Charlotte Hamilton (right), co-founder and CEO of Conamix, is an EV battery tech entrepreneur working to perfect lithium sulfur chemistry. She knows more than most about what makes lithium-sulfur batteries fail. She describes her and her company’s journey.
In hindsight, 2014 was a great year to start a new battery company, but it sure didn’t seem so at the time. The start-up world was littered with failed battery companies and there were lots of investors to whom “battery” was a bad word. I remember one early potential investor literally turned around and walked away. I was at a conference and as soon as I said that I had co-founded a battery company, they turned on their heel, “Batteries? Nope, no way. Lost too much money there already.”
The track record of bringing new battery technology all the way to market is poor, because batteries are such an incredibly complex system. An innovation in cathode, anode, or electrolyte can shine in an academic paper in Nature or Science by showing enhanced energy per kilogram of active material or enhanced ion conductivity, but capturing that breakthrough in a complete system is incredibly challenging.
Getting that innovation integrated with other technologies and all the way into the market is harder still. The road from academic advancement to a product in the market is long and challenging, and we’re only part of the way down this road here almost a decade on since I founded Conamix.
Originally worked on silicon anode
I started the company in 2014 initially to work on silicon anode, not on the sulfur cathodes that have now been our focus since 2016. The first licensed technology of the company was a method to make nanostructured silicon directly from silicon chloride through a bulk nucleation process at high temperatures.
That same distaste for battery companies with investors in 2014 coupled with the challenges of trying to raise money in Ithaca, New York, led to a very slow start for the company. We didn’t manage to get any outside funding until the spring of 2016 when we closed our first seed round and started working to make silicon nanowires at a slightly larger scale. The company was initially just two employees working in a single chemical hood in a start-up company incubation centre at Cornell University.
Growing lovely silicon nanowires
We were just starting to duplicate the academic work and we were growing some lovely silicon nanowires on copper from the Cornell process when we found out that the intellectual property the company had licensed wasn’t quite as unique as we had thought it was on our initial review. It ends up that methods similar to ours had been tried by other competitors and that our path to a unique material and method wasn’t quite as wide as we had initially thought. It wouldn’t have been prudent for us to continue spending our investors’ capital to try to catch up and pass others in the crowded silicon anode space without a truly different and competitive low-cost approach.
Facing this logic, we paused all spending and laboratory work and considered closing up shop altogether. I still have a scanning electron microscope picture on my office table of silicon nanowires that I grew in the laboratory, but the picture is all that remains of the effort after we pivoted entirely to sulfur cathode technology later that year in the autumn of 2016.
While we realised our approach to silicon wasn’t unique enough to justify a start-up, we did find three complementary pieces of sulfur cathode technology available for licence from Cornell, Stanford, and Berkeley. Multiple research groups had used core-shell particles to contain sulfur on the cathode side and attempt to control the polysulfide shuttling that had long been the primary failure mode for lithium-sulfur batteries.
The conversion reaction that stores electrochemical energy in a sulfur cathode involves dissolved polysulfide intermediates which, if not contained, will travel around the cell and lead to reduced performance every time you cycle the battery.
The approach that all three academic groups used was to contain the sulfur in a shell of different types of material that were ionically and electronically conductive so that the sulfur conversion could be physically contained. The approaches had all generated academic publications and patent applications, but the approach had not been significantly advanced by any commercial entity.
Up to that point, solving a sulfur cathode system for lithium batteries had been a two-part problem: polysulfide control and protecting a lithium metal anode. Sulfur cathodes are most easily made in the non-lithiated state as sulfur rather than as lithium sulfide. Most lithium-sulfur systems in academic and other settings were built with a lithium metal anode supplying the initial lithium to the battery system.
Solving the riddle
As a result, anyone trying to make a working lithium-sulfur battery had to solve how to protect a lithium metal anode from dendrite formation and keep the by-products of the lithium-sulfur conversion system where they were supposed to be on the cathode side of the battery. Many others in the battery industry, both start-ups and huge commercial R&D efforts, had been working on lithium metal protection through numerous routes. Our approach at Conamix was to focus solely on the cathode side initially and eventually pair the approach with an anode technology developed by others.
We figured out how to make the core-shell structures in different, reproducible ways and we designed a simple experiment to test whether our core-shell materials were trapping polysulfides on the cathode side.
First multimillion-dollar venture investment
With duplication of the academic work in the laboratory, the proof-of-concept data in hand and the core licences exclusively signed to Conamix from the three universities, we were able to secure our first multimillion-dollar venture investment in May of 2018.
