(Industrial Electrochemistry and Electrochemical Engineering Division Student Achievement Award) Mass Spectrometry Titration for Quantitative Probing of Lithium Plating and Solid-Electrolyte Interphase Formation

Abstract

Rapid charging of lithium-ion batteries is crucial to encourage widespread adoption of electric vehicles, yet the precipitous capacity fade which typically accompanies fast charge limits its utility. Li plating on the graphite anode, which occurs due to the high overpotentials enacted during fast charge, is known to instigate this capacity fade, making precisely identifying the onset and amount of Li plating imperative. Methods have been proposed to detect plating, but these methods typically detect Li indirectly and non-quantitatively. In this presentation, I will outline a novel mass spectrometry titration (MST) technique, which I use to quantify inactive Li (defined as electrically isolated Li metal and LixC6 that remains on the electrode after cycling) via the amount of H2 evolved upon exposure to a sulfuric acid titrant. I extend the technique to additionally quantify carbonate-containing species (via CO2 evolution upon titration) and lithium acetylide (Li2C2, via the C2H2 evolution upon titration) in the solid-electrolyte interphase (SEI), and I demonstrate the utility of MST in characterizing the SEI formed under novel electrolyte formulations. Finally, I will show how MST can be strategically used to determine the onset of Li plating and to distinguish between the multiple capacity fade mechanisms that arise during fast charge.