3 ms·

> This is somewhat mitigated by the fact that LiFePO4 handles 100% charges and 100% discharge I don't think that's quite true. LFP cells have a minimum voltag

by elihu 5y ago

> This is somewhat mitigated by the fact that LiFePO4 handles 100% charges and 100% discharge I don't think that's quite true. LFP cells have a minimum voltage; they may survive being discharged to zero, but it probably isn't a good idea for long-term longevity. (I'm currently working on an EV conversion that uses LFP cells, but I haven't actually done durability testing or anything like that, I'm just going by what people recommend.) Lithium ion and LFP batteries though don't have voltages that are linear with capacity; on an LFP once you're below 2.2 volts or so there's not much left. I do agree though that LFP cells are pretty amazing if you're a car manufacturer that wants to make a reasonably priced mass-market EV. I think in the near term (i.e. until there's some cheaper/better substitute), they could take over the non-luxury-car EV market and allow the rest of the world outside of China to start seeing pretty good EVs that are price competitive with equivalent ICE vehicles.

sudosysgen 5y ago
That's not quite what 100% discharge usually refers. 100% discharge means from the maximum charge voltage to the minimum discharge voltage. That corresponds to, normally, using up the rated capacity of the cell. On lithium batteries you'd normally only use 80% of the rated capacity if you want to maintain durability.
- deleted 5y ago
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- jacquesm 5y ago
  Exactly, depending on the make/model that's either 3.0V, 2.8V or 2.5V lowest discharge limit. If you go under that you basically can not longer trust the cell integrity and should dispose of it (no matter what miracle workers on the web say, the copper in the cell will have gone into solution and it can be deposited anywhere at all, but never again in the same spot where it was supposed to be so you are essentially the proud owner of an incendiary with a random length fuse...).
- elihu 5y ago
  Ah, that makes sense. I guess it's kind of arbitrary (I mean, you could just call 80% full "100%" if that's all you'd use in practice) but it does seem quite useful if the "full" voltage is generally agreed to be in a narrow range and not have a wide range of maximum values depending on whether you care more about absolute capacity or longevity.

by elihu 5y ago

sudosysgen 5y ago

That's not quite what 100% discharge usually refers. 100% discharge means from the maximum charge voltage to the minimum discharge voltage. That corresponds to, normally, using up the rated capacity of the cell. On lithium batteries you'd normally only use 80% of the rated capacity if you want to maintain durability.

deleted 5y ago
[deleted]
jacquesm 5y ago
Exactly, depending on the make/model that's either 3.0V, 2.8V or 2.5V lowest discharge limit. If you go under that you basically can not longer trust the cell integrity and should dispose of it (no matter what miracle workers on the web say, the copper in the cell will have gone into solution and it can be deposited anywhere at all, but never again in the same spot where it was supposed to be so you are essentially the proud owner of an incendiary with a random length fuse...).
elihu 5y ago
Ah, that makes sense. I guess it's kind of arbitrary (I mean, you could just call 80% full "100%" if that's all you'd use in practice) but it does seem quite useful if the "full" voltage is generally agreed to be in a narrow range and not have a wide range of maximum values depending on whether you care more about absolute capacity or longevity.