For decades, scientists have been wondering what to do with the liquid inside a lithium-ion battery. This electrolyte is the key to how batteries work, transporting ions from one end of the cell to the other. But it is also cumbersome, which adds weight and bulk, limiting how far electric vehicles can go on a charge – on top of that, it can catch fire when a battery short-circuits. A perfect solution would be to replace that liquid with a solid – ideally one that is light and airy. But the trick lies in making that switch while preserving all the other qualities a battery should have. A solid-state battery should not only send you further down the road on every charge, it should also quickly juice up and work in all kinds of weather. Getting everything right at once is among the most difficult questions in materials science.
In recent months, startups working on solid state batteries have made steady progress toward these goals. Small battery cells that once sputtered after being charged grow into larger ones that go much further. There is still a long way to go until these cells are ready for the road, but progress poses the next challenge: Once you have built a good enough battery under careful laboratory conditions, how do you build millions of them so quickly? “These companies are going to have to have a massive mindset change, from being R&D companies to manufacturing companies,” says Venkat Srinivasan, director of the Argonne Collaborative Center for Energy Storage Science. “It will not be easy.”
In recent weeks, Solid Power, among the more lavishly funded by these solid state firms, has launched a pilot line in Colorado that it hopes will address this issue. At full capacity, it will produce 300 cells a week, or about 15,000 a year. It’s a drip compared to the millions of cells produced each year by gigabytes, and getting there will still take months of refining tools and processes. But the goal, according to CEO Doug Campbell, is to start supplying cells to carmakers like BMW and Ford for car testing before the end of the year.
Once the car manufacturers are satisfied with how the batteries perform on the road, the company plans to pass on the baton to one of its gigafactory-owned battery partners, such as the Korean battery-powered SK Innovation. According to Campbell, it should be relatively simple. Solid Power has designed what he describes as a uniquely manufacturable “taste” of solid-state design that enables battery manufacturers to recycle existing processes and equipment designed for lithium-ion batteries. “In an ideal world, this is the last cell production line operated by Solid Power,” he says of the Colorado plant.
In principle, it makes sense. A battery is a battery. Like their fluid-filled cousins, solid state batteries require an anode, a cathode, and a way for ions to migrate between the two. This is where the electrolyte comes in. But it is not easy to make something that is porous to ions, yet solid enough not to crack. Researchers have spent years looking for the right materials and eventually settled on a range of ideas that include ceramics and plastic-like polymers. But not all are easy to make. Some are incredibly brittle and can fall apart when made or when placed between the electrodes; others are softer and more pliable but cannot be exposed to moisture. Plus, battery researchers do not have much practice in producing the kind of precursor materials required to make them. The story is just not there.
The second problem is the anode. The holy grail for solid-state involves changing the anode from the typical graphite to lithium metal. Combine it with a solid electrolyte and it’s a recipe for huge amounts of energy. The problem is the shape that lithium metal takes. Battery manufacturers are used to working with powdered materials for the anode and cathode that can be rolled out like a slurry. But lithium works best as a thin, free-standing foil – in the case of Solid Power’s it is 35 microns thick. “It has the consistency of wet tissue paper,” Campbell says. “And so you can imagine that when you make literally miles of material, it gets very difficult.”