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Freudenberg Sealing Technologies starts series production of DIAvent pressure equalization element for batteries for BJEV EV

Freudenberg Sealing Technologies is starting high-volume production of its DIAvent pressure compensation component for the first time for use in a Chinese passenger car: the new ARCFOX α-T electric car from the Chinese manufacturer Beijing Electric Vehicles (BJEV).

In 2017, Freudenberg introduced the innovative pressure compensation element DIAvent. In batteries for electric vehicles, a valve consisting of two nonwovens with different properties takes over pressure equalization during normal operation. Excess pressure reduction during emergency degassing is handled by a reversible umbrella valve.

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As simple as it sounds, the solution is technically sophisticated. While only a few liters of air per minute are exchanged in both directions during normal operation, in an emergency the entire quantity of gas emitted from a defective cell must be removed in a few seconds. Otherwise, the strong internal pressure—many times higher than the ambient pressure—could cause the housing to burst.

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The trend towards battery systems with even higher energy density increases the amount of gas that has to be quickly removed in case of an emergency, as well as the amount of air exchanged during normal operations.

Freudenberg's patented DIAvent valve replaces typically used microporous films such as PTFE with a combination of two nonwovens with different properties. The water-repellent nonwoven fabric on the outside allows air exchange of approximately eight liters per minute at a low pressure difference. It is watertight up to 100 millimeters of water column. If the water pressure rises above this, a second inner layer of nonwovens is activated so that no water can enter the housing.

Degassing in an emergency is made possible by a umbrella valve that is arranged in a ring around the nonwoven fabric. It opens reliably as soon as the pressure in the housing exceeds the atmospheric air pressure by more than 50 millibars, and can then discharge 40 liters of gas per second.

The umbrella valve closes again at the end, making it easier to safely remove a damaged battery after emergency degassing. Since it reversibly opens and closes, it can also support pressure equalization in normal operation, for example when batteries with very high energy density are exposed to rapid temperature fluctuations.

DIAvent takes over the functions that are usually performed by two separate components—a breathing element and a bursting disc. This means it is more economical and easier to install for vehicle manufacturers, since only one component has to be installed.

Right after prototype production, several vehicle manufacturers expressed their interest and tested the pressure compensation element. At the beginning of 2020, DIAvent went into series production for European customers for the first time.

Two years ago, Freudenberg’s sealing experts launched a joint development and test project with the Chinese manufacturer BJEV, which was successfully concluded with an agreement for series production in 2020.

BJEV, which has been operating successfully in the Chinese automotive market for about 30 years, now wants to establish a stronghold in the European market as well. That is why cooperation with established local suppliers was very important to the company, especially in view of the strict European safety standards for passenger cars.

Freudenberg Sealing Technologies also works with other OEMs on development projects for the DIAvent and expects further series orders by the end of this year.


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