Lithium depth profiling in NMC/Graphite commercial coin cells under high C-rate cycling

Abstract

This study examines the distribution and evolution of lithium in both anode and cathode materials of commercial lithium-ion coin cells subjected to high C-rate cycling, providing insights into the mechanisms of lithium loss, trapping, and plating. Cells were cycled at 1C to 3C rates, and post-mortem analysis was performed using Li nuclear reaction analysis (Li-NRA), x-ray diffraction (XRD), and scanning electron microscopy (SEM) equipped with energy-dispersive x-ray spectroscopy (EDS). Li-NRA, using the resonant nuclear reaction between an incident high-energy proton and lithium, was used to measure the depth distribution of Li in the cathode and anode layers. The Li-NRA analysis revealed a surface lithium peak on the anode, likely associated with SEI formation and lithium plating, while the cathode exhibited a decrease in lithium content by ~19.7%. XRD analysis of the cycled cathode showed an expansion of the c-lattice parameter and peak shifts consistent with lithium depletion and structural deformation, supported by SEM imaging. In contrast, the dead graphite anode shows an enhanced peak at 43.3{\deg}, which corresponds to the presence of Li2Co3. 3-C rate cycling also led to capacity fade and an increase in internal resistance, highlighting the impact of lithium plating on cell performance.