Thermal Characteristics Investigation of Lithium-Ion Battery Under High-Frequency AC Excitation in Low-Temperature Environment

At low operating temperatures, the power capability and charging/discharging capacity of lithium-ion (Li-ion) batteries can decay rapidly. Therefore, it is essential to preheat the Li-ion batteries in advance of the normal operations of a battery electric vehicle. High-frequency ac preheating methods are advantageous to achieve a miniaturized and lightweight design. In this article, a self-heating circuit topology is used for studying the characteristics of Li-ion batteries at low temperatures and under high-frequency ac excitation. The thermal behaviors of Li-ion batteries under high-frequency ac excitations are comprehensively analyzed with an improved heat generation model. Experimental results exhibit that heat generation due to electrochemical reactions has a significant influence on self-heating rates under the high-frequency ac excitation, and the heating rate is positively correlated with the current frequency and root-mean-square (rms) value. Specifically, when the current frequency is 90 kHz and the rms value is 3.51 A or 1.17 C, validated by experiment and numerical simulation, a 2.9-Ah 18650 Li-ion cell can be heated up from -20 degrees C to 5 degrees C in 7.33 min with an average electrochemical heat generation of 2.962 W.