Bis(trifluoromethanesulfonyl)Amide-Based Room Temperature Ionic Liquid for Potassium-Ion Batteries

Abstract

Rechargeable potassium-ion batteries are promising candidates for low-cost largescale energy storage systems due to their cost-effectiveness, sustainability and comparable energy density. With an increasing number of publications related to electrolytes for potassium-ion batteries, (1) room temperature ionic liquids (RTILs) have also been suggested as feasible electrolytes owing to their superior properties, such as non-flammability and wide electrochemical window.(2)In our research group, we reported bis(trifluoromethanesulfonyl) amide (TFSA)-based RTILs as suitable for the operation of potassium-ion battery when coupled to high voltage cathode materials.(3) In this study, we evaluate the physicochemical properties of TFSA-based RTILs with KTFSA, in addition to assessing their application for high-voltage potassium-ion battery with honeycomb layered cathode oxides. (4) N-methyl-N-propylpyrrolidinium (Pyr13) TFSA and 1-ethyl-3-methylimidazolium (EMI) TFSA were selected as RTILs in this study. A comparison of their physicochemical properties with same concentration of KTFSA, LiTFSA, and NaTFSA reveal RTILs containing KTFSA to show relatively high ionic conductivity and wide electrochemical window. When a symmetrical cell of potassium was constructed using Pyr13TFSA with 0.5 M of KTFSA, deposition and dissolution reaction could be performed repeatedly without increase in overvoltage. Finally, we evaluated the charge/discharge performance of K2Ni2-x Co x TeO6 (where x=0.25, 0.5 and 0.75) high-voltage cathode materials using Pyr13TFSA with 0.5 M of KTFSA as an electrolyte. Results show that each positive electrode has good cycle performance, and the average voltage changed depending on the Co content in the cathode. We conclude that TFSA-based RTILs are potential candidates for high-voltage potassium-ion battery.