We haven’t perfected lithium-ion batteries for electric cars but the race is already on to replace them. Solid-state batteries are getting the most buzz as the heir apparent: Their proponents promise they’ll deliver longer range, faster charging and more affordable electric cars compared to today’s top EVs like the Tesla Model 3 and Chevy Bolt.

A solid-state battery is exactly that: A tightly compressed arrangement of hard materials rather than the slightly mushy stew that makes up a typical lithium-ion (li-ion) battery. That solid state composition and construction yields an electrochemical device that promises a lot of improvements:

Greater energy density. This could mean an EV with two or more times the current range, or possibly an EV with the same range but with a much smaller, lighter and less expensive battery that charges faster.
Faster charging. Estimates of an 80% charge in 15 minutes get bandied about a lot with solid state, performance that would be on par or a bit faster than today’s best li-ion applications.
Longer life. Solid-state tech is a key part of GM’s plan to produce a million-mile life battery, changing the equation of EV affordability and reducing concerns about mountains of toxic batteries that need recycling after 100,000 to 150,000 miles.
Thermal stability. Solid-state designs promise less likelihood of thermal runaway, which can cause a fire. Li-ion batteries have developed a nasty reputation for this.

Read more: How solid-state batteries can transform electric cars