Traction batteries for electric vehicles, which run on voltages of several hundred volts, must be well protected. Electrical components are packed into a thin-walled yet stable metal housing. Housings of this kind are equipped with at least one pressure compensation valve mostly in the form of microporous film. A second valve is a safety measure: It only opens if damage to one or several battery cells results from a malfunction, and the buildup of gases has to be released. A smart pressure compensation element, the "DIAvent", combines both functions into a single component. It is designed to help engineers make electric vehicles more reliable and economical.
DIAvent is the ideal pressure management solution intended for large-scale batteries in electric and hybrid vehicles. It is made up of a patented multilayer, nonwoven fabric combined with an umbrella membrane that allows DIAvent to intelligently and reliably handle the bi-directional pressure equalization of any battery, even in the harshest of operating conditions. DIAvent provides extremely high gas permeation during normal operation and a reversible emergency degassing function while also meeting the requirements for water tightness according to protection category IP67 and higher.
DIAvent first resolves the apparent contradiction between the need for high air permeability related to surface area and, simultaneously, a very high degree of water-tightness. The key is to replace the usual microporous film with a combination of two nonwovens with differing characteristics. At a slight pressure difference, the water-repellent nonwoven element on the outer side enables an air exchange of about 8 liters per minute and is water-tight up to a water column of 100 mm. If the water pressure also rises, the outer layer is pressed onto an internal layer that is completely impermeable to media, allowing no water to penetrate the housing. In an emergency, degassing is enabled by an umbrella valve arranged in a ring around the nonwoven. One major advantage of the Freudenberg solution is that the umbrella valve then closes. In practical terms, this facilitates the safe removal of a damaged battery. Since it opens and closes completely reversibly, it can also support pressure compensation in normal operation, for instance, when batteries with a high energy density are exposed to rapid temperature fluctuations. There are also prospects for DIAvent to be used in industrial applications, where pressure compensation is needed in electrical and electronic systems.