Unknown rechargeable lithium cell - Page 1
Forum section: electronics / projects

author: Zom-B
author_rank: Regular Contributor
timestamp: August 26, 2017, 06:27:20 pm
content: Say I've got some flat-shaped rechargeable lithium cells from the dumpster, and I want to know if they are Li-Ion or Li-Po secondaries. I know the mAh (or approximately know by comparison with another cell of similar size (or by charging it from fully discharged state and noting the mAh from the charger)).Assuming I have all the lab equipment necessary, is there a sure-fire way to determine the type?Is the shape alone enough to conclude LiPo, or do there exist flat Li-Ion cells?When I charge them fully using the same procedure, is there a measurable difference in voltage?Do I need to plot a discharging curve to find out?Other non-destructive method?Is it even useful to know the type? For one, mychargerdifferentiates between LiPo and Li-Ion modes, but there could be a negligible difference that I don't know of.

author: sleemanj
author_rank: Super Contributor
timestamp: August 26, 2017, 09:47:28 pm
content: "Li-Po" is a (somewhat vague) sub classification of Lithium-Ion cells, what we typically call "li-po" are really just soft pouch cells, instead of hard shell cells we typically call "lithium-ion". There are some manufacturing differences but in terms of usage, voltages and charge the same. That is, "Li-Po" cells are "Li-ion" cells, just soft ones, not hard ones.Ot course the cells you have might not be lithium-ion at all, they could be perhaps LiFePo4, or other formulation with lower voltage spec, which is not impossible but unlikely since Li-Ion is cheaper and ubiquitous in consumer devices.

author: Zom-B
author_rank: Regular Contributor
timestamp: August 27, 2017, 08:56:28 am
content: With an open circuit voltage of 4.0V I doubt they're anything but Li-Ion. One coin-shaped cell was 0.1V which I disposed of, another coin-shaped was 3.0V (written on it) so not rechargeable but still ok.According to my charger manual, Li-Ion is 3.6V and Li-Po is 3.7V fully charged, 4.1V/4.2V cutoff, 3.7V/3.8V shelve and 2.9V/3.0V discharge, respectively. All values are 0.1V higher for Li-Ion.

author: sleemanj
author_rank: Super Contributor
timestamp: August 27, 2017, 10:19:27 am
content: Voltages are chemistry dependant. Lithium-ion is a catch-all phrase which encompasses many chemistry types (as noted already, "li-po" really is more about packaging than chemistry).But (excepting LiFePo4) 4.2v can be generally regarded as the maximum voltage. The nominal voltage isn't really that important to know.Some, older cells had a 4.1v max, there's nothing to say you have to charge a cell to it's maximum, so if you don't know you can always just call it done at 4.1v.The main difference in practice to be aware of is that LiFePo4is 3.6v fully charged, while typical lithium-ion cells are 3.7v nominal (4.2v fully charged).Some chemistry information.http://batteryuniversity.com/learn/article/types_of_lithium_ion

author: Kilrah
author_rank: Unknown
timestamp: August 27, 2017, 11:17:15 am
content: Anything newer than 10 or so years should be 4.2V. Could cycle it once at 4.1, and if you're quite far from rated capacity switch to 4.2 with supervision.There also might be a part no marked on the cell you could search for.