A solid-state battery is a battery that uses a solid electrolyte instead of the liquid or gel electrolyte found in many common lithium-ion batteries. The electrolyte is the material that lets charged particles move between the battery's positive and negative sides during charging and use.
The reason people are interested in solid-state batteries is that they may offer several improvements. A solid electrolyte can be less flammable than some liquid electrolytes. It may also allow different battery designs that store more energy in the same space. That could be useful for phones, laptops, electric vehicles, medical devices, and energy storage systems.
A solid-state battery still has familiar battery parts, including electrodes and an electrolyte. The difference is the material and structure between those electrodes. Some designs use ceramic materials, some use glass-like materials, and others use polymers. Each approach has tradeoffs in cost, manufacturing, durability, and performance.
One challenge is mass production. A battery that works well in a lab does not automatically become cheap, reliable, and easy to manufacture at large scale. Engineers must solve issues such as material contact, cracking, cycle life, and performance in different temperatures.
The simple definition is this: a solid-state battery is a battery design that replaces the liquid path inside the cell with a solid one. If the technology is produced well, it could make future devices safer, longer-lasting, and more energy dense.