For almost two decades, solid-state batteries have been hailed as the game-changer for electric vehicles. A breakthrough that promises to eliminate range anxiety, slash charging times and make electric cars as practical and convenient as gas-powered ones—without the nasty tailpipe emissions that pollute the air and harm human health.

And yet, solid-state batteries have felt like they’ve been trapped in the lab. So what’s holding them back? How close are they to powering EVs? Are they even real, or will this technology always be science fiction?

Experts told InsideEVs that solid-state battery progress isn’t as sluggish as it seems. Companies are closer than ever to commercialization, but hurdles remain. Just like lithium-ion batteries, their build-out is expected to be slow and gradual. Semi-solid-state batteries are set to hit the market first, serving as a “bridge technology” before fully solid-state packs reach mass production.

“We’re in the mode of trailblazing the breakthroughs to move them closer to automotive applications,” Siyu Huang, the CEO of battery startup Factorial told InsideEVs. “The main challenge for solid-state is scalability,” she added—the ability to produce them in mass quantities. 

How This Works

In a traditional lithium-ion cell, the electrolyte—the material that carries the charge-carrying ions between the charging and discharging cycles—is typically a lithium-based liquid chemical. Solid-state batteries swap that out for a solid electrolyte, often made of polymer, sulfides or oxides. The goal remains the same: shuttling electrons between the cathode and anode to power the vehicle.

Research has shown that this switch brings key advantages. Solid-state batteries pack more energy into a smaller space; they’re faster charging while also being safer and delivering better thermal stability than traditional lithium-ion batteries. In theory, this should eliminate many common and troubling problems with EVs: range losses in extreme temperatures, fire risks and more.

Semi-solid state batteries, on the other hand, use a gel-like electrolyte instead of a fully liquid or solid one, offering better energy density and safety. They’re a hybrid solution between conventional lithium-ion and all solid-state batteries.

Now, there’s a massive push to bring both these battery chemistries to life. Huang’s Massachusetts-based Factorial is among the leaders in this space. It has entered into joint development agreements with Mercedes-Benz, Stellantis and the Hyundai Motor Group (which may even reveal its own solid-state prototypes next month, according to reports.)

Several other players are also racing to develop this tech. California-based QuantumScape has an agreement with Volkswagen Group’s battery subsidiary PowerCo to industrialize solid-state batteries. The BMW Group and Ford have invested millions of dollars in Colorado-based Solid Power. And Toyota and Honda are leading their own in-house solid-state battery development efforts in Japan.

Last year, Factorial revealed its Solstice all-solid-state battery. It uses a sulfide-based electrolyte claimed to achieve a breakthrough energy density of 450 watt-hours per kilogram. Most lithium-ion cells currently used in EVs have an energy density of well under 300 Wh/kg. A higher energy density means an EV battery can store more power without getting bigger or heavier, leading to longer driving range.

However, mass-manufacturing solid-state batteries is a big hurdle. “Part of the timeline issue is that you can’t use the same manufacturing plants and processes for SSBs,” said Liz Najman, the director of market insights at battery health and data start-up Recurrent. “You need to build everything new, which requires money and time.”

Why Is It So Hard?

The U.S. government’s National Science Foundation explains in great detail the manufacturing requirements for solid-state batteries and how different they are from lithium-ion batteries. Simply put, battery manufacturing requires three main processes: electrode production, cell production, and cell conditioning.

These processes and the related supply chain is heavily optimized for the production of lithium-ion batteries. Now the challenge lies in reconfiguring those for solid-state batteries. That shift is akin to the transition from ink to laser printing, or replacing copper wires to fiber optic cables. It needs a redesign and rethink of the entire infrastructure. And since the technology is still new, researchers are working to overcome these hurdles to achieve consistent performance and reliability.

“All of these processes will be altered for solid-state batteries and are highly dependent on the material properties of the solid electrolyte,” the paper says, before concluding that the near-term solution to fast-track commercialization would likely “be a hybrid approach which adopts processes from both conventional LIBs and solid oxide fuel cell communities.”

Factorial is doing just that, incorporating its proprietary processes while carrying over some of the proven techniques used to make lithium-ion batteries.

Last year, it opened what’s claimed to be the largest solid-state battery manufacturing line in the U.S. in Methuen, Massachusetts. The 200 megawatt-hour line seems small compared to the giant battery plants being erected across the U.S. with hundreds of gigawatt-hours of capacity. But Factorial’s line is still a big milestone.

It has already sent a “B-sample” to Mercedes-Benz for testing, claiming to be the first battery company to send a sample of an all-solid-state battery to a global automaker. B-sample refers to a near-production prototype of a battery. It’s used for more advanced testing, such as performance validation, safety assessments and integration into EVs.

Building these cells without defects on an assembly line is also a challenge. “We’re able to get an 85% yield for the pilot line,” Huang said, referring to the rate of cells produced that meet quality standards and are considered usable. “Usually, in a big manufacturing line, you need to have more than 95% yield,” she said. So, there’s still some refinement and scalability left to achieve.

The 40Ah Solstice cells also use a novel production process called dry cathode coating—a process Tesla has also been reported to have been exploring for its next-generation cells.

According to the Oak Ridge National Laboratory, the electrodes in traditional lithium-ion batteries use a wet slurry that’s expensive, harmful to the environment and takes up a lot of space on the factory floor. The dry process eliminates this toxic slurry by mixing “dry powders with a binder,” which can cut costs, slash energy use, and shrink the environmental footprint of battery production.

Over 600 Miles Of Range?

The result? Factorial claims its energy-dense packs can deliver a driving range of over 600 miles. That’s more than double the average EPA-rated driving range in the U.S., which according to the Department of Energy was 283 miles. That in itself is a feat because it has tripled over the last decade. Factorial also claims operating temperatures of over 90 degrees Celsius and a 40% weight reduction over traditional batteries.

However, Factorial’s quasi-solid-state battery is a near-term solution that can also deliver a high performance and also easily scale up. It uses a gel-like material for the electrolyte along with a lithium metal anode and a high-capacity cathode. This combines the advantages of solid-state electrolytes with the manufacturability of conventional lithium-ion batteries, the company claims.

Semi-solid state batteries have already entered the Chinese market. Last year, a Nio ET7 owner achieved 554 miles (892 km) of range on a single charge, thanks to its 150-kilowatt-hour semi-solid state pack.

They’re soon coming to the U.S., too. Stellantis has promised to launch a demonstration fleet of the Dodge Charger Daytona equipped with Factorial’s quasi-solid-state batteries next year. It is claimed to have an energy density of 390 Wh/kg, much higher than the current industry standards of around 250-300 Wh/kg.

Photo by: InsideEVs

They also bring huge weight advantages. Huang added that solid-state batteries can save up to 200-300 pounds on the pack level. “On the vehicle level, SSBs can even save up to 1,000 pounds,” she said. “If we reduce the pack weight, we can also reduce the supporting structures.” Weight saving is directly tied to cost saving. With every pound eliminated, battery makers can save $5, Huang said. If they can slice 1,000 pounds, that’s a big cost differentiator.

“The U.S. loves really big, non-aerodynamic SUVs and trucks,” Recurrent’s Najman said. “These require huge batteries to compensate for their poor physics, and they get really heavy. SSBs can offer more power in a much lighter package, so they may find use in the SUV/truck segment,” she added. However, automakers are moving towards extended-range powertrains for larger vehicles, which have backup gas generators to charge the battery.

All said solid-state batteries are primed to live up to the hype, Najman added. “The hype is part of what has made manufacturers extra cautious,” she said. “With all the promise of SSBs, you don’t want to release one that flops.”

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