Solid State batteries use approx the same Lithium from my understanding as existing batteries. The breakthrough is the removal of the Graphite anode or Graphite/Slicon Anode completely which reduces the physical battery size and the replacement of the Liquid Electrolyte by using a solid separator. This effectively reduces physical the size of Battery without reducing the charge it can hold. Quantumscape has recently successfully tested the use a solid state Ceramic separator (Holy grail?) which enables this and also reduces/stops/limits the growth of dendrites which cause reduced life span for existing batteries. Hence increased energy density per Volume, less dendrites means longer life and safer batteries See the presentation at this link
