Foldable sealing gasket technology: Sealing is the key to battery system safety

Safety and efficiency are two core concerns in the development of today’s battery systems. Compared to batteries used in traditional internal combustion engine (ICE) vehicles, battery systems for new electric vehicles face additional new challenges. For example, thermal runaway of the battery system could endanger the lives of the driver and passengers, while corrosion issues with battery components could severely shorten the battery’s service life. Reliable sealing solutions in battery systems are essential to reduce these risks, as sealing products are the first line of defense to avoid these problems. Batteries must be properly sealed to prevent the intrusion of dust and moisture. To ensure electrical grounding of the battery cover, the conductive properties of the seal must also be considered.

Currently, the most commonly used battery case sealing solutions are based on silicone elastomers or adhesives, such as injecting sealants into the case sealing parts in the form of in-place dispensing (FIP) and waiting for curing. The current two solutions have many problems in material handling, pallet positioning, curing efficiency, and later maintenance and scrapping and recycling during installation. Therefore, we designed an innovative solution - a foldable sealing gasket - to solve all the above problems. This solution combines advanced elastomeric materials with thin metal sheets, which can be folded at the joints, have good overall rigidity, and are customized and spaced according to specific part geometries. It can be accurately installed either manually or automatically by robots.

Figure 1. Working principle of Datwyler's foldable sealing gasket

Challenges and Solutions

Normally, battery housings and their associated seals face very strict tolerance requirements, which must meet IP6x or equivalent waterproof and dustproof parameter requirements, and no gaps are allowed. Therefore, when designing the metal skeleton of the foldable sealing gasket, we can use precise dimensional control and extremely small error compensation design; at the same time, we can use the resilience of the rubber material to design a sealing gasket of a certain height to meet the requirements of specific parameters. Compared with FIP gaskets, our gaskets do not have a starting or ending point for sealing, so that no narrow gaps are generated, thus eliminating the influence of corrosion.

As battery manufacturers are developing larger capacity battery systems with more complex and diverse housings, the accuracy and reliability of collapsible sealing gasket installation has become critical. For these more complex battery pack designs, we need more precise gaskets to ensure that the integrity of the seal is not compromised, and the metal part of the collapsible sealing solution helps achieve this. We usually use the same metal skeleton as the housing itself, anodized and surface treated to ensure a tight bond with the rubber elastomer. This makes this sealing solution both more durable and conductive, which means that current can easily pass from the upper cover to the lower housing through the gasket, avoiding electrical corrosion caused by current accumulation. Neither pure rubber sealing gaskets nor FIP solutions have this function alone.

Figure 2. Exploded view of a battery with a foldable sealing gasket (blue).

Finally, electromagnetic interference (EMI) phenomena that could affect the functionality of sensors or critical control units can also be mitigated by special EMI shielding materials that can be applied on the rubber portion of the foldable liner.

Design optimization through simulation analysis

In the entire foldable sealing gasket design process, digital simulation of sealing performance is the core link. The simulation analysis can reflect the accurate mechanical and thermal performance of the sealing components under extreme conditions, ensuring the effectiveness and reliability of the seals in various critical situations. The simulation analysis starts with a two-dimensional finite element model to evaluate the contact pressure changes along the sealing rib (see Figure 1). Once the contact pressure and contact surface meet the specific requirements, the simulation analysis can be continued through the relevant three-dimensional finite element modeling to evaluate whether the prestress on all bolts can keep the sealing gasket in a fixed position. The prestress must also ensure the conductivity requirements between the shell components.

The last step focuses on the simulation analysis of the entire battery pack shell using a foldable sealing gasket, which can ensure the sealing integrity of the entire sealing rib. This series of simulation analysis work helps to optimize the sealing gasket in terms of geometric dimensions, material properties, and installation force during the design process.

(a)

(b)

Fig. 3 2D simulation analysis results of the four-lip foldable seal liner design: (a) maximum principal strain in the liner; (b) contact pressure variation at the seal boundary.

Inherent environmental protection

Battery manufacturers are also considering how to enable the battery pack to be opened multiple times during its service life for easy inspection and maintenance. Foldable liners make this possible. If a FIP liner is used, one side of the liner is permanently adhered to the shell. This means that it cannot be removed when the liner is opened. The foldable liner is removable and easy to replace because there is no bonding between the liner and the shell. The foldable sealing liner is fixed with ordinary self-tapping rivets or M5/M6 screws, so it is easy to disassemble and assemble; when the battery system needs to be inspected or maintained, or at the end of the battery's service life, people can easily disassemble the battery pack and remove the sealing liner without being damaged.

From an environmentally friendly design perspective, the design concept of the foldable sealing gasket allows battery manufacturers to benefit from this excellent sealing solution from initial transportation, handling and installation to effective application, maintenance and final recycling.

Datwyler - Market leader in high-quality system-critical seals and rubber elastomers

Datwyler focuses on the research and development and production of high-quality system-critical seals and rubber elastomers. It is a global market leader in sealing technology, and its products are widely used in fields such as mobility, healthcare, food and beverage, and general industry. With its leading technology and widely recognized core competitiveness, Datwyler provides value-added services to customers in various markets around the world. Headquartered in Switzerland, Datwyler has more than 20 operating companies on four continents, sales in more than 100 countries, approximately 7,000 employees, and annual sales of more than 1 billion Swiss francs. The company has been listed on the Swiss Stock Exchange since 1986.