Underwater Environmental Impact and Thermal Management of Unmanned Underwater Vehicle Li-Ion Batteries

This thesis explores the behavior of lithium-ion (Li-ion) batteries in underwater temperature environments and develops a thermal management system to control the battery’s temperature. When the battery is operating at low temperature conditions, the life span of the battery is shortened due to increasing internal resistance and results in reduced capacity. A Li-ion battery pack was tested inside a thermal chamber to simulate underwater conditions, which maintained room temperature during high discharge rates, but decreased to the environment temperature at low discharge rates. To maximize battery performance, a heat pad and thermal control mechanism is proposed. The thermal management system was able to reduce the internal resistance of the battery, thereby reducing the power loss. From this result, we expect the battery lifespan to increase with this method. The proposed system was tested with a 18Ah, 14.8V, 4 series 6 parallel 18650 Li-ion battery pack in a water-tight enclosure inside the thermal chamber simulating underwater temperature conditions.