Low Temperature Discharge Cycle Tests for a Lithium Ion Cell

As all drivers in cold countries know, operating HEV/EV´s at cold temperature is rather difficult. Indeed, cold weather increases the internal resistance of the battery system creating a high opposing force while operating the battery: slowdown of Li+ diffusivity and decrease of ionic conductivity of electrolyte. Thereby, it limits the amount of energy extracted and reduces cell energy and power capability. Therefore, Li-Ion sensitivity to temperature remains one of the major obstacles to HEV/VE´s market penetration. In fact, until now, investigations of low-temperature behaviors of Li-ion cells barely provide suitable information because they have only been extended to small battery capacities or non-currently used HEV/VE´s batteries. Therefore, a complete thermal characterization of an actual HEV/VE´s battery is missing. This characterization is described in this paper. Indeed; a 100 Ah lithium LiFePO₄M_n HEV battery was tested under various operating conditions. The experimental process includes charging at ambient temperature, and discharging under extreme cold weather. The experimentations was conducted at four different temperatures to study the effect of seasonal changes in temperature.