A Mercury-Free Path to Fusion Fuel
By Karl Tischler
A new method for lithium-6 enrichment could remove one of the most toxic barriers to commercial fusion.
On 21 March 2025, researchers from Texas A&M University and ETH Zürich, led by chemist Sarbajit Banerjee, published a breakthrough in the journal Chem: a mercury-free method to enrich lithium-6, one of the essential fuels for deuterium-tritium fusion.
The method uses an electrochemical process involving zeta-vanadium oxide (ζ-V₂O₅), which can selectively extract lithium-6 from natural lithium solutions without the use of toxic mercury—eliminating the need for the legacy COLEX process.
Developing a mercury-free method to enrich lithium-6, one of the essential fuels for deuterium-tritium fusion. © PublicDomainPictures
So what have they done, and why is it significant?
What have they done? – A new electrochemical alternative to the toxic COLEX process
The team developed an electrochemical cell using zeta-vanadium pentoxide (ζ-V₂O₅), a tunnel-structured material that selectively captures lithium-6 ions from a lithium salt solution. A small voltage causes lithium-6 to migrate into the structure while leaving lithium-7 behind.
Over multiple cycles, the researchers demonstrated enrichment of lithium-6 by up to 5.7%—comparable to the enrichment factor of the industrial COLEX process. But unlike COLEX, this process is entirely mercury-free, scalable, and potentially much safer to operate.
Why is it impressive? – Replacing a Cold War-era, banned process
The only industrial-scale lithium-6 enrichment method in use today—COLEX—was shut down in the US in 1963 due to mercury toxicity. Since then, lithium-6 has been sourced from Cold War stockpiles or small-scale overseas production.
This new method shows, for the first time, a promising path to scale up lithium-6 production using modern materials science and green chemistry. It’s a technical advance, but also an ethical one—freeing fusion fuel from its most toxic supply chain.
Indeed, Stephen Wheeler, Executive Director of Fusion Technology at the UK Atomic Energy Authority (UKAEA) said of the process: “All self-sustaining deuterium-tritium fusion power plants require lithium as part of a reaction chain to produce the tritium fuel; with most power plant designs requiring tonnage scales of highly enriched Li6 (30-90%). This has long represented a key supply chain challenge for the whole Fusion community. New methods of producing Li6, affordably and in and environmentally sustainable way, such as those proposed here, represent critical steps towards the realisation of a fusion powered future for humanity. We congratulate the research team on these exciting early results.”
Why is it important? – Unlocking tritium production for commercial fusion
Lithium has two naturally occurring isotopes: lithium-6 (Li-6) and lithium-7 (Li-7). In nature, lithium-6 makes up only about 7.5% of lithium atoms. But lithium-6 is the isotope that can breed tritium when bombarded with neutrons—making it a critical component in deuterium-tritium (D-T) fusion reactors.
Until now, the only practical way to enrich lithium-6 was the COLEX process, which uses liquid mercury—so toxic and environmentally damaging that it was banned in the US more than 60 years ago. As a result, most fusion research has relied on stockpiled lithium-6 from the Cold War era.
This new electrochemical method allows lithium-6 to be separated without mercury and offers a realistic path to producing fusion fuel at scale.
Without lithium-6, most D-T fusion reactors cannot operate sustainably. This breakthrough could:
- De-risk tritium supply chains for future reactors
- Enable domestic lithium-6 production in countries with mercury restrictions
- Reduce the environmental and regulatory burden of fusion fuel production
What’s next? – Scaling up and testing for real-world conditions
The process still needs to be scaled to industrial levels and tested with real-world lithium feedstocks. The stability of ζ-V₂O₅ under repeated cycling, the purity of separated lithium-6, and integration into fusion fuel supply chains will all require further work.
However, the team is confident the process is ready for the next stage. If successful, this could be the first serious alternative to COLEX since the 1950s—and a critical enabler for the fusion industry.
What about other industries? – A broader opportunity beyond fusion
While lithium-6 is central to fusion, this breakthrough has implications well beyond the fusion sector.
(1) Advanced fission reactors and space propulsion
Lithium-6 plays a role in molten salt reactors and certain fission designs, including breeder systems. It's also relevant in experimental nuclear propulsion systems. A clean, scalable source could enable these technologies without relying on legacy stockpiles.
(2) Battery and materials research
Standard lithium-ion batteries use natural lithium, which is about 92.5% lithium-7. They do not require enriched lithium-6. However, the membrane chemistry and ion-selective control used in this new process could have implications for advanced lithium separation, recycling, or resource extraction (e.g., from produced water or brine).
(3) Critical minerals and industrial water treatment
The process was initially discovered during research on membranes for cleaning produced water from oil and gas wells. That suggests possible crossover into critical mineral recovery and water purification—both major challenges in the energy and resource sectors.
Conclusion – A massive breakthrough hiding in plain sight
This is arguably one of the most important fusion-enabling advances of the decade. It removes a critical bottleneck that has long gone unaddressed: the safe, scalable production of lithium-6.
This breakthrough hasn’t made headlines. But it should.
Mark R. Gilbert, Head of Science of LIBRTI at the UK Atomic Energy Authority (UKAEA) says of the news: “A scalable, safe, environmentally sustainable Lithium enrichment process is a key requirement for successful development of fusion power. It is great to see alternative technologies being developed to this end. The process described is an exciting possibility as it promises to require relatively few cycles to achieve the Li enrichment levels needed for fusion. The LIBRTI (LIthium BReeding Tritium Innovation) programme, which is helping to develop tritium breeding technologies based on lithium, will be keen to see how this novel enrichment process can be developed and scaled to support not only LIBRTI’s needs, but also the next generation of prototype fusion devices, including UK’s STEP project.”
Overall, this is the kind of fundamental enabler that could quietly change the trajectory of the entire fusion field—and much more.