Solid-State Batteries Explained: What They Are and When They Arrive

A solid-state battery replaces the flammable liquid electrolyte in a lithium-ion cell with a solid material. The design promises longer range and better safety. But the fully solid version has not reached mass production. The International Energy Agency (IEA) classed all-solid-state cells as prototypes in May 2026. Carmakers' first launch targets fall in 2027 and 2028. The IEA expects the technology to stay in premium models until the first half of the 2030s.

What is a solid-state battery?

Every battery cell has two electrodes and, between them, an electrolyte. The electrolyte carries lithium ions from one electrode to the other as the cell charges and discharges. In today's lithium-ion cells the electrolyte is a liquid: a lithium salt dissolved in flammable organic solvents. A solid-state cell uses a solid electrolyte instead.

MIT Technology Review explains that without the liquid, a cell could hold more energy for its size. That, it says, is why the technology is linked to longer-range EVs. Toyota says all-solid-state cells could be smaller, more powerful and longer-lived than liquid-based batteries, and could charge faster.

Those remain promises. In its Global EV Outlook 2026, the IEA said the range and safety advantages had not yet been demonstrated in real-world use. A 2023 perspective in the journal Nature Communications adds a caution: solid electrolytes are not automatically fireproof. It says some can react with oxygen or water and release heat and toxic gases.

Are solid-state batteries in production yet?

It depends on which kind. Semi-solid-state cells are already on sale. MIT Technology Review reports on these hybrids, citing a BloombergNEF analyst. It says they keep some liquid, often in the form of a gel electrolyte. It says many Chinese companies plan to build them as a step toward fully solid cells.

SAIC's MG4 Anxin Edition was delivered to customers in China on December 18, 2025, according to trade publication Automotive Manufacturing Solutions. The publication says its battery contains about 5% liquid electrolyte, compared with roughly 20% in standard cells. Labels vary. The IEA applies the semi-solid term to polymer-electrolyte cells that must run at about 60 to 90°C.

All-solid-state cells, with no liquid at all, are a different matter. The IEA said they were being produced at small scale for testing. It classed them as prototypes, along with what it calls almost-solid-state designs. Those designs add a little liquid at the cathode, the positive electrode. The safety benefits most often cited belong to these two groups, the agency notes.

When will solid-state batteries arrive in cars?

The companies' stated targets:

• Toyota is aiming to launch battery electric vehicles with all-solid-state batteries in 2027-28. It restated that goal in an October 2025 announcement. MIT Technology Review notes that the company once planned to have such cells in vehicles by 2020. It says Toyota has pushed the date back several times.
• BYD plans to sell its first EV with all-solid-state cells from 2027 and to begin mass production from 2030, according to the IEA. The agency says Samsung has set similar timelines.
• SAIC confirmed on April 3, 2026 that it was keeping its 2027 target for full solid-state cells, Automotive Manufacturing Solutions reports.
• Mercedes-Benz says it drove a test EQS 1,205 kilometers on one charge in late August 2025. It says the car used what it calls a lithium-metal solid-state battery, with cells from U.S. developer Factorial Energy. Its stated goal is series production by the end of the decade.
• QuantumScape is at pilot scale. In a shareholder letter filed on July 22, 2026, it said its Eagle Line, a pilot production line in San Jose, was shipping sample cells to customers. The company said it aimed to double output in the second half of 2026. It also reported a partnership with Honda, announced on June 18.

Why do solid-state timelines keep slipping?

Making solid-state cells in the volumes carmakers need has long been the sticking point, MIT Technology Review reports.

The gap between a pilot line and a full factory is wide even for conventional batteries. The IEA says most plants can take more than five years after opening to approach their planned output. It says competing in today's market requires production yields above 90%.

Solid-state adds its own complications. The IEA describes all-solid-state manufacturing as more complex and costly than lithium-ion production. It says packs are harder to engineer because the cells must be held under higher pressure. The Mercedes test car uses pneumatic actuators to keep pressure on its cells as they change volume during charging and discharging, the company says.

Cost is the other hurdle. The IEA expects early solid-state batteries to be expensive because manufacturing processes and supply chains are immature. It suggests that premium cars, and possibly robots, could be the first markets.

What to watch

Three things will test the 2027-28 targets:

• whether Toyota's launch date holds
• whether QuantumScape's licensing partners commit to full-scale factories
• how BYD and SAIC label their 2027 cars, since semi-solid and all-solid describe different technologies

A launch date for one model is not mass production. BYD's plan, as the IEA describes it, puts three years between its first solid-state car and volume manufacturing.