Experimental Investigations of Combined DC-AC Charging Pattern for Li-ion Batteries at Low Temperatures

Abstract

At low temperatures, the available capacity and power of Li-ion batteries will significantly reduce, and charging is difficult. To improve the low temperature performance of Li-ion batteries, it is essential to preheat battery and ensure the battery to maintain a certain temperature. In this work, the charging characteristics of Li-ion batteries at low temperatures are investigated through Four- Stage dropping current charging regime, and 3°C is determined as a characteristic temperature for selecting the cut-off temperature for the battery heating. In order to maintain the temperature advantage after preheating, a Combined DC-AC (Co-DC-AC) charging strategy is proposed to implement the charging and heating simultaneously. Aiming at the maximum heat generation rate with a constant polarization, the preheating AC frequency can be obtained where the maximum amplitude of AC current can be found after determining the maximum polarization voltage and impedance of battery. Six tests were designed with different combinations of preheating, Co-DC-AC, and Three- Stage dropping current (TSDC) charging. The proposed charging strategy includes preheating, Co-DC-AC and TSDC charging, which can effectively improve the charging performance at low temperature.