Novel approach for liquid-heating lithium-ion battery pack to shorten low temperature charge time

The charging time for Li-ion power battery in hybrid electric vehicles (HEVs) and pure electric vehicles (EVs) is elongated at low temperature compared to that at the room temperature, which will deteriorate the customer using experience. Therefore, shortening the low-temperature charging time of battery is the critical technology to promote the popularization of electric vehicles. Many techniques have been proposed to shorten the lowtemperature charging time, but these technologies often lead to problems such as the increase of vehicle energy consumption, the high temperature of the battery pack system (BPS) at the end of charging and the poor BPS temperature uniformity during charging. To tackle these problems, this paper proposes an optimization simulation model for charging control strategy combined with thermal model (SCCS-ThM) and BPS offline parameters based on a liquid heating thermal management system (LHTMS). The BPS offline parameters determine the charging power threshold under different ambient temperature and the different state of capacity (SoC). The temperature rise and the temperature differences of the BPS during charging are calculated with the thermal model. The optimization model obtains the optimal charging strategy by simulating the potential feasible charging strategies. The battery pack charge time is reduced by introducing a pre-heating stage prior to charging. The pre-heating period which minimizes overall charge time, including the pre-heating time, is determined using the thermal model. The experimental results show that for an initial battery pack temperature of -10 degrees C, overall charge time is minimized by starting to charge after the battery pack has been heated to 1 degrees C. With the same charging energy, the optimal charging strategy shortens the charging time by 16 % and reduces battery coolant heater energy consumption by 15 %. Besides, the maximum temperature at the end of charging and the maximum temperature difference during the whole charging process are 36 degrees C and 6 degrees C respectively, which are better than the original charging strategy.