Li-ion nominal voltage, why so low?

[jsavukoski]

Hi,

Can someone shed a light on why the li-ion nominal cell voltage is only 3.6/3.7 and not higher? I'm just puffing here with my e-cig and wondering how much more efficient (FET driving, conductor losses -wise) it would be if the single cell voltage would be higher.

Is it a compromise with power density? Higher voltage would decrease that? Or something to do with chemistry? In some “natural” (compact) configuration you just happen to get that nominal voltage?


And, yea, no series-cells battery configurations yet for these compact devices; balance charging is a bit of a pita.

-Janne

[IanB]

Hi,

Can someone shed a light on why the li-ion nominal cell voltage is only 3.6/3.7 and not higher? I'm just puffing here with my e-cig and wondering how much more efficient (FET driving, conductor losses -wise) it would be if the single cell voltage would be higher.

Is it a compromise with power density? Higher voltage would decrease that? Or something to do with chemistry? In some “natural” (compact) configuration you just happen to get that nominal voltage?


And, yea, no series-cells battery configurations yet for these compact devices; balance charging is a bit of a pita.

-Janne

This question comes up from time to time, but the answer is simple. The voltage of a cell is governed by chemistry: by the electrode materials and the electrolyte. There is no free choice about what it is. It is fixed and immutable.

[danadak]

Ref material -


https://www.quora.com/How-does-a-battery-produce-its-potential-difference-voltage


https://chem.libretexts.org/Core/Analytical_Chemistry/Electrochemistry/Voltaic_Cells/The_Cell_Potential


Regards, Dana.

[Belrmar]

The nominal voltage of a LI-ion is governed by chemistry, we are not chemists but ee's so we can f*** ourselves and use cells on series  lipo cells are compact enough to use them in series , but the balancing circuitry is annoying

[Audioguru]

A normal Lithium Ion cell is fully charged at 4.2V, is 3.7V at half a discharge and is about 3.2V when almost dead. If it discharged lower than 3.2V then it is destroyed. If it is charged higher than 4.2V then it might blow up and/or catch on fire.

[sleemanj]

If it discharged lower than 3.2V then it is destroyed.

Maybe in the dim dark ages, but I will happily take any of your "destroyed" lithium ion cells if you are throwing them out at under 3.2v!

Even datashsets state the discharge voltage way less than that for typical cells.

[james_s]

There is also resting voltage vs voltage under load. At least with the high current LiPos I use in RC aircraft it is generally not advised to run them down below about 3.4V/cell. Doing so causes them to degrade faster, if you only discharge about 80% of the capacity they will last longer.

[metrologist]

This is good post for some questions I had about # of charge cycles for li-ion . I think I read that if you don't discharge below 90%, then that is not considered a cycle, and that if you don't discharge below what's been stated, you can 3-4x times the number of cycles. So I guess I should plug my phone in more often and charge up my ebike after every ride.

[Mjolinor]

Best not guessing and go looking for the truth on t'Interweb.

I run my phone 80% to 40% when ever I can.