Instantaneous estimation of internal temperature in lithium‐ion battery by impedance measurement

Due to the various drawbacks of collecting temperature using embedded or patch thermocouple sensor, the internal temperature estimation is getting more and more attention in the field of lithium power battery. In this paper, the commercial 18650 LiFePO4 battery is selected to analyze the characteristic of Electrochemical Impedance Spectroscopy (EIS) from 0°C to 55°C of 0.1 to 10 000 Hz. The results reveal that there exists intrinsic relationship between the alternating current (AC) impedance phase shift and the internal temperature in the range of 10 to 100 Hz from 5 to 55°C. And the intrinsic relationship is not interfered with the State-of-Charge (SOC) and the State-of-Health (SOH). Subsequently, the relationship is described with a modified Arrhenius equation under the excitation frequency of 12, 44, and 79 Hz. Finally, a novel internal temperature estimation method is proposed by the AC impedance phase shift. The applicability and accuracy of the method are further verified via 10 temperature points. The results indicate that the estimation error is within 1°C in the common operating temperature range (15-45°C), suggesting that the proposed method can be applied to estimate battery internal temperature. Finally, the implementation system of real-time estimation for engineering application is constructed.