Fast charging of lithium‐ion batteries can induce lithium plating on graphite, compromising safety and lifetime. We use operando 7 Li NMR to detect metallic lithium and intercalation stages in NMC811||graphite full cells with an anode‐to‐cathode capacity ratio (N/P) of 1.1, reflecting a commercial energy‐dense design. During formation, a metallic Li signal at a Knight shift of 270 ppm appeared above 4.1 V, whereas LiC 6 /LiC 12 resonances near 50 ppm emerged above 33% state‐of‐charge (SOC), consistent with LiC 12 . Upon discharge, both the metallic Li and LiC 6 /LiC 12 signals vanished, restoring the initial state, though a small fraction of dead Li may remain. After two formation cycles, cells were charged at up to 4 C and temperatures down to 5°C. In low N/P full cells, fast charging quickly advanced the upper cutoff, promoting plating at moderate SOC. No plating was detected below 4.2 V. Warming charged cells to 20°C reduced plated Li slightly, indicating kinetically limited transport. However, Li plated during 4 C pulses at room temperature was reabsorbed by the graphite after prolonged rest (4 days). Operando 7 Li NMR sensitively probes plating and recovery in commercially relevant cells and highlights voltage control and postcharge rest as practical levers to limit irreversible lithium.
Furtmair et al. (Mon,) studied this question.