What will replace lithium ion batteries in Tesla cars?

Who knows? There have been a number of promising ideas over the last few years, but none have panned out yet. Some of these may be pushing for research grants, so there’s a vested interest in making the new ideas look good. The Air cells for instance have serious unresolved issues. They more or less work with pure oxygen, but carbon dioxide in air limits their life severely.

It would be good to see new tech, but I’m not holding my breath. If we did manage to increase energy density significantly, we’d also likely be increasing the explosion risk if anything went wrong.