Sulfonylamide-Based Ionic Liquids for High-Voltage Potassium-Ion Batteries with Honeycomb Layered Cathode Oxides

The world is at the cusp of a new era where pivotal importance is being attached to the development of sustainable and high-performance energy storage systems. Potassium-ion batteries are deemed not only as cheap battery candidates, but also as the penultimate high-voltage energy storage systems within the monovalent-cation chemistries. However, their performance and sustainability are undermined by the lack of suitable electrolytes for high-voltage operation particularly due to the limited availability of cathode materials. Here, the potential of ionic liquids based on potassium bis(trifluoromethanesulfonyl)amide (KTFSA) as high-voltage electrolytes is presented by assessing their physicochemical properties, along with the electrochemical properties upon coupling with new high-voltage layered cathode materials. These ionic liquids demonstrate a lower redox potential for potassium dissolution / deposition (with a wide voltage tolerance of around $6.0$ $\rm V$), placing them as feasible and safe electrolytes for high-voltage potassium-ion battery configuration. This is proven by matching this electrolyte with new high-voltage layered cathode compositions, demonstrating stable electrochemical performance. The present findings of electrochemically stable ionic liquids based on potassium bis(trifluoromethanesulfonyl)amide will bolster further advancement of high-performance cathode materials, whose performance at high-voltage regimes were apparently restricted by the paucity of suitable and compatible electrolytes.