Visualizing\nLithium Deposition and Identifying Two\nTypes of Dendrites in Extreme-Fast-Charging Full Cells across the\nEntire Lifespan by <i>Operando</i> EPR and EPR Imaging

Metallic lithium deposition processes in NCM811∥graphite\nfull cells during extreme-fast charging of 4 C (fully charged within\n15 min) are detected via <i>operando</i> electron paramagnetic\nresonance (EPR) and EPR imaging over hundreds of cycles to quantify\nlithium deposits and visualize their spatial distribution. EPR imaging\nshows that constant-voltage charge generates loose Li dendrites with\ndivergent growth whereas overcharge leads to long dendrites with vertical\ngrowth, and these Li deposits accumulate at the anode edges, which\ncould deplete the Li resource at the cathode edges. Moreover, quantitative\nEPR indicates that the stripping current correlates to the deposit\nsurface areas, while the reintercalation current depends on the contact\nareas between plated Li and graphite. Overall, the results of EPR\nand EPR imaging suggest that the introduction of a relaxation period\nafter extreme-fast charge for Li reintercalation into graphite is\nimportant to mitigate the accumulation of dead Li.