Protection of High-Voltage Battery Systems Against Water Ingress and Condensation

摘要

To ensure the required lifetime and to avoid malfunctions in high-voltage battery systems, the battery cells and other system components must be protected from contamination, e.g. particles, liquids and humidity. Battery systems for PHEV and BEV cannot be hermetically sealed as pressure differences between environment and system interior, e.g. caused by uphill / downhill driving or air transport, can lead to plastic deformation or even cracks in the battery system housing, especially in lighweight designs. To avoid this, pressure balancing is required. This is achieved by using a semi-permeable PTFE membrane which lets gases pass, but holds back particles and liquids. Because of its repellant material properties, clogging of the membrane by dust and liquids is prevented, and protection class IP6k9k is reached. In addition, the membrane can be used as the active component for the degassing function, e.g. to reduce the negative impacts of a thermal runaway event. By means of a pin, the membrane is ruptured as soon as the trigger overpresure is reached fast. In combination with a large area which is released by the destruction of the membrane, the rapid pressure increase inside the battery system can be limited, and the pressure relief can take place immediately. As humidity can enter the battery system through air exchange, there is a risk of water condensation at cooling surfaces in case the coolant plate?s temperature falls below the Dew Point to achieve heat dissipation. Water condensation has to be avoided to prevent corrosion inside the battery system, or even electric shorts. By water vapor adsorption with an air dryer cartridge, the absoulte humidity inside the battery system can be reduced, so the Dew Point can be shifted to lower temperatures, thus enabling lower coolant temperatures which are required for efficient liquid colling, e.g. during fast charging. The poster will illustrate the physical background and current solutions.