There are now 1.5 V lithium rechargeable AAs. Here's a typical example [1], and there are a ton of others.

I am almost certain they are implemented as 3.7 V lithium rechargeable batteries combined with a buck converter to get the 1.5 V output.

I think they are relatively new. I don't recall noticing them a few years ago, which was the last time I was looking for rechargeable AA batteries.

[1] https://www.amazon.com/Deleepow-Rechargeable-Lithium-Batteri...