I wasn't sure what a solid state battery is, so I looked it up on Wikipedia.

Fun fact though:

> Between 1831 and 1834, Michael Faraday discovered the solid electrolytes silver sulfide and lead(II) fluoride, which laid the foundation for solid-state ionics. Through his research, Michael Faraday took note of these solid compounds transitioning from insulators to conductors after being heated. While this would take almost another century to be acknowledged by Michael O'Keeffe in 1976, this mixed ionic/electronic conductions became the first record of a solid-state battery

(emphasis mine)