Potting & encapsulation | Insight 41 balancing working time with cure time to enable high throughput,” White says. “By removing the need for vacuum assistance for penetration into a component or removing the need for heat curing, Henkel is developing solutions that reduce overall process costs and complexity.” Challenging systems According to ViscoTec, r&d is leading to materials with improved thermal conductivity, higher temperature resistance, improved fire protection, shorter curing times, and greater flexibility and environmental sustainability. “Faster-curing potting materials may challenge automated dispensing systems to provide the highest process reliability while also reducing waste and lowering the CO2 footprint,” says Paintmayer. The ability to dissipate heat is one of the main drivers in the development of new potting and encapsulation materials, to which thermal conductivity is critical, says Brown at C-Therm. “This is why fillers are used, but they are heavy and expensive. In formulating these materials, it is better not to just load up the filler ratio, as the material still has to be pumped, so viscosity and abrasiveness are important considerations. Ideally, as little filler as possible should be used to achieve the desired thermal conductivity within the polymer matrix. To do this well, it is essential to pay careful attention to filler distribution.” Thermal properties also have an impact on electrical properties and, together, they affect overall efficiency. Epic Resins’ Staller says tailored thermal conductivity is required to maintain optimum electrical conduction efficacy in both conductors and power electronics. He also points to the critical role played by sensors in EV safety and efficiency, arguing that protecting them from the effects of thermal and electrical stresses is vital to their sensitivity and longevity. In providing protection from electrical stresses, the move towards higher voltages requires materials with greater dielectric strength to provide adequate insulation for all components. White at Henkel says there are relatively few electrically insulating materials with good thermal conductivity, reasonable cost and availability, and suitable rheology for lowviscosity applications. “In a composite, thermal conductivity is essentially a function of the total volume occupied by the filler. And, in general, thermal conductivity builds up much more slowly than viscosity, leading to a number of challenging design trade-offs,” they add. “Silicones have a remarkable suite of mechanical properties owing to the silicon-oxygen backbone structure at the molecular level, but there are trade-offs in the adhesion strength and resistance to hydrocarbon fuels that are difficult to overcome, particularly with the extreme filler loadings required for thermal applications. “Epoxies are far superior to silicones with regard to adhesion, but it is difficult to control the modulus and glass transition temperature without loss in other critical properties, such as chemical resistance or upper operating temperatures.” Changing battery architectures New battery architectures, including cell-to-pack and cell-to-chassis configurations, are influencing the formulation and dispensing of materials, ViscoTec’s Paintmayer says, adding that they necessitate adaptations to cater to diverse form factors and methods of integration. “The focus is on customising potting and encapsulation solutions to meet specific design and performance requirements. Enhanced thermal conductivity and improved mechanical properties are crucial to ensuring efficient heat dissipation and structural integrity for various cell arrangements. “With cell-to-chassis concepts especially, potting materials also take on the tasks of mechanical fixation and structural bonding, combined with thermal management, including the prevention of thermal runaway. “Combined with the growing demand for repairability, which so far seems not to be under consideration for the next generations of EVs, this challenges material developers to provide strong structural bonding along with debonding capabilities.” These battery architectures also have an impact on automated dispensing systems, presenting a variety of requirements, ranging from many small, individual injections to a smaller number of larger shots at fewer points. E-Mobility Engineering | March/April 2024 Potting compounds applied to cylindrical cells in a battery module must flow into all the spaces between the cells to ensure good contact for heat dissipation (Image courtesy of ViscoTec)
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