For solid-state batteries, much risk and huge potential rewards

Electric vehicles still have less than 10 percent market share in Europe -- and are just a tiny fraction of worldwide sales -- but automakers and suppliers are already spending billions to develop solid-state batteries, the next generation of technology that promises faster charging, better energy storage and improved safety.

Automakers have offered various dates for when solid-state batteries will appear. The Chinese EV maker Nio has perhaps been the most aggressive, announcing that it will offer the technology by the end of 2022. 

Toyota and VW have invested heavily in solid-state batteries, and both say they will have vehicles with the technology on the road in 2025. Others are looking further ahead, including Stellantis (2026), BMW (2026), Daimler (2028), Renault-Nissan (after 2026) and Hyundai (no earlier than 2030).

Solid-state batteries will be a key driver in bringing down battery pack prices and making EVs both profitable and affordable. Bloomberg NEF says that solid-state batteries, produced at scale, can be made at 40 percent of the cost of current lithium ion batteries.

But independent experts are cautious, noting that there are a number of daunting technical hurdles yet to be cleared, including high operating temperatures, electrolyte durability and manufacturing challenges.  

"We have yet to see a commercially viable solid-state battery in the [automotive] sector," said Oliver Petschenyk, a powertrain analyst at LMC Automotive. "We remain skeptical about the dates that suppliers and designers can actually achieve. It may be the tail end of the [2020s] before solid-state cells come to fruition."

The Faraday Institution, the UK’s premier battery research institute, estimates that solid-state batteries will make up less than 5 percent of all transportation batteries in 2030, rising steadily to 30 percent by 2040 as battery makers scale up production.

Faraday says that research into solid-state batteries is "long-term and high-risk, but also has the potential to be high-reward." The main reward is 70 percent greater energy storage per unit volume versus current wet electrolyte lithium ion batteries.

Experts at Yole Developpement, a French analyst company, say solid-state batteries will roll out gradually, starting around 2025-26, with the first application in luxury or premium vehicles. 

The main challenge right now is finding the right material for the electrolyte, which moves ions between the anode and cathodes in the battery cell. All current solutions involve unacceptable trade-offs between ionic conductivity, battery life and safety, said Milan Rosina and Shalu Agarwal of Yole, which has recently released a comprehensive report on solid-state technology.

"Today, we don’t have a combination of materials that is compatible with high-volume production," said Rosina, principal analyst. power electronics and batteries at Yole. "This is why we have so many big players involved and are investing in startups with different technological approaches."

With that in mind, automakers are pressing ahead, striking up alliances and even acquiring startups with promising technology.

"The endgame, from our point of view, is solid state," Frank Blome, head of battery and systems at Volkswagen Group components, said at VW’s Power Day presentation this spring. "The simpler design leads to higher performance and lower costs."

VW estimates that range will be improved by 30 percent, largely due to weight reduction. The automaker’s showcase collaboration is with QuantumScape, a Stanford University spinoff that it has been working with for nearly a decade. 

It now holds a one-third stake with an investment of $300 million dollars as well as a seat on the board of QuantumScape, which has recently announced it is testing a 10-layer solid-state cell that can recharge in 15 minutes.

Renault, a pioneer in electric vehicles, also sees solid-state batteries as the next big step. With alliance partner Nissan, it has invested $65 million in Ionic Materials, a U.S. solid-state startup.

"Ultimately, the target is all-solid-state technology," Sophie Schmidlin, director of advanced engineering at Renault Group, said at Renault’s EWays EV event in July. "This appears to be the real game changer, from both performance and cost point of view, opening the way to many technological breakthroughs." 

Toyota is the only automaker to publicly road test solid-state batteries, in its lQ concept. It is working with Panasonic on a sulfite-based electrolyte, one of the more promising approaches, experts said.

Other publicly announced alliances including BMW and Ford with SolidPower, which plans to merge with a SPAC to go public, and Renault-Nissan with Ionic. 

Major battery players are walking a fine line. Rosina of Yole said they are already hugely invested in conventional lithium ion batteries, and see risky and costly solid-state technology as both a threat and a business opportunity.

