%0 Journal Article %A Haegyeom Kim %A Dong-Hwa Seo %A Alexander Urban %A Jinhyuk Lee %A Deok-Hwang Kwon %A Shou-Hang Bo %A Tan Shi %A Joseph K Papp %A Bryan D McCloskey %A Gerbrand Ceder %B Chemistry of Materials %D 2018 %G eng %N 18 %P 6532 - 6539 %R 10.1021/acs.chemmater.8b03228 %T Stoichiometric Layered Potassium Transition Metal Oxide for Rechargeable Potassium BatteriesStoichiometric Layered Potassium Transition Metal Oxide for Rechargeable Potassium Batteries %U https://pubs.acs.org/doi/10.1021/acs.chemmater.8b03228https://pubs.acs.org/doi/pdf/10.1021/acs.chemmater.8b03228https://pubs.acs.org/doi/suppl/10.1021/acs.chemmater.8b03228/suppl_file/cm8b03228_si_001.pdf %V 30 %8 08/2018 %! Chem. Mater. %X

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 KxCrO2 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.