Volta Energy Technologies, Hegemon Capital, and New York Ventures collectively invested an initial $10 million in the company. The investment was based on the cost savings of lithium-sulfur for high-energy electric vehicle (EV) batteries and the unique approach and IP that Conamix had secured.
When the money arrived, we were able to finally begin building a larger scientific team led by Stephen Burkhardt, who joined first as our director of R&D and now leads the technology at Conamix as our CTO. Thankfully, Stephen and the team quickly took over all the hands-on laboratory work from the CEO in 2018 and Conamix set out to prove that we could hit energy, power, cycle life and cost targets for automotive-grade lithium-sulfur.
The initial targets were to drive competitive capacity at the cathode level, and we were able to attain our targets late in 2018 as measured in capacity per gram of cathode material. We, and many others at the time, felt that this was a key metric to hitting eventual automotive performance.
A much more important metric
While capacity per unit mass of cathode active is an important measure of success for a lithium-sulfur battery, what we quickly realised was that a much more important metric was how much electrolyte there was in the system.
A scaled battery couldn’t have massive volumes of electrolyte and still have a competitive energy density, as the electrolyte is inactive, and largely a diluent to energy density.
Designing large format lithium-sulfur cells that exceed competitive watt-hours per kilogram and competitive watt-hours per litre requires them to perform with as little electrolyte as possible.
As we started to reduce the electrolyte in our cells, we saw additional failure modes of lithium-sulfur that had to be solved one by one. The purely core-shell structure to contain the polysulfides wasn’t enough for a commercial level of performance in a tight electrolyte environment.
Working quietly in stealth mode in our own new facilities and dry room and with strong outside funding, we pushed our systems further and further toward performance consistent with automotive specifications.
Solving lithium-sulfur battery failure
We like to say that we know more about making lithium-sulfur batteries fail than most organisations, because every time we find a failure mode, we can solve it with material science and further protect our innovations. One general approach involves multifunctional materials within the cathode active such as binders that do more than just hold materials together – they’re also electrochemically active materials.
We have also developed binders with both improved mechanical properties as well as improved energy and power via polysulfide chemical interactions and we have engineered cathode microstructure that enables us to precisely control electrolyte ratios and other parameters. Collectively, these innovations and others have allowed us to push performance to automotive levels on the cathode side of the system.
Along the way, we’ve developed an anode system that allows us to push the cathode material further and further toward other failure modes and additional innovations. Some of those have come with the electrolyte between the anode and the cathode, and we’ve developed new low-cost formulations unique to our system.
These innovations have allowed us to push the costs even lower and the performance even higher for a lithium-sulfur system. A complete combination of anode, electrolyte and cathode will have the correct requirements to overcome specific failure modes in a sulfur system while hitting the high targets needed for widely adoptable EVs.
Ultimately, the prize remains worth the time and the cost. Truly affordable EVs for the mass market require low-cost, high-energy battery systems. Our current battery performance and cost pricing model calculations show that our innovations allow complete systems at well below the cost of current LFP-based cathode batteries and that our systems are of comparable performance to high energy NMC 811 cathode batteries.
Our cathode material performs to these levels and our electrolytes further reduce costs, but our systems are still not ready for automotive performance as they’re not yet integrated with a complete protected lithium metal anode system. We’re actively working with multiple commercial and academic partners around the world to solve exactly this challenge.
Years of development ahead
Are we halfway down the road to a lithium-sulfur battery widely adopted and driving out of the automotive showroom with a consumer behind the wheel? Measured in the time since our founding, maybe. There are still years of development ahead before an auto-A sample is ready to be tested by future partners.
Even with mounting outside pressure for low-cost systems by major governments and consumers, the qualification time for new battery systems is still a multi-year process after the first complete batteries are third-party tested.
If we measure the road to commercial adoption in innovation, we’re much further down the road. We started our push to sulfur with the knowledge and partnership of great universities built on decades of innovation and enhanced mechanistic understanding of lithium-sulfur systems. We’ve broken our batteries here at Conamix time and time again with tighter and tighter electrolyte, and many other, parameters.
Broken batteries part of the innovation path
Every academic paper before us and every broken battery in our laboratory was part of the innovation path towards sulfur cathodes in commercial use. We’ve tested thousands of cells for over half a decade and each innovation has led to another brick in the road towards mass adoption of low-cost systems.
We’re not there yet though. We need partners and innovation from others, and we need to build a complete, competitive system that will be pulled into the world by market forces that demand better and cheaper batteries. We’re looking forward to the rest of the journey.