A current Mercedes-Benz EQS has an energy density of 550 Wh/liter, Mercedes CTO Sajjid Khan noted in July at a Daimler EV strategy event. Solid state batteries "will double the energy capacity and reduce the weight in the same packaging space," he said, as well as allow for more charging cycles. 

"With solid state, we have the opportunity to rethink the design of battery systems as a whole," Khan added.

Daimler is currently producing a test series of electric buses with solid-state batteries, the eCitaro G, using cells produced by the French company BlueSolutions. But the batteries need to be pre-heated, which is not practical for private passenger cars.

Solid-state batteries also have advantages in terms of charging time. Volkswagen estimates that an ID4 electric SUV with a 77 KWh battery now takes 25 minutes to add 450 km of range (going from 10 percent charge to 80 percent) -- but solid-state batteries can cut that time to 12 minutes.

Another critical benefit is safety. Battery recalls linked to fires have cost automakers and suppliers billions of euros in recent years. In the most recent case, Chevrolet recalled all 141,000 Bolt EVs it had built since the car was launched, at an estimated cost of $2 billion -- and LG Chem, the battery supplier, agreed to pay Chevrolet $1.9 billion to cover the cost.

In 2020, Ford recalled 69,000 Kuga plug-in hybrids at a cost of $800 million. And in February 2021 Hyundai said it would spend $900 million to replace battery systems in 82,000 electric vehicles.

Solid-state batteries can mitigate much of this risk, because they do not use a flammable electrolyte and because a solid electrolyte should act as a shield against the growth of dendrites -- spiky, algae-like lithium deposits that can form on the anode, move through the electrolyte and puncture the separator, causing short circuits that can lead to fires. 

"A reduction in dendrites results in a longer-lived cell that can take more load with less fire risk, especially as a flammable liquid electrolyte is no longer required," Petschenyk said.

Agarwal and Rosina, the Yole analysts, say the risk of dendritic formation is less, but still very real because even solid electrolytes have grains or faults than can allow them to grow.

Finally, there are some benefits that will appear only when solid-state cells are assembled into battery packs and integrated into electric cars, experts say.

If solid-state batteries are indeed much safer, that means electric vehicles will need less robust (and cheaper) components to ensure safe functioning. They could also require less cooling, Rosina said, meaning less energy would be drawn from the battery that could be used for range.

In traditional lithium ion battery cells, lithium ions flow between positive and negative electrodes, discharging and charging the battery. The negative electrode, called an anode, and the positive electrode, called a cathode, are divided by a separator that allows the ions to pass through. Between the anode and cathode is a liquid electrolyte.

In contrast, lithium ion solid-state batteries combine the separator and electrolyte into a single, solid item. As a result, the cells can be made much thinner, meaning more can fit into a similar space as "wet" electrolyte cells. 

In terms of energy density, solid-state batteries are capable of densities of 900 to 1,300 Wh/liter, while conventional lithium ion batteries potentially top out at about 1,000.

Automakers can take advantage of this by increasing range for the same size and weight, or reducing battery pack size by maintaining weight.

Despite the potential for use in fleets or public transit -- batteries that need to be pre-heated could be a technological dead end -- solid-state batteries are likely to appear first in premium vehicles or as performance options in less expensive models, experts say. That is because it’s not viable to build a Gigafactory with a capacity to supply the mass-market needs of a Tesla or VW, which will build hundreds of thousands of EVs a year, Agarwal and Rosina said. 

Initial demand is likely to be just 2 to 3 Gigawatt hours a year in 2025 and the following years, meaning higher costs at a time when conventional lithium ion battery prices are declining. 

Prices will fall as solid-state battery production scales up, but there is an unusual set of challenges ahead, experts said. 

Sulfite electrolytes, which Toyota, Samsung and others are pursuing, can produce toxic hydrogen sulfite (H2S gas). In general, cells must be assembled in a vacuum, which is not acceptable for mass production. And thin solid electrolytes are very fragile. 

Rosina said that, similar to the transition from internal combustion to electric vehicles, the transition to solid-state will necessitate a new set of competencies, potential job cuts, major changes to factory equipment, and new materials supply chains. 

"Fixed costs," he said, "will penalize the commercialization state of solid-state batteries."