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FEATURE
FASTENINGS & ADHESIVES
of adhesion, enabling direct bonding of battery cells to cooling plates. Applying the adhesive using automatic
Meeting the deMands of eV
battery pack design For the automotive industry, the transformation
to electrification is the future. Here, Parker LORD takes a look at how structural adhesives can help ease EV battery pack assembly
S
witching from internal combustion engines (ICEs) to electric vehicles (EVs) is accelerating, driven by advancements
in technology, society’s environmental awareness, and consumer behavioural changes. The rise of the EV is bringing about a broad change in customer expectations, a flood of new original equipment manufacturer (OEM) designs, and many new engineering needs, especially for the battery pack. The lifespan of an EV battery pack largely
depends on how effectively it stores charge and how well it gives energy back to the vehicle. At the same time, there is a need for lighter weight and more compact battery pack designs to gain additional energy density, thereby extending range while striving for simplicity and affordability. Excessive heat generated from the cells
can reduce the charge rate of the battery pack, resulting in longer charging times, and can also damage the cells. Thermal conductivity tests have shown that the battery’s lifetime effectively doubles with every 10˚C reduction in temperature. Battery pack manufacturers are therefore looking for both immediate and long-term thermal management solutions. Thermally conductive materials effectively
remove heat from within the battery and extend the life of the cells. However, many standard gap fillers or thermal pads do not provide the high bond strength requirements to securely attach battery cells to a cooling plate or cooling plate to the battery pack. When thermal conductivity and structural strength are needed, battery pack manufacturers instead turn to thermally conductive adhesives. The battery’s construction and the
manufacturing process determine the type of adhesive required. Generally speaking, there is a choice between using either a one- or two-part adhesive. Two-part, or 2K, adhesives are preferred as they have a significantly stronger bond strength than their one-part, or 1K, equivalents. They also cure at room temperature,
2 DESIGN SOLUTIONS MAY 2022 6
whereas 1K adhesives require heating which can damage the finished battery pack. The Parker LORD CoolTherm portfolio
covers a variety of thermal conductivities and chemistries, which provide a high dispense rate, reliable cure performance, and desired electrical properties. In addition, the material can make the bond, can be made permanent or formulated for repair and rework, and is dispensed in a thixotropic bead that can be used for any geometry and retain its shape while completely inverted on a surface before assembly.
ctp adhesive technologies
Parker LORD’s newest commercially available material includes a range of Cell-to-Pack (CTP) adhesive technologies, including a thermally conductive urethane 2K adhesive called CoolTherm TC-2002. This material delivers substantial thermal conductivity of 1.0 W/mK while also maintaining high levels
The EV battery’s construction and the manufacturing process determine the type of adhesive required
meter/mix/dispense (MMD) equipment is simple, and the glass beads incorporated within the mix maintain a bond line thickness of 100µm. The low viscosity, or easier flow, allows for the displacement of air within the application, which improves the rate at which heat is removed. In addition, the low dielectric constant enables battery manufacturers to build higher pack energy densities and reduce manufacturing costs. The mixed paste has a working life of up to eight minutes at room temperature, enabling readjustments during the assembly process. Handling strength is achieved within 25 minutes with full strength cure within three hours. An additional benefit for EV battery applications is that this material provides good isolation for managing current corrosion. To complement the thermal adhesives, new
non-silicone and environmentally friendly 2K gap fillers have been developed. Dispensable in any unit, the UR-2000 and UR-2000 FST thermally conductive urethane gap fillers have excellent flow properties with excellent sag and slump resistance. For the CoolTherm UR-2000 FST paste, the working time once mixed is 35 minutes with full cure within 5-7 days at room temperature. However, the cure time can be expedited at 80˚C to three hours. The working time for the CoolTherm UR-2000
paste, on the other hand, is 85 minutes at room temperature with full cure within 24 hours and an expedited cure at 120˚C for two hours. Both gap fillers provide secure adhesion to powder-coated and e-coated aluminium surfaces and offer excellent resistance to peel from PET film and aluminium-coated PET substrates. They also produce a flame retardant adhesive, which can meet the requirements of UL 94 V-0 standards. Application engineers from Parker LORD are
available to assist battery pack manufacturers in finding the best cost-targeted solution for their thermal management needs, helping to optimise processing and improve performance.
Parker LORD
www.lord.com/EV
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