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A couple of questions about lithium-based batteries

#1
I had these questions on my mind for quite a while now about lithium batteries:

Why are Lipo batteries used so much more in RC than Li-ion? I mean I get that Lipo batteries tend to be a bit more lightweight than Li-ion batteries, but that can't be all. Especially considering that lithium-ion batteries tend to have greater energy density and are usually cheaper. Is there a particular reason why lithium polymer batteries are this much more favourable than lithium ions for this application?

Also
Why are lithium-based batteries always 3.7v per cell? Whether it's a Lipo RC battery, Li-ion or Lipo phone battery or just a standard lithium button cell battery, I have never seen a lithium battery that's not rated at 3.7 (or sometimes 3.8) volts per cell. I know when fully charged they produce a higher voltage, but what makes them so similar in the voltages they produce per cell? Was there a gentlemen's agreement between major companies or perhaps a governmental regulation to make them more universal to different products? Or is there a scientific reason why they have to produce about 3.7v?
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#2
I had these questions on my mind for quite a while now about lithium batteries:

Why are Lipo batteries used so much more in RC than Li-ion? I mean I get that Lipo batteries tend to be a bit more lightweight than Li-ion batteries, but that can't be all. Especially considering that lithium-ion batteries tend to have greater energy density and are usually cheaper. Is there a particular reason why lithium polymer batteries are this much more favourable than lithium ions for this application?

Also
Why are lithium-based batteries always 3.7v per cell? Whether it's a Lipo RC battery, Li-ion or Lipo phone battery or just a standard lithium button cell battery, I have never seen a lithium battery that's not rated at 3.7 (or sometimes 3.8) volts per cell. I know when fully charged they produce a higher voltage, but what makes them so similar in the voltages they produce per cell? Was there a gentlemen's agreement between major companies or perhaps a governmental regulation to make them more universal to different products? Or is there a scientific reason why they have to produce about 3.7v?
LiPo Vs Li-ion You answered your own question! You mentioned that Li-ion have greater energy density and in the same sentence stated that LiPos are lighter! For a model aircraft the weight is EVERYTHING especially as energy density in an aircraft MUST also include the weight of the container. So energy density per unit weight is what is considered.

As for the 3.7 V per cell it is the same problem when describing a Lead Acid battery for a car. The Lead Acid battery is rated or described as being 2.0 V per cell, (hence a 12 v battery), yet a vehicles battery can be charged to 14.5 volts and 12 volts is considered as being close to flat! The nominal charged battery voltage for a 12 v car battery is 13.8 volts! GO figure!

I believe the cell voltage is the voltage measured on a freshly manufactured call before it is first charged! The voltage is determined by the chemistry of the cell!

Have fun!
 

ElectriSean

Eternal Student
Mentor
#3
LiPo Vs Li-ion You answered your own question! You mentioned that Li-ion have greater energy density and in the same sentence stated that LiPos are lighter! For a model aircraft the weight is EVERYTHING especially as energy density in an aircraft MUST also include the weight of the container. So energy density per unit weight is what is considered.
Another advantage LiPo has over Lion is discharge capacity. A really good Lion cell can discharge at 10C (realistic, not advertised) whereas a really good Lipo can probably realistically do 60C.