The Electric: The World of Potemkin Solid-State Batteries
In an industry known for braggadocio, Toyota has a decadeslong reputation for tight-lipped reserve, divulging little publicly about what it’s working on before a snazzy new feature or car appears in its showrooms. But it’s made a notable exception. Since 2012, Toyota has routinely touted “breakthrough” progress in an industrywide race to develop solid-state batteries, and predicted that it will be first to deploy the holy grail technology in electric vehicles. Its boasts have captured attention because success would mean the most energy-dense EV battery currently thought possible—lightweight yet able to power an EV for 500 or 600 miles. But if Toyota has been sticking its neck out, it has outsize reasons for doing so: Such an advance could quiet critics who have mercilessly needled the company for its sluggish development of EVs despite being the world’s largest carmaker for most of the last 15 years.
After so many claims, there are broad industry doubts whether Toyota is truly on the verge of a solid-state breakthrough, or whether its battery will be essentially for show. The skepticism reflects the general state of play at the very high end of EV batteries, in which investors from venture capitalists to automakers General Motors and Volkswagen have invested billions of dollars. In this world, solid state is the apex. If it were a brand, solid state would be the Rolls-Royce of batteries.
In 2020 and 2021, QuantumScape and Solid Power went public in mergers with special purpose acquisition companies on the promise of making solid-state batteries. Many investors saw them as the industry’s ultimate winners, as long as they could make what they promised, since their batteries would provide the greatest driving range.
But here’s the thing: These companies’ batteries wouldn’t deliver more range because they are solid state; they would do so because they use lithium-metal anodes. Lithium metal is superior to other anode materials because it’s by far the most energy-dense battery metal currently known. A lithium-metal battery could easily power a standard-size EV 500 miles on a charge, compared with 300 or so miles using a similarly sized conventional battery. But it’s highly volatile, especially when it’s around conventional liquid electrolytes. Solid-state designs are primarily intended to make lithium metal safer.
To use lithium metal, you need some form of solid separator. That sounds easier than it is—solid battery materials like oxide ceramics can be tricky to manufacture at large scale and with fast production. They can impede a battery’s performance, because it’s harder for lithium ions to move through a solid than a liquid, making an EV sluggish. And the material inside—the solid electrolyte along with the lithium metal—is superexpensive compared with the insides of a conventional EV battery. Either way, the thing to keep in mind is that it’s the lithium metal, not the solid package it comes in, that matters most in a solid-state battery. Investors who see it the other way are committing an error analogous to calling a hamburger a “bun,” when those couple of pieces of bread are really just a way to package the beef, or admiring a person for their skull when it’s the brains inside that matter. The more appropriate label is a lithium-metal battery.
The questions about Toyota aren’t only about one company’s attempts to regain its technological street cred, but reflect a wave of uncertainty about solid state itself. As far as I can tell, no prominent company is positioned to deploy a pure solid-state lithium-metal battery any time soon. That includes Toyota, which declined to divulge whether its solid state battery uses lithium metal. A number of lithium-metal battery companies say they have tried but failed to make pure solid-state lithium metal work. Qichao Hu, CEO of lithium battery developer SES AI, told me he couldn’t get such batteries to produce enough cycles before they failed, nor to generate enough power, meaning an EV equipped with such a battery would not accelerate fast enough. SES turned to what Hu calls a “hybrid” system that uses a liquid electrolyte called “solvent in salt” and a solid coating over the lithium metal. After also failing to make solid-state technology work, QuantumScape turned to a semisolid battery that uses a gel in the cathode to get enough power out of the battery.
“A lot of companies are just trying to plant a flag in the ground and say, ‘We did it first,’” said Pedro Pacheco, an auto industry analyst with consulting firm Gartner. “Therefore, you have a lot of companies coming forward and saying, ‘We’re working on solid state’ or ‘We’re about to launch solid state.’” But they aren’t—at least not authentic solid state.
A Decade of Promises
This is a big point of hype in batteries: A slew of solid-state developers—among them U.K.-based Ilika, China’s WeLion New Energy Technology, Taiwan’s ProLogium Technology and Colorado-based Solid Power—are using silicon as the anode, not lithium metal. This is because silicon is much easier to handle in a battery than lithium metal is; silicon is less volatile and doesn’t require the same care. It delivers less specific energy density than lithium metal does—around 330 watt-hours per kilogram versus 400 Wh/kg or more, respectively. But it can store 10 times as much energy as conventional graphite anodes, making silicon anodes extremely attractive for use in an EV.
The thing is, solid state isn’t necessary in a battery using a silicon anode, because silicon isn’t an inordinate fire hazard. Silicon anode developers like Sila Nanotechnologies and Group14 Technologies get roughly the same energy density using a liquid electrolyte as one would with a solid, with more power and at lower cost. That is, the solid state-silicon battery makers are employing an expensive structure for no good reason. They’re adorning themselves with the cachet of solid state, but using an inferior anode material that defeats the purpose of going through the trouble. It’s a kind of Potemkin solid state.
A small number of companies, including SES and QuantumScape, are attempting to go the lithium-metal route while shelving the hope of pure solid state. SES, a Massachusetts startup we have profiled, appears to be ahead of the pack. Last month, the company announced that it had reached the B-sample stage of validation with South Korea’s Hyundai Motor, and was on track to be in a commercial EV in 2025 or 2026. San Jose, Calif.-based QuantumScape says it has entered the earlier A-sample qualifications with a major automaker but hasn’t revealed which one.
A Practical View
Rory McNulty, a next-gen battery analyst at Benchmark Mineral Intelligence, a battery metals research firm, said it’s crucial to remember that lithium is hard to work with. Few companies produce lithium-metal foil at the size and quality required for EV batteries. So, he said, a lot of companies have gone to silicon as a way to start developing a solid-state battery, with the aim of moving on to lithium metal later, once they know what they are doing.
Arguably, one of these is WeLion. In April, China’s Nio plans to release an EV using WeLion’s solid state-silicon battery. WeLion claims the battery will deliver specific energy density of 360 Wh/kg, much better than the 240 Wh/kg achieved by conventional lithium ion, and will power the Nio around 390 miles on a charge, calculated using the U.S. mileage standard.
You could get similar performance from a silicon anode using conventional liquid electrolyte. But McNulty said WeLion’s advance is “important because they’re getting their first solid electrolytes out, and they can test and optimize their electrolyte system.”
What he says makes sense if these companies are teeing themselves up to tackle lithium metal next. But Toyota and others aren’t talking about solid state, or lithium metal, this way. They are suggesting that they are already poised to reach the pinnacle of battery technology. They aren’t.