How Theion wants to change electromobility and aviation Crystal batteries as enablers for sustainable electric flight

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GGB Heilbronn GmbH

The monoclinic gamma crystal structure of sulphur is set to push the boundaries of existing battery technologies. This is the promise of the Berlin start-up company Theion. This should make both road and air traffic more efficient and sustainable.

Rush hour, traffic jams and, in the worst case, traffic accidents: The increasing volume of traffic on the roads also brings with it many problems. Emission-free, CO₂-neutral electric mobility should provide a remedy. The switch to electric cars and trucks is a particularly important factor when it comes to sustainable mobility on land.

There are other unconventional approaches, especially for short distances: Electric vertical take-off and landing vehicles (eVTOLs) create new possibilities for short distances and significantly reduce commuting times. In urban environments, they could offer time savings of 20 to 80 minutes per journey. For medium-haul flights, lithium-sulphur batteries in electric aircraft could increase both range and payload capacity. Such developments not only minimize noise and CO₂ emissions, but also offer an environmentally conscious mobility solution.

Longer flight times and higher payloads

Today, electric aircraft are limited to a flight time of 30 to 60 minutes. The heavy batteries are still a technical problem. The key to electric flight lies in the battery itself. The last battery revolution of lithium-ion batteries was over 30 years ago. Since then, graphite, nickel, manganese and cobalt have been used. But there are alternatives: lithium instead of graphite, and sulphur in a specific crystal form instead of nickel manganese cobalt oxide (NMC).

With lighter batteries, longer flight times and higher payloads or more passengers are within reach. For medium-haul flights, lithium-sulphur batteries in electric aircraft could increase both range and payload capacity. Such developments not only reduce noise and CO₂ emissions, but also offer an ecologically responsible mobility solution.

Sulphur as a potential game changer?

For developers, the use of sulphur batteries means far more than just replacing the storage technology. Sulphur, a natural insulator, must first be made conductive. It is also important to eliminate the side effects of polysulphides, to compensate for volume expansion during charging and to avoid safety-endangering dendrites in the lithium metal anode.

The Berlin-based start-up Theion is tackling these complex challenges. Theion's co-founder Marek Slavik had the idea of overcoming these hurdles ten years ago and has been working with a steadily growing team to develop this technology since 2020. Numerous patents and the first prototypes in the form of button cell batteries underline the success of this approach.

The sulphur-crystal battery approach is showing promise in functional prototypes as button cells. The next development step is the completion of a more powerful pouch cell. This technological advance should make electric flight, whether manned or unmanned, in drones, air cabs or on medium-haul routes, economically feasible.

High number of charging and discharging cycles

Theion's unique approach lies in the use of the monoclinic gamma crystal structure of sulphur. This structure is particularly suitable for a high number of charging and discharging cycles, as confirmed by Drexel University in the USA. On this basis, the company is developing lithium-sulphur batteries with high energy density, low weight and an improved ecological profile. The aim is to achieve gravimetric energy densities of 500 Wh/kg to 1,000 Wh/kg, depending on the specification, compared to the 130 to 300 Wh/kg commonly used today. Cyclization tests with button cells show significantly better performance values than conventional sulphur in orthorhombic form.

New processes are necessary

The use of sulphur in the monoclinic crystal form requires new processes. The coating processes used today in the battery industry to produce the electrodes, with solvents, long drying distances and high energy input, are not suitable. Theion has therefore re-parameterized and combined processes that have already proven themselves in other industries in order to produce high-performance sulphur electrodes in an energy-saving and efficient manner. These processes include short-term but targeted irradiation processes for the functionalization of materials and surfaces as well as the use of high voltage for the large-area orientation of nanoparticles. All innovative processes are patent pending.

As energy density increases, so do the demands on inverters, DC/DC converters and OBCs (on-board chargers). Modern SiC/GaN semiconductors enable more efficient energy conversion, which helps to reduce the overall system weight. Despite the lower fire load compared to classic Li-ion cells, continuous monitoring systems for temperature and cell voltage control are crucial in order to detect degradation at an early stage.

Cycle stability is still limited

The cycle stability of the first Li-S prototypes is still limited. The decisive factor here is how the battery management system (BMS) manages degradation and reliably predicts the range during operation. Higher theoretical energy densities offer the possibility of greater ranges, but require adapted charging profiles and optimized fast-charging capabilities. Lighter battery packs create scope for integration into vehicle platforms, which has implications for power electronics and cooling concepts.

While the next development steps in road transportation are moving towards cost-efficient and long-lasting Li-S batteries, long-term applications are emerging in aviation. Here, eVTOLs could be used for short distances or electric aircraft for medium ranges. Although these scenarios are not yet an immediate everyday reality for developers, they offer a boost to innovation and set the course for technological progress.

The further development of battery technology not only affects materials research, but also directly affects the work of electronics developers in the automotive industry. Key tasks for the next generation of electric vehicles include the development of adaptive BMS algorithms for new cell chemistries, the safeguarding of safety and thermal management systems and integration into performance-optimized SiC/GaN-based drive and charging electronics. Electronics developers play a key role in determining how quickly and reliably sulphur and other innovative battery technologies find their way into products ready for series production.

This article was created with material from the start-up Theion. (heh)