LiFePO4 batteries come in a variety of formats

[bulrush]

Including 18650 and larger.
https://hypercellbattery.com/lifepo4-battery/

I was just wondering if they came in AA or 18650 formats. I don't see AA yet but this is interesting. But the 18650 capacity is only 1400mah, while other Lithium 18650s go up to 2500mah or so.

 

[morth]

https://www.batteryspace.com/lifepo4rechargeablesinglecells1c-30crate.aspx has many shapes and sizes.