Sulfur costs about 20 cents a kilogram. State-of-the-art cathode material costs about 20 euros.
That ratio is most of the case Ulrich Ehmes makes for lithium sulfur, and he arrives at it from a cost breakdown rather than from chemistry. Around 70% of what a cell costs is material. Anyone serious about cutting cell cost therefore has to attack the cathode, and attacking the cathode means changing what the cathode is made of. Disruption in battery technology, as Theion's chief executive puts it, goes through the materials.
The company's targets follow from that. Triple gravimetric energy density, up to 1,000 Wh per kilogram. Cut cost by a factor of three, down to 40 euros per kilowatt hour. And reach a third of the CO2 footprint. Ehmes frames the ambition as becoming a high volume producer of lithium sulfur cells rather than a materials supplier to other people's cells.
The screening exercise that landed on sulfur started more than ten years ago, run by one of Theion's co-founders, and it did not take long. Sulfur removes nickel, manganese and cobalt from the cell along with everything difficult about mining and sourcing them. It is abundant everywhere. And it carries over 1,000 mAh per gram, which Ehmes puts at five times what current cathode materials manage.
What sulfur takes out of the supply chain
The comparison he draws with LFP and NMC is not about the cell at all.
Those chemistries begin in mines in South America, Australia or China. The material is then shipped to China, where around 90% of cathode material is processed. NMC in particular needs a two-step calcination, which is very energy intensive.
Sulfur skips the whole sequence, because it is already a waste product, mainly from the oil industry. From an energy consumption point of view, Ehmes says, the starting point in Theion's case is zero, against a very high figure for every other raw material.
The processing end is where the second saving sits. Theion's own steps are short and take very little energy, in some cases 20 milliseconds, which removes the need for large coating machines and dryers.
Upcyclers, not recyclers
Ehmes is deliberate about the word. Theion does not recycle. It upcycles, turning waste into value.
The distinction carries a geographic argument. Wherever there is a refinery there are mountains of sulfur waste, and the large companies producing it do not know what to do with the material. That makes sulfur available everywhere, and it removes the dependence on the supply chains he has just described.
His check on whether the resource holds up is the sort of figure worth writing down. If all the batteries made in 2030, which he puts at 8 TWh, were produced with sulfur, that would consume 6% of sulfur waste.
Only 20% of the line has to change
The scaling question usually asked of a new chemistry is how much of the existing factory it invalidates. Ehmes's answer is 20%.
80% of state-of-the-art cell assembly is exactly the same for Theion's cells. What differs sits at the front of the line: mixing, coating, drying and calendering, which the company replaces with its own process.
Then there is the step before the factory. Theion makes its cathode active material in house rather than buying it in, which means no external partner has to prepare or purify the sulfur first. The material can be taken as it is. Ehmes treats that independence, rather than the equipment overlap, as the real argument for reaching gigawatt hour and terawatt hour capacity.
A material war, and the danger in cheap LFP
Asked at the European Battery Show in Stuttgart what he sees for the technology in Europe, Ehmes starts from a description of the industry as a whole.
The whole battery industry, he says, is a material war. Whoever has access to the best and the right materials, judged on cost, on supply chain and on specific energy, wins.
Which is why he reads the current moment as a trap rather than a relief. There is large overcapacity in the supply chain and it is pushing material costs down, and he calls that very dangerous, because it has everyone focused on cheap LFP. That is the wrong way for Europe, and not something Europe can rely on.
His comparison is with the last time the industry changed materials. Thirty years ago it went from nickel cadmium to lithium-ion and tripled capacity. The next step has to come the same way, from new materials, and specifically from materials accessible to all of us.
That accessibility is the part of the argument he keeps returning to, and the part that has nothing to do with the cell. A material sitting in heaps at every refinery is one nobody can corner.
This piece draws on the full conversation, which is available with a complete transcript on the episode page.