Real-Time Quantitative Detection of Lithium Plating by In Situ NMR Using a Parallel-Plate Resonator

The development and optimization of fast charging protocols requires detailed information about the lithium inventory inside the battery. We report the application of a parallel-plate NMR probe to the in situ monitoring of Li metal deposition on a graphite anode during the charging of a single layer prismatic cell constructed with electrodes harvested from a commercial electric vehicle battery. The probe provides an enhanced sensitivity and an ideal orientation of the electromagnetic field, which allows the quantification of the lithiation of the graphite anode throughout the duration of cell charging. The NMR data indicate that charging over a 4 h duration (C/4) occurs with well-defined stage transformations in the lithiated graphite, while the coexistence of several stages is observed when the cell charging occurs in 1 h (1C). We show that two types of lithium deposition can occur on graphite electrodes: (i) as a Li film on the surface of the electrode and (ii) as dendrites orthogonal to the electrode surface. Our data demonstrates that Li re-intercalation into the graphite electrode occurs primarily from the deposited Li metal film, while the lithium dendrites can partially dissolve into the electrolyte solution during the discharging of the cell subsequent to Li plating.