EV battery companies debate semisolid vs. solid-state tech

To gel or not — that's the latest debate among electric vehicle battery developers.

Long seen as the holy grail for EVs, automakers and suppliers are spending heavily on solid-state battery technology that is expected to improve range, charging speed and safety.

But others see a variation — semisolid-state batteries— as offering nearly the same benefit but with an advantage: They are closer to commercialization.

A semisolid-state battery has a small amount of liquid or gel that allows fast diffusion of ions — or atoms with an electric charge — to charge and discharge an EV battery. It has far less liquid than a traditional lithium ion battery.

"Semisolid isn't a pipe dream. It's just around the corner, and it's feasible and has many of the benefits of all-solid-state," said Max Reid, principal analyst at Wood Mackenzie, an energy research and consulting firm.

Both are designed to increase the amount of energy stored in a battery. The goal is to enable lithium ions to move quickly between the anode (the negative electrode) and the cathode (the positive electrode).

Today's EV battery cells are flooded with liquid electrolytes that move ions through a porous separator between the anode and cathode. A solid-state battery typically uses a solid electrolyte separator and requires a nearly perfect attachment and movement of ions between the anode and cathode, said Richard Laine, professor of materials science and engineering at the University of Michigan.

In contrast, a semisolid-state battery cell contains small amounts of liquid or gel for easier transfer of the ions.

No battery company has commercialized either technology for the U.S. market, analysts said. Many are trying. All want batteries that hold more energy, charge more quickly and are safer than today's cells.

Startups, such as Factorial Energy, StoreDot, SES AI, Lyten, QuantumScape and others are developing batteries with small amounts of liquid or gel. They have backing from major automakers, including General Motors, Volkswagen, Honda and Hyundai.

SK On, Samsung SDI and Toyota are each developing solid batteries with a ceramic or polymer electrolyte, rather than liquid or gel. Toyota plans to launch the batteries with Idemitsu Kosan by 2028. Startup Solid Power is working on a solid battery with a powder electrolyte.

Although development of the batteries is complicated, some companies are finding success on their test benches and sending samples to automaker customers.

The core of many companies' solid-state development is lithium metal, which allows the cell and battery pack to achieve much more energy density than what they have today, said Conrad Layson, alternative propulsion analyst at AutoForecast Solutions.
Both the semisolid- and solid-state battery technologies are potentially safer than lithium ion batteries in today's EVs because they eliminate or reduce flammable liquid electrolyte, experts who spoke with Automotive News said. And they have more energy density, which can lead to longer ranges.

But the advances in semisolid technology call into question whether solid-state batteries should still be the industry's ultimate goal.

Semisolid players contend that solid batteries are a lost cause.

A few years ago, Israeli battery company StoreDot saw promising results of solid-state cells in its testing labs. But near-term success was wishful thinking, said CEO Doron Myersdorf. He said he believes commercialized solid-state batteries are at least a decade away.

"I had 10 Ph.D.s here working on solid state, and every time we tried to fast charge it, we saw major problems with safety" because of the highly reactive lithium, he said. Overall, there was no breakthrough in the battery's performance compared with semisolid chemistries, he said.

Now StoreDot is focused on a semisolid battery that enables ultrafast charging. The first iteration of its battery, slated for 2024, is expected to charge at least 100 miles in five minutes.

Battery startup SES considered solid-state a dead end when it found drawbacks in the manufacturing and performance of solid lithium metal batteries, said CEO Qichao Hu.

The company pivoted to a liquid lithium metal. The liquid version is easier, cheaper and faster to build than fully solid lithium metal, and it can provide more energy density than today's lithium ion cells, Hu said.

Lithium metal, whether solid or liquid, is the key to unlocking battery performance and safety and reducing cost, Hu said.

"The [auto] companies don't really care if the batteries inside the car are solid or liquid. What they care about is range, safety and performance and cost," he said.

Still, a potential energy boost makes solid-state technology appealing for some.

Lyten, which uses a lithium-sulfur chemistry, has solid-state batteries on its technology road map.

A lithium-sulfur cell that contains small amounts of liquid could achieve 600 watt-hours per kilogram, roughly double the average of a lithium ion cell. But a solid-state battery could likely reach 1,000 watt-hours per kilogram, said Celina Mikolajczak, Lyten's chief battery technology officer. The energy density alone makes solid-state a target, but Lyten's primary focus is semisolid because it is within reach.

QuantumScape, which is developing a battery with a solid separator, a lithium-metal anode and some liquid in the cathode, is considering solid-state eventually, but its priority is launching its semisolid cell because "it's still such a powerful difference compared to what's out there today," said QuantumScape CMO Asim Hussain.

Battery developers pushing semisolid cells see an advantage in the $140 billion in U.S. investments for EV and lithium ion battery plants. Though semisolid cells contain less liquid than today's lithium ion batteries, the manufacturing processes and equipment are largely the same.

Manufacturers can use existing plants, speeding semisolid batteries to market and making them cost-competitive with today's cells, said Siyu Huang, CEO of Factorial Energy.

Retrofitting lithium ion battery production lines could be cost-prohibitive for solid batteries because production lines would need to be replaced, analysts said.

"If there is any solution that you want to implement in the next five years, it has to use the factories as they are," said Myersdorf of StoreDot.

Battery companies and analysts expect a combination of semisolid and solid-state batteries to launch in the late 2020s, with mass adoption in the early 2030s. Whether solid or semisolid, advanced battery technology can change the industry, Huang said.

"The battery industry has been awaiting disruption for 20 years," she said. "We want this technology to change the world. That's the fundamental vision for this company. It's really about when and how we can do that."