Micropipette Contact Method to Investigate High‐Energy Cathode Materials by using an Ionic Liquid

The ionic liquid 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide was used in the scanning micropipette contact method to extend the electrochemical window of the electrolyte solution and enable the study of lithium‐ion battery materials with higher oxidation potential. Localized electrochemical measurements were performed on lithium iron phosphate particles that were drop‐cast onto a glassy carbon substrate. Investigation of the active materials occurred on a small scale (ca. 10 μm diameter), defined by the area of meniscus contact between the electrolyte solution in the micropipette and the substrate. Our studies showed that the SMCM probe is stable and can be used to analyze high energy lithium‐ion battery materials in the range of 2.5 to 5.1 V vs. Li/Li+. Extended potential, higher efficiency: Scanning micropipette contact method (SMCM) is extended to ionic liquid studies. The potential window for 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI) ionic liquid is suitable to examine high‐energy lithium‐ion battery materials. The electrochemical properties of lithium iron phosphate (LFP) particles drop‐cast onto a glassy carbon substrate are probed under inert atmosphere. SMCM‐coulombic efficiency of LFP particles in EMI TFSI is estimated to be higher than 90 %.