Abstract
Research and/or Engineering Questions/Objective
During charging and discharging, the temperature distribution of the surface varies from that in the cell core. High temperature leads to battery thermal runaway, which may cause rupture and fire. Thus, battery internal temperature estimation is significant for battery management system (BMS). Surface temperature and temperature gradient is needed, for internal temperature cannot be measured directly. Surface temperature can be measured with thermocouples outer the cell, while temperature gradient should be obtained by another method, here in the paper, Electrochemical impedance spectroscopy (EIS).
Methodology
Firstly, the relationship between impedance and temperature gradient was obtained. In the experiment, five thermocouples are embedded into the 30Ah LiFePO4/Graphite battery. One side of the battery remains at the ambient temperature, the other side was heated. The impedance was measured at different temperature gradient to get the relationship. On a vehicle, impedance was estimated. Then the temperature gradient could be estimated, according to the relationship. Finally, the internal cell temperature was estimated by combining battery surface temperature and temperature gradient.
Results
Temperature distribution perpendicular to the electrodes is assumed to be linear. Temperature gradient changes with the phase shift and the internal temperature estimated accuracy is 2 Celsius degree. It is concluded that the method can be used on the vehicle.
Limitations of this study
Current and voltage should be combined to calculate the impedance, because the impedance cannot be obtained from EIS on the vehicle.
What does the paper offer that is new in the field including in comparison to other work by the authors?
The relationship between cell temperature gradient and impedance is uncovered by EIS test and thermocouples inner / outer cell. Using the relationship, the internal temperature is estimated with the surface temperature measured in practical application.
Conclusions
In a word, the method can be used on the vehicle. The internal temperature estimated accuracy is high enough to satisfy the application. Battery safety can be assured by the method.
Key words : Battery Temperature estimation; Embedded thermocouple; Temperature gradient; EIS