South Korea: Why electric car batteries need plastic

A thin film makes all the difference

In modern electric car batteries, plastic plays a vital protective role. A wafer-thin film keeps the positive and negative electrodes of a battery cell apart. If these two sides come into direct contact, a short circuit can occur.

At the same time, during charging and discharging, tiny, electrically charged lithium particles must be able to move between the electrodes. To this end, the film has countless tiny openings, known as pores. It separates the electrodes from one another, but allows the particles to pass through.

This separator film is known as a ‘’ separator. It is often made of polyethylene (PE) or polypropylene (PP) – plastics that are also used, for example, in packaging.

What does this have to do with the next charging session? The more easily the lithium particles pass through the film, the better it can support fast charging. If the film is particularly thin, there is also more space for the materials that store energy. This can increase the range without making the battery any larger.

However, the film must also be able to withstand heat. This is because plastic can warp at high temperatures. Samsung SDI therefore uses, amongst other things, special ceramic coatings that make the separator more heat-resistant.

But polymers can do even more. Samsung SDI and Columbia University have jointly investigated another component of the battery: the electrolyte. This enables the lithium particles to move between the electrodes. Whilst it is liquid in many of today’s batteries, the research team has developed a new variant – a fluorine-containing polymer gel.

The gel was developed for so-called anode-free lithium-metal batteries. In this particular design, the lithium layer on the negative terminal only forms during charging. In future, such batteries could store more energy and thus enable greater ranges. However, there is currently one problem: during charging, sharp lithium deposits can form, which damage the battery or cause short circuits. The new gel is designed to reduce such deposits, thereby making the batteries more durable and safer.

Initial trials demonstrate the potential of this approach. After several hundred charge and discharge cycles, the battery cells tested were still able to store more than 80 per cent of their original energy. A safety test also revealed a difference: the cells containing the new gel did not catch fire when drilled into, whilst comparable cells with liquid electrolytes did catch fire.

However, further development is needed before the technology can be used in electric cars. It remains to be seen how many extra kilometres of range it could enable.

How plastics could make batteries safer and more powerful

The development of better batteries affects not only battery manufacturers but also the plastics industry. One example is K-exhibitor Brückner Maschinenbau. The company develops machinery used, amongst other things, to manufacture the thin separator films for batteries.

Whether as a protective film or as a component of a gel, polymers perform important functions inside a battery. They help ensure that batteries operate safely, last longer and can store more energy in future.

When it comes to e-mobility, it is not just lithium and other metals that matter. The development and processing of plastics also play a decisive role in determining how powerful the batteries of tomorrow will be.