Lithium-ion batteries suffer severe energy loss, significant pulse power decline, and reduced life cycle under cold weather. It is imperative to preheat the lithium-ion batteries for electric vehicles (EVs) at low temperatures. At present, various internal alternative current (AC) heating methods have been proposed to achieve fast and high-efficiency battery preheating. However, there is still confusion in the selection of the AC frequency. Researchers have found that the simplified Bernardi heat generation model is not always suitable for AC preheating, especially at high AC frequencies. Under these scenarios, a frequency-dependent heat is generated, making the traditional thermal model inapplicable. In this paper, the source of frequency-dependent heat is analyzed experimentally. Based on the electrochemical impedance spectrum (EIS) data and entropy thermal coefficient of the cell in the experiment, controlled experiments in different frequencies are developed to compare the cell heat generation rate. The experiments showed that the heat generation rate is highly correlated to its frequency. Further analysis show that the frequency-dependent heat is not due to electrochemical reaction, partly due to Joule effect by current harmonics, and partly from unknown mechanism (nominate “extra-heat”).

锂离子电池在寒冷天气下会遭受严重的能量损失、脉冲功率显着下降和生命周期缩短。电动汽车 (EV) 的锂离子电池必须在低温下预热。目前，已经提出了各种内部交流（AC）加热方法来实现快速高效的电池预热。但是，在交流频率的选择上仍然存在混乱。研究人员发现，简化的 Bernardi 发热模型并不总是适用于交流预热，尤其是在高交流频率下。在这些情况下，会产生频率相关的热量，使传统的热模型不适用。本文对频率相关热源进行了实验分析。根据实验中电池的电化学阻抗谱（EIS）数据和熵热系数，开展了不同频率的对照实验，比较了电池的发热率。实验表明，发热率与其频率高度相关。进一步分析表明，频率相关的热量不是由于电化学反应，部分是由于电流谐波的焦耳效应，部分是由于未知机制（命名为“额外热量”）。