A Little Goes A Long Way: Epoxy Resins’ Enabling Role in E-mobility

At the Paris climate conference (COP21) in December 2015, 195 countries adopted the first universal and legally binding global climate agreement. In line with this agreement, which sets out a global action plan to avoid dangerous climate change by limiting global warming to well below 2°C,  it is expected that the transportation sector will already deliver 60% reduction in greenhouse gas emissions in the EU by 2050 thanks to the progress made in various vehicle electrification initiatives including battery-powered electric cars and hydrogen fuel cell cars.

Currently, electric vehicle (EV) sales in Europe are mainly driven by regulation and climate targets. In 2030, the CO² standards in Europe will require more than a third of car sales to be electric, whereas to meet 2050 climate goals, all vehicles sold will have to emit zero emissions by the early 2030s.

Consequently, the car industry is faced with huge technological changes and challenges. It will be a herculean feat to develop long-range batteries, fast charging technologies and to build a charging infrastructure across Europe. Over the next couple of years, automakers will invest at least $ 300 billion into EVs. This will transform the EV landscape, improve battery cost, performance, vehicle range and charging time.

So which roles do epoxies play now and in the future in this fast-paced scenario? Epoxies have been part of the automotive industry for decades. Proven applications are waterborne anti-corrosion basecoats to provide long-term protection to the car body or the use of epoxy adhesives to bond dissimilar materials, like alloy metals or polymers, together. In addition, epoxies play an important role in vehicle weight reduction with the use of glass or carbon fiber reinforced composites to replace steel or aluminum body parts.

With the advent of electric vehicles a few years back, light weighting of a car body was the engineering approach to offset the massive weight gain caused by the heavy battery packs. Due to the way electric motors and battery packs work together, costly weight management technology proved not to be the ultimate solution due to recuperation. When a vehicle accelerates, it’s gaining kinetic energy. In non-electric vehicles braking converts kinetic energy into heat via the friction between the brake pads and the brake discs.

 In electric vehicles, pushing on the brake pad engages the electric motors as brakes, while simultaneously also as a generator to produce electric energy which can be fed back into the car battery. The car is recuperating, i.e. recovering a significant amount of kinetic acceleration energy as electric energy, thus extending the range of the vehicle. Heavier vehicle weights, although they require more kinetic energy for acceleration, also allow for higher recuperation rates. Consequently, lighter car bodies reduce the total capacity to recuperate.

Does that mean light weighting of car bodies are obsolete? No, light weighting can still play an enabling role in efficient EVs as it has other positive attributes. This includes lower rolling resistance, enabling the design of smaller battery packages to achieve a given range, and improved long-term corrosion performance. Current Lithium-ion battery technology relies on rare earth metals which are in short supply. Having the option to reduce the size of the battery pack and thus the need to use rare earth metals for battery production, is a significant bonus!

Minimising weight and protecting passengers against the intrinsic risks of large battery structures that are stored beneath the passengers at chassis height, are instrumental to making EV technology safe. Battery housings of Li-ion batteries need to insulate, manage heat, withstand high voltage, provide flame retardancy at high temperatures, absorb crash energy and provide Electronic Magnetic Impulse (EMI) shielding.

Until now, steel and aluminum enclosures have been the materials of choice but with a weight disadvantage. Adding extra weight to heavy battery packs makes them more difficult to service and adds to the total vehicle weight. Here fiber reinforced thermoset resins come into play, fulfilling all the requirements with additional advantages like greater design flexibility, allowing for the easy integration of cooling circuits, leading to improved Noise, Vibration and Harshness (NVH) and offering lower replacement tooling expense compared to die cast tools for aluminum or steel.

Electric motors require insulation. The coils of the motor are typically insulated with a wire enamel followed by an impregnation (varnish) or encapsulation as a secondary insulation, which are commonly made from epoxy resins.

In the future, magnetless motors will be the preferred choice to avoid rare earth-metal based permanent magnets. These motors operate at high rotational speeds which can go up to 20 000 revolutions per minute. This could lead to motor imbalance and ultimately destruction, if the rotor coils are not fixed with a material providing high mechanical strength and excellent crack resistance at high operating temperatures of 150 – 200 ^o C. And yes, you’ve guessed it… For this task Epoxy resins are the material of choice!

Once again, it’s clear that a little goes a long way. Epoxies have an important part to play in the future of e-mobility, making our future cars more energy-efficient, durable, and safer to drive.  Epoxy systems will also continue to help society to tackle the challenges of climate change on the journey to a low emission future.