Experimental temperature variation in battery pack with unbalanced SOCs during charging process

The State of Charge (SOC) inconsistency is common for battery pack after long-term cycling. The unbalanced SOCs is a threat to thermal safety and performance. For this work, five cells were connected in series to build a pack with initial SOCs 0%,5%,10%,15%,20%. Charging experiments are taken with charging rates 12A (0.3C), 20A(0.5C), 40A(1C), respectively. The temperature distribution is analyzed. The results of this work demonstrate that the increase of SOC gap results in the increase of temperature non-uniformity. The temperature difference is little for cells with 5%–10% SOC gap, while the temperature difference reaches 6D for cells during charging at 40A with 20% SOC gap.