For decades, scientists Wondering what to do with the liquid inside a Li-ion battery. This electrolyte is key to how the battery works, shuttling ions from one end of the battery to the other. But it’s also cumbersome, adding weight and bulk, limiting the distance an EV can charge — and most importantly, catching fire when the battery shorts out. A perfect solution would be to replace that liquid with a solid – ideally a light and airy one. But the trick is to switch while maintaining all the other qualities a battery should have. Not only does a solid-state battery need to get you farther on each charge, it also has to charge quickly and work in all kinds of weather. Doing all of this at once is one of the hardest problems in materials science.
Startups working on solid-state batteries have made steady progress toward these goals in recent months. Small batteries that once sputtered after charging are growing into longer, larger batteries. There’s still a long way to go before these batteries are ready to hit the road, but progress is bringing the next challenge: how do you quickly build millions of cells once you’ve built a good enough battery under tough lab conditions ? “These companies are going to have to undergo a massive mindset shift from R&D companies to manufacturing companies,” said Venkate Srinivasan, director of the Argonne Energy Storage Science Collaborative Center. “It won’t be easy.”
In recent weeks, Solid Power, one of the most well-funded of these solid-state companies, has launched a pilot line in Colorado that it hopes will solve the problem. At full capacity, it will produce 300 cells per week, or about 15,000 per year. That’s a trickle compared to the millions of cells a Gigafactory produces each year, and it still requires months of ingenious tools and processes. But according to CEO Doug Campbell, the goal is to start supplying batteries to automakers such as BMW and Ford for vehicle testing by the end of the year.
Once the automaker is satisfied with the battery’s performance on the road, the company plans to pass the baton to one of its battery partners with gigafactories, such as South Korean battery giant SK Innovation. According to Campbell, this should be relatively simple. Solid Power has designed what he describes as a unique, manufacturable “flavor” of solid-state designs that allow battery manufacturers to reuse existing processes and equipment designed for lithium-ion batteries. “Ideally, this is the last battery production line run by Solid Power,” he said of the Colorado plant.
In principle, this makes sense. A battery is a battery. Like their liquid-filled cousins, solid-state batteries require an anode, a cathode, and some way for ions to move between the two. This is where electrolytes come in. But it’s not easy to make something that’s porous to ions but strong enough not to break. Researchers have been searching for suitable materials for years, finalizing a series of ideas including ceramics and plastic polymers. But not all of them are easy to make. Some are very brittle and tend to fall apart when manufactured or when grooved between electrodes; others are softer and more flexible, but cannot be exposed to moisture. Furthermore, battery scientists do not have the practice of mass-producing the precursor materials needed to make them. It’s just that history doesn’t exist.
The second problem is the anode. The holy grail of solid states involves changing the anode from typical graphite to lithium metal. Combine that with a solid electrolyte, and it’s the secret to generating a lot of energy. The problem is in the form of lithium metal. Battery manufacturers are accustomed to using anode and cathode powder materials that can be developed as slurries. But lithium works best as a thin, free-standing foil—in Solid Power’s case, it’s 35 microns thick. “It has the consistency of wet wipes,” says Campbell. “So as you can imagine, when you make kilometers of material, it can get really tricky.”