This new material series is processed by injection moulding, and is said to deliver superior sealing performance, ensure battery life and meet increasingly stringent environmental regulations.
In the growing electric vehicle market, improved battery performance with shorter charging times, maximum temperature resistance and a longer battery life are key factors for success. To meet these demands, OEMs in Europe and the United States need materials that also comply with stricter national and international environmental standards. One high-performance material for such applications comes from the elastomer material group.
Using material advantages – elastomer seals instead of thermoplastics
Thermoplastics that are traditionally used for battery seals have macromolecules with long-chain molecular structures that are not chemically cross-linked but instead held together by weak intermolecular forces. While thermoplastics can be elastically deformed to some degree, the constant charging and discharging of the battery cell also causes them to undergo functionally relevant plastic deformation over time. This is different in elastomers whose molecular chains are chemically cross-linked. In their basic state, the polymer chains form a tangled ball that stretches or compresses under tensile and compressive loads. Due to the entropy elasticity, these cross-linked materials react elastically and reversibly, maintaining their shape exceptionally well during the cyclical volume change of the battery cells under load.
“Our O-rings made from the new elastomer therefore prevent electrolyte from leaking out of the battery cell or impurities from entering the cell,” explained David Kuhne, application engineer at Freudenberg Sealing Technologies. “You shouldn’t think of a battery cell as a rigid construct – it ‘breathes’. When the temperature in the battery cell rises from ambient levels to – as a rule – ranges of up to 60°C, the cell expands and then contracts in the same way as it cools. Elastomers show significant advantages over thermoplastics during this continuous stress.”
Materials expertise – from cutting-edge research to large-scale production
The development of new battery materials prioritises sustainability as well as economic aspects. In general, the longer a battery can be used, the more sustainable the electric vehicles become. The new sealing material from Freudenberg Sealing Technologies contributes to this goal.
When used in customer projects, the new material was able to improve the performance-relevant leakage rate of the battery cells by an order of magnitude – in other words, resulting in a tenfold improvement compared to conventional thermoplastic seals.
Another essential aspect is the extreme sensitivity of battery cell electrochemistry to potential contamination. Dr. Stefan Schneider, head of material development at the O-Rings lead centre, explained: “Premature capacity loss, which has been observed in cells sealed with conventional elastomers, can result from minimal but still present impurities in the sealing material. The infiltration of moisture into the cell has a similar effect, as it can cause the decomposition of electrolyte components. These aspects were considered when the new material was developed.” In addition, Process Engineering has optimised manufacturing techniques to such a degree that it is possible to produce these high-performance battery cell seals in large series.
