<p>Lithium plating happens when batteries are charged at high C-rates or low temperatures, potentially damaging their capacity and compromising safety. Diagnosing lithium plating is crucial for the development of future onboard battery management systems (BMS). To address this, a diagnostic model for lithium plating incorporating a simplified electrochemical-thermal coupling (SETC) model is developed to predict the conditions under which lithium plating occurs, and its computational efficiency is significantly enhanced, as validated by the simulation times. The model is tested and verified using 18650-type LiMn₂O₄/graphite lithium-ion batteries. Key battery physical parameters, such as the open-circuit potential curve of the electrode materials and the full-cell entropy coefficient curve, are obtained through experiments and the least squares fitting (LSF) method. Electrochemical and thermal model parameters are obtained through designed current excitations and excitation response analysis methods. The coupled model’s accuracy is confirmed by testing its performance under constant charge–discharge conditions at various C-rates (0.5 C, 1 C, 1.5 C, 2 C, 5 C) and temperatures (5&#xa0;°C, 25&#xa0;°C, 45&#xa0;°C). Based on the predictions of the lithium plating diagnostic model, lithium plating cycles are designed, and scanning electron microscopy (SEM) characterization of the battery’s negative electrode is performed to further verify the model’s accuracy. Our diagnostic model offers new possibilities for optimizing rapid charging strategies and delaying battery failure.</p>