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.
BT - Chemistry of Materials DA - 08/2018 DO - 10.1021/acs.chemmater.8b03228 IS - 18 LA - eng N2 -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.
PY - 2018 SP - 6532 EP - 6539 ST - Chem. Mater. T2 - Chemistry of Materials TI - Stoichiometric Layered Potassium Transition Metal Oxide for Rechargeable Potassium BatteriesStoichiometric Layered Potassium Transition Metal Oxide for Rechargeable Potassium Batteries UR - 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 VL - 30 SN - 0897-4756 ER -