How Theion Revolutionizes Electromobility & Aviation

Sulfur-Lithium Batteries How Theion Wants to Change Electromobility and Aviation

2025-09-02 Source: with material from Theion | Translated by AI 5 min Reading Time

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The monoclinic gamma crystal structure of sulfur is said to push the boundaries of existing battery technologies. This is what the Berlin start-up company Theion promises. This is expected to make both road and air transport more efficient and sustainable.

Increasing the range of aircraft: The Berlin start-up company Theion aims to push the boundaries of existing battery technologies with the monoclinic gamma crystal structure of sulfur.(Image: freely licensed / Pixabay) — Increasing the range of aircraft: The Berlin start-up company Theion aims to push the boundaries of existing battery technologies with the monoclinic gamma crystal structure of sulfur.
(Image: freely licensed / Pixabay)

Rush hour, traffic jams, and in the worst case, traffic accidents: The increasing traffic volume on the roads also brings many problems. Emission-free, CO₂-neutral electromobility is expected to provide relief. Especially when it comes to sustainable mobility on land, the transition to electric cars and trucks is an important factor.

Especially for short distances, there are other and even unconventional approaches: electric vertical take-off and landing vehicles (eVTOLs) create new possibilities for short trips and significantly reduce commuting times. In urban environments, they could save 20 to 80 minutes per journey. For medium-haul flights, lithium-sulfur 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

The CO₂ footprint of various active material combinations in the anode and cathode of a 100-kWh battery. Current technology: Nickel-Manganese-Cobalt Oxide (NMC)/Graphite (C), Iron Phosphate (LFP)/Graphite (C). With sulfur technology, lithium (Li) is combined with sulfur (S).(Image: Theion) — The CO₂ footprint of various active material combinations in the anode and cathode of a 100-kWh battery. Current technology: Nickel-Manganese-Cobalt Oxide (NMC)/Graphite (C), Iron Phosphate (LFP)/Graphite (C). With sulfur technology, lithium (Li) is combined with sulfur (S).
(Image: Theion)

Electric airplanes are currently limited to a flight time of 30 to 60 minutes. The technical issue remains the heavy batteries. The key to electric flight lies in the battery itself. The last battery revolution, the lithium-ion battery, occurred over 30 years ago. Since then, materials like graphite, nickel, manganese, and cobalt have been used. However, there are alternatives: lithium instead of graphite, and sulfur in a specific crystalline form instead of nickel-manganese-cobalt oxide (NMC).

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

About the Person

Dr.-Ing. Ulrich Ehmes has been leading the Berlin battery start-up Theion, which specializes in the development of lithium-sulfur batteries, since February 2022. He brings over 15 years of experience in battery technology and manufacturing, along with deep industry knowledge, extensive expertise, and innovative approaches for new energy storage solutions. Prior to his time at Theion, he was CEO at the Swiss battery company Leclanché SA. Before that, he served as Managing Director at Leica Cameras' production site in Portugal and as Managing Director at SETA Consulting. Additionally, he is involved as a board member of the battery network KLIB and in battery research for the BMBF.

Sulfur as a potential game-changer?

Internal tests by Theion with a not yet optimized coin battery cell show the potential of the monoclinic gamma crystal structure (red curve) compared to a battery with orthorhombic sulfur (blue curve). A current rate of 1C was used.(Image: Theion) — Internal tests by Theion with a not yet optimized coin battery cell show the potential of the monoclinic gamma crystal structure (red curve) compared to a battery with orthorhombic sulfur (blue curve). A current rate of 1C was used.
(Image: Theion)

For developers, the use of sulfur batteries means far more than just replacing the storage technology. Sulfur, a natural insulator, must first be made conductive. Additionally, it is essential to eliminate the side effects of polysulfides, compensate for volume expansion during charging, and avoid safety-critical dendrites in the lithium metal anode.

The Berlin start-up Theion is tackling these complex challenges. Theion's co-founder Marek Slavik came up with the idea to overcome these hurdles ten years ago, and since 2020 he has been working with a steadily growing team on the development of this technology. Numerous patents and initial prototypes in the form of button cell batteries underscore the success of this approach.

The approach of the sulfur crystal battery appears promising in functional prototypes as coin cells. The next development step is the completion of a more powerful pouch cell. This technological advancement is intended to make electric flight, whether manned or unmanned, in drones, air taxis, or medium-range flights, economically viable.

High number of charge and discharge cycles

Weight comparison of various active material combinations in the anode and cathode of a 100-kWh battery. Current technology: Nickel-Manganese-Cobalt Oxide (NMC)/Graphite (C), Iron Phosphate (LFP)/Graphite (C). In sulfur technology, lithium (Li) is combined with sulfur (S).(Image: Theion) — Weight comparison of various active material combinations in the anode and cathode of a 100-kWh battery. Current technology: Nickel-Manganese-Cobalt Oxide (NMC)/Graphite (C), Iron Phosphate (LFP)/Graphite (C). In sulfur technology, lithium (Li) is combined with sulfur (S).
(Image: Theion)

The unique approach of Theion lies in utilizing the monoclinic gamma crystal structure of sulfur. This structure is particularly well-suited for a high number of charge and discharge cycles, as confirmed by Drexel University in the USA. Based on this, the company is developing lithium-sulfur batteries with high energy density, low weight, and an improved ecological profile. The goal is gravimetric energy densities ranging from 500 Wh/kg to 1,000 Wh/kg, depending on the specifications, compared to the current standard of 130 to 300 Wh/kg. Cyclization tests with button cells demonstrate significantly better performance values than conventional sulfur in orthorhombic form.

Innovative processes are necessary

The use of sulfur in its monoclinic crystal form requires novel processes. The coating methods currently used in the battery industry, involving solvents, long drying processes, and high energy consumption, are not suitable. Therefore, Theion has reparameterized and combined processes already proven in other industries to efficiently and energy-savingly produce high-performance sulfur electrodes. These processes include short but targeted irradiation techniques for material and surface functionalization, as well as the use of high voltage for large-scale orientation of nanoparticles. All innovative processes have been patented.

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Date: 08.12.2025

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With increasing energy density, the demands on inverters, DC/DC converters, and OBCs (On-Board Chargers) also grow. Modern SiC/GaN semiconductors enable more efficient energy conversion, contributing to a reduction in overall system weight. Despite the lower fire load compared to conventional Li-ion cells, continuous monitoring systems for temperature and cell voltage control are crucial to detect degradation at an early stage.

Cycle stability is still limited

The cycle stability of the first Li-S prototypes is still limited. A key factor is how the battery management system (BMS) manages degradation and reliably predicts 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 provide flexibility in vehicle platform integration, influencing power electronics and cooling concepts.

While the next development steps in road traffic focus on cost-efficient and durable Li-S batteries, long-term applications are emerging in aviation. Here, eVTOLs for short distances or electric aircraft for medium ranges could be utilized. Although these scenarios are not yet part of everyday life for developers, they provide an innovation boost and set the course for technological advancements.

The advancement of battery technology not only impacts material research but also directly affects the work of electronics developers in the automotive industry. Key tasks for the next generation of electric vehicles include developing adaptive BMS algorithms for new cell chemistries, ensuring the safety and thermal management systems, and integrating performance-optimized SiC-/GaN-based drive and charging electronics. Electronics developers play a decisive role in determining how quickly and reliably sulfur and other innovative battery technologies make their way into market-ready products.

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