Yes, most solid state batteries use lithium. The defining feature of a solid state battery is its electrolyte (the material ions travel through), which is solid rather than liquid. That’s a separate question from what type of ion carries the charge. The vast majority of solid state batteries in development today rely on lithium ions, and many go a step further by using pure lithium metal as one of their electrodes.
What Makes a Battery “Solid State”
In a conventional lithium-ion battery, lithium ions shuttle between two electrodes through a liquid electrolyte, typically an organic solvent. That liquid is flammable, which is the root cause of most battery fires. A solid state battery replaces that liquid with a solid material that still allows lithium ions to pass through. The chemistry is still lithium-based. The “solid state” label refers only to the physical state of the electrolyte.
Five main categories of solid electrolytes are in development: oxides, sulfides, polymers, nitrides, and halides. Each has trade-offs. Sulfide-based electrolytes conduct ions exceptionally well, reaching levels comparable to or even exceeding liquid electrolytes. Oxide-based versions offer excellent chemical and thermal stability. Polymer-based electrolytes are flexible and easier to manufacture. All of these are designed to transport lithium ions.
The Lithium Metal Advantage
Solid state designs don’t just use lithium ions. Many are built to use a pure lithium metal anode, something that’s too dangerous in batteries with liquid electrolytes because lithium metal forms needle-like structures (called dendrites) that can pierce the separator and cause a short circuit. A solid electrolyte is physically rigid enough to resist dendrite growth, at least in theory, which opens the door to lithium metal anodes.
This matters because lithium metal stores far more energy per unit of weight and volume than the graphite anodes used in today’s batteries. Solid state lithium metal batteries could reach energy densities upward of 500 watt-hours per kilogram and 1,000 watt-hours per liter. For context, the best conventional lithium-ion cells today top out around 250 to 300 watt-hours per kilogram. That potential leap is the main reason automakers are investing billions in this technology.
There are real challenges, though. When a lithium metal anode charges, lithium doesn’t always plate back evenly, which causes some active lithium to be lost each cycle. Engineers currently compensate by including excess lithium, but that extra material adds weight and cost. A recent techno-economic analysis published in Nature Energy estimated that lithium metal anodes would cost roughly $24 per kilowatt-hour, about double the $12 per kilowatt-hour for traditional graphite anodes. The total pack cost for a solid state cell came to about $158 per kilowatt-hour versus $126 for a conventional liquid-state cell.
Why Solid State Batteries Are Safer
One of the strongest selling points is thermal stability. The flammable liquid in conventional batteries starts generating dangerous heat at relatively low temperatures. In testing on lithium metal pouch cells, solid state cells with a sulfide-based electrolyte didn’t experience thermal runaway until reaching 275.5°C when fully charged. Comparable liquid electrolyte lithium metal batteries hit thermal runaway at 215.3°C, and they began self-heating as low as 112.2°C. At zero charge, the solid state cells showed only mild self-heating with no thermal runaway even up to 300°C. That wider safety margin could reduce the need for heavy cooling systems in electric vehicles, saving weight and cost elsewhere in the design.
Do Any Solid State Batteries Skip Lithium?
Researchers are exploring solid state batteries that use sodium or magnesium ions instead of lithium. Sodium is far more abundant and cheaper than lithium, making it an attractive long-term option. However, these alternatives are still in early development. No sodium or magnesium solid state battery is close to commercial production for electric vehicles or consumer electronics. For the foreseeable future, “solid state battery” effectively means “solid state lithium battery.”
When to Expect Them
Toyota holds over 8,400 patents related to solid state batteries and has partnered with materials suppliers to prepare for mass production. Toyota, QuantumScape, and Samsung SDI are considered the furthest along, with pilot production and field trials projected between 2026 and 2028. The lithium metal supply chain is a potential bottleneck. Industry reports have flagged that battery-grade lithium metal production may not keep pace with demand as these companies scale up, since manufacturing thin, uniform lithium metal foils at high volume is a process the industry is still refining.
The cost premium over conventional cells is real but potentially justifiable. Faster charging, higher energy density, and improved safety could offset the roughly 25% higher pack cost, especially in applications like electric vehicles where range and weight are critical constraints.