E-mobility Technology Winter 2020

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MATERIALS RESEARCH Adhesives and Sealants in Battery and Hybrid Electric Vehicles When I was a child, I used to see battery-powered milk floats trundling along at 15mph, holding up the traffic. How things have changed! Battery-powered sportscars are now zipping up and down the motorways and autobahns. Battery technology has moved on in leaps and bounds to make it a practical, economical and viable everyday driving solution for the modern-day motorist - whilst also helping cut emissions to improve local air quality. About the Author: Rebecca Wilmot 20 years at Permabond, starting in the laboratory, technical service department, and now on the business, sales, and marketing management side of activities. She loves the adhesive industry and finds the diversity of applications, markets, and products fascinating. Key areas of focus for battery development include: • Efficiency and size • Increased power output • Speed of charging • Cost of materials • Safety Whilst the whizz-kids are revolutionising batteries;materials suppliers are having to up-the-stakes with their offerings to the industry. For adhesives manufacturers, this means developing products that combine some quite specific features: #1 in this season’s must-haves is thermally conductive adhesive. Batteries get extremely hot whilst charging, the demand is to charge as quickly as possible, which tends to exacerbate the situation, so it is essential to dissipate heat away from battery cells quickly and effectively. Battery cells are arranged in modules which make up the battery pack (the large unit normally concealed under the floor in electric cars). The need to keep the battery size as small, yet efficient as possible, means tightly stacking battery cells - increasing the temperature within the battery module. Heat needs driving away from the battery cells, so they are potted with thermally conductive adhesive. The modules sit on top of a heat sink, to maximise heat transfer, a thermally conductive adhesive is used to bond them in place. The adhesive also couples as a way of absorbing shock and vibration whilst driving to prevent damage to sensitive components. Inclusion of thermally conductive fillers into adhesives can affect other properties, for example, viscosity. It is all very well asking for an adhesive with the maximum thermal conductivity possible, but can you dispense the material is the question?! High levels of thermally conductive filler material render the adhesive virtually solid and unable to be mixed or extruded easily. 90 e-mobility Technology International | www.e-motec.net
e-mobility Technology International | Vol 7 | Winter 2020 Ability to cope with expansion and contraction. Battery cells and other components expand and contract significantly as they heat up and cool down; there is also the issue of sudden temperature changes or “thermal shock.” Adhesives and sealants are used around the cells to hold them in place and need to have some flexibility to cope with expansion and contraction without inducing stress onto the components or cracking off. Different materials expand and contract at different rates, this is more evident with larger components, so choosing an adhesive with a degree of flexibility and optimising the glue line thickness will help cope with the stress of differential expansion and contraction without debonding or causing damage to the parts. Graph showing how the % content of metal oxide filler affects thermal conductivity and viscosity of adhesive material. Electrical resistance. It is important that whilst the adhesive is thermally conductive, it must also be electrically nonconductive. Otherwise there will be short circuits galore and a car full of frazzled occupants going nowhere. A high dielectric strength is essential (dielectric strength is the maximum electrical field a material can withstand before it becomes conductive). Another benefit of using adhesives for sealing battery housings is that they provide a 100% seal against moisture ingress, and potting adhesives surrounding the cells and other electrical components prevent contamination and possible malfunction. Safety. Non-burning, fire retardant adhesives help to maximise vehicle safety. Fire retardant fillers can be combined into the adhesive formulation, and these are often thermally conductive as well - so can kill two birds with one stone! These fillers are selfextinguishing – so if you try to set fire to the material and take the flame away, the fire does not propagate along the adhesive layer, and the flame dies out. Using toughened adhesives in the construction of battery packs helps absorb impact forces, reducing the level of damage to the battery during a collision. Toughened adhesives also help to protect the battery pack against the shocks and vibrations experienced when driving; they can also help with sound deadening for improved passenger comfort. Production considerations. There is no point in having a new technically advanced innovative adhesive that lacks practicality on a production line. Battery production is big business and getting bigger by the day as EV popularity and demand increases, so it is essential that the adhesive selected can lend itself to automatic dispensing and have a cure schedule that optimises production throughput and efficiency. Two-part adhesives may need metered dosing and mixing before dispensing onto parts, single-part adhesives may require an oven or UV lamp to cure the adhesive. Solvent-based products or other hazardous chemicals may no longer be allowed in the workplace, or less hazardous products preferred for easier handling. e-mobility Technology International | www.e-motec.net 91
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VOL 7 | WINTER 2020 FUTURE MOBILITY
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CONTENTS 4 ELECTRIFICATION PLANNING
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ELECTRIFICATION PLANNING The smart,
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Smart depots: Why software integrat
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ne of the big challenges in making
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LiDAR Integration in Autonomous Ele
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Sensing Singular Resolution and Obj
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Driving change: How materials scien
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Further critical factors to EV safe
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POWER ELECTRONICS Semiconductor cho
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INFOTAINMENT AND CONNECTIVITY Infor
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and software, smooth (firmware) upd
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MATERIALS RESEARCH Moving e-mobilit
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Surface solutions for a wide range
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INFOTAINMENT AND CONNECTIVITY Auton
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THE FIRST VIRTUAL TRADE FAIR IN THE
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Advancing EV Electronics with Light
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Adhesives Light-curable adhesives c
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Copper and aluminium wire splicing
Page 42 and 43: BATTERY TECHNOLOGY An application f
Page 44 and 45: Open Loop Fluxgate current sensor o
Page 46 and 47: MATERIALS RESEARCH As automakers st
Page 48: Another thing which must not be for
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Page 65 and 66: Smart Home and Smart Power Grid Com
Page 69 and 70: Accelerating ADAS and AD with End t
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Page 126 and 127: POWERTRAINS P2 hybrid modules enabl
Page 138 and 139: POWER ELECTRONICS New PCB technolog
Page 140 and 141: 3. Insulated Metal Substrates (IMS)
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Picture perfect E-mobility assembly
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Production system for Lithium-Ion m
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Towards operational excellence in z
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Register online for a free subscrip
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MANY ORGANIZATIONS HAVE A VISION. w
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E-mobility Technology Winter 2020

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