An Effective Impedance-Phase Method for Sensorless Measurement of Li-ion Battery Cells’ Internal Temperature

This paper proposes a sensorless method for measuring the internal temperature of lithium-ion (Li-ion) battery cells. The method calculates the impedance phase by injecting a small AC current to the battery. Afterward, the internal temperature is determined, in real-time, by an empirical fit model that correlates the internal temperature with the impedance phase of the battery cell at a predetermined frequency. The proposed method has high accuracy at a wide range of temperatures, in general, and at high temperatures, in specific, which is vital for preventing destructive temperature rise and thermal runaway. Derivation of the method followed by experimental verification using a commercial 3.8-V/2600-mAh Samsung Li-ion battery cell at temperatures between -20°C and +50°C is presented.