Analysis of heat generation in lithium-ion battery components and voltage rebound based on electrochemical and thermal coupled model

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It is particularly important to analyze the heat generation associated with the electrochemical process for thermal and safety management of ternary NMC lithium-ion batteries. In this paper, we develop an electrochemical-thermal coupled model to analyze the respective heat generation mechanisms of each battery component at both normal temperature and subzero temperature at different discharge rates. Taking 1C discharge rate as an example, at normal temperature the NE (negative electrode) heat generation rate is less than the PE (positive electrode) one. Although the NE polarization heat is higher than the PE one, there exists a large portion of reversible heat generation at PE as against a small portion at NE, leading to a lower level of heat generation at the NE. In addition, the transient heat generation rate of the NE keeps increasing with the discharge process and exceeds the PE one near the end of discharge. However, the NE heat generation rate at subzero temperature is much increased compared with the normal temperature case whereas the PE one changes little with temperature. The total NE heat generation rate at subzero temperature is higher than the PE one in that the NE polarization heat is much higher than the PE counterpart. It is noted that the polarization heat of the NE and PE is much higher than the ohmic heat throughout the temperature range. At the subzero temperature of −15 °C, the battery still functions at low to moderate discharge rates of 1– 1.5C by experiencing a voltage rebound without significant losing in capacity. The reversible heat occurring at NE exhibits heat release in the early stage of the discharge process at subzero temperature instead of heat absorption at normal temperature. In addition, the experimental test was also conducted to validate the present electrochemical and thermal coupled model.