A rapid low-temperature internal heating strategy with optimal frequency based on constant polarization voltage for lithium-ion batteries

The constant polarization voltage is managed for battery heating to achieve a good tradeoff between short heating time and less damage to battery lifetime based on an electro-thermal coupled model. The optimal frequency for maximum heat generation rate at a certain temperature is determined, which is different from the frequency for minimum total impedance. Heating under variable frequency is almost the same as under a constant frequency in terms of heating time and efficiency. However, engineering realization for variable frequency is more difficult, implying that constant frequency heating is a more promising candidate. The optimal frequency during the overall heating process, which is always lower than that at the initial temperature, can be evaluated from the intermediate temperature with low computational effort. Experimental results demonstrate that the heating time at the optimal frequency, corresponding to the maximum heat generation during the overall heating process, is the shortest with high efficiency. The battery is heated from -15.4 °C to 5.6 °C within 338 s, an average temperature-rise rate of 3.73 °C/min with an essentially uniform temperature distribution. The proposed heating strategy, which is experimentally verified with no apparent detrimental effect on battery health, is of great potential for rapidly improving operating performance of electric vehicles in cold weather.