Lithium (Li) plating is a critical barrier to fast charging in lithium-ion batteries as it accelerates degradation and compromises safety. In practice, however, identifying plating onset alone is insufficient; real-time evaluation of plating severity is more valuable for charging control. Here, a lithium plating grading framework is established using the evolution of negative-electrode potential in a three-electrode pouch cell. By operando tracking of the graphite anode potential during charging, the transition from stable Li intercalation to plating-prone conditions is identified and correlated with different degrees of metallic lithium deposition. Dynamic electrochemical impedance spectroscopy (DEIS) is employed as an auxiliary tool to probe the evolution of the overall interfacial response. Combined with post-mortem SEM, EDS, and XPS analyses, lithium plating is classified into four levels: plating-free, mild, moderate, and severe. The results show that increasingly negative anode potential corresponds to intensified Li deposition and progressive changes in surface morphology and interfacial chemistry. This work provides a severity-resolved approach to lithium plating diagnosis and offers a practical basis for fast-charging risk assessment and charging protocol optimization.