Experimental investigation and thermal modelling of a series connected LiFePO4 battery pack

The present paper reports the results from modelling and experimentation with a lithium-ion battery pack operating at room temperature and under varying discharge rates. The variation in the internal resistance of the cell with change in the temperature is investigated experimentally. The prismatic Li-ion battery pack is discharged at 1C, 2C, 3C and 4C and significant parameters, such as pack voltage, temperature, and state of charge, are obtained. This is accomplished by connecting three LiFePO4 20 A h capacity prismatic batteries in series and applying 18 thermocouples at various locations on the surface of all three cells. The results show that there is a significant increase in battery surface temperature with an increase in discharge rate. The highest average surface temperature of the battery pack (56.5 °C) is observed experimentally at a 4C discharge rate, and the lowest (30.7 °C) at 1C based on modelling. Similarly, the maximum total heat generation (59.2 kJ) is observed at 4C experimentally and the minimum (37.5 °C) at 1C from modelling. A comparison of the modelling results with the experimentally determined temperature, voltage and heat generation shows good agreement. Also, the internal resistance of the cell is observed to increase as the state of charge decreases, and to decrease with increasing cell temperature.