The range of applications for materials such as adhesives and sealants in batteries for electric vehicles is broad. John McKeen from Dow MobilityScience explains how they contribute to the safety, range and reliability of batteries.
springerprofessional.de: Adhesives and sealants are pivotal in the engineering and assembly of battery modules for hybrid and electric vehicles. What types of materials are employed, and what specific roles do they serve?
McKeen: Specially engineered materials – from adhesives and sealants, to polyurethane and silicone foams and pottants – play key roles in the assembly and performance of electrified-vehicle batteries. For example, in assembly, high-strength, thermally conductive adhesives ensure that batteries deliver the specified range and charging speed, reliably, throughout a vehicle’s life, and also enable efficiency on the assembly line. Pottants and foams are also used to ensure reliability and battery lifetime, and provide a layer of mitigation against propagation of an abnormal thermal event from one cell to neighboring cells. Sealants also play a critical role in battery reliability and safety by preventing water and roadway contaminants from entering the sealed battery pack, and ensuring proper venting of generated gasses in the unlikely event of a cell entering runaway.
How can these materials be optimized to enhance the efficiency of electric powertrains?
A hugely impactful area where materials can support here is thermal management. As battery technology delivers increased power density and faster charging, thermal management is increasingly critical to long-term performance and reliability. Materials play a pivotal part in this, and both silicone-based and polyurethane-based thermally conductive materials are used to assemble advanced, high energy-density, fast charging battery backs. Polyurethanes are often chosen for their exceptional strength and adhesive performance, while silicones offer superior stability and reliability over a broad temperature range, minimizing changes in mechanical properties that could lead to mechanical failure. Opting for the right material, formulated for the specific application is key to optimal processing in-build, and reliability and performance advantages in-use.
Thermal runaway is one of the most critical safety issues with lithium-ion batteries in electric vehicles. How do silicone foams, for instance, mitigate the risk of thermal runaway?
Standards for thermal-runaway protection are always developing, making choosing robust and adaptable materials crucial. Silicone foams are incredibly effective here; they have inherent temperature- and fire-resistant qualities, are highly effective for rapid room-temperature cure and, because they are comprised partially of inorganic elements (silicon oxide) and can be formulated to ceramify, are unmatched in their ability to encapsulate and self-extinguish – key to reducing thermal propagation risk. Their flexible composition and application also means they’re highly customizable for different cell types, as well as module and pack configurations – making them a bespoke but cost-efficient choice. Depending on cell type and size, and pack architecture, polyurethane foams’ thermal insulation properties also help prevent thermal propagation, giving battery designers a suite of tools to achieve pack safety via various layers of protection. We often see several material types used together to deliver maximum safety with minimum weight penalty and optimized cost.
Furthermore, how will advanced pack architectures, such as cell-to-everything designs, influence the selection and application of adhesives and sealants?
Concepts like these place even greater emphasis on manufacturers to optimize materials selection. Central to these ideas is enhancing battery packs’ energy to weight ratio; reducing component use has a positive impact on energy efficiency, while having the added benefit of reducing manufacturing costs. Achieving that balance is not a simple task, and means manufacturers need to meticulously analyse which materials will assist in best delivering a lighter design, effective thermal management and, ultimately, optimum performance. Material sustainability must also be a central consideration, as those with the right formulation will go a long way to maximizing circularity, while minimizing material loss in the assembly phase.
Applying adhesives demands varied technologies and approaches depending on the specific use case. What challenges do you foresee in the adhesive bonding processes involved in battery manufacturing?
Electric vehicles pose unique challenges that need to be met by higher and more stable bond strength to an increasing variety of substrates – aluminum, e-coat, PET, PP, and so on. Take vibration, for example; we have developed high-strength adhesives, standard and thermally conductive versions, to provide long-term performance under the vibrational loads caused by the diversity of roads that vehicles and drivers encounter. This ultimately makes battery packs safer and more reliable. At the same time, the industry needs to maintain a laser-focus on supporting sustainable development – which is why we help to reduce emissions with bio-sourced components and are working on materials to enable circularity. Smart solutions need to be developed for evolving challenges, and an intelligent approach to material formulation has never been more critical to helping the industry evolve for a greener future.