion battery technology. However, to construct practical rocking-chair K-ion batteries, an appropriate cathode material that can accommodate reversible K release and storage is still needed. We show that stoichiometric KCrO2 with a layered O3-type structure can function as a cathode for K-ion batteries and demonstrate a practical rocking-chair K-ion battery. In situ X-ray diffraction and electrochemical titration demonstrate that K x CrO2 is stable for a wide K content, allowing for topotactic K extraction and reinsertion. We further explain why stoichiometric KCrO2 is unique in forming the layered structure unlike other stoichiometric K-transition metal oxide compounds, which form nonlayered structures; this fundamental understanding provides insight for the future design of other layered cathodes for K-ion batteries.