Interplay between Lithium Intercalation and Plating during Fast Charging of Lithium‐Ion Batteries Investigated by Operando NMR Spectroscopy

During fast charging, metallic lithium can form on the negative graphite electrode, compromising both cycle life and safety. After deposition, plated lithium can re‐intercalate within graphite, be disconnected or chemically oxidized. To better understand these reactions and their kinetics, operando measurements on cells with electrochemical performances close to commercial ones are essential. Herein, a dedicated pouch‐cell design is developed to follow the dynamic of lithium using 7 Li nuclear magnetic resonance (NMR) spectroscopy. These developments provide 7 Li NMR spectra every 6 min leading to a good temporal resolution. The dynamics of lithium is investigated for various charging scenarios and temperatures within NMC 811/graphite pouch cells with industry‐standard electrodes. Introduction of an original method allows assessing the mass of plated lithium formed in operando mode, offering insights on the competition between graphite lithiation, plating, and reintercalation processes. Interestingly, the lithium deposition occurs mainly during the constant‐current step and early stage of the constant‐voltage (CV) step, and lithium reintercalation, oxidation, or disconnection during the subsequent CV hold, highlighting the interest of reducing the current during fast‐charge scenario. Comparison with three‐electrode monolayer pouch cells provides an onset of plating located between −100 and –150 mV versus Li.