An ultra-thin smart filter can significantly extend EV battery lifespan

Car manufacturers and others who need light, safe, powerful batteries are eager to adopt lithium-sulphur (Li-S) batteries. Not only do they store more energy, and are safer and faster to charge than today's lithium-ion batteries – they're cheaper to make, too.

Batteries with challenges

It's just that these next-generation wonder batteries have one big problem: They wear out very quickly. The reason is that they suffer from what is called the shuttle effect.

Postdoctoral fellow Önder Tekinalp at the Norwegian University of Science and Technology (NTNU's) Department of Chemical Engineering explains:

"This happens because chemical substances, lithium polysulfides (LPS), form when the battery is in operation. The substances move between the electrodes, the positive anode and the negative cathode, in the battery. It is these substances that cause LiS batteries to degrade quickly, lose capacity and have a short lifespan," he said.

This also explains why this type of battery has not yet moved into electric cars.

New, thin, smart filter

Tekinalp and his colleagues have developed a super-thin coating with very special properties that can change this. Through the HiSep-II project, they have patented the coating. It has been given the same name as the project.

Inside a battery is also a separator. There is a partition between the electrodes, which makes it work effectively and prevents short circuits. When the HiSep II coating is placed on the outside of the wall, it acts as a smart filter.

Many people working to improve lithium-sulphur batteries concentrate on pure chemistry in cathode and electrolytes. The NTNU researchers have thus focused on the partition instead.

"The coating blocks the harmful chemical substances and allows useful lithium ions to pass freely," Tekinalp said.

Slimmer, lighter battery pack

The lifespan of a battery is often measured in charge cycles. One cycle is the same as one full charge and one full discharge. The tests from the lab at NTNU show that Li-S batteries equipped with HiSep-II can increase the number of charging cycles from 200 to 1000. That lengthens the battery life by a factor of five.

The battery pack in an electric car consists of many parts. The researchers say the patented technology can slim down an 800-volt battery pack by over 200 kilograms. That, in turn, means significantly better efficiency and a much longer range. The fact that this next generation of electric car batteries are made from sulphur, of which there is a lot, also makes them cheap to produce.

"Real alternative for electric cars"

Önder Tekinalp believes their research is a breakthrough, which will contribute to Lithium sulphur batteries now moving up as a real alternative for electric cars.

"Although HiSep-II has not yet been used in electric cars, we have shown that it can handle the shuttle effect. It has been the major brake on commercial exploitation - until now," Tekinalp said.

HiSep-II patented the separator in 2023, and is working with NTNU Technology Transfer (TTO) to bring it to market.

Also at sea, on land and in the air

"The goal is to scale up the technology and license it to an industrial partner so that it can be used in everything from electric cars to storage of green energy," said Kristina Nydal, a business developer at TTO. 

She believes Hi-Sep II can contribute to increased battery safety, and says that the technology is ideal for use in areas such as aviation, aerospace, electric cars, drones and maritime transport.

"It is also an attractive and cost-effective alternative for storing energy. Especially where longevity and stability are crucial factors," she said.

The production process is environmentally friendly, the technology is designed to be easily scaled up, and it can work with today's lithium-based batteries

Must scale up and test

Before they are ready for the market, external players must test the technology. The filter must be built into Li-S batteries, and its performance must be checked and confirmed by an independent third party. Documenting that the technology is reliable and stable in the long term is crucial. They must also ensure that the new smart filter can be produced safely, economically profitably and with consistent quality.

Patent processes cost a lot and should be adapted to the industrial use of the technology. TTO is now looking for an interested licensee who can finance further patenting and commercialization and participate in the planned tests.

Batteries with benefits

"But we have heard several times about announced breakthroughs for sulphur batteries in recent years.  In what way do you think the NTNU technology stands out?

"Many Li-S breakthroughs focus on improving cathode materials or electrolytes.The HiSep-II targets the separator, or filter, alone. It is a simpler, more scalable solution without the use of complex materials. The production process is environmentally friendly, the technology is designed to be easily scaled up, and it can work together with today's lithium-based batteries,"  Tekinalp said.